The circuit is great for controlling the power delivered to a device
such as a fan, LED's or even transformers and coils. By adjusting the
pulse width you can easily control the speed of a fan without sacrificing
torque.
This particular transistor, the IRF740 is rated up to 400V and can switch
around 10A which makes it quite useful for power switching in inductive
loads. The circuit will run from a 6V - 12V DC supply and the output can
be made as 'open collector' for higher voltage switching.
This circuit diagram shows the load (coil, motor etc) connected to the
same supply as the rest of the circuit for simplicity. If you need to
switch a higher voltage, the +ve connector of the load can simply be connected
to an external supply.
Parts List
IC1
LM555
IC2
LM393
R1
10k
R2
10k
R3
2.2k
R4
10k
VR1
1M
VR2
10k
C1
47nF
T1
IRF740
If the circuit is to be used with inductive
loads a small capacitor should be connected across the load These
are often already fitted on small DC motors. An additional component such
as a varistor or 'freewheel diode' is also recommended if the pulse generator
is driving high voltage flyback transformers like ignition coils.
The two potentiometers VR1 and VR2 are used for controlling the frequency
and duty cycle of the output. VR1 adjusts the rate at which C1 is charged
for modifying frequency, while VR2 acts as a potential divider allowing
a specific voltage to be put on the inverting input of IC2. This voltage
is used to control the pulse width of the output. The output duty cycle
or pulse width of the device can also be controlled by an external voltage
such as a microcontrollers or analog signal. The analog voltage source
can simply be connected to the inverting input instead of the output from
VR2.
Features and Specifications
Input 9 to 12V 10A (120W)
Power Output - 9 to 12V DC Square wave 10A
Open collector output allows for use of separate voltage source for
pulses.
Independent frequency and pulse width / duty cycle controls
Frequency adjustable between 0Hz and 125kHz (C1 must be changed for
full range)
Pulse width fully adjustable between 0% and 100%
Example applications
(PWM) Motor Speed Control
Pulse Width Modulation (PWM) is used to accurately control the speed
of DC motors. The pulse frequency can be adjusted to match your motor
for performance or reducing noise. The speed of the motor can be adjusted
using the preset on the board, or it can be attached another variable
voltage source such as the analog output from a microcontrollers or
similar device.
Dimming or Flashing of LED's and Light bulbs
This module can be used to smoothly dim lights or make them flash at
regular intervals. The brightness is adjusted by a pulse width modulated
signal which can be set to and inaudible frequency
Tone Generator for small or large speakers
This circuit generates an adjustable square wave signal that is powerful
enough to drive anything from piezoelectric sounders to large bass speakers.
The frequency range can be adjusted between sub bass and ultrasonic
levels.
Solenoid or Relay Pulsing
Simple variable rate on/off function for driving relays, or moving solenoids
with repeated strokes.
Coil Pulsing
Drive coils and electromagnets with regular current pulses of up to
10 Amps. Ideal for magnetic launchers and many other pulsed coil experiments.
At higher pulse frequencies the PWM control can be used to adjust the
average field strength of a coil.
SMA Wire Driver
The variable pulse generator can be used as an adjustable current source
for powering muscle wire (shape memory alloy SMA wire). By using a medium
frequency setting, the PWM control can be used to adjust the average
current flowing through the muscle wires giving precise control over
the movement. At low frequencies muscle wire can be pulsed for repeated
movements.
We have a few of these pulse generators designed for use with high voltage
transformers which available on the cyber
circuits page. These are ready made on a PCB including a large heatsink
and fan on the MOSFET, overload protection, and back e.m.f. inductive
protection. Theses devices are quite resilient and are ideal for hobbyists
and experimenting due to the wide range of potential uses and durability
for handling varied loads. If you have random transformers or are making
your own coils, these power
pulse modulators are ideal for testing and driving them.
Questions and Comments on the DIY Pulse Controller
Some comments/questions are hidden. To include them below, click here
The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
Dear Sir,
What kind of diode(part) is the D1 at the A DIY Power Pulse Controller ?
I am looking to use this circut to drive for paralel ignition coils.
Thanx
Oops! Missed it off the list :). The diode used is just a 1n4007 or something similar. This diode is rated up to 1kV so it should be able to withstand any nasty spikes.
I tried this circuit today.Only had some old flash light bulbs to test it.
Now i have a Dimmer and flasher in 1 circuit.
Looking forward to playing ( experimenting ) with this.
Powered it up with a pp3 battery and it seems to run fine from that. 12 Volts later :-).
What is a wheel diode?. Never heard the expression before..
The term 'freewheel' or 'flywheel' diode is often used to describe a diode that is placed across an inductive load such as a motor.
The diode is used as a path for the current when the transistor is switched off. If you think of the current in the load as carrying momentum, when the transistor is off the current can continue through a diode. With out a current path the voltage accross the load can rise quite high which may damage components in the circuit.
Many thanks for the reply. Not fully understood by me yet, but i will go look for more info..
Update from Earlier post..
Found Ignition coil and 12Volt Supply.( wifes car lol ).
Connected it to the Pulse controller and blew the LM393, oops.Not good..Connected 4.7nf capacitor across the load ( ignition coil ) and tried again.Much Better. Coil produces sparks from 5Volts. At 10 volts the spark becomes and arc..Noted the IRF740 will warm up quite quickly if the coil is not tuned to well. With 12 Volts input I could easily run a jacobs ladder.
The best Ignition Coil driver I have tried.
Thanks for your feedback, I'm glad you like it. I blew quite a few MOSFET's and LM393's myself when driving ignition coils.
Its particualy susceptible when you are getting a high output from the ignition coil and you are making and breaking arcs. This is because breking of the arc causes HV spikes in the circuit which can damage sensitive parts like the 393 or 555. A capaictor helps, but a surge protector such as a varistor might be needed at high output levels.
Nice Video demonstration thankyou..
Oops another LM393 bites the dust.Running a 40 watt bulb as a plasma ball is ok till the negative croc clip drops off.Must buy better sticky tape..Awaiting LM393`s..
I wonder if smoking LM393`s is bad for my health..
Ooops! :) I can't imagine that smoking LM393's is gonna do you any good.
I'd add some surge supression if your gonna be stressing your circuit. Something like these Transient Voltage Supressors should help. You normally place them between a sensitive rail (like a signal input or output from 393) and ground.
It can sometimes help to just put one in parralel with your battery or DC supply so that if the voltage rises too high it will be shorted out. You will probably need a current limiting resistor too though if you do it like that.
Many thanks for the Information. I will take a look.
I made a small modification to you circuit over the weekend.Added an ampmeter so I can see what effect the tuning has on the current drawn,this should help a little.I am suprised at just how much the current will rise.
I will fit a pair of Inductors later to see what help they are, if any..
Many thanks for the help and tips..
My goal is the 12Volt tesla. I picked up 22 used 2n3055`s cheap, Looking out for heatsink now for 9?.. I am trying to Quit smoking LM393`s, honest Guv..
Yes, the current can vary greatly when adjusting the frequency or duty, so its important to have a driver that will tollerate the peak current at least for a few seconds.
I got lucky finding my mega heatsink in a local electronics shop. I have a couple of double T0-3 type heatsinks around somewhere. Let me know if you want them, and you can have em both for £5, or whatever international shiping costs if you are not in the UK.
I've also seen some allmost identical ones on ebay here
I used nine 2n3055's on the Power Pulse Generatorbecause it filled up the heatsink, but I think that its overkill really. It only ever gets warm when driving 4 ignition coils, but having nine leaves plenty of room for adding bigger or unknown loads like electromagnets.
Ok i have quit smoking the LM393`s ( yippee ).
I fitted the following. 2 Inductors, 1 to each input of the coil / coils. 2x1n4007, 1 to the power supply between the coil and lm393, and 1 on the negative of the lm393, Dont really know if it helps any but i have blown up nothing today. Tried driving 2 coils and found no problems, even when the spark is over 1 inch.
I can get a good 10mm arc with .5 amps. Jacobs ladder is no problem with 10 Volts into 2 coils.
***********************************************
Heatsinks for the 2n3055`s. At this time i am using CPU heatsinks. These work really well and have the added bonus of a fan. To use, drill the holes for the connections through the base into the channel for the retaining clip. Push the wire through the holes and then solder. Two self tapping screws to secure.Does that make sense?..
A fun day, thankyou again for all the help and advice..I may take you up on the offer of the heatsinks, I`ll see how i get on first..
Hello, i need de conection (pin out) for de lm393 at de circuit, eje: Pin 1?? Pin 2?? in the picture no have de conection por pins, please send my this info.
kilidjian@ciudad.com.ar
Tkanks !!!!!
Suggestion.. When buying the two potentiometers, pay a little extra and get a type that can handle a few amps.The 2 I bought a couple of weeks ago are already giving problems. Serves my right for buying the cheapest.( not purchased from this site ).
Fitted the 2n3055`s to the heatsinks, but not working yet.Need to look into that.
hi, i wanna use this circuit as a pwm fan controller for my pc.. i think i can build it, but some bigger pics of the front/side would be appreciated :)
thnx
I think I'm going to borrow this circuit to pulse the ignition coil used for the flame thrower on my vehicles exhaust pipes. It's perfect, 12v DC, and it was designed for a cars ignition coil.
I am fairly new to the electronics side of science but i understand the circut, so that is good. I had a few questions about the circut though? First of all i was wondering if the compassitor needs a specific voltage rating? Now for the next one i was wondering if the resistors needed to have a specific wattage rating, and the same for the potentiometers?
The voltage rating of your capacitors can be anything above your battery voltage. The power rating of resistors used on this are the typical 0.6W type. Potentiometers are 0.4W
Thank you for your response i was really stumped on this one, and i am going to use this pulse gen for electrolisis experiments and i will let you know how it works.
what kind of circut boards did you use with this circut and where could i purchace this kind of board? And one last one how would you recomend me going and putting all of this on the board? Thank you.
I have built a couple of the PWM they work fine.
I want to drive a pair of ignition coils then a Tesla
PLEASE recommend how to put Varistor or other safety features to protect the PWM
I have used two inductors made from biro cases on the ign. coil inputs in the past with the single sign. gen and ign. coils but Iam not sure this is enough.. A good tip is to keep checking each completed section of the circuit as you build it with a small loudspeaker or piezo -electric beeper( scraped microwave oven?)
Have a look through the comments below the Ignition Coil Driver Page. There's plenty of info and links that should help you learn how to protect your driver circuits.
came here while in search of links to sites I might possibly understand enough to build something useful
I got lucky...FINE site
neat time I come around it will be as a member, I hope
is this the most efficient circuit to use for frequency and ampereage control from a 12V DC source or do you recommend another circuit? I want to control 0-125MHz and 0-10A with 12V DC.
The efficieny of this circuit is totally dependant upon the load you are trying to drive with it.
There is no way of getting a frequency range of 0-125 MHz @ 10A with any circuit like this. The impedance in the MHz range is just too high for delivering that kind of current without any special power conversion.
The output voltage is just the same as the input voltage (minus the small drop across the transistor). At higher frequencies the output measured on a voltmeter could be varied by adjusting the pulse width, but this would be a pseudoanalogue voltage reading. The same principles would apply for measuring current.
The frequency range depends upon the capcitor value of C1, but the full range would be about 0-125kHz
RMCybernetics, thanks for your help. Just one more question. Other than getting my hands on a PCB printout, I would love to know how to mod this to handle more amperage. Thanks again.
To get more power handling you could replace the MOSFET with a larger one or use an IGBT
You may need to wire an IGBT using thick cable rather than PCB tracks.
I assume you would like to rectify (convert to DC) the output of your coil. If this is the case then the 1n1198 is not suitable. it has a max reverse voltage rating of only 600V.
The output voltage of an ignition coil depends on the specific model used, but I would say that 20kV is about average from a good 12V square wave driver.
The output current is only small and it is also pulsed. Semiconductor devices often have a rating for continuous current and a seperate rating for pulse or surge current.
If the coil steps up V from 12 to 20,000, we can assume that the current will be stepped down by the same amount (~1667 times). If the input current is 5A, then the output current will be about 2.9mA.
These values are pretty rough because of the pulsed nature and variablity of the system, but they should give you an idea of the minimum ratings for any component used on the output.
Maybe the BY8418 (22kV 100mA) would be suitable.
RMC is it possible to add another IRF740 to this circuit?
I'm thinking to add another coil, but trying to be able to control it individually from the other. is it possible with this circuit.
You can add another IRF740 in parallel with the original one to give you twice the current (I) rating, but they may not swith on at exactly the same time. This is down to slight differences in the components caused by the manufacturing process.
If you want to independantly control a seperate coil with a different frequency or pulse width, you will need a whole extra circuit.
Thanks a lot man
I am tryin to get the coil to spark at a different time.
the ony thing holding me back is the fact that i am using an electronic ignition from a 92 honda an it has 3 wires coming out
I know that one comes from the trigger ond another goes to ig. switch. and im guessing the other is for 12v straight as well.
Ill try using two cables(12v +) and one for +pulsing from circuit. I will also ground the coil. hope this works alright.
I'll be using this circuit to drive a transformer. Could you describe the proper way to protect this board from Back EMF? You have mentioned a veristor, but I was hoping you could provide a connection scheme and possibly a suggested P/N? I upgraded the MOSFET to an 18A unit (1000V Max), but other than that, I've built the circuit exactly to your specifications. Any help would be great.
There are quite a number of ways to protect driver circuits from back EMF, but they are often quite specific to the application. A varistor is a single component that will begin to conduct when the voltage across it breaches its preset value.
A varistor provides protection when it is placed between a pin of a voltage sensitive device and ground. The value of the varistor is chosen to be slightly lower than the max voltage of your device. With this setup, if the voltage on your protected pin rises too high, the varistor will activate and short the pin to ground. This can obviously have other concequences which would depend upon your specific application.
A varistor can be used in another way for protecting transistors. If it is placed between the collector/drain and the base/gate it will cause the transistor to switch on when the voltage rises too high. This then prevents over voltage between the collecter and emitter (drain and source).
A varistor will have will take a finite amount of time to activate. If the transients are rising too fast, the varistor is rather useless.
A zener diode can be used in a similar way. If one is connected in reverse bias mode between the pin you need to protect and ground, the zener will limit the voltage on that pin to the voltage ratin of the zener. These also have a finite response time.
Another method is to construct a snubber circuit. These come in many flavours, but are generally some combination of a resistor and capacitor. Thse can be made to limit the voltage rise, or they can limit the rate of rise of the transient. They can be placed in the DC part of your circuit, or they can be placed on the transformer output.
The design of switch mode power supplies (this is essentially what you are making) can be rather tricky, especially when the freqency is variable and the voltage difference between input and output is large. There will be a section on transient protection in the learn electronics section at some time, but I have not got a eta for its completion yet.
This circuit can handle around 120W. if you use a 12V supply, the max current available will be 10A. You will need to add a good heatsink to the transistor if it is being used near full power.
would it be possible to produce a linear variable frequency from your generator, I would be grateful for any advice you could offer. I am new to computers and am ammazed at the great quality of your site.thankyou
The output frequency is not quite linear through the full range of turning the pot. You could proably improve this with some additional resistors or maybe a logarithmic pot.
I've not tried this, so you may need to experiment a little.
The voltage rating for C1 can be anything above your power supply voltage. 100V is a typical rating for these caps but it's not important.
A trimpot is a type of variable resistor.
The tollerence (%) of the components indicates how much the actual value you get (resistance, capacitance, etc) might differ from the manufacturers stated value. The type is not too important, these were used for this project.
The 3rd terminal of VR1 is left unconnected.
There are often a few version of the same model. The CN in this case just indicates the package type (DIP 8). This is the easiest to solder.
If you use the same supply for the circuit and the transistor/load, the maxiumum is 12V @ 10A (120W)if the transistor is kept cool. If you are not using 100% of the duty the transistor will handle slightly more power.
your text above tells me that you have a few power pulse generators for sale in the science shop.Ihave looked there but cant locate them. I am new to computors please tell me what it is that I have to do. thank you.
Sorry but we sold out of those pretty quick. There is a new batch being made that will also include extra features and improved desgn. If you want to be informed when they are in stock just sign up for an account here and leave the 'recieve updades' box checked.
Can this be used to accept a pulsed signal from the imput of a coil or a fuel injector and change the out put faster or slower. ie; advance or retard timing or richen/lean fuel mixture
Thanks for answering
Another question same topic
If I got a 12v signal pulsing at 10 times a second could I delay that pulse, but still pulse at 10 times a second. And stay in sync(or same percentage of delay) if the 12v input pulse was to go up to 50 a second or would i need a different device?
Hi i am thirteen and was wondering about those symbols on the diagraming of the circut. Is there a websit/page i can visit for info or maybe even a tutorial?
I'm trying to drive an ignition coil to create an oscillating spark through a spark plug. It needs to run off a 12V car battery because i am going to use it to shoot flames out of my 50 fords exhaust will this set up work for this.
I would just buy a thrower kit but this seems a little more fun and reliable.
thanks, I know this seems odd
This is pretty much the circuit you need. You may need to make some sort of snubber to protect the circuit from HV spikes. We will have some for sale soon with this protection built in. Just register your details to recieve updades about when the items are available.
Hi RMC
I tried this circuit as a speed controller but no show, the dc motor still go at the same rate of speed. no matter how much I tweak the pots high or low.
I'm lost here please help
It seems like its stuck on. You can test to see if it is pulsing by using a bigger capacitor for C1. 220nf would allow you to pulse it at a rate you could see.
Thanks for the good work! I'm looking to use this to drive a bank of 490 led's, so my current load is going to be near 10A. Would you suggest using 2 IRF740's to split the load or just keep it simple and put a big heatsink on the one?
A continuous load of 10A will probably generate quite a lot of heat that would need to be dissapated. Maybe an alternative transistor would be better. This IRF740 is chosen because it is low cost and can handle up to 400 volts. If you are not driving an inductive load then you could just use a transistor rated for uch more current and a lower voltage. Maybe an IRFP240 would be good.
Thanks for the tip on the transistor. Another question now. I don't need the adjustable frequency since I'm going to just use this for dimming LED's. I calculated that replacing VR1 with a 27k ohm resistor would give a frequency of 480 Hz. Is that right or am I missing something?
Yep that's correct. The frequency will vary slightly with temperature variations and the types of capacitors used, but it should remain high enough to be inperceivable.
For anyone wondering how to calculate frequency of the circuit.... (The value of VR1 being whatever you adjust it to)
Frequency = 1.44 / ( (R1+VR1+VR1) * C)
= 1.44 / ( (10k+VR1+VR1) * 0.000000047)
Good project. Live in Zimbabwe, where we try to develop LED Lighting circuits.
Q: Can this circuit run on 6 Volts or can it be modified to be happy with 6 Volts only?
This circuit will run on 6V without the need for modification. The gate terminal of the MOSFET works better with a higher drive voltage, but it will still work well at just 6V. If you are intending to drive a load near to the max rating of the MOSFET (10 amps), it may get hot more easily because of the low gate voltage not switching it 'fully on'.
You could replace the mosfet with an equivalent bipolar transistor such as a TIP142 as this requires only a small voltage to activate fuly.
further to my question of wed 4th april re power pulse controller. can you please give me an estimate of when a new batch will be avaliable,an idea of the price,and if I can afford it could I order one in advance?
The PCB's are due to be dispached to us tomorrow. I estimate that the kits will be available early next week for around £30. The ready made units will be available about a week later for about £40.
There's no need to order in advance. There will be quite a few available, and if you register your details we will email you when they go on sale.
I built one of these and am using it to drive two LED flashlights in series from a 12 volt supply. It seems to work, except when I turn the frequency or width up too high instead of staying on the LEDs will dim down to nothing, then wait a bit, turn back on, and repeat. This doesn't seem to happen with a single LED, so I though maybe 98 of them would be pulling too much current, but they shouldn't be using any more than 10 watts. The power supply is rated to 5 amps. Any ideas?
RMCybernetics - I can't seem to get down to a 10% duty cycle unless I lower the frequency or the voltage. What I am trying to achieve is 2k Hz and 10% to 90% duty cycle running on 12VDC. Do you have any suggestions? Also, will running +5.0 VDC (as an external source) through IRF740 work?
An LM393 damaged by overvoltage or static discharge can cause the pulse width to get stuck higher.
Make sure that the valuse of R2 and R4 are the same. Some resistors have a large tollerence value which means that there could be a difference of 20% of the stated value between your resistors.
A small reduction in the value of R2 will help tip the pulse width towards the lower end. Alternativley you could increase the value of R4.
The IRF740 will switch a 5V load no problems when the circuit is used in 'open collector mode'.
further to my enquiry of 2nd May re purchasing a pulse controller I have not heard from you. As I am not yet confidant with computers I am wondering if I have missed something, if not would you please give me an update on when you will have one available my project is stalled until I get one.thank you
just having an uneducated guess here but is this correct. ic1,c1,r1,and vr1 are the timing circut where as the rest are all for the width modulation(duty cycle). as the timer goes directly into the opamp(comparator) input (high impendance). you could have a few duty cycle circuts run off one timer??
for independant duty cycle but common freq??
Jack2:
I have not yet sent out any newletter because there has been some delays in getting them made. The kit versions are available now in the Cyber Circuits section. If you want a ready made one, you can back order them and I will make them to order. The newsletter will go out when I've got a batch of ready made ones available.
hootsnboots:
You are exactly right. The duty cycle part works by simply comparing the oscilating voltage to a voltage you set with VR2.
thank you for your reply to my enquiry I wish to order one ready made power pulse controller is this message sufficient to do that? I am not clear about what "back order" means.thank you
'Back Order' is just used to show that it is out of stock and that the item will be shipped when available.
Just go to the cyber circuits page and use the 'back order' button to add the item to your shopping basket. It works in the exact same way as buying any other products the button is just different. Once you complete the order I will get one made and shipped asap.
Thanks very much for the circuit design and great info. I've looked at a few 555 and other circuits with adjustable frequency and duty cycle and your's is the best.
I intend to use the circuit in a similar, high voltage research type project and would be happy to share my findings with the list.
I'm wondering whether you have any recommendations for PCB design software? It would have to be something that's fairly easy for the likes of me to use.
Many thanks ZS
I personally use Altium Designer but this is very expensive as it can do far more than just PCB design. I think the popular choice for home users is Eagle or Protel. I have not really used either of these so I don't know how well they work.
Thanks for your recommendations re PCB software. I'm trying out Diptrace at the moment and I'm getting on ok with it. I'm a novice in this area :^). Can you tell me what function resistor #3 serves in this particular circuit (Power Pulse Generator)? Understanding the functions of the various components helps me to work out how the thing works. Many thanks ZS
There are now some Power pulse Modulators on sale on our cyber circuits page.
They provide all the features of this circuit and include extra features such as transient voltage spike protection and indicator.
These devices make an ideal compact yet powerful adjstable power supply or pulse controller. One of these circuits will help you with a huge variety of science and electronic projects. Get yours here.
dear rmc sorry im not on the topic but i have discovered somthing cool that i would think lots of people would like to know how to build.
using a tv you can make your very own ossiliscope by simple disconnecting the vertical defelctor and using that coil as an imput signal.
this is showing no signal and the vertical can clearly be seen.
I was looking at your small ignition and liked what I saw but I believe I am living in a place far away from you to make it impractical to want to buy and get sent one of such coils, so I think I'd rather ask from which scrap equipment can one get such small ignition coils?
Also how does one determine the polarity of ignition coils when they are not indicated on the coils?
Again, I saw a flyback for sale on the same page, I have similar flybacks for projects I'd like to undertake, but how does one determine between the leads; which is primary, secondary and feedback coils leads when there is hardly any indication on the flybacks?
Similar coils can be found attatched to the spark plugs in some cars such as a Renault.
The wiring is represented in the diagram here. The pins marked GND are connected together inside the casing of the ignition coil. Finding the polarity of the coils can be done with an inductace meter between the output and an input pin. The pin with the lowest inductance is the GND pin.
I tested the flyback you mentioned by simply connecting a Power Pulse Modulator to pairs of input pins and measured the output. By process of elimination two of the input pins were found to create a good output when being driven by the 12V pulses.
Thank you very much for your response. My problem is, however, there are no apparent marks or indications on the ignition coils that will elicite a guess as to the polarity. But may be the numbers, for example, 1 and 15 written against some Bosch ignition coils could mean something, do they?
What Inductance meter would you recommend?
Also what do you use to measure those very high voltages? What are the normal voltages one can expect to get from 12V Bosch ignition and flyback coils, for example.
I would also like to have your opinion on whether one can use PCB mounted DC-DC converters as shown here, (http://www.hitekpower.com/pcbmountdc.htm), for example, thereby eliminating bulky ignition or flybacks if one's design is not very high current or power?
Maybe 15 is the + pin, I don't know for sure. It will work either way around but it's better if it's correct. You could try measuring the resistance between the output and an input pin. The pin with lowest resistance is GND but it might be hard to measure the difference.
The Atlas LCR is pretty handy for measuring inductance, capacitance and resistance.
I use a Brandenburg high voltage meter which is basically a big voltage divider and a panel voltmeter.
To measure the output of an ignition coil I use a rectifier and capacitor so can measure a DC voltage. It's typically 20 - 30 kV from a big 12V SLA battery and a coil driver.
Those DC-DC converters are handy for low power and voltage but they are not good for things like Jacobs ladders and Tesla coils like ignition coils are.
Thanks for your replies. Those DC-DC converters are high voltage (even greater than 10KV) and they are advertised as for also charging capacitors, which is where my interest lies.
By the way, do you have good high voltage capacitors (>=3000V) for sale? If so what's their cost? if not where can one get some at good retails prices?
You can drive a step up transformer to give 400V pulses from a 12V source.
The MOSFET used is rated to a maximum of 400V so you could also use it to switch a HV source.
This looks like it could be useful for driving automotive fuel injectors in an "extra injector(s)" setup (I.E. to add more fuel only when need as in turbo boost mode activated by a boost pressure switch). Do you think so?
Further to my message yesterday re the pulse generator in which I asked for data regarding protection against electrical spikes. I neglected to ask you to tell me how to connect this item to the pulse generator. thank you for your patience
Driving an ignition coil without any load on the output may cause very large spikes. The PWM-OC10A will indicate when the back emf is too large. The simplest way to reduce back emf from an ignition coil would be to load the output (i.e. place a capacitor or resistor between the output of the coil and GND). Alternatively you can place a capacitor across the two input terminals of the ignition coil. The larger the capacitance of the capacitor, the larger the snubbing effect will be. This type of snubber is dissipative and therefore reduces the efficiency of your system.
Thanks for this grat project!
I'm just wondering if that LM555 could be replaced by the ordinary NE555. Because the former one is quite absent at my location?
I've been toying around with the idea of building this controller since I came across this site a few months back, and now think that I may have a valid project for it.
However, I wanted to seek out some advice as to whether or not this particular pulse controller is suitable to drive high (approx 250mW, 3v, 150mA) output laser diodes. If not in its native form, do you guys think that it would be feasible to change the component values to be more suited to these types of laser diodes?
It's possible the voltage spike is on your power rails. You could place a MOV across your supply, but make sure it has a good response time or it could latch on and short your supply.
Another way is to place a reverse biased zener diode or MOV between the 393's input and ground.
You could also use the spare amp in the 393 IC as a buffer for increasing its output impedance.
Most of these methods may have some small effect on performance such as increased switching time caused by extra capacitance.
It's also worth noting that using a battery as the supply means that your ground connection has limited current sinking abilities therefore it's not always going to stay at 0V when the circuit is active.
i have build your circuit and i want to use it for driving a fan, but i can't find any change in fan speed even varying vr1 and vr2? Im new in electronics. can you help me know that my circuit is working? thanks
Clearly it's not working. VR1 and VR2 should make obvious changes.
If your fan is stuck on full speed it means that either there is a short circuit which bypasses the transistor, or that the oscillator is not oscillating and is stuck high causing the transistor to be switched on permanently.
thanks in your reply, i will check my circuit connection and hopefully find the culprit, can i add a decoupling capacitor between pin 8 and 1 of the two ic's and a 100 ohm resistor in series connected to the 100 microfarad capacitor and input supply voltage to protect the ic from unwanted voltage? can i use 15 volts power supply in this circuit? thanks again
Yes you can add decouplers as you suggest. You mention "the 100 microfarad capacitor" but there is not one on the schematic. I assume that you placed one across the power rails to act as a smoothing cap. You would not want a resistor with this.
Use a MOV (varistor) pull any voltage spikes down to ground.
You probably shouldn't apply 15V directly to the circuit as it is shown because there are no resistor protecting the ICs. You would need to place a resistor between the ICs V+ and the +15V to keep the voltage within the manufacturers ratings. 15V is within the rated input range for both ICs (555 = 16V, 393 = 36V), but it would not be good practice to run them so close to the limits without some sort of current limiting resistor.
rmc , do you have plans for a high voltage switch , im building a solid state tesla coil running off a square wave and the power supply is a rectifiyed flyback producing dc up to 400 or more volts but i need a high voltage switch which will not effect frequency. do you have plans for this? signing off man cups are weird
Hi. I have been looking at the power pulse modultor kit. My application requires a fixed pulse width (10ms) and a varible frequency (0-50hz). When adjusting the frequency will the pulse width stay fixed? Also can the frequency be controlled with an external variable 0-5v voltage source? Thanks in advance for your assistance to a newbie.
Pulse width setting is as a percentage of one cycle (duty) therefore with a fixed duty of 50% for example, the pulse time would vary with the frequency. With two units you could set one to give a 10ms pulse at a low frequency and use another one to supply that one with its power. This would give you fixed 10ms pulses the frequency of which could change with the second unit. You could also use this setup to give double or multiple pulse bursts.
if i was to add a microwave cap in parrallel with the load wires of this circuit with a 1k resistor will this protect the circuit and ohh yes 6amp diodes as well but im not sure how i should wire them up
Hi there, love this page. Has been a source of great entertainment and education. In NZ some components are hard to get hold of. Namely the IRF740. Would it be possible to use an IRF540 instead? Thanks.
IRF540 will work fine as long as you are not diving highly inductive loads such as ignition coils. It has a voltage rating of just 100V compared to the 350V of the IRF740 so it will be less tolerant to back EMF.
can i put a condenser across the output to protect the circuit from back emf? can i use two series capacitor with a value 470 nf to beef up the frequency? thanks
See the ignition coil driver for protection methods.
you will need less than 235nF to get higher frequencies. 235nF will give a range of about 1Hz - 600Hz.
You can also increase the frequency by reducing the value of R1.
HI and thanks for all information.
I'm building my own coil driver using 2 IRF 530 (100V/17A) driving 2 antipararell coils. I,m using a commercial signal generator to drive the IRF:s (through a 180 ohm resistor) And I have enough power (12v/20A) But.. The circuit only draws 0.5-0.7 Amps and the output voltage is roughly 15-20kV. I expected more. Any suggestions anyone?
The drive frequency needs to be adjusted to match your coils for best performance.
What voltage does your input signal reach?, It typically needs to reach 10V to switch a MOSFET on fully but you can sometimes get away with voltages as low as 6V.
Yes it would, but you would need a suitable resistor to limit current or just connect the drain pin of the MOSFET to a seperate low voltage supply instead of the main supply rail.
(PS. I deleted the specs you posted as they took too much space on the page)
How can I limit current through 2n3055?
My induction coils can't create sparks at inaudiable freq. so i can't make audio modulated spark? Please help, it's for my school project.
PS. This site is the best!
You can limit the current using a large power resistor in series.
You can still audio modulate the spark but you will always have the sound of drive signal. The drive signal should be as high as possible because it will only allow for accurate modulation by frequency's which are half or lower than it.
Hello, I am almost done finishing this circuit to drive an ignition coil. For suppressing spikes I am planning to use
** a 1.5KE18CA transcient voltage suppressor diode: SHOULD it be across the load, or between pin 1 of the LN393 (output) and ground, or both?
** a capacitor across the load - WHAT value (nF, Volts) would you recommend?
Finally do you use a fat cable from ground to source of the IRF740? It is going to handle a lot of amps?
Many many thanks - Thomas
CrazyMadMan,
The datasheet tells you it can. The circuit here with a 393 allows the pulse width to be varied independently of frequency and it will co from 0-100% just from varying one pot. A 555 on its own can not do anything like this.
Thomas,
1.5KE18CA (MOV) would be ok on the output of the 393 like you suggest, but if you place it across the load it might heat up and be destroyed. It would also reduce the efficiency of the circuit.
This is because every time a spike goes above 18V (which will be almost every pulse if the ignition coil is not heavily loaded) all the power meant for the coil will go through the MOV for that instant. If you want a MOV across the coil it should be rated for hundreds of volts so it just clips the top of the highest spikes so they are within the voltage range of your transistor.
Any capacitor across the load should be rated for at least 1kV. The capacitance value would depend on the frequency you operate at. Higher frequency, smaller capacitance. You will need to experiment to find a suitable value. you should also place a resistor in series with this capacitor.
Yes, all power carrying cables should be thick.
Thanks for your explanations on the MOV. The 18CA will be between output and ground. I could not find high voltage bi-directionnal MOVs (at RS) - would a unidirectionnal be okay, and in which direction should it be connected? Should I use 2 in opposite dierctions?
Also, how would you test for best capacitor to connect across the load? I have heard that ignition coils usually operate best around 300-1000 Hz, so should I just put in a cap that starts conducting around 10 kHz?
Would you have any ignition coils that work well with this circuit for sale? My ignition coils always give pathetic sparks with either this circuit or the 2N3055 one. Many thanks!
RS have lots of bidirectional MOVs. Even in the hundreds of volts range.
The cap and resistor combination used for a snubber is usually chosen to be the largest capacitance you can use with acceptable losses in efficiency of your circuit.
We are currentl out of stock, but we should have some available soon. Check the high voltage surplus page
Are LM393N and LM393P the same as LM393?
I made an oscillator with NE555 and when I
connected ne555 pin3 to lm393p pin3, and other ( pot, v+,v-), voltage on output pin 1 and gnd was 0. I connected all properly. What do You think?
Thomas,
Maximum clamping voltage is the highest voltage that you can expect the MOV to keep between its terminals. If this value is 200V then you would not expect to see any voltages over 200V in your circuit (as long as it is used correctly).
The minimum breakdown voltage is the lowest voltage at which you can expect the device to begin to activate. If this value is 200V then your normal operating conditions must not reach this value.
CrazyMadMan,
Not exactly, but for this circuit it will not matter.
Pin 3 of the 555 outputs a square wave, there is no point in feeding that into the comparator and that is why pin 3 is not used in this circuit. If you have a 555 and a 393 why not build this circuit?
I tried to make it, but it ain't worked. Maybe my LM393's are dead. I will order new one's. I will keep you informed. And another thing, should I connect MOV between the lm393 output and gnd or parallel to load. You helped me a lot. I have already made a Tesla coil with my old
NE555 driver, but I want to make a new, just like that one on this site.
Great, very clear as usual. For this circuit, would a http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4864599 with 209V min breakdown Voltage and 388V max clamping voltage be okay? The 388V being under the IRF740 specs (400V), it should keep it protected?
Yes, that should help protect your MOSFET between its gate and drain terminals. You might sill want to protect the gate pin (between gate and gnd)with a smaller aster device rated for a low voltage.
hi! i am planning to use this circuit in driving an electromagnetic coil. i want to introduce a time varying current to the coil so that i will have a changing magnetic field. will this do the work for that purpose?
also, what kind of capacitor is C1? is it electrolytic, mylar, ceramic..etc?
i followed the circuit diagram above, however, when i connected it a light bulb as the load, it did not even light up. I am sure that the signal generator part is working (checked it using an oscilloscope and i used the circuit with pulse width modulation). the problem is in the IRF740. i don't what i'm doing wrong because i rechecked everything. HELP! I am attaching an image here. hope you can see what's wrong!??
If the bottom row on your breadboard is for GND, then it looks as if your IFR740 is the wrong way around. Just rotate it 180. Here's a link for the IRF740 Data sheet
hi, it's me again. i corrected the direction of my IRF740. i even replaced it with a new one just to be sure. it's still not working. i'm attaching an image of the revised circuit as well as the signal in the drain pin of the transistor. i really want to make this work. thanks for the help.
The circuit works... but when I tried drawing more current by tuning VR2, the IRF740 started to glow red (a spot between Drain and Source) then died! it is on a large heatsink (6C/W). What am I doing wrong? I have attached a pic of my small flyback. BTW if you would like one of these to tinker with, I'll send it to you for free - you've helped me a lot Thanks Tom
newbie,
Start with a low frequency, measure the signal on the gate pin (pin 1). This should be square and at a voltage just below your supply. If its not, remove the IRF740 and set the point which was connected to the gate pin. If it isn't square, then your circuit is wrong somewhere an you will have to just recheck your wiring. if it is square until you put the transistor in then there's possible something wrong with the transistor or the way you wired it.
Thomas,
This is happening because more than the rated current is passing through the device. I doesn't matter how big your heatsink is if you allow too much current to flow. When this occurred did it stop making sound (at the frequency of your drive circuit)? If so, this means the mosfet or other component was damaged by a voltage spike which caused it to permanently latch on therefore allowing the full current to flow through and melt it. See the ignition coil driver page for info on voltage spikes. Sure, I'll try out one of those xformers, I'll send u a couple of HV caps and diodes in return if you like. email us for the address. Cheers
Thanks... indeed the sound stopped when the IRF died. I used a MOV with 209V min breakdown Voltage and 388V max clamping between Drain and Sourge, so I assumed it would be okay. Also, I was measuring the amps when the IRF fried - it was about 1.4 amps. BTW would a high V high A diode in series from Drain to Load stop some of the spikes? I think this is used for small inductive load directly driven by a 555. cheers T
Sometimes the voltage spikes can be to quick for the MOV to respond. Maybe a neon bulb with a 1k resistor in parallel with load will give you an indication of when the voltage spikes are dangerously high. Does the rest of the circuit still function? A HV diode will drop too much voltage and is useless in a low voltage circuit. The one I linked to above drops <40V. A High amp diode with low enough voltage drop would be destroyed by the spikes. You would possibly need to employ one of the other snubber methods shown on the ignition coil page
hi. thank you for the suggestion. i followed it and it was a square wave for the gate pin. however, it was at a low voltage. more or less at 4V only. (under 9-12V supply) what do you think is the problem? Also, is it possible that my IRF740 is not turned on at such a low input voltage at the gate? Maybe my power supply is not that good? Should i address this insight? Thanks so much. Big help.
Added filter with (all 4 in parallel)
-60 nF 3000V cap (18 3.3 nF 3000V caps in parallel - I had a lot of these!) with a 10K resistor (1W) in series,
-a MOV (200V)
-one neon (Maplin RX70, I assume 0.8 mA since for 220V needs 270k resistor) in serie with a 1K resistor
**basically the three items described for the ignition coil driver.
-a fourth neon ((Maplin BK53H, "built in resistance for 220V")
The first neon (Maplin RX70) lights up. The second neon (BK53H) does NOT light up... am very confused now
I am using a 9V NiH 200mAh battery for this - using a PSU 16V 4 A max fried my IRF740 yesterday
newbie,
It should not be so low. You must have an error in your circuit but you will have to figure it out yourself. 4V is too low. 10V is a typical value for switching a MOSFET.
Thomas,
The resistor values normally used for the neons are chosen so that they can be lit constantly from the applied voltage source. In this case they only light briefly and we also use them to dissipate some energy. This is why the resistance value is significantly lower. If the voltage of the spike is high a larger current can flow through the neon and therefore more energy is dissipated as light and heat. The second neon will not light because the other snubbing devices are preventing the voltage from rising high enough to power the neon through its resistor.
Good point... I will add two more neons with different resistors to see if there is a cutoff. Since my neon is lighting up with its 1K resistor, can I estimate the value of the voltage spike? Is a neon lighting up from a specific voltage/current? Cheers
Shipped the flyback to you today BTW
Found the flybacks on eBay. Hooked the Pulse Controller to a real ignition coil. Get some nice corona, but all my neons lamps are lighting up (including the one with a 270k resistor, which is supposed to kick in at 220V) and the 200V MOV gets hot. Then the circuit stops working for a few seconds - I assume this is the MOV shorting then getting back to normal? I am out of ideas for snubbers... Is there any circuit that could keep the coil running for a long time without shorting?
Thomas,
Yes fortunatley the IRF740 is avalanche rated, meaning it can tollerate such a breakdown if it is only temporoary and within certian limits. Unfortunatly driving an ignition coil with a variable frequency and little or no load on the output will produce lots of back EMF. Imagine the flow of energy in the circuit as if it is a wave. It flows into the primary coil and then from there into the secondary coil via a changing magnetic field. As this energy reaches the output terminal of the coil it sees a huge change in impedance (low in the metal coil to very high in the air). A change in impeadence always causes reflections of waves. This means the energy wave is reflected back into the coil and eventually back to your transistor.
You either need to absorb/dissipate this energy before it hits the transistor, or you need to allow the wave to flow out of the coils output. Once an arc is formed there is a low impedance and energy is not reflected much, but before it forms the air has a huge impedance and causes lots of reflection.
If you are not concerned so much with varying the frequency or voltage then you can use some sort of self resonant or even mechanical oscilator.
tomu,
Square, it will distort and become rounded at higher frequencies.
No. The FET does not effect the input voltage you use. The voltage appled must not exceed that of the comonents ratings. Obviosly the 400V of this mosfet is fine, but the 555 and 393 have lower tollerence.
I have built this circuit, but instead of a 393 I used a lm2903, looked the same, and at c1 added a multi position switch so I could pick between 4 different values of capacitors. My problem is that the 555 is getting hot within about 20 seconds of operation. I am using this circuit for an electrolysis project. I have gone over the circuit to check my connections and everything looks good, can you help me out?
Hey RMC,
I recently bought a motor speed controller using a LM555. After completing the kit, it ran the included motor just fine, but when I connected my own DC motor, it would not move at all. At first test, nothing happened at first but then there was a burning smell and a pop. The LM555 was hot, so I thought that was why it wouldn't move that load. Is that the reason or is it because my motor draws too many amps? (sorry i don't know the specs right now, but i will test the motor tomorrow and find the amps). I have attached a picture of the speed controller and the motor which I wish to drive.
dexter,
Its getting hot because too much current is flowing through it. You can reduce the current by either lowering your supply voltage or increasing the resistance of the circuit. Insert a resistor (about 100 ohms) between the power supply and the IC's power pin.
Chris,
If the motor is physically larger then yes it is likley to have overloaded the circuit. Our PWM circuit will work with large motors.
what is the equivilant to a lm393 chip?
thankyou for taking the time to answer my question although some people abuse the privilage by asking questions that could be answered by googling lol thankyou great site by the way.
tomu,
I can't give you a direct replacement, you will need to search yourself. There are potentially hundreds that will work. It just needs to be a low offset comparator for use with a single voltage supply.
Chris,
Your picture will only be accepted if it is a jpeg (.jpg) and less than 200kB in size. The device mentioned will drive motors up to 10 amps.
RMC,
Yeah sorry I forgot about size. I will convert the image sometime today and upload it. The motor which I mentioned draws 1.35 amps @ 7.2 volts. You mentioned that the power pulse modulator will output up to 10 Amps of current, so can I assume that the circuit can run this motor?
Thanks for your help.
hi sir,
is it possible to use another device stead of lm393 for example a simple comparator in electronic workbench(for simulation)?
thanks alot for the quick reply
C1 can be either of those. Any non polarised capacitor is fine. Its voltage rating should be anything above that of your supply voltage.
Snubber capacitors should be multilayer or something that can handle a litle power.
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You can buy an advanced version of this circuit from 
dear rmc sorry im not on the topic but i have discovered somthing cool that i would think lots of people would like to know how to build.
Similar coils can be found attatched to the spark plugs in some cars such as a Renault.
Would this schematic work for a plasma globe? 
I found this circuit in NE555 datasheet. Can it be used for pulse width modulation? Is it better than LM393? What do you think?
i followed the circuit diagram above, however, when i connected it a light bulb as the load, it did not even light up. I am sure that the signal generator part is working (checked it using an oscilloscope and i used the circuit with pulse width modulation). the problem is in the IRF740. i don't what i'm doing wrong because i rechecked everything. HELP! I am attaching an image here. hope you can see what's wrong!?? 
hi, it's me again. i corrected the direction of my IRF740. i even replaced it with a new one just to be sure. it's still not working. i'm attaching an image of the revised circuit as well as the signal in the drain pin of the transistor. i really want to make this work. thanks for the help. 
this is the signal in the 2nd pin of the IRF740.
The circuit works... but when I tried drawing more current by tuning VR2, the IRF740 started to glow red (a spot between Drain and Source) then died! it is on a large heatsink (6C/W). What am I doing wrong? I have attached a pic of my small flyback. BTW if you would like one of these to tinker with, I'll send it to you for free - you've helped me a lot Thanks Tom
Ok so i finally got my pic resized (sorry im lazy) but here it is!