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A DIY Power Pulse Controller

This device uses a built in pulse width modulated signal generator circuit for triggering a power MOSFET.

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.

The transistor used is not critical but generally something with voltage and current ratings suited to your application should be used. We have a range of MOSFETs and IGBTs available. The circuit will run from a 6V - 12V DC supply and the output can be made as 'open collector' for higher voltage switching.

Don't fancy building it yourself? Check out our range of advanced pulse generators

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.

Pulse Generator


Parts List
IC1 LM555
IC2 LM393
R1 10k
R2 10k
R3 2.2k
R4 10k
VR1 1M
VR2 10k
C1 47nF
T1 IRF740 or simlar

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 15V,  10A
  • Power Output - 9 to 15V DC Square wave
  • 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%

We have a few of these pulse generators designed for use with high voltage transformers which available on the cyber circuits page. These are high quality, ready made on a PCB including a large heatsink and fan, 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.

Don't fancy building it yourself? Check out our advanced pulse control circuits. Buy our awesome PWM-OCXI now!

Comments and questions for DIY Power Pulse Controller

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