A DIY Power Pulse Controller
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.
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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.
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.
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