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Project Notes

#233 PWM/GeneralPurposeHighSideController

Build and test a general-purpose high-side PWM controller

GeneralPurposeHighSideController_build

Notes

This circuit cobines a variable-duty cycle PWM generator with a high-side p-channel MOSFET driver circuit, making it suitable for controlling loads up to 15V/23A.

PWM Generator

The PWM signal is generated with a modified 555 Timer astable oscillator.

Steering diodes are used to isolate the 100kΩ pot so that it primarily adjusts duty cycle with little change to the frequency.

A switch allows selection of 1nF & 10nF capacitors, selecting a base PWM frequency of:

  • 10nF - 1.25kHz
  • 1nF - 12.6kHz

High-side Driver

The PWM output switches an n-channel MOSFET which in turn controls the high-side p-channel Power MOSFET.

The shunt resistor R4 limits the bypass current when the n-channel MOSFET is on. At 1kΩ, it wastes up to 15mA (at 15V) but in return allows fast switching of the Power FET. A higher value of R4 (10kΩ, 100kΩ) saves power, but switching time is affected.

A pair of capacitors (220µF, 100nF) provide some smoothing of the power supply to the Power FET and decouple the PWM and FET loads.

Performance - 10kΩ Resistive Load at 1.25kHz PWM

At 50% duty cycle:

lo_f_mid_duty

At minimum duty cycle (~1.25%):

lo_f_low_duty

At maximum duty cycle, the output approaches 99.9% fully on.

Performance - 10kΩ Resistive Load at 12.6kHz PWM

At 50% duty cycle:

hi_f_mid_duty

At minimum duty cycle (~1.25%):

hi_f_low_duty

At maximum duty cycle, the output approaches 100% fully on.

Construction

Breadboard

The Schematic

GeneralPurposeHighSideController_breadboard_build

Protoboard/boxed construction:

GeneralPurposeHighSideController_protoboard_layout

GeneralPurposeHighSideController_wip_1

GeneralPurposeHighSideController_wip_2

GeneralPurposeHighSideController_build

Credits and References

About LEAP#233 PWM555 TimerOscillatorsPower
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.