# The Simpleton Controller.



## dougingraham (Jul 26, 2011)

You forgot the freewheeling diode across S1. Without one Q3 will fry quite possibly the first time it is turned off.


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## lazzer408 (May 18, 2008)

It's stated that they need to be added.


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## Duncan (Dec 8, 2008)

Hi lazzer408
What's the game?

_"Here's a simple controller I designed for you guys"_

In another thread you are asking about why putting capacitors in parallel reduces capacitance

These seem incompatible - what is going on?????


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## Tesseract (Sep 27, 2008)

lazzer408 said:


> It's stated that they need to be added.


Uh... that's about as basic an omission as leaving out the switch (e.g. - MOSFET, IGBT). Ergo, fail.

Also, this circuit is a straight throttle to PWM type of controller which is totally unacceptable for *traction* applications; you want throttle to control current instead, and that will require a current sensor and control loop. If you want to make a minimalistic traction motor controller, I'd start with a "current mode" PWM IC such as the classic Unitrode/TI part, UC3843. Use throttle to supply the reference voltage and let the IC adjust the duty cycle as necessary. Set the 0dB crossover point to around 1/3rd the switching frequency and you'll have crisp throttle response with little chance of oscillation, even above 50% duty cycle.


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## lazzer408 (May 18, 2008)

Does anyone read? 

"It is designed for education purposes and may lack features required for road use."

This circuit can be applied to much more then just traction motors requiring current limiting. It would be suitable for resistive loads, such as a heater, without the need for diodes. Or it can be adapted as a motor controller. It's very easy to add current limiting to it using a second LM393.

The current mode PWM controller ICs are nothing more then analog devices. I've posted circuits based on those as well. Controller ICs also lack the ability to reach 100% PWM do to the blanking feature of the IC for use in push-pull convertors.

I would say a traction controller "current limited" not "constant current". 

Anyways, This is open source and here for others to learn from and build on.

As for the parallel capacitors. I don't know why I didn't know that capacitance value is reduced. I guess I've never had a need to calculate it.


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