Simpler motor driver circuit

308

06:23:18

I just realised my simple motor driver circuit could be simpler for EC beginners. None of the components are adjusted except for the voltage source which is turned up to 9V.

Each transistor is a simple-as-possible common emitter amplifier. The NPN amplifies current for the PNP to amplifiy further, so that it's enough for the motor.

It could be more efficient, but it works.

published 7 years ago

BillyT

7 years ago

Nice, If you use a 12V PSU and a time base of 1second it would be more representative of a real life setup.

eekee

7 years ago

@BillyT, thanks, but the time base is 1s/s already, and you've got me wondering whatever happened to 9V power supplies and batteries. :)

BillyT

7 years ago

While the time base is 1s/s if you check the timing mark on the trace you will find that the screen is actually 5seconds / mark. That is in real time. Besides this, the motor is placed in the transistors collector circuit this is fine for an amplifier, (eg variable speed) but should be in the emitter circuit if you are just going to just switch it on, (do try 12v and 1second). http://everycircuit.com/circuit/4650516138426368

BillyT

7 years ago

A simple motor speed control. http://everycircuit.com/circuit/5993223578451968

eekee

7 years ago

By "amplifier" I assume you mean voltage amplification, while by "just switch it on" you must mean current amplification. It is in fact reasonable to put the motor in the emitter circuit for variable speed because that way the transistor will limit the voltage. By placing it in the collector circuit, the transistor will allow the motor whatever voltage is available, so long as it's turned on fully. Common-emitter, with the load on the collector, is in fact the normal way to use a transistor as a switch.

eekee

7 years ago

*sigh* BillyT, you failed to see that the very circuit you linked puts the motor "in the emitter circuit" for variable speed.

BillyT

7 years ago

eekee, please analyze those circuits very carefully, your circuit can only supply about 5v from a 9v power supply, the other circuits are designed to get past these limitations.

eekee

7 years ago

Oops! The NPN draws off too much current from the PNP. The motor speeds up if you make the base resistor larger. 7-10kR seems optimal. IRL, it would make more sense to put a resistor between the transistors.

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