Unregulated power to servo ?

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smarch
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Unregulated power to servo ?

Post by smarch »

So if I have a board running an avr micro and sensors via regulated 3.3v from a 6v dc source could I connect the power and ground of the servo requiring 4.8v to 6v in the circuit after the 6v dc input but before the 3.3v regulated output without any negative repercussions to the circuit. Also do servos need regulated power?
dyarker
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Re: Unregulated power to servo ?

Post by dyarker »

As long as the 6V supply never exceedes 6V the servo won't be hurt.

As long as operation of servo doesn't load down the 6V supply below the drop-out voltage of the 3.3V regulator the microcontroller/sensors shouldn't be affected at all. The 3.3V regulator may need some more capacitance on the input side for noise from the motor in the servo.

Cheers,
Dale Y
smarch
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Re: Unregulated power to servo ?

Post by smarch »

That completely answers my question, thanks.
Additionally if your in Iraq for service reasons thanks for that too and in any case be safe.
Rodney
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Re: Unregulated power to servo ?

Post by Rodney »

There is one possible problem doing this. Depending on the servo design, if the signal output from the receiver to the servo is limited in amplitude, the servo may not respond properly. For instance, it the servo requires an input with a peak amplitude of more than half the servo supply voltage (a common requirement) and the amplitude is low, the servo operation may become erratic or perhaps non responsive at all.
dyarker
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Re: Unregulated power to servo ?

Post by dyarker »

Rodney has a point. Put a pull-up resistor from servo control line to servo power line, then servo control line to collector of a small transistor (2N2222, 2N3904, etc). Output pin of microcontroller through a resistor to base of transistor, emitter to circuit common. Added bene is micro is protected from many possible failures on servo side of circuit.

Note- this will reverse the logic. Now the microcontroller pin must go low for servo to get a high.

I EWAGed that 1K would work for pull-up resistor. Base resistor could then be 10K to 33k, if you have to buy make it 27K.

A FET could be used instead of bipolar transistor, just be sure to use a FET that switches fully on with 3V on gate.

Cheers,
Dale Y
smarch
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Re: Unregulated power to servo ?

Post by smarch »

Thanks for the heads up on that. I got sidetracked for a few days but I'm back working on this now. I'll try it both w/ & w/o the transistor to see if there is any difference in performance. In either case good information for future reference.

Thank you for your time.
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