I'm using a standard RC servo in an automotive system. The servo is constantly moving and sucks alot of current. I can't control the servo off of 12volts without burning it out. I've used a 5 volt regulator in the test system, but with just one servo the regulator gets pretty hot. If I did it this way, I would need a single regulator for every servo that I used and even then the current requirements would be on the edge of the regulators abilities.

I need another way of reducing the voltage, but still getting a good amount of current. I don't care about clean power, the motor speed doesn't need to be extra smooth or precise. Would a voltage divider or Zener be a good solution, or would it cause other problems?

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Mark Higgins

 

Both of those would be far worse, you can't have a linear system without generating heat - what size regulator are you using, and what heatsink do you have on it?.

A cooler solution would be to use a switching regulator, but that's a little more complicated.

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I have a 1 amp 7805 running it. The servo is constantly changing direction and jumping back and forth (which is what it's supposed to do). I'll be running 3 servos. I was hoping for an easy way to avoid using 3 regulators with heatsinks, since I know input voltage will always be 12v. If there's no simple way to avoid it, I'll just deal with it and add a good sized heat sink.

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Mark Higgins

 

Sounds like you are going to need to change your 7805 to a higher rated chip. I thought that the servos consume somewhere between 400-700mA depending on load. I would check how much current the servo is using to have an idea of how much is the regulator going to have to deliver.
Say you use 1A (that is pretty high for a servo, not sure if it can handle it), then your 7805 will have to waste as heat 7W. A 7805 (in a TO-220)with infinite heat sink is able to waste 20W, check attached graph.

I have driven standard RC servos under 6V and 7.2V. The idea here being that the servo at a higer voltage, will consume less current, and at the same time the regulator has to waste less voltage, therfore reducing the heat.

You may want to also try to use a LM2576HVT-5.0 is a switching regulator. It needs a lot of external part (when compared to the 7805) but it can deliver more.

Ivancho

Attached Images

7805_Watts.jpg (28.8 KB, 598 views)

 

Hi DirtyLude,

You can try 5 or 6 diodes in series with the regulator input that is if you got room for them. This will take some heat of the regulator. If you use a LM78S05 it can supply 2 Amps and with a small heatsink it will run 3 servos for you. Why not bolt it to the car chassis the lug is negative so no problemo.

Ante :roll:

 

Thanks for the input everyone.

I have a bunch of regular 7805's in TO-220 packages that I'd like to use up, so I'd rather use 3 of these than buy a larger regulator just for this purpose. The microncontroller I'm using runs 3.3v, so this stash of 5v regulators I have doesn't get used much.

I have a heatsink that I stole from an old power supply and by drilling some new holes it should work for all three regulators quite easily. I didn't realize that you could push a regular linear so much farther with just a heatsink.

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Mark Higgins

 

Just like any power device, without a heatsink they have to be massively derated.

__________________
PIC programmer software, and PIC Tutorials at:
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