Circuitry design

I have a circuitry with 3 servo motors + pic.

I am using two parallel 7805 for the motors and one only for the pic.

Unfortunately I found that a choppy servo motor behaviour is due to not enough current being delivered - ie I am working with interrupts so two servos need current at the same time.

I found that one (of the parallel) 7805 remains cold while the other one is becoming very hot.

Should there be one 7805 for each motor + one for the pic, ie 4x7805 or should my current configuration be sufficient but one 7805 is faulty or some other solution?

Maximum current per 7805 is 1A accord. to the data sheet.

This is easier than getting the load balanced between multiple 7805 regulators.
http://www.national.com/mpf/LM/LM350.html
3 amps with heat sink.
Use the LM350 for the motors and a 7805 for the PIC.

If you still want to parallel the 7805s, bend the legs so one heat sink can be attached to all of them at the same time (chips side by side) . The legs should be bent enough to allow at least 0.20 inch traces on all legs. Do not use a set of capacitors for each regulator. Put together as stated and you have one big regulator.

Or you have a bad 7805.

Hi Security,

You also can use a PNP Ballast to boost the 7805 regulator output ...

See National Datasheets ( Lm 317,350,338 ) AND MC78xx Datasheets for such info.

Do not forget to use a Large value Low ESR capacitor to allow current "surges" ...

Alain

Quote:

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Originally Posted by mackrackit

This is easier than getting the load balanced between multiple 7805 regulators.
http://www.national.com/mpf/LM/LM350.html
3 amps with heat sink.

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As both 7805 are parallel does that mean I can just replace one of them with a LM350 and remove the other one?

Yes, one 350 will take the load of two 7805s. The pin out is different and you need external resistors to set the voltage of the 350 because it is adjustable, so it is not a direct replacement on a PCB.

I prefer to not redesign my current circuitry. What about other components doing the trick fitting in the position of my 7805?

PS: If I actually had to redesign my circuitry I would use http://www.elecfree.com/electronic/5...ly-by-tip2955/.

Quote:

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Originally Posted by Security

PS: If I actually had to redesign my circuitry I would use http://www.elecfree.com/electronic/5...ly-by-tip2955/.

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Yep, that would work to. Just like Alan suggested.

A 78S05 is a 2A version of the 7805.

Hi,

And a 78T05 CT ( Motorola ) is the 3Amps TO 220 model ...

also the LT 1085 CT 5 ...

in TO3 case, you have the LM 323 K

But do not forget the convenient heatsink !!! - what about your transformer and rectifiers ???

Alain

Good idea Acetronics, that is exactly what I want.

Problem solved.

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