Power Supply to run Prop from 15vdc-35vdc

Tired2

Hi everyone,

I am new to the Propeller, and new to this forum. I have been searching through old posts and reading a lot about filtering capacitors...

My application is a DC motor controller, and I'll be using the Propeller to monitor some things and control pwm.

I have prototyped my first power supply, and I was looking for some input...

My basic power supply (see schematic) runs 3 linear regulators... the LM7812, LM7805, and the LM2937-3.3.

I made the mistake of soldering in an electrolytic cap for the 10uF on the 3.3 supply, so I'll be swapping that out I think for a ceramic.

So, here are my questions:

Will this power supply hold up to the noise and transients present running off the same 24vdc battery pack that is running the Perm. Magnet DC Motor?

I read that electrolytic caps are not good on these regulators... is that only on the output stage?

How do Mylar caps compare to ceramics when it comes to ESR? Is ESR only important on the output stage of linear regulators?

Are Tantalum caps always recommended in place of ceramics?

===

I read the thread about the "singing" regulators, so we can let the major theory of linear regulators and output capacitors stay there, I'm looking for broader design rule sort of answers.

Thanks in advance to anyone who is willing to help.

Leon

Check the regulator data sheets to see what type of capacitors are required (ESR and so on).

I'd use a switcher instead of all those regulators - much cheaper and much more efficient.

Whether to use tantalum or ceramic depends on the regulator. If it isn't specified you can use either. Ceramic are cheaper.

I wouldn't use mylar, they are large (high working voltage) and have a high inductance.

You will need a lot of filtering on the 3.3 V supply, and careful PCB layout.

Leon

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Sapieha

Hi Tired2.

Tantalum will not be in place of ceramic.
Them will be parallel with ceramic caps. (22-47uF)
More power You dry from Reg biger Tantalum is recomended

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Sapieha

Nick Mueller

Voltage-regulators are quite good at running stable even without a cap behind them (read the datasheets). But what they are really bad at is suppressing transients on their input. So in a noisy environment like yours, it is best to have a choke coil and then a cap in front of the first regulator.


Nick

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Bobb Fwed

I usually use three capacitors: one on the incoming power, a larger electrolytic (470µF or 1000µF). The ESR is about 420mΩ or 250mΩ respectively.
On the output, most linear regulators aren't too picky, but if you are using a low-dropout regulator, it is very important. No matter what, I usually use a larger capacitor like on the input as well as a smaller (0.1µF or so which has probably about 10-20mΩ ESR) ceramic capacitor. The smaller cap is for higher frequency issues, but not usually necessary.

EDIT: For reference I use the 3.3V low-dropout (LDO) regulator: NTE1904 (through-hole TO-220). This can take a continuous input voltage of 40V.
Or I use LM2937IMP-3.3 (surface mount SOT-223) which can go up to 60V (transient) input, or 26V continuous.

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Post Edited (Bobb Fwed) : 6/26/2009 6:13:58 PM GMT

BradC

http://forums.parallax.com/showthread.php?p=818821

This power supply runs a propeller from 8-30v. If you removed the linear reg section (you won't need low power standby), hardwired the LM2576 on (ground pin 5) and replaced the LM2576 for a LM2576-HV you would have a board that functioned from 8-60v. The 330uH inductor in the switching regulator section is _extremely_ good for suppressing spikes and other nasties on the incoming supply.

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Peter Jakacki

Switching regulators are the way to go but they don't have to be bulky. In fact I have never had the need for TO220 type packages or bulky inductors. The LM2594 is quite happy to deliver 500ma with input voltages up to 60V for the HV version. A pin compatible upgrade to this is the higher frequency LM2675 which just needs an extra 10nF capacitor but works with a 47uH inductor.

What I like to do mostly is to switch regulate to +5V and then just use tiny SOT-23 LDO regulators for nice clean 3.3V supplies. The +5V usually goes off to those chips that need it plus I run LEDs directly off +5V through to the Prop as the LED voltage drop takes care of the problem of attaching loads to +5V.

*Peter*

Tired2

Thanks for the suggestions. I think for my current project, I'll stick with what I have, but I like the idea of using LM2576-HV instead.

Would you recommend against using the LM2576-HV for the 3.3v supply? For my next power unit, I think 2xLM2576-HV would be nice for 12v and 5v, then I'd probably run the LM2937-3.3 linear regulator off the 5v supply.

BradC - Currently I do not have a need for a low power standby, but I like the idea in the thread you posted. Do you have a schematic?

Thanks.