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  • Author Author: rsc
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Experimenting with Polymer Capacitors - Basic Regulator

rsc

I'm starting out with a simple regulator circuit as shown below:

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I built 2 circuits on prototyping pcb material, one with my regular caps, and one with the poly caps.

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When I checked the first circuit, the regulator was working fine with about +_2mv ripple/noise.

When I checked the circuit with the poly caps, the regulator wouldn't regulate, and was drawing 500ma.

Nothing was shorted, and the caps still read ok in-circuit.

After disassembly, it seems as if I damaged the 4.7uf surface mount poly cap when I soldered it on the pcb.

it now reads 9.3uf - while I was testing the cap it jumped out of the 'gater clip and vanished.

I need these tweezers:

image

I will attempt to rebuild the circuit with the remaining sample cap. and try this again.

Scott

  • in reply to rsc

    Oh.. well, at least that's one characterization of polymer caps done, it seems they don't like reverse power!

    I've still to purchase some of those (I did order some metal can ones to experiment with).

  • in reply to shabaz

    Damn! You're right, I had the 4.7uf poly cap installed backwards.

    The mark is for positive.

    image

    image

  • Hi Scott!

     

    This is really great that you're documenting your experiences with the polymer caps with voltage regulators. I've not had the chance to try any polymer caps yet.

    I have the same issue with probe tweezers (I have some cheap variety), really easy to lose the part! : (

    Are the rectangular polymer caps marked like the round caps, or like rectangular tantalum caps?

    It's annoying that usual rectangular tantalums use the band to indicate positive, whereas on any cylinder cap (SMD or otherwise) the band or marking is nearly always negative. I don't know if the polymer rectangulars are sticking with the tantalum convention or not, but that could be something to check just-in-case.

    It is confusing enough, that when creating PCBs, I'll put a deliberate '+' on the silkscreen, as well as the band marking (i.e. I use the marking below, for tantalum (rectangular), and alu electrolytic (cylinder).

    image

    image

  • Nice work. Those probes do look useful - I didn't know they made those as well.

     

    Rod