Re: Very strange standard voltage regulator behaviour

From: Alex (music_at_xatomic.ch)
Date: 06/26/04 

Date: 26 Jun 2004 07:13:33 -0700

legg <legg@nospam.magma.ca> wrote in message news:<75djd05ddidkl5bof8h1eo24i9i8pc2bf6@4ax.com>...
> On 22 Jun 2004 15:45:22 -0700, music@xatomic.ch (Alex) wrote:
>
>
> >The whole psu is built on a PCB carefully designed regarding the
> >needed gaps between mains and secondary side, no gnd loops etc.
>
> Perhaps you used the wrong regulator puppet in your layout, this time.
>
> LM320 series isn't the same as LM340. Perhaps you've missed routing
> the ground line through the regulator, in the new layout.
>
> Check the layout on the actual board, anyways, because it's one of the
> things that always changes, whether you intend it to change, or not.
>
> RL

Hello,

many thanks for all your answers. As there were no errors in the
layout/pcb (I always make multiple checks before I etch a pcb), it
must have been in one of the components. And finally the fault was in
the 220nF bypass caps, surrounding the voltage regs. These are 100V
MKS caps and they had a leakage current of several milliamps, which
increased over time until the psu was overloaded. Very strange, I
never experienced this before. Usually I get all components from my
local electronics supplier. But this time I took the components from
our lab as this is a semester project. Probably someone killed this
caps and put them back in the labs component inventory.

Now the psu is working fine with "my" caps. An further I replaced the
filter cap with a smaller one (4700u) and a 1ohm series resistor to be
withing the specs of the B40C800 rectifier bridge.

Again many thanks for your help

and kind regards,

Alex

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