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Subject: Re: Power supply power-up issue.
Date: Mon, 21 Oct 2002 18:57:10 +0200
Organization: XS4ALL Internet BV
NNTP-Posting-Date: 21 Oct 2002 16:57:10 GMT
X-Newsreader: Forte Agent 1.92/32.570
On Sun, 20 Oct 2002 19:17:06 GMT, Rogue wrote:
>I built a standard +5V regulated power supply (12V transformer, bridge
>rectifier, 1000uF capacitor, 7805 regulator, 100uF and .1uF capacitors)
>and am having power-up problems with a CMOS daughter board I'm working
>The manufacturer mentions that the module is finicky about getting a
>quick power-up and recommends using an MCP101-475DI voltage supervisor
>(which I am) on the reset pin.
>It holds the module in reset for 350ms after the supply voltage reaches
>a stable operating level (4.75V).
>Apparently this isn't enough because if I plug it in to the wall it
>doesn't work, but if I switch power between the 1000uF capacitor and
>the regulator it does... same thing happens when using a wall wart.
>Can anyone give me a clue as to how I might go about getting a cleaner,
>quicker initial power-up from the power supply? Adding more decoupling
>capacitors doesn't help.
After 350 ms - is the voltage still ramping up while the 100 or 120 Hz
ripple may cross the reset treshold a few times? Peak ripple may set
off the "voltage OK" level, while bottom ripple still creates
In critical ckts I always measure voltage overhead between "raw" and
stabilized voltage. If the ripple band is known, a safe startup *and*
shutdown (i.e. while stabilized power supply is still nominal) is
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