From: Winfield Hill
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: 18 Jan 2003 09:08:07 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
> Winfield Hill wrote...
>> The Intersil HIP5600 is an adjustable three-terminal regulator
>> that can be thought of as a 500V version of the LM317. I've
>> used it in many of my lab instrument designs and found it to
>> be reliable and, like the LM317, an elegant design simplifier.
>> For example, here's a simple adjustable 0 to 400V regulator,
>> with a fixed-voltage feature.
>>. +480V ___ HIP5600
>>. ---| |---+---+-----------(O) HV out
>>. |___| | |
>>. | | 1.5k
>>. | | | adjust, 0 - 400V
>>. '---- | --+----o->o--------,
>>. | o--, |
>>. 10uF === 300V | 500k
>>. 450V | fixed | pot
>>. | 380k |
>> The switch allows one to select a fixed 300V output, or to
>> adjust the voltage to any value between 1.2 and 400 volts.
>> But this circuit has one potential problem that can cause
>> a component failure. As a design quiz, tell us what the
>> problem is, and find a solution that doesn't significantly
>> affect any of the circuit's functionality. Hint, the '5600
>> isn't the vulnerable part.
> While changing the switch, the output goes +480V for
> a very short moment. The capacitor may not like that.
> A higher rated cap is the easy way out, or place a
> cap from the resistor to ground, so the short moment
> the switch is filtered out.
That's true, the output can jump. However the 450V cap,
while pushed for an instant, doesn't seem to mind. Of
course I'd like a higher voltage safety margin, 450V parts
operated continuously at 400V aren't a good idea. Anyway,
you haven't found the problem, keep looking.