From: Winfield Hill
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: 18 Jan 2003 10:06:26 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
>Winfield Hill wrote:
>>. +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.
> Well I will assume it is the capacitor which can see 480v
> during switch changeover (The 1k5 and pot also get hammered
> but given no specification I assume they can take it).
> The capacitor solution
> | |
> 1M5 |
> | /
> --o o---/
> \ 500k
> o pot
> | |
> --------------------- gnd
> If that isn't clear - leave the pot in circuit and either
> ground the wiper or a parallel 1M5 resistor.
I don't understand your solution, the job for the switch is
to select a fixed 300V setting, irrespective of the pot's
setting. In fact, after some time at 300V one can go back
to the origianl pot setting, so it's like a memory. :>)
But you were getting close. Thomas did get the answer:
the 500k pot can be destroyed from discharging the 10uF cap
if it's setting is low enough, where only a portion of the
pot is available to absorb the nearly 1 joule of energy.
The pot has been observed to open near the bottom of its
BTW, the 1.5k resistor doesn't seem to mind the discharge.
Now the question remains, what's a solution that doesn't
substantially affect the circuit's intended functionality?