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From: Winfield Hill
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: 18 Jan 2003 10:15:35 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
> nospam wrote...
>>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 ...
OK, I thought a bit more and see it; you'll wire the
pot as a pot, rather than as a rheostat as I used it.
. +480V ___ HIP5600
. ---| |---+---+--------------+----(O) HV out
. |___| | | |
. | | 1.5k 0 - 400V |
. | | | adjust 500k
. '---- | --+--o->o------>pot
. | o--, |
. 10uF === 300V | |
. 450V | fixed | |
. | 380k |
> 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
> slider path.
As you can see, the 1.5k + pot still has to absorb the cap's
energy if the pot is set near zero, and we know the pot has
failed when used this way (the 1.5k seems not to mind).
> Now the question remains, what's a solution that doesn't
> substantially affect the circuit's intended functionality?
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