Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: Sat, 18 Jan 2003 20:26:49 +0000
NNTP-Posting-Date: Sat, 18 Jan 2003 20:22:57 +0000 (UTC)
User-Agent: tin/1.4.2-20000205 ("Possession") (UNIX) (Linux/2.4.19 (i686))
Winfield Hill wrote:
> Frank wrote...
>> 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.
When switching from 300V to 0V the energy stored in the cap will
be disipated by the resistor, 10uF@300V is about half a joule and the
timeconstant is 15ms, peak power disipation is 60W.
While managable this will require some care in the selection of the
If a minimum voltage of around 22v is acceptable than a 27K fixed resistor
in series with a 470K pot would reduce the peak power disipation to 3W
and thus solve the problem.
Voltage ratings of resistors and in particular the voltage rating of the
pot will need to be considered.
Just guessing here......
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