From: Winfield Hill
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: 18 Jan 2003 12:20:35 -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.
> Ooh, a quiz for the group. Does it matter if we don't write
> our name at the top of our answer?
I'd love to see your real name added to the top, analog. :>)
> Ok, I have two recipes to serve up your design without cooking
> the pot.
> Pot ala shunt d'la protection: Gently lift the bottom leg of the
> pot and toss in parallel one beefy NPN transistor (collect-base).
> Add one finely grounded 1k resistor (base-emitter) and pSpice to
> taste. (May require some additional series resistance.)
This is the first recipe? It seems uncooked, perhaps it needs
some spice added to the base to make a constant-current sink?
> Output surprise: stir in a series diode before adding the
> capacitor to the cathode side. (Not recommended for those fond
> of fine regulation.)
That's a reasonably acceptable idea.