Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!sdd.hp.com!hp-pcd!hplsla!deanp
From: deanp@hplsla.HP.COM (Dean Payne)
Newsgroups: sci.electronics
Subject: Re: How to make 600VDC from 800VDC
Message-ID: <5170094@hplsla.HP.COM>
Date: 24 Oct 90 00:21:10 GMT
References: <92@decabo.enet.dec.com>
Organization: HP Lake Stevens, WA
Lines: 21

>From: ssave@srvr1 (Shailendra Anant Save)
>Subject: Re: How to make 600VDC from 800VDC

[picture of 7805 regulator and 195V zener deleted]

Make that a 595 volt zener.

>        Note that here, the o/p will be Zener volatage plus the last
>two digits of the 75XX series regulators. They have very good regulation
>and a good current capability (1 Amp.)  The ground should be common 
>on either side.  You can use 7508 and use 192V Zener etc... Use a good 
>heat sink. Also any other good feature of the 75XX is that they have
>thermal shutdown.  Cost is about $2 at the Rack. (Radio Shack)

The greatest fault of this design is that most 78xx parts have a maximum
input voltage of 35V.  Even an LM317HV adjustable regulator can handle
only 60V.  This design will apply over 200V to the regulator, smoking it.

As drawn, the regulator would reach its internal thermal shutdown at a
lower output current than the requested 150-200mA, even when attached to
an infinite heat sink.