high voltage by 78

It is Possible, Using a High Voltage Value, Zener in the ground lead to Ground. But it Requires Special Care with the Current Draw at that voltage.

Reply to
Gary Lecomte
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How could I regulate 190 V DC whit a 78xx? I knew these devices can be used at this high voltage.


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I believe you mean "Memento Audere Semper" (remember always to be daring or audacious). That's what happens when you copy mottoes off statues.

The LMXX regulators are good for 35V maximum input voltage. You could shoehorn one into a scheme for a 190VDC linear regulator, but it would be more trouble than it's worth. Even as a reference voltage, you'd have to provide a preregulator to keep from smoking it.

It's possible you saw a 7812 or 7805 as the IC that provided the low voltage power for the control circuitry in the high voltage power supply you were looking at.

Be careful. High voltage kills.


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I figured he was thinking of the LM317, which because of its different arrangement, can regulate much higher voltage. I'm not sure of the limit. I'm sure it's spelled out in the datasheet.


Reply to
Michael Black


The script on Roman statues would have used the letter 'V' not 'U' :-) A 'smilee' on the other hand would not be found there unless it was spray-painted on. Cheers - Joe

Reply to
Joe McElvenney

These devices attempt to keep a constant voltage between their common input and output. Thus, you might be able to make a high voltage regulator by floating them, like this:

.--------. Vin | | ----o 78xx o----o---------. | | | | '----o---' .-. | | | | | | | | | | '-' | | | | '--------o | | | .-. .-. | | | | Load | | | | '-' '-' | | GND ------------------o---------'

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The voltage divider forces the device to attempt to create a voltage of xx volts across the top resistor.

I haven't considered startup situations, or high load currents.

Regards, Bob Monsen

Reply to
Robert C Monsen


You are correct sir. "In God We Trvst." I'm not so sure about the smilie face, those Romans were wild and crazy guys.

Reply to
Tom Biasi

Why does "MEMENTO AVDERE SEMPER" excite curiosity? It's 'cos latin? That motto was wrote by Gabriele D'Annunzio, do u know that poet?


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thanks all. Now I understand. example: I need 190VDC, so using a 7824 and Im going to put one 166V zener between common and gnd, is it ok?


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Mottoes are curious things, I guess. I personally prefer the one etched on the sword of Oscar of Gordon, Hero of Heinlein's "Glory Road" (1963) (view in fixed font or M$ Notepad) ;-) :

"Dum vivimus, Vivamus" or "While we live, let us live!"

Very appropriate for those who want to vigorously seek out and enjoy the best things in life, as well as those working with high voltage.

But seriously, the idea of just placing a 166V zener in series with the GND terminal of a 7824 isn't going to cut it. Among other things, a 1uF output cap is required to stabilize the output. At turn-on, you'll have 190V between IN and OUT, and smoke. There are other reasons why it just won't work, but that will do.

If you really need 190VDC at small current (0 to 15 mA), you might want to try something like this (view in fixed font or M$ Notepad):

Q&D 190VDC Supply 4700 Ohm 20 Watt 192VDC _/ ____ 1N4007 ___ + o -o/ o--|_--_|-. ,-------. ,--o-----o---->|-o-|___|-o-------o 1/4A )|( )|( | | | + | )|( )|( | | ### - .-'|( )|'----. | --- ^ | |( )| | | | | | '-.|( )|,--' | | ___ | String of )|( )|( | .---|___|-o | Sixteen )|( )|( | | | 100 | 1N4742 o----------------' '-------' '----o-' | 2W | + | (12V Zener) 120/240V Pri | ### - 12V Sec | --- ^ X 2 | | | '----|

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You would probably have to use a high voltage transistor to ensure the input to the regulator remains within the 35v rating. you may find that even with a zener, or floating the regulator, the change in unregulated voltage may exced its rating otherwise.

If you look through the many voltage regulator spec sheets youl find some have an amasing colection of novel and useful circuit applications.

Colin =^.^=

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Uhm, do you really think that one has to be "wild and crazy" to created an empire that lasted 1,000 years? Gene

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On Saturday 11 September 2004 07:38 am, Michael Black did deign to grace us with the following:

The only "limit" on either is the voltage across the chip itself. You could use a 7812 to regulate 190V, as long as the supply doesn't go over 225V or under about 193, and you have a stiff reference at +178V. (Include all the rest of the standard caveats/disclaimers, of course.)

HTH! Rich

Reply to
Rich Grise

On Sunday 12 September 2004 11:12 am, CFoley1064 did deign to grace us with the following:

I can corroborate this. When I was in the USAF as an electronics tech, we were required by regulation to take off all jewelry, i.e. rings/watches, and keep one hand in our pocket. They didn't even like us to wear our dog tags.

Another little thing you can do is ground one finger while poking around - like, let your little finger rest against the chassis, as if you're steadying the probe - that way, when you get zapped, you get a burn on your hand, rather than cardiac arrest.

Good Luck! Rich

Reply to
Rich Grise

Hi Chris, thank you! ...

**** The "stupid" questions are only stupid if you don't know and _don't_ ask them **** that is a good motto!!!

thanks again if you lost time to me, your advices are my precious.



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No. But it helps

Reply to
Tom Biasi

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