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Old 20th August 2015, 07:31 PM   #1
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Default TL783, extending voltage range

Hello everyone,

Here is a question for the more informed.

Is it possible to extend the range of a TL783 to regulate +175 to +200 vdc?

Is it as simple as putting a zener (75 volt) below the adj pot?
Max current 10ma.

Thanks
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Old 20th August 2015, 08:33 PM   #2
Nisbeth is offline Nisbeth  Denmark
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What's the application? The TL783 is a floating regulator (just like an LM317) so it's the difference between in and out that can't exceed 125V. This means you should be able to regulate 200V or higher as long as the in/out differential stays below 125V. In normal operating I expect it would be OK, but you of course lose the short-circuit protection.

/U.
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Old 20th August 2015, 08:37 PM   #3
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That might not be the best way to do that. Yes you can use a voltage
regulator at higher than it's rated voltage but when you do you usualy
would build a preregulator to limit the voltage across the regulator. In
that case you would be better off using a Lm317t on a 150v zener, Here
is an aplication note about this.

http://www.ti.com/lit/an/snva583/snva583.pdf
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Old 20th August 2015, 09:25 PM   #4
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Hi,
You can use the LR8N3. It is a 480 volts regulator. Mouser part number 689-LR8N3-G .
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Old 21st August 2015, 02:15 AM   #5
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Quote:
Originally Posted by tauro0221 View Post
Hi,
You can use the LR8N3. It is a 480 volts regulator. Mouser part number 689-LR8N3-G .
LR8N3 will only dissipate 0.15mW in the TO92 package. It could be used driving the gate of a high voltage MOSFET, however. Maida solution is a nice idea which has been around for decades!
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Old 21st August 2015, 02:09 PM   #6
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Hi,
Yes, You can not use it directly. You just use the LR8N3 to feed the adjustment output voltage to the gate of the mosfet. I also use the TL783 in this way.
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Old 21st August 2015, 03:12 PM   #7
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Look at the attached diagram fo a way to run the TL783 beyond 125V. Zener D3 pulls up the adj pin during startup. Together with D4 it also protects the regulator from any discharges during power down. Max input voltage variation (incl. ripple) is now limited to the zener voltage.

Note the minimum load current on the TL783 is 10mA at all times, iirc.
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