Electronics > Beginners

High voltage linear regulators.

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Zero999:

--- Quote from: Wolfgang on August 13, 2018, 10:51:57 pm ---In order to avoid SOAR problems, linear MOSFETs are a better choice for pass transistors than bipolar units.
They can also be paralleled, if you provide equalizing resistors just like with bipolar transistors.
I dont know any commercial HV power supply design for more than 100mA that relies on bipolar transistors.
Foldback current limiting is OK, but can lead to startup problems with loads that soak up a lot of current during startup.

--- End quote ---
The standard fix for start-up problems is to add a short time delay to the current fold-back.


--- Quote from: sureshot on August 13, 2018, 10:56:24 pm ---Thank you for your replys, links and schematics. I will definitely read up on this stuff before attempting to put a higher voltage adjustable linear power supply together. Thanks for the suggestion on the other regulator, I will go carefully over that also. I've wanted to use a mosfet as a series pass element, but believe it's voltage driven over normal BJT's current driven.
Thanks again for all the help.

--- End quote ---
A MOSFET can be used as a pass element, but the turn on voltage is higher than a BJT, so it will drop more voltage, than a BJT, but that might not matter. It's also possible to use a low drop-out configuration with a P-MOSFET, but it's difficult to stabilise.

mikerj:

--- Quote from: sureshot on August 13, 2018, 07:05:56 pm ---Thanks for the help with this, so is it not possible to current boost the TL783  ? I know the current will be far less at higher voltages. Something like 3 Amps at 15 Volts, and half that 1.5 Amps at say 30 Volts. And maybe 1 Amp or close to it at 60 Volts. Would that be possible ? Thanks again for the help.

--- End quote ---

How are you intending to power this regulator?  Is it from a fixed voltage a little above your maximum requirement (e.g. 65v) or do you have pre-regulator to minimise the voltage drop across the regulator?  If the first one then high current and low voltage is the worst possible case for power dissipation, which may be a limiting factor.

iMo:
What about an LM723??
You may build a low-noise (as the people report here), good stability, almost any ampers/volts linear regulator out of it..

sureshot:
An LM723 is something I've yet to do, but i expect it will be one of the general schematics for that regulator. I know there expensive, but toroidal transformers as i prefer there low profile over chassis mount types. I did try feeding an LM317 circuit with darlington, and smps for the input, but the final output was unstable up or down a volt from the output fluctuating.

Wolfgang:
Hi,

some thoughts about the LM723 at high voltages:

- The LM723 datasheets have some HV regulators that are floating. The problem: They have a minimum load requirement, and their stability is not as good as the low voltages ones.

- You can make a good and stable floating LM723 high voltage supply, but you need to make a separate little power supply for the LM723 itself (make it 12-15V stabilized) That works really fine.

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