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| High voltage linear regulators. |
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| sureshot:
I'm currently looking at high voltage linear regulators, with the intensions of going up to 50 - 60 Volts maximum output. I've come across two candidates that might be worth using. The circuit is the general linear regulator layout with the addition of two series pass transistors to boost current. I've messed about with the LM317 with 2 x and 4 x series pass transistors with good results. But as I'm looking to go up to 60 Volts is there any specific i need to take in to consideration ? Below are the two data sheets of the regulators im thinking of trying. Its the one with the higher maximum voltage that I'm most interested in. What i think could be an issue is the higher voltage on the emitter base chain of the transistors and resistors, as 1.25 - 60 Volts is a large differential to cover. Thanks for reading any help appropriated. PS. PDF files are to large to post. Its the LM317HV and the TL783 Voltage regulators. And the later of the two I'm most interested in. Thanks again |
| Zero999:
The LM317 has no upper limit to the maximum output voltage. It's a floating regulator, so all that's important is the difference between the input and output voltage, which mustn't exceed 40V for the standard part, or 40V for the HV variant. The main issue with higher input, than the LM317s maximum rating, when the over-temperature/current protection kicks-in, is the full supply voltage will appear across the regulator. Another transistor can be added in series with the LM317, to drop most of the voltage and ensure the maximum voltage rating is not exceeded. Note that the above circuit drops about 40V across the LM317, which is too much. The zener should be changed to a <30V part to drop more voltage across the transistor. |
| sureshot:
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. |
| sureshot:
I couldn't post data sheets, it said file to large. But here are a couple of the circuits from the data sheets. Although one has very little current capability, and the other looks similar to an LM317 circuit. But I don't need nowhere close to 125 Volts, but wandering if series pass transistors can be added to the more LM317 type looking circuit. |
| Wolfgang:
Hi, both the LM317 and the TL783 are not extremely robust at high voltages. When I get you correctly, your output current requirement is a few Amps, this means you have to use external pass elements anyway just because of dissipation, especially when the output get shorted. Transistor SOAR will be an important limiting factor then. After some bad and smelly experiences with the National Semiconductor LM317 high voltage example circuit (same as you have below) I tried a TL431 based one with a well-cooled linear MOSFET pass element. IMHO, it has the following advantages: - input voltage can be up to 400V - output voltage from 2.5V to Input voltagev - 20V - exact current limiting - output current could be up to a feq amps, depending on power FET used, voltage difference and (fan) cooling - low ripple Some info can be found at: https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/ or here : https://electronicprojectsforfun.wordpress.com/power-supplies/ or here: https://www.changpuak.ch/electronics/VB408.php - this is where I got the idea from, thanks, Alex. |
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