One question: Can someone recommend a high voltage NPN transistor?
I want to build a lab bench power supply for use with vacuum tube amp prototype design. I need variable voltage from about 500V to 100V DC I'd like to design for up to 1KV (2X safety factor) but I'd never use more than about 650V Current up to about 100 mA if I can
I don't need good regulation but I want continuos variable voltage. So my plan is to use an LM317 to compare output volts to a set point and control the base of this transistor so that the LM317's input end is about 5 to 10V higher than the set point. Very simple. The LM317 will shunt the last 10V
But the transistor needs to take 1Kv C to E at 100ma. That is 100W worst case.
Does such a transistor exist. If there are several I want the "most generic" and easy to source part.
Yes I can hunt parts catalogs but I want a common part that "everyone" knows and is easy to source in the US. Parametric searches don't give you that kind of info
I want to build a lab bench power supply for use with vacuum tube amp prototype design. I need variable voltage from about 500V to 100V DC I'd like to design for up to 1KV (2X safety factor) but I'd never use more than about 650V Current up to about 100 mA if I can
I don't need good regulation but I want continuos variable voltage. So my plan is to use an LM317 to compare output volts to a set point and control the base of this transistor so that the LM317's input end is about 5 to 10V higher than the set point. Very simple. The LM317 will shunt the last 10V
But the transistor needs to take 1Kv C to E at 100ma. That is 100W worst case.
Does such a transistor exist. If there are several I want the "most generic" and easy to source part.
Yes I can hunt parts catalogs but I want a common part that "everyone" knows and is easy to source in the US. Parametric searches don't give you that kind of info
Look at BUT2520F although power dissipation may require you to parallel (with current sharing)
http://docs-europe.origin.electrocomponents.com/webdocs/0027/0900766b80027ad0.pdf
Apart from power rating there are many suitable devices.
Edit... why not use FET's such as 2SK1120 etc
http://www.datasheetcatalog.org/datasheet/toshiba/2998.pdf
http://docs-europe.origin.electrocomponents.com/webdocs/0027/0900766b80027ad0.pdf
Apart from power rating there are many suitable devices.
Edit... why not use FET's such as 2SK1120 etc
http://www.datasheetcatalog.org/datasheet/toshiba/2998.pdf
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The problem with bipolars is their frighteningly small SOAR at high voltages: the BUT2520 in the example above only accepts less than 30mA Ic at 800V.
This is the case for most high voltage bipolars.
Some have a Vceo of 1.5KV; maybe they could do a little better, but I don't have detailed data:
2SD300, 2SC643, BU500, MJ12005...
The best solution IMHO is to use a MOS: this guy could easily handle the job:
http://www.st.com/stonline/products/literature/ds/11262/stw4n150.pdf
This is the case for most high voltage bipolars.
Some have a Vceo of 1.5KV; maybe they could do a little better, but I don't have detailed data:
2SD300, 2SC643, BU500, MJ12005...
The best solution IMHO is to use a MOS: this guy could easily handle the job:
http://www.st.com/stonline/products/literature/ds/11262/stw4n150.pdf
I think 2x Vmax as a safety margin is unreasonable. ( a linear AC/DC converter it doesn't happen) I would agree with an added current and power requirement. Because the hardest part of a lab supply design will be current limiting the thing!
Offline Flybacks need 2x voltage, but it's almost impossible to design for 5 to 1 output voltage control. They like PWM for current/power control. You will probably need 2 stable loops under all conditions to even attempt it.
a very long time ago when I was young and careless (stupid) I drove a tube output transformer backwards with a square wave and a "H" switch. A "H" switch is just another name for a bridge. The bridge was driven by a square wave generator, ne555 timer, and appropriate current drivers. I used a single power supply +48 volts and a bridge on the output of the transformer with a small value high voltage cap. The bridge was a stack of 1n4007's. My VTVM ( vacuum tube voltmeter) could not read the output as it was was greater than 1.5KVdc.
since you want to vary the output DC you would have to use something like a high power audio amp to drive the transformer to vary the output DC. If you drive the transformer with a square wave, the output rectified DC would not need a lot of filtering. You could also use a higher frequency 1khz for example. Picture a square wave going thru a bridge rectifier, you end up almost with DC with very little ripple.
since you want to vary the output DC you would have to use something like a high power audio amp to drive the transformer to vary the output DC. If you drive the transformer with a square wave, the output rectified DC would not need a lot of filtering. You could also use a higher frequency 1khz for example. Picture a square wave going thru a bridge rectifier, you end up almost with DC with very little ripple.
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My suggestion -- regulate the primary -- you can use an opto-isolator to sense the output voltage and drive the error amp on the primary side. Back when I was a lab RAT we used this to derive very clean voltages for our NMR stuff.
It's not difficult -- you can use an amplifier and a sine source to drive the primary -- even a paralleled LM4780 type. Yes, you'll need a DC power supply, but You'll also burn less power this way -- just the power dissipated by the amplifier in Class AB.
Make sure that the insulation on the secondary can stand off the voltage.
It's not difficult -- you can use an amplifier and a sine source to drive the primary -- even a paralleled LM4780 type. Yes, you'll need a DC power supply, but You'll also burn less power this way -- just the power dissipated by the amplifier in Class AB.
Make sure that the insulation on the secondary can stand off the voltage.
My current bench supply uses a way-big tubular ceramic power resister it has a metal tap that is clamped down with a band. To change voltage you power down, drain the filter caps, loosen the band with a screw driver and move it down the tube, tighten it, power back up and measure voltage. Repeat as required. The thing works well and I can get anything from 650V to under 100v but what a hassle to use and then there is that 200W heater and the fan to keep it cool
I'm just looking to reuse most of the parts and make it easier to use
Fuses make great current limiters. I like to use several of them in something like this
I can also place a resister down stream of the regulator to limit short circuit current. I don't care about performance in this application
Or low tech:
Use a variac.
You specify you don;t need much in the way of regulation. And really not a lot of current. SO make regular basic conventional power supply of the highest voltage you will need. Just rectifiers, filter caps, transformer. Then dial the primary up and down to suit, from that voltage down to whatever lower voltage you need. You could put a small variac in a box with this, or just make the box, and plug that into your bench variac.
One might object that transformer ratings and other performance parameters might be compromised, but we are not asking for any huge output. If I need 100ma and I have a 1A winding, I don;t care if I have to derate it to 750ma.
In fact I recently picked up a piece of lab gear at the MSU Surplus store, an electrophoresis power supply. It made adjustable B+ voltage exactly that way. A small (3" or 4") variac controlled the supply. 0-500VDC @ 125ma.
Gelman Model 38206 electrophoresis power supply - Phoenix Equipment, Inc.
Use a variac.
You specify you don;t need much in the way of regulation. And really not a lot of current. SO make regular basic conventional power supply of the highest voltage you will need. Just rectifiers, filter caps, transformer. Then dial the primary up and down to suit, from that voltage down to whatever lower voltage you need. You could put a small variac in a box with this, or just make the box, and plug that into your bench variac.
One might object that transformer ratings and other performance parameters might be compromised, but we are not asking for any huge output. If I need 100ma and I have a 1A winding, I don;t care if I have to derate it to 750ma.
In fact I recently picked up a piece of lab gear at the MSU Surplus store, an electrophoresis power supply. It made adjustable B+ voltage exactly that way. A small (3" or 4") variac controlled the supply. 0-500VDC @ 125ma.
Gelman Model 38206 electrophoresis power supply - Phoenix Equipment, Inc.
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