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Old 22nd August 2012, 08:31 PM   #1
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Default Bipolar bench power supply for testing audio circuits

Hi all!! I found a 0-50v, 1A power supply circuit in a RCA SOLID STATE DEVICES MANUAL SC16, pages 680-681. Has anyone here had experience with this circuit. It uses CA3086 as a zener reference and a CA3130 as an error amplifier. Someone said that the RCA line was taken over by Harris Intersil??? I know this is old but I haven't seen anything that will go to + and - 80v. If I wanted bi-polar positive and negative tracking voltages to 80 v, then I was thinking about using mj15003 and mj15004 as the pass transistors. But what is the advantage of having bipolar bjt's versus just building two identical power supplies. It must be tracking ability between the two. I would appreciate any advice and or pointing me toward a an article that is more up to date than 1980. I've looked but they are always Lm337 and LM317 and that's not gona cut it to 80v. Thanks Ray
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Old 22nd August 2012, 11:19 PM   #2
Enzo is offline Enzo  United States
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They make high voltage regulator ICs. For example, this one goes to 125v, and the 700ma current rating can be increased with pass traqnsistors.

http://www.ti.com/lit/ds/symlink/tl783.pdf
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Old 23rd August 2012, 09:56 AM   #3
AndrewT is offline AndrewT  Scotland
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Tracking is nice to have.
But I think adjustable current limiting is far more important and useful.
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Old 23rd August 2012, 01:15 PM   #4
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Thanks, Enzo and Andrew. Yes, the RCA circuit has current limiting adjustment and yes I would like that very much. I would like to know what is the advantage of a mirror imaged bi-polar PS where the - side is pnp and the positive side is npn versus building two identical PS say with both npn pass transistors and connecting them where the bottom one puts out negative voltage. My HP power supply does this and is not mirror imaged.
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Old 23rd August 2012, 03:36 PM   #5
AndrewT is offline AndrewT  Scotland
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if you do build a dual channel PSU then you MUST build them so that they are isolated.

That isolation requirement removes the option to combine a pair of opposite polarity supplies.
You need two supplies from separate windings and through separate rectifiers.

This arrangement allows you to series connect the supplies if you need so and also allows parallel connection if extra current capability is needed.

The isolation also allows one supply to power a circuit and the other supply to fit into some elevated voltage tapping in the circuit. That could not be done if there were a common ground between the dual supplies.
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Old 23rd August 2012, 04:25 PM   #6
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For amp testing I use a couple of bipolar supplies -- the easiest is one with a variac controlling the primary of a big toroid transformer with separate rectifiers and caps.

You can use depletion MOSFET's as an "easy to implement" current limiter. Walt Jung has some discussion in his article "Current Sources 101" on the waltjung.org website.
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Old 5th September 2012, 07:31 PM   #7
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Default RCA power supply in solid state manual

OK, I looked at the Jung article and I didn't see much of anything above 18v. I'm sure there are more up to date solutions than this one but I live far from an engineering library. I looked at the Linear Technology at the LT1083 but again nothing that would go to 80 volts. I will build two identical power supplies and connect them where the bottom serves - 80v. But how do I get them to track obviously with some type of opamp circuit. I will use mj15003-4 and the modern mj transistor cor the 2n2102. But I really unsure as to the reliability of the cmos or dmos harris opamp and transistor array.
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Old 5th September 2012, 10:22 PM   #8
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A major problem of wide range, high voltage/current linear regulated supplies is that unless you use them near their max. voltage, the dissipation and construction cost become enormous. This is why you see so few high voltage linear supplies and those that are about, usually only offer low current.

Jackinnj's suggestion to use a variac or multi-tapped transformer is adequate and much simpler, whilst it could still track voltage reasonably and can easily include the all important current limiting, since amps seldom need voltage regulation but do need this for amp. testing and setup.

Randy Slone published a good, basic and relatively inexpensive adjustable limiting dual supply design. It's on p389 of his "High Power Amplifier Construction Manual" (Mc Graw-Hill) with recommendations for use. This is an older title but easily read and cheap from Amazon etc.
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Old 6th September 2012, 12:25 AM   #9
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Default Thanks Ian!

Very much appreciate the McGraw Hill book reference. Ray
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Old 6th September 2012, 12:43 AM   #10
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IMO, tracking is nice if you get it for free, but completely unnecessary. I run twin Kepco supplies on my bench and the ability to run constant current is a huge feature I use constantly (no pun intended). You don't just want current limiting for protection, but also the ability to run at an adjustable constant current setting.

Just for fun, download some Kepco, Lambda, HP and similar supply manuals and study the schematics.
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