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    0-30 Vdc Stabilized Power Supply

    I thought it might be interesting to look at the input voltages of U2 under various conditions in my current design (iteration 18) in Multisim.  I could get the NI input of U2 as low as -1.1v by setting current and voltage pots to 0.0 and reducing R17 to zero. In my current design, R17 goes to...
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    0-30 Vdc Stabilized Power Supply

    Yes, I understand this. Responding to your numbered points: 1) Agreed. 2) "Voltage is set to 20.0V and current is set to 1.0A. A load of 10 ohms is applied. The output voltage must drop to 10 ohms x 1A= 10V and the output of U3 drops to about +3.13V. The input of U2 is about +3.73V." I think...
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    0-30 Vdc Stabilized Power Supply

    Ok, here's my question. The D9 diode pulls down towards the -1.3v supply when current limiting is in effect. Depending on the op amp selected, the output of U3 can go as low as its negative supply (-1.3v) or 0.3 higher than that (-1.0v). The D9 drop is 0.7 volts max, so doesn't the input of U2...
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    0-30 Vdc Stabilized Power Supply

    Ok, continuing on. Although I think U2 *could* be driven from a regulator, my current design doesnt do that. It uses a 44v OA, probably the TLE2141, although I haven't made a final selection. The reasons are: 1) the voltage requirements 2) the null offset pins available. 3) the PSRR pwr...
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    0-30 Vdc Stabilized Power Supply

    As to the 33v lm317, I wasn't clear.  Let's look at the output. From ground, we need 1.35 volts at 5A across thecurrent sense resistor R7. We need 30v across the output. We need another .5v assuming 1.6A through each 2N3055, another .6v base to emitter in the 3055s and another .6 across the base...
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    0-30 Vdc Stabilized Power Supply

    I'll try to reply. First, itried to repost the rev 7 schematic.  I'm stuck using a smartphone, so it may  take me a while to get it correctly posted.  The rev  7 schematic is marked as 3 amps maximum. However I'm just using that schematic for reference numbers.. I've referred to many other...
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    0-30 Vdc Stabilized Power Supply

    I agree, keeping the ref numbers unchanged is important.  I've kept your numbers on all my schematics. My ver7 schematic has what you posted above for the "original schematic". It "has U3 as the current regulator, U1 as the voltage reference and U2 as the voltage regulator." P2 is the CL pot...
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    0-30 Vdc Stabilized Power Supply

    To get the same terminology, I'm referring to the rev 7 schematic, where U3 is the current limit control and U1 is the 11.2v ref voltage and U2 is the voltage control. I understand that U3 has to go negative. That's why it's connected to the -1.3v supply. However, U1 does not need to go negative...
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    0-30 Vdc Stabilized Power Supply

    Another change I'm thinking about is the Vref for the current limit IC U3. I'd like to be able to press a button and have the current display show the current limit setting. The rev7 design (all the rev designs) use the same refvoltage from U1 and the 5.6v zener D8 for both current limit...
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    0-30 Vdc Stabilized Power Supply

    I'm building the Rev7 0-30v 5A design, but I'm modifying it as I go. I'm disabled and bedridden, so I can only work on it for short periods, but I can think about it for long periods :-)  I'm trying to learn as I go, and I've chosen this project as my learning platform. I look at the various...
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    0-30 Vdc Stabilized Power Supply

    Thanks for the reply.  I was looking at several generic charts of zener tempcos, not realizing they varied that much. I had a few 5.6v zeners and tested them (just used mild hot air and watched the voltage change), and all seemed to have significant positive tempcos at 5.6mA. Adding a series...
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    0-30 Vdc Stabilized Power Supply

    I've a couple of questions. Although the MC34071 isn't available any more in through hole packaging, the MC33072APG is (same or better specs than the MC34071).  Although there aren't any offset null pins in this dual OA package,  is there any reason not to use it for U1 and U3? It's cheaper...
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