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0-30 Vdc Stabilized Power Supply


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Here is a version modified for 36v ac

You forgot to calculate that the single 2N3055 output transistor and the tiny 2N2219 driver transistor will melt if the output current is 3A and the output voltage is low or is shorted.

36VAC produces a peak of 50.9V which causes the positive unregulated supply to be 48.9V. Then the output transistor heats with 47.5V x 3A= 142.5W. 60W is very hot fore it so it will be destroyed with 142.5W.
You can work out the heating of the tiny 2N2219 driver transistor yourself.

That is why our fixed and improved version uses a 28VAC or 30VAC transformer, two 2N3055 output transistors and a BD139 modern power transistor as their driver.
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  • 4 weeks later...

Guest liquibyte

I have a question: on the prts list there is a D7, two diodes, but there is no D7 in the schematic!  where do they go?

They're the unmarked 1N4148's in series on the schematic.  Bottom left, two in series on the right below the ground signal.
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  • 2 months later...

I have problem is that when i switch of the 230VAC supply from transformer the DC output voltage reaches maximum voltage.
please give me a solution.

The solution is to make the project properly using a 28VAC or 30VAC transformer then the rectified and filtered unregulated voltage with no load is 31VAC x 1.414= 43.8VDC - 1.4V= +42.4VDC. With a 3A load on the project then the rectified and filtered unregulated voltage will be +40.4VDC.

It is silly to use a transformer with an output voltage too high because then the output and driver transistors will get much too hot.   
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  • 5 months later...
Guest ammar1262


My first post here. I have tried to simulate PicMaster's version of power supply on multisim but it doesn't simulate instead it gives convergence error .
Here are the files of multisim that I've made..
Testing psu has added 0.27ohm 10W resistor.


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I made this circuit but i changed Q2 with one Tip41C with 50 hfe.Is it enough?

The TIP41 has an fT of only 3MHz so it is slow and its delays will probably cause the output amplifier to oscillate and have transient problems. The BD139 that should be used is very fast with an fT of 190MHz.

The hFE is not important because the minimum hFE of one of the two 2N3055 output transistors at 1.5A is 41 then the collector current of the BD139 must be a maximum of only (1.5A/41) x 2= 73mA where its minimum hFE is about 70 so the maximum output from opamp U2 must be only 73mA/70= 1mA but the minimum output from a TLE2141 opamp is much more at 20 so there is plenty of hFE available. 
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  • 6 months later...

It's not too critical, as long as the op-amp can tolerate 44V but unfortunately not many modern op-amps can.

You could use the OP27 but you'll need to modify it because the offset trim configuration is different.

Another possibility is the NE5534 but it requires a compensation capacitor and has higher bias currents.

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  • 2 weeks later...
  • 6 months later...

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 than the TLE 2141 ($0.53 per amp compared to $1.86 for the TLE) and it runs cooler. The TLE will be used for U2 where offset null is needed.

The writeup describes the 5.6v zener as being operated at its zero tempco current, but my research shows that the zero tempco current is closer to 0.01 mA than 5.6 mA where it runs in this design.  At 5-6 mA, the tempco for a 5.6v zener is about 2 mv/C, which is about equal to and opposite to the tempco of a Si diode. That's why you often find 5.6v zeners in series with a Si diode when used as a vref. Is there any reason not to add a Si diode in series with D8 and adjust R5 R6 to get the 11.2 voltage reference? It seems to me that would improve performance at almost no cost.

Thanks for any comments.


Edited by Flight17
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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 diode with negative tempco helped a lot.

 I located a BZX79C5V6RL datasheet and see why you chose it.  I see that it is marked at -2 to +2.5 mV/C at 5mA, so I guess mine are in that range, as they seem close to +2. Since I've already roughly tested them, I might as well use the series diode.


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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 design choices and options, and the different changes made by others, and try to understand the effects of each change, then try to choose modifications based on what is cheap and what I've already got in stock (scavenged parts). I'd like to ask a lot of questions,  but I hesitate to bother people here, so I try to work out the answers myself.

I don't want to imply that the published design is less than optimal, when what I'm really interested in is learning and trying to understand what options there are.Here's an example. I'm going to use an lm317 to hold 33v instead of the D13 zener. It lets me widen the range of usable op amps.


Edited by Flight17
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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 setting and voltage setting. However, the vref is relative to the negative output, not ground. That's required for voltage setting, but it creates problems if you want to use the + input of the current limit comparator op amp U3 to know the current limit setting. IOW, the voltage that sets the current limit changes as the current changes.  I'm thinking about using a second  vref for current limit control that is relative to ground, not neg out. That way, I can switch between the two inputs of U3 to display the actual current when looking at the inverting input and the current limit setting when looking at the noninverting input.

It adds another component, but I've got several TL431 devices, which are cheap, so the cost is low.

Another thing I'm trying to understand, is why U1 is powered between negative out (not ground) and the unregulated supply. That means that its operating current and the current supplied to the vref pass through the sense resistor R7 and are part of the current being limited. I wonder if it can be connected to ground and allow a more accurate current limit setting. I'm not saying the rev7 design is wrong. I'm very much a beginner, but I'm having fun trying to understand why certain design choices were made, and what effect other choices would have.

Using an lm317 to power the op amps has the benefit of limiting the OA voltage to 36v or less, and that opens up the choices for op amps to more than the 44v only ones being used. If I go with the option to have the current meter display the CL setting, I need another OA with high input impedance to prevent loading the CL limit input of U3. That has the added benefit of letting me adjust the gain, so the 1.3v on the current sensing resistor R7 at full current will display 5.0v=> 5.0amps and I can use one of those cheap low impedance ebay high accuracy voltmeters for current display without modifying it. (They have 350k input impedance).

I'll also have multiple choices for 36v dual OAs that are cheap. I'm thinking of a dual OA for CL comparator and current/CL display and something that is either very low Vio or with nulling inputs for the voltage comparator OA U2.

 I'm playing with design, and simulation software and having fun. It's better than staring at the ceiling in a hospital bed.

Comments are always welcome, but, truly, I'm a beginner, so don't take any of this as criticisms of the published designs.

PS. I'm thinking of using the TL431as the vref since it has a low tempco compared to zeners I've looked at.

Edited by Flight17
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The output of opamp U1 must go negative in order for D9 to reduce the input of opamp U2 to near 0V when the output is shorted so that the output current is regulated.

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 (and its V- is connected to the negative pwr supply output at R7, which is always above ground potential). U1's output is always 11.2v above the negative pwr supply output, so it doesn't need connection to the negative supply.

I'm really a beginner, so don't take this as criticism of the design. It's not, but it looks to me like U1 could have V- pin4 connected to the negative output (as in the rev 7 design), to ground, or to the -1.3v supply (assuming one doesn't exceed the 44v limit). Either of those changes would cause the U1 idle current to skip the current sense resistor R7.

In the rev7 design, it really doesn't matter that idle current flows through the current sense resistor. The current limit voltage at the  noninverting input of U3 is only relevant when the current limit is reached, so the fact that that voltage changes (relative to ground) as the current changes isn't important. It will be correct when the P2 set current limit is reached. (I'll note, however, that it makes the current limit pot very slightly nonlinear, due to effects on the offset zero point at R17).

However, I'd like to use the U3 input voltages to display the current limit setting and actual current, so I don't want the CL limit voltage to change as the current changes. I can do that by changing the reference voltage for the CL setting to be based relative to ground, while still leaving V- of U3 connected to -1.3. Further, it might be nice for 0v at the CL pin to correspond to 0mA CL setting. That's a problem since the rev 7 design has current flowing through the R7 sense resistor that isn't flowing through the load connected to the output terminals.  The U1 quiescent idle current (2-4 mA, depending on the OA used) flows through R7. Also the 5.6mA used for the D8, R4 vref, the R5-R6 gain resistors around U1 (another ~0.5mA) and the P1 voltage set pot current (another ~1mA) all flow through R7 current sense.

Those last 3 have to go through R7 (although they can be reduced somewhat with design mods), but it looks to me like the U1 quiescent idle current could go directly to ground and bypass R7. If I understand the circuit, the purpose of R17, below the P2 adjust pot is to counteract for those effects that cause the 0 amp CL setting to be above 0v across R7 current sense.

None of this is important unless you want to use the voltage at the input pins of U3 to display the actual current and CL setting, as I do.

As I said,I'm trying to learn, and one way is to try various modifications and try to understand the effects. I could just offset the voltage at my voltmeter (used to display current and CL limit) to null out the quiescent current so that the meter reads zero when the voltage across the R7 sense resistor equals the quiescent current due to those effects described above. I think I can do that by measuring relative to the voltage at the top of R17, which should equal that quiescent current times R7. But I can also just reduce those effects by making them small enough to ignore. 

I'm considering eliminating U1 and replacing it with a TL431 which can run at a milliamp or two. That removes the U1 quiescent current, the D8 zener current and the R5-R6 gain resistor current.

Then increasing the resistance of the P1 voltage pot cuts the total current down to levels I can probably ignore. I'm playing with simulating that approach (Multisim) and with just offsetting the quiescent voltage on R7 current sense by measuring voltages relative to R17, not ground. (This may be best).

I freely admit I may be off base here, but I'm learning as I go, and it's fun. I do hope others with more design experience will point out flaws in my thinking, but if they don't, and I end up building something that doesn't work, I'm happy with that, so long as I figure out what went wrong. I can always build version 2. <smile>

Edited by Flight17
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I hate it when people copy a schematic and change all the parts numbers around.

The original schematic has U3 as the current regulator, U1 as the voltage reference and U2 as the voltage regulator. I kept them on all my updates.

Rev7 was drawn by Liquibyte and has U1 as the current regulator, U2 as the voltage reference and U3 as the voltage regulator which is VERY confusing.

Even his resistors, capacitors and transistors have different numbers.

Instead of you changing the wiring and causing idle current errors and maybe even having hum on the negative supply affecting your voltage readings simply use the circuit's 0V as the meters ground and measure the voltage across the current-setting pot for the current limit setting and measure the voltage across the current sensing resistor as the actual current of the load.    

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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 that sets that current limit.

Originally, I planned to do exactly as you suggested, "simply use the circuit's 0V as the meters ground and measure the voltage across the current-setting pot for the current limit setting and measure the voltage across the current sensing resistor as the actual current of the load."

But that doesn't work. The "voltage across the current sensing resistor" does work, almost.  It is close to "the actual current of the load." except it includes some idle current as described above. That's not a big problem, and I can work around it.

 However the "voltage across the current-setting pot for the current limit setting" isn't even close to the CL setting when measured relative to 0v ground. The voltage across P2 is a percentage of 11.2v plus the voltage across the current sensing resistor R7. That's because the reference voltage 11.2v floats at that reference level above the end of the current sense resistor connected to the supply negative output (to hold the supply output voltage constant) while P2 is connected in a resistor divider arrangement between 11.2v plus the measured load current voltage and ground.

Basically, the voltage on the wiper of P2, which sets the CL and is connected to the U3 NI input, changes its voltage significantly as the load current changes. It's only at the "correct" CL voltage when the  load current is at that same voltage across R7.  It was kind of surprising to me when I first realized that. Because of that, I can't just measure the voltage on the P2 wiper to know the CL setting. As discussed above, that has other effects. It makes the CL pot control slightly nonlinear, and I've got some numerical 10 turn pot dials I'd like to use, so I'd prefer better linearity. 

Example: At full current, the voltage across the load resistor is .27Rx5A=1.35 v 

The voltage from ground to the 11.2v ref is thus 12.55v and ignoring the small R17 below P2, P2 will have 1.35 volts across it, with the wiper at the top, and that is 10.76% of that total 12.55v.  However, if the load current now drops by 50%, then the resistor divider with P2 at its bottom will only see 11.2v + .675v=11.875v and P2 still has 10.76% of that decreased voltage or 1.28v across it instead of 1.35 volts. If we measured the wiper voltage now, we'd think the CL setting had been reduced, even though the wiper is still at the top of P2 and the CL is still at 100%. When the load current actually reaches the set limit, then the P2 wiper will have 1.35v on it, but until the load current actually reaches that limit, we can't know the CL  setting just from the voltage on the P2 wiper.

If we now wanted to change the current limit to 50% of max output, P2's wiper would need to be set to half of 1.35v to get 50% of max CL, so P2's wiper needs to be set to 52.8% of its range not 50% since 52.8% of the 10.76% of the total 11.875v is 50% of 1.35v.  IOW, setting P2 to 52.8% is needed to get the correct 50% CL. The nonlinearity problem gets worse at 25%.

I know, its not much, and I'd ignore it if not for the fact that the voltage on the P2 wiper varies significantly as the load current varies. That voltage just doesn't tell us what the CL setting is.


Edited by Flight17
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