0-30V Stabilized Power Supply

[Kevin Weddle]

I was looking to modify Q2 with a BE diode and a VCE zener and an upstream transistor to drop the voltage for the zener. If Q2 has a low BE operating voltage and the parallel diode doesn't go low impedance, U2 will work fine. It's good to hold Q2 at a constant VCE and VBE. As long as the parallel diode doesn't lose impedance, Q2 can supply adequate current to function Q4 and small signal regulation will only be lost under higher current. But all is not lost if you don't exceed the maximum of U2. The voltage will only follow the small signal.

 

[Kevin Weddle]

I modfied this posting.

 

[Kevin Weddle]

Impedance is slightly different from maxing opamp current. Especially when Q2 handles all the current.

 

[audioguru2]

The voltage reference from U1 is 11.2V and the maximum output from the project is 30.0V. Then the output amplifier must have a gain of 30V/11.2V= 2.679 times.

The power output transistors operate poorly at high frequencies. C6 and C9 make sure that their phase shift does not cause oscillation at a high frequency.
C7 makes the output a low impedance at high frequencies.
Usually a circuit that is powered has a supply bypass capacitor so its supply is a low impedance at high frequencies.

Q2 is the driver transistor and is an emitter-follower. Its base is fed from opamp U2 and its emitter feeds the bases of the output transistor emitter-followers Q4 and Q5. The output is fed back to U2 as negative feedback so the entire amplifier is very accurate and stable.

The output voltage of U2 (and the base voltage of Q2, Q4 and Q5) vary a little when the output current varies so that the output voltage is constant.

Kevin, your idea will allow the output voltage to bounce up and down when the output current changes.  

 

[jegues1]

Hello,

I'm looking to build my own lab power supply, but am still fairly new to the "practical" aspects of electronics.(i.e. wiring circuits up to mains voltages)

I've taken two university level courses on electronics, but I still feel I have a lot to learn. (Currently reading "The Art of Electronics")

Is this a good first power supply project for me, or should I go for something easier to start with? If so, is there a "latest and greatest" version of the schematic and BOM?

Thanks for your input!

 

[deepak.roy.alchemist]

Hello Jegues! the latest schematic posted here would prove to be too complicated for you as you would not be able to detect any flaw in its working as i can make out that you are still a beginner in this field. i would rather suggest you to try certain basic level circuits using LM723. That is all time proven chip to start with.

 

[xristost]

I'm sorry to interrupt the conversation. I know it isn't said here often enough. But our programmers are what makes are world all the possible. Even you can take a lesson. Remember.

Your latest posts are very cryptic, weird and not connected with the subject. Are you OK?

 

[audioguru2]

Your latest posts are very cryptic, weird and not connected with the subject. Are you OK?

Maybe Kevin needs to be de-fragged or re-formatted.

 

[deepak.roy.alchemist]

everybody needs to see the mirror once in a while to keep one self grounded.

 

[WinDTrek]

How do I connect an ammeter to this project?

 

[audioguru2]

How do I connect an ammeter to this project?

An ammeter has a resistance that spoils the excellent voltage regulation of this project because its resistance is in series with the load.

Instead, measure the voltage aross R7 then calibrate it in Amps.
R7 is inside the negative feedback loop so it does not affect the output voltage.

 

[WinDTrek]

Thanks Guru. One more question, i have completed already the 5A version. I made 2 actually and put some switches to interconnect the 2 x 5A version in series (to get 60V max) or in parallel (to double the amperage). However, one thing i noticed is that when I turn on the power supply the LED of the 2 x 5Aversion will light up (P2 or the current limiter pot is at minimum position). What i do normally is rotate P2 about /8 turn clockwise and the LED will turn of. After that putting P2 back to min LED will no longer light. Is this normal?  Aside from that everything works fine. I will post some pictures later.

 

[WinDTrek]

or if I put P2 to >1/8 position before powering on the power supply LED will not light up. It will only light up when I put load into it but it will turn the LED of once I adjust P2 towards max position.

 

[audioguru2]

This power supply should not have two or more connected in parallel because the voltage and current regulators will fight each other. It will be very difficult to set the output voltages exactly the same anyway.

The current regulator reduces the output voltage when the output current exceeds the settting of P2 so that the output voltage and current are both reduced. Then the LED lights to warn you that the output voltage is reduced.

 

[WinDTrek]

i think i found the reason why LED lights up when power is applied to this power supply. Pin 3 of U3 is less than 5.6mV (1.2mV and 0.6mV) when P2 is at minimum position. Adjusting the P2 to 1/8 turn will give me around 5.6mV. At this position of P2 LED will not light up when power is applied. I'm thinking of replacing R17 (33 ohms) to a higher value to get 5.6mV. Also, what is the maximum voltage should i set Pin 3 of U3 to get 5A maximum?

 

[audioguru2]

i think i found the reason why LED lights up when power is applied to this power supply. Pin 3 of U3 is less than 5.6mV (1.2mV and 0.6mV) when P2 is at minimum position. Adjusting the P2 to 1/8 turn will give me around 5.6mV. At this position of P2 LED will not light up when power is applied. I'm thinking of replacing R17 (33 ohms) to a higher value to get 5.6mV. Also, what is the maximum voltage should i set Pin 3 of U3 to get 5A maximum?

If you use 56k for R18 or 33k with a 100k series calibration trimpot set to about 23k, your P2 is 10k and R17 is 33 ohms then pin 3 of U3 should be about +5.6mV when P2 is at minimum.

The LED will be off if your opamp has normal very low input current and low input offset voltage.
But I do not know the value of your R18 or if you have a calibration trimpot in series with it and I do not know which opamp you are using.
Increase the value of R17 to fix your problem.

The value of R7 and the setting of the calibration trimpot in series with R18 set the maximum current. I do not know the values you are using. Simply short the output and set the current to 5.0A by adjusting the trimpot.

 

[WinDTrek]

My R18 is 20K with a 200K trimpot. P2 is 10K R17 is 33 ohms . Just check redwire's schematic  page 1 and values is already been changed to the values that you have specified. RV2 and Rf11 was also changed. I will replace this then and see what happens. Btw 'm using MC34071. Thanks Guru..

 

[audioguru2]

What points of circuit should be measured, when RV1 is turned to make 0V (and what value should be)?

The modified parts list shows that a 5k trimpot if the opamp U2 is a TLE2141 and should be a 10k trimpot if the opamp U2 is an MC34071.
Also, R10 should be 1k if the opamp is a TLE2141 and R10 should be a piece of wire for an MC34071.

RV1 should be adjusted so that the output with or without a load is 0.0V when the voltage control pot P1 is set to minimum.

I still have a problem with glowing LED when P2 is set to minimum. I tried to increase R17 to 100ohm, 150ohm; short R10; use 10uF film capacitor with a resistor on the output; but none of this helps

The LED lights to show that the current regulator is reducing the output voltage. With P2 set to minimum then it provides about +5.6V to the non-inverting input of U3 when R17 is 33 ohms and provides +25.5mV when R17 is 150 ohms. With no load then there is no current in R7 and no voltage across it so the inverting input of U3 is 0.0V. Then the output of U3 will go as high as it can and NOT turn on Q3 and the LED.

Which opamps are you using?

 

[_pike]

Hello to all!!!!! I am intrested of building this power supply but i saw that lot of modifications have been made and i would like to know if someone can tell me where to find the final parts with the improvements that have been made...

Best Regards

 

[audioguru2]

I am using TLE2141, so those trimpots and resistors are exactly as you said for TLE2141.

I think, that adjusting RV1 does not change anything..

With the voltage control P1 set to zero then adjusting RV1 should change the output voltage of the project from about -30mV to +30mV. Then it can be set to 0.0V.