Author Topic: LM324 Power Supply with variable voltage and current  (Read 24357 times)

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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #25 on: March 14, 2019, 12:26:38 pm »
Is there any way to measure that current using a standard multimeter or an oscilloscope with standard 1x/10x probe ?
Is there the possibility to estimate that current ?
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #26 on: March 14, 2019, 12:29:25 pm »
And finally how the Fast CC limit depends on the BD244 base current (ib=5mA..80mA) for constant emitter resistor R1=0.33ohm.
 
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #27 on: March 14, 2019, 12:40:36 pm »
It will be safe for the transistor the maximum value from the above graphic about 3.4A  ?
I think that this depends on the SOA of the transistor...
« Last Edit: March 14, 2019, 12:55:03 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #28 on: March 14, 2019, 12:59:34 pm »
For 2N3055 the max Ice=15A. It depends on the Vce as well, of course. According to the datasheet at Ice=15A and Vce=40V and a short 50us pulse the transistor is within the spec.

Still the question is how to set the BD244 emitter resistor value in my schematics (R8=10ohm). It limits the Ic current of the BD139 during the pulse, it creates a significant voltage drop on it during the pulse as well. Under normal operation the voltage drop on it will be 0..3V I guess.


 
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #29 on: March 14, 2019, 01:05:05 pm »
If I will use TIP35C, it should also work as TIP35C has Ic=25A while 2N3055 has Ic=15A ?
I can also use TIP3055 (Ic=15A)...
I currently have TIP35C and TIP3055 and I want to use one of them. I am interested especially if I can use TIP3055.
« Last Edit: March 14, 2019, 01:15:57 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #30 on: March 14, 2019, 01:22:00 pm »
Well, the fast cc limit currents in my schematics depends on the I_base of the BD244, R8 value, 3055 emitter resistors, and real transistor's parameters.. I do not know how your transient will be long (50us??) - the width of it depends on the number of opamps in the control loop, their speed, their compensation, etc.
It needs to be elaborated..
Best would be to download the LTspice and simulate with your schematics, parts and conditions. And then to measure and compare.
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #31 on: March 14, 2019, 02:05:00 pm »
1.Is there any way to measure that current using a standard multimeter or an oscilloscope with standard 1x/10x probe ?
2.Is there the possibility to estimate that current ?

1. the worst case scenario would be to set the output voltage to your max, for example 20V, set the slow current limit to your min (for example 100mA).
Hook the oscilloscope probe at the shunt resistor and short the output. You have to see a voltage pulse on the shunt resistor.
See below a simulation with a PSU as above (2xLT1022 - current sense and voltage sense, BD139+2n3055, 0.33ohm in 3055's emitter, Fast CC as above, R_Shunt 0.22ohm, output capacitor 100uF (100mOhm ESR).
The 20V output shorted (slow current limit 100mA) at 300ms.
The R15 is the 3055's 0.33ohm emitter resistor.

2. sure, see above.
« Last Edit: March 14, 2019, 03:58:42 pm by imo »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #32 on: March 14, 2019, 02:48:59 pm »
I will check using the scope and I will come back with the results.
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #33 on: March 14, 2019, 04:09:02 pm »
I have attached the results from the oscilloscope.
I hope that I measured correctly, on the Rx1, Rx2 and Rx3.
I used TIP3055 instead of 2N3055 (currently I have a PCB with TIP3055 and I only attached the BD139 and resistors, 0.33 ohms in E of TIP3055, LM324, 20.3V output voltage, 0.1A output current, output capacitor 100uF). I put the scope alligator to the GND and the probe to the other side of Rx. R13,R14,R15 = 0.33 ohms.
Here are the screenshots:

https://ibb.co/ZMq3Dq5
https://ibb.co/TYR7bkN
https://ibb.co/cc4hR0S
https://ibb.co/3hTNkWz
https://ibb.co/TmwHy6s
https://ibb.co/kJyfnxy
https://ibb.co/ySRB7rB
https://ibb.co/nLvB6mz
https://ibb.co/By6ZDz4
https://ibb.co/Ngh9sxC
https://ibb.co/pWvkxTr
https://ibb.co/Bz09dv4
https://ibb.co/ChHj97b
https://ibb.co/0hWgChJ
https://ibb.co/f9f4kgM
https://ibb.co/42yqRCd
https://ibb.co/0cS5KYn
https://ibb.co/S59SQqP
https://ibb.co/F6HhDbw
https://ibb.co/hW5CRMW
https://ibb.co/wQnGNyc
https://ibb.co/PCWgLyr
« Last Edit: March 14, 2019, 04:13:21 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #34 on: March 14, 2019, 05:12:13 pm »
Which schematics do you refer to?
Is the Shunt 3x0.68ohm in parallel?
I can see 3.2V max peak there (typically 1.2V) - that will be 14Amperes (typically 5.3A). Right?
« Last Edit: March 14, 2019, 05:32:17 pm by imo »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #35 on: March 14, 2019, 05:22:19 pm »
1. The schematic is the one attached, with the difference that I used 4xTIP3055 with 0.33 ohm Emitter resistor instead of 2N3055 with 0.22 ohm Emitter resistor. I also added a 100uF capacitor on the output. I also added the fast current limit from the attached image.
2. Yes, the shunt is 3x0.68 ohm in parallel rated at 5W each.
3. Yes.
« Last Edit: March 14, 2019, 05:25:06 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #36 on: March 14, 2019, 05:51:35 pm »
That is 1.3-3.5A per transistor in the pulses based on the oscilloscope pictures (1.2-3V pulse on the Shunt's 0.226 ohm). That seems good, imho.
 
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #37 on: March 14, 2019, 06:05:05 pm »
There is one thing that I did not observe correctly: I put the alligator clip of the probe on the GND, but the other end of the probe I put on the Anode of D5 (BY500). Is the measurement still correct in this case ? The distance between the Anode of D5 and the resistor pin is about 10mm...
« Last Edit: March 14, 2019, 06:07:32 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #38 on: March 14, 2019, 06:13:56 pm »
Your probe's gnd wire (ending at the alligator clip) is around 10cm, therefore those 10mm play no role..
 
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #39 on: March 17, 2019, 12:15:28 pm »
Hello @imo, I made a short simulation of the circuit in LTSpice. I found that the Ic and Ie of BD139 is higher than the datasheet values, which are 1.5A. Please have a look at the attached images because I don't know if the simulation is 100% correct.
Should be a good idea to replace BD139 by a higher Ic transistor ? For example, I have in my workshop a BD243C...
« Last Edit: March 17, 2019, 12:22:10 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #40 on: March 17, 2019, 12:32:26 pm »
There are 2 potential issues with the Fast CC in my schematics:
1. the pulse is indeed higher current, but rather short pulse. Of course it has to be within spec.
2. the 10ohm resistor limits the current, but it also creates a drop with larger drive current for the Nx3055.

So it would be a better design to control the base of the BD244 pnp instead.
That cannot be done by the BD139 directly, however.
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #41 on: March 17, 2019, 12:40:16 pm »
R8 could be changed to something low like 1Ω. Some clamping diodes in series between the rail and the Base of Q5 will limit the allowed voltage across R8.
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #42 on: March 17, 2019, 12:47:56 pm »
There are 2 potential issues with the Fast CC in my schematics:
1. the pulse is indeed higher current, but rather short pulse. Of course it has to be within spec.
2. the 10ohm resistor limits the current, but it also creates a drop with larger drive current for the Nx3055.

So it would be a better design to control the base of the BD244 pnp instead.
That cannot be done by the BD139 directly, however.
Is there any simple solution to this problem ? Might the problem be solved by replacing BD139 or by increasing the 10R resistor value ?

Later edit: replacing 10 ohms resistor by 47 ohms resistor gives me the attached results...
and replacing the 10 ohms by 39 ohms resistor...

That cannot be done by the BD139 directly, however.
Does it require a transistor connected to the base of BD244 ?

2. the 10ohm resistor limits the current, but it also creates a drop with larger drive current for the Nx3055.
Can the voltage drop across the 10 ohm resistor be compensated by a transformer with higher secondary voltage ? I have a 30V/200VA output transformer...
« Last Edit: March 17, 2019, 01:14:38 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #43 on: March 17, 2019, 01:26:08 pm »
This is something which may work fine.

In the simulation the FCC limits the current of a single 3055 to aprox 1.2A in the pulse.

In the simulation you may decrease the "1ohm Load" resistor to 0.01ohm with the same results.

In the simulation the collector current of the BD244 is about 3.5A for about 250ns (charging the capacitancies inside the 3055), that should be ok with that transistor.

The Q8 on the left hand side in my schematics is the T1 in your green schematics (together with 3x1k resistors around it).
« Last Edit: March 17, 2019, 02:37:26 pm by imo »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #44 on: March 17, 2019, 01:42:06 pm »
 I will try it and I will come back later with the results.
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #45 on: March 17, 2019, 01:53:28 pm »
And the sim res.
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #46 on: March 17, 2019, 04:15:04 pm »
And a simulation with all relevant parts (based on the "green" schematics). It seems it works  :).
Shorting the output.
Vout=15V, I_Load=100mA, I_Limit=1A, FCC=5A.
« Last Edit: March 17, 2019, 05:17:03 pm by imo »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #47 on: March 17, 2019, 07:02:25 pm »
I uploaded on the site the screenshots from the oscilloscope.
Please have a look and tell me what you think.
I used BC556B and BC337-40. Only those transistors I have in my workshop at this moment.
V out = 25.5V, I out = 0.1A
https://ibb.co/1K0XCKh
https://ibb.co/QnT1v5M
https://ibb.co/MCT0sfG
https://ibb.co/58Ys04y
https://ibb.co/7GMKTnJ
https://ibb.co/2tyB5zL
https://ibb.co/Pjn2s1j
https://ibb.co/xCZf0fM
https://ibb.co/QvnGBxH
https://ibb.co/tLG0t3z
https://ibb.co/jbWDHVP
https://ibb.co/nrqz4s1
https://ibb.co/Wn2h5T7
https://ibb.co/PZKHSsB
https://ibb.co/DfvmsqL
https://ibb.co/GxwD9QS
https://ibb.co/p48HRFp
https://ibb.co/TgPYRqp
https://ibb.co/gRGMTsY
https://ibb.co/4M9g39h
https://ibb.co/HzFdwsW
https://ibb.co/199QQSp
https://ibb.co/cJ8F91X
https://ibb.co/dfDHrS8
https://ibb.co/vs0SXHG
https://ibb.co/D8h0b1x
https://ibb.co/bJCyWgj
https://ibb.co/TMGknVh

Later Edit: but something is not working, because if I set the output voltage to 25.5V and if I connect a 24V/60W light bulb, the voltage drops to 19.4V. The slow current limit is set to maximum and the LED does not lit.
I checked the circuit and it seems to be ok.
« Last Edit: March 17, 2019, 08:14:51 pm by mike_mike »
 

Offline imo

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Re: LM324 Power Supply with variable voltage and current
« Reply #48 on: March 17, 2019, 09:46:44 pm »
You have to debug it step by step.
It has no sense to mess with 60W loads until it works with 1W load.

It looks like it is unstable. You may try to increase the feedback capacitors values.
PS: in the simulation it oscillates with 470pF feedback caps.

Also good decoupling and wiring style is important - with large currents the voltage drops on the thin/long wires may create instabilities.

We do not know what are the screenshots about. What did you measure? How?

First do measure how the input voltage changes under the load. Voltage drop, ripple, etc. The powering of the pass transistors and opamps must be stable.
Then do check how the voltage setting works.
Then do check how the slow current setting works.
Doublecheck and note all voltages at various nodes in the schematics during the tests, especially their changes. The


« Last Edit: March 17, 2019, 10:06:12 pm by imo »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #49 on: March 17, 2019, 09:56:15 pm »
We do not know what are the screenshots about. What did you measure? How?
I measured with the probe on the Rx resistor (3x0.68R in parallel). I took the screenshots in the moment when I made a short circuit on the output of the power supply. I measured the voltage drop on the Rx resistors when a short circuit occurred on the output of the power supply.
 


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