LM324 Power supply help

Thread Starter

greenisland

Joined Jan 7, 2020
63
I have a few questions about a power supply using a LM324 quad op-amp.
I am new to this forum with very limited knowledge of electronics, I am keen to learn about op-amp circuits in particular and open to advice.
I have received much help previously on a similar topic.

I seen this circuit online many months ago, sold as a complete kit. I constructed it on a breadboard, but it would not work.
Now looking at it again I noticed the schematic seems to have the power supply to the chip the wrong way round?, but the layout on the board is correct.
Will this circuit work if this is corrected?
Is the "A" circuit simply there to power the led and show current limiting is on, can it be removed and not impact the circuit?
Can I use a single Tip41A instead of T1 and T2?
 

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sghioto

Joined Dec 31, 2017
2,084
Now looking at it again I noticed the schematic seems to have the power supply to the chip the wrong way round?, but the layout on the board is correct.
Will this circuit work if this is corrected?
The board layout is correct, the schematic is incorrect, pin4 is the positive supply.
Can I use a single Tip41A instead of T1 and T2?
No. The two transistors are wired in what is called a darlington configuration.
You could replace with a TIP120 or 125 possibly.
You could eliminate the LED circuit for now.
 
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Thread Starter

greenisland

Joined Jan 7, 2020
63
The board layout is correct, the schematic is incorrect, pin4 is the positive supply.

No. The two transistors are wired in what is called a darlington configuration.
You could replace with a TIP120 or 125 possibly.
You could eliminate the LED circuit for now.
Thanks Sghioto, for your help in this and my op-amp voltage drop topic
I could and have spent many hours online going down rabbit holes and looking for answers to questions that more informed people could answer so easily.

I did think a tip41 was a darlington transistor, I stand corrected.
Is a dual supply superior to a single rail for op-amp used as a comparator in power supply circuits?
 

Thread Starter

greenisland

Joined Jan 7, 2020
63
I will put it together on a breadboard armed with my new knowledge and test, thanks again
Just one question, do you think an oscilloscope would be helpful in understanding op amp circuits?, what I mean is; one schematic I was looking at, there was a diode, well two in series at the output of the op amp(used as a comparator in a bench power supply). I incorrectly thought this was some kind of protection circuit, but after a lot of googling I discovered it clips the negative wave form at a certain voltage, so why place them there?.
 

Audioguru again

Joined Oct 21, 2019
2,687
The LM324 quad opamp will have its absolute maximum power supply voltage of 32VDC exceeded if the transformer is 25V at full load because with a low current load the transformer voltage will be about 27V (or more) which when rectified produces 35VDC or more.
A transformer voltage of 25VAC is too low for a 30VDC/1A output from this circuit anyway.
This circuit might oscillate since it is missing important frequency compensation capacitors.

The Hyland power supply circuit that I improved uses a 28VAC transformer and TLE2141 single opamps (or one TLE2144 quad) that also have inputs that work down to ground without needing an additional negative supply and have a max allowed power supply voltage of 44VDC.

The LED circuit gives you an important warning that the current regulation circuit is reducing the entire circuit's output voltage.
 

Thread Starter

greenisland

Joined Jan 7, 2020
63
The LM324 quad opamp will have its absolute maximum power supply voltage of 32VDC exceeded if the transformer is 25V at full load because with a low current load the transformer voltage will be about 27V (or more) which when rectified produces 35VDC or more.
A transformer voltage of 25VAC is too low for a 30VDC/1A output from this circuit anyway.
This circuit might oscillate since it is missing important frequency compensation capacitors.

The Hyland power supply circuit that I improved uses a 28VAC transformer and TLE2141 single opamps (or one TLE2144 quad) that also have inputs that work down to ground without needing an additional negative supply and have a max allowed power supply voltage of 44VDC.

The LED circuit gives you an important warning that the current regulation circuit is reducing the entire circuit's output voltage.
Hello Audioguru

I was going to test it with using my 23v dc single rail supply used on the previous post.
I asked the question relating to the led circuit being removed simply to confirm my own suspicion that it was an indicator and not part of the voltage regulator.
The Hyland circuit has diodes that confuse me, to be honest, near the transformer D5 D6 and two in series, are they creating a neg rail
 

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kaindub

Joined Oct 28, 2019
53
This circuit or a very similar one appeared in Elektor magazine about 10 or more years ago.
Yes the supply to the op amp is shown incorrectly. You would know this because the op amp would blow up.
I built this circuit. Whist it does work, its sort of.
Voltage regulation is not very good and current limit function is very imprecise.
Also power dissipation in T2 is very high when in current limit
For a hobby project this is ok, but not very good if you are looking at using it for experimentation where a good supply to protect your project circuit is required.
 

mortenlund

Joined Mar 20, 2020
1
Hello Audioguru

I was going to test it with using my 23v dc single rail supply used on the previous post.
I asked the question relating to the led circuit being removed simply to confirm my own suspicion that it was an indicator and not part of the voltage regulator.
The Hyland circuit has diodes that confuse me, to be honest, near the transformer D5 D6 and two in series, are they creating a neg rail
Hello

I think the D5 and D6 is for making it possible to go 2 x 0,6 V further down - which means it is close to 0 V. Each semi-conductor usually uses 0,6 V.
 

Audioguru again

Joined Oct 21, 2019
2,687
Hello Audioguru
The Hyland circuit has diodes that confuse me, to be honest, near the transformer D5 D6 and two in series, are they creating a neg rail
Sorry, I missed your question.
The small negative supply is needed so that when the output of this power supply circuit is shorted then D9 can cause the output voltage to go down to 0V. Without a negative supply to opamp U3 then the shorted output will try to be +0.8V with unlimited current but lots of smoke. The output of the TLE2141 opamp can go down to about +0.1V above its negative supply.
 

drtidrow

Joined Feb 26, 2018
1
Unless you need to adjust voltages down below 1.5V or so, a LM317 variable voltage regulator would be a better choice, and much less complex.
 
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