I have a problem. I designed a 30V, 5A power supply using this proposal:

Everything works great in simulation, but in the real circuit, there is a problem. I can regulate the input voltage on the operational amplifier (OA) using P1 from 0V to approximately 36V, but the output voltage remains at 0.7V (which seems to be due to parasitic properties of the PN junction). At one of the extremes of P1, it is also possible to get 0V. I am using the LM10CN OA (with a differential input voltage of ±40V) and a non-symmetrical power supply. The only thing I haven't used is Ro, but I think it should work without it. I have attached all the files I have for it.

Thanks for your help, I'm getting a bit desperate.

 

Nice, clean PCB.

How many volts do you get across Zener D1?

No need R0 so T1 can limit the current.

 

This will not fix your problem but.
Feed back at wrong point.
You need a resistor at the output of U1.

Is the current limit LED on? LED1

 

There are much less complicated ways of doing this .........
Check out the Chip below .......
It also has Current-Limiting, as well as a Zero-Drop-Out-Voltage,
and will control any large N-Channel FET,
and has Remote-Enable / Disable, Under-Voltage-Lock-Out, and
a "Loss-of-Regulation" Warning-Output.

BTW, your Transformer and Bridge-Rectifiers will only produce ~32.2-Peak-Volts under ideal conditions,
and your Bulk-Storage Capacitors are probably too small for ~50/60hz Mains-Power.

At ~165-Watts, You really should consider going to a Buck-Converter instead of a Linear-Supply.
A Buck-Converter will waste a lot less Energy generating Heat.

Cut your Rectifier-Heat in half with some Schottkey Diodes # SBR12A45SD1-TDICT-ND
and put that wasted Heat to work making Voltage instead.
Only 0.35-Volts Forward-Voltage each at 5-Amps, ( instead of more than 0.7-Volts ).

And, if You really want to smooth things out,
add an Inductor before your Bulk-Storage-Caps,
this will also help your Bridge-Rectifier to run cooler too.

The below suggested Chip, with a beefed-up Bridge, a 1.8mH-Inductor, and
20-paralleled 1,000uF Capacitors, will deliver a very quiet, well Regulated, ~25-Volts at ~6-Amps.
( If You want more Voltage, You can add another ~10 more Turns of Hook-up-Wire to your Transformer,
or just install an entirely new ~14-gauge, (Solid-Copper THHN), Secondary-Winding ).

Or, just completely start over using a Buck-Converter topology.

What You have now will probably be disappointing when You finally get it working as expected.

What specifications do You expect to need from your Power-Supply ?
What is the "V/A" Rating of your Transformer ?
.
.
.

 

Nice, clean PCB.

How many volts do you get across Zener D1?

No need R0 so T1 can limit the current.

Uzd is 33V

 

This will not fix your problem but.
Feed back at wrong point.
You need a resistor at the output of U1.
View attachment 288094
Is the current limit LED on? LED1

So adding resistor on OA output should fix my problem? And what the value of the resistor should be?
Yes the LED1 branch makes current limit.

 

There are much less complicated ways of doing this .........
Check out the Chip below .......
It also has Current-Limiting, as well as a Zero-Drop-Out-Voltage,
and will control any large N-Channel FET,
and has Remote-Enable / Disable, Under-Voltage-Lock-Out, and
a "Loss-of-Regulation" Warning-Output.

BTW, your Transformer and Bridge-Rectifiers will only produce ~32.2-Peak-Volts under ideal conditions,
and your Bulk-Storage Capacitors are probably too small for ~50/60hz Mains-Power.

At ~165-Watts, You really should consider going to a Buck-Converter instead of a Linear-Supply.
A Buck-Converter will waste a lot less Energy generating Heat.

Cut your Rectifier-Heat in half with some Schottkey Diodes # SBR12A45SD1-TDICT-ND
and put that wasted Heat to work making Voltage instead.
Only 0.35-Volts Forward-Voltage each at 5-Amps, ( instead of more than 0.7-Volts ).

And, if You really want to smooth things out,
add an Inductor before your Bulk-Storage-Caps,
this will also help your Bridge-Rectifier to run cooler too.

The below suggested Chip, with a beefed-up Bridge, a 1.8mH-Inductor, and
20-paralleled 1,000uF Capacitors, will deliver a very quiet, well Regulated, ~25-Volts at ~6-Amps.
( If You want more Voltage, You can add another ~10 more Turns of Hook-up-Wire to your Transformer,
or just install an entirely new ~14-gauge, (Solid-Copper THHN), Secondary-Winding ).

Or, just completely start over using a Buck-Converter topology.

What You have now will probably be disappointing when You finally get it working as expected.

What specifications do You expect to need from your Power-Supply ?
What is the "V/A" Rating of your Transformer ?
.
.
.

Firstly, I would like to familiarize myself with this topology, mainly for educational purposes, and then I can start experimenting with it further. The transformer's output is 27V AC and 6.25A. I would like to obtain 30V and a maximum of 5A.

 

The transformer's output is 27V AC and 6.25A. I would like to obtain 30V and a maximum of 5A.

The average value of the high peak transformer RMS currents drawn by a bridge-diode capacitor supply are 1.6-1.8 times the DC output current, so the DC should be limited to about 3.5A continuous for the 6.25A rated transformer, to avoid overheating it.

 

Also note that Q1's dissipation for a 3.5A short circuit output would be over 120W.

 

Also note that Q1's dissipation for a 3.5A short circuit output would be over 120W.

I know I'm counting with 150W, but the main problem is that I'm unable to get more than 0.7V. :,(

 

The methods for measuring the Output of your Transformer make a huge difference.
The Peak-to-Peak-AC-Voltage is not very useful except for "back-calculating" the RMS-Voltage,
which is approximately ~0.7 X Peak-to-Peak Voltage,
which will also "sag" to some small degree under maximum Load.
( although, Toroidal-Transformers tend not to sag as much as other designs )

27-Peak-Volts X 0.7 = ~19-RMS-Volts.

With a Toroidal type Transformer it's usually quite easy to
wind your own new Secondary on to the Core, or "add to" the existing Secondary-Winding.
This can sometimes offer the advantage of using heavier gauge Wire,
which can reduce "Copper-Losses" and therefore, reduce the amount of Heat generated.

Note .......
You can't get more Power out of a Transformer than what the manufacturer rates it in "V/A".
Transformers are rated in "V/A" because they are a little bit "squishy" in the way they operate,
they don't strictly follow the rules of Volts X Amps = Watts, therefore they are not rated in "Watts".

What is your Transformers Power rating in "V/A" ?
( V/A and Watts are usually fairly close to each other and You are asking for 30V X 5A = 150-Watts )

To get the maximum rated Power out of a Transformer,
it must produce more than the expected Regulated Power Supply Voltage that is wanted,
in RMS AC-Voltage, not Peak-to-Peak AC-Voltage.

A "Choke-Input" Bridge-Rectifier-Filter will allow getting the most RMS Power from your Transformer.
This is where the Output of the Bridge-Rectifiers goes directly into a large Inductor,
and then into the Bulk-Storage-Capacitors.
This design will "spread-out" the Current drawn from the Transformer-Secondary
which will substantially reduce the amount of Power lost, and therefore Heat generated,
because of having very narrow Current "spikes"
caused by trying to rectify the Peaks of the AC-Voltage with only Capacitors.
This also adds a certain degree of "Voltage-Regulation",
before the Voltage gets to the actual Regulator, which will further increase Efficiency and reduce Heat.

Being able to create your own Secondary-Winding is a huge bonus when
You are planning on using a Linear-Voltage-Regulator because You can make the
Transformers Secondary-Voltage anything You want, ( within reason ).

If the Secondary-Output-Voltage is too much lower than the Regulated-Output-Voltage,
then You will get excessive "Ripple" on the Output.
If the Secondary-Output-Voltage is too much higher than the Regulated-Output-Voltage,
then all that extra Voltage will turn into Heat which must be dissipated into the Air,
( and this is Power that is permanently lost forever ).

You will need around 55-Peak-Ac-Volts for a 30-VDC Regulated-Power-Supply.
( 55V X 0.7 = 38.5-RMS-AC-Volts )

What type of device do You plan on Powering with Your new Power-Supply ?
How much "Power-Supply-Ripple-Voltage" will be acceptable ?
.
.
.

 

Transformers are rated in "V/A" because they are a little bit "squishy" in the way they operate,
they don't strictly follow the rules of Volts X Amps = Watts,

Transformers are rated in VA (not V/A) not because they are "squishy" but due to load power factor considerations.
It's the maximum current that mostly determines the transformer rating due to I²R winding losses, not their power output, thus for low power factor loads the output watts are less than the VA output.
For pure resistive loads the two values are the same.

 

The methods for measuring the Output of your Transformer make a huge difference.
The Peak-to-Peak-AC-Voltage is not very useful except for "back-calculating" the RMS-Voltage,
which is approximately ~0.7 X Peak-to-Peak Voltage,
which will also "sag" to some small degree under maximum Load.
( although, Toroidal-Transformers tend not to sag as much as other designs )

27-Peak-Volts X 0.7 = ~19-RMS-Volts.

With a Toroidal type Transformer it's usually quite easy to
wind your own new Secondary on to the Core, or "add to" the existing Secondary-Winding.
This can sometimes offer the advantage of using heavier gauge Wire,
which can reduce "Copper-Losses" and therefore, reduce the amount of Heat generated.

Note .......
You can't get more Power out of a Transformer than what the manufacturer rates it in "V/A".
Transformers are rated in "V/A" because they are a little bit "squishy" in the way they operate,
they don't strictly follow the rules of Volts X Amps = Watts, therefore they are not rated in "Watts".

What is your Transformers Power rating in "V/A" ?
( V/A and Watts are usually fairly close to each other and You are asking for 30V X 5A = 150-Watts )

To get the maximum rated Power out of a Transformer,
it must produce more than the expected Regulated Power Supply Voltage that is wanted,
in RMS AC-Voltage, not Peak-to-Peak AC-Voltage.

A "Choke-Input" Bridge-Rectifier-Filter will allow getting the most RMS Power from your Transformer.
This is where the Output of the Bridge-Rectifiers goes directly into a large Inductor,
and then into the Bulk-Storage-Capacitors.
This design will "spread-out" the Current drawn from the Transformer-Secondary
which will substantially reduce the amount of Power lost, and therefore Heat generated,
because of having very narrow Current "spikes"
caused by trying to rectify the Peaks of the AC-Voltage with only Capacitors.
This also adds a certain degree of "Voltage-Regulation",
before the Voltage gets to the actual Regulator, which will further increase Efficiency and reduce Heat.

Being able to create your own Secondary-Winding is a huge bonus when
You are planning on using a Linear-Voltage-Regulator because You can make the
Transformers Secondary-Voltage anything You want, ( within reason ).

If the Secondary-Output-Voltage is too much lower than the Regulated-Output-Voltage,
then You will get excessive "Ripple" on the Output.
If the Secondary-Output-Voltage is too much higher than the Regulated-Output-Voltage,
then all that extra Voltage will turn into Heat which must be dissipated into the Air,
( and this is Power that is permanently lost forever ).

You will need around 55-Peak-Ac-Volts for a 30-VDC Regulated-Power-Supply.
( 55V X 0.7 = 38.5-RMS-AC-Volts )

What type of device do You plan on Powering with Your new Power-Supply ?
How much "Power-Supply-Ripple-Voltage" will be acceptable ?
.
.
.

I have 300VA transoformer rating, but this is the thing Im

The methods for measuring the Output of your Transformer make a huge difference.
The Peak-to-Peak-AC-Voltage is not very useful except for "back-calculating" the RMS-Voltage,
which is approximately ~0.7 X Peak-to-Peak Voltage,
which will also "sag" to some small degree under maximum Load.
( although, Toroidal-Transformers tend not to sag as much as other designs )

27-Peak-Volts X 0.7 = ~19-RMS-Volts.

With a Toroidal type Transformer it's usually quite easy to
wind your own new Secondary on to the Core, or "add to" the existing Secondary-Winding.
This can sometimes offer the advantage of using heavier gauge Wire,
which can reduce "Copper-Losses" and therefore, reduce the amount of Heat generated.

Note .......
You can't get more Power out of a Transformer than what the manufacturer rates it in "V/A".
Transformers are rated in "V/A" because they are a little bit "squishy" in the way they operate,
they don't strictly follow the rules of Volts X Amps = Watts, therefore they are not rated in "Watts".

What is your Transformers Power rating in "V/A" ?
( V/A and Watts are usually fairly close to each other and You are asking for 30V X 5A = 150-Watts )

To get the maximum rated Power out of a Transformer,
it must produce more than the expected Regulated Power Supply Voltage that is wanted,
in RMS AC-Voltage, not Peak-to-Peak AC-Voltage.

A "Choke-Input" Bridge-Rectifier-Filter will allow getting the most RMS Power from your Transformer.
This is where the Output of the Bridge-Rectifiers goes directly into a large Inductor,
and then into the Bulk-Storage-Capacitors.
This design will "spread-out" the Current drawn from the Transformer-Secondary
which will substantially reduce the amount of Power lost, and therefore Heat generated,
because of having very narrow Current "spikes"
caused by trying to rectify the Peaks of the AC-Voltage with only Capacitors.
This also adds a certain degree of "Voltage-Regulation",
before the Voltage gets to the actual Regulator, which will further increase Efficiency and reduce Heat.

Being able to create your own Secondary-Winding is a huge bonus when
You are planning on using a Linear-Voltage-Regulator because You can make the
Transformers Secondary-Voltage anything You want, ( within reason ).

If the Secondary-Output-Voltage is too much lower than the Regulated-Output-Voltage,
then You will get excessive "Ripple" on the Output.
If the Secondary-Output-Voltage is too much higher than the Regulated-Output-Voltage,
then all that extra Voltage will turn into Heat which must be dissipated into the Air,
( and this is Power that is permanently lost forever ).

You will need around 55-Peak-Ac-Volts for a 30-VDC Regulated-Power-Supply.
( 55V X 0.7 = 38.5-RMS-AC-Volts )

What type of device do You plan on Powering with Your new Power-Supply ?
How much "Power-Supply-Ripple-Voltage" will be acceptable ?
.
.
.

The transformer is 300VA, but that's not what I care about right now. I'm asking for help with the regulation part of my power supply. Does anybody here know how to fix it?

 

Does anybody here know how to fix it?

Nor without more info.
Measure the voltage at all the nodes, note them on your schematic, and then post the notated schematic.

 

Nor without more info.
Measure the voltage at all the nodes, note them on your schematic, and then post the notated schematic.

Here it is, is there something more i can measure on it?

The problem is that the voltage on the OA output never changes and remains at 0.7V.

 

Here it is, is there something more i can measure on it?
View attachment 288211
The problem is that the voltage on the OA output never changes and remains at 0.7V.

Ok remove Q5 collector, and see if the voltage can be adjusted.

 

Ok remove Q5 collector, and see if the voltage can be adjusted.

Yes, thank you very much, that was the mistake. But now I am thinking about how to fix the currently disconected current limit by increasing R2 to close the base of Q5?

 

Yes, thank you very much, that was the mistake. But now I am thinking about how to fix the currently disconectedconnected current limit by increasing R2 to close the base of Q5?

What is the voltage across R3 at the maximum output, does the led light up,,maybe Q5 is faulty?

 

Texas Instruments posts the rought electrical diagram for their LM on their website. Their "shouldn't be" any confusion as to operation.

Now, I've been surprised myself since I can't read LM's diagrams In general: they work best if input and output are close. They can't "steer up". And steering down causes heat and shutdown. Your Vin-Vout is way too large.

Other than that: they work as advertised.

 

Transformers are "an art in themselves". Hopefully google makes it easy to find 1980's posts on that (or, maybe they've hunted it down and removed it for competitive reasons). Everything used to run off transformers right?

Your transformer will be "nearly useless" unless you match your application to the exact number of TAP windings and wire guage. You could punch holes through or melt your winding's shelac. You need to be rigorous to protect your transformer since they're expensive. Else buy one that is "pre designed" (like a "power pack") exactly for your application that has a 30day warrantee

Today, on mouser.com, custom transformers are insanely expensive. So much so you should design "around a transformer you can afford".