0-30V Stabilized Power Supply

[audioguru2]

So how do you think, will I be able to work with this transformer?

Its voltage might be too low and cause ripple when the project output is 30V/3A.
The transformer will not get too hot. Try it.

 

[audioguru2]

Most people's problems with this project are ICs or transistors with their pins connected backwards.
Double check the pins with the pictures in the datasheets.

If your 2N3055 transistors have not been over-heated and are not fakes then they should work fine.

 

[rombe570]

Hello, Can you tell me what changes should i make for 12amps??
The power supply is http://www.electronics-lab.com/projects/power/001/index.html

 

[audioguru2]

Hello, Can you tell me what changes should i make for 12amps??
The power supply is http://www.electronics-lab.com/projects/power/001/index.html

The project you copied is not reliable, does not produce 30V at 3A and has many parts overloaded.
I fixed it and the new schematic and parts list are in these threads.
The fixed version uses a newer real power transistor for the driver Q2 and two output transistors (each with an emitter resistor) instead of one transistor. I made a 5A version that uses three output transistors.

For an output of 12A then you will need 8 output transistors, 3 driver transistors plus additional pre-driver transistors.
But it will need to be re-designed for the output voltage to be as high as 30V.

 

[rombe570]

I made some changes in original shematic, Ihave 3 tip35c in parralel( soon i'll put another 3) q2 is bd 139 and r7 is 0.1ohm. I don't need 10-12 amps constantly, but you'll never know when you need them.
P.S. Can i use OPA604 instead of TL081??

 

[audioguru2]

Six TIP35 output transistors on a HUGE heatsink and fan will be able to have a maximum continuous output current of 9A or 10A. Then the BD139 driver transistor Q2 will melt. If you use two or three BD139 driver transistors in parallel then opamp U2 that drives them will melt. It is difficult to parallel opamps so a pre-driver transistor is needed but then the output will not reach 30VDC. If the transformer has a higher voltage then many resistors will get too hot.

The original circuit has many problems that were fixed in my fixed version that uses a higher transformer voltage and TLE2141 or MC34071 opamps that have inputs that work at the negative supply voltage.
OPA604 opamps will not work in the fixed version unless their negative power supply voltage is increased, but then they might get too hot.

 

[rombe570]

Thanks audioguru, i think i'll try this one

sursa_1_schema.pdf

 

[audioguru2]

Thanks audioguru, i think i'll try this one

It uses an expensive custom-made transformer.

 

[audioguru2]

I am sorry, but can you answer, please, this question. Thanks.

I answered this question on Feb 19:
"Most people's problems with this project are ICs or transistors with their pins connected backwards.
Double check the pins with the pictures in the datasheets."

The pots set the output to 0V and 30.0V, a few mA to 3.0A.

 

[electronicslab]

My project is here :

 

[audioguru2]

My project is here :

It looks like you made the defective old kit but used a tiny little transformer so the maximum output is 18.6V at only 48mA.

 

[electronicslab]

Yes,the transformer must be changed with 24V ,3-4A .
Now , the maxim output is 18,6V , 1.85A .

View attachment 41830

View attachment 41831

 

[audioguru2]

Yes,the transformer must be changed with 24V ,3-4A .
Now , the maxim output is 18,6V , 1.85A .

Sorry, I made a mistake. I thought your tiny transformer was rated for 1.2W but instead it is rated at 1.2A. Then its maximum power is 18V x 1.2A= 21.6VA.
Its peak voltage is 18V x 1.414= 25.5V so it is overloaded when your output current is more than 21.6VA/25.5V= 0.85A.

The original circuit uses TL081 opamps that have a maximum allowed total supply of only 36VDC.
a 24V transformer might produce 25V with a low current load so its peak voltage is 25V x 1.414= 35.4V and the rectifier bridge reduces it to 34.0V which will be the positive supply to the opamps. But the circuit also supplies a negative 5.6V to the opamps then their total supply is 34.0V + 5.6V= 40.6V which is higher than their maximum allowed voltage.

A 24V transformer is too low for this project anyway. Then the maximum output at 3A will be only about 25VDC, not 30VDC.

My fixed version of this project uses a 28V or 30V transformer and opamps that have a maximum total supply rating of 44VDC. They work with a negative supply of zero or -1.3VDC. 

 

[electronicslab]

Understand but look at this photo :

View attachment 41832

 

[audioguru2]

Understand but look at this photo :

You NEVER add a resistor in series with the power supply pin of an opamp.
If you reduce the supply voltage of the opamps then the maximum output voltage of the project is also reduced.
Then you do not need a high supply voltage.

 

[JoeBlow1]

Hello, this is my first post. I have spent the last month reading most of this post. Thanks for all the great info. My question is... I just finish building this circuit on a breadboard but have no transformer yet. Can the circuit be powered using a 30V bench power supply for testing purposes? I was going to bypass the bridge rectifier and filtering caps and connect the supply to what would be the output of the bridge rectifier. Thanks for the help.

Joe

 

[audioguru2]

I just finish building this circuit on a breadboard but have no transformer yet.

A solderless breadboard frequently causes modern opamps to oscillate at a high frequency. Use a pcb instead.

Can the circuit be powered using a 30V bench power supply for testing purposes? I was going to bypass the bridge rectifier and filtering caps and connect the supply to what would be the output of the bridge rectifier.

The peak voltage of the 28VAC or 30VAC transformer is 1.414 times higher which is 39.6VDC or 42.4VDC then the bridge rectifier reduces the positive supply to 37.6VDC to 40.4VDC.
The transformer is also half-wave rectified to produce the -1.3V negative supply that is important.
So use a transformer.

 

[electronicslab]

Those two potentiometers are for voltage and current control?
Yes , see photo .

What means that letter "P." ?
Is that tumbler main ON/OFF switch?
Yes , when switch is ON , P. lights .

Those green numbers show voltage value?
Yes .

What circuit have you used for those LED numbers?
http://www.ebay.com/itm/DC-0-99V-Mini-Digital-Voltmeter-Blue-3-Wire-0-36-LED-Display-Panel-Volt-Meter-/160914959288?pt=LH_DefaultDomain_0&hash=item2577476bb8

View attachment 41833

 

[audioguru2]

The trimpot in the negative feedback of the output stage is adjusted for 30.0V when the voltage pot is turned up to maximum.
The trimpot near U3 is adjusted for 3.0A when the load is drawing 3.0A and the current pot is turned up to maximum.
Adjust the offset voltage trimpot for an output of 0.0V when the voltage pot is set to minimum.

Your transformer voltage is low so I think the voltage regulation will fail and not produce 30V at 3A. It might produce 25V at 3A instead. When the voltage regulation fails then the output will have high 100Hz or 120Hz ripple.

Test the voltage regulation at a lower voltage. The voltage should not drop more than about 0.02V when a load of 3A is connected.

 

[JoeBlow1]

Thanks for the reply and the information.

A solderless breadboard frequently causes modern opamps to oscillate at a high frequency. Use a pcb instead.

Since I have the circuit built I am going to give it a try. Besides I do not have a pcb for it. I guess I will be learning how to make my own soon.

So use a transformer.

Working on getting a transformer

Thanks again.

Joe