PSU 20A

[regata1600]

Hello
I need a power supply 0-30V 0-20A
Found this but the restriction of stream is up to 15A
Please help

[looser]

Regata

The PSU you found is ok for 20A . Just go ahead. The power transistors  2N3773 are can easyly handle 20A. If you would like to feel confortable you may add another T4 and R2 combination parallel to other four.
For current adjustment to reach 20A you will only need to change the value of R11 a little. Instead of 5K6 you can put 6K8 and can control 20A.

Mind ; you will need quite big cooler.

Regards.

[Parmin]

There is something wrong with that circuit.
Power input should not came from pin 11 of the IC1!
Also the power input to the IC1 pin 12 came from a 1N4001 which is limited to err.. 1 amp??
Typical LM723N circuit is easily available.

If this circuit work and you need bigger power, just add a few more 2N3772

[regata1600]

Hello looser
Thank you for reply
The problem is when the load grab 16Α
The current in the out has instability plays between 10A and 16A
Thank you

[savnik20]

There is something wrong with that circuit.
Power input should not came from pin 11 of the IC1!
Also the power input to the IC1 pin 12 came from a 1N4001 which is limited to err.. 1 amp??
Typical LM723N circuit is easily available.

If this circuit work and you need bigger power, just add a few more 2N3772

Here is the right

[regata1600]

hello Parmin
I had made error the file
Now I corrected him
Thank you very much

[zuisti]

The current in the out has instability plays between 10A and 16A

Hi;
The circuit is also usable as a 3...30 V (and not 0...30 V!) 20 A supply I think too.
(to make a 0... xx V supply also a negative voltage is needed ...) 

  But:

1.
The instability is caused (maybe) by the too big value of the cap C2 (play with smaller values like 500pF, see the datasheets), and ..
  I think in this case it's not a good idea the using a big diode seriell with the current limiting resistor  R17. This diode's forward voltage has a long time temp drift and this can be caused instability too. Use a well valued pure resistor instead!

2.
There is a big danger: without any output load (or with a small load) the DC input voltage (getting from the 28v AC input) maybe (sure!) exceeded the 40 V limit of the IC. Use a simple Zener circuit to solve it!  Study the example apps in datasheets!

3.

For current adjustment to reach 20A you will only need to change the value of R11 a little. Instead of 5K6 you can put 6K8 and can control 20A.

I don't agree! It (the changing of the value of the R11) is unnecessary in this case, with the pot R15 you can set any current limit (to 1000 A :-). The R11's value determined the min. settable current limit value only).
 
4.
For some big output current (and for a low output ripple if needed) increase the values of the filter caps C4 and C5 (to 100 000 uF... or more)!


Only according to my opinion...
Greetings
zuisti

[regata1600]

Hello zuisti
Thank you for reply
I remove the D4 and to change the value of C2 500pF
I am irrelevant with power supply I found the drawing In the internet
http://rapidshare.com/files/170156865/PSU_Schematic_Eagle.sch
Thank you very much

[regata1600]

Hello
Thank you very much zuisti
I could add in the Optical clue in the current limit
Thank you

[Malcolm]

Hello regata1600
http://rapidshare.com/files/170156865/PSU_Schematic_Eagle.sch

What is SCH -File? How to open this file?
Please help me.
Thanks

[regata1600]

Hello Malcolm
The schematic diagram is the power supply
And opens with EAGLE

[Jehan]

Add two more N3773 stages in parallel, add one more 20000 microfarad capacitor to C4, change fuse rating to 30Amp, change power rating of transformer. this will change the rating to 22.5 Amp power supply,
of course the heat sink size and the power dissipation goes up,

mind you the thermal management will be very difficult, the system will end up dissipating more than 750 watt at the lower voltage of the power supply, and cooling 750 watt is very very expensive

one crude way to reduce the dissipation is to have a single or dual taps in the secondary of the transformer, with tap one you can have 0 to 15 volt range and with the second tap you can have the full range of 0 to 30 volt,  or 0-10, 10 to 20 and 20 to 30 volt for the dual tap version . in this way the dissipation can be brought down to around 250 watt which is manageable. still you may require a large heatsink for 250 watt cooling, kindly check the SOA of the power transistors.

another way is to have a triac preregulator which will keep the voltage difference of 4 volt across the linear stage, this will reduce the dissipation in the power transistors to a manageable 80 watt.

As for the instability, try increasing the output capacitor

[regata1600]

Thank you all for the help
The power supply works well
The problem is the resistor of 0.1 ohm 20 w  very very  hot
How I could combine 0.1 ohm resistors 5w To make 0.1 ohm 40W
Please help me
Thank you very much

[pickit2]

use a choke.
look at top right of drawing
4 x 0.1 ohm 10W in serial/parallel and the wattage = 40W
or you could use 16 yes 16 x 0.1 ohm 5W if you have the space.

[praksk]

you could also try 2N5586 for your pass device bank