High current power supply

[sanaprog]

**broken link removed**

hi everybody....m using the circuit given in above link but the transistors do not respond...means the current through it is zero..n further the output of regulator 7812 is 22.5V..(without transistors output of regulator is Ok i.e 12V )
.i am using 24V 120A battery to operate the circuit...and want to draw atleast 15A...can anybody suggest where could be the fault?????

 

[WimRFP]

22.5V, is this without any load? If so, what is the output when you load the supply with about 100 to 1k Ohm?

Did you wire the transistors correctly? Do you have an oscilloscope to check whether the circuit is oscillating?

For safety, do you have a fuse mounted very close to the plus terminal of the battery in case of a short circuit?

 

[chuckey]

You must load the circuit, to cause the voltage drop across R7 to be .8V. At zero current out (no load) the leakage through the power transistors are trying to push a current into the 7812, which of course it won't sink, putting a load resistor in the PSU will sink this leakage and if you are lucky the circuit will spring to life.
Frank

 

[goldsmith]

Hi all
I think this circuit is awful . because of three reason :
1- very low efficiency
2-high cost
3- bad ripple rejection ratio .
Why this circuit ? why not a simple SMPS ?
Regards
Goldsmith

 

[chuckey]

This circuit is cheap, go out and buy a SMPS tailor made transformer cheaper. And you still need regulation components.
Frank

 

[goldsmith]

Dear chuckey
Hi
What i meant by SMPS ? it is regulated and without iron core transformer.
I built a 1KW SMPS , just with 7$ !
Regards
Goldsmith

 

[emontllo]

Totally agree with Goldsmith,

this is design is extremely inefficient, huge, heavy and will inject harmonics to the network due to its transformer-rectifier topology...
Why not using a SMPS? 15 A 12 V is not that much. You can find it in Digikey for 70$

 

[chuckey]

I checked the Digikey UK price list for 230V AC - 12V 15 A and it was £283. :-(
Frank

 

[goldsmith]

Wow , what the high price is that , Dear Frank !
And if you try to design it , what will be the price ?
Regards
Goldsmith

 

[emontllo]

Digikey:
271-2790-ND
Q652-ND
102-2165-ND
The transformer mentioned above would cost at least twice the cost of these power supplies.
I still cannot find a technical reason for building such a huge, heavy and inefficient converter :-D.

Ernest

 

[goldsmith]

Dear Ernest Hi
Yes , i can't understand it's technical reason too . and i think for this low power (360W ) , a simple forward converter can help ( with very low size ) . Isn't it ?
Regards
Goldsmith

 

[betwixt]

I'm going to be controversial.

There is a good reason for using a design like this in some circumstances. For example, here I need 12V at about 25A to power a bank of extremely sensitive radio equipment covering a frequency range of 30KHz to 13GHz and even nW emissions from equipment is a huge problem. I have not found a single SMPS that has sufficiently low emission to be usable but linear supplies are no problem. Most emissions are down the power lines rather than the output wires or are produced across the input and output points. I even have trouble with interference from a 125KHz RFID reader several hundred metres away!

I do have some doubt about the ability of a 7812 to handle the base currents of six low gain power transistors though.

Brian.

 

[goldsmith]

Dear Brian
Hi
I still think that is awful supply .
Look at those dissipative and expensive transistors ( with that big heat sink ) and that large value capacitor , and that big and funny iron core transformer and bad regulation ratio !!!!!
And take a look at a simple forward converter , please . it is isolated with a simple ferrite core transformer with lowest size . and with low number of windings . with very low size components and lowest price and best quality at ripple rejection ratio and regulation . and best efficiency . and very compact design .
So i think that circuit is obsolete .
Best Regards
Goldsmith

 

[chuckey]

Goldsmith, my labour costs would be > £1K. When I worked we bought EVERYTHING in we could, why re-invent the wheel? Only when there was no one who made what we wanted, would we consider building it ourselves, such as a change over system for satellite drives that used the ONE reserve in place of any active device.
As for building a power supply for 7$, I doubt if I could buy the case for it for that price.
Frank

 

[goldsmith]

I built it with just 7$ ( without case ) . i bought three ferrite core with 4$ , and a mosfet and a driver and some resistors and capacitors , and diodes with 3$ , , and then i built it , simply .
However your idea is respectful for me , but i just said my idea , because , we can design a simple 12v 30A , with lower price and better quality . but if you want build that circuit , it has no problem , because you want to do that ! :smile:
Regards
Goldsmith

 

[betwixt]

It amazes me that in some countries it is so easy to buy electronic components. I see many messages, especially from India & Pakistan suggesting the best roads and shops to visit. Where I am, the nearest shop is about 100Km away so everything has to be ordered by telephone or Internet and takes days to arrive. In the UK we can get hold of a huge range of parts but the cost is very high compared to other countries. There is no way I could build a power supply for $7, even a small PSU would cost several times that amount and parts for one rated at 30A would cost around $150.

Brian.

 

[tpetar]

Brian,

China is closer to them then us.

What to say I found air conditioner 12000BTU split system in china for 35USD indoor and outdoor in packages, the same split in EU is 200-300eur. We cant buy only compressor or chiller for that money, money will be just only for copper pipes.

Honestly the amount was 10000 pieces minimum.

 

[sanaprog]

thnx everybody for suggestions...iv got the fault of the circuit..Two of the TIPs were faulty...now it is working...

 

[tpetar]

Sanaprog,

What is Your expirience with this circuit, did you try it with some loads ? How power supplz react on load?

Did You try 50% load ? How is heating of transistors ? What voltage says on higher amperage ?


Your expirience will be usefull for others who whant to build this power supply.

 

[mister_rf]

I built it with just 7$ ( without case ) . i bought three ferrite core with 4$ , and a mosfet and a driver and some resistors and capacitors , and diodes with 3$ , , and then i built it , simply .
However your idea is respectful for me , but i just said my idea , because , we can design a simple 12v 30A , with lower price and better quality . but if you want build that circuit , it has no problem , because you want to do that ! :smile:
Regards
Goldsmith

OFF TOPIC
@Goldsmith
Although it's been a very long time since my last home-made SMPS experiments , please share with us your experience in this field. I'm always ready to learn how to obtain up to 1KW SMPS using just a bunch of cheap components... So why not, be my guest and open a new thread here:
https://www.edaboard.com/forums/18/