How to use 1A regulator for 3A load applications?

[narithota]

Hi

I required 12V 3A. For this one iam using L7812 CT (TO-3)

But this component is not working properly.

I have 12V, 1A (L7812CV) Regulator, this is working well.

Can I use L7812CV for 3A load applications?

Please suggest me how to use 1A regulator for 3A load applications.

I have TIP122 transistor, please provide me circuit-using TIP122 .

Regards

nari

 

[max0412]

lm 7812 3a

See fig 18 of the application note on your reg.Just use an external pass transistor.

http://www.ortodoxism.ro/datasheets/SGSThomsonMicroelectronics/mXwrtr.pdf

Just make sure the transistor is properly sized.

 

[IanP]

lm7812 configuration

The basic method of boosting the output current of 78XX voltage regulator is by adding an external PNP power transistor, and that is readily described in most of 78XX-series data sheets ..
Now, you try to use TIP122, which is NPN power darlington ..
Of course, it is possible, and all what you have to do is to convert this NPN configuration to PNP by adding small signal PNP transistor to your TIP122 - see attached picture ..

Also, make sure that the input can supply at least 3A @ U(unregulated)>16Vdc ..

Regards,
IanP

 

[mtl]

tps5410

This is 5v 3a, you can use it for 12v 3a, replace IC1 with LM7812.
If you want replace T2 2N2955 with bigger transistor like ...
MJ4502, 2N6609 ...

 

[hanklu]

lm7812 pnp

I will suggesting TI

TPS5430
Vin=5.5V~36V
Vout=1.23~31
Iout=3A


If you want Iout=1A,you can chose TPS5410

They are almost pin to pin.

TPS5430 can do Buck-Boost ...etc application.

 

[narithota]

l7812cv aplication

Thanks for the valuable Information


Aim using TIP122 (NPN), 2N3906(PNP), 15V(3A) Transformer, 3A load and L7812CV Regulator.

How to find out the resister values and Wattage of Resister for above circuit

It is a basic formula V=IR, P=I2R but iam not getting how to find out Exact values

Please provide me Resister values and Wattage of Resister.

Regards

nari

 

[IanP]

Re: 3A load

Take a look at the attached picture ..
As R2 select 100Ω (1/4W) ..

To select R1 you have to make an assumption: if you don't want to mount the LM7812 regulator on a heatsink you have to limit current flowing through it ..
Let's say the max current will be 0.1A - that is, for currents below 0.1A the LM7812 feeds the output, and for currents above 0.1A the output current consists of 0.1A from the LM7812 and the rest goes through power PNP (in your case 2N3906+TIP122) ..

So, the approximate value of R1 is:

(Ube+Ur2) ≈ 1V

R1 ≈ 1V/0.1A => 10Ω, resistor wattage>> R*I² => 0.1W, go for >0.5W ..

If you wish to select different current follow the above procedure ..

Regards,
IanP