19volt to 12v + 5v conversion

[daemon123]

Hi,

Basically i have 19v 4A laptop PSU, i have want to use it for my IDE->USB converter as is orignal PSU unit gives 1 amp on both 12v and 5v,

i know that i can use 7805/7812 directly but there output is 1A, is there any way i can get 2A on both out using simple schematic ?

please help me

 

[IanP]

Use LM2576-12 and LM2576-5 (or LM2576-adj) and you will have close to 3A on both outputs ..
**broken link removed**

Rgds,
IanP

 

[daemon123]

thanks for the quick reply IanP

but i am afraid i cant find this IC here, have very limited things avialble locally,
any other alternative which doesnt use special ic nor Inductors.

A friend told me that it can be done with a transister on top of 78xx serires ic but he didnt gave me any schematic..

plz any simple alternative which uses general purposes components

 

[IanP]

That's true, you can boost the output current of 78XX regulators by adding an external power transistor .. see attached picture ..
Be aware that droping voltage from 19V to 5V means that the equivalent power of [19V-5V]*Current is converted to heat, so you have to mount power transistor and voltage regulator on a decent heatsink ..

Rgds,
IanP

 

[BADFLOPPY]

Just Open your PS and adjust the biasing in the feedback circuit in the 431 IC. If require, just read the TL431 Datasheet from Internet. Then fix it at 12 Volt. Make 5 volt with any linear regulator like 7805 if it';s load requirement not too much (I Think). Adjusting 431 biasing is the best idea.

Thanks

 

[DaMoose]

you might want to use a nation semiconductor
simple switcher

they have online cad that lets you input your:

in voltage
out voltage and current requirement and desired ripple performance


it will pic the part, and components etc

a linear regulator is not a good idea going from 19v down to 5
or even from 19 to 12

because every one of those volts has to be dissipated of as heat and additional current load to the 19 volt supply

so at the least I would use a switcher to get down to 12 then a LM7805 for the 5 volts

the best deal of course would be switchers on both

Moose