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View Full Version : DC to DC : Help please



kp_chd
07-29-2008, 10:29 PM
I am making a couple of circuits:

The first one needs a 5v 100 mA supply from AC and i wish to avoid using a transformer.

The second one is for a Line Follower which has a 6v battery pack BUT a 12v motor.

So i need 2 dc-to-dc converters

one step-down ; small current requirement (~100mA)
second step up ; high (~1 Ampere) current requirement

i searched and found that buck / buck-boost /charge pump
are the most used.

CAN ANYONE GIVE ME AN IDEA ABOUT WHICH ONES TO USE HERE ?
Also,
I have heard about ICs like those from maxim.
I also wish to avoid these if possible due to monetary reasons and availability problems.
Thanx in advance.
Prateek.

ashish_agarwal123456
07-30-2008, 10:48 AM
don't know about ics but a mobile charger can prove really useful....... i recently got a chrger for 60/- and it gives 5v 350mA from ac supply........ you can remove the outer plastic coating if you wish to install it onboard.....

samurai_01
07-30-2008, 03:24 PM
6v battery pack and 12v motor.
it means you want to increase the dc voltage. obviously you cannot use a transformer here.go for rectifier system with diodes, given in any basic electronics book( Boylstead).
i think you cannot even increase dc 6v to dc 12v without sacrificing huge amount of current,so forget about 1A current until your battery is super current provider.
better buy a battery of 6v and connect it in series.
use this link
http://www.coolcircuit.com/circuit/voltage/index.html

ashish_agarwal123456
07-30-2008, 05:05 PM
samurai is right.......... even with 50% efficiency, you need to give 4A at input to get 1A at output....... even if your battery permit it other components may not

kp_chd
07-30-2008, 06:15 PM
@ samurai
[quote=" obviously you cannot use a transformer here.go for rectifier system with diodes, given in any basic electronics book( Boylstead).
i think you cannot even increase dc 6v to dc 12v without sacrificing huge amount of current[/quote]

Sorry i didn't quite get the idea of rectifier.Its a battery and hence it gives 6 v DC. So no use of a rectifier there. Right ?
As for the "current sacrifice"...i just read about the buck dc-to-dc conv. on wikipedia. It says that these converters have a high efficiency....around 95%
That's what got me excited.

Actually i was thinking that since dc-to-dc converters are so widely used there must be a DIY way to them....
But looks like i will have to put in more batteries.


as for the ac to dc requirement , a rectifier system is what i would normally use. But since this circuit is going to run 24x7 and we don't good AND cheap transformers, i wanted to avoid it.


but thanx anyways !

@ ashish
yeah cell chargers are great. I'm using one very similar to yours for nearly all my breadboarding needs.
so i guess this is a better alternatives to using a transformer.

as for the 6v to 12 volt :: these chargers have a rectifier and then dc-to-dc converter
so i guess i'll try to rip apart one of these,try to use the dc-to-dc part i and post back.After all there's no harm in a little experimenting ;-)

thanx for the idea !

pratikmahale
07-31-2008, 12:52 AM
Hi

Check this link

http://www.elecfree.com/circuit/power-supply/lm2577-5v-to-12v-dc-converter-step-up-voltage-regulator/

But I don’t know about the availability & price of the LM2577 IC

Check the datasheet of LM2577 first u will get all the details

kp_chd
07-31-2008, 08:11 AM
@ pratikmahale
thanx buddy.Looks like a simple circuit......now only if i could get the IC..............wil try to search it out.



@ ashish
hacked a chinese cell charger.
good for my voltage step-down needs.
It rectifies ac to 330v dc . Then makes it ac again but at some radio-frequency.Then steps it down using a RF transformer.And then rectifies it again.
So i can't use it for stepping voltage up.But good as a little power supply.