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vikas
11-02-2010, 07:45 AM
I have a gadget which works on Li-ion @ 3.7 V , now i want to power it from my car battery. The gadget does not really consume that much current as such.

I made a LM 317 based circuit but the circuit which gets hot , on further googling i found that the LM317 is not really efficient. I also tried 7805 with 2 diodes , this too gets hot.

So any alternative guys ? for 12 v -> 3.7 to 4.2 V conversion.

pratheek
11-02-2010, 09:09 AM
How much current is your circuit consuming? If your circuit is consuming very less current, then the LM317 should not generate a lot of heat.

Anyway, why don't you try a Switcher Power Converter based regulator like the LM2672.

asimov_18
11-02-2010, 11:47 AM
make a switching dc dc regulator!!! IC 723 should do it well

allbits
11-02-2010, 05:43 PM
The circuit should be taking more power, and there is no other reason why 317 should heat up like that. At about 9V drop out, a good heat sink should take care of the problem.

Did you check the current the circuit consumes, when connected to the car battery?
Is the power supply critical? as in does it need a very clean supply?

78xxs has shown unreliability with high drop outs. Heat sinks are a must at about more than 5V drop.

vikas
11-02-2010, 11:18 PM
I did have it running it does heat up at start , but then cools down after first few minutes . Maybe the GPS and GSM initialization take more current at start :). It a GPS tracker which i hacked the Li Ion to run 24x7 .

But i will look at the other solutions offered.

allbits
11-03-2010, 08:10 AM
Yes, it should be taking close to/more than 1A at start up, but a good heat sink should do the trick. But I cannot find another cheap and locally available solution @1A. 723 cant handle much current.

To have a reliable supply, its always suggested to have double the rating of the surge current. So, I would have gone for a 2A converter.

http://www.national.com/cat/index.cgi?i=i//200
and from the list, LM2592HV seems to be a good option for you. it comes in TO220.

karanpreetsingh
11-05-2010, 12:29 AM
Hi ,
a good alternative for this is the MC34063 which is a dc to dc converter which is very famous and it can step up as well as step down the voltages for upto 1.5 A and is very easy to use, very reliable and jelly been kind of part available everywhere

docel
11-08-2010, 06:59 PM
Try a LM338 T or K Take your pick. You cant eliminate the heatsink though.
Another trick; use a 7805 to reduce the 12v to 5v , and feed it to a 3.3v LDO like LM1117, LM2950 etc.,
Cascading 2 Voltage regulators will split the start-up current / power dissipation.
But i'd personally go the miserly way - simply use the LM317 with a small heatsink that can double up for the cabinet/ clamp etc.,
That way I have 2 birds - a Voltage regulator AND a reliable overload fuse built into 1 component :)

Another intelligent thing is to always use a low value resistor in series between the battery and the Regulator.