# Thread: Could this work for a Solid +12V of 8-14V in ?

1. ## Could this work for a Solid +12V of 8-14V in ?

http://geocities.com/andrewmuck/PSU.htm

Power supply description
PC style power supply running off a car battery with input voltage range of 8V to 14V
You may ask why bother, others have already done it. The reason is this: I wanted to have heaps of Amps for running old hardware and didn't want any brownouts when starting the car.

5V at 10 Amps
-12V at 0.5 Amp
-5V at 100mA

5 Volts done using an LM2576 with a 2N5038 external switch
12 Volts using an LM2577 to step up to 15V then a 7812 with a pnp pass transistor to regulate back to 12V
-12V is obtained by winding an extra coil over the 15V inductor with its own catch diode and capacitor, regulating using a 7912

This relies on at least some load on the 12V line and supply current will be limited.
-5v using a 79L05 off of the -12V line

So far I have found that less than 7.6 volts input causes the output to start wobbling. 8V is a definite low limit (you really don't want you car that flat anyway!)
I also find the -12v line is happier with more than 9v. The 15v inductor starts to make an audible noise below 9v incoming supply. A bigger inductor may help this as I am only using a small 100uH coil.

12 Volt
12 Volts is done by stepping up to 15V then regulating back down.
the Lm2577 is used with an MJ15004 transistor to increase switching current. Similar to the 5 Volt method.
A 7812 is used to provide the 12V reference, with its output connected to the load; with a 1 Ohm resistor on its input pin.
A MJE2955 PNP power transistor provides the high current path with its base triggered by any voltage drop across the 1 Ohm resistor.

2. car batt. in car can go from 8V to 15V and this will fry this psu.

3. Originally Posted by danon
car batt. in car can go from 8V to 15V and this will fry this psu.
I don't think so - he's using a LM2577 (switching regulator) in boost mode to get regulated +15V output which is then regulated down to +12V using a linear regulator + series pass transistor.

The LM2577's input is rated up to 40V max so it should not have any problems with an battery voltage of 15V.

4. oops, sorry just refering to "input voltage range of 8V to 14V"...

this won't work on an atx though as it doesn't have 3.3, powergood, etc... but in my case, i already build a sproggy, although i'm not getting enough power from the 12v rail, this psu will be the answer as it has 5Amps on the 12v rail. i would incorporate this into my excisting psu and will just see how it goes...