# 12 v dc input pc power supply

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#### alizan.electronic

##### New Member
I need an ATX power supply circuit diagram for using PC in my car.I want to modify ATX 300 watts power supply to do that. please help me...

#### MikeMl

##### Well-Known Member
I would buy a cheap 12Vdc to 120V not-pure-sine inverter, and feed that to the PC

#### alizan.electronic

##### New Member
I would buy a cheap 12Vdc to 120V not-pure-sine inverter, and feed that to the PC
It had a problems:unused a lot of watts

#### MikeMl

##### Well-Known Member
It had a problems:unused a lot of watts
Efficiency of the inverter should be better than 75%, while the ATX is a switcher which is about 80% efficent, so you are only wasting about 80W, overall efficiency is about 60%. How hard are you going to work to save maybe an additional 20% of 200W?

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#### Externet

##### Active Member
Your car supplies 12 to 14V DC.

Your PC wants +12, -12, +5, +3.3 VDC.

You do not need to modify the ATX power supply. You do not need neccesarely to go into AC inverters. You need to downregulate with beefy DC-DC converters.
It will not be cheap. Probably more $than an used laptop plugged direct to the cigarette lighter. ATX power supplies schematics are somewhere on the net. Miguel #### alizan.electronic ##### New Member Your car supplies 12 to 14V DC. Your PC wants +12, -12, +5, +3.3 VDC. You do not need to modify the ATX power supply. You do not need neccesarely to go into AC inverters. You need to downregulate with beefy DC-DC converters. It will not be cheap. Probably more$ than an used laptop plugged direct to the cigarette lighter.

ATX power supplies schematics are somewhere on the net.
Miguel
current of +5 and +3.3 is very high and if I use downregulated,the sum of current to be use is go high(because current in the Input and Output of regulator is same),but when use an ATX power supply,current is low.

#### Externet

##### Active Member
Current for +5 and +3.3 is whatever it has to be for your PC to run.
And that same exact current is the one supplied by the ATX supply if you use it.
Why do you say the ATX supply current is low ?

Yo do not waste Amperes; you waste Watts !

Miguel

#### alizan.electronic

##### New Member
Current for +5 and +3.3 is whatever it has to be for your PC to run.
And that same exact current is the one supplied by the ATX supply if you use it.
Why do you say the ATX supply current is low ?

Yo do not waste Amperes; you waste Watts !

Miguel
if you notic:for example: pc use +5V\20A and +3.3V\15A then sum of watts is about 150watt,if I use regulator to reduse +12 to +5 and +3.3 the used current from +12 is 35A and the used watts is 420 watt,in this metod the unused wattsis 420-150=270 watt and thet so much for car battry.

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#### snakecircuit

##### New Member
i want to design a rechargable lamp using LED's and recircled notebook batteries. please can someone help me with useful circut diagram both for the lamp and the charger to use.
Thanks

#### tcmtech

##### Banned
want to design a rechargable lamp using LED's and recircled notebook batteries. please can someone help me with useful circut diagram both for the lamp and the charger to use.
Thanks
Make a new thread. This ones taken!

#### tcmtech

##### Banned
Digikey and most of the bigger name electronics supply companies carry a DC- DC converters that can easily take the standard automotive voltages and change them into the low voltage high amp capacity sources you need.

However in theory it is also possible to rewind the HF transformer in your ATX and change the primary side circuits to take in the automotive voltages while still giving out the right voltages as well.

Most ATX type power supplies are based on common switching IC's and specs sheets with basic use diagrams are not hard to find for them.

#### OutToLunch

##### New Member
if you notic:for example: pc use +5V\20A and +3.3V\15A then sum of watts is about 150watt,if I use regulator to reduse +12 to +5 and +3.3 the used current from +12 is 35A and the used watts is 420 watt,in this metod the unused wattsis 420-150=270 watt and thet so much for car battry.
That would be assuming that you are using a linear regulator as your supply (output current equals input current). There is no way you're going to use linears for the 5V and 3.3V rails. You would have to use buck regulators. Assuming an efficiency of, say, 85% for each regulator, the power from the 12V rail would be about 176W, or about 15A.

I would suspect that if you, personally, were to design and build a buck regulator you would likely not see great efficiency. The previous suggestion of getting a 12V to 120V inverter would be the easiest route.

#### blueroomelectronics

##### Well-Known Member
Many mini-itx motherboard supplies use 15V DC

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