Hello.
I am after some help with a DC-DC supply for a headphone amplifier power supply for my car.
It currently runs on two 1.5AAA batteries but I want to generate a permenant supply from the car live.
Any help would be greatly appreciated. 500ma max (seems high to me though)
Simple DC-DC 12volt to 3 volts supply
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Re: Simple DC-DC 12volt to 3 volts supply
Hi
You need a voltage regulator - either an LM317 adjustable regulator or a 3V fixed regulator. The datasheet for the LM317 can be found at http://www.national.com/ds/LM/LM117.pdf and includes a typical application circuit on page 1. For a 3V output resistor R1 should be 240 ohms and the variable resistor shown for R2 can be replaced by a fixed 330 ohms. You will need a heatsink on the LM317 - the power dissipation will be around 4.5 watts with a 500mA load, higher if the input voltage is higher (as it normally is when the engine is running).
Alternatively if you want a ready-made regulator use an adjustable DC power supply designed to plug into a cigarette lighter socket - I think Maplin (and others) stock them. You could always open it up and mount the circuit board seperately if you want it hard-wired.
Whickever method you choose make sure the supply is fused correctly.
You need a voltage regulator - either an LM317 adjustable regulator or a 3V fixed regulator. The datasheet for the LM317 can be found at http://www.national.com/ds/LM/LM117.pdf and includes a typical application circuit on page 1. For a 3V output resistor R1 should be 240 ohms and the variable resistor shown for R2 can be replaced by a fixed 330 ohms. You will need a heatsink on the LM317 - the power dissipation will be around 4.5 watts with a 500mA load, higher if the input voltage is higher (as it normally is when the engine is running).
Alternatively if you want a ready-made regulator use an adjustable DC power supply designed to plug into a cigarette lighter socket - I think Maplin (and others) stock them. You could always open it up and mount the circuit board seperately if you want it hard-wired.
Whickever method you choose make sure the supply is fused correctly.