12V to 5V?

[Arkan]

Hi,
Im am installing some electronics in my car and they need a 5V power supply. How can I change 12V into 5V.

Thanks

 

[Russlk]

LM340T-5.0 or 7805 IC, look up the data sheet.

 

[John Sorensen]

Automotive applications are very difficult from a power point of view. You should do some research on that before you start messing with your electrical system in your car. Autos are a notoriously noisy environment (electrically) and the +12V supply is rarely 12V.

j.

 

[Hivolt]

Depending on how much current you need, a 7805 is good for up to 1.0 A but depending on the manufacturer some claim 1.5A. There are also 5 V regulators that are higher current ( 3-4 amps) at a higher cost. The important things to remember is proper filtering and heatsinking. As far as filtering goes, use a 1000 uf 35V electrolytic capacitor on the input and a 10 uf 25V electrolytic capacitor in parallel with a 0.1 uF mylar capacitor on the output. This combination will provide noise filtering and kill any oscillations that can occur. As far as heatsinking goes, the case of the regulator is connected to the ground terminal anyway so no insulating washer is needed. A commercal heatsink can be used or a piece of aluminum 1/8" thick about 10 sq inches. To get an idea of the maximum power dissipation - use 14.4V - 5v X output current ( say 1 Amp ) =9.4 watts. Always choose a larger heatsink, on cool days it won't matter, but on summer days the regulator will run hotter due to higher ambient air temperature and you won't the regulator to thermally shut down. Mounting the heat sink to metal on the car will help sink away some of the heat. No insulating washer is required for a 7805 or equiv. since the tab is connected to it's ground lead anyway. In automotive applications, always make sure that the body ground ( wire from batt "-" to inner fender ) is intact and in good condition, this will reduce headaches with noise and voltage fluctuations when accessories, headlights, wipers etc. are turned on. Search 7805 on google , or go to TI ( Texas Instruments ), National Semiconductor, or Motorola for data sheets and optional devices.

 

[Hivolt]

On my last post I forgot to mention, that although you do not need an insulator for the regulator, you do need to put some thermal compound between the regulator and the heatsink. A sil-pad could be used instead of thermal compound if you wish on a commercial heatsink, but depending on how smooth the heatsink surface is, ( if you use an aluminum plate wet sand the contact area ) a thermal compound grease or epoxy will fill the imperfections the best.

 

[Sebi]

Over 0.5A i strongly recommend to use a Simple Switcher from National Semiconductor. Just a few components, 90% efficiency ( without or with small heatsink), and online design help.

 

[Arkan]

Thanks guys