schematic for 12v to 5v using LM350T regulator

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schematic for 12v to 5v using LM350T regulator

Postby delcowizzid » Fri May 01, 2009 6:13 pm

hopefully VL400 sees this i just bought an LM350T 3amp regulator to add a second +5v supply in my JAW wideband for running my map sensor 5v fan and maybe a knock filter board all to be logged with the JAW apart from the fan.now i thought the reg might just be plug and play 12v to 5v but of course it isnt LOL ive found a few schematics online but all have a variable resistor and silly equations to calculate the output im hoping someone can give me an idea on what size resistors i need and maybe a tried and true schematic to get this thing to output 5v.or should i pull a reg out of my VS ecu thats for parts and use it or am i going to have the same issues with needing a simple circuit to get 5v from that too.cheers guys
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Re: schematic for 12v to 5v using LM350T regulator

Postby VL400 » Fri May 01, 2009 7:19 pm

The LM350 will do the job but it will get hot if you draw lots of current through it when its regulating 5V. A dedicated 5V reg is a LM7805, but they are 1 amp and will have the same prob of heat. For the MAP sensor the 5V is pretty critical for stable and accurate readings so need a reasonable power supply. You could tap into the JAW for that i reckon, the MAP does not use much current and it has a 5V reg already. You would be better off with a 12V fan really.


Anyway if you really want to use a LM350 have a look at the data sheet here... http://www.fairchildsemi.com/ds/LM/LM350.pdf

On page 5 there is a basic circuit that will be marginal for vehicle use - some zeners for spike protection are nice to have. But using the schematic, i would add a little more capacitance than the 0.1uF and 1uF, add a 100uF in parallel to the 0.1uF and replace the 1uF with a 10uF.

The resistors, they show a 120R for R1 and you need to calc R2. The calc is VO = 1.25V(1+R2/R1) + IADJ R2 . Forget about the Iadj R2 bit as its very minor. So the calc for determing R2 is R2 = R1((Vo/1.25)-1). For 5V a 360R resistor is needed as R2.

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Re: schematic for 12v to 5v using LM350T regulator

Postby delcowizzid » Fri May 01, 2009 7:46 pm

chears mate bloody awesome .i havnt had any sleep and the maths of the resistors was gonna do my head in LOL.i would use the jaw but it gets warm allready and i want to try not to induce any unnessicary interferance.i have a vs ecu thats stuffed does it have a sutiable reg in it.the only fan i had came out the laptop was nice and small only realised when i was installing it that it was 5v not 12 :cry: but its in and fits nice the map sensor is only to veiw in the logs with rpm so i can work out what cell im in.
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Re: schematic for 12v to 5v using LM350T regulator

Postby VL400 » Fri May 01, 2009 7:51 pm

I wouldnt bother with the ECM voltage reg, I reckon that would be more trouble than its worth. A simple LM7805 with a heatsink would do the job, what is the power consumption of the fan??

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Re: schematic for 12v to 5v using LM350T regulator

Postby delcowizzid » Fri May 01, 2009 7:58 pm

hahaha 0.07amps pretty much nothing LOL.ill see if they have an LM7805 i need to go get another zenor diode anyway as the one i gots too low of a voltage.just getting ready for the final mounting in the box dont want to have to pull it again.got a good 1.5 metres of cable for the sensor now all soldered ready to go and it plugs into the JAW box now.trying to make it a whole complete tuning tool with knock etc included was going to use a vn knock filter board in there and feed the output trigger into the spare 0-5v input.
If Its Got Gas Or Ass Count Me In.if it cant be fixed with a hammer you have an electrical problem

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