wil this work ok?

[stuee]

Will this work ok, and need some help.
Would it be possible to change the var resistor to a digi pot meter so i can get more precise changing of voltage.
Also can i attach a digi voltmeter to it to show the voltage, the input is 12v from the car so would have to drop that down to 5v+/- i think.

Ideas, schematics drawings will be most helpfull, thanks :D

[ante]

Hi Stuee,

Yes it will work, but you don

[Kevin Weddle]

I would forget the 10 uf capacitor that is on the output. You have to know that this regulator is looking for a certain amount of current. That current is the operating current of the regulator and the mid current of the transistor. The tranistor current can of course fluctuate by means of the regulator, but it will not be by much. So I would make sure the load current is rated for half the current of the transistor and regulator current combined.

[MP]

Kevin,
I think the point you are making is: If you have power supply ripple getting past the regulator, you should increase the *input* side cap, not the output side. The output side of a reg should already be a very low impedance, and adding caps to it beyond that needed to suppress HF noise should not be necessary, and can in fact drive a reg into oscillation under some conditions.

On the input side, you must simply ensure that at the max load current, the bottoms of the AC ripple are above the min dropout voltage of the regulator. So more cap = less ripple, until you get above the dropout voltage.

However, 10 uf is not a large capacitance. This capacitor will keep whatever is attached to this regulator from loading it down. For example, if the circuit is connected to a device high in EMF, then the noise (spiking) from this device might be transmitted through the circuit to other devices with only a 0.1 uf cap on the output.
A 0.1 uf cap would only protect against very high frequencies. I think the 10 uf cap would be a good insurance policy in this application to keep the output voltage constant.

MP