396XT and GPS Power Supply

[box23]

I'm designing a circuit to power both my 396XT and GPS in my mobile. I understand the subject quite well, but I'm hoping I can get a check on my math.

The power requirements are as follows:
396XT, 6V (800 mA max.)
GPS, 5V (80 mA max.)

My plan is to use a small 12v regulator, capable of 1A, feeding two voltage divider circuits in parallel. The voltage divider circuits are shown in the attached picture.

By my calculations resistors R1 and R2 would need to be 7.5 Ohm, 5W.
R3 would be 87.5 Ohms and slightly larger than 1/2 W rating. R4 would be 62.5 Ohm, 1/2 W.

Any questions let me know.
Thanks for the help.

 

[slicerwizard]

I understand the subject quite well

No, you do not. Your devices are not constant current loads. You can't just toss a cheesy voltage divider at the problem. Never mind the fact that you'd be wasting gobs of power (10 watts full time), running your regulator hot all the time and under-driving your devices. Your radio would not get the 6 volts it needs, for example - assuming it draws about 200mA, it would get 12V x 44% = 5.3V; crank the volume and it would sag under 5V (well, it would if the radio actually worked on 5V)

Use a 5V (7805, etc.) regulator for the GPS and a 6V (7806) for the radio.

Don't mess with a 12V regulator just because you have one kicking around your parts bin.

 

[box23]

OK, Thanks.