Different ADC problem

[kalaman]

Hi there,
I would like to measure a voltage between VCC and Mosfet's drain. How can i succeed with a PIC? I can use adc functions well but this is an unusual problem for me.

The circuit is this:

 

[Pommie]

Just measure the voltage at the drain with a simple resistive divider. The voltage across the load is 20-Vdrain.

Can I ask, why you want to? The value will always be one of two values unless the load is capacitive or a motor. Assuming you want to know the current in the load, it would make more sense to put a low value resistor in the ground leg and measure the voltage across that.

Mike.

 

[kalaman]

I would like to make a circuit that lights 100-150 leds groups which are series. I don't want to use resistor with every 3 leds. My circuit will decide to give 10V for leds.
Maybe different method will be better. But I don't want to use resistor for every 3 leds.
Any idea?

 

[matc]

yeah, use a resistor for every 3 LED's

 

[kalaman]

matc
Using 100-150 resistors causes power lost. I don't want it. For example what will i do 30V power supply when i use resistors. My MCU have to decide how it drives suitable voltage (10V for 3 leds) to the leds.

 

[matc]

Ideally you want to drive LED's with constant current - so if you want to avoid losses you need to losslessy vary the voltage. Have you looked at the LED driver chips you can get? They incorporate a stepup/down controller and are pretty efficient

 

[kalaman]

Ok matc,
Is there any IC that allows dimming controlled by any MCU.

 

[matc]

https://www.google.com/search?q=led driver with dimming

 

[kalaman]

Thank you very much