Question about current control

Brad03

I am trying to use a BS2 to make a current control system for LEDs. My thought was to use the devices PWM function and a resistor capacitor hold circuit to make a controllable voltage input (for a voltage to current amplifier). I'm just wondering if this is a sensible approach.

stamptrol

Brad,

With suitable design, the LED can be controlled with the Stamp's PWM command without the capacitor.

Of course, it means the Stamp can't do too much else because the PWM command must be continually refreshed.

Going back to your original idea, the PWM command with the capacitor will indeed give you a variable voltage to feed into a V-to-I amplifier.
With attention to the charge/discharge time of the capacitor, the Stamp will have considerable "extra" time to do other tasks.

You could also have the LEDS driven by an independent constant-current-source which the Stamp switches on and off.

Regards,

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Tom Sisk

http://www.siskconsult.com
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allanlane5

Why do you want to "control current" through an LED again? Most people control the voltage across it, or use "HIGH" and "LOW" with "pause" to pseudo-PWM to control the brightness.

Phil Pilgrim (PhiPi)

allanlane5,

Brad's approach is the correct one. LEDs are current-based devices, with forward voltages that can vary from model to model, from lot to lot, and with temperature. Controlling the current gives the best output uniformity over these variables and prevents over-current conditions which can shorten an LED's life considerably.

-Phil