fungus:
davivid:
CrossRoads:
http://www.onsemi.com/pub_link/Collateral/NSI50350AS-D.PDF
Circuit follows the device's data sheet, except for C11.I was advised elsewhere to add C11 to reduce any EMI effects (also mentioned in the data sheet), as the rest of the circuit is a touch sensor.
I was confused when you said this was a "built" circuit. I thought you couldn't modify it.
C11 is preventing you from using the BJT for PWM control. If you remove C11 you can connect a PWM signal to the base of Q2 (any current sink chip will do the job - just place a smallish resistor between Vcc and the chip input and connect the base of Q2 to the resistor).
EMI effects? They're almost inevitable in a PWM circuit. You'll need to add lots of decoupling and maybe try different PWM frequencies to minimize them.
Built as in my PCB's are fabricated and populated... but I could replace C or R with other values.
The circuit works fine with C11? (should it not?) I have it connected to a PWM output on an arduino. Now I will try connecting it up to a current sink chip with a pull up resistor - hopefully this will work too!