My main goal is to create constant current source as laser diode driver between 0-200mA, controllable by 0-3.3V analog input from MCU, And can be modulated (ON/OFF only) by square 0/3.3V PWM signal (changeable frequency up to 10khz and DC 0-100% from MCU).
V3 In my schematic should provide the analog 0-3.3V (MCU PWM with MCP4725 PWM to analog) and V2 should modulate the signal by PWM from MCU.
Attached are schematics of two switching concepts variations(BJT, MOSFET).
I already built the entire circuit with BJT option but since the BJT acted in saturation (the analog input 0-3.3v is smaller than the switching voltage), i received negative current in the analog input power supply and increasing the analog voltage didn't had any effect (does it make sense?)
besides that, rest of the circuit is working.
The MOSFET version use opamp since my MCU is 3.3v and unless it will be fully opened I'll ran into saturation at some point . (is it the right way to increase VGS from 3.3V?)
I'm not sure about high side switching / low side switching , BJT/MOSFET... Hopefully you will be able to help me solve the switching issue.
and last remark the opamps VCC is 7V since I'm using MCP602 and from the datasheet I understood that's the maximum voltage range.