Hello,
I design supercapacitor charger/discharger. Output voltage 0-15V. Output current 0-10A. Capacitors capacitance: few hunderts F. I plan use LT3761 IC.
How to charge, set current, and voltage I know. Question is how to extend this circuit for discharging?
As default this will be charger/discharger controlled by microcontroller. I must measure current and voltage. So how to implement discharger in this circuit? Should I use some relay and second transistor with resistor?
If you have an output from the µC to control the discharge, just connect that to the base of an NPN transistor through a resistor, emitter to ground, collector through a resistor to the cap. How fast do you need to discharge the cap and what's the cap size?
How do you want to control the value of the discharge current, some type of voltage signal? For that you could use a constant current circuit consisting of an op amp and a transistor.
This is the question, can I use f.e. DAC output of uC and digital potentiometer in base circuit of transistor to regulate base current and through this collector current?
The base current versus collector current depends upon the particular gain of the transistor you use (which typically varies over a range of 3 or 4 to 1, so if you want to current to accurately reflect the voltage from the DAC you should use an op amp in a feedback circuit to make a constant current, such as this. The pot is not needed, the DAC output goes directly to the (+) op amp input. The capacitor is connected to the MOSFET drain. The discharge current equals the DAC voltage divided by the source resistor value.