Charger/discharger for supercapacitors

[konrad_gom]

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?

Regards

 

[crutschow]

That circuit is designed to only supply current, not sink it. Use a transistor switch in series with a resistor to discharge the cap.

 

[konrad_gom]

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?

 

[crutschow]

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?

 

[konrad_gom]

Discharging current must be adjustable from mA to few Amps. Capacitor capacitances from less than 1F to few hundreds F.

 

[crutschow]

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.

 

[konrad_gom]

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?

 

[crutschow]

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.