I am building an electrical load, capable of "sinking" 0 – 3A on a maximum of 60VDC. I want to control the load with a microcontrollers ADC (0-3V). On the internet you find hundereds of circuit propositions, that build around bipolar transistors or FET. I chose a design with a NMOS FET as actual sink.
The circuits principally work – but a FET is a capacitive load. So the circuit I built (following an article on design ideas (google "Power-MOSFET-is-core-of-regulated-dc-electronic-load") is oscillating.
I need my design to be as failsafe as possible. Merging all information I have I ended with this around a PowerFET and a PI control loop.
I started by a simulation with TINA-TI. But I have some doubts about the results:
- Why do I have this huge Peak in the beginning of a transient analysis (Zero initial values)?
- The current sense IC INA168 should provide a linear output tension – why do I have 72mA flowing after a step response of 500mV, 3.4A after 3V and nothing useful after 50mV?
- Is it normal that the OP Amps are staying at -VCC with 0V input? shouldnt the have 0V at the output aswell?
- Does this transient analyses make sense at all? Which other analysis should I perform?
Unfortunately stackexchange doesn't let me post more than 2 links, so I cannot post the other simulation results.