when testing of dc power supply, DC-DC convertor, Linear regulators, and battery we need some kind of instrument which sink constant current from source.

Step 1: Need for Dc Load

we can use constant value resistor but in case of battery we need to change resistor with voltage droop so it become complicate

Step 2: Power Sink Device

hear i use IRF250 power MOSFET for power sink device. while MOSFET sink power is convert into heat so for cooling MOSFET i use old processer's heat sink and also added 100k 2w resistor across Gate and source terminal

Step 3: Power MOSFET As Power Resistor

hear i connect one source to drain and source and other source between gate and source by increasing gate terminal voltage other power supply sink current hear MOSFET is work as electronic resistor

Step 4: Control Concept

for control current we need to measure current reading for measuring current i use Shunt resistor method

Step 5: Shunt Resistor

hear i take 0.1 ohm 10w resistor and by calculation we get max current from resistor is 10A and max voltage is 1V which is very low for operation

Step 6: Amplify Current Signal

i deside to make circuit to give 1v for 1a and for that i desigh this differintial opamp circuit with gain of 100 and for that i take 1k and 100k rsistor

Step 7: Comparator

after gating current signal from differential OPAMP i give that signal to comparator and compare that with potentiometer , if differential OPAMP's out put is lase than pot then comparator OPAMP give high out put else it give low output. hear i make circuit for 5A max so i give 5v to potentiometer