PROJECT: Constant Current Load

General description:

An electronic constant current load

Function description:

Operational amplifier IC2A is used to control current limiting N- mosfet gate to correspond the current setpoint adjusted by the potentiometer. Load current goes through 1-ohm 50 Watt shunt resistor causing voltage drop fed back to IC1A's negative input.

Set/read switch selects input voltage, either the set current or the actual load current to buffer amplifier IC1B to drive the display unit (terminals MTR+, MTR-) configured to display 0- 20 A using voltage divider resistors (full scale = 0,2V after the divider) in the display board.

Output mosfet and shunt resistor are mounted on a heatsink. In the heatsink there is an NTC-resistor which is used to control the cooling fan (connected to terminal SV1, 1-2) , op-amp comparator IC1B and over temp led, op-amp comparator IC1A. Both thresholds for fan motor start and led illumination can be adjusted by trimpots.

Auxiliary supply voltage to unit is through the backplane terminals, 12VDC. Allowable continuous load input voltage and current are limited by the 50W resistor or mosfet max power dissipation. An example with 15V supply voltage limits allowable load current to 7A (resistor limits). Mosfet dissipates at that point about 56 W.









Power mosfet: IRFZ44N

Shunt resistor: 1 ohm, 50W

NTC resistor: b57045k45

Display: pandm3dcv

Software: None