Adjustable constant current source

When comes to electronic designing and testing, adjustable current sources facilitates to simulate "load" on the circuit(s). The most common use of "constant current source" is to test the performance of power supply units and battery packs.

The current source introduced in this article is capable to handle current up to 6A with a maximum input voltage of 50V. This is an operational amplifier based adjustable current source and it uses LM358 in a general voltage follower configuration. To handle large currents we use four 0.1Ω 20W resistors as "load resistor", and those load resistors are drive through pair of 55N06 N-channel MOSFET transistors.

Final view of adjustable constant current source prototype.

The power supply unit of this project is built around 9V × 2 (2A) step-down transformer and it is designed to get regulated 12V DC voltage. In our design, this 12V power source is used to drive LM358 Op-Amp and 12V cooling fan.

In our PCB design, we did not include high current paths into PCB track layout. We connect all of those connections using point-to-point wiring. Large heatsink is recommended for both 0.1Ω load resistors and for 55N06 MOSFET transistors. In our prototype design, we use 250mm × 72mm × 50mm heatsink to mount all of those resistors and transistors. To transfer heat we also attach standard 80mm cooling fan into our enclosure.

The schematics, PCB designs and wiring diagrams related to this project are available to download at google drive.

Comments

AnuraS said…

Hello Dilshan,

I have build a electronic load based on your design, but with following changes.

1- MOSFET is IRF250
2- Used 50K 10 turn volume control to adjust the load.
3- Although the device is powered using 12V, reduced the supply voltage to 9V using 7809 regulator for the OP-Amp and to the Volume Control.
4 - Current sensing resistor is 1 ohm 5W.
5 - Used now commonly available Chinese DC Volt and amp meter to display the Load voltage and current.

It works fine, but still not tested above 2.5 Amp as I donot have a power supply capable of supplying more than 2.5 amp.

Thanks for your design which inspired me to build a similar unit.

Kind Regards
Anura Senarathna

April 26, 2021 at 10:30 PM

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