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

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Calculator for audio output transformers

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...