150W40A double-tube constant current electronic load based on LM324

1. The LM324 constant current electronic load is a popular DIY project for beginners, but it often uses 0.22Ω cement resistors for current sampling. A large number of straight plug-ins are used on the board, which is bulky and the heat dissipation design is not reasonable enough. This project has complete thermal design calculations, and the maximum power is calculated within the safe working range of the MOS tube: leaving a margin, the maximum power is 150W. 2. Comparing the resistance of the sampling resistor with the reference voltage after reducing it will easily introduce interference and is not conducive to accurate control of small currents. Therefore, the design of cascading two operational amplifiers per tube is used. The first operational amplifier amplifies the current in phase by more than 20 times. At this time, due to the GBW characteristics of the operational amplifier, a 50k pole is introduced. If the second operational amplifier does not To compensate, the loop will become unstable. Therefore, through calculation and simulation, the second op amp applies Type II compensation of the error amplifier to stabilize the loop.

3. The following is the finished product of the first version. At that time, I wanted to use numbers to provide a reference voltage to intervene in the loop, but this project itself is mainly about simplicity. If digital control is introduced, it is better to use a DAC to directly output the voltage to the gate. Digital loop feedback, and realize constant voltage, constant current, constant resistance and constant power control. Let’s talk about the digital electronic load project later. In addition, the shape of the radiator is not conducive to stacking and is not suitable for use as an instrument. However, second-hand AMD CPU coolers are low-cost, priced around 5 yuan, and are still very suitable for DIY.

The new version of the electronic load will be tested after proofing.