Simple electronic load (economical model)

Electronic constant current load adjusted by potentiometer

Load, as the name suggests, is used to waste electricity.

Constant current means wasting electricity with a constant current, such as 1A or 1.5A.

(Just do it for fun, as long as it works, it’s enough, and it’s simple)

Power supply VMAX: 50V

Current: 4A

• Actual measurement: 60W, 20v, 3A,
• The temperature is 50 degrees, (room temperature is 27C^). I haven’t tested the maximum power, so I can’t just test it out.

Control auxiliary power supply adopts 12V, DC head power supply

12V comes in, mainly used for op amp operation and fan power supply.

Fans and radiators are common

The fan is 5V, but I don’t want it to run at 5V. I want to give it 7V to 10V.

Place the NTC resistor next to the heat sink,

This 3435 thermistor has a negative temperature coefficient. When the temperature increases, the resistance value decreases.

The feedback terminal of the 7805 linear voltage regulator is generally connected to ground, so the result is 5V.

But after connecting the resistor to divide the voltage, the voltage it outputs will have a formula. The specific formula Baidu says is Uref*(1+R1/R7)

This is not the case in my actual testing .

• Anyway, you just need to understand that after the circuit is connected like this, the voltage output by the 7805, the higher the NTC temperature, the greater the output voltage, and the faster the fan rotates.
• Put it close to the heat sink for sensing. You can also use silicone to stick it next to the heat sink.
• It’s okay if you don’t buy it. Just use two identical resistors. The voltage will be around 8V and the fan will spin very fast.

A constant current source or constant current load composed of an operational amplifier. For the principle, please go to my Bilibili article.

Constant current load principle (click to enter)

The operational amplifier is a cheap old man’s LM358, 30 cents each, dual operational amplifiers

One is used as a comparator to work in open loop to control constant current.

One is used as an amplifier to display the current value

The sampling resistor uses a 0.1R metal film resistor, or an alloy resistor can be used.

If a 0.1R sampling resistor is used, then the ratio of R5/R6 is 9, the formula VOUT=U*(1+R5/R6)

In this way, 1A current flows through the sampling resistor. According to European and American laws, the voltage difference between the two ends is 0.1V. We amplify 0.1V 10 times to get 1V. We use a voltmeter to display it.

It is possible to use a voltmeter to display the current. In this way, the accuracy depends on the temperature drift of the sampling resistor, the precision of the operational amplifier, and the accuracy of the proportional resistor.

If there is no such multiple, you can connect a precision adjustable resistor and calibrate the meter to 9 times yourself.

By analogy, with a 10mR sampling resistor, the ratio is 99.

To replace other resistors, note the maximum current allowed to flow through the resistor

This TL431 stabilizes the voltage at 2.5V, and then uses the potentiometer knob to adjust the set current value.

(Of course, you can not use it. You can also use 12V to divide the voltage to generate the voltage for setting the current)

I use it, mainly because I happen to have it on hand. I use 2.5V to divide the voltage to generate it, and it will not jump due to unstable auxiliary power supply voltage.

If you want to realize numerical control, just connect the DAC of the microcontroller to the IN+ of the op amp.

Power MOS tube,

Use whatever you have on hand, and note that the smaller the internal resistance, the better.

I use IRF3205, 55V, 110A, 8mr, the price is 80 cents each

Installation method is like this. Pay attention to placing it flat on the PCB so that the radiator can be close to it, otherwise it will affect the heat dissipation effect.

Overall design:

The radiator and fan are the key. If you don’t have one like me, you have to buy one from Baoshang. It doesn’t have to be exactly the same.

Use this instead, it’s a better buy

Buy a 5V fan with a speed of 9,000 and it costs four yuan.

Overall BOOM:

A pair of red and black crocodile clips, 0.1 yuan, buy from Uxin

DC -005-5.5-2.1, 0.04 yuan, buy on Uxin

L7805, 0.6 yuan, buy from Uxin

Small heat dissipation (for 7805) 0.1 yuan, buy it from Uxin

Radiator 37*37*24 2.5 yuan, buy from Uxin

Fan 4010 4 yuan, search and buy

Silicone thermal adhesive 3 yuan, buy from Uxin

IRF3205, 0.8 yuan, search and buy

NTC (10k) 0.15 yuan, (you don’t have to buy it)

TL431, 3 Yuan, (you don’t have to buy it, it’s Feiganxian) Search and buy 50 pcs for 3 Yuan, free shipping

m3 copper pillar 40MM + screws 1.6 + 1.7 yuan, search and buy

Precision adjustable potentiometer costs 4.1 yuan. You can buy it from Uxin. If it’s too expensive, you can also use the small blue one. It costs 30 cents. Use a screwdriver to slowly twist it.

There are two voltmeters, one measures voltage and the other measures current.

It is best to use a voltmeter that can measure more than 50V. It is best to use an ammeter with a range of about 30V, so that the accuracy is higher.

The estimated total price on the table is 8 yuan.

Total: about 27 yuan

I actually spent 4 yuan on a precision adjustable potentiometer~~~~~