How to use a single chip microcomputer to make a constant current source

This can be done with the 3-terminal chips of the 78xx series. The peripheral circuit is very simple, and there is no need to use a single-chip microcomputer. If you make a constant current source with adjustable current, you can consider single-chip microcomputer +78xx (such as ).

The constant current source can be done with several transistors or CMOS tubes, what do you want to do here?

You can use the FET to read the output of the hidden blue high current, as for PWM, the ordinary Zaipai 51 single-chip microcomputer can also be done, such as 89 C51, if you don't understand, you can ask me to help you get it.

The main ideas are:

1. The single-chip microcomputer controls the opening and closing of the switch tube (if it is a small current < 20mA, it can also be the on-on size of the single-chip microcomputer to control the triode, and the transistor works in the amplified state instead of the saturation switch state).

2. The size of the sampling current of the single-chip microcomputer, which is usually realized by milli-beating resistor, with milli-beating resistor (10MR is better) more, plus comparator to form feedback, of course, you can also use milli-beating resistance plus AD converter to form feedback, but the speed of feedback is far less than that of the comparator to form feedback.

3. According to the size of the feedback current, adjust the opening and closing of the switch tube specifically, you have to have a circuit, if you just use a single-chip microcomputer, just to do a constant current charging circuit, it is recommended that you use milliohm resistance plus LM339 to do, such a constant current is simple to achieve, and the main thing is that the accuracy and speed of current control are relatively high.

It should be understood in this way, if a single-chip microcomputer I O port has a current sink load capacity of 20mA, that is, this I O port can input 0-20mA current, it can be seen that the current is determined by the load, for example: drive the red LED light-emitting tube; When the LED is connected in series with the 220 resistor to the I-O port, the I-O port will absorb about 16mA current to light up the LED, and when the LED is connected in series with the 470 resistor to the I-O port, the I-O port will absorb the current to light up the LED.

No, it can be regarded as a constant voltage source with an upper limit of output load, the output high level of the general single-chip microcomputer is VCC, and the low level is close to 0V, his current is directly related to its load, and cannot be regarded as a constant current source.

It should be related to the outside world.

The parallel voltage regulator circuit is used to turn the constant current source into the constant voltage power supply required by the single-chip microcomputer.

What the single-chip microcomputer needs is a constant voltage power supply, why should it be given a constant current source?

The constant current source is only used in LED lighting, if it is only an indicator light, it is not necessary, and it can be lit directly.

It feels a bit of a problem! But theoretically, yes! It's up to reality!

It's OK to connect a pull-up resistor, of course, the power supply is a must.

It's the first time you've heard of this statement, can you elaborate on that?

I've done it, it's already part of the product, look at the picture.

DC current sources require op amps and power tubes. If you use a single-chip microcomputer, you can get the voltage signal by adding an integrator or RC filter to the PWM output, and then connect the op amp and the power tube into a V i conversion circuit.

You do this as if you move a computer to make a calculator, not only the cost, but also the big and the little use, the discrimination against the single-chip microcomputer, I have also thought about it. Later it turned out to be wasteful, so....

Constant voltage: A power supply, when the load resistance changes within a certain range, can keep the terminal voltage of the load resistance unchanged, which is called a constant voltage power supply.

Constant current: A power supply, when the load resistance changes within a certain range, can keep the current through the load resistance unchanged, called a constant current power supply.

Therefore, it is impossible for any power supply to be both a constant voltage power supply and a constant current power supply at the same time.

However, through the switching of the control circuit, the constant voltage power supply becomes a constant current power supply, and vice versa.

Constant voltage and constant current, in fact, is just a misunderstanding caused by the description of the power supply function, because current = voltage impedance.

As a power supply to control the voltage, can not change the load characteristics, so constant voltage and constant current actually refers to the limited power, the current will not be boosted, for example, a 3V 1A power supply, assuming a 1 ohm resistor, the output voltage will be limited to 1V, because the current has reached 1A, so the output is limited.

It can be made in the following parts:

1. The single-chip microcomputer is responsible for display. Sampling, analog-to-digital conversion, processing, display 2, use 317 adjustable voltage regulator circuit as adjustable power supply.

3. Make an adjustable constant current source.

It is also possible to make a constant current circuit and a voltage stabilizing circuit together.

At the same time, constant pressure and constant current are not possible. But a single-chip microcomputer can control a switch tube, or constant voltage, or constant current is possible.