## Monday, May 1, 2023

we are going to make an adjustable constant current regulator using a mosfet and an op-amp. This regulator will allow us to precisely control the current flowing through our circuit, which is essential for controlling electronics and appliances.

This tutorial on making an adjustable constant current regulator is a great way to learn about electronic circuits and create your own adjustable regulator. By the end of this video, you will be able to build your own adjustable regulator and use it to precisely control the current flowing through your circuits

The value of the current flowing in the load (load represented here by the resistor RC) is defined by the value of the zener voltage of D1, and the value of the resistor Rx. The voltage across the terminals of the zener diode is relatively constant, as long as the current flowing through it does not vary too much. And it is the same for the voltage of the Base-Emitter junction of the transistor Q1. It can therefore be deduced that the voltage across the terminals of resistor Rx is just as constant. And since the resistor Rx is a resistor whose ohmic value does not vary too much in normal times, we can see a relatively constant current in the latter. If the transistor Q1 has a fairly large gain (say greater than 100), the value of the base current can be neglected with respect to the current flowing in the emitter junction. Assuming this, the collector current is substantially equal to the emitter current. And as the collector current is the one circulating in the load, we conclude that the current in the load does not depend on the load, within certain limits of use it is necessary to specify all the same. In the previous example, the current in the load, named Irc, is defined by the following formula:

If we want to simplify the calculation, it is possible to insert a conventional silicon diode of the 1N4148 type in series with the zener diode, so as to compensate for the "loss" of 0.6V from the base-emitter junction of Q1, as shown in the following diagram.

We can therefore use the following approximate formula:

Irc=Vz/Rx

Personally, I find it a bit luxurious to add a diode just to simplify the calculation. Up to you.

In reality, this formula is rather approximate, but it is well suited to get an idea of the real value. That said, if the real value is not exactly equal to the value obtained by calculation (which is not very surprising in electronics), the stability of the current on variation of the load is relatively good. I have used this type of assembly several times, notably for the power supply of several LEDs connected in series (see LED power supply page), and in particular for my 002 LED projector (in which the RC load is connected at the top of the diagram and not at the bottom, but that does not change much).

we are going to make an adjustable constant current regulator using a mosfet and an op-amp. This regulator will allow us to precisely control the current flowing through our circuit, which is essential for controlling electronics and appliances.

This tutorial on making an adjustable constant current regulator is a great way to learn about electronic circuits and create your own adjustable regulator. By the end of this video, you will be able to build your own adjustable regulator and use it to precisely control the current flowing through your circuits

The value of the current flowing in the load (load represented here by the resistor RC) is defined by the value of the zener voltage of D1, and the value of the resistor Rx. The voltage across the terminals of the zener diode is relatively constant, as long as the current flowing through it does not vary too much. And it is the same for the voltage of the Base-Emitter junction of the transistor Q1. It can therefore be deduced that the voltage across the terminals of resistor Rx is just as constant. And since the resistor Rx is a resistor whose ohmic value does not vary too much in normal times, we can see a relatively constant current in the latter. If the transistor Q1 has a fairly large gain (say greater than 100), the value of the base current can be neglected with respect to the current flowing in the emitter junction. Assuming this, the collector current is substantially equal to the emitter current. And as the collector current is the one circulating in the load, we conclude that the current in the load does not depend on the load, within certain limits of use it is necessary to specify all the same. In the previous example, the current in the load, named Irc, is defined by the following formula:

If we want to simplify the calculation, it is possible to insert a conventional silicon diode of the 1N4148 type in series with the zener diode, so as to compensate for the "loss" of 0.6V from the base-emitter junction of Q1, as shown in the following diagram.

We can therefore use the following approximate formula:

Irc=Vz/Rx

Personally, I find it a bit luxurious to add a diode just to simplify the calculation. Up to you.

In reality, this formula is rather approximate, but it is well suited to get an idea of the real value. That said, if the real value is not exactly equal to the value obtained by calculation (which is not very surprising in electronics), the stability of the current on variation of the load is relatively good. I have used this type of assembly several times, notably for the power supply of several LEDs connected in series (see LED power supply page), and in particular for my 002 LED projector (in which the RC load is connected at the top of the diagram and not at the bottom, but that does not change much).