The working principle of the constant current power supply is to sample the output current and feed it back to the regulator tube or op-amp to change the conduction state to achieve a constant ratio of loop voltage to resistance, thus achieving a constant current. Switching power supply is a kind of power supply that uses modern power electronic technology to control the time ratio of switching on and off to maintain a stable output voltage.
The constant voltage and constant current power supply is actually a switching power supply, but it has two control units, constant voltage, and constant current, in two working states(offline uninterruptible power supply). When in the constant voltage state, it works according to the characteristics of the constant voltage power supply. In the current state, it works according to the characteristics of the constant current power supply.
When the load resistance of the constant voltage and constant current power supply is a certain value, the power supply is at the critical point of constant voltage and constant current (that is, when the voltage and current are both at the maximum value at the time). As the load resistance increases, the internal constant voltage of the power supply The control unit starts to work.
At this time, the output voltage remains unchanged, and the current changes with the change of the load resistance; when the load resistance decreases and is less than the critical value, the constant current control unit inside the power supply starts to work, and the output current can be Keep the same, the voltage changes with the change of load resistance.