How to distinguish LED switching power supply is constant current and constant voltage

LED Switching power supply is generally divided into constant voltage output and constant current output, the former output voltage is constant, the latter output current is constant, so use a multimeter to measure their output voltage, you can know whether constant voltage output or constant current output.

The figure above is a constant-current drive circuit composed of PT4115 constant-current drive IC. The LED beads to be driven are connected to the Out end (i.e. between a and b). Normal work, no matter LED lamp bead Out side by one or three LED lamp bead, is a constant current through the lamp bead, even if the supply voltage within a certain range of change, is still a constant current through the lamp bead, but the output voltage of the LED driver circuit will change with the number of LED lamp bead, assuming that drive a white LED lamp bead, the voltage of the Out about 3 v at the moment; If three series of white LED beads are driven, the voltage at the Out end can reach 9V. If the Out end is empty (that is, no LED beads are connected between a and b), then the output voltage of the Out end can be close to the supply voltage of PT4115.

The figure above shows the LED constant voltage drive circuit. The output voltage of this drive circuit is constant Vout. If Vout is assumed to be 12V, the output voltage will be 12V regardless of the number of LED beads connected to the output end, and will not change with the number of beads. Therefore, in order to judge whether the LED Switching Power Supply is a constant voltage output or a constant current output, we only need to use a multimeter to measure the output voltage of the driving Power Supply when there is no load and when there is a lamp bead connected. According to the change of the voltage, we can distinguish whether the driving power supply is a constant voltage output or a constant current output.

Best Regrds,

Ada Zheng