LED drive circuit using low-frequency transformer and resistor current-limiting half-wave or full-wave rectification

The advantages of this circuit are: simple circuit and low cost. The disadvantages are: large size, voltage drive mode, LED brightness will change with changes in supply voltage; unable to provide constant current output; large surge current. The circuit structure of this LED driving power supply is very simple, requiring only a low-frequency transformer , rectifier, filter capacitor, and a variable resistor for adjusting brightness . The number of LEDs in series is mainly determined by the turns ratio of the transformer. Once the turns ratio of the transformer is fixed, it is difficult to change the number of LEDs to obtain the same brightness of 9.