Homemade LED constant current driver

LED lighting is very popular now because it has the advantages of energy saving and long life. Since LED requires a low-voltage DC power supply, in order to use 220V (or 110V) AC mains to drive LED, a power conversion circuit is required. Common linear power supplies are not suitable for use here due to their large size and low efficiency, but the commonly used switching power supply requires a transformer to be designed. The design and production process is relatively complicated and not suitable for DIY by enthusiasts.

The LED driver power supply circuit introduced below is very simple. And all the components that are easy to buy on the market are used, which is very suitable for enthusiasts to make by themselves. This power supply supports 90V~265V AC mains input. It outputs a constant current of 100mA and can drive 4~5 LED modules in series.

Figure 1 is the schematic diagram of the circuit produced this time. The LNK304 chip with an integrated switch tube is used. The circuit topology is a buck-boost structure. The 90V~265V AC mains is rectified by D4 and filtered by C5 before entering U1. U1 has a reference source inside, which will generate a 1.65V reference voltage between the FB pin and the S pin. This voltage and R12, R2 and R4 jointly determine the output current. The specific calculation formula is:

I=1.65x(R2+R1)／(R2xR4)

According to the values ​​in the figure, the output current is about 100mA.

In the figure, C4 is the chip filter capacitor, C1 filters out the burrs on R4. C2 is the output ripple capacitor. In order to prevent the output voltage from being too high when no LED is connected, D2 and D1 form a voltage limiting circuit. When no load is applied, the output voltage is determined by the voltage regulation value of D1.

The production can be completed on a perforated board. R3 is a fuse resistor. It can also be replaced by a 250W1A fuse. C3 and C10 are electrolytic capacitors, and C4 and C2 are ceramic capacitors. In particular, C2 cannot be replaced by an electrolytic capacitor, otherwise it will heat up seriously. D2 and D5 require ultra-fast recovery diodes with a withstand voltage of more than 500V. The models that can be replaced are HER107, MUR160, etc. L1 uses an I-shaped inductor with a diameter of about 10mm.

The completed circuit is shown in Figure 2 (omitted). After the production is completed, you can connect the light-emitting diode for testing. You can use 4 to 5 power LEDs in series or five groups (4 to 5 in series per group) of ordinary high-brightness LEDs in parallel, with a current of about 20mA per group. Do not directly connect to the 220V mains during the test. To avoid danger. You can adjust the adjustable DC regulated power supply to about 30V and connect it to the input end. If the LED can emit light normally and the current is about 100mA, you can directly connect to the mains. Pay special attention to safety during the connection process, because the entire circuit is not isolated. Touching any part may cause electric shock.

The production is successful, this can be used to make an LED desk lamp. Figure 3 (omitted) shows the actual working picture, lighting up five 1W LEDs.