Practical circuit diagram of an LED lamp cup

The figure below is a practical circuit diagram of an LED lamp cup. The lamp is powered by a 220V power supply. The 220V AC power is stepped down by the C1 step-down capacitor, then rectified by the full bridge, filtered by C2, and then supplied to 38 LEDs in series through the current limiting resistor R3. The LED provides constant current power. The rated current of LED is 20mA, but when we make energy-saving lamps, we have to consider the impact of many factors on LEDs, including light decay and heat. When we make this kind of lamp, because the installation density of LEDs is relatively high, Heat is not easy to dissipate. The temperature of LED has a great impact on light decay and life. If the heat dissipation is not good, light decay will easily occur because the characteristic of LED is that the current will increase as the temperature increases, so it is generally used when doing high-power lighting. The issue of heat dissipation is the most important and will affect the stability of the LED. Low power generally adopts self-heating method, so the current should not be too large during circuit design. In the figure, R1 is the protection resistor, R2 is the discharge resistor of capacitor C1, R3 is the current limiting resistor to prevent the LED current from increasing due to voltage increase and temperature increase, and C2 is the filter capacitor. In fact, the filter circuit is not needed in the LED circuit. C2 is used to prevent damage to the LED due to the inrush current when the light is turned on. There will be a large charging current due to the presence of C1 at the moment the light is turned on. This current flowing through the LED will cause damage to the LED. With the intervention of C2 , the charging current when turning on the light is completely absorbed by C2, which provides anti-shock protection when turning on the light. This circuit is the most practical circuit for low-power lamp cups. It occupies a small size and can be easily installed in a lamp cup with a small space. It is now widely used in lamp cup products. Advantages: constant current source, low power consumption, small size, economical and practical. However, when designing, the step-down capacitor should use polyester capacitors or CBB capacitors with a voltage resistance of more than 400V, and the filter capacitor should use a voltage resistance of more than 250V. This circuit is suitable for driving 20-40 20mA LEDs.