Flicker-free LED luminaire drive design - Power Circuit - Circuit Diagram

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Conventional halogen cup lamps use electronic transformers and use AC input. Therefore, the current LED lighting products on the market can be directly replaced with conventional halogen cup lamps by adding rectifier circuits inside. Although the traditional electronic transformer is cheap, the relative quality is not good. Because the electronic transformer is actually controlled by half-bridge rectification, the output varies with the load impedance, so the circuit stability is poor. When there is a problem with the circuit matching, the LED - The MR16 luminaire is prone to flicker or no light.

In the current reference design of the 3-5W LED-MR16 lamp, three 1W LEDs are used in series, and the input voltage is AC 12V±10%. If the LED drive circuit architecture adopts DC buck mode, it can output effectively under normal power supply conditions, but due to the stability of the electronic transformer, the input voltage of the LED drive circuit may be higher or lower than the output voltage, resulting in DC buck. The drive circuit does not work, and the LED current cannot be continuously turned on, which is the main cause of the LED-MR16 lamp flickering.

solution:

• The circuit architecture uses a buck-boost converter

• Wide drive voltage range and input protection

In order to solve the above-mentioned flicker problem, the LED driver circuit architecture uses a buck-boost converter as a better choice. The LED series circuit can be driven with an input voltage higher or lower than the output voltage. The buck-boost conversion circuit can achieve an efficiency of more than 85%, and suppress the change of the input voltage in the discontinuous operation mode to provide excellent line voltage regulation.

The new RT8450 can be specifically designed for driving applications in MR16LED lamps. Its internal circuit design architecture makes it easy to implement a buck-boost circuit, as shown in Figure 1.

Figure 3: Channel 1 is the AC output voltage of the electronic transformer, channel 2 is the rectified and filtered input voltage, channel 3 is the AC input voltage, and channel 4 is the LED output current.

In addition, the RT8450 buck-boost architecture is characterized by the fact that the LED driver circuit is not affected by input voltage variations, and can support the pre-stage circuit to implement a triac TRIAC dimming scheme because this chip can utilize the TRIAC cutoff. After switching to the PWM signal, the RT8450 linear brightness adjustment pin can be controlled to control the brightness and brightness of the overall lighting scheme without flickering.