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when the change makes the LED's rated power is less than 9W, the long-term work will affect the use of LED life and color. Again, the power of compatibility issues. The constant power control mode are pre-configured output power, when the received light power and pre-set does not match the power, LED lights do not work. When the connection of the lamp power is less than the default power,[link widoczny dla zalogowanych], or even burned LED lights.
There is a problem of no-load loss, due to constant power control scheme of the output power only with the input voltage and the size of the conduction angle, and then when there is no LED lights,[link widoczny dla zalogowanych], still have the corresponding power output, making the no-load loss change very large. Finally, dimmer compatibility issues. Because LED is used to replace incandescent lamps before, so also must be dimming LED SCR dimming.
Incandescent lamp is a pure resistive load, the conduction of the SCR will not be affected,[link widoczny dla zalogowanych], but the LED driver circuit formed by the switching power supply, it is not a pure load, so the SCR would have been affected. SCR chopper can easily lead to distortion of the waveform, in particular, is difficult to maintain a good on-state.
Therefore, the drive will be added on the general stability of silicon circuits. Constant power control method because of its pure hardware implementation, even if the addition of SCR stable circuit, dimmer adaptability is limited. The constant power control has its simple structure and low cost advantages, and disadvantages some short period of time may not be reflected, many semiconductor companies have adopted this method.
However, if the MCU control with constant current program, these problems can be a good solution. 3 MCU-based control program Secom Telecom constant current proposed solution based on MCU control of the overall block diagram of constant current as shown in Figure 3.1. Program consists of two components, the first level is FLYBACK, closed loop control to output a stable power supply voltage to the second level, second level uses MCU control, constant current control circuit to form a BUCK. MCU to complete the functions of which include;
1: SCR conduction angle according to the size, corresponding dimming signal. 2: According to the distortion of the shape of silicon cut Bohou Bo decision on whether to change the dimming signal. 3: Detection LED current feedback, give the corresponding duty cycle, stability,[link widoczny dla zalogowanych], the current flowing through the LED, constant current control to achieve. Figure 3.1 MCU controlled constant current programs based on the overall block diagram of the 3.1 theoretical basis for the constant current control circuit topology of the circuit for the BUCK.