Power supply, detection, and drive.
1. Power supply: The S4225xx series is powered through the vcCc pin. In the application, the vcc pin is connected to the positive pole of the power output through a current limiting resistor.
Since the operating current of the IC is approximately 0.8mA, considering factors such as temperature changes that affect the operating current, a margin must be left in the design. It is recommended that the maximum value of the current limiting resistor of the power supply pin is R2 ( max)=(Vo- 13)/1.5 (KQ), ensure that the IC power supply current is greater than 1.5mA.
The vcc pin of the IC has a built-in clamp circuit, and its maximum clamping current is 5mA, so the minimum value of the current limiting resistor of the power supply pin is R2(min)=(Vo- 13)/5 (KQ).
2. Detection: The detection pin of the chip is clk. In the application, the clk pin is connected to one end of the constant current power supply inductor through the detection resistor R1, as shown in the typical application diagram. The chip determines whether the input switch is closed or open through the clk pin.
When the input switch is closed, the clk pin detects the square wave waveform. When the input switch is disconnected, the square wave detected by the clk pin disappears. In order to filter out noise and avoid false triggering, S4225xx is internally designed with a delay time Td(on) for judging the switch closed state and a delay time Tdloff) for judging the switch open state.
The selection of the detection resistor R1 must ensure that when a negative voltage appears at the other end of the detection resistor, the current flowing through R1 must be less than 2mA.
Related expansion
Main description:
The S4225B series chip is a dedicated chip for switching color temperature. The chip has a built-in 400V switch tube, which simplifies the peripheral circuit structure. This series of chips uses Xinfeiling's patented technology, which can not only simplify the number of peripheral components to the greatest extent, but also ensure logical consistency when multiple power supplies are used at the same time.
In order to expand the application field, the S4225B series can be used in isolated flyback, Buck or Buck-Boost structures, providing convenience in power supply design.