Application of high-performance non-isolated constant current drive chip

　　Working principle: The circuit is shown in Figure 1. The AC voltage of 176~265V is rectified by the fuse, the crystal rectifier diode, and the capacitor C1 is filtered to provide the DC voltage to the VCC ④ pin of the LY1126 high-performance non-isolated constant current drive chip. At the same time, the capacitor C2 is charged. When the pin voltage reaches the chip turn-on threshold, the internal control circuit of the chip starts to work. The LY1126 high-performance non-isolated constant current drive chip has a built-in voltage regulator to clamp the voltage of pin ④. When the chip is working normally, the VCC current required is very low, so there is no need for auxiliary winding power supply. CS pin ⑧ is connected to the internal peak current comparison The input terminal of the device is compared with the internal threshold voltage. When the voltage of CS reaches the internal control threshold, the power tube is turned off. R4 and R5 adopt high-precision resistors to ensure reliable operation.

　　The energy storage inductor and the chip work in the critical mode of the inductor current. When the internal power tube is turned on, the current flowing through the energy storage inductor rises from zero. When the LED is short-circuited, the chip works at low frequency, and the CS turn-off threshold is reduced, so the power The power consumption is very low. When an abnormal situation occurs, such as the short circuit of the CS sampling resistor or the saturation of the transformer, the internal fast control circuit of the chip will trigger the protection logic control chip to immediately stop working and enter the protection state. The VCC voltage begins to drop. When VCC reaches the undervoltage protection threshold, the chip will restart, and the chip will continuously control the load status. If the fault is removed, the chip will restart to work. The LY1126 high-performance non-isolated constant current driver chip has a thermal regulation function. When the drive power adapter is overheated, the output current is gradually reduced, thereby controlling the output power and temperature rise, so that the temperature protection of the standard power adapter is at the set value to improve the circuit. Reliable and stable. The crystal diode, L inductance coil, resistor R6, and capacitor C3 form the DC voltage of the filter stabilization circuit to provide 18 LED patch light-emitting diodes for lighting.

　　Selection of 5V1A power adapter components and precautions: use 1N4007 for crystal diodes D1～D4, use electrolytic capacitors of CD11G for capacitors C1 and C3, use capacitors of CD110 for C2, use 0.5W±1% for resistors R1, and use 1/ for R2 and R3. The error of 8W is ±1%, and the resistance of R4, R5, R6 is 1/8W of error of ±1%. Why choose high-precision resistors? First of all, the entire circuit works in a high voltage and current state, and the output DC voltage must ensure a stable constant current and constant voltage. When the LED is short-circuited, overheated, or overheated, the inside of the chip can be controlled to turn off, thereby protecting the safety of the LED light-emitting diode . D5 uses fast recovery diodes, ordinary crystal diodes can not be used, this point should be noted that the inductor coil L selects finished products, and the patch light-emitting diodes use 0.5W.

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