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.
Read recommendations:
18W European standard Power Adapter
24W Chinese standard
18W European standard Power Adapter
The working principle of PFC regulated switching power supply.chinese adapter factory
Maintenance Methods for 12V Switching Power Supply