The application of optical coupling in LED power driver chip

Switch power supply of light coupling mainly isolation, provide feedback signal and switch. From high frequency switch power supply circuit in the power of the light coupling transformer secondary voltage, when the output voltage is lower than the voltage regulator tube is to signal light coupling connected, increase the duty ratio, raising the output voltage; Turn off the light coupling conversely reduce the duty ratio, the output voltage is reduced. Denier high-frequency transformer overload or secondary load switch circuit fault, there is no light coupling power supply, optical coupling is controlling the switching circuit can't start up, thus protecting switch tube not be breakdown burned.

light coupling and TL431 usually used together. Here is a led power driver chip ( Switching power supply chip) Part of the circuit. Two sampling resistor in series to 431 r side comparing with internal comparator. Then according to the ratio of signal to control the end 431 k ( Anode pick light coupling the end) Resistance to ground, and then to control the light coupling inside the brightness of the light emitting diode. ( Decoupling internal light is a light emitting diode, while is the light activated triode) Through the luminous intensity. Control the other end of the triode CE side resistance is also changed the led power driver chip ( Switching power supply chip) Current of the foot ( 1 foot: voltage feedback pin, by connecting the light coupling to the ground to adjust control than) 。 According to the size of the current, the led power driver chip ( Switching power supply chip) Will automatically adjust the duty ratio of the output signal to achieve the objective of the voltage regulator.

the above is a high level of integration, high performance PWM chip + MOSFET tube combined the current mode of an off-line switching power supply controller. Applicable to the charger, power adapter, LED driver power supply and other kinds of small power switch power supply. Using DIP8 encapsulation, don't need to add the radiator can be 0 ~ 36 w power ( Add cooling can do more) 。 The circuit has simple structure, low cost. Have perfect protection function, including overvoltage, undervoltage, over temperature, overload and short circuit protection. Fixed function of oscillation frequency and vibrating frequency, can reduce EMI. Standby power is low, jump into the cycle when in standby mode, in line with the 'energy star' and so on standby power consumption standards.