L6566B is an extremely versatile current mode master controller IC designed for high performance off-line flyback converters. It is also suitable for single-stage single-switch input current shaping converters (single-stage PFC) for applications that should comply with en61000-3-2 or JeitA-MITI regulations. Support fixed frequency (FF) and quasi resonant (QR) operation. The user can choose either of these options based on the needs of the application. The device has an external programmable oscillator: it defines the switching frequency of the converter in FF mode and the maximum switching frequency allowed in QR mode.
When FF operation is selected, the IC operates like a standard current mode controller, limiting the maximum duty cycle to 70% minutes. The oscillator frequency can be modulated to mitigate EMI emission.
When selecting QR operation, it will be carried out under heavy load, and through the transformer demagnetization induction input triggered MOSFET conduction to achieve. Under certain conditions, zero voltage switching can be realized. The power capacity of the converter increases as the grid voltage increases and is compensated by line voltage feedforward. Under medium and light loads, since the QR operating frequency is equal to the oscillator frequency, a function (valley hopping) is activated to prevent the frequency from rising further and to keep the operation as close to ZVS as possible.
Whether FF or QR operation, the IC goes into controlled burst mode operation under very light loads. Together with the built-in non-dissipative high voltage start circuit and low static current, it helps to keep the power consumption low and meet energy saving recommendations.
The innovative adaptive UVLO helps to minimize the problems associated with self-supplied voltage fluctuations caused by transformer parasitism.
Protection function of the device contains include: unlocked input voltage (power), output OVP (automatic restart or optional lock mode), the level of OCP delay closed, under the condition of overload or short circuit protection system (can choose automatic restart or atresia mode), secondary OCP in transformer saturation or short circuit when the secondary diode. Latch disable input allows OTP to be easily implemented using external NTC, while internal thermal shutdown prevents the IC from overheating.
The unit is complete with programmable soft start, leading edge blanking on current sensing input for higher immunity, ramp compensation (only in FF mode), and shutdown functions for externally controlled burst mode operation or remote on/off control.
All functions
Lock or automatically restart OVP
Reduce EMI programmable frequency modulation
-600/+800 mA Totem pole gate driver with active pull-down function during UVLO
Electricity protection
SO16N encapsulation
One-pulse OCP, overload stop (lock or automatic restart)
Constant power capacity with grid voltage line feedforward
Optional multi-mode operation: fixed frequency or quasi resonant
Advanced light load management
Car 700 V high voltage start
Adaptive UVLO
Transformer saturation detection
Low static current (<3 mA)