AC/DC flyback (Flyback) controller

AC/DC flyback controllers (Flyback Controller) are used to convert alternating current into stable, isolated DC power supply to the application system. The alternating current must first be rectified to a high voltage DC. The flyback controller works like a liter-buck controller (buck-boost), but uses a separate inductor to form a transformer. The Flyback controller controls the conduction and closing of high voltage switching MOSFET Q1 on the primary side to produce a change in the magnetic field. Based on the principle of electromagnetic mutual inductance, the changing magnetic field causes the second conductor to produce potential difference, and transmits the current, thereby charging the output capacitor. In addition, Transformers also achieve the necessary isolation of safety.

Two output voltages are compared with reference voltages in the resistor circuit. The regulator feedback signal is then returned to the one-side controller through the Optocoupler, which is the basis for adjusting the MOSFET on-time adjustment to ensure the steady output voltage of the two-time side.

The Flyback controller supplies power from the transformer through the auxiliary windings. It is widely used in applications ranging from small charger adapters (Adapter) to around 100W power supplies.

Some applications require low input power when in standby mode, and the switching loss of the Power module must be reduced. Most flyback controllers achieve this type of light load demand by entering special energy-saving modes. Flyback controllers also have some important features, including protection modes, EMI suppression methods, and high-voltage start-up circuitry for fast start-up.

Flyback controllers for lower power applications often use a one-side correction (Primary Side Regulation, PSR) Such controllers do not need to pass through a two-sided optocoupler to provide a return, but to sense the switching voltage of the auxiliary windings, which is derived from the auxiliary switching waveform and the primary-side current to derive two-sided output voltages.

Power supply with power ratings higher than 75W (e.g. open-frame industrial host power supply) must meet power factor requirements, so a PFC boost controller needs to be added to the pre-treatment stage. The controller controls the input current to meet the requirements of power factor and current harmonics.

Many isolated led drivers also use flyback topologies, which use primary-side sensing to control the current of the two-stage windings to provide accurate LED current control and eliminate the need for optocouplers.

AC LED Lighting applications must conform to the specifications for power factor (Power Factor, PF) and AC current harmonics. Therefore, many LED flyback controllers use a special design to achieve good power factor (PF) and low total harmonic output (THDi)

AC/DC flyback (Flyback) controller