The PFC circuit is divided into three modes according to the operation of the input current: CCM current continuous type, DCM current discontinuity and the TCM criticality between the two.
The L6563 is designed with a 350WPFC pre-converter circuit with a fixed output voltage (V0=400V). To make the output voltage constant over a wide range of inputs from 88 to 264V, pin 6 (TB0) of the L6563 in the circuit is left floating. The function of diode D1 is to provide a path for the charge output capacitor C9 at system startup to ensure that the energy storage in inductor L1 is zero when the MOSFET (M1A and M1B) is first turned on. L1 uses E42 & TImes; 21 & TImes; 15 cores (B2 material), with 20 & TImes;! The 0.2 mm stranded wire is wound 58 turns, the air gap on the center column is 1.9 mm, and the inductance value is 550 μH.
The L6563 is the most advanced TM-PFC controller available. In addition to the basic characteristics of ordinary TM-PFC controllers, the control IC also provides THD optimization circuit, tracking boost function, voltage feedforward (1/V2) function, remote on/off control, and overvoltage protection. And feedback fail-safe and other functions, and can provide an interface for the cascaded DC-DC converter.
If the output voltage suddenly has a
The abrupt change in the INV pin is maintained at 2.5V through the feedback error amplifier, and the network connected between the INV pin and the COMP pin provides a long time constant. At this time, the current flowing through R2 is still equal to 2.5/R2, but the current flowing through R1 becomes
The differential current will flow into the compensation network and the error amplifier (pin COMP). This current is monitored inside the IC and as long as it reaches 18uA, the output voltage of the op amp is forced to decrease, thus reducing the energy drawn from the input. If this current exceeds 20uA, the OVP will be triggered and the external power transistor will be turned off until the current drops below approximately 5uA. However, if the overvoltage persists (such as the load is not connected at all), the error amplifier output will eventually become completely low, thus triggering an internal comparator (static OVP), which will keep the external power switch off until the output voltage drops to the specified value. The output voltage change that will trigger the OVP function is:
An important advantage of this technique is that the overvoltage level can be set independently of the specified output voltage: the latter depends on the ratio of R1 to R2, the former relying only on the value of R1. Another advantage is accuracy: the detection current has a tolerance of 15%, which means an accuracy of 15%.
When any of the OVPs is activated, the quiescent current will be reduced to minimize the discharge current of the Vcc capacitor.
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