The operation of a bridge voltage converter circuit with series resonant (also known as variable frequency resonant) circuit (Figure 1), the method used in the circuit analysis can be used to calculate other types of resonant converters. They share a common characteristic - utilizing the resonant properties of LC circuits can achieve nearly sinusoidal transients, and the analysis of the circuit can be almost simplified to the calculation of serial or parallel RLC circuits.
Figure 1 shows a bridge resonant voltage converter with a series resonant circuit.
The load with a series resonant LC circuit is periodically connected to the VCC input power supply through a semiconductor switch. During the open state interval of the transistor, a resonance process of energy storage occurs in capacitor C, and some energy is transferred to the load. In the closed state interval of the transistor, the energy stored in the capacitor is transmitted to the load through the return diode and partially returned to the power supply. The regulation of output voltage is achieved by changing the delay angle of the transistor. The loss of the transistor during the turn off period is equal to zero, because the voltage front of the drain only begins after the drain current flows through zero. The conduction loss depends on the conduction delay angle of the transistor. As the load increases, the delay angle decreases and the switching transistor appears at lower current values. This provides less power loss.
The mode of continuous or intermittent current of the inductor is possible depending on the value of the delay angle connected in the converter.
In the intermittent current mode of the inductor, the transistor will only turn on when the current through the return diode is zero, and the losses including the transistor are also zero.
If the output terminal of the rectifier has sufficient capacity, the converter can operate continuously in the intermittent current mode of the inductor. In this case, the so-called output voltage regulation is used. Relay operation mode.
In the intermittent current mode of the inductor, the time dependence of the current passing through the series resonant circuit is shown in Figure 2, where Tp is the natural oscillation period of the circuit, Tpr is the transition period, and Tn is the pause time.
