Resonant converter control strategy with analog and digital circuits

 

The resonant converter adjusts the output by changing the switching frequency. In traditional converters, the output voltage is first compared with a fixed reference voltage through an error amplifier. The output of the error amplifier determines the frequency of the output waveform of the voltage-controlled oscillator (VCO). The VCO controller can be implemented with a combination of digital-analog integrated circuits or a microprocessor. Figure 5.26 shows a push-pull resonant converter VCO controller implemented by a digital-analog circuit. It includes a CD4046 digital phase-locked loop, a CD4013 D flip-flop, a resettable monostable multivibrator CD4528, a 16-bit buffer CD4050 and two AND gates CD4081. CD4046 generates a switching pulse signal vy (t) with a frequency change according to the error voltage vx (t) output by the error amplifier, as shown in Figure 5.27. These pulse signals are connected to the input of CD4013 D-FF and CD4528. CD4013 D-FF generates two anti-phase signals Q and Q (needed to drive the push-pull converter). By adjusting the 5kΩ potentiometer connected to the 2nd foot of CD4528, the pulse width is controlled by CD4528 and CD4011. The CD4050 provides the driving capability to the gate drive circuit, while the fast switching of the power MOSFET is usually realized by the totem pole structure.