A 75 W Tv Power Supply Operating In Quasi-square Wave Resonant Mode Using Ncp1207 Controller

Quasi−square wave resonant converters, also known as quasi−resonant (QR) converters, allow designing flyback Switch−Mode Power Supplies (SMPS) with reduced Electro−Magnetic Interference (EMI) signature and improved efficiency. Due to the low level of generated noise, QR SMPS are therefore very well suited to applications dealing with RF signals, such as TVs ON Semiconductor NCP1207 is a QR controller that will ease your design of an EMI−friendly TV power supply with only a few additional components, and able to lower its standby power down to 1.0 W. What is Quasi−Resonance, The term quasi−resonance is normally related to the association of a real hard−switching converter and a resonant tank. While the operation in terms of control is similar to that of a standard PWM Controller an additional network is added to shape the variables around the MOSFET: current or voltage. Depending on the operating mode, it becomes possible to either Switch at zero current (ZCS) or zero voltage (ZVS). Compared to a conventional PWM converter, a QR operation offers less switching losses but the RMS current circulating through the MOSFET increases and forces higher conduction losses; with a careful design, efficiency CAN be improved. However, one of the main advantages in favor of the quasi−resonance is the reduced spectrum content either conducted or radiated. True ZVS quasi−resonance means that the voltage present on the Switch looks like a sinusoidal arch. Figure 1 shows how such a signal could look like.
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Simulation Schematic of the TV Power Supply
Simulation Schematic of the TV Power Supply

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