Introduction The VIPer53 is a new generation of highly integrated offline switching integrated circuit, employing STMicroelectronics' patented Vertical Intelligent Power (VlPower) technology. It features high integration and integrates a power MOSFET using a multi-drain mesh (MD-Mesh) process. Target applications include power converters for set-top boxes, DVD players, and VCRs, as well as auxiliary power supplies in televisions, PCs, and travel adapters. The VIPer53 uses a system-on-a-chip (SoC) architecture, integrating the system's control section and power MOSFET within a single package. This new packaging technology meets application requirements that monolithic integrated circuits cannot satisfy, especially for power converters with ever-increasing power demands and increasingly stringent thermal design cost controls. This paper presents a 30W set-top box-specific switching power supply design using the VIPer53, outlining the design method and experimental results. 1. VIPer53 Working Principle The VIPer53 integrates an enhanced current-mode PWM controller and a high-voltage MD-Mesh power MOSFET. The internal structure of the VIPer53 is shown in Figure 1, including all the modules required for the primary side of the switching circuit: the control section includes a high-voltage current source for converter startup, a pulse width modulation driver, and various protection functions such as overvoltage protection, thermal shutdown, cycle-by-cycle current limiting, and load protection. The minimum breakdown voltage of the power MOSFET is 620 V, and the on-state resistance of the RDSFET is 1 Ω at 25%. Pin VDD is the power supply for the control circuit, charging the externally connected capacitor during startup, and includes four threshold voltages: VDDcm is the turn-on voltage, typically 11.5V; VDDoff is the shutdown voltage, typically 8.4V; VDDreg is the voltage start point for primary-side feedback operation, precisely 15V; and VDDovp is the overvoltage protection voltage, typically 18V. Pin SOURCE is the source of the power MOSFET and the circuit reference ground. Pin DRAIN is the drain of the power MOSFET, connected to the primary winding of the high-frequency transformer, and is utilized by the internal high-voltage current source during power-up to charge the external capacitor on pin VDD. The TOVL pin is connected to an external capacitor to generate an overload protection delay. Overload protection occurs when the voltage on the COMP pin exceeds 435V. The OSC pin determines the switching frequency via an externally connected RC network RT-CT. The COMP pin is the input of the current-mode MOSFET and the output of the internal error amplifier, allowing the dynamic characteristics of the SMPS to be set via an external passive network. The usable voltage range is 0.5V to 4.5V. The power MOSFET turns off when the voltage is below 0.5V and overvoltage protection occurs when the voltage is above 4.35V. The delay time for this action is determined by the size of the timing capacitor connected to the TOVL pin. Figure 1 shows the internal structure of the VIPer53. The switching frequency can be set externally via the RC network connected to the OSC pin, up to 300kHz. When the switching power supply is powered on, the internal high-voltage current source located between the drain pin and the VDD pin supplies power to the device and charges an external capacitor connected to VDD. When the VDD voltage reaches the voltage threshold VDDon, the internal high-voltage current source turns off, the device begins normal operation, and the high-frequency transformer auxiliary winding continues to supply power to the VIPer53 device. The VIPer53's feedback control system is current-controlled, implemented via pin COMP. This control compares the current flowing through the power MOSFET and flyback transformer with a feedback signal generated by the output voltage of the regulating circuit; the comparison result determines the MOSFET's on-time. The advantages of the VIPer53 are: firstly, it reduces power consumption to near zero under no-load conditions, enabling power supply manufacturers to meet newer and more stringent eco-standards, such as the Energy Star program; secondly, its low on-state resistance RDS(on) significantly improves power conversion efficiency, and it eliminates the need for a heatsink, thus avoiding increased manufacturing costs. Typically, the DIP-8 package outputs 30W, and the Power-SO-10 package outputs 40W, with an operating voltage range of ACR5 to 265V. A key feature of the VIPer53 is the overload delay via pin TOVL. If the COMP pin voltage exceeds 4.35V, overload protection is activated, the external capacitor connected to the TOVL pin begins charging, and the MOSFET begins continuous switching. During this period, the drain current is limited to 1.6A. If the overload condition remains unchanged, the MOSFET will turn off when the TOVL capacitor voltage reaches the threshold voltage VOVLth. At this time, the VDD voltage drops, and when it reaches the VDDoff threshold voltage, the internal high-voltage current source turns on, and a new startup cycle begins. If the overload or short-circuit condition persists, the VIPer53 will enter an endless restart sequence. The charging time of the external capacitor on the TFOVL pin is a delay time, which must be greater than the startup time tss of the switching power supply because the auxiliary winding cannot provide sufficient power to the system during this time. 2. Set-top Box Power Supply Requirements In all functional modules of a digital set-top box, from the receiver, 32-bit microprocessor, digital circuits with different biases to peripheral devices and input/output circuits, each has specific power supply voltage requirements. Digital set-top boxes use digital signal processors (DSIs) and microprocessors (MPUs) and support embedded operating systems to meet the high-speed computing and low-power requirements of today's embedded audio, video, and communication applications. To fully utilize dynamic power management capabilities, some processors integrate an on-chip switching regulator. This regulator can generate a settable core operating voltage of 0.7–1.2 V using an external power supply voltage of 2.25–3.6 V, thus saving on external power supply components. In set-top box power supplies, in addition to +3V and +5V outputs powering the control chipsets such as digital signal processors and microprocessors, +12V, +24V, and +30V outputs are also required. For example, in new-generation set-top boxes, many peripherals such as hard drives and DVDs require +12V power. For set-top box power supplies, due to high output power and numerous output channels, and because linear regulators are inefficient, have a narrow voltage range, poor voltage regulation performance, and are bulky, there is a growing trend towards using mature switching power supplies. Design of a 30W Set-Top Box Switching Power Supply High-Frequency Transformer The technical specifications of a 5-output set-top box power supply are as follows: 1) Output 3.3V/2A; 2) Output 5.3V/1A; 3) Output 12V/100mA; 4) Output 24V/500mA; 5) Output 30V/50mA; 6) Total power output close to 30W. The high-frequency transformer for the set-top box is designed using the general design method for flyback switching power supplies or the dedicated VIPERSCOFT software. The auxiliary winding provides a 15V operating voltage. Since the error amplifier connected to pin VDD is set to 15V, the number of turns in the secondary winding must be determined by the turns ratio of the secondary winding to the auxiliary winding. First, the turns ratio of the primary winding and the secondary winding with the lowest output voltage, Np/NoL, is selected. Then, the voltage value per turn, V1, is calculated: V1 = (VOL + VD)/NoL, where VD is the forward voltage drop of the diode, and the PN junction diode is set to 0. 7V, Schottky diode is 0.4V. A set of high-frequency transformer parameters was finally established, as shown in Figure 2. Figure 2: Technical requirements for high-frequency transformer winding parameters: EE28 vertical core, core material is PC40. The transformer is oil-immersed; the insulation withstand voltage between each winding is not less than AC 2500V for 1 minute; the insulation voltage between each layer is not less than AC 1500V for 1 minute. The insulation voltage between all coils and the casing is not less than AC 2500V for 1 minute. 4. Circuit design of the set-top box switching power supply: VIPer53, peripheral devices, and the entire transformer input and output circuits and parameters are shown in Figure 3. The auxiliary winding directly provides a stable 15V voltage to VIPer53 through diode D1D. The overload delay circuit consists of R2D and C3D, and the device parameters ensure that the delay time is greater than the startup time of the switching power supply. The enhanced current mode control peripheral circuit consists of R3D, C4D, and C5D, which can set the dynamic characteristics of the switching power supply. Figure 3 shows the circuit principle of the set-top box switching power supply. The input EMI filter uses a filter network composed of a common-mode coil, common-mode and differential-mode capacitors, which can simultaneously filter out differential-mode and common-mode interference, as shown in Figure 3. An NTC resistor is added to the power input terminal to limit the inrush current amplitude when the system is powered on. The primary winding of the high-frequency transformer uses a standard RCD clamping circuit, or a TRANSIL circuit can be used to reduce standby power loss. Capacitors C1E and C2F are used to reduce common-mode interference generated by the high-frequency transformer. The switching frequency is 100kHz, set by resistors R1D and C1D-n. In standby and light load conditions, the built-in burst mode circuit can skip some switching cycles, reducing the equivalent switching frequency. Depending on the voltage of pin COMP, VIPer53 provides a dual blanking time, i.e., 150ns and 400ns for 0.5V and 1V respectively. In this design, the maximum output power and output current is +3V. The system provides 3V, +5V, and +24V outputs. Since 24V is the selected output, and the +3.3V and +5V outputs have similar power, the main voltage feedback uses +3.3V and 5V outputs. Feedback voltage is provided through an adjustable precision parallel regulator TL431 and an optocoupler. The voltage at the optocoupler's collector determines the peak drain current of the BIPer53. The feedback comparator circuit is connected across the cathode and reference pin of the TL431. C6D and R5D form the frequency compensation network for the TL431. R7D, R8D, and R9D are proportional feedback resistors, ensuring that the +3.3V and +5V outputs are fed back proportionally, achieving a load regulation rate of ±5% for both outputs. The remaining outputs are determined by the turns ratio of the high-frequency transformer. Given the relatively high power of the +3.3V, +5V, and +24V outputs, a downstream LC filter is added to reduce ripple voltage. 5. Experimental Results and Analysis The set-top box switching power supply was fabricated and tested in the laboratory. The circuit board size is 74mm × 186mm. The measured maximum duty cycle was 45% with a minimum input AC voltage of 85V and 28% with a rated input AC voltage of 220V. The quasi-peak and average value curves of continuous conducted interference at the power input terminal both conform to EN55022 CLASSB standard. Under 220V AC power supply, the auxiliary winding provides 15V under both light and full load conditions, with a maximum operating current of 20mA. Under light load, the average output values ​​for +3.3V, +5V, +12V, +24V, and +30V are 3.48V, 5.52V, 14.0V, 25.0V, and 30.8V, respectively. The maximum peak-to-peak ripple voltage is less than 20mV. Under full load, the output voltages are 3.20V, 5.20V, 12.1V, 23.1V, and 30.0V, with maximum peak-to-peak ripple voltages of 175mV, 150mV, 250mV, 80mV, and 80mV, respectively. The output voltage waveforms and corresponding ripple voltage waveforms for +3.3V, +5V, and +24V under full load are shown in Figures 4, 5, and 6, respectively. The voltage VCE between the collector D and emitter S of the power MOSFET is shown in Figure 7. It can be seen that the duty cycle is 28%, less than 50%, and the peak VCE is 540V. Furthermore, the peak VCE under no-load conditions is 450V, both less than the MOSFET's breakdown voltage of 620V. 6. Conclusion Based on the analysis of the requirements of set-top boxes for switching power supplies, this paper presents a power supply with 5 outputs, suitable for general AC input, and exhibiting good EMI conduction performance, utilizing the VIPer53 power integrated circuit. Experiments show that the set-top box power supply using the VIPer53 has advantages such as convenient design, high efficiency, small size, and light weight. Furthermore, it has low standby power consumption and requires no additional heat sink, making it an ideal power IC for switching power supplies.