Abstract: This paper introduces the practical application circuit design program of PWM-SG1524 in high-voltage switching power supplies. Keywords: high-voltage power supply; SG1524; application circuit; design With the continuous development and maturity of power supply technology, switching power supplies, as small, lightweight, high-frequency, and high-efficiency power conversion devices, are widely used in various fields. Radar displays, as the "eyes" of radar systems, require high reliability, and the reliability of their power supplies is even more critical. The following are the technical requirements of a certain type of radar display for high voltage power supply: (1) Input voltage: 400 Hz/220 V±10% (2) Output voltage: +4500 V -1600 V (3) Output current: +4500 V/1 mA -1600 V/1 mA (4) Load stability: ≤10-3 (5) Voltage stability: ≤5×10-3 (6) Output voltage ripple: ≤1×10-3 (7) MTBF: ≥5000 h (8) Delay time: ≥20 s 1 Overview In order to meet the above requirements, this converter adopts the dual-ended output pulse width modulator SG1524, which has more functions, is more flexible in use, and is cheaper. The entire circuit consists of several parts as shown in Figure 1. The input voltage is rectified and filtered by a full-bridge rectifier and then sent to the VICOR module (VI-J63CZ) for DC/DC conversion. The output is a DC voltage of 24 V, which is then regulated to 15 V by a 78LM15 and directly supplies power to the SG1524. The output pulse of pin 11 of the SG1524 is amplified by V11 and isolated by T1, then amplified by V21, stepped up by the pulse transformer, and then rectified and filtered to output a high voltage. 2 Circuit Design (1) Delay Circuit Since the filament of the oscilloscope tube of the monitor needs a warm-up time of 20 s, a delay circuit needs to be set to delay the application of high voltage to the anode of the oscilloscope tube. Since the SG1524 has a completely independent control shutdown circuit, the output of the entire pulse width modulator can be controlled by controlling the potential of its pin 10. As shown in Figure 2. Power on → R32, R33 divide the voltage → C2 is charged through R2 → V5 conducts → the potential of pin 10 of SG1524 decreases → SG1524 works and outputs pulses. (2) Oscillator frequency The oscillator frequency fosc of SG1524 is determined by external components R6 and R4, i.e., fosc = 1/R6C4, where the unit of R6 is Ω, the unit of C4 is μF, the charging current of capacitor C4 is I = 3.6 V/RT, the capacitance of capacitor C4 directly affects the output pulse width of the oscillator, so C4 cannot be too small. If the output pulse width of the oscillator is less than 0.5μs, it cannot be guaranteed that each pulse can trigger the flip. In order to ensure the reliable operation of the trigger, the capacitance of C4 is generally between 0.001μF and 0.1. (3) Compensation network Pin 9 is the compensation terminal. A PC compensation network is connected here to introduce a zero point to the circuit to cancel the pole in the circuit output filter, thereby eliminating the parasitic oscillation of the circuit. The RC compensation network here is composed of a 56 kΩ potentiometer and a 0.001 μF capacitor. (4) The reference power supply Vref (5 V) of the feedback SG1524 is divided by resistors R7 and R5. 1/2 Vref = 25 V is applied to the non-inverting input terminal 2 of the error amplifier EA. The high voltage is filtered by R30 and R31 and sent to the field effect transistor V17. After being amplified by the voltage of V17, it is output through the emitter follower and sent to terminal 1 of SG1524. Assuming that the output voltage decreases due to the decrease of the power supply voltage or the decrease of the load resistance, the voltage at the inverting input terminal 1 of the error amplifier in SG1524 will decrease, the output voltage of the error amplifier will increase, thereby increasing the voltage applied to the inverting input terminal of the pulse width modulation comparator, increasing the conduction time of the output transistor, and thus increasing the conduction time of the power transistor, increasing the duty cycle Q, so that the output voltage Vo can return to the original stable value. The feedback circuit is shown in Figure 3. (5) The drive and rectification are isolated by T1. The pulse width of the input V21 is changed by adjusting the resistor R13 to achieve the purpose of voltage regulation. The accelerating capacitor C5 and the resistor R13 are determined according to the steady-state drive current of V21. The drive and rectification circuit is shown in Figure 4. The energy feedback coil (demagnetizing coil) feeds back the excess energy of the transformer to the power supply through the rectifier diode V24 (2CK29) to improve efficiency. Since the turn-off process of transistor V21 is the time when the switching transistor is most vulnerable to damage, the measure taken is to reduce the collector current as the collector voltage rises when the transistor is turned off. When the RC buffer is connected to the CE terminals of the transistor in Figure 4, the collector current of the transistor is reduced when the transistor is turned off. Its working principle is that when the transistor is turned off, the capacitor C10 is charged to Vc-1.4 through the diode V22, so the collector current is shunted and the collector current can be reduced more quickly. When transistor V21 is turned on, C10 discharges through resistor R23 and transistor V21. The parameters can be selected using empirical formulas: Where: Ic is the maximum collector current (A); Vce is the maximum collector-emitter voltage (V); Tf is the maximum collector voltage rise time (μs); Tr is the maximum collector current fall time (μs); Note: The calculated resistance value must limit the discharge current Idis (Idis = Ic × 1/4). (6) Overcurrent and overvoltage protection When the load is overcurrent, the primary winding of the pulse transformer is also overcurrent through the secondary coupling. The voltage drop across R24 increases, the optocoupler PHT turns on, the voltage at pin 10 of SG1524 is raised, SG1524 turns off, and there is no output voltage, thus protecting the power supply. When the load is overvoltage, the voltage at pin 1 of SG1524 is fed back through the LED V6, raising the voltage at pin 10 of SG1524. SG1524 turns off, and there is no output voltage, thus protecting the power supply. 3 Conclusion With the increasing application of this type of power supply, it has been proven that it has high working efficiency and good reliability, fully meeting the design requirements of radar systems for each sub-unit. References [1] Sha Zhanyou. Latest Application Technology of Special Integrated Power Supply [M]. Beijing: People's Posts and Telecommunications Press, 2000. [2] Zhang Zhansong. Principles and Design of Switching Power Supply [M]. Beijing: Electronic Industry Press, 1999. [3] Su Kaicai. Modern Power Electronics Technology [M]. Beijing: National Defense Industry Press, 1995.