1. Introduction In the information age, pagers have become a common communication tool. Currently, the transmitting equipment of pager stations in China is all imported, with an output voltage of 13.8V and a current of 15-20A. Imported power supplies do not include thyristor components, and given the significant fluctuations in China's power grid, this low-cost regulated power supply was designed. This design adds a thyristor phase control device to a series feedback regulation power supply, using the voltage drop across the regulating transistor to control the conduction angle of the thyristor trigger, maintaining a constant voltage drop across the regulating transistor, thus creating a tracking high-power DC regulated power supply. This regulated power supply limits the power consumption of the regulating transistor, achieving high power output. The power supply mainly consists of a single-phase semi-controlled bridge rectifier and filter, a linear regulator, and thyristor phase control components, and includes overcurrent protection, short-circuit protection, overheat protection devices, and a display section. Under a 220V mains voltage fluctuation of ±15%, the output voltage is 13.8V, and the output current can reach 20A. Thanks to the adoption of thyristor phase control technology, the voltage drop across the regulating transistor can be limited to around 3V, with power consumption not exceeding 40W, thus improving power supply efficiency. When the output current exceeds 20A, current limiting protection can reduce the output current. If the output is short-circuited, the short-circuit protection output block signal shuts off the thyristor. The fan starts when the regulating transistor temperature is above 60℃, shuts off when the temperature is below 40℃, and shuts off the thyristor when the temperature is above 80℃. This power supply uses an integrated thyristor trigger, dual operational amplifiers, and a temperature-compensated Zener diode as the reference source, and is equipped with a three-terminal regulator as an auxiliary power supply, achieving high precision. 2. Specific Circuit Implementation The circuit structure block diagram is shown in Figure 1. This circuit selects a unidirectional bridge semi-controlled rectifier circuit, reducing costs. High-power or high-current regulated power supplies generally use L-C filter circuits. However, high-current filter reactors are large, heavy, and expensive; therefore, a large capacitor filter is still used in the design of this regulated power supply. The linear regulator section still adopts the series feedback regulation regulator principle, forming a closed-loop feedback system. It mainly includes: a regulating transistor, a sampling circuit, a reference voltage source, and an error comparator amplifier. Since the power supply outputs a large current of 20A, a parallel configuration is used to reduce the power consumption of the regulating transistor. In this power supply, two high-power transistors are connected in parallel, so that the current flowing through each transistor is about 10A. This way, the power consumption of each transistor is no more than 40W, reducing the power consumption of the regulating transistor. The collector current of the regulating transistor is about 10A, therefore a high-power transistor should be used, with β = 40-50, so the base current should reach 2 × 0.3A, or 600mA. However, the output current of a typical integrated operational amplifier is only in the tens of milliamperes range, so the output of the comparator amplifier circuit cannot directly drive the regulating transistor. Therefore, a driver stage is added between the output of the comparator amplifier circuit and the base of the regulating transistor. Here, a small-power transistor is selected to form a composite transistor. The starting resistor Rc is 2kΩ. The anti-vibration capacitor C is 10μF. In a voltage regulator circuit, the reference source serves as the reference for the entire voltage regulation system, and the final voltage regulation effect depends on the level of the reference source. Therefore, in this power supply, a 2CW234 series silicon Zener diode with temperature compensation characteristics is selected as the reference source, and its stable voltage is chosen to be 6.4V. It is powered by a three-terminal integrated voltage regulator with good characteristics, and a precision metal film resistor R (temperature coefficient approximately ±1×10⁻⁵/℃) is used as the current-limiting resistor. To reduce the impact of noise, the Zener diode is encapsulated in a small oil-filled container, which will significantly improve the noise performance. Voltage sampling is shown in Figure 2. The collector-emitter voltage of the Zener diode is divided by resistors, and the divided emitter voltage is sent to the inverting input of the comparator amplifier through a resistor. A Zener diode is connected in series in the collector voltage sampling circuit, and this diode determines the magnitude of the Zener diode voltage drop. Here, 3.3V is selected. The collector voltage is subtracted from the Zener diode's regulated voltage, and the resulting voltage is divided and sent to the non-inverting input of the comparator amplifier. To ensure sampling accuracy, the collector-emitter sampling resistors should be perfectly symmetrical, and precision metal film resistors of the same model with good temperature characteristics should be selected. The comparator amplifier uses an integrated operational amplifier connected in a negative feedback configuration. Let R1 = R3, R2 = R4; let the voltage divider coefficient n = R2 / (R1 + R2); the integrated operational amplifier output is Uo; the amplification factor is K; the collector voltage of the regulating transistor is UC; the emitter voltage of the regulating transistor is UE; the voltage at point A is UA; the voltage at point B is UB; then: When the voltage drop across the regulating transistor increases, UcE rises, causing Uo to increase, i.e., the control voltage Ub of the trigger increases. Since the integrated trigger KJ785 is a negative type: as the control voltage increases, the conduction angle decreases. Therefore, the trigger pulse shifts backward, and the rectified output decreases. The thyristor rectification performs the first step of voltage regulation, and its output voltage change is determined by the change in the conduction angle. The phase control section changes the thyristor conduction angle based on the change in the voltage drop across the regulating transistor, thereby changing the output voltage of the rectifier filter circuit and maintaining the voltage drop across the regulating transistor at approximately 3V. This regulated power supply uses a KJ785 thyristor phase-shift trigger circuit. As a power supply product, it strives for high device performance, simple circuitry, and ease of implementation while achieving the same functionality. This trigger circuit can output two trigger pulses 180 degrees out of phase, allowing phase shifting within the 0-180 degree range, and can be used to control single-phase, bidirectional thyristors, and transistors. The KJ785 consists of a synchronous detection register circuit, a reference power supply, a sawtooth wave forming circuit, a phase-shift voltage and sawtooth wave comprehensive comparison circuit, and logic control power amplifier components. The sawtooth wave slope is determined by the external resistor at pin 9 and the external capacitor at pin 10. The pulse width is determined by the external capacitor at pin 10; without this capacitor, the pulse width is determined by the internal capacitor, approximately 30μs. The KJ785 only requires a single power supply, and the trigger circuit operates with negative polarity, meaning that as the phase-shift voltage increases, the conduction angle decreases. The synchronous voltage is input from pin 5, which can be directly taken from the mains voltage. The step-down current-limiting resistor is taken as the mains voltage × 10³Ω, or a synchronous transformer can be used for input isolation. Pins 7 and 6 provide control terminals for pulse train and pulse blocking. The functions of each pin are shown in Table 1. Since this regulated power supply is a high-power supply, it contains a transformer, rectifier diodes, thyristors, integrated voltage regulators, etc., which generate significant heat. More importantly, the regulating transistor is a high-power transistor that generates considerable heat. Therefore, this regulated power supply uses a fan for airflow, and the inexpensive and high-performance thermistor AD590 is selected and mounted on the heatsink of the regulating transistor. When the temperature reaches approximately 60℃, the fan is activated to cool it down; when the temperature drops to approximately 40℃, the fan is turned off. When the temperature reaches 85℃, a blocking signal is sent to the thyristor trigger circuit, turning off the thyristor and thus shutting down the circuit to prevent the regulating transistor from overheating and being damaged. The circuit is shown in Figure 3. The external characteristics of the AD590 are as follows: At 0℃, its current is 273μA; for every 1℃ increase in temperature, the current increases by 1μA; for every 1℃ decrease in temperature, the current decreases by 1μA; the operating temperature is -50℃ to +150℃; to avoid frequent or malfunctioning comparator operation, a hysteresis width of 1V is selected. R = 40kΩ is chosen; the integrated operational amplifier is selected and powered by a single +5V supply, which can be obtained by voltage division using a CW78M15. Assuming the comparator reference voltage at 65℃ is EmH, we have: Assuming the comparator reference voltage at 40℃ is EmmL, we have: R1 = 2kΩ; Rf = 10kΩ. Verification: Therefore: when the temperature is 61℃, the fan starts; when it drops to 40℃, the fan stops. When the temperature of the regulating transistor reaches approximately 80℃, the comparator outputs a zero level, blocking the SCR and thus shutting down the circuit. In this regulated power supply, the short-circuit protection function is to determine a short circuit when the output voltage is detected to be below 2V and a delay of 2 seconds is applied. A blocking signal is issued to shut down the thyristor and the circuit, preventing damage to the device. The current-limiting protection reduces the base current of the regulating transistor when the load current exceeds 20A, thus reducing the output current. 3. Conclusion This new type of tracking thyristor DC regulated power supply is low-cost, performs well, and has high accuracy, making it suitable for use in pager transmitters. The output voltage range is 12V to 15V, and the current can reach 20A. A key feature of this power supply is its phase control, which combines the advantages of thyristors and series feedback regulators, overcoming the excessive power consumption of the regulating transistor in traditional series feedback regulation power supplies.