Design of AC/DC power supply module with multiple output DC voltages

1 Introduction

With the continuous development of science and technology, the requirements for the detection of equipment status are getting higher and higher, which requires the test equipment to provide high-precision and accurate testing. To achieve high-precision and accurate testing, the voltage signal in the test equipment must provide an accurate voltage value after passing through the circuit, which places high demands on the accuracy of the power module.

In the development process of a certain test equipment, in order to complete the test task, the equipment requires multiple DC voltage signals and requires the ability to control the output of some voltage signals. Through analysis, it is found that the space provided for the power module of the test equipment is very small, and the three-way DC voltage output is controlled by external high and low levels. The existing power module cannot meet this requirement; in order to solve this problem, a DC power supply module with controllable output voltage is designed to provide ±12 V, +5 V, +9 V and +6 V DC voltage signal output for the test equipment. At the same time, it can realize the output control of ±12 V and +5 V voltage signals according to the voltage of the control signal input terminal, and has over-voltage and under-voltage protection and six-way optocoupler output control functions. The realization of this module provides a stable, reliable and high-precision power supply for the test equipment that requires the above DC voltage signals, meeting the voltage control requirements.

2 Overall design

The system structure diagram of the power module is shown in Figure 1. It can be seen that after the 220 V AC voltage signal is input, it is first filtered by the filter circuit module, and then divided into two paths to realize AC-DC conversion. One path directly passes through the rectifier bridge to obtain a +300 V DC voltage signal, which is converted into ±12 V and +5 V DC voltage signals through DC/DC; the other path is stepped down by a 10:1 transformer and then rectified by a rectifier to obtain a 23 V DC voltage signal, and a DC voltage integrated regulator is used to generate +9 V and +12 V voltages respectively. +9 V is powered by the reference voltage source, and together with the supporting circuit, a corresponding DC voltage signal is generated to serve as a reference signal in the control circuit, and a positive voltage is provided for the indicator light. The control protection circuit is mainly divided into a control circuit and an over-voltage and under-voltage protection circuit. The control circuit is mainly used to realize the output control of the controllable DC voltage, while the over-voltage and under-voltage protection circuit is mainly used to realize over-voltage and under-voltage protection, which plays a role in protecting the three DC/DCs when necessary.

Figure 1 System overall structure diagram

3 Hardware Design

(1) Design objectives.

The module is designed as an AC/DC power supply module with an input voltage of 220 V/50 Hz AC input and an output DC voltage of ±12 V, +5 V, +9 V and +6 V.

(2) Filter and rectifier circuit.

In order to filter out the interference in the circuit, the power input uses a two-stage filter SCHAFFNER FN 410-3/02, the rated current of which is 3 A, the maximum operating voltage is 250 V AC, the frequency is 50/60 Hz, the operating temperature is -25℃~+100℃, and the mean time between failures is 675,000 hours. In this power module, since each voltage regulator module, reference source, and DC voltage output terminal need to be filtered, electrolytic capacitors are mostly used, and the value of electrolytic capacitors ranges from 47 μF/25 V to 1000 μF/16 V.

The choice of rectifier bridge is divided into two types according to the different rectifier circuits. One is to rectify 220 V AC to 300 V DC circuit. The KBPC 108 rectifier bridge is selected with an input voltage of 50~1000 V and an input current of 3 A to achieve high-voltage rectification.

The other is low-voltage rectification. In this circuit, the 220V AC power is first transformed by a 10:1 transformer and then rectified by a rectifier bridge, and the output DC voltage is 23V.

(3) DC/DC circuit design.

In order to obtain stable and reliable ±12 V and +5 V DC voltages, high-reliability DC/DC modules are selected in the DC/DC circuit to achieve low-voltage DC output. On the low-voltage side, 23 V DC voltage is obtained after rectification, and +9 V and +12 V output are achieved by using different integrated voltage regulators. Electrolytic capacitors of 100 μF/25 V and 47 μF/25 V are added to the input and output of each module for filtering. On the high-voltage side, three ±12 V and +5 V DC voltages are generated, and it is required to be able to input high and low levels through the external interface to control the output of these three voltage signals. Therefore, VICOR's VI-J61-IZ, VI-J61-IY and VI-J60-IX power modules are selected to achieve ±12 V and +5 V voltage output. The power input terminals of these three modules are connected to a 300 V DC power supply to obtain high-precision ±12 V and +5 V voltages. To control the output of the DC/DC, you only need to control the Gate In terminals of the three power modules. The schematic diagram of the three DC/DC circuits is shown in Figure 2. In Figure 2, when the control terminal signal is high, VT1, VT2 and VT3 work. At this time, the two terminals of the DC/DC are grounded, the DC/DC does not work, and the ±12V and +5V voltages are not output; when the control terminal signal is low, VT1, VT2 and VT3 do not work. At this time, the DC/DC works normally and the ±12V and +5V voltages are output.

Figure 2 Schematic diagram of three DC/DC circuits.

(4) DC voltage control circuit.

The schematic diagram of the DC voltage control circuit is shown in Figure 3. The circuit mainly consists of two parts: an over-voltage and under-voltage protection circuit and an external voltage control circuit. The over-voltage and under-voltage protection circuit mainly refers to the voltage of the voltage comparator MAX973 jumping after the input voltage is too high (or too low) and a certain proportion of voltage exceeding (lower than) 300 V is generated through the conditioning circuit, thereby changing the output of the control signal, causing the voltage at the Gate In terminal of the DC/DC to jump, and then stopping the DC/DC from working. The external voltage control circuit refers to the voltage at the output terminal of the control signal jumping when the level of the external control signal input terminal changes, thereby changing the voltage at the Gate In terminal of the DC/DC, and stopping (or starting) the DC/DC from working.

When the external control signal input is low, the trigger output in the NAND gate circuit is high, and the counter is cleared. After the counting trigger circuit and the inverter are inverted, the control signal output is high, which further verifies that the three DC-DCs are not working, and the corresponding DC/DC working indicator lights are not on. When the external control signal input is high, the trigger output in the NAND gate circuit is low, and the counter starts counting. After the counting trigger circuit and the inverter are inverted, the control signal output is low, which further verifies that the three DC-DCs are working normally, ±12 V and +5 V voltages are output, and the corresponding DC/DC working indicator lights are on.

Figure 3 Schematic diagram of the DC voltage control circuit.

4 Experimental Results

The multi-channel output DC regulated power supply module has been applied in actual equipment. After adding 220 V/50 Hz AC power to the power supply module, ±12 V, +5 V, +6 V and +9 V output voltages are obtained.

The measured waveforms of the ±12 V and +5 V voltage output terminals are shown in Figure 4. The power module was tested at -55℃~105℃, and it was found that under the same power supply, the measured DC output voltage remained unchanged.

(a) +5 V DC voltage output waveform.

(b) +12 V DC voltage output waveform.

(b) -12 V DC voltage output waveform.

Figure 4: Measured DC voltage output waveform.

5 Conclusion

Practical application shows that the power module meets the design requirements. It not only has the function of multi-channel DC voltage output, but also has the characteristics of stable and reliable output voltage and high precision.