Design of Virtual Test System for AC/DC and DC/DC Power Supply Modules

The composition and functions of the power module virtual test system are summarized, and the design of the system is briefly introduced, including program-controlled AC source, program-controlled DC source, electronic load, dual-channel test box and system software design. Finally, the characteristics of the system are explained.

Keywords: power module; virtual instrument; measurement; optoelectronic isolator

0 Introduction

In recent years, as the requirements for the diversity and complexity of power supply products have increased, how to scientifically and quickly detect their performance and indicators has become a major problem. The original manual measurement method can no longer meet the requirements of manufacturers and users, and test automation has become the goal pursued by power module testing [1].

With the development of virtual instrument technology and computer testing technology, it is possible to introduce computer virtual testing technology into the traditional power supply testing field. According to the market demand, we have designed a new type of power supply testing instrument, which uses a virtual measurement method based on digital adjustment and computer analysis to replace the original analog measurement method, and realizes accurate and rapid measurement of various performance indicators of power supply products, and can make various data statistics and analysis.

1 System composition and functions

According to the test requirements, the system consists of a computer host, a data acquisition and control card, a programmable AC source, a programmable DC source, a 4-way electronic load, a power supply test box and some auxiliary circuits. The system block diagram is shown in Figure 1.

Figure 1 System Block Diagram

The system can test the output voltage, source effect (voltage regulation), load effect (current regulation), efficiency, ripple of the power module, and can also test whether the module has over-current protection and short-circuit protection functions.

The system can create a power module database, store module data, delete modules, and perform statistics on test data and print test data reports. The system also has a dual-channel test fixture to increase test speed.

2 Design of each part of the system

2.1 Design of programmable AC source

The function of the programmable AC source is to output AC voltage according to the requirements of the power module for the input power supply. The system uses an autotransformer to output the required voltages. The transformer input is AC220V, and each group of outputs uses relay switching to obtain the required voltages. The on and off signals of each relay are controlled by the computer through the I/O port of the control interface board.

Install AC voltage test module and active power test module at the output end of the power supply to test the output voltage and output power of the AC source respectively, convert the collected signal into a low-voltage DC voltage signal, and send it to the computer through the A/D port for display and comparison with the required value. If the signal is larger than the standard value, it means that the voltage or current output by the power supply is too large, and the alarm circuit and protection circuit can be activated to disconnect the input voltage of the program-controlled AC source with a relay, and remind the operator to detect the fault.

2.2 Design of programmable DC source

The function of the programmable DC source is to generate a DC voltage to supply the input end of the DC/DC power module. The system uses a transformer to step down the voltage, and then rectifies and filters to obtain a DC power supply. Then, according to the system requirements, the D/A output port of the computer obtains the required adjusted voltage according to the working range of the power adjustment tube.

The transformer output is divided into 4 levels, and the control signal is adjusted by the D/A port. The circuit samples the output voltage and current, and samples the product of the voltage and current signals, and inputs these signals into the protection circuit respectively. If the signal is greater than the voltage value set by the protection, the system starts the protection circuit, cuts off the power supply, and reminds the user to eliminate the fault in time.

2.3 Design of electronic load

This system uses a power adjustment tube as an electronic load, that is, the control signal output through the D/A port of the computer, after passing through the operational amplifier, adjusts the base voltage of the power tube to simulate the power tube for use as a load.

The voltage and current signals sampled at the output end of the power tube are processed and sent to the computer for processing, and compared with the required parameter values. If there is a deviation, the control signal can be output through the D/A port of the interface board to readjust the working state of the power tube. In addition, the sampled voltage and current signals are sent to the system protection circuit respectively, and the voltage and current signals are processed into success rate signals and sent to the system protection circuit for comparison with the set value. If the signal is too large, the protection circuit is activated, the input circuit and the output circuit are cut off, and the alarm circuit is activated to remind the user. After the fault is eliminated, the reset circuit can be used to reset the protection circuit.

2.4 Design of two-way test box

According to the test requirements, the test box must have two channels connected to the power module under test. The system uses relay switching to test the two channels separately. When channel 1 starts working, channel 2 is disconnected through the relay, and the switch signal indicating that channel 1 is working is sent to the computer, so that the computer tests channel 1. The voltage signal and ripple signal obtained from the test are sent to the system for processing. After the test is completed, channel 1 is disconnected, channel 2 is closed, and the switch signal is sent to the computer, and the computer starts to test the performance indicators of the power module on channel 2.

2.5 System Isolation and Coupling

Since the system requires many A/D and D/A ports on the interface board and they need to be isolated, this solution uses two interface boards, A and B, to complete it.

1) Board A provides 2 D/A ports, 1 of which is used to adjust the programmable DC power supply; provides 16 A/D input ports as input channels for power signals, voltage signals, current signals, and ripple signals; provides 16 I/O output ports for controlling the output of programmable AC sources and other signals; provides 16 I/O input ports for input control of switch signals. The logic level of the I/O port must comply with the TTL level standard.

2) Board B provides 4 mutually isolated D/A outputs, which are provided to 4 electronic loads as adjustment signals. The 4 output signals are isolated from the computer and each signal is isolated from each other by a high-speed optoelectronic isolator. This ensures the isolation effect and achieves the best linearity of the system.

2.6 System Software Design

In virtual instrument test software, LabVIEW is an extremely powerful software development platform. However, LabVIEW is a structured interpreted development platform. Software developed with it cannot be directly run under the Windows operating system [2]. After comprehensive consideration, the software interface design uses the Chinese Visual Basic 6.0 programming language, and the control design uses the controls provided by LabVIEW. The software interface designed in this way is simple, easy to develop, and easy to maintain, which is convenient for data maintenance and management [3]. At the same time, it has the characteristics of fast speed, powerful functions, and simple operation.

After logging into the system, users can complete the following functions:

1) Initialization can input and edit the parameters of various power modules, set standard values, and query, update and delete modules;

2) The module test system can perform automatic or single-step tests on the parameters of the power module as needed, can set the test model and data, test conditions, test items, and test sequence, can select automatic testing or single-step testing, and can set the test standards.

3) Data analysis and statistics: The software can view the test data, analyze product performance and error exceeding the standard, classify the data, and make statistics on the product qualification rate or other data;

4) Data processing and output: The software can convert the generated data, display it graphically, generate reports, and print and preview them;

5) System maintenance: The software can diagnose system failures and give prompts, and can personalize the interface. The system also has user management and help functions.

The main interface of the system software is shown in Figure 2.

Figure 2 Main interface of the system software

3 Characteristics of Virtual Test System

The features of this test system are as follows:

1) Low test cost. The system test circuit is simple and does not require any additional instruments;

2) Wide measurement range can test various performance indicators of power supply products;

3) The test automation level is high, and it can be fully automatic, semi-automatic or single item test;

4) High test accuracy. There is no human error in the entire test;

5) Fast test speed. Proprietary virtual instrument sampling technology ensures test efficiency;

6) High reliability: The system complies with the requirements of electromagnetic compatibility standards and operates reliably;

7) High security The system adopts a variety of security protection measures to ensure the safety of users and modules;

8) Convenient data viewing and automatic saving of statistical data, and graphical information display.

4 Conclusion

This article introduces the function and design of the power module virtual test system. After experiments and tests, the system fully meets the national requirements for power module testing and has been recognized by the trial manufacturers. With the development and improvement of virtual testing technology and the increasing demand for intelligent instruments and equipment in China, the power module virtual test system will inevitably be used more and more in power module manufacturers and users.