Automated Test Equipment for Power Supplies

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Automated Test Equipment for Power Supplies

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The Challenge

Implementing a reliable and precise test and measurement platform for automated testing of board mounted DC power supplies in a Manufacturing floor with minimum testing time and at a reduced cost.

The Solution

Developing a reliable and flexible power supply test system using PXI based switches, instruments, programmable power sources, loads and necessary current and voltage sensors. All test modules were developed using Lab VIEW, SQL & Report Generation toolkits for Lab VIEW and were integrated under Test stand

Background

The test system is designed to perform high-speed automated testing of power supplies. NesT Power Electronics Production facility located at Cochin, India manufactures hundreds of DC power supply units for various electronic equipments per day. After assembly of the power supply circuit components the power supply unit has to pass functionality and stringent quality tests for meeting parameter specifications of the power supply.

Considering the fact that number of power supply units assembled every day is very high, NesT Power Electronics desired a test system, which can cater for the high speed-testing requirement without compromising on the quality of measurement. The solution provided by us, using NI hardware and Software drastically improved the total time requirement for testing each Power Supply from the existing 2 minutes to less than 35 seconds. It was also done at nearly half the cost of a dedicated Power Supply test system.

System Configurations

The Unit Under Test (UUT) is placed on a glass jig (bed of nails) and test probes are connected to the UUT input and output terminals. The UUT has four output terminals at different voltages and one Power Good and Ground Line. We used the PXI-1010, a PXI-SCXI combination chassis; the Analog to Digital conversion is done by the PXI-6052E. SCXI-1160 switches are used to switch various instruments to the UUT’s input and output terminals to perform different measurements on the UUT. A Digital I/O card 6527 drives an external relay unit to enable a transient load for the UUT and also to enable mains for GPIB Programmable Power Supply and Load. NI DMM 4060 is used for voltage and current measurements at various points. Hall Effect voltage & current sensors acted as the necessary transducers whose outputs are fed to two channels of the NI Scope 5112, which is also used for measuring ripple on the output terminal of the UUT. Load and power are applied to the UUT using Chroma Electronic Load 6812 and Chroma Power Supply 6404 respectively, which are controlled by the PXI system through GPIB.

Figure 1: Schematic of the Automatic Power Supply Tester

Tests Performed and Design Challenges

Tests performed on the UUT are regulation, efficiency, hold over with respect to the loss AC main and also hold over with respect to the loss of Power good, short circuit protection, output voltage, Ripple measurement, transient load and startup overshoot test. Individual tests are developed using LabVIEW and each test VI is integrated using TestStand software, which has off-the-shelf, customizable test executives and high-speed execution engine

The main design challenges in implementing the automated test system are:

Synchronizing a number of different instruments for measurement.
Efficient coding and use of devices in order to reduce the test time.
Flexible and modular tests for sequential or independent execution.
Selection of Hardware to ensure low cost as well as accuracy.
Developing a flexible and customizable test report generation.

System Implementation

For all the tests different voltages are applied to the UUT input terminal as well as load is applied to UUT output terminal by programmable GPIB based Chroma power source 6404 and Chroma DC load 6810 respectively as per Manufacturing Test Requirements.. The following are the tests performed on the UUT.

1.	Regulation tests are performed with different input voltage and different load values. Four Regulation tests are performed two with all outputs at full load but with different input voltage. Other two regulation tests are performed with constant input voltage but on different load conditions. Output voltages of the UUT are measured using the NI DMM. SCXI switches provide appropriate switching to connect the DMM to the measuring point.
2.	For efficiency test the DMM is used for finding input RMS Voltage and Current to the UUT. Phase difference between input Voltage and Current is measured by acquiring data from Hall effect voltage & current sensors through the NI Scope. Software finds the phase difference between them and the Power factor, which is used to calculate the input power. Output power is calculated by measuring the Voltages and Current on all the output terminal of the UUT. Input and output power is used to determine the efficiency of the UUT
3.	In order to check whether the output voltage is retained for a minimum time after drop of AC input voltage, Hold-over tests are performed. The tests also check for the time, the output is retained after drop of Power Good line. These tests are performed by acquiring AC input, Power Good & Output voltages with respect to time with the PXI-6052E.
4.	Short circuit protection test is performed by shorting the UUT output terminals via SCXI switches for two seconds and then performing a full load regulation test to check the recovery of the UUT.
5.	Ripple measurement is performed using NI scope on each of the output terminal of the UUT. Ripple measurement during the Transient load test is performed using an external Transient load connected to one of the output of the UUT and all other outputs are connected to GPIB load.
6.	Startup overshoot is determined for all the four outputs of the UUT by acquiring voltages of all the four outputs before and after input power is applied to the UUT and then finding the maximum output voltage attained.

Figure 2: Automated Test Equipment for Power Supplies

Conclusion

The system is capable of performing high-speed testing of the UUT. It greatly improved test times from the existing Two minutes to less than 35 seconds. We could also deliver an extremely flexible system capable of removing or adding any new test module if any new tests are required to be performed.