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Agilent AN 372-1
Power Supply Testing
Application Note
An electronic load offers a broad range of
operating modes, providing versatile loading
configurations needed for characterizing and
verifying DC power supply design specifications.
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Introduction As regulated-power supply technology evolves, they are relatively inefficient when compared to testing methods for design verification and product switching power supplies, and tend to be large function require more sophisticated electronic equip- and heavy due to the heat sinks required to contin- ment. The different power supply architectures uously dissipate power from the series transistors and output combinations also dictate the need for and due to the magnetics used in this
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An Overview of Power Supply Testing Needs Power supplies are used in a wide variety of prod- The tests covered in the following section are con- ucts and test systems. As a result, the tests per- figured with standard instrumentation: electronic formed to determine operating specifications can loads, digital oscilloscopes, digital multimeters, differ from manufacturer to manufacturer, or from true rms voltmeters, wattmeters, and AC power end user to end user. For instance, the tests per- sources
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Power Supply Tests Table 2 Load Transient Current Limit Efficiency and Recovery Time Load Effect Characterization PARD Power Factor Start-Up Electronic Load t ≤15 μs 1% programming 1% programming 1% programming 1% programming 1% programming rise accuracy accuracy accuracy accuracy accuracy Trigger output to CC or CR mode CR or CC mode CC or CR mode CC or CV mode CR mode the oscilloscope Low PARD Digital t ≤100 ns N/A N/A t ≤25 ns N/A t ≤1 μs sample sample sample Oscilloscope DC to 20 MHz Record
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For a step change in load current, a marginally used in this test should have a risetime at least stable CV power supply will have a ringing voltage five times faster than the power supply under test, output. This defeats the purpose of the power sup- and should be able to operate in CC mode (or CR ply’s regulation circuitry and can be damaging mode) up to the maximum current rating of the to voltage-sensitive loads. An example of a voltage- power supply. Measuring the load transient recov- sen
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For multiple output CV power supplies, cross Load Effect (Load Regulation) load effect is determined. This is an extension of Load Effect or Load Regulation is a static perform- the load effect test for a single output power sup- ance measurement which defines the ability of a ply, and determines the ability of all outputs of a power supply under test to remain within specified CV power supply to remain within their specified output limits for a predetermined load change (see voltage rating for
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Test Overview/ Procedures Current Limit Characterization A measurement of the output voltage and current Current limit measurements demonstrate the degree of the power supply under test is required while to which a constant voltage power supply limits its decrementing the electronic load resistance (or maximum output current to a preset value. This current in CC mode) by steps from an initial value preset value can be fixed or variable throughout a that produces the power supply’s full rated vol
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some applications, a low output ripple specifica- PARD (Periodic and Random Deviation) tion is critical. An example would be where the PARD (formerly known as ripple and noise) is the power supply is providing power to a high gain periodic and random deviation of the DC output amplifier with inadequate ripple rejection for the voltage from its average value, over a specified application. In this case, a portion of the power bandwidth, and with all other parameters con- supply PARD would be ampli
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Test Overview/Procedures The first set of PARD measurements should be To make PARD measurements, the electronic load made with the AC source voltage and frequency used should operate in CR mode for constant volt- set at the lowest specified values, and with the age and constant current power supplies. The load power supply under test at its minimum and then should also have lower PARD than the power sup- maximum rated load value. A second set of meas- ply being tested. This is especially import
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Efficiency Start-Up The efficiency of a power supply is simply the The start-up delay of a power supply is the amount ratio of its total output power to its total input of time between the application of AC input and power. To obtain the true input power (rms voltage the time at which the outputs are within their reg- x in-phase rms current) of a typical AC-to-DC ulation specification. For switching power supplies converting power supply, commercially available or power supplies with current lim
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To fully characterize the start-up sequence of the control the AC input frequency and amplitude to power supply under test, measurements must be the power supply under test, a regulated AC source made of the output voltage response to the instan- should be used. Turn-on of the AC source at selected taneous application of the AC input (see Figure 11). 60 Hz (50 Hz) phases (zero-crossing and positive or A digital oscilloscope should be used so that stor- negative peak voltage, for example) is impo
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Other Power Supply Tests An observation of any DC power supply data sheet Short Circuit Output Current from a power supply manufacturer reveals a number This test measures the steady-state current of the of design specifications that must be verified and power supply under test after the output terminals tested. These tests often differ in technique and in have been shorted. The short circuit can be provided the test equipment that is used to measure the var- by an electronic load operating in C
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Power Supply Testing with Agilent Electronic Loads The Agilent Electronic Load Family offers the power For testing multiple output power supplies, Agilent supply tester the solution for many of the tests that offers the 6050A 1800 Watt Load Mainframe. This must be performed. For bench or system applica- product provides an economical alternative to the tions in large or small scale testing environments, 6060A and 6063A for large scale testing environ- Agilent Electronic Loads provide high qualit
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By internet, phone, or fax, get assistance with all your test and measurement needs. Online Assistance www.agilent.com/find/assist Phone or Fax United States: (tel) 1 800 452 4844 Canada: (tel) 1 877 894 4414 (fax) (905) 282 6495 Europe: (tel) (31 20) 547 2323 (fax) (31 20) 547 2390 Japan: (tel) (81) 426 56 7832 (fax) (81) 426 56 7840 Latin America: (tel) (305) 269 7500 (fax) (305) 269 7599 Australia: (tel) 1 800 629 485 (fax) (61 3) 9210 5947 New Zealand: (tel) 0 800 738 378 (fax) (64 4) 495
