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Below are the common functional test performed on a AC-DC or DC-DC Power supply.
Current Share Test or Parallel Test
- Two units are connected in parallel. Outputs of both power supplies were connected together. Each power supply should share the total set current. Ideally, each power supply should drawn 40% to 60 of the total current to achieved best current sharing performance.
- Measurements can be acquired using a shunt or a current meter. Connection and length of cables is very critical in this test. The length of the cable connected to each power supply's outputs from the load should be of the same length and type.Shunt should be connected along of each of the output load cable.
Efficiency Test
- A power supply is set to specified line and load conditions. Input voltage, Input current, Ouput voltage and output current are measured to calculate for the efficiency. Input power factor also will be included in the case on AC input power supplies. Limits and result are in percentage.
- Critical measurements:
- Output voltage measurement should consider the remote sensing connection.
- Remote sense of the input source should be connected right at the uut's input terminal to get the corrected input voltage and eliminate voltage drop.
Start up Delay Test
- Start up with ps_Enable
- A power supply is set to specified line and load conditions, set ps_enable off. Turn on input, wait for couple of seconds, then set ps_Enable to turn on power supply main outputs. Time from ps_enable edge to ouput voltage reaching 90% (or specified percentage) of nominal is measured. Limits and measurement are in seconds.
- Measurements will be taken with the oscilloscope. Trigger for the scope should be on ps_Enable pin. Usually ps_Enable is an active low signal, meaning once this signal is pulled to low, main output will be enabled.
- Start up with vin (input voltage)
- A power supply is set to specified line and load conditions, set ps_enable on, then turn on input. Time from input turns on to ouput voltage reaching 90% (or specified percentage) of nominal is measured. Limits and measurement are in seconds.
- Measurements will be taken with the oscilloscope. Trigger for the scope should be on the input source.
- For AC input, trigger will be from the ac source TTL output state signal. The ac source TTL signal will generate a TTL signal on every change on ac source output. Connect the TTL signal to the external trigger of the oscilloscope. Connect the ouput on channel1 of the oscilloscope and connect the ac source output thru a differential probe to channel2. Once the trigger from the TTL signal is achieved it will capture the input and output waveform.
- For DC input, the actual source output is triggered at a specified level. Use differential probe for the input voltage.
Hold up Time
Rise Time Test
- Unit Under Test is set to specified line and load conditions. Turn on unit and capture the output waveform. Rise time can be measured from 10% to 90% of nominal output.
- Measurement will be taken from oscilloscope. Trigger to the oscilloscope should be on the channel where the output is connected. Make sure that the time per division set on the oscilloscope should be observed. Set the time per division approximately twice the specified rise time limit of the output.
Inrush Current Test
- Load condition is set on the power supply.Set the oscilloscope for input voltage and input current. Input current is measured using a current probes, input voltage should be captured using a differential probe. Turn on the unit under test by turning on the input source and capture both input voltage and input current. Get the peak current. Results will be in Amps Peak.
Regulation Test
- Load Regulation Test
- A power supply is subjected on different load condition with constant line input condition. This will be tested on different load combination, from minimum load to maximum load conditions.
- Line Regulation Test
- A power supply is subjected on different line condition with constant load condition. Ideally, this test will be from the lowest tolerable input voltage to the highest tolerable voltage. The power supply's output should be in specified output regulation on both line conditions.
- Measurements will be taken from right at the output connector. Output sense should be consider in taking the measurement.
Over-Current Protection Test
- This test will check if the power supply will protect itself from over current condition.
- A power supply is subjected to over current load by ramping the output current above the specified maximum load condition. Check the output if it will shutdown on the specified limits. Output will also recover after cycling the input.
Over-Voltage Protection Test
- This test will check if the power supply will protect itself from over voltage condition
- A power supply is subjected to over voltage by ramping the output voltage above the specified regulation limits.
- Types of over voltage test
- Over voltage by backdrive by external power supply
- Use an external dc supply to simulate over voltage condition on the output.
- Ramp the external voltage and check if the power supply latch or shutdown. To check the right ovp level, check the other output, not the output where ovp test is performed.
- Shorting pins on the ovp circuit to simulate ouput peak
- Use oscilloscope to capture the voltage peak when shorting the pins.
- Output will simulate peak before it shutsdown.
- Over voltage by a trim pot
- Connect an external resistor on ovp circuit to simulate ovp.
- Over voltage by epot (electronic potentionmeter)
- Ramp the output voltage by writing values to the microcontroller to increase the output voltage.
- Check the level where the output highest voltage before it shutsdown.
Line Drop out Test
- Power supply is set on load and line condition. Drop the input voltage on specified level lower to initial setting, usually it drop to 0 volt on specified time or cycle.
- Check power supply output if it remains on or with out in glitch during the drop out period.
- An oscilloscope is use to capture both signals, input voltage and the output.
- Input voltage should be connected on the differential probe for monitoring.
- Test Criteria will depend on how the power supply output should behave during the drop out.
Ripple and Noise Test
- A power supply is set at specified line and load condition, set the oscilloscope at ac coupling.
- Measurement will be taken using a coax shielded cable or a X1 or X10 scope probes.
- Measurement can be taken either on 20Mhz bandwidth or 100Mhz bandwitdh.
Output Turn On voltage
- This test will determine the input voltage on which the output turned on.
- A power supply is set at specified load condition, ps_Enable is set to low (on).
- Ramp the input voltage start at the non operating voltage of the power supply. Monitor closely on the output as the input voltage is being ramp. The input voltage on which the output turns on will be the turn on voltage of the power supply.
- Stand by outputs and main outputs may not be the same turn on voltage level. Both outputs should be tested independently.
Brown out Test
- This test will determine the input volateg on which the output shutsdown.
- A power supply is turned on on specified line and load condition.
- Ramp the input voltage down and monitor closely the output. The level on which the output voltage shutsdown will be the turn off voltage of the power supply.
- Others call this test as Input turn off voltage.
SMB Alert Test
- This test will check smb_Alert function of the power supply. A power supply is set to specified line and load conditions. Inject a fault either over current, over voltage or under input voltage. Closely monitor smb_Alert_L, from normal condition, this signal is in low state. Then as the warning or fault occured, this signal will have a transistion from low state to high state. This will remain high even if the fault was removed unless either of this actions were done
- SMB_Alert deassertion:
- Recycle input, this will reset the smb_Alert_L to low state.
- Send a smb_alert deassertion command to the power supply. This is standard for PSMI complaint power supplies.
PSMI Fan Test
- Here's the steps to perform Fan Test Override for PSMI Compliant Power supply
- Read the following registers:
- Register 0x24 - Fan speed setting in PWM
- Register 0x20 - Fan speed sensor in RPM
- if the PSU has two fans then the second fan properties will be in this registers:
- Register 0x25 - Fan speed setting in PWM
- Register 0x21 - Fan speed sensor in RPM
- Set the bit0 on x63 (Control Register) to 1. This will enable the RPM1 Control Mode to Host control.
- RPM Control Modes:
- 0 - Power Supply control
- 1 - Host Control
- After setting the RPM1 Control Mode to Host control, you can manually override the Fan speed by writing to the following registers:
- Register 0x24 - Fan1 speed setting in PWM
- Register 0x25 - Fan1 speed setting in PWM
- Usually the range will be x0 to xFF (full speed)
- Dependent on the data written to this registers Fan speed will adjust accordingly.
- Once x63 Control Register will set back to 0, Power Supply micro controller should restore back the original speed which is the speed before the Host cake control of the Fan.
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