Guide to Power Supply Testing with MaxBotix

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MAXBOTIX
Input Power
Whether you believe your power supply may be faulty or you are doing routine
testing, it is important to verify the performance. Issues with a power supply can
limit the performance of your equipment, and it even has the potential to damage
your fine electronics. Proper and regular power supply testing can help minimize
this risk.
Guide to Power Supply Testing
info@maxbotix.com (1)
High Performance Ultrasonic Range Finders
Properly calibrated voltmeters and current meters
(resolution should be 10 times the parameter being measured)
Oscilloscope with bandwidth up to 20MHz
Sufficient input power source
Programmable adjustable load
Required Equipment
The power provided by your power supply is the key factor, but the first parameter
to test is the voltage and current on the input side of your power supply. Verify the
input power supply falls in the operating range for your power supply, as listed in
the specification or datasheet. Just like our sensors, improper input voltage to a
power supply hinders proper operation whether you are using an AC/DC or a
DC/DC power supply.

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Test Setup Test Procedure
1. Set the input voltage to the nominal
requirement for your power supply.
2. Set the output voltage load to its maximum
rated value.
3. Measure the output voltage (VOUT) with the
calibrated voltmeter.
4. The output voltage accuracy can be
calculated using the following formula
Note that DC/DC power supplies typically have a set output voltage where AC/DC
have a variable output voltage. This displayed or set output voltage is (VNOM).
The LED display (when applicable) on your power supply may read 5.00VDC, but
this may not always be accurate. Checking the accuracy of the output voltage with
a properly calibrated voltmeter is a great way to verify this output voltage. Strictly
speaking, you only need to verify that the output voltage is stable and within the
operating range of your device. However, you may wish to continue to calculate the
output voltage accuracy.
Output Voltage Accuracy

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Our sensors operate at peak performance when they receive smooth and clean
voltage with minimum noise and output ripple. Output ripple and noise are also
known as Periodic And Random Deviation (PARD). When there is noise on the
voltage entering the part, it gets added to the amount of noise the part sees.
Specifically, output ripple and noise can be split into separate factors. Noise is a set of
random high or low frequency spikes to the power supply. Noise is best mitigated by
shielding the wires and operating as far from electrical noise sources as possible.
Output ripple is periodic where noise is random. Output ripple is a periodic shift
visible in the output voltage. This ripple is often generated by the periodic nature of
AC power.
Viewing the power supply with an oscilloscope is required to view both output ripple
and noise. Excess ripple or noise outside of a window that you would typically see in
a controlled environment will degrade sensor performance. When testing the noise
and output ripple the bandwidth should be sufficient to capture the full cycle of any
output ripple.
Additional noise can be picked up on the oscilloscope probe itself. Using the shortest
probe to ground length possible minimizes the amount of noise the probe receives.
Take care to minimize any error and noise that you may add to the system.
Test Setup
Noise & Output Ripple

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When there is a ripple or instability to the input voltage, it affects the output voltage.
Line regulation specification indicates how much a change in output voltage you can
expect due to a change in input voltage. The specification is typically presented as
the change from the minimum to the maximum operating input voltage. Testing the
line regulation may not be feasible if you are using an AC/DC power supply.
Line Regulation
requirement for your power supply
2. Measure the output voltage
(VOUTNUM )using the calibrated voltmeter
3. Set the input voltage to the maximum
operating voltage of the power supply
4. Measure the output voltage (VOUTMIN) using
the calibrated voltmeter
5. Set the input voltage to the minimum operating voltage of the power supply
6. Measure the output voltage (VOUTMAX) using the calibrated voltmeter
7. Find (VDEV), the maximum deviation from (VOUTNUM)
(VDEV) is the maximum of |VOUTNUM – VOUTMIN| or |VOUTNUM – VOUTMAX|
8. Line regulation can be calculated using the following formula

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Load Regulation
The system being powered by the sensor will draw current from the power supply.
The voltage will be affected by the total current drawn. On the DC output we can
review Ohm’s Law to see that V=IR. If we instantly increase the resistance of the
circuit, the voltage will shift. Load regulation works to minimize any shifts due to a
change in the loading of the circuit.
An output load change, a change in the resistance of the circuit, in terms of
percentage of the max load should also be mentioned. The load regulation should be
tested to these values.
2. Apply the maximum rated load,
resistance, to the power supply
3. Measure the output voltage at max
load (VOUTML) using the calibrated
voltmeter
4. Set the load to the specified level for load regulation
5. Measure the output voltage at the new load (VOUTNL) using the calibrated
voltmeter
6. Load regulation can be calculated using the following formula

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Transient Recovery Time
Load regulation allows a power supply to adjust itself to continue providing the
proper voltage after a change in load, but this adjustment doesn’t happen
instantaneously. The amount of time required for the voltage to return to the proper
level (within an error band) is the transient recovery time.
The transient recovery time will be rated between two levels of the rated load. Please
check your power supply datasheet to find the rated levels. As an additional note, the
transient recovery time is measured from the moment that the load is changed until
the voltage returns within the error band.
2. Locate the step load change specified
for the power supply
3. Program your adjustable load stepper
according to the previous step
4. Externally trigger your oscilloscope and switch the load over the specified range
5. Measure the transient recovery time on your oscilloscope

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Efficiency
Efficiency is a ratio that relates the total output power to the input power. While
efficiency will exist for both AC/DC and DC/DC power supplies, it may not be feasible
for all users to measure the efficiency of an AC/DC power supply.
1. Set the input voltage to the
nominal requirement for your
power supply
2. Apply the maximum rated
load to the power supply
3. Measure the current (IIN) and
voltage (VIN) to the power
supply as well as the current
(IOUT) and the voltage (VOUT) of
the power supply
4. Calculate the efficiency with the following equation

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You may continue to have issues after verifying all of the outlined issues in this
article. If this is the case, you may wish to retest Output Voltage Accuracy at the pins
of the sensor. Voltage droop can happen when running power through circuity.
Additionally, circuits with more than one ground reference may have issues with
ground loops. The power supply may be outputting a steady 5VDC, but these issues
may create a droop or spike in the voltage at the point of the sensor. Testing at the
pins of the sensor will help isolate this issue.
When testing Noise and Output Ripple, we minimize the length of wire runs to
minimize the amount of additional noise that is picked up. When power runs
through the circuit, it will pick up additional noise. This means it is also a good idea
to check for Noise and Output Ripple directly at the sensor’s pins to isolate this issue
as well.
Not all problems are caused directly by the power supply, but testing your power
supply is a great place to start. As it can be viewed as the beginning of any circuit,
any problems with the power supply will continue to appear throughout the circuit.
Contact our technical support team if you are still having problems with your power
supply. We are here to help you succeed.
Locating Persistent Issues

Guide to Power Supply Testing with MaxBotix

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