Evaluation Engineering - 25

Short interruptions
Table 2. Test level and durations for short interruptions.

Class*

Test level and durations for voltage dips (50Hz/60Hz)

Class 1

Case-by-case according to the equipment requirements

Class 2

0%, 250/300 cycle

Class 3

0%, 250/300 cycle

Class X** X
* Classes as per IEC61000-2-4; see **.
** To be defined by product committee. For equipment connected directly or
indirectly to the public network, the levels must be less severe than Class 2.

Tests at 0% testing level for voltage dips are 1 cycle at maximum
for both Classes 2 and 3. Converting this period to time results
in 20 ms (@ 50 Hz).
Next, looking at the duration of short interruptions, both
Classes 2 and 3 have 250 cycles (@ 50 Hz)/300 cycles (60 Hz).
Converting this period to time gives 5 s. Testing at the 0% test
level of the voltage dip is up to one cycle in both Classes 2 and
3. Converting this period to time results in 20 ms (@ 50 Hz).
Next, looking at the short break period, both classes 2 and 3
have 250 cycles (@ 50 Hz)/300 cycles (60 Hz). Converting this
period to time is 5 s. Have you confirmed that your equipment
will not break if a power interruptions occurs for 20 ms to 5 s?

Actual condition of short interruptions

these functions may not work during power recovery, and an
overcurrent may flow.
In addition, in the DC/DC circuit, the voltage decreases because the charge stored in the capacitor inside the power supply
decreases at the time of a power failure. Since the power supply controller tries to maintain the output by maximizing the
PWM duty, the control response may not be in time at the time
of power recovery, and an overcurrent may flow.
In the case of a simple protection circuit such as a power
thermistor, intermittent ON/OFF may reduce the resistance
and may cause an overcurrent. Even if failure does not occur,
differences in the timing of individual circuit shutdowns may
cause equipment to malfunction or fail to operate properly. In
order to prevent them, it is necessary to monitor the input voltage and internal power supply voltage at appropriate timing and
reset the entire system to prepare for recovery.

The power line disturbance simulation function
Test by extending the dip time required by the standard to see
if any problems such as failure occur. Gradually increase the
dip time from 0.5 period to 5 s to see if any problems occur.
Additionally, it is good to test while changing the phase because
the current value that flows is different depending on the voltage
phase angle (Figure 4).
The test uses an AC power supply for testing. Some products
have application software for 4-11 standard tests, although tests
can only be performed on the main unit.

There are many momentary power interruptions over 20 ms
(Figure 3). In addition, it may occur intermittently, and the
total time exceeds 20 ms. What happens to your equipment
in this case? In the worst case, the inrush current at the time
of power recovery may cause the destruction of diodes and
MOSFETs in PFC circuits and DC/DC circuits, burnout of PCB
patterns, burnout of fuses.

Figure 3. Interruption duration

During normal startup, the input current is limited by the
inrush current prevention circuit or the soft start function to
prevent the inrush current from flowing into the capacitor, but

Figure 4. Example of changing angle and duration.

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Evaluation Engineering

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