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Load Transient Recovery Time
A constant voltage DC power supply is designed
with a feedback loop which continuously acts to
maintain the output voltage at a steady-state level.
The feedback loop has a finite bandwidth, which
limits the ability of the power supply to respond
to a change in the load current. If the time delay
between the power supply feedback loop input and
output approaches a critical value at its unity gain
crossover, the power supply will become unstable
and oscillate. Typically, this time delay is measured
as an angular difference and is expressed as a degree
of phase shift. The critical value is 180 degrees of
phase shift between the loop input and output.
Power Supply Tests
Table 2
Load Transient Current Limit Efficiency and
Recovery Time Load Effect Characterization PARD Power Factor Start-Up
Electronic Load t
rise
≤15 µs 1% programming 1% programming 1% programming 1% programming 1% programming
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
sample
≤100 ns N/A N/A t
sample
≤25 ns N/A t
sample
≤1 µs
Oscilloscope DC to 20 MHz Record length 1 K
minimum bandwidth samples minimum
Record length
≥2 K samples
100 µ/Div (linears)
1 mV/Div (switchers)
Digital N/A 5
1
/2 Digits 5
1
/2 Digits N/A N/A N/A
Multimeter ±0.005% accuracy ±0.005% accuracy
Wattmeter N/A N/A N/A N/A 1% accuracy with N/A
crest factors to
10:1 in current
waveforms
Regulated >1% regulation >1% regulation N/A >1% regulation >1% regulation >1% regulation
AC Source Adjustable peak Adjustable peak Adjustable peak Adjustable peak Adjustable peak
and frequency and frequency and frequency and frequency and frequency
Power factor Phase control
measurement
capability
RF rms N/A N/A N/A 100 µV Full scale N/A N/A
Voltmeter DC to 20 MHz
minimum bandwidth
Figure 1. Load Transient Recovery Time
Load transient recovery time measurements require an electronic
load with a risetime and falltime at least five times faster than the
power supply under test.