NF FRA51615, Instruction Manual

Page: 18 / 306

1.2 Applications
1
-
4
FRA 51615
■ Example of loop gain characteristic measurement
The loop gain characteristic is obtained by injecting a perturbance signal into a negative feedback loop and
measuring the response to the perturbance signal.
The internal signal generator of the instrument is in a floating state with respect to the enclosure, so it is
possible to measure the linking characteristic without using an isolation transformer for signal injection.
The high withstand voltage isolation of up to 600 V (CAT II) enables measurement on the primary side of
inverters and switching power supplies that are connected directly to the mains.
Figure 1-2 Example of loop gain measurement
By measuring the characteristics with this instrument, it is possible to obtain the phase margin, gain margin,
and other indices that are needed to determine negative feedback loop stability.
+
A
β
input
output
v2 v1
=
v2
×
A
β
～
PWM
Vref
ErrorAmp
CH1
CH2
OSC
LO
A
D
(EUT)
switching power supply
-
-
-
+
+
+