EPR-00011 - 70 W Adapter 22-Jan-01
Page 32 of 46
Power Integrations Inc
Tel: +1 408 414 9200 Fax: +1 408 414 9201
ww: http://www.powerint.com
11 Control Loop Characteristics
The control loop characteristics were measured with a Venable measurement system,
which breaks the control loop between the emitter of the opto-isolator (U2) and the
control pin of the TOP249Y (U1) and its associated components; C11, R11, and C17.
The results are tabulated below, followed by graphs of the last five table entries:
Result #
V
IN
(V
AC
)
I
OUT
(A
DC
)
Crossover
Freq.
Phase
Margin
1 130 3.16 1000 Hz 53 deg.
2 85 3.16 1220 Hz 55 deg.
3 85 0.71 435 Hz 45 deg.
4 265 0.70 556 Hz 50 deg.
5 265 3.16 1000 Hz 50 deg.
6
85 1.0 800 Hz 52 deg.
7
85 3.66 1600 Hz 62 deg.
8
265 3.66 1000 Hz 56 deg.
9 265 0 530 Hz 95 deg.
10 115 1.0 380 Hz 45 deg.
11 115 0 500 Hz 120 deg
Note results for 9, 10 and 11 are shown without adding a 180 deg offset for the
secondary error amplifier. Therefore phase margin is referenced to –180 deg.
Measurements were made at zero load to confirm stability during the lower switching
frequency operation at no-load.
