Philips 27PS60S321 Technical Service Data page 50

SPMS Page 23 of 32
Figure:
Over Voltage Protection
The Over Voltage Protection ensures that theoutput voltage will remain below an adjustable
level. This worksby sensing the auxiliary voltage via the current flowing into pin4 (DEM) during
the secondary stroke. This voltage is a well-defined replicaof the output voltage. Any voltage
spikes are averaged by an internalfilter.
If the output voltage exceeds the OVP trip level, theOVP circuit switches the power MOSFET
'off'.
Next, the controller waits until the 'under voltagelock out' level (UVLO = ± 9 V) is reachedon
pin 1 (V ).This is followed by a safe restart cycle, after which switchingstarts again. This
CC
process is repeated as long as the OVP conditionexists. The output voltage at which the OVP
function trips, is setby the demagnetization resistor R3522.
Over Current Protection
The internal OCP protection circuit limitsthe 'sense' voltage on pin 5 to an internal level.
Over Power Protection
7/8/2004