THOMSON VK231PS, Technical Manual

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23
SECONDARY REGULATION
Transistor TP071 and optocoupler IP050 are used in conjunction for secondary regulation. The
current in the optocoupler diode is controlled by the regulation error voltage from the collector
of TP071. (This error voltage is obtained by comparing a reference voltage on the base of the
transistor and the 5VE image).
This current sets the value of the internal resistor in the optocoupler transistor. The switching
transistor is blocked according to the addition of the voltage obtained at the terminals of
Resistor RP020 and the voltage brought back by the internal resistor of the optocoupler
transistor. These two voltages polarise the base of TP022.
CP068 allows IP050 to handle abrupt variations of 14VE (motor start-up).
SECURITY
To avoid security problems, a new component called Protector Module (e.g. FP044) has
replaced classic fuses in several positions.
The advantage of the Protector Module is the ratio between its maximum current and the
current that destroys it. This ratio is 3, whereas the ratio is greater than 15 for a classic fuse.
In the event of an excessive increase in the conduction time of Transistor TP20 (overload of a
secondary), the voltage induced on winding 4-6 of LP050 during this phase increases and
charges Capacitor CP040. From a certain threshold, this will saturate TP022, block TP020,
and therefore shut off the power supply until CP040 discharges and allows TP022 to be
become blocked to re-start the power supply.