Toshiba TLP-X2000B, Service Manual

Page: 53 / 91

6–11
Chapter 6
OPERATION OF EACH SECTION
1. Input Line Filter
The Input line filter circuit is made up of capacitors (e.g. C1, C2, C101) and inductor chokes (e.g. L1, L2,
L101) on APS-T602 unit and a part of APS-T603 unit,
This section protects the noise generated by the power supply circuit from leaking out to AC line
and from entering of the external noise inside the power supply circuit.
This circuit is effective for both normal and common noise.
The fuse F1 becomes open in order to protect other parts, when excessive current flows in abnormal
conditions.
The connector CN2 is connected to thermal sensing element (e.g. thermal protector). Power Supply is
operated by CN2 shorted condition. In other words, when 2 terminals of CN2 become open by thermal
protector, power supply to subsequent circuit is shut off.
2. Power Factor Correction Circuit (PFC circuit)
The main parts of this switching converter are choke coil T101, switching MOSFET Q101, Q102, control
IC IC101 and diode D104. This circuit has mainly 4 functions as following.
a. Generate stable voltage
This PFC circuit operates so that the output always is set to 370Vdc(typ.). Actually, the switching
operation of Q101 and Q102 is controlled by IC101. Initial voltage setting of 370V output is set at
370Vdc(typ.) by VR101. (Input voltage: 100Vac, maximum load)
* Please don’ t turn although there are 2 variable resisters for this output voltage setup and for
the overvoltage protection setup. The case which needs to turn the volume means that the failure
mode cannot be repaired easily.
b. Reduce input harmonic current
Main purpose of Power Factor Correction Circuit is reducing input harmonic current by bringing the
input current waveform closer to a sine wave.
This circuit is CCM (Continuous Conduction Mode) PFC circuit which used resettable integrator.
The gate pulse width is adjusted per one cycle by detecting DC output voltage at the VF pin of IC101
and peak current at the ISNS pin of IC101. The amplitude and shape of the input current is controlled
so as to be proportional to and in phase with the input voltage.
c. Over current protection
The current sense pin ISNS of IC101 is the input to the current sense amplifier and the overcurrent
protection comparator.
There are essentially two levels of current limitation provided by the IC101. There is a “ soft” current
limit, which is essentially a duty cycle limiting fold back type: the converter duty cycle is limited to the
point where output power is limited and the output voltage begins to decrease. There is also a “ peak”
current limit feature which immediately terminates the present drive pulse once the peak limit
threshold, = -1.0V, is exceeded.
d. Over voltage protection
The voltage in proportion to output voltage by resistors R112, R113, R114, R115 and VR102 is added to
the OVP pin of IC101. When the OVP threshold(7.49V(typ.)) is triggered, the IC101 will disable the gate
drive signal.