Power Supply Circuit; Power Factor Improvement Block; Power Regulator For The Main Power Supply - Sony TRINITRON PVM-14L2 Service Manual

5-3. Power Supply Circuit

The power supply block consists of the following two switching regulators.
1. The power regulator for improving power factor to conform to the power supply harmonics regula-
tion.
2. The power regulator for the main power supply that supplies the necessary voltages to the signal
system circuit and to the deflection and high voltage circuits.

1. Power factor improvement block

The power factor improvement block uses the active filter IC module (IC601) of the current-critical type
boost-chopper system to conform to the power supply harmonics regulation.
The power factor improvement block consists of IC601, L602, C608, C617 and the related parts.
IC601 the module IC that contains the control IC, switching FET, boost diode and input/output voltage
detector inside the module.
The basic operation of the power factor improvement block is described below. When the VCC power is
supplied, it turns on FET so that a current starts flowing in the primary winding of L602 and FET. This
current increases with the slope of Vin (RMS)/L. Here, L is the inductance value of the primary winding
of L602. This FET current is monitored by the source current detecting resistor connected between pin-4
and pin-7 of IC601. When the detected voltage increases and reaches the set value that is determined by
the multiplier located inside the control IC, the FET is turned off. Then a current that decreases with the
slop of (Vd - Vin (rms))/L flows in the boost diode. When this current becomes zero, the FET is turned
on. By the circuit operation as described above, the current-critical operation is realized. (Vd : Voltage
across C617, Vin : Input power voltage)
The above-described single cycle of the circuit operation is repeated all the time. When this circuit
operation is observed during a half-cycle period of a commercial power frequency, the control IC controls
the ON/OFF timing of the FET so that the peak value of the choke current resembles to the sine wave-
form of the input power voltage.
As the result of this control by the control IC, the input voltage waveform resembles to the input current
waveform so that the power factor is improved. As the result of this control, the voltage Vd across C617
becomes higher than the peak value of the input power voltage, and is set to about 380 V regardless of the
input power voltage.

2. Power regulator for the main power supply

The circuit system of this power regulator is the PWM type fly-back converter of the separate-excitation.
The main power supply block consists of the PWM drive IC : IC602, the main switching FET : Q606 the
converter transformer : T602, the rectifier diode in the secondary circuit and the smoothing capacitor.
Circuit operation of this regulator is as follows. The drive pulse that is output from IC602 is buffered by
Q617/Q618 and sent to the Q606 gate that activates the switching operation. IC603 performs the constant
voltage control over the secondary circuit output : +115 V power line in order to control the above-
described switching operation. First, the signal that is output from IC603 is returned to IC602 through the
isolator PH601 and is used to control the ON-duty period of the drive pulse so that the secondary output
voltage is controlled to be a constant voltage.
The secondary output of T602 supplies +115 V output voltage and other various output voltages in
addition to the +115 V power voltage such as +200 V, +15 V, _15 V, +6 V, _6 V and HEATER
voltages.
The voltages of the +15 V, +6 V, and _6 V power supplies are power-regulated by the three-terminal
regulator so that they are regulated to the +12 V, +5 V, and _5 V power supplies that are distributed to
each circuit board.
5-4
PVM-14L2/20L2