2
POWER SUPPLY
GeneralStart up
The power supply is a mains isolated Switched Mode PowerAfter switching on with the mains switch and when triac
Supply (SMPS). Mains isolation is provided by transformerDfc11 (on the micropower control) conducts, capacitor Co15
Mo2. The mains voltage is full wave rectified by diodesis charged via resistors Ro9, Ro11, Ro70 and thyristor To15.
Do1...Do4 and filtered by capacitor Co10. This filtered volt-When the start up voltage on pin 16 of ICo1 reaches the
age is fed to the switching transistor To1 (MOSFET) via theswitch-on threshold level, that is typically +11.8 V, the IC
primary winding 11 and 5 of the mains transformer. Dur-starts to operate.
ing the conduct period of To1, energy is stored in the pri-The supply voltage of ICo1 is then taken from the second-
mary winding 11 and 5. When transistor To1 is switchedary winding pin 3 via half wave rectifier diode Do8. The
off, energy flows to the secondary windings. These pulsessame winding pin 3 supplies pulses to diode Do9. This
are rectified by secondary diodes Do11...14 and Do16.voltage drives transistor To9 to conduct putting the gate of
The following supply voltages are available from the sec-thyristor To15 to ground, and thus switching off the start
ondary diodes:up voltage.
The same DC voltage that is taken from the cathode of di-
+130 Vhorizontal output stageode Do9 is used for power supply regulation. The DC volt-
+28 Vaudio amplifier, subwoofer and audio featureage is fed via the filter network Ro26, Co28 and Ro24 to the
moduleerror amplifier input pin 6. The error amplifier compares
+17 V+12 V regulator IC, horizontal driver and +8 Vpthe input voltage with the internal reference (+2.5 V) and
regulator transistorvaries the burst time. Resistors ro4 and ro10 set the volt-
+7 Vfbfeature boxage to the proper level.
+7 V+5 Vr regulator IC, +5 Vstb regulator IC and +7 VFurthermore, a possible magnetization state of the trans-
supply voltageformer can be checked by sensing the voltage across the
winding pins 3 and 2. This information is fed via resistor
Note! The voltage levels may vary depending on the pic-Ro15 to pin 1 of ICo1, and if the specified level is exceeded,
ture tube. More detailed values are given in the schematicthe output pulses can not be generated.
diagrams.To avoid magnetization during the start up phase, the op-
eration will be started with the internal oscillatorOs operat-
The power supply is designed to operate with a master-ing frequency divided by four, until voltage on soft start
slave structure, where the power supply controller ICo1pin 9 reaches a level of +2.5 V. The operating frequency of
operates as a slave and the secondary controller ICo2 as athe oscillator is set to 27 kHz by capacitor Co16 on pin 10
master. The power supply operates in the following waysand resistor Ro3 on pin 11.
in different operation states:
Drive of the switching transistor
Start up phase:Pin 14 outputs square wave pulses to the gate of switching
Power supply is in the primary regulation mode (bursttransistor To1. Resistors Ro2 and Ro13 limit the gate cur-
mode). Power supply controller ICo1 generates independ-rent. To1 conducts during the positive going pulse and drain
ent drive pulses for switching transistor.current flows through the primary winding pins 11 and 5.
The clamping circuit Do6, Co11 and Ro16 limits the volt-
Normal on mode:age spikes, when To1 is switched off. The source of To1 is
Power supply is in the secondary regulation mode (mas-connected to ground via current limiting resistors Ro18,
ter-slave mode). Secondary controller ICo2 generates driveRo19, Ro21 and Ro22. Information about the current is fed
pulses for power supply controller ICo1. The secondaryto pin 3 of the power supply controller.
controller is synchronized to the line flyback pulses.
After the start up phase, when supply voltages are gener-
Recording mode:ated, the power supply moves from primary regulation
Power supply is in the secondary regulation mode (mas-mode to secondary regulation mode. The microcontroller
ter-slave mode). Secondary controller ICo2 generates drivewill be reset and itOs pins 48 (P_on) and 49 (R_on) will go
pulses for power supply controller ICo1. The secondarylow. The R_on line allows, via transistor to6, regulator ICo3
controller is synchronized to the free running frequency ofto feed +12 Vr out. This voltage is fed to the secondary
an internal oscillator.controller ICo2 (pin 2) and the IC starts operation.
The capacitor co58 on pin 1 operates as a soft-start capaci-
Switching off to standby phase:tor causing the duration of soft-start to be around 20ms.
Power supply is in the primary regulation mode (burst
mode). Power supply controller ICo1 generates independ-The free running frequency of an internal oscillator is set
ent drive pulses for switching transistor.to 32 kHz by capacitor co72 on pin 7 and resistor Ro37 on
pin 8. In normal operating mode, the oscillator is synchro-
Standby mode:nized using the line flyback pulses via differentiator Ck6,
Due to the micropower control, the power supply is com-resistor ro38 and diode Do18.
pletely without voltage.In recording mode, the Vp voltages are switched off and
The power supply also has a so-called Service standbytherefore the line flyback signal is not available. In this case,
mode. The receiver is in service standby mode when it isthe oscillator is in free running mode.
set to the service mode by pressing the buttons -vol / menu,
TV and i, but has not yet been switched on by pushing theThe internal pulse width modulator is controlled by com-
TV button twice. In this mode, the power supply operatesparing the input voltage level on pin 5 with the oscillatorOs
(burst mode), but the Vr and Vp voltages are not available.sawtooth pulses. Pin 5 is connected to +140 V via resistor |
ACEC
HITACHI
