Circuit Description; Input Circuit; Primary Rectifier/Smoothing Circuit; Start Circuit And Vcc Supply - Philips DVD 950 Service Manual

Hide thumbs Also See for DVD 950:
Table of Contents

Advertisement

GB 60
10.

10.9 Circuit description

10.9.1 Input circuit

The input circuit consists of a lightning protection circuit and an
EMI filter.
The lightning protection comprises R3120, gasarrestor 1125
and R3124. The EMI filter is formed by C2120, L5120, C2125
and C2126. It prevents inflow of noises into the mains.

10.9.2 Primary rectifier/smoothing circuit

The AC input is rectified by rectifier bridge 6120 and smoothed
into C2121. The voltage over C2121 is approximately 300V. It
can vary from 100V to 390V.

10.9.3 Start circuit and Vcc supply

This circuit is formed by R3123, R3134, C2129, D6129, R3129,
R3111, C2133 and C2111.
When the power plug is connected to the mains voltage, the
stabilised voltage over D6129(24V) will charge C2133 via
R3129. When the voltage reaches 14.5V across C2111, the
control circuit of IC7110 is turned on and the regulation starts.
During regulation, Vcc of IC7110 will be supplied by the
rectified voltage from winding 7-9 via R3135, D6132 and
C2133.
10.9.4 Control circuit
The control circuit exists of IC7110, C2102, 2104, 2107, 2109,
2110, R3102, 3103, 3104, 3107, 3108, 3109 and 3110. The
frequency of the oscillator is defined by C2102 and R3110.
Power switch circuit
This circuit comprises MOSFET 7125, Rsense 3126, 3127 and
3128, R3125 , C2127, L5125, R3112 and R3113. R3125 is a
pull-down resistor to remove static charges from the gate of the
MOSFET.
10.9.5 Regulation circuit
The regulation circuit comprises opto-coupler 7200 which
isolates the error signal from the control IC on the primary side
and a reference component 7201. The TL431(7201) can be
represented by two components:
a very stable and accurate reference diode
a high gain amplifier
R
2.5V
CL 96532065_071.eps
Figure 10-8
TL431 will conduct from cathode to anode when the reference
is higher than the internal reference voltage of about 2.5V. If the
reference voltage is lower, the cathode current is almost zero.
The cathode current flows through the LED of the opto-coupler.
The collector current of the opto-coupler flows through R3106,
producing an error voltage, connected to voltage feedback pin
14 of IC7110.
DVD 950
Current mode power supply 30PS203
K
A
130799
10.9.6 Demagnetisation
The auxiliary winding (7-9) voltage is used to detect magnetic
saturation of the transformer core and connected via R3101 to
pin 8 of IC7110. During the demagnetisation phase, the output
will be disabled.
10.9.7 Overvoltage protection circuit
This circuit consist of D6114, C2114, R3115 and R3116.
When the regulation circuit is interrupted due to an error in the
control loop, the regulated output voltage will increase
(overvoltage). This overvoltage is sensed on the primary
winding 7-9.
When an overvoltage longer than 2.0 (s is detected, the output
is disabled until VCC is removed and then re-applied. The
power supply will come in a hiccup mode as long as the error
in the control loop is present.
10.9.8 Secondary rectifier/smoothing circuit
There are 5 rectifier/smoothing circuits on the secondary side.
Each voltage depends on the number of windings of the
transformer.
The +5Vstby power supply is derived from the +12Vstby by
voltage regulator 7233, C2233 and L5233.
The -5V voltage is regulated by voltage regulator 7259 and will
be switched off via D6256, T7256 and T7255 during standby
(control signal STAND BY is high). When jumper 4250 is
mounted instead of this circuit, a supply voltage -8Vstby will be
present at pin 9 of connector 0205. -5V is used in DVD730 MK
II, DVD 930 MK II and DVD710. -8Vstby is used in DVD750 and
DVD950.
The +5V power supply is derived from +6Vstby by the loader-
up circuit formed by MOSFET 7236, reference component
7237, R3236, R3237 and C2239. This voltage will be switched
off during STAND BY via T7235.
The 3V3 power supply is regulated by the control loop (7201,
7200, 7110) of the switched mode PSU.

Hide quick links:

Advertisement

Table of Contents
loading

This manual is also suitable for:

Dvd950/171

Table of Contents