Sharp 28JW-73H (serv.man2) Service Manual ▷ View online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 2
SUPPLY
MANAGEMENT
internal
supply
UVLO start
VOLTAGE
CONTRLLED
OSCILATOR
FREQUENCY
CONTROL
OVER-
TEMPERATURE
PROTECTION
POWER-ON
RESET
-1
S1
~
MAXIMUM
ON-TIME
PROTECTION
Q
Q
SET
CLR
S
R
UVLO
LODGIC
LODGIC
START-UP
CURRENT SOURCE
VALLEY
DRIVER
LEB
blank
OCP
short
winding
+
+
+
-
-
-
OVERPOWER
PROTECTION
soft
start
OVERVOLTAGE
PROTECTION
+
-
Drain (start)
Demag
Drive
I
sense
4
8
6
5
3
2
1
TEA1507
Iss
Supply (Pin 1)
Initially, the IC is self supplying from the rectified mains voltage via pin 8 (drain). External supply
capacitor, C705 at pin 1 is charged by the internal start-up current source to a level of about 4 V or
higher, depending on the drain voltage. Once the drain voltage exceeds the M-level (mains-
dependent operation-enabling level), the start-up current source will continue charging capacitor C705
(switch S1 will be opened, see TEA1507 block diagram). The IC will activate the power converter as
soon as the voltage on pin V
capacitor, C705 at pin 1 is charged by the internal start-up current source to a level of about 4 V or
higher, depending on the drain voltage. Once the drain voltage exceeds the M-level (mains-
dependent operation-enabling level), the start-up current source will continue charging capacitor C705
(switch S1 will be opened, see TEA1507 block diagram). The IC will activate the power converter as
soon as the voltage on pin V
CC
passes the V
CC
(start) level. The IC supply is then taken over by the
secondary winding of T703, (pins 1 and 2), as soon as the output voltage reaches its intended level.
The IC supply from the mains voltage is subsequently stopped for high efficiency operation (green
function).
The moment the voltage on the V
The IC supply from the mains voltage is subsequently stopped for high efficiency operation (green
function).
The moment the voltage on the V
CC
pin drops below the UVLO (undervoltage lock out) level, the IC
stops and restart from the rectified mains voltage. Inhibiting the Vcc supply by external means causes
the TEA1507 to operate in a stable burst mode.
Typical Vcc voltages
Start > 10.3 v
UVLO < 8.1 v
the TEA1507 to operate in a stable burst mode.
Typical Vcc voltages
Start > 10.3 v
UVLO < 8.1 v
Over-Temperature
An accurate temperature protection is provided in the circuit. When the junction temperature exceeds
the thermal shutdown temperature, the IC will stop switching. When V
the thermal shutdown temperature, the IC will stop switching. When V
CC
drops to UVLO, capacitor
C705 will be recharged to the Vstart level. If the temperature is still too high, VCC will drop again to
the UVLO level. (safe restart mode).
Drain (Pin 8)
Initially, the IC is self supplying from the rectified mains voltage via pin 8 (Drain)
the UVLO level. (safe restart mode).
Drain (Pin 8)
Initially, the IC is self supplying from the rectified mains voltage via pin 8 (Drain)
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 3
Control (Pin 3)
Burst Standby mode
The CTRL pin (pin 3) is also used to implement the burst mode standby. In burst mode standby, the
power supply enters a special low dissipation state, where it typically consumes less than 1W of input
power, but is still able to supply a microprocessor. The system enters burst mode standby when the
microprocessor turns on Q754 in the isolated side of the power supply which will result in the opto-
coupler, IC702 turning on, taking the control pin of the TEA1507 high. In response to this signal, the
IC stops switching and enters a ‘hiccup’ mode. This burst activation signal should be present for a
period, longer than 30 ms.
power supply enters a special low dissipation state, where it typically consumes less than 1W of input
power, but is still able to supply a microprocessor. The system enters burst mode standby when the
microprocessor turns on Q754 in the isolated side of the power supply which will result in the opto-
coupler, IC702 turning on, taking the control pin of the TEA1507 high. In response to this signal, the
IC stops switching and enters a ‘hiccup’ mode. This burst activation signal should be present for a
period, longer than 30 ms.
Hiccup Mode
The hiccup mode during burst mode standby operation does not differ from the hiccup mode in safe-
restart mode during a system fault condition (e.g. OVP or output short circuit).
restart mode during a system fault condition (e.g. OVP or output short circuit).
Demagnetization (Pin 4)
The system will be in discontinuous conduction mode all the time. The internal oscillator will not start
a new primary stroke until the secondary stroke has ended. Demagnetization features a cycle-by-
cycle output short-circuit protection by immediately lowering the frequency (longer off-time), thereby
reducing the power level.
Demagnetization recognition is suppressed during the first tsuppr time. This suppression may be
necessary in applications where the transformer has a large leakage inductance and at low output
voltages/start-up.
a new primary stroke until the secondary stroke has ended. Demagnetization features a cycle-by-
cycle output short-circuit protection by immediately lowering the frequency (longer off-time), thereby
reducing the power level.
Demagnetization recognition is suppressed during the first tsuppr time. This suppression may be
necessary in applications where the transformer has a large leakage inductance and at low output
voltages/start-up.
Overvoltage
An overvoltage (OVP) mode is implemented by sensing the voltage via the current flowing into pin 4
DEM during the secondary stroke. The secondary winding voltage is a well-defined replica of the
output voltage. Any voltage spikes are averaged by an internal filter. If the output voltage exceeds the
OVP trip level, the OVP circuit switches Q702. Next, the controller waits until the UVLO level is
reached on pin 1, VCC. This is followed by a safe restart cycle, after which switching starts again.
This process is repeated as long as the OVP condition exists. The output voltage at which the OVP
function trips, Vo(OVP) is set by the series/parallel network comprising of R706, R709, R710, R714
and D701
DEM during the secondary stroke. The secondary winding voltage is a well-defined replica of the
output voltage. Any voltage spikes are averaged by an internal filter. If the output voltage exceeds the
OVP trip level, the OVP circuit switches Q702. Next, the controller waits until the UVLO level is
reached on pin 1, VCC. This is followed by a safe restart cycle, after which switching starts again.
This process is repeated as long as the OVP condition exists. The output voltage at which the OVP
function trips, Vo(OVP) is set by the series/parallel network comprising of R706, R709, R710, R714
and D701
Overpower
This pin is also used to monitor the power that is being drawn 'Overpower Protection' (OPP) During
the primary stroke, the rectified mains input voltage is measured by sensing the current drawn from
pin 4 (DEM).
The current information is used to adjust the peak drain current, which is measured via pin 5 (I
the primary stroke, the rectified mains input voltage is measured by sensing the current drawn from
pin 4 (DEM).
The current information is used to adjust the peak drain current, which is measured via pin 5 (I
sense
).
The internal compensation is such that an almost mains independent maximum output power can be
realised.
realised.
Current Sense (Pin 5)
Short Winding Protection
After the leading edge blanking time, the short winding protection circuit is activated. If the ‘sense’
voltage exceeds the short winding protection voltage Vswp, the converter will stop switching. Once
V
voltage exceeds the short winding protection voltage Vswp, the converter will stop switching. Once
V
CC
drops below the UVLO level, capacitor C705 will be recharged and the supply will restart again.
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 4
This cycle will be repeated until the short circuit is removed (safe restart mode). The short winding
protection will also protect in case of a secondary diode short circuit.
protection will also protect in case of a secondary diode short circuit.
Overcurrent
The cycle-by-cycle peak drain current limit circuit uses the external source resistor (R715) to measure
the current accurately. The circuit is activated after the leading edge. The Overcurrent Protection
(OCP) circuit limits the ‘sense’ voltage to an internal level.
Typical Voltage at pin 5 <0.56v
the current accurately. The circuit is activated after the leading edge. The Overcurrent Protection
(OCP) circuit limits the ‘sense’ voltage to an internal level.
Typical Voltage at pin 5 <0.56v
Soft Start
To prevent transformer rattle during hiccup mode, the transformer peak current is slowly increased by
the soft start function. This is be achieved by inserting a resistor (R713) and a capacitor (C706)
between pin 5 (I
the soft start function. This is be achieved by inserting a resistor (R713) and a capacitor (C706)
between pin 5 (I
sense
) and the sense resistor (R715). An internal current source charges the capacitor
to a voltage that is derived from Iss X R713 to a maximum value of approximately 0.5 V.
Drive (Pin 6)
This is the drive to Q702 gate. the duty cycle of this signal is dependant on the conditions at the other
pins of the TEA1507. The driver circuit to the gate of Q702 has a current sourcing capability of
typically 125 mA and a current sink capability of typical 540 mA. This permits fast turn-on and turn-off
of Q702 for efficient operation. This low driver source current reduces Electro Magnetic Interference
(EMI) and also limits the current spikes across R715.
pins of the TEA1507. The driver circuit to the gate of Q702 has a current sourcing capability of
typically 125 mA and a current sink capability of typical 540 mA. This permits fast turn-on and turn-off
of Q702 for efficient operation. This low driver source current reduces Electro Magnetic Interference
(EMI) and also limits the current spikes across R715.
HT
R
EGULATION
D758 is a variable zener diode. When the voltage increases on the control pin the zener point fails.
This control pin is connected to the 150v rail via the potential divider network of R750, R751, R752
and R753. Therefore for an increase in HT D758 turns on earlier, which in turn will turn on the opto-
coupler IC702, turning off the power supply. For a low HT then the zener point of D758 increases
keeping IC703 turned off.
This control pin is connected to the 150v rail via the potential divider network of R750, R751, R752
and R753. Therefore for an increase in HT D758 turns on earlier, which in turn will turn on the opto-
coupler IC702, turning off the power supply. For a low HT then the zener point of D758 increases
keeping IC703 turned off.
IC702
D776
R744
1K
D754
R757
47K
D712
C12
D757
Q754
C753
0.27µF
D758
R742
47R
C751
1µF
R748
330K
330K
R752
4K7
R753
47K
R751
120K
120K
R750
120K
120K
IC751
+5v
CTL
IN
150v
IC1001 pin 33
(Standby)
14
13
Part
of
T703
+7.5v
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 5
S
TANDBY
During standby Q754 is turned on by the microprocessor which has the effect of connecting D757 and
D712 in parallel across D758. This will keep the opto-coupler (IC702) turned on, simulating an over
voltage condition. IC701 is now operating in burst mode.
D712 in parallel across D758. This will keep the opto-coupler (IC702) turned on, simulating an over
voltage condition. IC701 is now operating in burst mode.
S
ECONDARY
P
ROTECTION
In the event that a secondary supply rails fails due to excessive current or increases beyond safe
limits then this power supply is designed to return to the burst start-up mode.
limits then this power supply is designed to return to the burst start-up mode.
Q704
D712
Q701
R717
10K
R719
10K
D706
R723
2K2
R707
150K
R703
150K
D710
C15
R725
2K7
D708
R724
10R
+350v
IC701 Pin 4
(demag)
1
2
Part
of
T703
IC702
IC701 Pin 1
(vcc)
IC701 Pin 3
(ctl)
IC703
C714
22µF
C705
22µF
This is achieved by a supply rail monitoring circuit which consisting of Q751, Q752, Q753, Q762 and
Q759, and a control circuit consisting of IC703, Q701, D706 and D712.
The opto-coupler (IC703) is normally turned off. If it is turns on, then thyristor D706 will conduct,
turning on Q701. Q701 emitter is connected to power supply ground and its collector is connected via
D712 to IC701 pin 1 (VCC ). Therefore, while Q701 is turned on it is impossible for the voltage at
IC701 pin 1 (VCC) to reach its turn on threshold, hence the power supply remains in burst mode.
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