GRUNDIG Service
2 - 9
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TVR 3710 …, TVR 5100 …,TVR 5500 …
Descriptions
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Description
1. Power Chassis (PLSP)
1.1 Power Chassis – Power Supply
Typical Data:
Mains voltage:
196…265V~
Mains frequency:
45…65Hz
Maximum power:
130W
Switching frequency: 30…85kHz
Efficiency:
80% at maximum load
Short-circuit protection provided for all outputs
Principle of the Blocking-Oscillator Type Transformer
During the conducting phase of the switching transistor T7330 energy
is transferred from the mains to the transformer. This energy is fed out
to the load during the phase the transistor is switched off. By means of
the switch-on period and the frequency the energy transfer during each
cycle is so controlled that the output voltages are independent of
changes in the load or the input voltage. Controlling and driving the
switching transistor is effected by IC7310.
The Different Load Conditions
– No-load operation (STANDBY / TIMER record programming):
From the power consumption the IC7310 recognizes no-load con-
dition and reduces the frequency to 30kHz to minimize the switching
losses at the Power-MOS transistor T7330.
– Normal operation (control range):
The switching frequency decreases along with the increasing load.
The duty cycle is mainly controlled by the mains voltage. The output
voltages are influenced by the load to a minor extent.
– Reversal point:
At this point of the output characteristic the maximum power is
transferred.
– Overload:
The power supply operates in Burst Mode (polling operation mode),
i.e. the energy of each cycle is limited so that the output power is low.
Circuit Description
The mains voltage is rectified by the bridge rectifier D6313…D6316
and filtered by C2315. L5311 is provided to protect the power supply
against interfering pulses from the mains. During the starting phase the
power for IC7310 is supplied to
Pin 1 via R3331 and C2310.
After the starting phase the
power is obtained from the
transformer winding 4 / 3 and
D6334. The inductance of the
primary windings 1 / 5…7 de-
termines the natural frequency
of the switched mode power
supply in normal operating
mode. The maximum frequency
is determined by C2327 at
IC7310-(10).
During the switch-on period of
the switching transistor T7330
the current of the rectified mains
voltage flows through the pri-
mary winding of the transformer
(contacts 1 / 5…7), T7330 and
R3334, R3335 to ground (in the primary side). Since the voltage at
contact 1 of the transformer is almost constant the current rises
linearly. The intensity of this current depends on the mains voltage and
the inductance of the primary winding. In the transformer, a magnetic
field develops which corresponds to a certain amount of energy.
During this phase, the diodes are cut off due to the polarity of the
secondary voltages. Via the resistors R3334, R3335, R3359 a voltage
which represents the primary current is fed to Pin 7 of IC7310. If this
voltage exceeds a certain level depending on the control voltage at
IC7310-(14), the switching transistor T7330 is switched off. This
process is repeated whenever the switching transistor T7330 is
switched on.
As soon as the switching transistor T7330 is switched off the energy
transfer to the transformer is stopped. The energy accumulated in the
transformer is now transferred to the secondary windings. Due to the
fact that the polarities of the voltages are reversed by the transformer
+U
U
GS
IC7310-(8)
-U
t
t
t
t
I
Dmax
Point of Reversal
U
DS
I
D
IC7310-(3)
T7330
T7330
current flows through the secondary windings of the transformer,
through the diodes, electrolytic capacitors into the load.
When the whole amount of energy stored in the transformer has been
transferred to the load and no magnetic field is left in the transformer,
the voltages at the secondary windings fall below 0V. These zero
passages are detected by IC7310 at Pin 8. The transistor T7330 is
switched on again and the next cycle is started.
Control of the switched mode power supply is effected by varying the
conducting phase of the switching transistor to the effect that the
energy transferred from the mains to the transformer is increased or
reduced. The control information is obtained from the transformer
winding 3 / 4 and is taken via D6335 / C2337 and R3356…R3358 to
Pin 14 of IC7310. The amplifier "ERROR AMP" IC7310 compares this
voltage with an internal 2.5V reference voltage. By means of this
comparison the level of the voltage used to be compared with the
voltage at Pin 7 of IC7310 (representing the primary current) is
changed.
During the period T7330 is switched off, C2332 / D6332 and C2331 /
R3345 limit the voltage peaks in the primary side.
To avoid static charges the gate of the switching transistor T7330 is
provided with the pull-down resistor R3339. The voltage at Pin 5 of
IC7310 is used for stepping down the current and the voltage in short-
circuit conditions (FOLD BACK).
The maximum power possible to be taken from the secondary side is
determined by R3334 / R3335. At 1V (typically) on IC7310-(7) the
power supply unit reaches the reversal point.
The external circuit at Pin 11 is an option of IC7310. By means of
C2320 the pulses in the start-up phase are shorter so that the switching
frequency is outside the audible range.
From the secondary side, eleven voltages (Ubat, 33A, 14H, 14/9M1,
14M1, 14M2, 9A, 5D1, 5D, 5A and -7V) are available which are rectified
and filtered by the respective components (diodes / capacitors / chokes).
In Standby mode, the 5D1, 5D, and 5A voltages are switched off by the
"STBY" switching voltage via T7351 / T7532.
The Start-up Phase
When connecting the video recorder to the mains the following
voltages at the pins of IC7310 start to rise at time t
0
(see fig.):
– The voltage V
cc
,
IC7310-(1), increases
according to the half-
wave charge via R3331
until it reaches the volt-
age level V
cc Start
at the
typical current con-
sumption (I
cc
) of 0.3mA.
The internal reference
voltage Vref
of IC7310
is switched on as soon
as V
cc Start
is reached
and the current con-
sumption increases to
17mA.
– The voltage at Pin 11 of
IC7310 rises linearly up
to 2.4V. During this pe-
riod, IC7310 drives the
Power-MOS transistor
T7330 by shortened
pulses.
– If the voltage V
cc
,
IC7310-(1), falls below
the limit value V
dis2
be-
fore the reversal point is
reached the start-up is
stopped. For this, the
drive to T7330 is
stopped and IC7310
switches off the internal
V
ref
(I
cc
= 0.3mA). The
voltage Vcc increases according to a half-wave charge via R3331.
The next start-up cycle commences.
Normal Operation, Overload and Standby Operation
As soon as the power supply stage is working, IC7310 operates in the
normal mode (control range). The voltage at IC7310-(14) is 2.5V
(typically). If the load in the secondary side increases, the switch-on
period of T7330 is increased. As a result the peak voltage value at
IC7310-(7) "representation of drain current" increases.
IC7310-(1)
IC7310 int.
IC7310 int.
IC7310-(11)
IC7310 int.
IC7310-(3)
IC7310-(1)
V
cc
V
cc prot
V
cc start
V
ref
V
dis2
V
dis1
V
pin11
UVLO1
V
ovp out
Output
I
cc
17mA
0,3mA
No-Take Over
Re-Start
Start-Up
Normal Mode
Loop Failure
>2ms
t
t
t
t
t
t
t
