Circuit Description; Power Supply; System Control - Grundig STR 600 AP Service Manual

Schaltungsbeschreibung / Circuit Description

Circuit Description

GB

1. Power Supply

1.1 General
The TOPSwitch family of the switched-mode power supply units
distinguishes itself by a minimum number of peripheral components
connected to the PowerMOSFET-IC1600 and a fixed switching fre-
quency of 100kHz. Control and error signal identification is exclusively
effected with a pulse width modulator (PWM).
IC1600 pin configuation
Drain Pin:
Drain output of the internal MOSFET transistor T1. Supplies the
internal current during the start-up phase via an integrated high-
voltage switch and is the current sense point via Z
Control Pin:
Error signal identification and control input for the internal shunt
regulator during normal operation. It is also the operating voltage input,
the trigger input for the protection and auto-restart stages.
Source Pin:
Source output of the internal MOSFET transistor T1. Primary-side
chassis return for the power supply unit and reference point.
1.2 Function
The supply voltage for the Drain of IC1600 is delivered by the rectifier D1600
via winding 11, 7 of the converter transformer TR1600. The electrolytic
capacitor C1612 charges to about 320V from a 230V mains supply.
On application of the operating voltage the internal oscillator starts to
oscillate. During the conducting phase of the IC, engery is stored in the
transformer which is fed to the secondary winding during the cut-off
phase. To hold the secondary voltages at a constant level, the Control
input of IC1600 (typ. 5.7V) is controlled by means of a reference
voltage via the optocoupler OK1601.
1.3 Control
An increasing load in the transformer causes all voltages to decrease
and with them also the voltage at the control amplifier TL431-(3) via the
voltage divider CR3050, CR3052. Consequently, less current will flow
through the cathode of TL431 so that the LED in optocoupler OK1601
becomes darker. The transistor between pin 4 and pin 5 becomes high
resistance. In proportion to the sawtooth voltage on pin 5 the voltage
decreases and consequently the conducting phase of the high-voltage
transistor T1 in IC1601 becomes longer. The voltage will increase.
With a short circuit in the secondary side, the current flowing through
the MOSFET rises and the built-in protection circuit triggers the power
supply unit at a cycle of 1-2 seconds. When the load is removed, the
power supply is started automatically by the Auto-Restart stage in the IC.
Diodes D1633, D1632 are provided to limit the voltage peaks of
overshoots at the Drain output of IC1600.
V C
Control
Z C
Shunt Regulator/
Error Amplifier
-
5.7V
T2
4.7V
+
5.7V
Externally
Triggered
Shutdown
Thermal
Shutdown
I FB
Oscillator
D
Max
Clock
SAW
PWM
Comparator
R E
2 - 4
.
C
0
Internal
Supply
1
Shutdown/
Auto-Restart
+
8
-
S Q
Power-up
R Q
Reset
-
S Q
+
R Q
1.4 Secondary Voltages
+33V: tuning voltage for SAT Tuner and modulator via diode
D1641.
+19V: LNC supply voltage via diode D1661.
+12V: supply voltage for signal processing, via diode D1691.
-12V: supply voltage via diode D1651 for setting the SKEW
IC1300.
+5V: supply voltage via diode D1681 for generating the +5V
OSD, for the modulator, motor control, the tuner and the
SKEW setting stage.
+5V/OSD: supply voltage for the OSD processor CIC1331 generated
from the +5V supply provided on CIC1331-(17).
+5VExt: external supply via diode D1672 from the connecting block
of the STR 600 AP.
+5V/D: supply voltage from the supplementary power supply
IC1601, TR3030, D3033 and IC3033 for µP CIC1401 and
the keyboard control unit.
1.5 LNC Switching Voltage 14/18V
The switching command U
14/18V
via transistor CT1675 and the linear control IC1655. The adjusting
control R1663 allows to increase the LNC higher voltage on request.
1.6 LNC Voltage Switch-off
For switching off the LNC supply, the switching voltage U
nects IC1655-(1) via CT1709 to ground.
1.7 Stand-by Mode
For changing to the Stand-by mode the switching command U
used to connect the Control input of IC1600 via OK1600 and CT1610
to ground. Consequently, the supply voltages of the secondary side are
switched off.
Power consumption of the satellite receiver in Stand-by mode < 2W.
1.8 The 22kHz Switching Frequency
The switching voltage U applies the 22kHz switching frequency,
22kHz
IC2100-(29), via CT1650, CT1710 to the linear control IC1650-(1). As
a result, the LNB voltage is superimposed with a 22kHz signal at about
600mVpp. This 22kHz output signal can optionally also be pulse-
modulated with a Simple DiSEqC Protocol.

2. System Control

This system contains an OTP or a mask-programmed microcomputer
(CIC1401) and the NVM-type EPROM CIC1141 for the programme
data like channel table, station ident, deviation, and so on. The
exchange of data between the µP and IC2100, CIC1331 and the SAT
Tuner is carried out on the I 2 C-bus and CS
Communication with the control unit is effected via the leads "DATA",
"CLK" and "ACK".
2.1 Pin Configuration of Processor CIC1401
Pin 30:
Power-on reset for the processor CIC1401 and IC86020 (keyboard
control unit), generated by IC1402. The programme sequence will not
start before all supplies of the receiver have built up.
Drain
+
V I
-
Limit
Controlled Turn-on
Gate Driver
T1
Leading
Edge
Blanking
Minimum
On-Time
Delay
Source
STR 600 AP
is used to switch over the LNC polarity
LNCOFF
Standby
.
OSD
Pin Configuration IC1725
DRAIN
SOURCE (TAB)
CONTROL
TOP201
Block Diagram IC1725
GRUNDIG Service
con-
is