The principle functions carried out by the circuit are to chop the DC
voltage at a frequency of 62.5 kHz, to transform and rectify so that the
load relationship is correctly maintained on the secondaries.
The inductance (L) is connected to the DC voltage source (U,) viaa
switch (S) activated by a control circuit, so that during the conduction
phase of the switch a linear rising current in the inductance causes a
magnetic field to build up and for energy to be stored. The rectifying
diode (D) is cut off and decouples the secondary jcad from the input
circuit. After the switch is open, the EMF becomes effective, the diode
conducts and connects the load and the charging capacitor to the
inductance.
The expanded basic circuit as used in the television sets
In this expanded circuit a transformer takes over the function of the
coil; the switch is replaced by a transistor, The energy source for the
secondary is during the switch-off phase of the transistor via the diode
(D). This switch-moade power supply with line-frequency synchroniza-
tion assures a very high stabilising factor due to variation of the duty
cyle.
The appropriate upper and lower limiting values are fixed by the circuit
and by physical values.
Primary Side
In this line-frequency-coupled blocking-oscillator converter mains
stage the IC 6100 takes over the function of driving the MOS power
transistor T 634 as well as all control and monitoring functions. The
power supply of IC 6100 is provided on pin 9 via the resistor R 637 and
diode D 637 until the switch-on threshold is achieved. After start-up
the supply voltage is obtained via the diode D 634 and the resistor L
634 from the winding 11/9 of the converter transformer.
The serial circuit of the power transistor T 634 and the primary winding
5/1 of the blocking oscillator converter is connected to the rectified
mains voltage (C 626). During the conduction phase of the transistor
energy is stored in the transformer; this energy is transferred via the
secondary winding during the switch-off period. The !C 6100 controls
12
Overload cut-out circuit
lf the power from the mains supply circuit exceeds the permissible
level the voltage dropped on the test resistor R 627 increases and
turns on the transistor T 6140. Pin 5 of IC 6100 is thus connected to
chassis level and the mains supply unit switches off.
Due to the mains isolation, a data transfer from the secondary to the
primary side is only possible via optocouplers.
Stand-by mode
On stand-by mode the biocking-oscillator converter mains stage is
completely switched off by the stand-by function of iC 6100/TDA 4601
(pin 5; < 2.1 V). The base of transistor T 6130 is taken to HIGH.
Consequently, all secondary voltages are absent.
Due to this circuit concept the power consumption on stand-by mode
is reduced to about 8 Wh.
To allow the operating control unit to be in operation a separate mains
supply is used to generate the +5V voltage (+H). It supplies the
operating voltage for both processors iC 860 and IC 810.
IC 810 (pin 8) drives the blocking-oscillator converter mains stage via
the stand-by lead and evaluates the data of the IR pre-amplifier (IC
1201). Communication between the master processor IC 860 and IC
810 is accomplished via the lead "IR Data" and "IR Clock" (pin 39, 11).
