Siera CTS-AA, Руководство по обслуживанию

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- Output regulation (pins 1, 2, 8): IC7514 stabilizes output voltage by controlling T-on and so the frequency and the duty
cycle.
Start pulse to T7525 is determined by pin 8 circuit (see fig 7.5).
Then a sawtooth voltage V2 is generated at pin 2. Stop pulse to T7525 is produced when V2 reaches Vcont.
Output control is done by the following way:
If output is higher, V1 is higher, Vcont is lower, T-on and output will be reduced.
If output is lower, output will be increased.
Output voltage of supply can be adjusted by R3518.
Mains voltage variation is stabilized in the following way:
If mains voltage is higher, slope in the sawtooth voltage V2 is higher, stop point is reached before and T-on is
reduced.
If mains voltage is lower, T-on is increased.
7.5.3 Protections
- Overload protection (pin 2): This is produced if T-on is increased till V2 voltage reaches the foldback point (see fig 7.5).
The IC will switch into overload mode (off and on continuously).
- Output voltage protections (pin 6): Limiting values of V6 voltage (7.25V and 16V) provide under and overvoltage protections
for the circuit.
- Mains overvoltage (pin 3): The voltage at pin 3 IC7515 is a measure for the mains voltage and so the DC voltage across
C2505. As soon as the voltage V3 reaches 6.6V, the supply will stop running.
7.5.4 Secondary side
- Line supply: Line supply present at capacitor C2530 should be adjusted to the correct value (depending on the
TRC) by means of P3518. This supply is also used to 33V varicap voltage by D6602 (see diagram E).
- Sound supply (+11V): This supply is used for sound output amplifier and to feed following stabilizers.
- +8V stabilizer: A reference voltage obtained by a resistor divider R3503 and R3505 is amplified in T7501 and T7502
transistors till diode D6572 conducts stabi8V output. When the set switch to stand by, standby voltage is 0V,
then T7501 is cut, and +8V is reduced to 0V.
- +5V stabilizer: +5V for small signal is made by and D6573 T7577 circuit. R3577 is connected to +8V to switch off +5V
when the set is in stand by mode.
- +5V stand by: +5STB is regulated by T7575 and D6570. A positive power on reset signal (POR) is obtained in the
collector of T7571, which one is cut during start up till R3576 has 0.6V.
Figure 7.5 Power supply signals