Philips FW-C50/37, Руководство по обслуживанию

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+12V-regulator
(pos. numbers refer to circuit diagram chapter 11-9)
Is used to supply all motors (+12M) and all analogue circuits (+12A) in the set. +12C is provisional only.
• Power on/off:
Switching on/off is done via the STBY-line from the microprocessor. H=ON, L=OFF
If the STBY line is high - transistor 7222 is conductive. Base of 7224 becomes less positive than the emitter.
This causes transistor 7224 to switch trough and supply the base of 7221. Consequently 7221 swiches trough
too.
Via 3218 transistor 3228 is conductive as soon as B2 is available. Consequently switching transistor 7227 is
also switched through.
If the STBY line is switched to low level base current for 7222 is blocked. In turn 7224 and 7221 are blocked. >>
OFF.
• Regulation:
Key components are power-transistor 7221, reference diode 6221 and transistor 7223.
After power is switched on via the STBY line as described above the +12A increases until 7223 becomes
conductive via reference diode 6221 >> 7223 reduces base current of 7221 >> +12A is stable (t12,4V).
In normal operating mode 7227 is always switched trough as described above.
• Protections:
In case of overcurrent (typical 2,5A) 7227 gets out of saturation >> 7226 becomes conductive >> 7225 becomes
conductive via 6225 >> 7228 is blocked (no base current anymore) >> 7227 is blocked too no +12V.
Restarting is only possible with power OFF>>ON.
In case of overvoltage (more than +15V on emitter of 7221) 7225 is now activated via 6233 >> 7228 is blocked
(no base current anymore) >> 7227 is blocked too >> no +12V.
These protections are implemented for saving the set-electronic in any fault-condition.
-30V-regulator
• Grid supply for the FTD switched by the microprocessor.
Simple regulation with 6251 as reference. Typical value: -29V. Maximum current: 30mA
VCD- Supply:
Is a provision for versions with a Video CD Player.
This circuitry consists of a switched supply with a regulator to 5,1V (±0,15V).
• Switching on/off is done via the VCD_ON line from the microprocessor (H=on, L=off). If the VCD_ON line is
high - transistor 7236 becomes conductive. This causes transistor 7238 to switch through. +5VCD is available. If
the VCD_ON is low - transistor 7236 is blocked >> no base current through 7238 >> transistor 7238 is blocked
too >> +5VCD is switched off.
• Regulation is done via Z- diode 6244 and transistor 7237.
If the +5VCD exceeds 5,1V the basis of transistor 7237 becomes higher than 0,6V via Z- diode 6244.
Consequently transistor 7237 becomes conductive. This causes a reduced base current through 7236. Transistor
7236 becomes less conductive and reduces the base current trough 7238. Transistor 7238 becomes less
conductive too and reduces the +5VCD.
Amplifier:
Attention: In the POWER 4 module the power amplifier IC AN7164 is used as a bridge-amplifier.
Any connection from output to ground will destroy the outpout stages!
• Via the AMP_ON control line, connected to pins 6 (Stby), the power amplifiers are switched on/off by the µP.
High level (approx. 4,5V): power amplifiers switched on
Low level (approx. 0V): power amplifiers switched off