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BE
PMA.S2
SAF 2S Re
a a
a
a
Te
ETT,
FUNCTION OF NEW CIRCUIT
1. CHARACTERISTIC OF THIS CIRCUIT
The junction temperature of power amplifier output transistor always varies by an ambient temperature and music signal.
Occurrence of junction temperature varying causes in change of bias current, unstable function, thus pure music signal
playback is unable to do.
To maintain fixed bias current and to make pure music signal playback possible is the purpose of this circuit. This circuit
holds stable bias current condition within a few seconds after turning on the power.
2. BLOCK DIAGRAM OF BIAS CONTROL CIRCUIT FUNCTION
As explained in Fig. 1, detects a voltage across the emitter resistors (RE) of TR1, TR2. Converts the detected voltage and
comparing with the reference voltage to make the bias current value in stable state. Actually, these functions are performed
by 1 chip IC.
.
oo 1 Chip IC
TR1, TR2: Output transistor
RE
: Emitter resistor
Fig. 1
3. POWER SUPPLY FOR ACTUATING CONTROL CIRCUIT
TR
- [ 5,
> ToIC (V*)
The circuit (IC) controlling bias current actuates by
Power supply circuit
floating.
RE
Output
Accordingly, the power supply is also needed to be
floated.
In this circuit, as indicated in Fig. 2, output is common
Fig. 2
10
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