In an actual application where a music signal is used, it is impractical to estimate the power dissipation based on the con- tinuous signal as shown above, because too large a heat sink must be used. It is reasonable to estimate the power dissipa- tion as 1/10 Po max. (EIAJ).
That is, Pd = 43W at 8 , Pd = 55W at 4 Thermal resistance c-a of a heat sink for this IC power dissipation (Pd) is ﬁxed under conditions 1 and 2 shown below.
Condition 1: Tc = Pd × c-a + Ta 125°C
Ta : Speciﬁed ambient temperature
Tc : Operating substrate temperature
Condition 2: Tj= Pd × ( c-a) + Pd/4 × ( j-c) + Ta 150°C
where Tj : Junction temperature of power transistor
Assuming that the power dissipation is shared equally among the four power transistors (2 channels × 2), thermal resis- tance j-c is 1.8°C/W and
Pd × ( c-a + 1.8/4) + Ta 150°C
Thermal resistance c-a of a heat sink must satisfy ine-qualities (1) and (3).
- °C/W Figure 3 shows the relation between Pd and c-a given from (1) and (3) with Ta as a parameter.
c-a [Example] The thermal resistance of a heat sink is obtained when the ambient temperature speci- ﬁed for a stereo ampliﬁer is 50°C.
Assuming VCC = ±35V, RL = 8 , VCC = ±31V, RL = 4 , RL = 8 : Pd1 = 43W at 1/10 Po max.
RL = 4 : Pd2 = 55W at 1/10 Po max.
The thermal resistance of a heat sink is obtained from Figure 3.
RL = 8 : c-a1 = 1.75°C/W RL = 4 : c-a2 = 1.35°C/W Tj when a heat sink is used is obtained from
RL = 8 : Tj = 144.6°C
RL = 4 : Tj = 149°C
A ﬁlter formed with R3 or R4 can be used to reduce noise at high frequencies.
Input coupling capacitors
Used to block DC current. When the reactance of the capacitor increases at low frequencies, the dependence of 1/f noise on signal source
resistance causes the output noise to worsen. It is better to decrease the reactance.
To reduce the pop noise at the time of application of power, it is effective to increase C3, C4 that ﬁx the time constant onthe input side and
to decrease C5, C6 on the NF side.
These capacitors ﬁx the low cutoff frequency as shown below.
f = 1
L --- [Hz]
2 C5 R5
To provide the desired voltage gain at low frequencies, it is better to increase C5. However, do not increase C5 more than needed because
the pop noise level becomes higher at the time of application of power.
Used to eliminate the ripple components that mix into the input side from the power line (+VCC). Bootstrap capacitors
When the capacitor value is decreased, the distortion is liable to be higher at low frequencies. Oscillation blocking capacitors
Must be inserted as close to the IC power supply pins as possible so that the power supply impedance is decreased to operate the IC stably.
Electrolytic capacitors are recommended for C9, C10.
Capacitor for ripple ﬁlter
Capacitor for the TR10-used ripple ﬁlter in the IC system Oscillation blocking capacitor
A polyester ﬁlm capacitor, being excellent in temperature characteristic, frequency characteristic, is recommended for C7.
Resistors for input ﬁlter Input bias resistors
Used to bias the input pin potential to zero. These resistors ﬁx the input impedance practically. These resistors ﬁx voltage gain VG.
It is recommended to use R5 (R6) = 560 , R9 (R10) = 56k for VG = 40dB.
To adjust VG, it is desirable to change R9 (or R10).
When R9 (or R10) is changed to adjust VG, R1 (=R2) =R9 (=R10) must be set to ensure VN balance.
The quiescent current is set by these resistors 3.3k + 3.3k . It is recommended to use this resistor value.
Resistor for ripple ﬁlter
Limiting resistor for predriver transistor at the time of load short
Used to ensure plus/minus balance at the time of clip. Resistor for ripple ﬁlter
When muting TR11 is turned ON, current ﬂows from ground to -VCC through TR 11. It is recommended to use 1k (1W) + 1k (1W)
allowing for the power that may be dissipated on that occasion. Oscillation blocking resistors
Interrupter Circuit STK 4192 Comparison / Similar / Equivalent is : STK 4142