Sansui AU-X1 Service Manual page 4

i
AU-X1
• The relation between switching time, fT and hFE.
(x,
ll, 0,.
showing the quantity of transistor & distribution)
10
Fig. 7
Fig.
6
(NPN)
50
tstg- h FE
(NPN)
30
i
20
' i l. 2
~
.;:;
~
10
0.5
3
0.3
10 30 50
lOO
300 IM 3M 5M
hFE(5V/IA)
Next, the following Figs show that the relation between high fT of
power transistor and short periode of tstg influences the improve-
ment of distortion (THD) effectively in audio amplifier.
Fig. 9),
10)
show the THD becomes better when tstg is faster.
Fig. 11), 12) illustrate the relation between output current wave-
form of emitter and distortion wave-form. From these Figs, it is
• OutPl,lt wave-form & distortion wave-form near at clipping point.
O.l%range
IOV/div
Fig.9
T.H.D. 0.1%
t
stg = 1.6,us
I
switching distortion
• Wave-forms of emitter current and distortion
(con dition )
Po~ 40W
Fig. 11
RL ~ 8fl
.-
f ~ 50KHz
lE
wa veform ( NPN )
2A/DIV
lE waveform( PNP)
monitor waveform of
distortion meter
0.1
%
range
O.5V/div
T.H .D. 0052%
fT(NPN/PNP) = 4.0/8.0MHz
NPN
tf- IT
Fig. 8
tON- fT
1.0
(NPN)
0.5
\
!
0.3
5
0.2
0.1
0.05
IOM 30M 50 M lOOMz
IM 3M
5M IOM 30M SOM lOOMz
fT(5V/IA)
fT(5V/IA)
obvious when the fT of power transistor is low the output current
wave-form becomes dull, and the switching function at B class push-
pull operation is not performed precisely .
These above phenomenon causes the increase of ope rating current
and deterioration of distortion.
Fig. 10
T.H.D. 0.035%, tstg
=0.5,us
Fig. 12
T.H.D. 0025%
fr
(NPN/PNP) = 30/21MHz
NPN
d\A}
v
~L-
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