Sharp SD-AT50H, Service Manual

Page: 43 / 76

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SD-AT50H
WAVEFORMS OF 1-BIT CIRCUIT
T
2
1
2.00V/div
500 ns/div 194.545465
µ
s 520 mV
2.00V/div
AD IC Output
+ Side
- Side
5 V
Amplitude
from 0 to 5 V
1
2
T
10.0 V/div
500 ns/div 194.545465
µ
s -12.3 V
10.0 V/div
+ SIDE
+ FETOUT
- SIDE
Waveforms before low-pass filters at both
ends of the speaker.
H-bridge may be considered as BTL.
However, here and at the gate drive, dead
time is not observed; since bootstrap
operates based on output, DEAD TIME
part is in floating condition. The waveform
on the HIGH side shows that only the
booted voltage lowers.
2
1
11
12
2
1
2.00 V/div
500 ns/div 194.545465
µ
s -12.30 V
2.00 V/div
AD IC NF IN
In partial pressure OUT, 4 to 7 V amplitude
of GND reference is observed.
In IC of 75 kohms, the reference is 2.5 V
because of VREF. Due to imaginary GND
of operational amplifier inside IC, the
waveform cannot be monitored.
This waveform is partial pressure OUT.
3
4
T
2.00 V/div
50.0 ns/div 0.0 s -12.30 V
2.00 V/div
LEVEL SHIFT OUT
DEAD TIME
ZOOM UP
Dead time is generated by level
shift input.
Leading edge is delayed at CR,
passing R at DI.
Set value: 20 - 25 nsec.
5
6