Philips 37PF9631D/37 Service Manual page 109

Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.2.2 Over-Current Protection
If an over current error occurs (short-circuit on the output),
transistors 7D30 and 7D12-1 will conduct and 7D12-2, 7D26-2
and 7D26-1 will block. This causes the MUTE output to be
Over Current Protection + Mute
Under-volt supply
protection (18V)
"HIGH': SOUND DIS ABLED
"LOW": SOUND ENABLED
OVER-CURRENT PROTECTION
SIGNAL LEVELS
During start-up, diode 6D11 is blocked causing transistors
7D12, 7D26-2 and 7D26-1 to be blocked. MUTE is then "high".
This prevents an audio plop during start-up. When supply is at
normal level, diode 6D11 will conduct causing transistors
7D12-2, 7D26-2 and 7D26-1 to conduct as well. A sound mute
is then depending on the signal on the SOUND_ENABLE line:
"high" causes a sound mute (MUTE is "high") and "low" causes
sound enabled (MUTE is "low").
6D11
L
3D24
10k
H
3D82
7D25-1
47k
2D51 3D83
1n 47k
3D26
2k2
7D12-1
Amplifier output
Figure 9-7 Over-current protection and sound mute
"high". See figure "Over-current protection and sound mute" for
details. The arrows indicate the signal levels during over-
current protection active.
If mute 2V to 4V
In play mode = 0V
3D25
3D85
47k
47k
7D25-2
3D75
3D84
47k
47k
7D26-2
H
3D42
47k
H
3D87 3D86
47k 47k
7D12-2
L
7D26-1
3D88
33k
3D77
22k
7D30
3D23
2k2
3D60
EJ2.0U LA 9.
- MUTE ACTIVE: 2V TO 4V
- MUTE NOT ACTIVE: 0V (PLAY MODE)
0R1
G_15940_066.eps
260506
EN 109