Circuit Operation Of Cordless Base Unit - Panasonic KX-F900 Service Manual

13-4. CIRCUIT OPERATION OF CORDLESS BASE UNIT
I KX-F900
(1) Power Circuit (charging circuit power supply)
Pins 1 and 8 are switcl4ed in the clock period which is determined by capacitor C559 connected to pin 3 of the
switching regulator IC (IC504). The switching output turns Q509 ON or OFF and reduces the 24V voltage to 12V.
Pin 5 of IC504 is the feedback input pin whose input signal is used to stabilize the output voltage.
Circuit Diagram
VT(12V) +24v
_J502 0 ANALOG
CN501
(1,2)
L519
O
o
_8
Q509
nr"
I I IC504
÷ co
Z
- O
(2) Charge Circuit
When the portable handset is places on the charging stand, Q505 is turned ON, and the charging information is
supplied to MPU pin 37 as a logical high signal. When the charging information is supplied to the MPU, the MPU
sends the ID signal from pin 44. This ID signal switches Q506, and it is supplied to the portable handset via the
charging pin of Q506. In the same way, when the spare battery is inserted into the charging stand, Q508, is
turned ON, and the charging information is supplied to MPU pin 36. When both the portable handset and spare
battery are to be charged, the MPU outputs a logical low signal from pin 27 which turns Q507 OFF and also turns
Q510 OFF, thereby limiting the charging current to the spare battery. When only the spare battery is to be
charged, the MPU outputs a logical high signal from pin 27 which turns Q507 and Q510 ON so that the charging
current is increased.
Circuit Diagram
CN503
@
R535
R539
C511 R540
I cs, l 7"
T
T ( _-'_Q506
C513 - '
l _ _________4 R543
.,_R551
R546 R545
At# 'W_
'.fT
R534 D503vt I
Q505
D504 R541
R542
Q508 _07
D506 R549
D505 w
,., I
1' R599
R548
44
37
27
"_R550
MPU
(IC501)
o
o
C
-I
0
"O
m
"-4
O
Z
-173-