Kenwood TH-28A Service Manual page 6

TH-28A/E
CIRCUIT DESCRIPTION
* Economic low-power circuit
The economic low-power circuit is used to send the
drive circuit output directly to the antenna without
passing through the power module. When this is done,
the bias power at the base of the power module is
turned off. This reduces the power consumption.
The E-LOW pin is made low when the transmission
output is set to EL. The transmission circuit then oper-
ates as follows:
1. Q210 and Q211 are turned off, and the 5V of the
power module is set to OV. D209 is turned off at the
same time and the power module output is opened.
LPF
iC202 POWER MODULE
CVI 5V cve OUT
D207
ON(OFF)
1
2 3
4
5 08
DRIVES, . MAIN RX
Our
59
ee
fl
i
OFF)
D208
Ore
on
ae
ON(OFF)
¢—_|__«
(OFF)
DC V
- ON(OFF)
=
o
AM
7
ON(OFF)
oot
ON(OFF)
Q210
ON(OFF)
Qe
——= Hi, Mid or Low power
ON(OFF)
="
EL (Economic low-power)
A A ( ):EL
5T
FB
EL
Fig. 7 Economic low-power circuit