Power Supply - Kenwood TK-2118 Service Manual

TK-2118
5) APC
The automatic power control (APC) circuit stabilizes the
transmitter output power at a predetermined level by sensing
the drain current of the final amplifier Field Effect Transistor
(FET) . The voltage comparator, IC3 (2/2), compares the
voltage obtained from the above drain current with a reference
voltage which is set using the microprocessor. An APC
voltage proportional to the difference between the sensed
voltage and the reference voltage appears at the output of IC3
(1/2). This output voltage controls the gate of the FET power
amplifier, which keeps the transmitter output power constant.
The transmitter output power can be varied by the
microprocessor which in turn changes the reference voltage
and hence, the output power.
6) Terminal protection circuit
When the thermistor (TH1) reaches about 80˚C, the
protection circuit turns on Q14 to protect transmitting final
amplifier (Q22) from the over heating.

5. Power supply

The battery power source is internally regulated by the circuit
(IC305) and outputs 3.5V DC (3.5V).
This 3.5V DC (3.5M) is also supplied to the microprocessor
(IC300) and reset IC (IC304).
In the meantime, the microprocessor and switching
transistor also generate a [3.5MS] reference voltage from this
sources.
This reference voltage is used for the following DC power
sources:
3.5V DC (3.5R for the receiver, 3.5C for both the receiver
and transmitter) 5.0V DC (5R for the receiver, 5T for the
transmitter, and 5C for both the receiver and transmitter).
6. Control system
The microprocessor (IC300) is operating at a clock of 7.37
MHz. The clock oscillator has an additional circuit to shift the
oscillating frequency, using a switching transistor (Q303) to
remove the internal beat interference that may be caused by
this oscillator. This microprocessor controls the LCD display,
key operations, PLL data and other various functions.
TK-260 :K, K2
16
CIRCUIT DESCRIPTION /
电路说明
5) 自动功率控制
自动功率控制 (APC) 电路,通过测检末级放大器场效应管的
集极电流来稳定发射的输出功率。电压比较电路, IC3 (2/2) 用微
处理机设定的参考电压来比较从末级电流所获得的电压。自动
功率控制电压与IC3 (1/2) 输出的自动检测电压和参考电压之间
的差值成正比。此输出电压控制场效应管功率放大器，保持发
射部输出功率常数。发射部输出功率可以通过微处理器进行改
变，在微处理器中改变参考电压来控制输出功率。
6) 温度保护电路
当热敏电阻 (TH1) 的温度达到80℃时，保护电路开启Q14来
保护末级放大器避免过热。
5.电源
电池电源由电路 (IC305) 内部调整并输出3.5V直流。
3 . 5 V 直流 ( 3 . 5 M ) 也提供到微处理器 ( I C 3 0 0 ) 和复位I C
(IC304)。
同时，微处理器和开关晶体管也从该电源生成[ 3 . 5 M S ] 参考
电压。
该参考电压用于以下直流电源：
3.5V直流 (3.5R用于接收，3.5C用于接收和发射) 5.0V直流
(5R用于接收，5T用于发射，5C用于接收和发射)。
6.控制系统
微处理器（IC300）正在7.37MHz时钟下运行。时钟振荡器有
其它电路转换振荡频率，并使用开关晶体管（Q303）来消除可
能由该振荡器引起的内部拍频干扰。该微处理器控制L C D 显示
器、按钮操作、锁相环电路数据和其它各种功能。