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HA998ⅡP型电话机是一种全电子脉冲按键电话机,它具有全电子化自动音量控制、电子式双音频振铃、增音以及闭音功能与重拨、暂停等功能。图1所示的是HA998ⅡP型电话机的电路原理图。一、工作原理当用户摘机后,交换总机通过外线传送过来的直流电压加到由二极管V6—V10组成的极性转换电路中去,将其改变为极性固定的工作电压供给拨号电路与通话电路工作。此时由于有启动电阻R18的作用,所以给三极管V16及V18提供了一个正向偏置电流,
HA998 Ⅱ P-type phone is a full electronic pulse button phone, it has full electronic automatic volume control, electronic dual tone ringing, increasing and closing function and redial, pause and other functions. Figure 1 shows the circuit diagram of the HA998ⅡP telephone. First, the working principle When the user picks up the machine, the switchboard through the external transmission over the DC voltage added to the diode V6-V10 formed by the polarity of the conversion circuit to change it to a fixed operating voltage polarity supply dialing circuit and the call Circuit work. At this point due to the role of start-up resistor R18, so to the transistor V16 and V18 provide a forward bias current,