近期,在各种电子报刊上看到许多有关制作电话防盗装置的文章。经过认真探讨,发现有些朋友在设计电话防盗装置电路时,只考虑不影响电话机的拨号、通话功能,而忽视了电话机的收铃功能。目前普遍应用的是电子电话,其振铃功能是由话机内部的收铃电路对电信局发来的25Hz、90V的振铃信号进行降压、整流、稳压等处理后,去控制讯响器发出音频铃信号而实现的。电子电话机收铃电路大体分为两种,如图1、图2所示。从两个电路上可以看出电容Cl Recently, many articles on the production of telephone anti-theft devices have been seen in various electronic newspapers and periodicals. After careful discussion, I found that some of my friends in the design of telephone anti-theft device circuit, only consider does not affect the telephone dial-up, call functions, while ignoring the telephone set-bell function. Currently used in general is the electronic phone, the ringing function is by the phone’s internal ringing circuit to the bureau sent 25Hz, 90V ring signal to step-down, rectifier, regulator and other treatment, to control the signal speaker issued Audio bell signal and achieve. Electronic telephone ringing circuit can be roughly divided into two kinds, shown in Figure 1, Figure 2. From the two circuits can be seen capacitance Cl