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本文介绍的电话防盗报警器具有元件少、组装方便及性能稳定的特点。 防盗报警器电路图如附图所示。其工作原理为: (1)当外线正常时:①在挂机状态,L1与L2之间电压为48V左右,12V稳压管VD5导通,A、C之间电压为1.4V左右,三极管V1导通、V2截止,微型直流音响器不能发声报警。②在摘机状态,L1与L2之间降至10V以下,此时稳压管VD5不
This article describes the telephone anti-theft alarm with fewer components, easy assembly and stable performance characteristics. Burglar alarm circuit as shown in the figure. Its working principle is as follows: (1) When the outside line is normal: ① In hang up state, the voltage between L1 and L2 is about 48V, the voltage regulator of 12V is on, the voltage between A and C is about 1.4V, Pass, V2 deadline, miniature DC audible alarm can not sound. ② In the off-hook state, between L1 and L2 down to 10V below the regulator VD5 at this time is not