I am attempting to build a ringer interface circuit, and I’m running into problems that are over my head. The purpose of the circuit is to buffer the output of a central telephone system that goes to several ringers spaced throughout the building. The reason for the circuit is that whenever the line rings, it overloads and needs to be reset, thus this circuit will buffer the line and offer a lot more output capability.
The schematic is below:
EDIT: R7 goes to +24V, not +12V
Now, my problem is this: when everything is on, and the line is ringing (4N27 triggered), I only get 12V out , instead of 24. I went through and checked voltages, and it seems like none of the transistors are turning on (or off as the case may be) completely. When I tie the base resistor of the first (closest to the 4N27) signal transistor to ground (turning it 100% off), I then get the correct 24V out.
Also, it exhibits the same problem with a 5V supply, so I don’t think that’s it.
Anyone have any ideas as to what may be causing this? I’m a bit of a novice at circuit design, so any and all help is much appreciated.