Re: Boost the ringer current instead of ...
I have (I hope) attached a reverse-engineered (by me) circuit diagram of the ringer booster that was commonly sold in the UK some years ago (maybe BT-badged).
Note that the opto-isolator is a rather odd one with a very high current transfer ratio (ratio of LED current to output current). It will not work with just 'any old optoisolator'.
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