op amp ringer circuit old telephone

Posted on Feb 6, 2014

In the process of adapting an old phone to be used as an Bluetooth phone. I am currently testing the ringer circuit, which I build using the schematics provided by Sparkfun. Now, when I hook up just the right part of the schematic to a 3. 5V source (Vcc), I get a nice 45V on the output (with a steady current draw of about 130mA). But as soon

op amp ringer circuit old telephone
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as I connect this to the ringer part, I measure an output voltage of only about 7 volts. Increasing Vcc keeps the `45V`-voltage at about twice the Vcc. I have to turn up Vcc to about 9V to get the `45V`-voltage to about 18V, and then phone rings if I set RING1 and RING2 alternately to high (alternating at roughly 20Hz). It is not very loud, but it does work. My question: why do I measure a lower voltage at the 45V output when I connect the ringer circuit Why does this drop to a lot lower values I don`t want to need to provide 10V to the schematic, for what I know it should run on 3. 5V.

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