| 摘要 |
<p>The circuit includes a pair of controlled transformerless current sources that supplies DC current to a tip lead (T) and ring lead (R) respectively. Each current source includes high gain NPN and PNP transistors (Q1,Q2), whose collectors terminals are connected to ground (GND) and voltage source (V1) respectively. The current source also includes base terminals which are connected to ground and voltage source respectively. Emitters in the current source are connected to respective leads. A pair of control circuits senses the voltage across the respective current sources and controls the current source to supply current that is inversely proportional to sensed voltage. The control circuits controls the current sources to interrupt current supply when sensed voltage exceed predetermined voltage.</p> |
