| 摘要 |
PURPOSE:To protect the output transistor(TR) from being damaged without complicating the circuit by using a thermosensing element to detect an overload if an output TR is overloaded to open the output TR. CONSTITUTION:A charging circuit 20 employing an photelectromotive force type photodetector 21 is provided to a relay circuit 50 and the photoelectromotive force of the photodetector 21 charges a gate of the output TR 10 when the optical signal is given to close the TR 10. A discharge circuit 30 is provided in parallel with the charging circuit 20 to open the output TR 10 when the optical signal is lost. The temperature of the output TR 10 is detected by the thermosensing element 40 and when the temperature exceeds the prescribed value, the discharge resistance of the discharge circuit 30 is decreased to open the output TR 10 regardless of the blinking state of the optical signal. |
