| 摘要 |
PURPOSE:To protect effectively a load from an abnormal voltage by making a large current flow and melting a fuse, by operating a bias circuit by an integral output of a power amplifier output, and applying the forward bias to an output transistor. CONSTITUTION:When a DC voltage of plus has been generated in an outut terminal of a common emitter of complementary transistor (Tr) Q1, Q2, this output is detected by an integration circuit of a capacitor C3 and a resistance R1, this output is provided to an input terminal 7 of a bias circuit, and a current flows to a TrQ4. Accordingly, the forward bias is applid to the base of the TrQ2, but since the potential of an input terminal 3 is fixed, a large current flows through the Trs Q1, Q2 from a power source, a fuse F1 of a power source transformer T1 is melted and an AC power supply voltage is cut off. Accordingly, a load RL can be protected from a breakdown by cutting the DC voltage generated in the output terminal of the common emitter of the Trs Q1, Q2. |
