| 摘要 |
PURPOSE:To prevent a switching element from breaking down without deteriorating switching characteristics, by providing a resistor for overcurrent detection in LPF. CONSTITUTION:A sound signal from input terminal 1 is supplied to load 14 by way of pulse-width modulation circuit 3, a pulse-width-modulated signal amplifier and LPF13. Here, resistor 15 for overecurrrnt detection is provided in LPF13. Further, transistors TR17 and TR18 are transistors for detecting forward and backward overcurrents. Now, since a current flowing through resistance 15 is below a prescribed value in an adequate load state, the input signal from terminal 1 is not limited at all. However, the current through resistance exceeds the prescribed value in an overload state, and consequently either of TR17 or TR18 turns ON while TR22 and FET23 also turn ON. Therefore, the input signal is never supplied to circuit 3. Thus, switching elements 11 and 12 can be prevented from breaking down without deteriorating switching characteristics. |
