| 摘要 |
PURPOSE:To realize an amplifier protective circuit of the BTL (Balanced Transformer Less) system by setting the detection point at the loard side where the DC potential varies at the normal operation time and the abnormal operation time such as the short circuit or the like. CONSTITUTION:The serial connection of the equal impedance 7 and 8 are provided in parallel to load 3 between the output ends of amplifiers 1 and 2, and the DC at contact (a) is connected to the reverse input side of comparator 9. The potential at contact (a) features the fixed output potential of amplifiers 1 and 2 regardless of the AC output waveform. And if this potential is set to VCC/2 against power voltage VCC, contact (a) features 1/2 AC output, i.e., VCC/4 or less in case load 3 (speaker) is short-circuited to the earth potential by some reason. This is detected by comparator 9, and transistors 10 and 11 are turned off to bias the current flowing into amplifiers 1 and 2. Thus the protection is ensured for amplifiers 1 and 2. |
