Hearing aid with automatic excessive output sound control
View Patent ↗A technique is disclosed, which can shorten attack time and release time without using RC filter with time constant. According to this technique, diodes 51 and 52 rectify AC signal at output stage of an amplifier 30 by voltage doubler rectification, and a smoothing capacitor 53 smoothens the signals rectified by the diodes 51 and 52 . A transistor 41 of an attenuation circuit 40 turns on when DC voltage smoothened by the smoothing capacitor exceeds a predetermined level, and level of the output signal of the amplifier is attenuated by drawing the input signal of the amplifier.
1. A hearing aid with automatic excessive output sound control, the hearing aid comprising:
an amplifier for amplifying an input signal from an input transducer;
a rectifying circuit for rectifying an output signal of said amplifier;
a smoothing capacitor for smoothening direct current rectified by said rectifying circuit;
an attenuation circuit for attenuating the level of the output signal of said amplifier when a DC voltage smoothened by the smoothing capacitor exceeds a certain fixed level; and
a charging circuit for charging said smoothing capacitor when power turns on, wherein
said attenuation circuit comprises a first transistor, that turns on and draws the input signal of the amplifier when the DC voltage smoothened by said smoothing capacitor exceeds the certain fixed level.
2. The hearing aid with automatic excessive output sound control according to claim 1 , further comprising:
a second transistor to add bias to the base of said first transistor, wherein
said first transistor and said second transistor have the same characteristics.
3. The hearing aid with automatic excessive output sound control according to claim 1 , wherein said rectifying circuit comprises a plurality of diodes, and said rectifying circuit carries out a voltage doubler rectification.
4. A hearing aid with automatic excessive output sound control, the hearing aid comprising:
an amplifier for amplifying an input signal from an input transducer;
a rectifying circuit for rectifying an output signal of said amplifier;
a smoothing capacitor for smoothing direct current rectified by said rectifying circuit; and
an attenuation circuit for attenuating the level of the output signal of said amplifier when DC voltage smoothed by the smoothing capacitor exceeds a certain fixed level, wherein:
said attenuation circuit comprises a variable resistance and a first transistor, the variable resistance determines a signal suppression amount applied to the input stage of the amplifier, and
the first transistor turns on and draws the input signal of the amplifier when the DC voltage smoothened by said smoothing capacitor exceeds the certain fixed level.
5. The hearing aid with automatic excessive output sound control according to claim 4 , further comprising a charging circuit for charging said smoothing capacitor when power turns on.
6. The hearing aid with automatic excessive output sound control according to claim 5 , further comprising:
a second transistor to add bias to the base of said first transistor, wherein
said first transistor and said second transistor have the same characteristics.
7. The hearing aid with automatic excessive output sound control according to claim 4 , wherein said rectifying circuit comprises a plurality of diodes, and said rectifying circuit carries out a voltage doubler rectification.