Apparatus and methods for limiting sound volume
Exemplary embodiments or implementations are disclosed of methods, apparatus, and systems for a volume limiter circuit. A rectifier sub-circuit is configured to rectify at least a portion of an audio signal received from an audio source. A junction field effect transistor (JFET) has a channel connected in series between the audio source and a speaker. A feedback sub-circuit is configured to provide a gate signal at a gate of the JFET and to modulate a control signal in accordance with the audio signal crossing the JFET channel. The feedback sub-circuit is connected with the rectifier sub-circuit so as to extend a range of variable resistance of the JFET channel. The limiter circuit provides functionality that changes in response to varying audio voltages.
1. A volume limiter circuit comprising:
a half-wave rectifier sub-circuit configured to rectify at least a portion of an audio signal received from an audio source and to provide a negative control signal;
a junction field effect transistor (JFET) having a channel connected in series between the audio source and a speaker; and
a feedback sub-circuit configured to provide a gate signal at a gate of the JFET and to modulate the control signal in accordance with the audio signal crossing the JFET channel;
the feedback sub-circuit connected with the half-wave rectifier sub-circuit so as to extend a range of variable resistance of the JFET channel.
2. The circuit of claim 1 , further comprising a capacitor configured to be charged by the rectifier sub-circuit to a negative value to lower a voltage of the JFET gate.
3. The circuit of claim 1 , further comprising a limiting sub-circuit configured to limit the audio signal, the limiting sub-circuit having at least one pair of anti-parallel diodes in series with a resistance.
4. The circuit of claim 3 , configured to:
until the audio signal activates the rectifier sub-circuit, reduce voltage at the speaker using substantially only a series resistance;
when the rectifier sub-circuit has become activated, apply a negative voltage to the JFET gate through the feedback circuit; and
when the limiting sub-circuit has become activated, reduce voltage at the speaker through the limiting sub-circuit.
5. The circuit of claim 1 , further comprising a second JFET having a channel connected in series between the audio source and the speaker; and
a second feedback sub-circuit configured to provide a second gate signal at a gate of the second JFET and to modulate the control signal in accordance with the audio signal crossing the second JFET channel.
6. The circuit of claim 1 , wherein the feedback sub-circuit comprises a first resistance connected between the drain and gate of the JFET and a second resistance connected between the first resistance and the half-wave rectifier sub-circuit.
7. The circuit of claim 1 , further configured to:
(a) receive and conduct the audio signal to the speaker through a series resistance including the JFET channel;
(b) rectify a negative portion of the audio signal, and using the rectified signal portion to charge a capacitor; and
(c) limit the voltage of the audio signal, the limiting performed using a pair of anti-parallel diodes in series with a resistor; and
perform (a), (b) and/or (c) alone and/or together based on an input voltage of the audio signal.
8. A headset comprising the circuit of claim 1 .