Power circuit for condenser microphone

Power circuit for a condenser microphone capable of automatically switching both internal power source and external power source without carrying out the switching operation of a switch.

A positive side output line comprises a power switch for turning off the positive side output line to selectively connecting it to a ground side output line; a first diode connected with an input direction from the external power source being a forward direction between the power switch and an output terminal of the positive side output line; and a capacitor connected parallel with said power switch and said first diode so as to bypass them, a series circuit comprising the internal power source, a second diode and a load resistor with a direction from the ground side output line to the positive side output line being a forward direction being connected between a connection point of the power switch and the first diode and the ground side output line.

The condenser microphone is provided with a microphone unit including diaphragms arranged opposedly at predetermined intervals and a fixed electrode, and is widely popularized irrespective of general public welfare or business because of high fidelity of sound and easy miniaturization thereof.

The microphone unit requires an electronic circuit for removing a voice electric signal according to a sound wave and a driving power source. The driving power source is roughly divided into a built-in type in which a power source is mounted on a microphone body and an external supply type. For the general public welfare, generally, the former is of a battery driving system, and the latter is of a plug-in power system in which power is supplied from apparatuses to be connected, for example, a tape recorder, a mini-disk recorder, a video cam coder, etc.

It is an object of the present invention to provide a power circuit for a condenser microphone which can automatically switch both an internal power source and an external power source, without carrying out troublesome switching operation of a switch, and which can further miniaturize a microphone body and can reduce the cost.

A power circuit for a condenser microphone according to one embodiment of the present invention comprises a microphone unit; either internal power source or external power source for supplying a DC operating power through a positive side output line and a ground side output line of the microphone unit; said positive side output line comprising a power switch for turning off said positive side output line to selectively connecting it to said ground side output line; a first diode connected with an input direction of said external power source from said output terminal being a forward direction between said power switch and an output terminal of said positive side output line; a capacitor connected parallel with said power switch and said first diode so as to bypass them; a series circuit connected between a connection