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 point of said power switch and said first diode and said ground side output line, said series circuit comprising a second diode and a load resistor with a direction from said internal power source and said ground side output line to said positive side output line being a forward direction; and means for switching a drive power source driven by an external power source from an external apparatus when in a plug-in power.
In a further embodiment, the power switch is removed from the above-described embodiment, and the internal power source and the plug-in power from the external apparatus are automatically switched.
With the constitution described above, the internal battery and the external power source (plug-in power) can be used in common.
Even if the internal battery and the external power source are used in common as described above, the power switching can be automatically carried out. Therefore, no burden in operation such as switching is imposed on a user as in prior art, and no interruption of absorption of sound occurs as power switching takes place. In this case, generally, the internal battery is higher in voltage than the external power source so that the power switching is carried out first from the external power source, thus preventing wasteful consumption of the battery.
Further, since the power switch is provided on the microphone body, the switch operation can be done at hand. When the power is off, the output line of the voice signal is grounded in an AC manner. Therefore, on the apparatus side to which the microphone is connected, its input is short-circuited in an AC manner, and even if the volume is increased, no noise occurs.
The power switch may be of a 2-contact switching system, which is small and inexpensive. Accordingly, it is possible to further miniaturize the microphone itself, reducing the cost. As the case may be, even if the power switch is omitted, the internal battery and the external power source can be automatically switched.
The present invention relates to a power circuit for a condenser microphone capable of supplying an operating power from either internal power source (mounted power source) or external power source to a microphone unit.
Power circuit for condenser microphone
By: Saphia
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