JP5414594B2 - Phantom power circuit - Google Patents

Description

  The present invention relates to a phantom power supply circuit used for a condenser microphone. More specifically, when a condenser microphone is connected, the output circuit of the condenser microphone may be destroyed by an inrush current caused by instantaneously disturbing the equilibrium state. The present invention relates to a phantom power supply circuit that can automatically limit power supply at that moment so that there is no such problem.

  A power supply system for a condenser microphone or the like is defined in the EIAJ standard (RC-8162A). This EIAJ standard relates to a phantom power supply, and three types (12V, 24V, 48V) of supply voltages are defined.

The phantom power source applies a DC voltage to each of the HOT terminal and the COLD terminal of the condenser microphone via a supply resistor. Therefore, when the phantom power supply is connected to the condenser microphone, if the connection of the HOT terminal and the connection of the COLD terminal are slightly shifted in time, an inrush current (rush current) will be generated for a short time at that moment, but the condenser microphone. Flows toward the output circuit.
As a result, the output circuit of the condenser microphone may be destroyed.

The inrush current as described above is likely to occur when connecting a measuring instrument for measuring characteristics or connecting a jig for circuit testing, particularly in the manufacturing process of a condenser microphone. That is, the capacitor microphone is often attached / detached without turning off the power switch (while the power is being supplied).
In particular, since the power supply is frequently attached and detached in the manufacturing process of the condenser microphone, inrush currents are generated at short time intervals, and all of them flow into the output circuit of the condenser microphone.

In particular, an output circuit using a transformerless circuit is easily destroyed by the inrush current as described above.
Such an inrush current is a large current, but it takes only a short time, so only when this inrush current occurs, the power supply to the condenser microphone is limited so that the power supply is stopped after the inrush current has subsided. There is a need for a power circuit that automatically recovers.

  The above-mentioned technical problem, that is, a phantom power supply that supplies a power supply for a condenser microphone, is intended to solve the problem that the output circuit of the condenser microphone is destroyed by an inrush current generated when the condenser microphone is connected. Although no technical document was found, Patent Document 1 can be cited as a prior art document related to the present invention.

  The invention described in Patent Document 1 relates to a connecting method of a cylindrical body that can be used for a connector housing of a condenser microphone unit, and includes a zener diode element for preventing overcurrent on a circuit board housed in the connector housing. I have.

JP 2009-290639 A

  The present invention has been made in view of the above problems, and is a phantom power supply circuit used for a condenser microphone. When a condenser microphone is connected, the condenser microphone is caused by an inrush current that is generated by instantaneously disturbing an equilibrium state. An object of the present invention is to provide a phantom power supply circuit capable of automatically limiting power supply only at that moment so that the output circuit of the power supply is not destroyed.

  The present invention is a phantom power supply circuit that supplies power to a condenser microphone via two supply resistors, and includes a limiting circuit that restricts power supply to the condenser microphone, and an inrush current generated when the condenser microphone is connected. And a detection circuit for detecting, and when the detection circuit detects an inrush current, the main feature is that the power supply to the condenser microphone is limited by operating the limiting circuit.

  According to the present invention, in the above phantom power supply circuit, the detection circuit includes a transformer that connects both ends to two power supply lines that supply power to the capacitor microphone, and a transistor that turns on the output by a current from the middle point of the transformer And a circuit.

  According to the present invention, in the above phantom power supply circuit, the limiting circuit includes a photo MOS relay including a light emitting element that emits light by an output of the transistor circuit and an active element that operates by light emission of the light emitting element. Features.

  According to the present invention, in a phantom power supply circuit that supplies power to a condenser microphone, power supply from the phantom power supply circuit is limited by restricting power supply to the condenser microphone only while an inrush current is generated when the condenser microphone is attached or detached. Since the amount can be kept low and power supply to the condenser microphone can be started automatically after the inrush current has subsided, the destruction of the output circuit of the condenser microphone due to the inrush current can be prevented.

It is a circuit diagram which shows the Example of the phantom power supply circuit which concerns on this invention.

  An embodiment of a condenser microphone according to the present invention will be described with reference to FIG. In the phantom power supply circuit 10 shown in FIG. 1, reference numerals T1, T2, and T3 are terminals to which a condenser microphone (not shown) is connected. The terminals T1 and T2 are connected to the HOT terminal and the COLD terminal of the condenser microphone, not shown, respectively. As a result, the power from the phantom power supply circuit 1 is supplied. Terminal T3 is a ground terminal.

Symbols T4, T5, and T6 are terminals to which a measuring instrument (not shown) is connected. The terminals T4 and T5 are terminals connected to the HOT terminal and the COLD terminal of a condenser microphone (not shown) via capacitors C3 and C4, respectively. It is. Terminal T6 is a ground terminal.
A resistor R5 that connects the terminal T4 and the ground is a resistor that defines the potential at both ends of the capacitor C3. A resistor R6 that connects the terminal T5 and the ground is a resistor that defines the potential at both ends of the capacitor C4.

  A voltage from the power supply unit PW is applied to the terminal T1 through the supply resistor R1, and a voltage from the power supply unit PW is applied to the terminal T2 through the supply resistor R2. Since the voltage value of the power supply unit PW is 48 volts, for example, the voltage applied between the terminals T1 and T2 is 48 volts.

  A limiting circuit 1 is provided between the power source PW and the supply resistors R1 and R2 for limiting the power supply to the condenser microphone only while an inrush current is generated. The limiting circuit 1 includes a photo MOS relay SW and a resistor R7 for switching a power feeding path from the power source PW to the supply resistors R1 and R2. As shown in FIG. 1, the photo MOS relay SW and the resistor R7 constituting the limiting circuit 1 are connected in parallel, and the limiting circuit 1 including the photo MOS relay SW and the resistor R7 is connected in series with the power source PW, and Are connected in series to each of the supply resistors R1 and R2.

The photo MOS relay SW is a switch that opens and closes the contact according to the light emission state of the diode D1 described later. The contact is opened when the diode D1 is not emitting light, and the contact is opened when the diode D1 is emitting light. Works to close. Therefore, when the diode D1 is emitting light, power is supplied to the condenser microphone via the photo MOS relay SW.
When the diode D1 is not emitting light, power is supplied to the condenser microphone via the resistor R7.
The resistor R7 is for limiting the current supplied from the power source PW to the supply resistors R1 and R2 when the photo MOS relay SW is open. A constant current diode may be used instead of the resistor R7.

A transformer TRS is connected between a terminal T1 connected to a condenser microphone (not shown) and an end T2. In FIG. 1, a connection point between the terminal T1 and the transformer TRS is P1, and a connection point between the terminal T2 and the transformer TRS is P2.
The transformer TRS is a bifilar wound transformer, and is provided with a center tap S.
The center tap S is connected to the ground via a capacitor C1 and a resistor R3 connected in series. The connection point between the capacitor C1 and the resistor R3 is connected to the base of the transistor Q1, and the connection point between the capacitor C1 and the resistor R3 is connected to the emitter of the transistor Q2.

That is, the current that flows between P1 and P2, which are both ends of the transformer TRS, flows into the base of the transistor Q1 and the emitter of the transistor Q2 in the form of a pulse by the differentiation circuit formed by the capacitor C1 and the resistor R3. It is configured as follows.
Since the base potential of the transistor Q1 and the emitter potential of the transistor Q2 change due to the current flowing in the transformer TRS, when the current flows from the center tap S toward the ground, the base potential of the transistor Q1 and the emitter potential of the transistor Q2 are changed. It has a fluctuating configuration.

  If the balanced state between the terminal T1 and the terminal T2 is maintained (when normal), the potentials of P1 and P2 of the transformer TRS are the same. Therefore, there is no current flowing from the center tap S to the ground, and the base potential of the transistor Q1 and the emitter potential of the transistor Q2 do not fluctuate.

Since the base of the transistor Q1 is grounded via the resistor R3, when there is no input from the center tap S, the transistor Q1 is off.
Since the emitter of the transistor Q2 is also grounded through the resistor R3, when there is no input from the center tap S, the base potential and the emitter potential of the transistor Q2 are substantially the same, so the transistor Q2 is also turned off. Yes.

The collectors of the transistors Q1 and Q2 are connected to each other, and the base of the transistor Q3 is connected to this collector.
The base of the transistor Q3 is normally at a predetermined potential by the capacitor C2. Therefore, this potential is maintained until either of the transistors Q1 and Q2 is turned on, and the transistor Q3 is turned on.
A light emitting diode D1 is connected to the collector of the transistor Q3. Therefore, the normal light emitting diode D1 emits light.

  Thus, if the terminal T1 and the terminal T2 are in a balanced state, there is no current generated from the center tap S of the transformer TRS, and both the transistors Q1 and Q2 are off, and the light emitting diode D1 continues to emit light. Therefore, the contact point of the photo MOS relay constituting the limiting circuit 1 is closed, and the condenser microphone (not shown) connected to the terminals T1 and T2 is supplied with power from the power source PW.

In the phantom power supply circuit 10 having the above configuration, a series of circuits for controlling the light emission of the diode D1 by the input from the center tap S of the transformer TRS is a detection circuit.
The photo MOS relay SW that constitutes the limiting circuit 1 includes a MOSFET as an active element that operates by light emission of the light emitting diode D1.

  Next, the operation of the detection circuit and the operation of the limiting circuit 1 when the balance between the terminal T1 and the terminal T2 is broken in the phantom power supply circuit 10 having the above configuration will be described.

  When a microphone (not shown) is connected to the terminals T1 and T2, there is no problem as long as the terminals T1 and T2 are connected at the same time. However, in an actual connection mode, one of the terminals T1 and T2 is connected first. The other terminal is connected after a short delay.

  Then, although it is a short time, the potential of either P1 or P2 connected to the terminals T1 and T2 connected to the condenser microphone is lowered first. If the potential of either P1 or P2 falls first, the balance between the terminal T1 and the terminal T2 is broken only during that time. When this balance is lost, a rush current (inrush current) flows through the condenser microphone, causing a failure in the output circuit.

  The balance between the terminal T1 and the terminal T2 is lost not only when the condenser microphone is connected to the phantom power supply circuit 10, but also when the condenser microphone is disconnected from the phantom power supply circuit 10.

In the phantom power supply circuit 10 shown in FIG. 1, when the equilibrium state between the terminal T1 and the terminal T2 is lost, a potential difference is generated between P1 and P2 as described above, and a current flows through the transformer TRS. The current flowing through the transformer TRS becomes a pulsed current from the center tap S through the differentiation circuit of the capacitor C1 and the resistor R3.
If this current is a positive potential, the potential at the base of the transistor Q1 increases, so that the transistor Q1 is turned on.
Transistor Q2 remains off because the emitter potential is higher than the base potential.

  If this current is a negative potential, the potential at the base of the transistor Q1 does not increase, so that the transistor Q1 remains off. The transistor Q2 has its emitter potential lowered, so that the base potential is relatively raised and turned on.

  As described above, when either one of the transistors Q1 and Q2 is turned on, the capacitor C2 is short-circuited to discharge the charge, and the base potential of the transistor Q3 is lowered to approximately the ground potential. This turns off transistor Q3.

  Whether the pulsed current becomes a positive potential or a negative potential depends on which potential of the terminal T1 and the terminal T2 first decreases (rises).

When the transistor Q3 is turned off, no current flows to the light emitting diode D1 connected to the collector, and thus light emission stops.
When the light emission of the light emitting diode D1 stops, the contact of the photo MOS relay constituting the limiting circuit 1 is opened, so that power supply from the power supply PW to the condenser microphone (not shown) is performed via the resistor R7, which is limited. The

Since the equilibrium state between the terminal T1 and the terminal T2 is maintained after the momentary collapse, the potential difference between P1 and P2 disappears when the equilibrium state is reached, and the current flowing from the center tap S of the transformer TRS to the ground becomes zero. .
If there is no current flowing from the center tap S, the transistors Q1 and Q2 are both turned off as described above.

  When both the transistors Q1 and Q2 are turned off, the capacitor C2 is charged through the resistor R4 to a predetermined potential, the base potential of the transistor Q3 is increased, and the transistor Q3 is turned on. Accordingly, when the equilibrium state is restored, the light emitting diode D1 automatically emits light, the photo MOS relay SW constituting the limiting circuit 1 is closed, and power is supplied from the power source PW to the terminals T1 and T2.

  As described above, according to the phantom power supply circuit according to the present embodiment, the inrush current to the output circuit of the connected condenser microphone can be automatically suppressed, and the normal operation is performed as a normal phantom power supply circuit. To do.

  By using the power supply circuit including the present invention, a capacitor microphone excellent in maintainability can be obtained without causing a failure of the output circuit even if hot-plugging of the power supply is complicatedly performed.

  1 Limit circuit

Claims (3)

A phantom power supply circuit that supplies power to a condenser microphone via two supply resistors,
A limiting circuit that limits power supply to the condenser microphone;
A detection circuit for detecting an inrush current generated when the condenser microphone is connected,
A phantom power supply circuit, wherein when the detection circuit detects the inrush current, the power supply to the condenser microphone is restricted by operating the restriction circuit. The detection circuit is
A transformer connecting both ends to two power supply lines for supplying power to the condenser microphone;
2. A phantom power supply circuit according to claim 1, further comprising: a transistor circuit that turns on an output by a current from a middle point of the transformer.   2. The phantom according to claim 1, wherein the limiting circuit includes a photo MOS relay including a light emitting element that emits light by the output of the transistor circuit and an active element that operates by light emission of the light emitting element. Power supply circuit.

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