JPS6027965Y2 - Meter drive circuit - Google Patents

Description

[Detailed description of the invention] A logarithmic compression circuit is usually inserted into the meter that monitors the output of an amplifier, which widens the output indication range and improves the accuracy of low-level output indications. I have to.

Conventionally, in order to logarithmically compress signals, circuits have been used in which a large number of silicon diodes and germanium diodes are connected in series or in parallel through resistors. In such a circuit, the number of diodes increases, and the characteristic curve of logarithmic compression becomes a polygonal line that bends at a plurality of points.

The present invention aims to avoid these drawbacks and provide a meter drive circuit that uses one transistor and utilizes its variable impedance characteristic to appropriately logarithmically compress a signal.

To explain with reference to FIG. 1, in the present invention, an impedance element such as a resistor 2 and a transistor 3 are connected to a signal source 1.
Connect the collector emitter of transistor 3 in series, and connect the resistor 4 in parallel with the collector emitter of transistor 3.
The midpoint of this resistor 4 is connected to the base of the transistor 3, and a series circuit consisting of a diode 5 and a meter 6 is connected in parallel with the collector emitter of the transistor 3.

In order to derive the midpoint of this resistor 4, a variable resistor is used as the resistor 4 in this example, and its movable element is connected to the base.

In the example shown in the drawing, a diode 7 is connected in parallel with the collector emitter of the transistor 3 and in a direction opposite to the direction of the current passing through it, and the meter 6 is further connected with a thermistor 8 and a resistor 9 connected in series. resistor 10 to the circuit
The circuits 11 are connected in series.

Note that a normal ammeter can be used as the meter 6.

To explain the operation of the circuit according to the present invention, a signal from a signal source 1 (for example, an audio signal) is applied to both ends of a diode 7 through a resistor 2, so that the signal is half-wave rectified, and is connected between the collector and emitter of the transistor 3. is applied to

Therefore, in the example shown in the drawings, the collector has a positive polarity voltage.

On the other hand, the above-mentioned half-wave rectified voltage is applied to the base of this transistor 3 after being divided by a variable resistor 4. Therefore, when the voltage between the collector and emitter increases, the impedance between the collector and emitter decreases. The current passing through this (so-called collector current ■c)
Since the voltage increases, the collector-emitter voltage ■.

As E increases, the current IC increases exponentially.

That is, the collector-emitter impedance of the transistor 3 decreases exponentially.

This situation is shown in FIG.

In FIG. 2, the horizontal axis shows the voltage VCE, and the vertical axis shows the current Ic.

As is clear from this, the impedance between the collector and emitter of the transistor 3 changes as shown in FIG. As shown in the figure, the deflection angle θ of the meter 6 corresponds logarithmically to the current 1.

This makes it possible to display a large output, that is, to display a wide range of output levels.

Of course, it is possible to display low output levels with relatively high precision, as is the case with the prior art.

The thermistor 8 is for temperature compensation for the transistor 3 and the diode 5, and due to temperature changes, the transistor 3
And when the impedance of the diode 5 changes and the current passing through it changes, this is compensated for.

FIG. 2 shows the VcE-to-characteristics using temperature as a parameter.

As explained above, according to the present invention, there is no need to use a large number of diodes compared to conventional circuits, and only one transistor 3 and one or two diodes are used. It has the feature that the circuit can be configured and the circuit as a whole can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an example of a meter drive circuit according to the present invention, and FIGS. 2 and 3 are characteristic curve diagrams thereof, respectively. 1 is a signal source, 3 is a transistor, and 6 is a meter.

Claims (1)

[Scope of utility model registration request] A meter drive circuit comprising: a collector emitter of a transistor connected to an input signal source, a resistor connected, a midpoint of the resistor connected to the base of the transistor, and a collector emitter of the transistor connected to a meter through a diode.