JPS6339791Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a limiter circuit that limits an input voltage within a range determined by a reference voltage.

Generally, such a limiter circuit matches an input voltage and a reference voltage through a diode, and utilizes the conduction of the diode to select the larger one,
Alternatively, a device that selectively outputs the smaller voltage has been put into practical use. FIG. 1 is a block diagram showing an example of a conventional limiter circuit. In the figure, A1 is an operational amplifier, D is a diode, R1 is a resistor, and Es is a reference voltage. Operational amplifier A1 constitutes a voltage follower circuit VF. As shown in the figure, the input voltage Vi is matched with the reference voltage Es via the diode D, and the larger voltage is outputted via the voltage follower circuit VF. That is, when Vi>Es, the diode D becomes non-conductive, the input voltage Vi is applied to the voltage follower circuit VF, and the output voltage Vo becomes Vo=Vi. Furthermore, when Vi<Es, the diode D becomes conductive, and the reference voltage Es is now applied to the voltage follower circuit VF, setting the output voltage Vo to Vo=Es. Therefore, for the input voltage Vi, the output voltage
Vo can be limited to the range Vo≧Es, and operates as a lower limiter.

However, in such a circuit, the output voltage Vo cannot be accurately set to Vo≧Es due to the influence of the layer voltage and conduction resistance of the diode D.

In order to solve this problem, a limiter circuit as shown in FIG. 2 has also been proposed. In the figure, the same parts as in FIG. 1 are designated by the same reference numerals. A2 is an operational amplifier, R2 and R3 are resistors (R2=R3), and the operational amplifier A2 constitutes an idealized diode circuit DI in which a diode D is inserted in its feedback circuit. That is, the idealized diode circuit DI can eliminate the influence of the layer voltage and conduction resistance in the diode D, and the output voltage Vo can be accurately limited to the magnitude of the reference voltage Es.

However, in such a limiter circuit,
When Vi>Es, the input voltage Vi is between resistor R1 and
The voltage is divided by R3, and the output voltage Vo decreases.

The present invention eliminates the drawbacks of the conventional device as described above, can accurately limit the output voltage to the magnitude of the reference voltage, and can obtain an output voltage equal to the input voltage before the limiter is applied. The purpose is to realize a limiter circuit with a simple configuration.

The limiter circuit of the present invention matches an input voltage and a reference voltage via an idealized diode circuit, and outputs the voltage at the matching point via a voltage follower circuit. The feedback is applied from the output side of the voltage follower circuit.

FIG. 3 is a block diagram showing an embodiment of the limiter circuit of the present invention. In the figure, the same parts as in FIG. 2 are designated by the same reference numerals. As shown in the figure, the feedback voltage in the idealized diode circuit DI is obtained from the output side of the voltage follower circuit VF. Here, since the input and output in the voltage follower circuit VF are always at the same potential, even if the potential on the output end side of the diode D is fed back via the voltage follower circuit VF, the ideal diode circuit
There is no adverse effect on the operation of DI.

Now, if you configure the limiter circuit like this,
When the input voltage Vi is Vi>Es, the diode D becomes non-conductive, and the output voltage Vo obtained via the voltage follower circuit VF becomes Vo=Vi. Furthermore, when the input voltage Vi is Vi<Es, the diode D becomes conductive, so the reference voltage Es is applied to the voltage follower circuit VF via the diode D, and its output voltage Vo becomes Vo=Es.

Now, considering the case where Vi>Es, the potential at the point where the input voltage Vi and the reference voltage Es meet is equal to the input voltage Vi because the diode D is non-conducting, and the voltage follower circuit An output voltage Vo equal to the input voltage Vi is obtained from the output of VF. Further, the polarity of the input voltage Vi can be operated with either positive or negative polarity.

In this way, by obtaining the feedback voltage in the idealized diode circuit DI from the output side of the voltage follower circuit VF, the output voltage Vo can be accurately limited to the magnitude of the reference voltage Es, and
Before the limiter is applied, an output voltage Vo equal to the input voltage Vi can be obtained.

In the above explanation, a lower limiter circuit was exemplified, but the present invention is not limited to this.If the direction of the diode D is reversed, it can be used as an upper limiter circuit. If a diode circuit DI is used, it can be made into an upper and lower limiter circuit.

As explained above, in the limiter circuit of the present invention, the input voltage and the reference voltage are matched through the idealized diode circuit, and the voltage at the matching point is outputted through the voltage follower circuit. Since the feedback of the idealized diode circuit is applied from the output side of the voltage follower circuit, the output voltage can be accurately limited to the magnitude of the reference voltage, and
A limiter circuit that can obtain an output voltage equal to the input voltage before the limiter is applied can be realized with a simple configuration.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing a conventional limiter circuit, and FIG. 3 is a block diagram showing an embodiment of the limiter circuit of the present invention. D...diode, A1, A2... operational amplifier, VF... voltage follower circuit, DI... idealized diode circuit.

Claims (1)

[Scope of utility model registration request] In a limiter circuit that matches an input voltage and a reference voltage via an idealizing diode circuit and outputs the voltage at the matching point via a voltage follower circuit, the feedback of the idealizing diode circuit is connected to the voltage follower circuit. The limiter circuit is applied from the output side.