JPH0520414U - Limit circuit using transistors - Google Patents

Abstract

(57) [Abstract] [Purpose] The main feature of the present invention is to provide a limit circuit using a transistor in which an emitter follower circuit of the transistor can be used to set the limit voltage accurately and freely. [Structure] An upper limit voltage is set to the variable resistor VR1 and is given to the base of the transistor TR1.
The lower limit voltage is set by R2 and given to the base of the transistor TR2, the upper limit voltage and the lower limit voltage are output from the emitters of the transistors TR1 and TR2, and the input voltage input to one end of the resistor R1 is limited to the upper limit. Output with voltage and lower limit voltage.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a limit circuit using a transistor, and particularly to a limit circuit using a transistor that limits the output voltage of a voltage output type sensor.

[0002]

[Prior Art]

FIG. 5 is a diagram showing a conventional limit circuit. Referring to FIG. 5, the input voltage V _in is input to one end of a resistor R1, a Zener diode D 1, D2 is connected between the other end of the resistor R1 and the ground, the input voltage limit Zener diodes D1, D2 Then, the output voltage V _out is output. In the limit circuit shown in FIG. 5, the limit voltage V _lim is expressed by the following equation.

V _lim = V _z + V _F V _z : Zener voltage V _F : Forward voltage

[0004]

[Problems to be solved by the device]

As described above, since the limit circuit shown in FIG. 5 is determined by the Zener voltage V _z and the forward voltage V _F , the limit value cannot be freely selected, and the limit value is not accurate. was there. A limit circuit using an operational amplifier is also considered, but it has a problem that the circuit becomes complicated and the cost becomes high.

Therefore, a main object of the present invention is to provide a limit circuit using a transistor in which an emitter follower circuit of the transistor can be used to set a limit value accurately and freely.

[0006]

[Means for Solving the Problems]

 The invention according to claim 1 is a limit circuit for limiting an input voltage by using a transistor, and includes a variable resistor for setting an upper limiter voltage of the input voltage and an upper limit voltage set by the variable resistor. It is configured with a transistor that receives at its base and outputs a limit voltage that limits the upper limit of the input voltage from its emitter.

According to a second aspect of the present invention, a variable resistor for setting a lower limit voltage of the input voltage and a lower limit voltage set by the variable resistor are received at its base, and the input voltage is changed from the emitter. And a transistor that outputs a limit voltage that limits the value.

According to a third aspect of the invention, a first variable resistor for setting an upper limit voltage of the input voltage, a second variable resistor for setting a lower limit voltage, and a first variable resistor. It receives the upper limit voltage set by the base and outputs the limit voltage that limits the upper limit of the input voltage from its emitter, and the lower limit voltage set by the second variable resistor. It is configured to include a second transistor which receives at the base and outputs a limit voltage from the emitter that limits the lower limit value of the input voltage.

[0009]

[Action]

The limit circuit using a transistor according to the present invention simplifies the circuit configuration by setting the upper limit value or the lower limit value of the limit voltage with a variable resistor, giving it to the base of the transistor, and outputting the limit voltage from the emitter. Not only can the limit voltage be set, but the limit voltage can be accurately set by the base voltage set by the variable resistance, the transistor base and the emitter-to-emitter voltage V _BE .

[0010]

[Example of device]

FIG. 1 is an electric circuit diagram showing an upper limit circuit of an embodiment of the present invention. In FIG. 1, a variable resistor VR1 is connected between the power supplies + Vcc and -Vcc. The variable resistor VR sets the upper limit voltage. The set voltage of the variable resistor VR1 is given to the base of the transistor TR1. The power supply -Vcc is applied to the collector of the transistor TR1. The input voltage V _in is applied to the negative terminal of the resistor R1, and the other terminal is connected to the emitter of the transistor TR1 and the limited voltage is output from there.

In the upper limit circuit shown in FIG. 1, the upper limit voltage V _Hlim is _expressed by the following equation.

V_Hlim= V_B1+ V_BE1 V_B1: Base potential of the transistor TR1 (set arbitrarily by the variable resistor VR1) V_BE1: Voltage between emitter and base when transistor TR1 is ON (about 0.6V) Therefore, input voltage V_inIs V_B1+ V_BE1When it becomes larger, the base current of the transistor TR1 flows, the transistor TR1 is turned on, and the output voltage is V_out= V _B1 + V_BE1= V_HlimBecomes Therefore, the upper limit is V_in≤V_Hlim TR1: OFF operation V_out= V_in V_in> V_Hlim TR1: ON operation V_out= V_Hlim Becomes

FIG. 2 is an electric circuit diagram showing a lower limit circuit of another embodiment of the present invention. Referring to FIG. 2, variable resistor VR2 is connected between power supplies + Vcc and -Vcc. The variable resistor VR2 sets the lower limit voltage. The set voltage of the variable resistor VR2 is given to the base of the transistor TR2. The power supply + Vcc is applied to the collector of the transistor TR2. One end of the resistor R1 is given an input voltage V _in, the other end is connected to the emitter of the transistor TR2, the lower limit of the limit voltage therefrom is output.

[0014] In the lower limit circuit shown in FIG. 2, the lower limit voltage V _{Llim is, V Llim = V B2 -V BE2} V B2: base potential of the transistor TR2 (is set arbitrarily by the variable resistor VR2.) V _BE2 : It is represented by the emitter-base voltage (about 0.6 V) when the transistor TR2 is _{turned on} . Therefore, when the input voltage V _in is smaller than V _B2 -V _BE2, flows the base current of the bets transistor TR2, transistor TR2 is turned ON, the output voltage is _{V out = V B2 -V BE2 =} V Llim.

Accordingly, the lower limit is: V _in ≧ V _Llim TR2: OFF operation V _out = V _in Vin _in <V _Llim TR2: ON operation V _out = V _Llim

FIG. 3 is an electric circuit diagram showing still another embodiment of the present invention. The embodiment shown in FIG. 3 is a combination of the upper limit circuit shown in FIG. 1 and the lower limit circuit shown in FIG.

FIG. 4 is a diagram showing the voltage limited by the upper limit circuit and the lower limit circuit shown in FIG. As apparent from FIG. 4, when the input voltage V _in is lower Limit voltage V _Llim smaller than the output voltage is set to V _Llim, the input voltage V _in exceeds the upper limit voltage V _Hlim, the output voltage V _out becomes the upper limit voltage V _Hlim .

[0018]

[Effect of the device]

 As described above, according to the present invention, the upper limit value or the lower limit value of the limit voltage is set by the variable resistor and is given to the base of the transistor, and the emitter follower of the transistor outputs the emitter voltage, thereby simplifying the circuit configuration. Not only that, but the limit voltage can be set accurately by the base voltage set by the variable resistor and the base-emitter voltage of the transistor.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an upper limit circuit of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a lower limit circuit showing another embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing still another embodiment of the present invention.

4 is a diagram showing a relationship between an input voltage and an output voltage in the limit circuit shown in FIG.

FIG. 5 is a diagram showing an example of a conventional limit circuit.

[Explanation of symbols]

 VR1, VR2 Variable resistor TR1, TR2 Transistor R1 Resistance

Claims (3)

[Scope of utility model registration request] 1. A limit circuit for limiting input data using a transistor, comprising: a variable resistor for setting an upper limit limiter voltage of an input voltage, and an upper limit voltage set by the variable resistor at its base. A limit circuit using a transistor, comprising a transistor that outputs a limit voltage that limits the upper limit value of the input voltage from its emitter. 2. A limit circuit for limiting an input voltage using a transistor, comprising: a variable resistor for setting a lower limit voltage of the input voltage, and a lower limit voltage set by the variable resistor at its base. A limit circuit using a transistor, the transistor including a transistor outputting a limit voltage for limiting a variable value of the input voltage from its emitter. 3. A limit circuit using a transistor, comprising: a first variable resistor for setting an upper limit voltage of an input voltage; a second variable resistor for setting a lower limit voltage of an input voltage; A first transistor that receives the upper limit voltage set by the first variable resistor at its base and outputs a limit voltage that limits the upper limit value of the input voltage from its emitter, and the second variable resistor. A limit circuit using a transistor, comprising a second transistor that receives a lower limit voltage at its base and outputs a limit voltage that limits the lower limit value of the input voltage from its emitter.