JPS5844669Y2 - Schmidt trigger circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Schmidts) Riga circuit using an operational amplifier.

As shown in FIG. 1, a typical conventional Schmitt trigger circuit includes an open collector operational amplifier 1, an input line 2 connected to the inverting input terminal, and a non-inverting input terminal connected to +Vc.
a threshold setting resistor R1 connected between the power supply terminal 3 of c, a threshold setting resistor R2 connected between the non-inverting input terminal and ground, and the output of the operational amplifier 1. A hysteresis setting resistor R3 connected between the terminal and the non-inverting input terminal, a pull-up resistor R4 connected between the output terminal of the operational amplifier 1 and the power supply terminal 3, and the operational amplifier 1
and a load resistor RL connected between the output line 4 and the power supply terminal 3.

In the Schmitt trigger circuit shown in Fig. 1, the input line 2
For example, when input signal 5 shown in FIG. 2A is applied to , the upper trip point voltage ■.

The second point at tl when the input signal crosses from bottom to top
As shown in Figure B, the voltage of output line 4 is at a high level (+Vcc)
to a low level (0 volts), and changes from a low level to a high level at a time point t2 when the input signal crosses the lower trip point voltage 1- from top to bottom.

By the way, when the upper triso point voltage VU is determined as follows, the following equation is obtained.

Further, the lower trip point voltage VL is expressed as follows.

Therefore, trip point voltages Vu and VL are independent of load resistance RL as long as the condition R4<RL is satisfied.

However, there is a drawback that a large load current cannot be obtained.

If the relationship R4<RL is violated in an attempt to increase the load current, VU and (2) will change depending on the value of RL, resulting in a predetermined value (2).

In order to obtain (1) and (1), it is necessary to reset the resistances R1 to R4.

Incidentally, the above-mentioned problem also occurs in a circuit in which the load resistor R1- is connected between the output line 4 and the ground.

Therefore, the purpose of the present invention is to create a Schmitt trigger that provides first and second outputs with opposite polarities and that does not change the trip point voltage even if the value of one load resistance coupled to one output is changed. The purpose is to provide circuits.

To achieve the above object, the present invention includes an operational amplifier, an input line connected to one input terminal of the operational amplifier, and an input line connected between one DC power line and an output terminal of the operational amplifier. a first resistor; a second resistor connected between the other input terminal of the operational amplifier and the other DC power supply line; and a second resistor, the base of which is connected to the output terminal of the operational amplifier directly or via a resistor. a transistor whose emitter is connected to the one DC power supply line; a third resistor and a first diode connected between the collector of the transistor and the other input terminal of the operational amplifier; a second series circuit consisting of a fourth resistor and a second diode connected between the output terminal of the operational amplifier and the other input terminal; a collector of the transistor and the second series circuit; a Schmitt trigger circuit separated from a first load connected between the other DC power line and a second load connected between the output terminal of the operational amplifier and the other DC power line; It is related.

With the configuration of the present invention described above, the trip point voltage does not change even if the value of the first load resistance is changed.

Further, first and second outputs having different polarities can be obtained relatively easily.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The Schmitt trigger circuit according to an embodiment of the present invention shown in FIG. 3 includes an open collector operational amplifier 11, an input line 12 connected to one input terminal (inverting input terminal) of the operational amplifier 11, ■The first resistor R1 is connected between one DC power supply line 13 to which CC is supplied and the output terminal of the operational amplifier 11, and the other input terminal (non-inverting input terminal) of the operational amplifier 11 is connected. a second resistor R2 connected to the other DC power supply line 14; and a PNP transistor 1 whose emitter is connected to the +Vcc power supply line 13.
5, a first series circuit consisting of a third resistor R3 and a first diode D1 connected between the collector of the transistor 15 and the non-inverting input terminal of the operational amplifier 11, and an output terminal of the operational amplifier 11. A second series circuit consisting of a fourth resistor R4 and a second diode D2 is connected between the output terminal of the operational amplifier 11 and the base of the transistor 15. The fifth resistor R
5, a first output line 16 connected to the collector of the transistor 15, a second output line 17 connected to the output terminal of the operational amplifier 11, the first output line 16 and the ground power line 1
4, and a second load resistor RL2 connected between the second output line 17 and the ground power line 14.

Note that the second load resistance RL□ is set to R1 (RL□).

However, the first load resistance RLI may be freely set up to the maximum collector current of the transistor 15.

In the circuit described above, when the input signal 18 shown in FIG. 4A is supplied to the input line 12, the output voltage of the operational amplifier 11 becomes +Vcc volts before time 11.

Therefore, the output voltage obtained on the second output line 17 is also
As shown in , it is +Vcc volts.

However, since transistor 15 is off, the output voltage available at its collector or first output line 16 is 0 volts.

Therefore, the first diode D1 is turned off and the second diode D2 is turned on.

As a result, the upper trip point voltage in relation to the circuit formed by the first resistor R1, the fourth resistor R4, the second diode D2, and the second resistor R2 is .

is determined, and Vu becomes the following formula. However, Vd is the voltage drop value of the second diode D2.

Then, if R1 (R4), then it becomes.

Therefore, the upper trip point voltage Vu is determined regardless of the first load resistance R+-.

At time 11, human power signal 18 is ■.

, the output of operational amplifier 11 switches from high level (+Vcc) to low level (0 volts) and the second
The output line 17 becomes 0 volts as shown in FIG. 4C.

Also, since the base of transistor 15 is at a low level,
This transistor 15 is turned on.

Therefore, the first output line 16 becomes a high level (+Vcc) as shown in FIG. 4B, and the first diode D1 is turned on and the second diode D2 is turned off.

Therefore, the lower trip point voltage ■1 is the fourth
is determined by a circuit consisting of a resistor R3, a first diode D1, and a second resistor R2, and is determined by the following equation.

However, Vd is the voltage drop value of the first diode D1.

As is clear from this formula ■. is the first load resistance R17
, is determined regardless of the value of .

When the input signal crosses the level mentioned above at point 12,
The output of the operational amplifier 11 becomes high level again.

By the way, the upper and lower trip point voltages mentioned above.

When determining (1) and (2), first determine the value of the second resistor R2 related to both, and then determine the values of the remaining resistors.

This allows the upper and lower trip points to be determined extremely easily.

As is clear from the above, in this Schmitt trigger circuit, the trip point does not change even if the value of the first load resistor R1-1 is changed.

Then, the maximum collector current of the transistor 15 can be diverted.

Therefore, it is suitable for driving power transistors.

Also, the second load resistance RL2 must have a value that satisfies R<: RI-2, but the second output line 17
Since an output with a polarity opposite to that of the first output line 16 can be obtained, it has great utility value.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above description and can be further modified.

For example, one power line 13 is grounded and the other power line 14
It is also applicable to the case where is set to +Vcc.

It is also applicable to the case where the other power supply line 14 is set to a negative level.

Alternatively, the fifth resistor R5 may be omitted and the output terminal of the operational amplifier 11 may be directly connected to the base of the transistor 15.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional Schmitt trigger circuit, Figure 2 is a waveform diagram showing the states of points A and B in Figure 1, and Figure 3 is a circuit diagram showing a conventional Schmitt trigger circuit.
The figure is a circuit diagram showing a Schmidts) trigger circuit according to an embodiment of the present invention, and FIG. 4 is a waveform diagram showing the state at point A-C in FIG. 3. In the symbols used in the drawings, 11 is an operational amplifier, 12 is a human power line, 13 is one DC power line, 14 is the other DC power line, 15 is a transistor, 16 is a first output line, and 17 is a Second output line, 18 is the input signal, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4
is the fourth resistor, R5 is the fifth resistor, RLI is the first load resistor, and RL2 is the second load resistor.

Claims (1)

[Scope of utility model registration request] an operational amplifier, an input line connected to one input terminal of the operational amplifier, a first resistor connected between one DC power supply line and an output terminal of the operational amplifier, and the other of the operational amplifier. a second resistor connected between the input terminal of the operational amplifier and the other DC power line; a base connected to the output terminal of the operational amplifier directly or via a resistor; and an emitter connected to the one DC power line; a third resistor and a first diode connected between the collector of the transistor and the other input terminal of the operational amplifier; and an output terminal of the operational amplifier; a second series circuit including a fourth resistor and a second diode connected between the other input terminal; and a second series circuit connected between the collector of the transistor and the other DC power supply line. 1 and a second load connected between the output terminal of the operational amplifier and the other DC power supply line.