Hysteresis comparator circuit capable of externally setting threshold value

Abstract

The utility model discloses a hysteresis comparator circuit capable of externally setting a threshold value, which comprises an input voltage ui, a positive and negative threshold voltage preset circuit, a comparator A1, a comparator A2, a comparator A3 and an A3 in-phase end voltage bias circuit, and an output voltage uo, + / -Vcc and + Vcc are connected with-Vcc through a resistor R1, potentiometers P1 and P2 which are connected in parallel, a resistor R2 and form the positive and negative threshold voltage preset circuit. The sliding end of the P1 is connected with the anti-phase end of the A1, the sliding end of the P2 is connected with the anti-phase end of the A2, the voltage ui is connected with the in-phase ends of the operational amplifiers A1 and A2 at the same time, the output end of the A1 is connected with the in-phase end of the A3 through the R3, the output end of the operational amplifier A2 is connected with the in-phase input end of the operational amplifier A3 through the resistor R4, the anti-phase input end of the operational amplifier A3 is connected with the working ground, and the output end of the operational amplifier A3 is connected with the in-phase input end of the operational amplifier A3 through the resistor R5. And the output end of the operational amplifier A3 outputs the output voltage uo.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of circuit of hysteresis comparator threshold voltage preset, especially a kind of hysteresis comparator circuit with independent external threshold value, the threshold voltage of the hysteresis comparator has no any relationship with the output voltage of comparator, and only with external power supply voltage and external resistance preset. BACKGROUND

[0002] Hysteresis comparator (hysteresis comparator) or Schmidt trigger is a kind of special switch gate circuit, unlike ordinary switch gate circuit, hysteresis comparator has two threshold voltages, respectively called positive threshold voltage U + And negative threshold voltage U -- , the input voltage that makes the circuit state change in the process that input signal rises from low level to high level is called positive threshold voltage, the input voltage that makes the circuit state change in the process that input signal drops from high level to low level is called negative threshold voltage.The difference between positive threshold voltage and negative threshold voltage is called hysteresis voltage.The voltage transmission characteristic curve is called the "hysteresis loop" of hysteresis comparator, and hysteresis comparator is divided into same-phase hysteresis comparator and opposite-phase hysteresis comparator.

[0003] The accurate calculation of threshold voltage of traditional hysteresis comparator depends on the precision of hysteresis resistance and the stable output voltage of this comparator, and if single power supply, the output voltage value of this comparator is either 0V or power supply voltage;When symmetrical dual power supply, output voltage is either +Vcc or negative power supply voltage-Vcc.

[0004] The precision of resistance can be very high, such as 0.1% precision resistance, higher precision can be 0.01% precision, that is, one ten-thousandth precision of electronic engineer, and such resistance is generally thin-film resistance, and resistance of this material generally meets the production process requirements.

[0005] However, according to the above description, whether the hysteresis comparator can output voltage stably or output voltage correctly depends on the correct presetting or calculation of the threshold voltage of the hysteresis comparator, once the positive threshold voltage U + And negative threshold voltage U — Of hysteresis comparator is calculated incorrectly, the output voltage of the hysteresis comparator may not be output correctly at the expected time;The output voltage of hysteresis comparator in time leads to the incorrect calculation of threshold voltage, and the precision is dependent on each other, which finally leads to the possible misoperation of the hysteresis comparator switch, causing unnecessary loss to industrial and agricultural production.

[0006] The 555 time base circuit can also constitute a hysteresis comparator, the threshold voltage of which depends on the supply voltage Vcc and three 5k resistors connected in series inside the chip, the rising edge threshold voltage being 2 / 3 Vcc and the falling edge threshold being 1 / 3 Vcc, so the hysteresis comparator constituted by the 555 circuit is obviously different from the traditional hysteresis comparator, the difference being in the calculation or acquisition of the threshold voltage, the acquisition of the threshold of the 555 hysteresis comparator being only related to the supply and the three resistors, and having nothing to do with the output value Uo of the 555 circuit; but the threshold of the hysteresis comparator constituted by the 555 time base circuit is fixed (2 / 3 Vcc, 1 / 3 Vcc), which is not very flexible, and the 555 circuit is not suitable if different threshold voltages are required in the circuit design.

[0007] Since the supply voltage Vcc of the comparator circuit is theoretically stable, it can be envisaged that the threshold voltage or threshold voltage of the hysteresis comparator is independently preset (or referred to as externally preset), that is, it is not dependent on the output voltage calculation of the hysteresis comparator, and both the positive threshold voltage U + and the negative threshold voltage U — are directly calculated according to the supply voltage Vcc and the resistor or potentiometer, so the accuracy of the threshold voltage is greatly improved, and the action of the hysteresis switch is more accurate and flexible. SUMMARY

[0008] The technical problem to be solved by the utility model is to provide a hysteresis comparator circuit which is simple in structure, low in cost, reliable in use and capable of independently externally presetting a threshold value.

[0009] To achieve the above-mentioned purpose, the utility model provides a hysteresis comparator circuit which can externally preset a threshold value, comprising an input voltage u i , a positive and negative threshold voltage preset circuit, a comparator A1 circuit, a comparator A2 circuit, a comparator A3 same phase terminal voltage biasing circuit, a comparator A3 circuit, an output voltage u o , a supply +Vcc and a supply -Vcc; the supply +Vcc passes through a resistor R1, a potentiometer P1 and a potentiometer P2 connected in parallel, a resistor R2 and the supply -Vcc in sequence to constitute the positive and negative threshold voltage preset circuit, an operational amplifier A1 constitutes the comparator A1 circuit, an operational amplifier A2 constitutes the comparator A2 circuit, and an operational amplifier A3 constitutes the comparator A3 circuit, the sliding end of the potentiometer P1 is connected to the inverting input terminal of the operational amplifier A1, the sliding end of the potentiometer P2 is connected to the inverting input terminal of the operational amplifier A2, and the input voltage u iThe same phase input end of the operational amplifier A1 and the same phase input end of the operational amplifier A2 are connected at the same time, the resistor R3, the resistor R4 and the resistor R5 form the voltage bias circuit of the same phase end of the comparator A3, the output end of the operational amplifier A1 is connected to the same phase input end of the operational amplifier A3 through the resistor R3, the output end of the operational amplifier A2 is connected to the same phase input end of the operational amplifier A3 through the resistor R4, the opposite phase input end of the operational amplifier A3 is connected to the working ground, the output end of the operational amplifier A3 is connected to the same phase input end of the operational amplifier A3 through the resistor R5, and the output end of the operational amplifier A3 outputs the output voltage u o .

[0010] The positive and negative threshold voltage preset circuit, the sliding end voltage of the potentiometer P1 presets the positive threshold voltage, the sliding end voltage of the potentiometer P2 presets the negative threshold voltage, and vice versa, that is, the sliding end voltage of the potentiometer P1 presets the negative threshold voltage, and the sliding end voltage of the potentiometer P2 presets the positive threshold voltage.

[0011] The comparator A3 circuit, the three resistors R3, R4 and R5 of the same phase input end of the operational amplifier A3 have the same resistance value.

[0012] The comparator A1 circuit, the comparator A2 circuit and the comparator A3 circuit belong to the integrated circuit IC1, the model is TL084, the power supply +Vcc is connected to the 4th pin of the IC1, and the power supply -Vcc is connected to the 11th pin of the IC1. BRIEF DESCRIPTION OF DRAWINGS

[0013] ATTACHMENT Figure 1 , ATTACHMENT Figure 2 , ATTACHMENT Figure 3 , ATTACHMENT Figure 4 , ATTACHMENT Figure 5 to provide further understanding of the present application, constitute a part of the present application, and the accompanying drawings Figure 1 is a traditional hysteresis comparator circuit; ATTACHMENT Figure 2 is the voltage transmission characteristic of the hysteresis comparator; ATTACHMENT Figure 3 is a hysteresis comparator circuit with an external threshold value; ATTACHMENT Figure 4 is a waveform diagram of the hysteresis comparator with an external threshold value; ATTACHMENT Figure 5 is the voltage transmission characteristic curve (the same phase) of the hysteresis comparator with an external threshold value. DETAILED DESCRIPTION

[0014] The embodiments of the present application are further described below in combination with the accompanying drawings. First, the threshold voltage calculation formula of the traditional hysteresis comparator is introduced, and the creativity of the present application can be seen through comparison.

[0015] The hysteresis comparator has the hysteresis characteristic, that is, has inertia, and thus has certain anti-interference ability. The circuit of the hysteresis comparator input from the opposite phase input end is as follows Figure 2As shown, positive feedback is introduced in the hysteresis comparator circuit.

[0016] From the limiting circuit at the output of the integrated operational amplifier A, we can see that u o =± U Z , the potential at the inverting input of the integrated operational amplifier u N = u I , the potential at the non-inverting input

[0017]

[0018] Let u N = u P , the value obtained is the threshold voltage, so we get u I

[0019]

[0020] where U T is called the rising threshold voltage, and U T is called the falling threshold voltage.

[0021] So, how does the output voltage change when the input voltage u i is equal to the threshold voltage; assume u i is less than U T , then u N must be less than u P , so u O =+ U Z , therefore u P =+ U T . Only when the input voltage u i increases to U T , and increases by an infinitesimal amount, will the output voltage u O jump from U Z to U Z .

[0022] Similarly, assume​u i greater than U T then u N greater than u P therefore u O = U Z so u P = U T The output voltage u i decreases to U T and then decreases by an infinitesimal amount, the output voltage u O jumps from U Z to U Z .

[0023] It can be seen that u O jumps from U Z to U Z and u O jumps from U Z to U Z The threshold voltage is different, and the voltage transfer characteristic is as shown in Figure 2 , which shows that the hysteresis comparator is an inverting hysteresis comparator.

[0024] Hysteresis comparator circuit with independent preset threshold value

[0025] Most of the trigger of the switching hysteresis (including the Smith trigger or hysteresis comparator) has a poor preset switching threshold value, because these threshold values and the output values of the trigger affect each other until the switching action of the trigger is affected, causing unnecessary losses to industrial and agricultural production.

[0026] The threshold voltage of the hysteresis comparator composed of 555 time base circuit is U T Although the output voltage of the time base circuit is independent u O , or u OIrrelevant, but its positive and negative threshold voltage can only be fixed equal to 2 / 3 Vcc and 1 / 3 Vcc, where Vcc is the supply voltage of the 555 circuit, very inflexible.

[0027] A hysteresis comparator circuit can be designed to externalize the threshold value, by analyzing its working principle and describing the characteristic relationship between input voltage and output voltage in detail, and comparing it with the above traditional hysteresis comparator, it is found that the calculation or acquisition of its threshold value has nothing to do with the output voltage of the comparator, but can be calculated independently through the supply voltage and resistance network, which is very flexible and the accuracy can be guaranteed, such as Figure 3 As shown, it includes input voltage u i , positive and negative threshold voltage preset circuit, comparator A1 circuit, comparator A2 circuit, comparator A3 same phase terminal voltage bias circuit, comparator A3 circuit, output voltage u o .

[0028] The acquisition of the two thresholds of the external threshold hysteresis comparator

[0029] By observing Figure 3 , +15V power supply is connected to -15V power supply through resistance R1, parallel potentiometers P1 and P2, and resistance R2, it can be found that the rising threshold voltage U T+ of the external threshold hysteresis comparator is obtained from the sliding end of potentiometer P1, and the falling threshold voltage U T- is obtained from the sliding end of potentiometer P2, the rising threshold voltage U T+ is connected to the inverting input terminal of op-amp A1, and the falling threshold voltage U T- is connected to the inverting input terminal of op-amp A2.

[0030] Based on the "virtual break" characteristics of ideal op-amp, that is, the input current of the two input terminals of the op-amp is "0", then it can be considered that the calculation of the rising threshold voltage U T+ and the falling threshold voltage U T- has nothing to do with op-amps A1 and A2, and the two threshold voltages are only related to the supply voltage ±15V and resistances R1, R2, potentiometers P1 and P2.

[0031] Therefore, the acquisition of the two thresholds of the external threshold hysteresis comparator in this design is very simple and flexible, as long as the sliding end of potentiometer P1 or P2 is adjusted to obtain U T+ or U T-- , whether P1 produces U T+ or P2 produces U T+ , or P1 produces U T-- or P2 produces U T-- , analysis Figure 3Two potentiometers P1, P2 are in parallel state, and the input current of operational amplifier A1, A2 is "0" (virtual break), so P1, P2 can generate U T+ Or U T-- , further known to the inverting input terminal of operational amplifier A1 gets threshold voltage U T+ Or U T-- , or the inverting input terminal of A2 gets threshold voltage U T+ Or U T-- , can be arranged flexibly.

[0032] For the sake of convenience, we temporarily stipulate that the rising threshold U T+ Generated by the sliding end of potentiometer P1, connected to the inverting input terminal of operational amplifier A1; the falling threshold U T-- Generated by the sliding end of potentiometer P2, connected to the inverting input terminal of operational amplifier A2.

[0033] Two threshold values of external threshold hysteresis comparator

[0034] Because the resistance R1, the parallel potentiometer P1 and P2, the resistance R2 and other resistance network can independently generate threshold voltage, and the core of the resistance network is potentiometer P1 and potentiometer P2, the first is P1, P2 parallel connection, the second is both can adjust the resistance, resulting in mutual voltage clamping, so it is expected to accurately calculate the threshold value of U T+ Or U T— It is troublesome in practice, two high-precision voltmeters can be directly connected between the sliding end of P1 and P2 and the working ground, adjusting the sliding end of the two, until the value of the two voltmeters meets the expected threshold voltage value, of course, the sliding end of P1 outputs the rising threshold U T+ , the sliding end of P2 outputs the falling threshold U T-- .

[0035] If it is really necessary to calculate the threshold value of the hysteresis comparator through formula, it can be analyzed and calculated through this idea.

[0036] Because two potentiometers interfere with each other and clamp, and based on the characteristics of "virtual break" of operational amplifier, that is, completely do not consider the influence of operational amplifier A1, A2 on the current through resistance R1, P1, P2, R2, so first calculate the voltage of A point and B point in Figure 3 , that is, the voltage output by the sliding end of potentiometer P1 and P2 can be easily calculated.

[0037] The voltage of A point can be calculated as follows (relative to -V CC That is, the potential of -15V)

[0038]

[0039] The voltage at point B can be calculated as follows (relative to -V CC i.e. -15V)

[0040]

[0041] The voltage at the wiper of potentiometer P1 can be calculated as follows

[0042] (1)

[0043] Since this voltage U P1-2 is relative to the working ground (GND) voltage, the -Vcc voltage 15V needs to be subtracted, where P 1-2 represents the lower half resistance of potentiometer P1, U P1-2 represents the voltage at the wiper of potentiometer P1, i.e. the rising edge threshold voltage U T+ .

[0044] The voltage at the wiper of potentiometer P2 can be calculated as follows

[0045] (2)

[0046] This voltage U P2-2 is relative to the working ground (GND) voltage, so the -Vcc voltage 15V needs to be subtracted, where P 2-2 represents the lower half resistance of potentiometer P2, U P2-2 represents the voltage at the wiper of potentiometer P2, i.e. the falling edge threshold voltage U T-- .

[0047] By comparing formula (1) and formula (2), it can be seen that the calculation formula of the rising edge threshold U T+ and the falling edge threshold U T— is the same, which fully explains the argument that both potentiometer P1 and potentiometer P2 can output the rising edge threshold U T+ and the falling edge threshold U T— value. If it is necessary to specify that P1 outputs the rising edge threshold U T+ and P2 outputs the falling edge threshold U T-- , and because the rising edge threshold U T+ is certainly greater than the falling edge threshold U T— , then attention must be paid to the sliding position of potentiometer P1 and P2.

[0048] If the adjustment result is opposite, i.e. U T+ is less than U T— , then the rising edge threshold and the falling edge threshold can be used in reverse, which does not affect the final result.

[0049] The correctness of formulas (1) and (2) can be demonstrated by examples. If the desired threshold voltage is desired, U T+ =12V, U T— =-5V, the voltage at the sliding end of the potentiometer can be calculated by reversing the above formulas (1) and (2). From formula (1), we can know that P 1-2 = (12+15)*7 / 15=189 / 15=12.6K; P can be obtained from formula (2). 2-2 =(-5+15)*7 / 15=70 / 15=4.67K.

[0050] Since P1 = 10K, P in the above calculation 1-2 =12.6k is incorrect, so formulas (1) and (2) are not entirely accurate. U can be calculated. p1-2 The maximum value is: U p1-2max = (30 / 7) * 6 - 15 = 10.7V, that is Figure 3 Given the voltage at point A to ground, the maximum rising edge threshold voltage U in this design is... T+ It can only be set to 10.7V.

[0051] Similarly, U can be calculated. p2-2 The minimum value is: U p2-2min = (30 / 7) * 1 - 15 = -10.7V, that is Figure 3 Given the voltage at point B to ground, therefore, in this design, the minimum falling edge threshold voltage U... T-- It can only be set to -10.7V.

[0052] In summary, since the maximum rising edge threshold voltage U is already known through calculation... T+ and minimum falling edge threshold voltage U T— Given the value of , in practical applications, the simplest method is still to use two precision voltmeters to obtain two threshold voltages, as mentioned above. No matter which potentiometer is adjusted, as long as the threshold voltage is between 10.7V and -10.7V, it is acceptable.

[0053] Voltage transfer characteristic curve analysis of hysteresis comparators with external threshold values

[0054] The rising edge threshold voltage U has been calculated above. T+ (Output from the sliding end of P1) and falling edge threshold voltage U T-- (Output from the sliding contact of P2), when the input voltage u in Equal to the rising edge threshold voltage U T+Again increase the infinitesimal value, the comparator A1 outputs high level "+15V", the comparator A2 outputs high level "+15V", then the non-inverting terminal of the operational amplifier A3 is certainly greater than the voltage "0" of the inverting terminal, the operational amplifier A3 outputs high level +15V, namely U OUT is high level +15V, as shown in Fig. Figure 4 , wherein U1 is the voltage of the output terminal 1 of the operational amplifier A1, and U7 is the voltage of the output terminal 7 of the operational amplifier A2.

[0055] When the input voltage u in drops, it is less than the rising edge threshold voltage U T+ but greater than the falling edge threshold voltage U T-- , the comparator A1 outputs level "-15V", the comparator A2 outputs level "+15V", since the output of A3 is still "+15V" at this time, then the non-inverting terminal of the operational amplifier A3 is still greater than the voltage "0" of the inverting terminal, the operational amplifier A3 outputs level +15V, namely U OUT is +15V, as shown in Fig. Figure 4 .

[0056] When the input voltage u in continues to drop, and drops to the falling edge threshold voltage U T— , again decreases by an infinitesimal value, the comparator A1 outputs level "-15V", the comparator A2 outputs level "-15V", since the output of the operational amplifier A3 is still +15V at this moment, then when u in the voltage drops to the falling edge threshold voltage U T— , the instantaneous current I5 flowing into the endpoint of the pin 10 (the non-inverting input terminal of A3) by the feedback resistance R5 is calculated by the following formula, wherein U 10 is the voltage of the pin 10 of the operational amplifier A3, and the similar below is not repeated.

[0057] (3)

[0058] The current flowing out of the endpoint of the pin 10 is divided into two parts I3 and I4, wherein I3 is the current flowing through the resistance R3, and I4 is the current flowing through the resistance R4, and the calculation formulas are as follows:

[0059] (4)

[0060] (5)

[0061] For the endpoint of the non-inverting terminal (the pin 10) of the operational amplifier A3, according to the Kirchhoff's current law, also known as the node current law, at any time, the sum of the currents flowing into a node in a circuit is equal to the sum of the currents flowing out of the node, so

[0062] (6)

[0063] Substitute R3, R4, R5, U OUT = +15V, U1 = -15V, U7 = -15V into (3), (4), (5), (6), we can get the voltage of pin 10 of op-amp A3: U 10 = -5V.

[0064] Therefore u in The voltage drops to the falling edge threshold voltage U T— Again, the voltage of pin 10 of op-amp A3 -5V is less than the voltage of the inverting terminal of A3 "0" V at the moment when the voltage drops to an infinitesimal value, the output U OUT of op-amp A3 is reversed to -15V, as shown in the figure. Figure 4

[0065] When u in The voltage rises to the falling edge threshold voltage U T— Again, the output of op-amp A2 is +15V, and the output of op-amp A1 is -15V, at this time U OUT is still -15V, and based on the above Kirchhoff's current law, the voltage of pin 10 of op-amp A3 is still -5V, and the output of op-amp A3 still remains -15V, as shown in the figure. Figure 4

[0066] When u in The voltage rises to the rising edge threshold voltage U T+ Again, the output of op-amp A1 is +15V, and the output of op-amp A2 is +15V, at this time the output of op-amp A3 is still -15V, and based on the above Kirchhoff's current law, the voltage of pin 10 of op-amp A3 is now +5V, which is greater than the voltage of the inverting terminal of A3 "0" V, and the output of op-amp A3 is reversed to +15V.

[0067] The above changes circulate repeatedly, forming a waveform as shown in the figure, and the voltage transfer characteristic curve is as shown in the figure, which shows that the hysteresis comparator is a non-inverting hysteresis comparator. Figure 4 Figure 5 As can be seen, the hysteresis comparator shown in the figure has the same voltage transfer characteristic curve as the hysteresis comparator shown in the figure, which proves that it can fully realize all the functions of the traditional hysteresis comparator, and can obtain more flexible and more accurate threshold voltage than the traditional hysteresis comparator, and can further improve the efficiency of the hysteresis comparator in actual production application.

[0068] Figure 3 Figure 1

[0069] ​​​​​The innovation points of the present application are three, the first is that the calculation of the hysteresis comparator is no longer related to the output voltage of the comparator; the second is that the calculation of the hysteresis comparator is only related to the external resistance network, and can be flexibly adjusted; the third is that the acquisition points of the rising edge threshold voltage and the falling edge threshold voltage of the hysteresis comparator can be replaced, so that the threshold voltage test is more convenient.

[0070] The above examples are only used to illustrate but not to limit the technical solutions of the present application, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that; the present application can still be modified or equivalently replaced without departing from the spirit and scope of the present application, any modification or partial replacement, which should be covered in the scope of the claims of the present application.

Claims

1. A hysteretic comparator circuit with an externally settable threshold, characterized by, The hysteresis comparator circuit includes an input voltage u i , positive and negative threshold voltage preset circuit, comparator A1 circuit, comparator A2 circuit, comparator A3 same phase terminal voltage bias circuit, comparator A3 circuit, output voltage u o , power supply +Vcc, power supply-Vcc; the power supply +Vcc passes through resistor R1, potentiometer P1 and potentiometer P2 in parallel, resistor R2 in turn, connects the power supply-Vcc to constitute the positive and negative threshold voltage preset circuit, operational amplifier A1 constitutes the comparator A1 circuit, operational amplifier A2 constitutes the comparator A2 circuit, operational amplifier A3 constitutes the comparator A3 circuit, the sliding end of potentiometer P1 is connected with the inverting input terminal of operational amplifier A1, the sliding end of potentiometer P2 is connected with the inverting input terminal of operational amplifier A2, the input voltage u i is connected with the non-inverting input terminal of operational amplifier A3 simultaneously, resistor R3, resistor R4, resistor R5 constitute the comparator A3 same phase terminal voltage bias circuit, the output terminal of operational amplifier A1 is connected with the non-inverting input terminal of operational amplifier A3 through resistor R3, the output terminal of operational amplifier A2 is connected with the non-inverting input terminal of operational amplifier A3 through resistor R4, the inverting input terminal of operational amplifier A3 is connected with the working ground, the output terminal of operational amplifier A3 is connected with the non-inverting input terminal of operational amplifier A3 through resistor R5, and the output terminal of operational amplifier A3 outputs the output voltage u o .

2. The externally thresholded hysteretic comparator circuit of claim 1, wherein: The comparator A1 circuit, comparator A2 circuit, comparator A3 circuit belong to integrated circuit IC1, model is TL084, the power supply +Vcc connects the 4th pin of IC1, the power supply -Vcc connects the 11th pin of IC1.

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