Pulse constant current source generating circuit

Abstract

The utility model belongs to the field of constant current signals, and relates to a pulse constant current source generating circuit, which is characterized in that a resistor R9 inputs a DA signal, the R9 is connected with a resistor R10, a capacitor C23 is connected with the R9, the R9 is connected with a non-inverting input end of an operational amplifier U5, a positive input end of a power supply of the U5 and a capacitor C24 are connected with a 3.3 V power supply, an output end of the U5 is connected with a resistor R13, a capacitor C8 and an emitting electrode of a triode Q4, a base electrode of the Q4 is connected with a resistor R29, and a collector electrode of the Q4, the capacitor C8, the R29, a resistor R15 and an inverting input end of the U5 are connected. An R13 is connected with a grid electrode of an MOS tube Q1, a drain electrode of the Q1 is connected with a load J1, a source electrode of the Q1 is connected with an R15 and a resistor R16, a pin 1 of an analog switch U6 inputs a PWM signal, a pin 4 of the analog switch U6 inputs a DA1 signal, a pin 5 of the analog switch U6 is connected with a resistor R14, the R14 is connected with a reverse input end of the U6, and a pin 2 of the analog switch U6 is connected with a 3.3 V power supply. According to the utility model, a pulse constant current source signal is accurate and controllable, a subtractor is formed by using the characteristics of the operational amplifier, and a square wave signal constant current signal of 0.6 ma / 0ma at a high level and a square wave signal constant current signal of 0.3 ma / 0ma at a low level are controlled and generated.

Description

Technical Field

[0001] The utility model belongs to the technical field of constant current signals, and in particular relates to a pulse constant current source generating circuit. Background Art

[0002] Pulse constant current source is a current signal that can output stably. Pulse constant current source has a very wide range of applications. For example, when performing dental care, sodium fluoride solution can be immersed in the cotton strip in the mouth mold. By providing a DC pulse current signal for the penetration of fluoride, the sodium fluoride solution ionizes fluoride ions under the action of the electric field and enters the tooth tissue, which plays a role in protecting teeth, making good teeth better and preventing bad teeth from developing.

[0003] At present, constant current diodes can be used directly to generate pulse constant current sources, but the constant current characteristics of constant current diodes are not very good, the current specifications are relatively few, and the price is relatively expensive. You can also use two transistors of the same type to form a constant current source, using the relatively stable BE voltage of the transistor as a reference, but the BE voltage of transistors of different models is not a fixed value, even the same model has certain individual differences, and at the same time, under different working currents, this voltage will also have certain fluctuations, which is not suitable for the needs of precise constant current sources.

[0004] Therefore, for some applications that require high precision of constant current sources, it is necessary to solve the technical problem of accurate control of pulse constant current source signals. Utility Model Content

[0005] In order to solve the above technical problems, the utility model provides a pulse constant current source generating circuit. The technical solution adopted by the utility model is as follows:

[0006] A pulse constant current source generating circuit, wherein one end of resistor R9 inputs DA signal, the other end of R9 is connected to one end of resistor R10, the other end of R10 is grounded, one end of capacitor C23 is connected to one end of R9, the other end of C23 is grounded, the other end of R9 is simultaneously connected to the same-direction input end of operational amplifier U5, the positive power input end of U5 and one end of capacitor C24 are connected to a 3.3V power supply, the other end of C24 is grounded, the negative power input end of U5 is grounded, the output end of U5 is connected to one end of resistor R13, one end of capacitor C8 and the emitter of transistor Q4, the base of Q4 is connected to one end of resistor R29, the collector of Q4 is connected to one end of resistor R29, and the base of Q4 is connected to one end of resistor R29. , the other end of C8, the other end of R29, one end of resistor R15 and the reverse input end of U5, the other end of R13 is connected to the gate of MOS tube Q1, the drain of Q1 is connected to one end of load J1, the source of Q1 is connected to the other end of R15 and one end of resistor R16, the other end of R16 is grounded, pin 1 of analog switch U6 inputs PWM signal, pin 4 of U6 inputs DA1 signal, pin 6 of U6 is suspended, pin 5 of U6 is connected to one end of resistor R14, the other end of R14 is connected to the reverse input end of U5, pin 2 of U6 is connected to 3.3V power supply, and pin 3 of U6 is grounded.

[0007] Preferably, the other end of J1 is connected to the cathode of the light emitting diode D21, the anode of D21 is connected to one end of the fuse F1, and the other end of F1 is connected to a positive voltage of 24V.

[0008] Preferably, the DA signal is generated by a PWM to DAC circuit, one end of resistor R70 is connected to the T3C2 input signal, T3C2 is the second channel of the single-chip microcomputer timer, the other end of R70 is connected to one end of resistor R71, the other end of R71 is connected to one end of resistor R72, the other end of R72 is connected to the same-direction input end of the operational amplifier U17A, the reverse input end and the output end of U17A are connected to one end of resistor R76, the positive input end of the power supply of U17A is connected to a 3.3V positive voltage, the negative input end of the power supply of U17A is grounded, one end of capacitors C40 and C41 is connected between R70 and R71, the other end of C40 and C41 is grounded, one end of capacitor C42 is connected between R71 and R72, the other end of C42 is connected to one end of R76, one end of capacitor C43 is connected between R72 and the same-direction input end of U17A, and the other end of C43 is connected to the ground. One end is grounded, the other end of R76 is connected to one end of resistor R77, the other end of R77 is connected to one end of resistor R78, the other end of R78 is connected to the same-direction input terminal of operational amplifier U17B, the positive power input terminal of U17B is connected to 3.3V positive voltage, the negative power input terminal of U17B is grounded, the reverse input and output terminals of U17B are connected to one end of capacitor C48, the other end of C48 is connected between R77 and R78, one end of capacitors C45 and C46 is connected between R76 and R77, the other ends of C45 and C46 are grounded, one end of capacitor C49 is connected between R72 and the same-direction input terminal of U17B, the other end of C49 is grounded, the output terminal of U17B is also connected to one end of capacitor C47 and one end of resistor R79, the other end of C47 is grounded, and the other end of R79 is connected to one end of R9 and one end of C23 in the pulse constant current source generating circuit.

[0009] Preferably, U5 uses an operational amplifier of model tlv2211, Q4 uses a transistor of model N3904 SOT-23, Q1 uses a MOS tube of model 2N7002 SOT-23, and U6 uses an analog switch of model ADG719.

[0010] Preferably, U17A and U17B use operational amplifiers of model Im358.

[0011] Beneficial effects of the utility model:

[0012] The utility model can make the pulse constant current source signal precisely controllable, and utilizes the characteristics of the operational amplifier itself to form a subtractor, which controls the constant current signal of 0.6ma / 0ma when the square wave signal is at a high level and the constant current signal of 0.3ma / 0ma when the square wave signal is at a low level. The transistor Q4 improves the reaction speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0014] Figure 1 It is a structural schematic diagram of a pulse constant current source generating circuit of an embodiment of the utility model;

[0015] Figure 2 It is a structural schematic diagram of a PWM to DAC circuit according to an embodiment of the utility model. DETAILED DESCRIPTION

[0016] The technical solution of the present utility model will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present utility model, rather than all of the embodiments.

[0017] like Figure 1 As shown, a pulse constant current source generating circuit is an improved circuit of a high-precision operational amplifier constant current source, including a constant current operational amplifier circuit and a pulse control circuit. The constant current operational amplifier circuit includes an operational amplifier U5, an analog switch U6, a transistor Q4 and a MOS tube Q1, a resistor R9 inputs a DA signal at one end, the other end of R9 is connected to one end of a resistor R10, the other end of R10 is grounded, one end of a capacitor C23 is connected to one end of R9, the other end of C23 is grounded, and the other end of R9 is simultaneously connected to the same-direction input end of the operational amplifier U5. U5 can preferably use an operational amplifier of model tlv2211, the positive input end of the power supply of U5 and one end of the capacitor C24 are connected to a 3.3V power supply, the other end of C24 is grounded, the negative input end of the power supply of U5 is grounded, the output end of U5 is connected to one end of the resistor R13, one end of the capacitor C8 and the emitter of the transistor Q4, and the transistor Q4 can preferably use a model N3904 The SOT-23 triode, the base of Q4 is connected to one end of the resistor R29, the collector of Q4, the other end of C8, the other end of R29, one end of the resistor R15 and the reverse input end of U5 are connected, the other end of R13 is connected to the gate of the MOS tube Q1, and the MOS tube Q1 can preferably be a 2N7002 SOT-23 MOS tube, the drain of Q1 is connected to one end of the load J1, the other end of J1 is connected to the negative electrode of the light-emitting diode D21, the positive electrode of D21 is connected to one end of the fuse F1, and the other end of F1 is connected to a positive voltage of 24V, which is obtained by a boost circuit, and the boost circuit is a prior art, the source of Q1 is connected to the other end of R15 and one end of the resistor R16, and the other end of R16 is grounded. The core of the pulse control circuit is the analog switch U6. U6 can preferably use an analog switch of model ADG719. Pin 1 of U6 inputs a PWM signal, pin 4 of U6 inputs a DA1 signal, pin 6 of U6 is suspended, pin 5 of U6 is connected to one end of resistor R14, the other end of R14 is connected to the reverse input end of U5, pin 2 of U6 is connected to a 3.3V power supply, and pin 3 of U6 is grounded. Load J1 acts on the sodium fluoride solution on the cotton strip, providing a DC pulse current signal for the penetration of fluoride. Under the action of the electric field, the sodium fluoride solution ionizes fluoride ions and enters the tooth tissue.

[0018] The DA1 signal is obtained by power supply voltage division. The voltage division circuit is a prior art. The DA signal is generated by the PWM to DAC circuit of the previous stage, such as Figure 2 As shown, the PWM to DAC circuit is formed by cascading two Butterworth third-order low-pass filters to form a sixth-order low-pass filter circuit, one end of resistor R70 is connected to the T3C2 input signal, T3C2 is the second channel of the single-chip timer, the other end of R70 is connected to one end of resistor R71, the other end of R71 is connected to one end of resistor R72, the other end of R72 is connected to the same-direction input end of operational amplifier U17A, U17A can preferably use an operational amplifier of model Im358, the reverse input and output ends of U17A are connected to one end of resistor R76, the positive input end of the power supply of U17A is connected to a 3.3V positive voltage, the negative input end of the power supply of U17A is grounded, one end of capacitors C40 and C41 is connected between R70 and R71, the other ends of C40 and C41 are grounded, one end of capacitor C42 is connected between R71 and R72, the other end of C42 is connected to one end of R76, and one end of capacitor C43 is connected to the same-direction input end of R72 and U17A. The other end of C43 is grounded, the other end of R76 is connected to one end of resistor R77, the other end of R77 is connected to one end of resistor R78, the other end of R78 is connected to the same-direction input end of operational amplifier U17B, U17B can preferably use an operational amplifier of model Im358, the positive input end of U17B is connected to a 3.3V positive voltage, the negative input end of U17B is grounded, the reverse input end and output end of U17B are connected to one end of capacitor C48, and the other end of C48 is connected to the same-direction input end of operational amplifier U17B. One end is connected between R77 and R78, one end of capacitors C45 and C46 is connected between R76 and R77, the other ends of C45 and C46 are grounded, one end of capacitor C49 is connected between R72 and the same-direction input end of U17B, the other end of C49 is grounded, the output end of U17B is also connected to one end of capacitor C47 and one end of resistor R79, the other end of C47 is grounded, and the other end of R79 is connected to one end of R9 and one end of C23 in the pulse constant current source generating circuit.

[0019] The pulse constant current source generating circuit of the utility model embodiment is based on the constant current circuit and adds a pulse control circuit, introduces different DA1 / DA levels at high and low levels respectively, and uses the characteristics of the operational amplifier itself to form a subtractor, which controls the constant current signal of 0.6ma / 0ma when the square wave signal is at a high level and the constant current signal of 0.3ma / 0ma when the square wave signal is at a low level. The frequency of the pulse circuit is 1k Hz, and the period is 1ms. The difficulty lies in that within each 1ms, the high level time of 500us is a controllable constant current value of 0.3ma / 0.6ma, and the current value of the low level time of 500us is a stable 0ma. Fast switching and accurate switching are required, which requires accurate selection of hardware operational amplifiers and analog switches to design a stable circuit. The role of transistor Q4 is to improve the reaction speed and make the waveform of the pulse more accurate and beautiful.

[0020] The output of this circuit is a pulse voltage based on the 0 point, that is, the high level is a positive voltage and the low level is 0. The value of DA1 is greater than DA. When DA / DA1 are added to the op amp input at the same time, because DA1 is greater than DA, the op amp output is 0. When PWM is high, pin 4 and pin 5 of U6 are connected. At this time, the voltage at the reverse input of U5 is greater than the voltage at the same input. U5 is cut off and the output is 0; when PWM is low, pin 6 and pin 5 of U6 are connected. At this time, the voltage at the reverse input of U5 is equal to the voltage at the same input, and a constant current (0.3 or 0.6, depending on the gear) is output. The innovation is to use the characteristics of the operational amplifier itself to form a subtractor to generate pulses based on the constant current circuit.

[0021] The PWM to DAC circuit of the embodiment of the utility model is a circuit for generating the control signal DA. Due to the lack of DAC function of the single-chip microcomputer itself, the general single-chip microcomputer has at most three DAC outputs, and some single-chip microcomputers do not even have DAC. The PWM to DAC circuit of the utility model can provide a single-channel six DAC signal. The solution is to use the single-chip microcomputer's own more PWM signals plus an operational amplifier to generate the DAC signal itself. The advantage is that it is more cost-effective and has higher precision. The utility model uses the PWM to DAC circuit to expand the DAC signal output by the single-chip microcomputer DAC, and can better output high-precision pulse signals. The sixth-order filter circuit composed of two groups of third-order filters can ensure the accuracy and reliability of the DC component.

[0022] In the embodiments of the utility model, the technical features not described in detail are all existing technologies or conventional technical means and will not be described in detail here.

[0023] Finally, it should be noted that the above embodiments are only specific implementation methods of the present utility model, which are used to illustrate the technical solution of the present utility model, rather than to limit it, and the protection scope of the present utility model is not limited thereto. Those skilled in the art should understand that any technician familiar with the technical field can modify the technical solution recorded in the above embodiments within the technical scope disclosed by the present utility model, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solution of the embodiment of the present utility model, and should be covered within the protection scope of the present utility model.

Claims

1. A pulse constant current source generating circuit, characterized in that: One end of resistor R9 inputs DA signal, the other end of R9 is connected to one end of resistor R10, the other end of R10 is grounded, one end of capacitor C23 is connected to one end of R9, the other end of C23 is grounded, the other end of R9 is connected to the same-direction input end of operational amplifier U5, the positive power input end of U5 and one end of capacitor C24 are connected to a 3.3V power supply, the other end of C24 is grounded, the negative power input end of U5 is grounded, the output end of U5 is connected to one end of resistor R13, one end of capacitor C8 and the emitter of transistor Q4, the base of Q4 is connected to one end of resistor R29, the collector of Q4 and the other end of C8 are connected. The first end of R29 is connected to the reverse input end of U5, the other end of R13 is connected to the gate of MOS tube Q1, the drain of Q1 is connected to one end of load J1, the source of Q1 is connected to the other end of R15 and one end of resistor R16, the other end of R16 is grounded, pin 1 of analog switch U6 inputs PWM signal, pin 4 of U6 inputs DA1 signal, pin 6 of U6 is suspended, pin 5 of U6 is connected to one end of resistor R14, the other end of R14 is connected to the reverse input end of U5, pin 2 of U6 is connected to 3.3V power supply, and pin 3 of U6 is grounded.

2. The pulse constant current source generating circuit according to claim 1, characterized in that: The other end of J1 is connected to the cathode of the light emitting diode D21, the anode of D21 is connected to one end of the fuse F1, and the other end of F1 is connected to a positive voltage of 24V.

3. The pulse constant current source generating circuit according to claim 2, characterized in that: The DA signal is generated by a PWM to DAC circuit, one end of resistor R70 is connected to the T3C2 input signal, T3C2 is the second channel of the single-chip microcomputer timer, the other end of R70 is connected to one end of resistor R71, the other end of R71 is connected to one end of resistor R72, the other end of R72 is connected to the same-direction input terminal of the operational amplifier U17A, the reverse input terminal and output terminal of U17A are connected to one end of resistor R76, the positive input terminal of the power supply of U17A is connected to a 3.3V positive voltage, the negative input terminal of the power supply of U17A is grounded, one end of capacitors C40 and C41 is connected between R70 and R71, the other end of C40 and C41 is grounded, one end of capacitor C42 is connected between R71 and R72, the other end of C42 is connected to one end of R76, one end of capacitor C43 is connected between R72 and the same-direction input terminal of U17A, the other end of C43 Grounded, the other end of R76 is connected to one end of resistor R77, the other end of R77 is connected to one end of resistor R78, the other end of R78 is connected to the same-direction input terminal of operational amplifier U17B, the positive power input terminal of U17B is connected to 3.3V positive voltage, the negative power input terminal of U17B is grounded, the reverse input and output terminals of U17B are connected to one end of capacitor C48, the other end of C48 is connected between R77 and R78, one end of capacitors C45 and C46 is connected between R76 and R77, the other end of C45 and C46 is grounded, one end of capacitor C49 is connected between R72 and the same-direction input terminal of U17B, the other end of C49 is grounded, the output terminal of U17B is also connected to one end of capacitor C47 and one end of resistor R79, the other end of C47 is grounded, and the other end of R79 is connected to one end of R9 and one end of C23 in the pulse constant current source generating circuit.

4. The pulse constant current source generating circuit according to any one of claims 1 to 3, characterized in that: U5 uses an operational amplifier of model tlv2211, Q4 uses a transistor of model N3904 SOT-23, Q1 uses a MOS tube of model 2N7002 SOT-23, and U6 uses an analog switch of model ADG719.

5. The pulse constant current source generating circuit according to claim 3, characterized in that: U17A and U17B use the operational amplifier model Im358.

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