Circuit of dust sensor

Abstract

The utility model relates to a circuit of a dust sensor. The circuit of the dust sensor comprises a driving circuit, an amplifying circuit and a judging circuit. The driving circuit is serially connected with the light-emitting element; the light receiving element, the amplifying circuit and the judging circuit are sequentially connected in series; the light receiving element is a photoelectric transistor. According to the utility model, by using the phototransistor, a micro photocurrent signal can be easily amplified, so that the circuit is simplified and the cost is reduced; the photodiodes are typically 1 / 200 to 1 / 2000 of the phototransistors.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of dust sensor circuit, in particular to a kind of circuit of dust sensor. BACKGROUND

[0002] Dust sensor detects dust in air using the scattering principle of light, including light emitting element, light receiving element;The circuit of dust sensor includes driving circuit, amplification circuit, judging circuit.Driving circuit is connected in series with light emitting element;Light receiving element, amplification circuit, judging circuit are connected in series in proper order.Driving circuit supplies power to light emitting element, so that light emitting element emits light of design light intensity;The light scattering phenomenon occurs when the light meets dust particles, and the light intensity attenuates by being absorbed by part of energy by dust particles.Light receiving element receives light after light intensity attenuation, generates weak electric signal;The electric signal is amplified by amplification circuit, and then noise voltage is screened out by judging circuit, and finally the electric signal output reflecting dust concentration is left.Reference Figure 2 、 Figure 3 Conventional light receiving element has two, which are photodiode and photoelectronic integrated circuit respectively.The photocurrent generated by photodiode is small, and it is difficult to improve detection sensitivity;Photoelectronic integrated circuit is high in cost and poor in versatility. INVENTION CONTENTS

[0003] The utility model aims at solving the above problems, and provides a kind of circuit of dust sensor.

[0004] The technical scheme of the utility model is as follows: a kind of circuit of dust sensor includes light emitting subcircuit and light receiving subcircuit;The light emitting subcircuit includes light emitting driving unit and light emitting element connected in series in proper order, and the light receiving subcircuit includes light receiving element, amplification circuit unit, judging circuit unit or microcomputer connected in proper order, the light of light emitting element is towards light receiving element, judging circuit unit or microcomputer outputs signal, and the light receiving element is phototransistor;By using phototransistor, small photocurrent signal can be easily amplified, so as to simplify circuit and reduce cost;Phototransistor is usually 1 / 200 to 1 / 2000 of photodiode;Using phototransistor can improve detection sensitivity;Photoelectronic integrated circuit is poor in versatility and high in cost;Phototransistor is relatively better in versatility and lower in cost.

[0005] Preferably, gain adjustment loop is connected in parallel between amplification circuit unit and microcomputer;Microcomputer can act on amplification circuit unit through gain adjustment loop according to the signal intensity output by amplification circuit unit, corrects the photosensitivity variation of phototransistor, and improves detection sensitivity;By using microcomputer to adjust gain, through the setting program in microcomputer, automatic adjustment can be carried out, and it is very easy to adjust in manufacturing process.No need to change circuit structure and adjust electrical element.

[0006] Preferably, the light receiving element of the photonic circuit is further connected with a trans-impedance amplifier unit and an amplification circuit unit.

[0007] The photo transistor is usually a high impedance current output element. When the scattered light hits it, it converts the current signal flowing through it into a voltage, and then amplifies the voltage to determine the amount of dust.

[0008] When the current signal is converted into a voltage signal, if the equivalent impedance Z connected to the photo transistor is large, the parasitic capacitance C of the photo transistor will affect the response speed, and if the Z is small, the response speed will be fast. The relationship between the response speed and the equivalent impedance Z connected to the photo transistor and the parasitic capacitance C of the photo transistor is: response speed ∝ 1 / Z and ∝ 1 / C; when using a trans-impedance amplifier unit, because the equivalent impedance Z connected to the transistor is small, the response speed of the photo transistor is fast.

[0009] Further, the trans-impedance amplifier unit includes a transistor, a photo transistor, and an operational amplifier;

[0010] The emitter of the photo transistor is grounded, the collector is connected to the inverting input terminal of the operational amplifier, and the collector of the photo transistor is also connected to the output terminal of the operational amplifier through a parallel resistor B and a capacitor A;

[0011] The emitter of the transistor is grounded, the collector is connected to the base in parallel, and then connected to the positive input terminal of the amplifier; one end of the resistor A is connected to the positive input terminal of the amplifier, and the other end is connected to a +5V voltage.

[0012] The power supply noise elimination capability is determined by the noise voltage V cc_Collector ; The power supply noise removal capability PSRR can be calculated by the following formula:

[0013] PSRR = V cc_n / V cc_Collector .

[0014] Preferably, the amplification circuit unit is a multi-stage differential operational amplifier circuit; each stage of the differential operational amplifier circuit includes a differential operational amplifier;

[0015] One end of the impedance B is grounded, and the other end is connected to the positive input terminal of the differential operational amplifier; the other end of the impedance A is also connected to the impedance B in series, and then connected to the power supply noise voltage; the noise voltage is input to the positive input terminal of the differential operational amplifier;

[0016] The reverse input end of the differential operational amplifier is connected with the output end of the differential operational amplifier in series with impedance B, and the reverse input end of the differential operational amplifier is also connected with the ground in series with impedance C. The effect of not amplifying the power supply noise is achieved. The voltage division ratio of the bias voltage is Z2 / (Z1+Z2), and the voltage gain of the circuit is Gain((Z3+Z4) / Z3), and Z2 / (Z1+Z2) x (Z3+Z4) / Z3<1. Therefore, if the above conditions are met, it means that the power supply noise will not be amplified.

[0017] Further, the operational amplifier commonly used in the amplification circuit uses two integrated circuits with two circuits, which is the most cost-effective choice.

[0018] Preferably, the microcomputer is a single-chip microcomputer or a chip with the same function as the single-chip microcomputer.

[0019] The dust sensor circuit of the utility model has the following advantages:

[0020] (1) The utility model discloses a photoelectric transistor, which can easily amplify a small photoelectric current signal, thereby simplifying the circuit and reducing the cost. The photoelectric diode is usually 1 / 200 to 1 / 2000 of the photoelectric transistor. Using the photoelectric transistor can improve the detection sensitivity. The photoelectron integrated circuit has poor versatility and high cost. The photoelectric transistor has relatively better versatility and reduced cost.

[0021] (2) The gain adjustment loop of the utility model can correct the photosensitivity change of the photoelectric transistor and improve the high precision. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a schematic diagram of the circuit of the dust sensor of the utility model in embodiment one.

[0023] Figure 2 It is a schematic diagram of the circuit of the existing dust sensor Figure 1 .

[0024] Figure 3 It is a schematic diagram of the circuit of the existing dust sensor Figure 2 .

[0025] Figure 4 It is a schematic diagram of the circuit of the dust sensor of the utility model in embodiment two.

[0026] Figure 5 It is a schematic diagram of the circuit of the dust sensor of the utility model in embodiment three.

[0027] Figure 6is the equivalent resistance schematic diagram of the response characteristic in example three;

[0028] Figure 7 is the power supply noise equivalent circuit schematic diagram in example three;

[0029] Figure 8 is the power supply noise equivalent circuit schematic diagram in example four;

[0030] Figure 9 is the schematic diagram of the circuit of the dust sensor of the utility model in example five;

[0031] Figure 10 is the alternative circuit in example five Figure 1 ;

[0032] Figure 11 is the alternative circuit in example five Figure 2 ;

[0033] In the figure: 01. photodiode, 02. optoelectronic integrated circuit, 1. light emitting drive unit, 2. amplification circuit, 21. amplifier, 22. gain adjustment loop, 3. judgment circuit unit or microcomputer, 4. light emitting element, 5. phototransistor, 61. transistor, 62. resistance A, 63. resistance B, 64. capacitor A, 71. impedance A, 72 impedance B, 73. impedance C, 74. impedance D, 75. differential operational amplifier. DETAILED DESCRIPTION

[0034] Example one: refer to Figure 1 A circuit of a dust sensor includes a light emitting sub-circuit and a light receiving sub-circuit; the light emitting sub-circuit includes a light emitting drive unit 1 and a light emitting element 4 connected in series; the light receiving sub-circuit includes a light receiving element, an amplification circuit 2 unit, a judgment circuit 3 unit or a microcomputer 3 connected in series; the light emitted by the light emitting element 4 is directed to the light receiving element; the judgment circuit 3 unit or the microcomputer 3 outputs a signal; the light receiving element is a phototransistor 615; by using the phototransistor 615, a tiny photocurrent signal can be easily amplified, thereby simplifying the circuit and reducing the cost; a photodiode is usually 1 / 200 to 1 / 2000 of the phototransistor 615; using the phototransistor 615 can improve the detection sensitivity; the optoelectronic integrated circuit 02 has relatively poor versatility and high cost; the phototransistor 615 has relatively better versatility and reduced cost.

[0035] Example two: refer to Figure 4, the embodiment two is basically same with the embodiment one, the same place is not repeated, the different place is: the gain adjustment circuit 22 is connected between the amplification circuit 2 unit and the microcomputer 3; the microcomputer 3 can correct the photosensitivity change of the phototransistor 615 and improve the detection sensitivity by adjusting the gain of the amplification circuit 2 unit through the gain adjustment circuit 22; by using the microcomputer 3 to adjust the gain, the automatic adjustment can be carried out through the setting program in the microcomputer 3, and the adjustment can be easily carried out in the manufacturing process. Without changing the circuit structure and adjusting the electrical elements.

[0036] Embodiment three: see Figures 5-7 , the embodiment three is basically same with the embodiment one, the same place is not repeated, the different place is: the light receiving element of the light receiving circuit is also connected with the transimpedance amplifier 21 unit between the amplification circuit 2 unit.

[0037] When the current signal is converted into voltage signal, if the equivalent impedance Z connected with the phototransistor 615 is large, the influence of the parasitic capacitance C of the phototransistor 615 will make the response speed slow, but if Z is small, the response speed will be fast. The relationship between the response speed and the equivalent impedance Z connected with the phototransistor 615 and the parasitic capacitance C of the phototransistor 615 is: the response speed ∝1 / Z and ∝1 / C; when the transimpedance amplifier 21 unit is used, because the equivalent impedance Z connected with the transistor 61 is small, the response speed of the phototransistor 615 is fast.

[0038] See Figure 6 , the phototransistor 615 is usually a high-impedance current output element. When the scattered light hits it, the current signal flowing through it is converted into voltage, and then the voltage is amplified to determine the amount of dust.

[0039] When the current signal is converted into voltage signal, if the equivalent impedance Z connected with the phototransistor 615 is large, the influence of the parasitic capacitance C of the phototransistor 615 will make the response speed slow, but if Z is small, the response speed will be fast. The relationship between the response speed and the equivalent impedance Z connected with the phototransistor 615 and the parasitic capacitance C of the phototransistor 615 is: the response speed ∝1 / Z and ∝1 / C; when the transimpedance amplifier 21 unit is used, because the equivalent impedance Z connected with the transistor 61 is small, the response speed of the phototransistor 615 is fast.

[0040] The transimpedance amplifier 21 unit comprises a transistor 61, a phototransistor 615 and an operational amplifier 21;

[0041] The emitter of the phototransistor 615 is grounded, the collector is connected with the inverting input end of the operational amplifier 21, and the collector of the phototransistor 615 is also connected to the output end of the operational amplifier 21 through the parallel connection of resistor B 63 and capacitor A 64;

[0042] Transistor 61 emitter ground, collector and base in parallel after the positive input terminal of amplifier 21; resistance A 62 one end and the positive input terminal of amplifier 21, the other end connected to +5v voltage.

[0043] Referring to Figure 7 , the power supply noise elimination ability by adding noise voltage V cc_Collector The power supply noise voltage V cc_n In series, the equivalent resistance is grounded in turn; the parasitic capacitance C of the phototransistor 615 is connected in parallel with the equivalent impedance Z; the phototransistor 615 is connected in parallel with the equivalent impedance Z; the sharing resistance R in this embodiment is selected as impedance A 71.

[0044] The power supply noise removal capability PSRR can be calculated by the following formula:

[0045] PSRR=V cc_n / V cc_Collector =(R+Z) / Z.

[0046] Example four: refer to Figure 8 , example four and example one are basically the same, the same place no longer elaborated, the different is: the single unit of amplifier circuit 2 is multi-stage differential operational amplifier 21 circuit; each stage differential operational amplifier 21 circuit includes differential operational amplifier 21;

[0047] Impedance B 72 one end ground, the other end and the positive input terminal of differential operational amplifier 21; impedance A 71 the other end is also connected with impedance B 72 in series, and is connected with the power supply noise voltage; the noise voltage is input to the positive input terminal of differential operational amplifier 21;

[0048] The reverse input terminal of differential operational amplifier 7521 is connected in series with impedance D 74, and is connected with the output terminal of differential operational amplifier 7521; the reverse input terminal of differential operational amplifier 7521 is also connected in series with impedance C 73 and grounded. The effect of not being amplified by the power supply noise. The value of impedance A 71 in this embodiment is Z1, the value of impedance B 72 is Z2, the value of impedance C 73 is Z3, and the value of impedance D 74 is Z4; the voltage division ratio of the bias voltage: Z2 / (Z1+Z2), the voltage gain Gain of the circuit ((Z3+Z4) / Z3), Z2 / (Z1+Z2)×(Z3+Z4) / Z3<1; the output amplitude of the amplifier circuit 2 caused by the power supply noise = the power supply noise amplitude × Z2 / (Z1+Z2)×(Z3+Z4) / Z3, therefore, if the above conditions are met, it means that the power supply noise will not be amplified.

[0049] Example five: refer to Figures 9-11Example five is basically the same as example one, and the same parts will not be repeated. The difference is that the operational amplifier 21 in the amplification circuit 2 uses two integrated circuits with two circuits. This is the most cost-effective choice.

[0050] Referring to Figure 10 The operational amplifier 21 in the amplification circuit 2 can also use four integrated circuits with one circuit each. However, this increases the number of parts and the cost. The cost of the power supply wiring is also increased.

[0051] Referring to Figure 11 The operational amplifier 21 in the amplification circuit 2 can also use one integrated circuit with four circuits. However, in this case, the circuits are too close to each other, and the interference is serious. It is difficult to achieve the desired performance. In addition, the pins of the operational amplifier 21 are dense, which increases the difficulty of layout.

[0052] Therefore, in this embodiment, the operational amplifier 21 in the amplification circuit 2 uses two integrated circuits with two circuits.

Claims

1. A circuit of a dust sensor comprising a light-emitting sub-circuit and a light-receiving sub-circuit, characterized by, The light-emitting sub-circuit comprises a light-emitting driving unit and a light-emitting element connected in series, the light-receiving sub-circuit comprises a light-receiving element, an amplifying circuit unit, a judging circuit unit or a microcomputer connected in series, the light-emitting element emits light towards the light-receiving element, the judging circuit unit or the microcomputer outputs a signal, and the light-receiving element is a phototransistor.

2. The circuit of the dust sensor according to claim 1, characterized in that: A gain adjusting loop is connected in parallel between the amplifying circuit unit and the microcomputer.

3. The circuit of dust sensor according to claim 1, characterized in that: A transimpedance amplifier unit is further connected between the light-receiving element and the amplifying circuit unit of the light-receiving sub-circuit.

4. The circuit of dust sensor according to claim 3, characterized in that: The transimpedance amplifier unit comprises a transistor, a phototransistor and an operational amplifier. The emitter of the phototransistor is grounded, the collector is connected to the inverting input terminal of the operational amplifier, and the collector is further connected to the output terminal of the operational amplifier through a parallel connection of a resistor B and a capacitor A. The emitter of the transistor is grounded, the collector is connected to the non-inverting input terminal of the amplifier after being connected in parallel with the base, and the resistor A is connected to the non-inverting input terminal of the amplifier at one end and to a +5V voltage at the other end.

5. The circuit of dust sensor according to claim 1, characterized in that: The amplifying circuit unit is a multi-stage differential operational amplifier circuit, and each stage of the differential operational amplifier circuit comprises a differential operational amplifier. The resistor B is connected to the non-inverting input terminal of the differential operational amplifier at one end and to the other end of the resistor A in series with the resistor B and connected to a power supply noise voltage, and the noise voltage is input to the non-inverting input terminal of the differential operational amplifier. The inverting input terminal of the differential operational amplifier is connected in series with the resistor D and connected to the output terminal of the differential operational amplifier, and the inverting input terminal of the differential operational amplifier is further connected in series with the resistor C and grounded.

6. A circuit for a dust sensor according to any one of claims 3 to 5, characterised in that: The operational amplifier commonly used in the amplifying circuit unit uses two integrated circuits with two circuits.

7. The circuit of dust sensor according to claim 1 or 2, characterized in that: The microcomputer is a single-chip microcomputer or a chip with the same function as the single-chip microcomputer.

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