Intelligent electric meter and its signal transmission optical coupling isolation circuit

Abstract

The application belongs to the technical field of power systems, and particularly relates to an intelligent electric meter and an optical coupling isolation circuit for signal transmission of the intelligent electric meter. The optical coupling isolation circuit comprises an optical coupling and a shaping branch connected with an output end of the optical coupling. A control end of the optical coupling is used for connecting a pulse output end of a control unit of the intelligent electric meter, so as to input a pulse signal of the control unit of the intelligent electric meter into the optical coupling isolation circuit. The shaping branch comprises a first switch tube and a voltage stabilizing branch connected with the first switch tube. A conduction end of the first switch tube is used for connecting an input end of a communication circuit for external communication of the intelligent electric meter. A control end of the voltage stabilizing branch is connected with the output end of the optical coupling, so as to control the on-off state of the first switch tube by controlling the presence or absence of voltage of the voltage stabilizing branch through the output end of the optical coupling, to realize signal transmission. When there is voltage, the first switch tube is provided with a conduction voltage drop to control the conduction of the first switch tube, and the first switch tube is controlled to be in a non-saturation state, thereby ensuring the transmission efficiency of the optical coupling isolation circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power systems, and particularly relates to an intelligent electric meter and an optical coupling isolation circuit for signal transmission thereof. BACKGROUND

[0002] In the field of electric energy metering, a smart internet electric energy meter is a new type of electric energy metering instrument, which is composed of a metering module, a management module and an expansion module. The communication baud rate of the expansion module is up to 460800bps, which is 48 times higher than the communication rate 9600bps of the previous generation of smart electric energy meters. The LTV-816 ordinary optical coupling isolation circuit used for realizing communication transmission of the original smart electric energy meter cannot meet the requirements of isolated communication. Therefore, a new circuit needs to be researched for the smart internet electric energy meter to realize the requirement of 460800bps high-speed communication at a low cost.

[0003] In order to improve the communication rate, the prior art designs a circuit as shown in Figure 1 The primary side of the optical coupling P1 is driven by a T1 triode. The pulse input passes through a signal driving circuit composed of C2 and R3, R6, and the optical coupling input signal provides driving. The secondary side of P1 passes through a receiving signal shaping circuit composed of C1, R2 and R4, T2 to complete the shaping of the optical coupling output signal. The shaped signal is output through the collector of T2.

[0004] The R4 resistor provides a working reference voltage for T2. When the primary side of the optical coupling has a signal, the resistance of the secondary side of the optical coupling P1 decreases, the current flowing through the secondary resistance of P1 increases, and the voltage generated on R4 exceeds the working voltage of T2. When the voltage generated on R4 is lower than the working voltage 0.7V of the triode T2, the triode cannot be turned on, and signal transmission cannot be realized. When the transmission ratio of P1 increases, the voltage of R4 increases, and P1 and T2 will enter a deep saturation conduction state, which limits the improvement of the transmission rate.

[0005] Therefore, the circuit provided by the prior art still has the following problems: 1. The communication rate is limited, and after using this scheme, the low-speed optical coupling can achieve about 4 times the transmission rate of the original optical coupling; 2. The temperature has a great influence on the signal rate, especially in the industrial field, the environmental temperature is as high as 70℃, and the communication rate will be unstable, which cannot meet the communication requirements; 3. The long-term operation stability is low, and under the condition of long-term operation, when the transmission ratio of the optical coupling decreases to 70% of the initial value, the communication rate will be unstable, which cannot meet the communication requirements. SUMMARY

[0006] The purpose of the present application is to provide an intelligent electric meter and its signal transmission optical coupling isolation circuit to solve the problem that the transmission rate of the optical coupling isolation circuit of the prior art still cannot meet the communication rate of the intelligent connected electric meter.

[0007] To solve the above technical problems, the present application provides an intelligent electric meter signal transmission optical coupling isolation circuit, which comprises an optical coupling and a shaping branch connected with the output end of the optical coupling; the control end of the optical coupling is used to connect the pulse output end of the control unit of the intelligent electric meter to input the pulse signal of the control unit of the intelligent electric meter into the optical coupling isolation circuit and realize the transmission of the pulse signal by controlling the on-off of the optical coupling through the pulse signal; the shaping branch comprises a first switch tube and a voltage stabilizing branch connected with the first switch tube; the conduction end of the first switch tube is used to connect the input end of the communication circuit of the intelligent electric meter to realize signal transmission by the on-off state of the first switch tube; the control end of the voltage stabilizing branch is connected with the output end of the optical coupling to control the on-off state of the first switch tube by controlling the voltage of the voltage stabilizing branch through the output end of the optical coupling to realize signal transmission, and provide the conduction voltage drop for the first switch tube when there is voltage to control the first switch tube to be in the non-saturated state.

[0008] The beneficial effects are that the optical coupling isolation circuit of the present application connects the voltage stabilizing circuit with the control end of the first switch tube to provide the conduction voltage drop for the first switch tube when there is voltage in the voltage stabilizing circuit, and the first switch tube is in the non-saturated state when it is in the conduction state, so it will not limit the transmission efficiency of the first switch tube, thus meeting the communication requirements of the intelligent connected electric meter, and based on the voltage stabilizing control of the voltage stabilizing circuit, temperature compensation can be realized, that is, the conduction voltage drop provided by the voltage stabilizing circuit for the first switch tube changes with the needs of the first switch tube. Moreover, the control end of the optical coupling of the present application is used to connect the pulse output end of the control unit of the intelligent electric meter, and because the input signal rate of the pulse output end is already very high, there is no need to increase other circuits to improve the input pulse rate of the control end of the optical coupling, so the present application does not increase other acceleration circuits at the control end of the optical coupling, thus simplifying this part of the circuit compared with the improvement of the prior art on this circuit.

[0009] Further, the voltage stabilizing branch comprises a first voltage dividing branch and a second voltage dividing branch connected in parallel; the output end of the optical coupling is connected to the ground through the first voltage dividing branch to provide voltage for the first voltage dividing branch when the optical coupling is in the conduction state, and control the voltage at both ends of the second voltage dividing branch through the voltage at both ends of the first voltage dividing branch; the second voltage dividing branch comprises a first voltage dividing resistor and a second voltage dividing resistor connected in series, wherein the voltage dividing resistors connected with the ground end are also connected in parallel with the control end of the first switch tube to provide the conduction voltage drop for the first switch tube when there is voltage at both ends of the voltage dividing resistors connected with the ground end.

[0010] The first voltage dividing branch and the second voltage dividing branch are in parallel, so that the voltage across the first voltage dividing branch and the second voltage dividing branch is equal, and the voltage across the second voltage dividing branch can be controlled through the first voltage dividing branch, and the voltage across the first voltage dividing resistor and the second voltage dividing resistor in the second voltage dividing branch can be controlled based on the voltage across the second voltage dividing branch, so as to control the voltage across the first voltage dividing resistor and the second voltage dividing resistor, and further control the on-state voltage drop of the control end of the first switch tube, and based on the voltage control, the current flowing through the first voltage dividing resistor and the second voltage dividing resistor is also controlled, and the current flowing through the control end of the first switch tube is controlled, so that the first switch tube is in a non-saturation state when it is turned on.

[0011] Further, the first switch tube is a triode, the first voltage dividing branch includes a third voltage dividing resistor, a second switch tube and a third switch tube which are the same as the first switch tube, the base of the third switch tube is connected to the emitter of the second switch tube, and the base of the second switch tube and the emitter of the third switch tube are respectively connected to the two ends of the third voltage dividing resistor, so as to control the voltage across the first voltage dividing branch through the second switch tube and the third switch tube.

[0012] Through the connection of the second switch tube and the third switch tube, the voltage across the first voltage dividing branch is equal to the on-state voltage drop of the second switch tube and the on-state voltage drop of the third switch tube based on the on-state voltage drop of the second switch tube and the third switch tube when the optocoupler is turned on, and based on the fact that the first switch tube, the second switch tube and the third switch tube are all the same triode, the same voltage as the on-state voltage drop of the second switch tube (the third switch tube) is formed at the control end of the first switch tube, so that the first switch tube can be turned on when the optocoupler is turned on, and based on the control of the on-state voltage drop of the control end of the first switch tube, the voltage across one of the voltage dividing resistors in the second voltage dividing branch is controlled, and the voltage across the two voltage dividing resistors in the second voltage dividing branch is controlled, and the current flowing through the voltage dividing resistors is controlled, so that the first switch tube can be controlled to be in a non-saturation state when it is turned on.

[0013] Further, the second voltage dividing resistor is connected to the ground, and the first voltage dividing resistor is further connected in parallel with a capacitor.

[0014] Through the capacitor, the stored charges of the first switch tube, the second switch tube and the third switch tube are neutralized quickly due to the stored charges of the capacitor when the optocoupler changes from the on state to the off state, so that the first switch tube, the second switch tube and the third switch tube quickly enter the off state.

[0015] Further, the negative input end of the optocoupler is the control end of the optocoupler, and the positive input end of the optocoupler is connected to the first power supply end after passing through the negative temperature coefficient thermistor and the current limiting resistor in parallel.

[0016] By arranging the negative temperature coefficient thermistor and the current limiting resistor in parallel between the positive input end of the optocoupler and the first power supply end, the resistance of the parallel circuit (i.e. the parallel circuit composed of the negative temperature coefficient thermistor and the current limiting resistor) can be changed according to the change of temperature, i.e. the resistance of the parallel circuit decreases at high temperature, and then the current input of the optocoupler increases, which can compensate the problem that the current transmission ratio of the optocoupler decreases due to the temperature rise.

[0017] To solve the above technical problems, the application further provides an intelligent electric meter, which comprises a control unit, a communication circuit for external communication, and an optocoupler isolation circuit for realizing signal transmission between the control unit and the communication circuit, wherein the optocoupler isolation circuit comprises an optocoupler and a shaping branch connected with the output end of the optocoupler; the control end of the optocoupler is connected with the pulse output end of the control unit, so as to input the pulse signal of the control unit into the optocoupler isolation circuit and realize the transmission of the pulse signal by controlling the on-off of the optocoupler; the shaping branch comprises a first switch tube and a voltage stabilizing branch connected with the first switch tube; the conducting end of the first switch tube is connected with the input end of the communication circuit, so as to realize signal transmission by the on-off state of the first switch tube; the control end of the voltage stabilizing branch is connected with the output end of the optocoupler, so as to realize signal transmission by controlling the on-off state of the first switch tube through controlling the voltage of the voltage stabilizing branch, and provide the conducting voltage drop for the first switch tube to control the first switch tube to be in the non-saturated state when there is voltage.

[0018] The optocoupler isolation circuit of the application connects the voltage stabilizing circuit with the control end of the first switch tube, so as to provide the conducting voltage drop for the first switch tube when there is voltage in the voltage stabilizing circuit, and the first switch tube is in the non-saturated state when it is conducting, so as not to limit the transmission efficiency of the first switch tube, thus meeting the communication demand of the intelligent electric meter, and realizing temperature compensation based on the voltage stabilizing control of the voltage stabilizing circuit, i.e. the conducting voltage drop provided by the voltage stabilizing circuit for the first switch tube changes with the need of the first switch tube. The control end of the optocoupler of the application is used to connect the pulse output end of the control unit of the intelligent electric meter, and the input signal rate of the pulse output end is already high, so there is no need to increase other circuits to improve the input pulse rate of the control end of the optocoupler, thus the application does not increase other accelerating circuits in the control end of the optocoupler, and the part of the circuit is simplified compared with the prior art.

[0019] Further, the voltage stabilizing branch comprises a first voltage dividing branch and a second voltage dividing branch arranged in parallel; the light coupling output end is connected to the ground through the first voltage dividing branch to provide voltage for the first voltage dividing branch when the light coupling is turned on, and the voltage across the first voltage dividing branch is used to control the voltage across the second voltage dividing branch; the second voltage dividing branch comprises a first voltage dividing resistor and a second voltage dividing resistor arranged in series, wherein the voltage dividing resistor connected to the ground is further connected in parallel to the control end of the first switch tube to provide a turn-on voltage drop for the first switch tube when there is voltage across the voltage dividing resistor connected to the ground.

[0020] Since the first voltage dividing branch and the second voltage dividing branch are arranged in parallel, the voltage across the first voltage dividing branch and the second voltage dividing branch is equal, so the voltage across the second voltage dividing branch can be controlled through the first voltage dividing branch, and based on the first voltage dividing resistor and the second voltage dividing resistor arranged in series in the second voltage dividing branch, the voltage across the first voltage dividing resistor and the second voltage dividing resistor can be controlled by controlling the voltage across the second voltage dividing branch, thereby controlling the turn-on voltage drop of the control end of the first switch tube, and based on the voltage control, the current flowing through the first voltage dividing resistor and the second voltage dividing resistor is also controlled, thereby controlling the current flowing through the control end of the first switch tube to make the first switch tube in a non-saturated state when it is turned on.

[0021] Further, the first switch tube is a triode; the first voltage dividing branch comprises a third voltage dividing resistor, a second switch tube and a third switch tube which are the same as the first switch tube; the base of the third switch tube is connected to the emitter of the second switch tube, and the base of the second switch tube and the emitter of the third switch tube are respectively connected to the two ends of the third voltage dividing resistor to control the voltage across the first voltage dividing branch through the second switch tube and the third switch tube.

[0022] Through the connection of the second switch tube and the third switch tube in the present application, when the light coupling is turned on, the voltage across the first voltage dividing branch is equal to the turn-on voltage drop of the second switch tube and the turn-on voltage drop of the third switch tube based on the turn-on voltage drop of the second switch tube and the third switch tube, and based on the fact that the first switch tube, the second switch tube and the third switch tube are all the same triode, the same voltage as the turn-on voltage drop of the second switch tube(third switch tube) is formed at the control end of the first switch tube, which ensures that the first switch tube can be turned on when the light coupling is turned on; and based on the control of the turn-on voltage drop of the control end of the first switch tube, the voltage across one of the voltage dividing resistors of the second voltage dividing branch is controlled, and the voltage across the two voltage dividing resistors of the second voltage dividing branch is further controlled, and the current flowing through the voltage dividing resistors is controlled, thereby achieving the control of the first switch tube in a non-saturated state when it is turned on.

[0023] Further, the second voltage dividing resistor is connected to the ground, and a capacitor is further connected in parallel across the first voltage dividing resistor.

[0024] Through the capacitor setting of the application, when the photo-coupler is changed from the on state to the off state, the stored charges of the first switch tube, the second switch tube and the third switch tube are neutralized quickly due to the stored charges on the capacitor, so that the first switch tube, the second switch tube and the third switch tube quickly enter the off state.

[0025] Further, the negative input end of the photo-coupler is the control end of the photo-coupler, and the positive input end of the photo-coupler is connected to the first power supply end through the parallelly arranged negative temperature coefficient thermistor and current limiting resistor.

[0026] By arranging the negative temperature coefficient thermistor and the current limiting resistor in parallel between the positive input end of the photo-coupler and the first power supply end, the resistance value of the parallel circuit (i.e. the parallel circuit composed of the negative temperature coefficient thermistor and the current limiting resistor) can be changed according to the change of temperature, i.e. the resistance value of the parallel circuit decreases at high temperature, and then the input current of the photo-coupler increases, which can compensate for the problem of the decrease of the current transfer ratio of the photo-coupler due to the temperature rise. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the photo-coupler isolation circuit of the prior art;

[0028] Figure 2 is a schematic diagram of the photo-coupler isolation circuit structure of the application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the application more clear and explicit, the application will be further described in detail below in combination with the drawings and examples.

[0030] The photo-coupler isolation circuit for signal transmission of the smart meter:

[0031] The photo-coupler isolation circuit of the present embodiment is arranged with a voltage stabilizing branch in order to meet the demand of the smart meter for communication rate, and the photo-coupler in the circuit and the switch tube for transmitting signals to the outside are both in linear working state (i.e. non-saturation state) through the voltage stabilizing branch, thereby ensuring the transmission efficiency of the photo-coupler isolation circuit.

[0032] Specifically, the photo-coupler isolation circuit in the present embodiment is as shown in Figure 2As shown, the circuit includes an optocoupler and a shaping branch connected to the optocoupler's output. The control terminal of the optocoupler is used to connect to the pulse output terminal of the smart meter control unit, so as to input the pulse signal of the smart meter control unit into the optocoupler isolation circuit, and to control the on / off state of the optocoupler through the pulse signal to realize the transmission of the pulse signal. The shaping branch includes a first switching transistor Q1 and a voltage regulator branch controlling the connection of the first switching transistor. The conducting terminal of the first switching transistor Q1 is used to connect to the communication circuit input terminal of the smart meter for external communication, so as to transmit signals through the on / off state of the first switching transistor Q1 (i.e., through...). Figure 2 The signal output point between the first switch Q1 and resistor R1 shown outputs a signal to the outside; the voltage regulation branch includes a first voltage divider branch connected in parallel ( Figure 2 R5, Q2, and Q3 form the first voltage divider branch and the second voltage divider branch. Figure 2 R3, R4, and C1 form the second voltage divider branch; the optocoupler output is grounded through the first voltage divider branch (i.e., a voltage regulator branch is set up between the optocoupler output and the grounding terminal) to provide voltage to the first voltage divider branch when the optocoupler is turned on, and the voltage across the second voltage divider branch is controlled by the voltage across the first voltage divider branch; the second voltage divider branch includes a first voltage divider resistor (i.e., R3) and a second voltage divider resistor (i.e., R4) connected in series, wherein the voltage divider resistor (i.e., R4) connected to the grounding terminal is also connected in parallel with the control terminal of the first switching transistor to provide a turn-on voltage drop for the first switching transistor when there is voltage across the voltage divider resistor connected to the grounding terminal. The first voltage divider branch includes a third voltage divider resistor (R5) and a second switch Q2 and a third switch Q3, identical to the first switch Q1. The base of the third switch Q3 is connected to the emitter of the second switch Q2. The base of the second switch Q2 and the emitter of the third switch Q3 are respectively connected to the two ends of the third voltage divider resistor (the collectors of Q2 and Q3 are left floating), so as to control the voltage across the first voltage divider branch through the second switch Q2 and the third switch Q3. In this embodiment, a capacitor is also connected in parallel across the first voltage divider resistor. The negative input terminal of the optocoupler is the control terminal of the optocoupler. The pulse output terminal of the smart meter control unit is connected to the control terminal of the optocoupler through resistor R2. The positive input terminal of the optocoupler is connected to the first power supply terminal (i.e., R5) after passing through a negative temperature coefficient thermistor RT1 and a current limiting resistor R6 connected in parallel. Figure 2 VDD1 is the power supply terminal for the control unit of the smart meter, and VDD2 is the power supply terminal for the communication circuit of the smart meter for external communication.

[0033] The optocoupler isolation circuit design based on this embodiment can meet the communication rate requirements under normal temperature, high temperature and low temperature conditions. The specific process is as follows:

[0034] (a) Under normal temperature conditions:

[0035] 1) OP1 optocoupler emission state:

[0036] a) OP1 primary current: OP1 primary current through the current limiting circuit composed of R2 resistor, RT1 (RT1 is NTC (negative temperature coefficient thermistor)) and R6, the resistance value of RT1 is 10kΩ, after being connected in parallel with R6 resistor at normal temperature, the resistance value is 10k / / 560=530Ω, the total resistance of the primary circuit is 630Ω, the thermistor circuit has little effect on the primary current at normal temperature. In this way, when OP1 emits light, the primary current is controlled at about 3mA.

[0037] b) OP1 secondary current: the secondary current of OP1 is the product of CTR and the primary current (i.e. CTR x primary current = (300%~600%) x 3mA = 9mA~18mA) under the condition that the current transfer ratio CTR of the optocoupler is 300~600.

[0038] c) Secondary circuit current condition: the pulse signal of OP1 forms a voltage drop of about 1.4V at Q2 and Q3 after passing through the optocoupler, Q2 and Q3 are the same type of triode as Q1, i.e. 0.7V voltage is generated on R4, so the voltage generated on C1 and R3 is 0.7V, and the base current of the third stage of Q1 is: 0.7V / R3-0.7V / R4=0.7mA, which is basically stable and unchanged. The BE junction of Q2 and Q3 adjusts the current in the loop, and when the transfer ratio changes, the excess current is shunted through Q2 and Q3; the working state of Q1 is basically not affected by the change of the transfer ratio of the optocoupler.

[0039] d) OP1 is in the linear amplification region: due to the voltage stabilizing effect of Q2 and Q3, the voltage of the secondary of the optocoupler OP1 is VDD2-1.4V, so that it is in the linear working region and can quickly respond to the change of the input signal, thereby further improving the transmission rate of the optocoupler.

[0040] e) Working state of Q1: when the primary input of the optocoupler is 0 level, Q1 is in saturated conduction state, and the collector output of Q1 is 0 level.

[0041] 2) OP1 optocoupler non-emitting state:

[0042] a) OP1 primary current: when the input is 1 level, the optocoupler OP1 does not emit light, and the primary circuit current is 0mA;

[0043] b) OP1 secondary current: the secondary current of OP1 is the product of CTR and the primary current: 0mA.

[0044] c) Secondary circuit current situation: after OP1 is turned off, the charge stored on C1 capacitor is quickly neutralized with the charge stored in Q2\Q3\Q1, making Q1\Q2\Q3 quickly enter the off state, in addition, R4 and R5 also play a role in quickly discharging the charge stored in the BE junction of Q1\Q2\Q3.

[0045] d) Secondary state of OP1: since OP1 is in linear amplification state in the previous stage, OP1 can quickly enter the off state when the primary input is high, and the secondary resistance quickly becomes high impedance.

[0046] e) Working state of Q1: when the primary input of the optocoupler is at 1 level, the charge of the BE junction of Q1 is quickly discharged, and the voltage is lower than its working voltage 0.7V, the collector output of Q1 is at 1 level.

[0047] (II) High temperature 70℃ case:

[0048] 1) OP1 light emitting state

[0049] a) OP1 primary current: the primary current of OP1 passes through the current limiting loop composed of R2 resistor, RT1 (NTC (negative temperature coefficient thermistor)) and R6, the resistance of RT1 is 1.5kΩ, after being connected in parallel with R6 at normal temperature, the resistance drops to 10k / / 560=407Ω, the total resistance of the primary circuit is 507Ω, the thermistor decreases at high temperature, increasing the primary circuit current, so that when the primary diode of OP1 emits light, the circuit current increases by about 30%, and the optocoupler primary current increases to about 4mA.

[0050] b) Secondary current of OP1: under the condition that the transfer ratio CTR of the optocoupler is 300-600, the transfer ratio of the optocoupler changes to 0.7 times the normal value at high temperature, the secondary current of OP1 is:

[0051] CTR x primary current x 0.7=(300%-600%) x 4mA x 0.7=8.4mA-16.8mA. The resistance of thermistor RT1 decreases at high temperature, increasing the primary current of optocoupler OP1, compensating for the decrease of the transfer ratio of the optocoupler at high temperature.

[0052] c) Secondary circuit current situation: the pulse signal of OP1 after passing through the optocoupler forms a voltage drop of about 1.2V at Q2 and Q3 (the BE junction voltage of the transistor decreases at high temperature), Q2 and Q3 are the same type of transistor as Q1, so the voltage generated on C1 and R3 is 0.6V, the base current of Q1 is: 0.6V / R3-0.6V / R4=0.64mA. The BE junction of Q2 and Q3 regulates the current of the circuit, when the transfer ratio changes, the excess current is shunted through Q2 and Q3; the working state of Q1 is basically not affected by the change of the transfer ratio of the optocoupler.

[0053] d) OP1 is in the linear amplification zone: due to the voltage stabilization of Q2 and Q3, the voltage of OP1 photo-coupling secondary is VDD2-1.2V, so that OP1 is in the linear working zone, thereby further improving the transmission rate of the photo-coupler.

[0054] e) Working state of Q1: when the photo-coupler primary input is 0 level, Q1 is in the saturated conduction state, and the collector output of Q1 is 0 level.

[0055] 2) OP1 photo-coupler non-lighting state:

[0056] a) Primary current of OP1: when the input is 1 level, the photo-coupler OP1 does not emit light, and the primary loop current is 0 mA;

[0057] b) Secondary current of OP1: the secondary current of OP1 is the product of CTR and the primary current: 0 mA.

[0058] c) Secondary loop current condition: after OP1 is turned off, the charge stored on C1 capacitor is neutralized with the charge stored in Q2\Q3\Q1, so that Q1\Q2\Q3 quickly enter the off state, and R4 and R5 also play a role in quickly discharging the charge stored in the BE junction of Q1\Q2\Q3.

[0059] d) Secondary state of OP1: since OP1 is in the linear amplification state in the previous stage, when the primary input is high level, OP1 can quickly enter the off state, and the secondary resistance quickly becomes high impedance.

[0060] e) Working state of Q1: when the photo-coupler primary input is 1 level, the charge of the BE junction of Q1 is quickly released, and the voltage is lower than the working voltage 0.6V, so that the collector output of Q1 is 1 level.

[0061] (Three) low temperature-40℃:

[0062] 1) OP1 photo-coupler lighting state:

[0063] a) Primary current of OP1: the primary current of OP1 passes through the current limiting loop composed of R2 resistor, RT1 (RT1 is NTC (negative temperature coefficient thermistor)) and R6, and the resistance of RT1 is 388kΩ. At normal temperature, the resistance decreases to 10k / / 560=560Ω after being connected in parallel with R6 resistor, and the total resistance of the primary loop is 660Ω. In this way, when the primary diode of OP1 emits light, the photo-coupler primary current is about 2.8mA, which is about 5% lower than that at normal temperature.

[0064] b) Secondary current of OP1: under the condition that the transmission ratio CTR of the photo-coupler is 300-600, the transmission ratio decreases to 0.9 times the normal value, and the secondary current of OP1 is:

[0065] CTR x primary current x 0.9 = (300%~600%) x 2.8mA x 0.9 = 7.56mA~15.12mA.

[0066] c) Secondary circuit current situation: the pulse signal of OP1 after passing through the optocoupler forms a voltage drop of about 1.6V at Q2 and Q3 (the voltage drop of the diode (the BE junction voltage of the triode) increases at low temperature), Q2 and Q3 are the same type of triode as Q1, so the voltage generated on C1 and R3 is 0.8V, and the base current of the tertiary tube of Q1 is: 0.8V / R3-0.8V / R4 = 0.8mA, which is basically stable and unchanged. The BE junction of Q2 and Q3 adjusts the current generated by the circuit, and when the transmission ratio changes, the excess current is shunted through Q2 and Q3; the working state of Q1 is basically not affected by the transmission ratio change of the optocoupler.

[0067] d) OP1 is in the linear amplification zone: due to the voltage stabilization effect of Q2 and Q3, the voltage of the secondary of the optocoupler OP1 is VDD2-1.6V, which makes it work in the linear zone, thereby further improving the transmission rate of the optocoupler.

[0068] e) Working state of Q1: when the primary input of the optocoupler is 0 level, Q1 is in a saturated conduction state, and the collector output of Q1 is 0 level.

[0069] 2) OP1 optocoupler non-emitting state:

[0070] a) Primary current of OP1: when the input is 1 level, the optocoupler OP1 does not emit light, and the primary circuit current is 0mA;

[0071] b) Secondary current of OP1: the secondary current of OP1 is the product of CTR and the primary current: 0mA.

[0072] c) Secondary circuit current situation: after OP1 is turned off, the charge stored on C1 capacitor is quickly neutralized with the charge stored in Q2\Q3\Q1, which makes Q1\Q2\Q3 quickly enter the off state, in addition, R4 and R5 also play a role in quickly discharging the charge stored in the BE junction of Q1\Q2\Q3.

[0073] d) Secondary state of OP1: since OP1 is in the linear amplification state in the previous stage, when the primary input is high level, OP1 can quickly enter the off state, and the secondary resistance quickly becomes high impedance.

[0074] e) Working state of Q1: when the primary input of the optocoupler is 1 level, the BE junction of Q1 releases the charge quickly, and the voltage is lower than its working voltage 0.8V, the collector output of Q1 is 1 level.

[0075] The circuit of the present application is provided with the first voltage division branch and the second voltage division branch in parallel, so that the voltage across the first voltage division branch and the second voltage division branch is equal, and thus the voltage across the second voltage division branch can be controlled through the first voltage division branch, and based on the first voltage division resistor and the second voltage division resistor connected in series in the second voltage division branch, the voltage across the first voltage division resistor and the voltage across the second voltage division resistor can be controlled by controlling the voltage across the second voltage division branch, and thus the on-voltage drop of the control end of the first switch tube is controlled, and based on the voltage control, the current flowing through the first voltage division resistor and the second voltage division resistor is also controlled, and thus the current flowing through the control end of the first switch tube is controlled, so that the first switch tube is in a non-saturation state when it is turned on. And through the connection of the second switch tube and the third switch tube in the present application, when the optocoupler is turned on, the voltage across the first voltage division branch is equal to the on-voltage drop of the second switch tube and the on-voltage drop of the third switch tube based on the on-voltage drop of the second switch tube and the third switch tube, and based on the fact that the first switch tube, the second switch tube and the third switch tube are all the same triode, the same voltage as the on-voltage drop of the second switch tube (the third switch tube) is formed at the control end of the first switch tube, so that the first switch tube can be turned on when the optocoupler is turned on; and based on the control of the on-voltage drop of the control end of the first switch tube, the voltage across one of the voltage division resistors in the second voltage division branch is controlled, and thus the voltage across the two voltage division resistors in the second voltage division branch is controlled, and the voltage control is the control of the current flowing through the voltage division resistors, and thus the first switch tube can be controlled to be in a non-saturation state when it is turned on. And the circuit of the present application adds the negative temperature coefficient thermistor RT1 and the resistor R6 of the primary side of the OP1 optocoupler, which functions to adjust the input current to increase at high temperature, and further compensate for the problem of the decrease of the optocoupler transfer ratio at high temperature; at the same time, the current is less affected at low temperature, and the optocoupler transfer characteristics at high and low temperatures are better compensated.

[0076] The smart meter embodiment:

[0077] The smart meter of the present embodiment comprises a control unit and a communication circuit for external communication, and further comprises an optocoupler isolation circuit for realizing signal transmission between the control unit and the communication circuit. The optocoupler isolation circuit can be arranged at the terminal of the electric energy meter to realize data transmission of the electric energy meter, or arranged at the terminal of the electric meter to realize data transmission of the terminal. The specific arrangement of the optocoupler isolation circuit has been described in detail in the optocoupler isolation circuit embodiment for signal transmission of the smart meter, and will not be repeated here.

[0078] The above is only a preferred embodiment of the present application, and does not limit the present application. The patent protection scope of the present application is subject to the claims, and any equivalent structural changes made according to the content of the specification and drawings of the present application shall also be included in the protection scope of the present application.

Claims

1. An optocoupler isolation circuit for signal transmission in a smart meter, characterized in that, The system includes an optocoupler and a shaping branch connected to the negative output terminal of the optocoupler. The control terminal of the optocoupler is used to connect to the pulse output terminal of the smart meter control unit, so as to input the pulse signal of the smart meter control unit into the optocoupler isolation circuit, and to realize the transmission of the pulse signal by controlling the on / off state of the optocoupler through the pulse signal. The shaping branch includes a first transistor and a voltage regulator branch controlling the connection of the first transistor. The collector of the first transistor is used to connect to the input terminal of the communication circuit for external communication of the smart meter, so as to realize signal transmission through the on / off state of the first transistor. The voltage regulator branch includes first, second and third voltage dividers. The resistor also includes a second transistor and a third transistor of the same type as the first transistor; one end of the third voltage divider resistor is connected to the negative output terminal of the optocoupler, and the other end is grounded; the base of the second transistor is connected to the negative output terminal of the optocoupler, the emitter is connected to the base of the third transistor, and the emitter of the third transistor is grounded; one end of the first voltage divider resistor is connected to the negative output terminal of the optocoupler, and the other end is connected to one end of the second voltage divider resistor, and the other end of the second voltage divider resistor is grounded; the series connection point of the first voltage divider resistor and the second voltage divider resistor is connected to the base of the first transistor, the emitter of the first transistor is grounded, and the collectors of the second and third transistors are left floating.

2. The optocoupler isolation circuit for smart meter signal transmission according to claim 1, characterized in that, A capacitor is also connected in parallel across the first voltage divider resistor.

3. The optocoupler isolation circuit for smart meter signal transmission according to claim 1, characterized in that, The negative input terminal of the optocoupler is the control terminal of the optocoupler, and the positive input terminal of the optocoupler is connected to the first power supply terminal after passing through a negative temperature coefficient thermistor and a current limiting resistor connected in parallel.

4. The optocoupler isolation circuit for smart meter signal transmission according to claim 1, characterized in that, The collector of the first transistor is connected to the power supply via a pull-up resistor.

5. The optocoupler isolation circuit for smart meter signal transmission according to claim 1, characterized in that, An optocoupler consists of a light-emitting diode and a phototransistor.

6. A smart meter, comprising a control unit and a communication circuit for external communication, characterized in that, It also includes an optocoupler isolation circuit for signal transmission between the control unit and the communication circuit. The optocoupler isolation circuit includes an optocoupler and a shaping branch connected to the output terminal of the optocoupler. The control terminal of the optocoupler is connected to the pulse output terminal of the control unit to input the pulse signal from the control unit into the optocoupler isolation circuit, and the pulse signal is used to control the on / off state of the optocoupler to achieve pulse signal transmission. The shaping branch includes a first transistor and a voltage regulator branch controlling the connection to the first transistor. The conducting terminal of the first transistor is connected to the input terminal of the communication circuit to transmit signals through the on / off state of the first transistor. The voltage regulator branch includes a first and a second... The second and third voltage divider resistors also include a second transistor and a third transistor of the same type as the first transistor; one end of the third voltage divider resistor is connected to the negative output terminal of the optocoupler, and the other end is grounded; the base of the second transistor is connected to the negative output terminal of the optocoupler, the emitter is connected to the base of the third transistor, and the emitter of the third transistor is grounded; one end of the first voltage divider resistor is connected to the negative output terminal of the optocoupler, and the other end is connected to one end of the second voltage divider resistor, and the other end of the second voltage divider resistor is grounded; the series connection point of the first and second voltage divider resistors is connected to the base of the first transistor, the emitter of the first transistor is grounded, and the collectors of the second and third transistors are left floating.

7. The smart meter according to claim 6, characterized in that, A capacitor is also connected in parallel across the first voltage divider resistor.

8. The smart meter according to claim 6, characterized in that, The negative input terminal of the optocoupler is the control terminal of the optocoupler, and the positive input terminal of the optocoupler is connected to the first power supply terminal after passing through a negative temperature coefficient thermistor and a current limiting resistor connected in parallel.

9. The smart meter according to claim 8, characterized in that, The collector of the first transistor is connected to the power supply via a pull-up resistor.

10. The smart meter according to claim 9, characterized in that, An optocoupler consists of a light-emitting diode and a phototransistor.

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