Power supply circuit of an electric meter

Abstract

The present invention discloses a power supply circuit of an electric meter, comprising a flyback main circuit, the flyback main circuit comprising a switch tube S1, a transformer T1, a resistor Rs, and a diode D1 and a capacitor C1 connected in series with a secondary winding of the transformer T1, the output end after rectification by D1 and C1 serves as the output end of the power supply circuit, the resistor Rs is connected in series in a loop between the switch tube S1 and the primary winding of the transformer, the voltage across the resistor Rs serves as a current detection signal of the switch tube S1, and the present invention is characterized in that it also comprises a control circuit, the control circuit comprises a magnetic field unit 1, a current limiting unit 2, a voltage stabilizing unit 3, and a drive generating unit 4. As the power supply circuit of the electric meter, the present invention can avoid interference from an external strong magnetic field, has a simple structure, and is low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of smart electric meters, and in particular to a power supply circuit of an electric meter. Background Art

[0002] In recent years, smart meters have been widely used. However, there is a problem with smart meters. If there is strong magnetic field interference outside the smart meter, the power supply circuit of the meter will have problems, which will cause problems with the smart meter's electricity metering. Therefore, how to prevent the power supply circuit of the meter from being interfered with is an urgent problem to be solved in the industry.

[0003] The existing solutions are shielding, such as adding a magnetic field shielding device to the periphery of the meter to avoid interference from the external strong magnetic field, but this method is too complicated and expensive. In addition, for example, Chinese patent CN204758820 compensates for the difference in the meter caused by interference by catching up on the amount of electricity, which requires complex algorithms and programs to solve the problem. Summary of the invention

[0004] The object of the present invention is to provide a power supply circuit for an electric meter to solve the problem raised in the above background technology and prevent the electric meter from being disturbed by an external strong magnetic field.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A power supply circuit of an electric meter, comprising a flyback main circuit, the flyback main circuit comprising a switch tube S1, a transformer T1, a resistor Rs, and a diode D1 and a capacitor C1 connected in series with a secondary winding of the transformer T1, an output end rectified by D1 and C1 serving as an output end of the power supply circuit, the resistor Rs being connected in series in a loop between the switch tube S1 and a primary winding of the transformer, a voltage across the resistor Rs serving as a current detection signal of the switch tube S1, and a control circuit comprising a magnetic field unit, a current limiting unit, a voltage stabilization unit, and a drive generation unit;

[0007] The magnetic field unit detects the strength of the magnetic field, and when it is detected that the magnetic field strength exceeds a preset value, outputs a compensation signal Vc to the current limiting unit;

[0008] The current limiting unit compares the current detection signal of the switch tube S1 with the current preset value Iref, and when the current detection signal is greater than the current preset value Iref, outputs a current limiting signal Vi to the drive generation unit; and when receiving the compensation signal Vc output by the magnetic field unit, controls the value of the current limiting signal Vi to increase as the compensation signal Vc increases;

[0009] The voltage stabilization unit detects the output voltage Vo of the power supply circuit, presets a voltage preset value Vref, and outputs a feedback signal Vf to the drive generation unit, wherein the feedback signal Vf represents the difference between the output voltage Vo and the voltage preset value Vref, and the voltage stabilization unit is used to control the output voltage to be equal to the voltage preset value Vref;

[0010] The drive generating unit receives the current limiting signal Vi and the feedback signal Vf. When only the feedback signal Vf is received, the drive signal Vd is generated according to the feedback signal, so that the duty cycle of the drive signal changes according to the change of the feedback signal; and as long as the current limiting signal Vi is received, the drive signal Vd is generated according to the current limiting signal, and the duty cycle of the drive signal is controlled to increase with the increase of the current limiting signal Vi.

[0011] Preferably, the magnetic field unit includes a Hall element H, a first operational amplifier, a transistor Q1 and a resistor R1. The Hall element H is powered by a constant current source, and both ends are connected to the input end of the first operational amplifier. The output end of the first operational amplifier is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the constant current source, and the emitter is connected in series with the resistor R1 and then grounded. The non-grounded end of the resistor R1 serves as the output end of the magnetic field unit, and the voltage on the resistor R1 is the compensation signal Vc.

[0012] Preferably, the magnetic field unit further comprises a comparison unit, which receives a slope signal of the current of the switch tube S1, compares the slope signal with a set value, and outputs a compensation signal Vc when the slope signal is greater than the set value.

[0013] Preferably, the comparison unit further controls the amplitude of the compensation signal Vc outputted by the comparison unit to increase as the slope signal increases.

[0014] Preferably, the current limiting unit includes a first comparator and resistors R2 and R3, the inverting input terminal of the first comparator is connected to the resistor Rs for receiving the current detection signal, the current preset value Iref is input to the non-phase input terminal of the first comparator through the resistor R2, the compensation signal Vc is input to the non-phase input terminal of the first comparator through the resistor R3, and the output terminal of the first comparator serves as the output terminal of the current limiting unit to output the current limiting signal Vi.

[0015] Preferably, the current limiting unit includes a second comparator, a third comparator and resistors R9 and R10, the inverting input of the second comparator is connected to the resistor Rs for receiving the current detection signal, the current preset value Iref is input to the non-inverting input of the second comparator through the resistor R9, the inverting input of the third comparator is connected to a small voltage Vcs with an amplitude close to zero, the compensation signal Vc is input to the non-inverting input of the third comparator, the output of the third comparator is connected to the non-inverting input of the second comparator through the resistor R10, and the output of the second comparator serves as the output of the current limiting unit to output the current limiting signal Vi.

[0016] Preferably, the voltage stabilization unit includes a second operational amplifier and a peripheral circuit, the peripheral circuit includes a capacitor C1 and resistors R4, R5, and R6, the two ends of the resistors R4 and R5 are connected in series and are respectively connected to the two ends of the output of the power supply circuit, the common end of the resistors R4 and R5 is connected to the inverting input end of the second operational amplifier, one end of the resistor R6 is connected to the inverting input end of the second operational amplifier, and the other end is connected in series with the capacitor C1 and connected to the output end of the second operational amplifier, the non-phase input end of the second operational amplifier inputs the voltage preset value Vref, and the output end of the second operational amplifier serves as the output end of the voltage stabilization unit, and outputs the feedback signal Vf.

[0017] Preferably, the drive generating unit is an SR trigger, the Q end of the SR trigger serves as the output end of the drive generating unit, for outputting the drive signal Vd, the output end S is connected to the control end of the switch tube S1 of the flyback main circuit, the input end R7 is connected to the output end of the current limiting unit, for receiving the current limiting signal Vi, and the input end R8 is connected to the output end of the voltage stabilization unit, for receiving the feedback signal Vf.

[0018] Preferably, the input terminal R7 has a higher priority than the input terminal R8.

[0019] The present invention provides a power supply circuit for an electric meter, which has the following beneficial effects: as the power supply circuit for the electric meter, the interference of an external strong magnetic field can be avoided, the structure is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the circuit structure of the present invention;

[0021] Figure 2 Schematic diagram of the circuit structure of the magnetic field unit of the present invention;

[0022] Figure 3 This is a schematic diagram of the circuit structure of the first embodiment of the current limiting unit of the present invention;

[0023] Figure 4 It is a schematic diagram of the circuit structure of the second embodiment of the current limiting unit of the present invention;

[0024] Figure 5 It is a schematic diagram of the circuit structure of the voltage stabilization unit of the present invention;

[0025] Figure 6 Schematic diagram of the circuit structure of the drive generation unit of the present invention;

[0026] Figure 7 It is a period diagram of the intermittent mode of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0028] like Figure 1 As shown, a power supply circuit of an electric meter includes a flyback main circuit, the flyback main circuit includes a switch tube S1, a transformer T1, a resistor Rs, and a diode D1 and a capacitor C1 connected in series with the secondary winding of the transformer T1, the output end after rectification by D1 and C1 is used as the output end of the power supply circuit, the resistor Rs is connected in series in the loop of the switch tube S1 and the primary winding of the transformer, the voltage across the resistor Rs is used as the current detection signal of the switch tube S1, and also includes a control circuit, the control circuit includes a magnetic field unit 1, a current limiting unit 2, a voltage stabilization unit 3, and a drive generation unit 4;

[0029] The magnetic field unit 1 detects the strength of the magnetic field, and when it is detected that the magnetic field strength exceeds a preset value, outputs a compensation signal Vc to the current limiting unit 2;

[0030] The current limiting unit 2 compares the current detection signal of the switch tube S1 with the current preset value Iref, and when the current detection signal is greater than the current preset value Iref, outputs a current limiting signal Vi to the drive generating unit 4; and when receiving the compensation signal Vc output by the magnetic field unit 1, controls the value of the current limiting signal Vi to increase as the compensation signal Vc increases;

[0031] The voltage stabilization unit 3 detects the output voltage Vo of the power supply circuit, presets a voltage preset value Vref, and outputs a feedback signal Vf to the drive generation unit 4, wherein the feedback signal Vf represents the difference between the output voltage Vo and the voltage preset value Vref, and the voltage stabilization unit 3 is used to control the output voltage to be equal to the voltage preset value Vref;

[0032] The drive generating unit 4 receives the current limiting signal Vi and the feedback signal Vf. When only the feedback signal Vf is received, the drive signal Vd is generated according to the feedback signal, so that the duty cycle of the drive signal changes according to the change of the feedback signal; and as long as the current limiting signal Vi is received, the drive signal Vd is generated according to the current limiting signal, and the duty cycle of the drive signal is controlled to increase with the increase of the current limiting signal Vi.

[0033] like Figure 2 As shown, the magnetic field unit 1 includes a Hall element H, a first operational amplifier 5, a transistor Q1 and a resistor R1. The Hall element H is powered by a constant current source 6, and both ends are connected to the input end of the first operational amplifier 5. The output end of the first operational amplifier 5 is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the constant current source 6, and the emitter is connected in series with the resistor R1 and then grounded. The non-grounded end of the resistor R1 serves as the output end of the magnetic field unit, and the voltage on the resistor R1 is the compensation signal Vc.

[0034] Furthermore, the magnetic field unit further includes a comparison unit, which receives a slope signal of the current of the switch tube S1, compares the slope signal with a set value, and outputs a compensation signal Vc when the slope signal is greater than the set value.

[0035] Furthermore, the comparison unit also controls the amplitude of the compensation signal Vc outputted by the comparison unit to increase as the slope signal increases.

[0036] like Figure 3As shown, the current limiting unit 2 includes a first comparator 7 and resistors R2 and R3. The inverting input terminal of the first comparator 7 is connected to the resistor Rs for receiving the current detection signal. The current preset value Iref is input to the positive input terminal of the first comparator 7 through the resistor R2. The compensation signal Vc is input to the positive input terminal of the first comparator 7 through the resistor R3. The output terminal of the first comparator 7 serves as the output terminal of the current limiting unit 2, and outputs the current limiting signal Vi. Rs is connected in series in the loop between the switch tube S1 and the primary winding of the transformer, and is used to detect the current of the switch tube S1. The detected current signal is input to the inverting input terminal of the first comparator 7, and the current preset value Iref is input to the positive input terminal of the first comparator 7 through the resistor R2. When the current of the switch tube S1 is greater than the current preset value Iref, the current limiting signal Vi is output to the drive generation unit 4, and the power supply circuit works in the current limiting control state. When the detection current signal of the switch tube S1 is not greater than the current preset value Iref, the output current limiting signal Vi does not control the drive generation unit 4, and the drive generation unit 4 is controlled by the voltage stabilization unit 3 at this time. When the magnetic field unit 1 does not detect that the magnetic field strength exceeds the preset value, it will not output the compensation signal Vc, and the current limiting unit 2 only works according to the above working principle. When the magnetic field unit 1 detects that the magnetic field strength exceeds the preset value, it outputs the compensation signal Vc to the current limiting unit 2, and the compensation signal Vc is superimposed with the current preset value Iref through R2 and R3, and then input to the positive phase input terminal of the first comparator 7 after superposition. Therefore, when the external magnetic field strength continues to increase, the amplitude of the compensation signal Vc output by the magnetic field unit 1 increases accordingly, and the signal amplitude input to the positive phase input terminal of the first comparator 7 continues to increase, so that the amplitude of the current limiting signal Vi output by the current limiting unit 2 also continues to increase, and the duty cycle of the drive signal generated by the drive generation unit 4 continues to increase, compensating for the output power reduced due to strong magnetic interference. That is to say, when the magnetic field outside the electric meter interferes with the electric meter, the parameters of the magnetic components of the power supply circuit of the electric meter change, resulting in a decrease in output power and output voltage. At this time, under the control of the voltage stabilization unit 3, the current of the switch tube S1 exceeds the preset current value, and the power supply circuit works under the control of the current limiting unit 2. The current limiting unit 2 of the present application increases the duty cycle of the switch tube S1 according to the compensation signal Vc of the magnetic field unit, thereby increasing the output voltage and compensating for the problem of the electric meter caused by the interference of the external strong magnetic field. It should be pointed out that this embodiment takes the increase in the intensity of the external magnetic field as an example. Another identical embodiment can also be replaced Figure 3In the embodiment, that is, Vc passes through the inverting follower and then is superimposed with the current signal of the switch tube S1 (the voltage on Rs) through resistors R3 and R2, the same result can be obtained, that is, the stronger the magnetism, the larger the amplitude of Vc, and after passing through the inverting follower, the smaller its amplitude is, and the smaller the value after superposition is, which is input to the inverting input terminal of the first comparator 7, which is also reflected in the increase of the output current limiting signal Vi.

[0037] Further, such as Figure 4 The current limiting unit 2 includes a second comparator 8, a third comparator 9 and resistors R9 and R10. The inverting input terminal of the second comparator 8 is connected to the resistor Rs for receiving the current detection signal. The current preset value Iref is input to the non-inverting input terminal of the second comparator 8 through the resistor R9. The inverting input terminal of the third comparator 9 is connected to a small voltage Vcs with an amplitude close to zero. The compensation signal Vc is input to the non-inverting input terminal of the third comparator 9. The output terminal of the third comparator 9 is connected to the non-inverting input terminal of the second comparator 8 through the resistor R10. The output terminal of the second comparator 8 serves as the output terminal of the current limiting unit 2, and outputs the current limiting signal Vi.

[0038] like Figure 5 As shown, the voltage stabilization unit 3 includes a second operational amplifier 10 and a peripheral circuit, and the peripheral circuit includes a capacitor C1 and resistors R4, R5, and R6. The resistors R4 and R5 are connected in series at both ends and are respectively connected to the output ends of the power supply circuit. The common end of the resistors R4 and R5 is connected to the inverting input end of the second operational amplifier 10, one end of the resistor R6 is connected to the inverting input end of the second operational amplifier 10, and the other end is connected in series with the capacitor C1 and then connected to the output end of the second operational amplifier 10. The non-phase input end of the second operational amplifier 10 inputs the voltage preset value Vref, and the output end of the second operational amplifier 10 serves as the output end of the voltage stabilization unit 3, and outputs the feedback signal Vf.

[0039] like Figure 6 As shown, the drive generating unit 4 is an SR trigger, and the Q end of the SR trigger serves as the output end of the drive generating unit 4, which is used to output the drive signal Vd, the output end S is connected to the control end of the switch tube S1 of the flyback main circuit, the input end R7 is connected to the output end of the current limiting unit 2, which is used to receive the current limiting signal Vi, and the input end R8 is connected to the output end of the voltage stabilization unit 3, which is used to receive the feedback signal Vf.

[0040] The priority of the input terminal R7 is higher than that of the input terminal R8, that is, when R7 receives a trigger signal, the trigger starts to work according to the signal of R7, and only when R7 does not receive a trigger signal, the trigger works according to the signal received by R8.

[0041] Furthermore, the control circuit also controls the flyback main circuit to operate in discontinuous mode. Specifically, when the power supply circuit is fully loaded, the flyback main circuit operates in discontinuous mode. Discontinuous mode means that the sum of the duration Toff during which the secondary current of the transformer is not zero and the switch tube conduction time Ton (that is, the duration during which the primary current is not zero) is less than the switching period Tm.

[0042] like Figure 7 As shown, the sum of the switch on time Ton, the transformer primary current, i.e. the switch current Is, the secondary current Ir, and the duration Toff during which the secondary current is not zero is less than the switch period Tm of the switch. The flyback main circuit operates in discontinuous mode to ensure that the flyback main circuit can still operate in discontinuous mode when the compensation signal is at its maximum value.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A power supply circuit of an electric meter, comprising a flyback main circuit, the flyback main circuit comprising a switch tube S1, a transformer T1, a resistor Rs, and a diode D1 and a capacitor C1 connected in series with the secondary winding of the transformer T1, the output end after rectification by D1 and C1 is used as the output end of the power supply circuit, the resistor Rs is connected in series in the loop of the switch tube S1 and the primary winding of the transformer, the voltage across the resistor Rs is used as the current detection signal of the switch tube S1, and the characteristics are: It also includes a control circuit, which includes a magnetic field unit (1), a current limiting unit (2), a voltage stabilization unit (3), and a drive generation unit (4); The magnetic field unit (1) detects the intensity of the magnetic field, and when it is detected that the magnetic field intensity exceeds a preset value, outputs a compensation signal Vc to the current limiting unit (2); the magnetic field unit (1) comprises a Hall element H, a first operational amplifier (5), a transistor Q1 and a resistor R1, the Hall element H is powered by a constant current source (6), two ends of which are connected to the input end of the first operational amplifier (5), the output end of the first operational amplifier (5) is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the constant current source (6), the emitter is connected in series with a resistor R1 and then grounded, the non-grounded end of the resistor R1 serves as the output end of the magnetic field unit, and the voltage on the resistor R1 is the compensation signal Vc; the magnetic field unit also comprises a comparison unit, the comparison unit receives a slope signal of the current of the switch tube S1, compares the slope signal with a set value, and outputs a compensation signal Vc when the slope signal is greater than the set value; the comparison unit also controls the amplitude of the compensation signal Vc outputted by it to increase as the slope signal increases; The current limiting unit (2) compares the current detection signal of the switch tube S1 with the current preset value Iref, and when the current detection signal is greater than the current preset value Iref, outputs a current limiting signal Vi to the drive generation unit (4); and when receiving the compensation signal Vc output by the magnetic field unit (1), controls the value of the current limiting signal Vi to increase as the compensation signal Vc increases; the current limiting unit (2) comprises a first comparator (7) and resistors R2 and R3, the inverting input end of the first comparator (7) is connected to the resistor Rs for receiving the current detection signal, the current preset value Iref is input to the non-inverting input end of the first comparator (7) through the resistor R2, the compensation signal Vc is input to the non-inverting input end of the first comparator (7) through the resistor R3, the output end of the first comparator (7) serves as the output end of the current limiting unit (2), and outputs the current limiting signal Vi; The voltage stabilization unit (3) detects the output voltage Vo of the power supply circuit, presets a voltage preset value Vref, and outputs a feedback signal Vf to the drive generation unit (4), wherein the feedback signal Vf represents the difference between the output voltage Vo and the voltage preset value Vref, and the voltage stabilization unit (3) is used to control the output voltage to be equal to the voltage preset value Vref; The drive generating unit (4) receives the current limiting signal Vi and the feedback signal Vf. When only the feedback signal Vf is received, the drive generating unit (4) generates a drive signal Vd according to the feedback signal, so that the duty cycle of the drive signal changes according to the change of the feedback signal; and when only the current limiting signal Vi is received, the drive signal Vd is generated according to the current limiting signal, and the duty cycle of the drive signal is controlled to increase as the current limiting signal Vi increases.

2. The power supply circuit of an electric meter according to claim 1, characterized in that: The current limiting unit (2) comprises a second comparator (8), a third comparator (9) and resistors R9 and R10. The inverting input terminal of the second comparator (8) is connected to the resistor Rs for receiving the current detection signal. The current preset value Iref is input to the positive input terminal of the second comparator (8) through the resistor R9. The inverting input terminal of the third comparator (9) is connected to a small voltage Vcs with an amplitude close to zero. The compensation signal Vc is input to the positive input terminal of the third comparator (9). The output terminal of the third comparator (9) is connected to the positive input terminal of the second comparator (8) through the resistor R10. The output terminal of the second comparator (8) serves as the output terminal of the current limiting unit (2) and outputs the current limiting signal Vi.

3. The power supply circuit of an electric meter according to claim 1, characterized in that: The voltage stabilization unit (3) comprises a second operational amplifier (10) and a peripheral circuit, wherein the peripheral circuit comprises a capacitor C1 and resistors R4, R5 and R6, wherein the resistors R4 and R5 are connected in series and their two ends are respectively connected to the two ends of the output of the power supply circuit, the common end of the resistors R4 and R5 is connected to the inverting input end of the second operational amplifier (10), one end of the resistor R6 is connected to the inverting input end of the second operational amplifier (10), and the other end is connected in series with the capacitor C1 and then connected to the output end of the second operational amplifier (10), the non-inverting input end of the second operational amplifier (10) inputs the preset voltage value Vref, and the output end of the second operational amplifier (10) serves as the output end of the voltage stabilization unit (3) and outputs a feedback signal Vf.

4. The power supply circuit of an electric meter according to claim 1, characterized in that: The drive generation unit (4) is an SR trigger, the Q end of the SR trigger serves as the output end of the drive generation unit (4) and is used to output a drive signal Vd, the output end S is connected to the control end of the switch tube S1 of the flyback main circuit, the input end R7 is connected to the output end of the current limiting unit (2) and is used to receive the current limiting signal Vi, and the input end R8 is connected to the output end of the voltage stabilization unit (3) and is used to receive the feedback signal Vf.

5. The power supply circuit of an electric meter according to claim 4, characterized in that: The input terminal R7 has a higher priority than the input terminal R8.

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