A constant current pulse width modulation circuit for contactor coil

Abstract

The present invention provides a contactor coil constant current pulse width modulation circuit. The present invention can replace conventional double-coil contactors, reduce volume and weight; can simplify the circuit form, can realize thick film circuit packaging, highly miniaturized, and conveniently applicable to various types of contactors; and can realize complete control of the contactor coil current without using a device with embedded software.

Description

Technical Field

[0001] The invention relates to a constant current pulse width modulation circuit for a contactor coil. Background Art

[0002] After the traditional contactor is energized by the coil, the magnetic force generated by the iron core drives the moving contact to contact the static contact to promote the normal operation of the contactor. The magnitude of the magnetic force generated by the iron core is proportional to the magnitude of the contactor coil current. Therefore, when the contactor coil is initially attracted, it needs to generate a large current, and only a small current is needed after attraction to maintain normal operation. Conventional single-coil contactors consume a lot of power when working for a long time and have serious heat because the current after attraction is consistent with the current before attraction. Now a double-coil contactor (starting coil and holding coil) has been born on the conventional single-coil contactor. After the contactor is attracted, the holding coil is connected in series with the starting coil to reduce power consumption. The double-coil contactor solves the problem of high power consumption, but at the same time the size and weight of the contactor are also increased. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a contactor coil constant current pulse width modulation circuit.

[0004] The present invention is achieved through the following technical solutions.

[0005] The present invention provides a contactor coil constant current pulse width modulation circuit; comprising an EMI circuit, a protection circuit, a power supply circuit, a current adjustment circuit, a start circuit, a pulse width modulation drive circuit, a coil control circuit, and a current acquisition circuit, wherein the EMI circuit is connected to an external power supply, and the external power supply is respectively transmitted to the power supply circuit, the coil control circuit, and the contactor coil through the protection circuit, a diode D14 is connected between the protection circuit and the coil control circuit, a diode D13 is connected between the contactor coil and the protection circuit, the power supply circuit converts the voltage into a reference voltage to supply power to components in the circuit, the protection circuit is connected to the start circuit, the start circuit is connected to the current adjustment circuit, the current adjustment circuit is connected to the pulse width modulation drive circuit through a diode D11, the pulse width modulation drive circuit is connected to the current acquisition circuit and the coil control circuit, and the coil control circuit is connected to the positive electrode of the contactor coil through a diode D15.

[0006] The protection circuit includes a diode D19, the anode of the diode D19 is connected to the EMI circuit, the cathode of the diode D19 is connected to the collector of a transistor T22, the emitter of the transistor T22 is connected to the power supply circuit and the startup circuit, the base of the transistor T22 is connected to the cathode of the Zener diode D21, the anode of the Zener diode D21 is grounded, and the base and collector of the transistor T22 are connected through a resistor R20.

[0007] The power supply circuit includes a voltage regulator U25, whose input end is connected to the protection circuit and grounded through capacitor C26, and whose output end is connected to a 5V power supply terminal and a resistor R28, and the other end of the resistor R28 is connected to a 2.5V power supply terminal and a resistor R29, and the other end of the resistor R29 is grounded.

[0008] The startup circuit includes a comparator U37, the positive input terminal of the comparator U37 is connected to the resistor R34, the other end of the resistor R34 is connected in parallel with the resistor R31 and the resistor R33, the other end of the resistor R31 is connected to the protection circuit, and the resistor R33 and the capacitor C32 are connected in parallel to the ground; the negative input terminal of the amplifier U37 is connected to the 2.5V power terminal in the power supply circuit, the output terminal of the amplifier U37 is connected to the negative electrode of the diode D12 and is connected to the 5V power terminal through the resistor R36, and the negative electrode of the diode D12 is connected to the pulse width modulation drive circuit.

[0009] The current regulating circuit includes an amplifier U46, the positive electrode of the input end of the amplifier U46 is connected to the 2.5V power supply terminal through a resistor R41, and the negative electrode of the input end is respectively connected to a capacitor C45 and a resistor R43, the other end of the resistor R43 is connected to a resistor R42, the other end of the resistor R42 is connected to the negative electrode of a diode D12, the resistor 43 is also connected in parallel with a diode D44, the other end of the capacitor 45 is grounded, and the output end of the amplifier U46 is connected to the positive electrode of a diode D11 through a resistor R48.

[0010] The pulse width modulation drive circuit includes a comparator U56, the positive input terminal of the comparator U56 is respectively connected to the negative electrode of the resistor R50, the resistor R51 and the diode D11, the other end of the resistor R50 is connected to the 5V power supply terminal, the negative electrode of the comparator U56 is grounded through the capacitor C52 and the resistor R51, the output terminal of the comparator U56 is respectively connected to the resistor R55 and the resistor R54, the other end of the resistor R54 is connected to the 5V power supply terminal, and the other end of the resistor R55 is connected to the coil control circuit.

[0011] The current acquisition circuit includes an amplifier U60, the positive electrode of the input end of the amplifier U60 is connected to the coil control circuit, the negative electrode of the input end of the amplifier U60 is grounded through a resistor R61, the output end of the amplifier U60 is connected to the positive electrode of the diode D63, the negative electrode of the diode D63 is connected to the pulse width modulation drive circuit through a resistor R64, and the negative electrode of the diode D63 and the negative electrode of the input end of the amplifier U60 are also connected to a resistor R62.

[0012] The coil control circuit includes a switch tube D73 and a switch tube D74. The gate of the switch tube D73 is connected to a resistor R67, a resistor R68, a cathode of a voltage-stabilizing diode D69, and a capacitor 70. The other end of the resistor R67 is connected to a cathode of a diode D14. The other end of the resistor R68, the anode of a voltage-stabilizing diode D69, and the other end of the capacitor C70 are connected in parallel to a source of the switch tube D73 and a drain of the switch tube D74. The drain and source of the switch tube D73 are respectively connected to the cathode of the contactor coil and the anode of the coil. The drain and source of the switch tube D73 are also respectively connected to the cathode and anode of a voltage-stabilizing diode D75. The gate of the switch tube D74 is connected to a pulse width modulation drive circuit through a resistor R71 and is grounded through a capacitor 72. The source of the switch tube D74 is grounded through a resistor R16.

[0013] The output end of the power supply circuit is connected to the start-up circuit, the current acquisition circuit, the pulse width modulation drive circuit, and the current adjustment circuit, and mainly provides power supply and reference voltage.

[0014] The input end of the starting circuit is connected to the protection circuit, and the output end is connected to the current adjustment circuit and the pulse width modulation drive circuit; the contactor coil is started according to the state of the input voltage, and the current modulation circuit is activated at the same time, prompting the contactor coil to switch from starting large current to holding current.

[0015] The input end of the current acquisition circuit is connected to the external contactor, and the output end is connected to the pulse width modulation drive circuit; the current of the contactor coil is converted and processed and then fed back to the pulse width modulation drive circuit as a prerequisite for pulse width modulation drive.

[0016] The input end of the pulse width modulation drive circuit is connected to the current adjustment circuit and the current collection circuit, and the output end is connected to the coil control circuit; when the contactor coil current reaches a preset value, it drives the modulation MOSFET in the coil control circuit to turn on and off.

[0017] The output end of the current adjustment circuit is connected to the pulse width modulation drive circuit to complete the conversion of the current preset value during initial startup and after startup, thereby completing the conversion of the contactor current from a large current to a holding current.

[0018] The coil control circuit is connected to the pulse width modulation drive circuit and is the executive mechanism in the whole invention; it controls the change of the contactor coil current according to the output signal of the drive circuit.

[0019] Preferably, it also includes an EMI circuit, which is connected in parallel with the protection circuit; it mainly suppresses electromagnetic interference.

[0020] The beneficial effects of the present invention are: it can replace conventional double-coil contactors, reduce volume and weight; it can simplify the circuit form, realize thick film circuit packaging, be highly miniaturized, and be conveniently applicable to various types of contactors; and it can achieve complete control of the contactor coil current without using a device with embedded software. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a constant current pulse width modulation circuit of a contactor coil of the present invention;

[0022] Figure 2 yes Figure 1 Circuit diagram of the protection circuit;

[0023] Figure 3 yes Figure 1 Circuit diagram of the power supply circuit;

[0024] Figure 4 yes Figure 1 Circuit diagram of the starter circuit;

[0025] Figure 5 yes Figure 1 Circuit diagram of medium current regulation circuit;

[0026] Figure 6 yes Figure 1 Circuit diagram of pulse width modulation driving circuit;

[0027] Figure 7 yes Figure 1 Circuit diagram of medium current collection circuit;

[0028] Figure 8 yes Figure 1 Circuit diagram of the middle coil control circuit. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0030] A contactor coil constant current pulse width modulation circuit; including an EMI circuit, a protection circuit, a power supply circuit, a current adjustment circuit, a start circuit, a pulse width modulation drive circuit, a coil control circuit, and a current acquisition circuit. The EMI circuit is connected to an external power supply, and the external power is respectively transmitted to the power supply circuit, the coil control circuit, and the contactor coil through the protection circuit. A diode D14 is connected between the protection circuit and the coil control circuit, and a diode D13 is connected between the contactor coil and the protection circuit. The power supply circuit converts the voltage into a reference voltage to supply power to the components in the circuit. The protection circuit is connected to the start circuit, and the start circuit is connected to the current adjustment circuit. The current adjustment circuit is connected to the pulse width modulation drive circuit through a diode D11, and the pulse width modulation drive circuit is connected to the current acquisition circuit and the coil control circuit. The coil control circuit is connected to the positive pole of the contactor coil through a diode D15; the EMI circuit is connected to the external power supply, mainly to suppress electromagnetic interference, and is composed of a capacitor. The protection circuit is connected to the power supply circuit and the start circuit to protect sensitive devices in the power supply circuit and the start circuit. The power supply circuit provides voltage for active devices in all circuits, provides driving voltage for control switches, and also provides a reference voltage for comparison. The starting circuit is connected to the protection circuit in order to control the start-up of the coil control circuit according to the size of the external input voltage. The current adjustment circuit is connected to the starting circuit, mainly to complete the conversion from large current to small current after a delay after the coil is started. The pulse width modulation drive circuit is connected to the current adjustment circuit, the current acquisition circuit, and the coil control circuit. It is the core control mechanism of the entire invention and mainly realizes the control of the MOS tube of the coil control circuit. The coil control circuit is the executive mechanism of the entire invention. It realizes the opening and closing of the MOSFET in the circuit according to the output signal of the pulse width modulation drive circuit, so that the current of the contactor coil is kept in a constant state.

[0031] The protection circuit includes a diode D19, the anode of the diode D19 is connected to the EMI circuit, the cathode of the diode D19 is connected to the collector of a transistor T22, the emitter of the transistor T22 is connected to the power supply circuit and the startup circuit, the base of the transistor T22 is connected to the cathode of the Zener diode D21, the anode of the Zener diode D21 is grounded, and the base and collector of the transistor T22 are connected through a resistor R20.

[0032] The power supply circuit includes a voltage regulator U25, whose input end is connected to the protection circuit and grounded through capacitor C26, and whose output end is connected to a 5V power supply terminal and a resistor R28, and the other end of the resistor R28 is connected to a 2.5V power supply terminal and a resistor R29, and the other end of the resistor R29 is grounded.

[0033] The startup circuit includes a comparator U37, the positive input terminal of the comparator U37 is connected to the resistor R34, the other end of the resistor R34 is connected in parallel with the resistor R31 and the resistor R33, the other end of the resistor R31 is connected to the protection circuit, and the resistor R33 and the capacitor C32 are connected in parallel to the ground; the negative input terminal of the amplifier U37 is connected to the 2.5V power terminal in the power supply circuit, the output terminal of the amplifier U37 is connected to the negative electrode of the diode D12 and is connected to the 5V power terminal through the resistor R36, and the negative electrode of the diode D12 is connected to the pulse width modulation drive circuit.

[0034] The current regulating circuit includes an amplifier U46, the positive electrode of the input end of the amplifier U46 is connected to the 2.5V power supply terminal through a resistor R41, and the negative electrode of the input end is respectively connected to a capacitor C45 and a resistor R43, the other end of the resistor R43 is connected to a resistor R42, the other end of the resistor R42 is connected to the negative electrode of a diode D12, the resistor 43 is also connected in parallel with a diode D44, the other end of the capacitor 45 is grounded, and the output end of the amplifier U46 is connected to the positive electrode of a diode D11 through a resistor R48.

[0035] The pulse width modulation drive circuit includes a comparator U56, the positive input terminal of the comparator U56 is respectively connected to the negative electrode of the resistor R50, the resistor R51 and the diode D11, the other end of the resistor R50 is connected to the 5V power supply terminal, the negative electrode of the comparator U56 is grounded through the capacitor C52 and the resistor R51, the output terminal of the comparator U56 is respectively connected to the resistor R55 and the resistor R54, the other end of the resistor R54 is connected to the 5V power supply terminal, and the other end of the resistor R55 is connected to the coil control circuit.

[0036] The current acquisition circuit includes an amplifier U60, the positive electrode of the input end of the amplifier U60 is connected to the coil control circuit, the negative electrode of the input end of the amplifier U60 is grounded through a resistor R61, the output end of the amplifier U60 is connected to the positive electrode of the diode D63, the negative electrode of the diode D63 is connected to the pulse width modulation drive circuit through a resistor R64, and the negative electrode of the diode D63 and the negative electrode of the input end of the amplifier U60 are also connected to a resistor R62.

[0037] The coil control circuit includes a switch tube D73 and a switch tube D74. The gate of the switch tube D73 is connected to a resistor R67, a resistor R68, a cathode of a voltage-stabilizing diode D69, and a capacitor 70. The other end of the resistor R67 is connected to a cathode of a diode D14. The other end of the resistor R68, the anode of a voltage-stabilizing diode D69, and the other end of the capacitor C70 are connected in parallel to a source of the switch tube D73 and a drain of the switch tube D74. The drain and source of the switch tube D73 are respectively connected to the cathode of the contactor coil and the anode of the coil. The drain and source of the switch tube D73 are also respectively connected to the cathode and anode of a voltage-stabilizing diode D75. The gate of the switch tube D74 is connected to a pulse width modulation drive circuit through a resistor R71 and is grounded through a capacitor 72. The source of the switch tube D74 is grounded through a resistor R16.

[0038] The working principle of the present invention is as follows. The positive and negative poles of the external contactor coil ( Figure 1 When there is external power input, the current flows through Figure 1 The diode D13 in the coil flows into the coil and then flows to the negative end of the input power supply through the coil control circuit and the current sampling resistor R16, forming a contactor coil power supply path. The current is converted into a voltage value through the sampling resistor R16 and input to the current collection circuit. Figure 7 The operational amplifier U60, resistor R61 and resistor R62 form a common-mode amplifier, which amplifies the converted voltage value and inputs it to the pulse width modulation drive circuit.

[0039] Figure 7 The resistor R61, resistor R62, diode D63, resistor R64 and Figure 6 The charge and discharge circuit formed by the capacitor C52 is used to adjust the duty cycle of the pulse width. Figure 6 When the capacitor C52 in is charged, Figure 7 The current output by the operational amplifier U60 passes through the diode D63, the resistor R64, and the capacitor C52. When the capacitor C52 discharges, it passes through Figure 7 The resistors R64, R62 and R61 in the circuit are discharged. Figure 6 The duty cycle is modulated by making the charge and discharge times of the capacitor C52 inconsistent.

[0040] Figure 8 For the execution part of the whole invention, Figure 8The resistor R67, the resistor R68, the voltage zener diode D69, the capacitor C70, the N-channel MOSFET tube D73, and the voltage zener tube D75 constitute the freewheeling path. When the N-channel MOSFET tube D74 is turned on, the N-channel MOSFET D73 is turned on immediately. When the N-channel MOSFET D74 is turned off, the gate voltage of the N-channel MOSFET D73 is discharged through the resistor R68. When the N-channel MOSFET D74 is turned off, the reverse electromotive force generated by the contactor coil is discharged through Figure 8 Medium N-channel MOSFET D73, Figure 1 The diode D15 in the contactor flows into the positive end of the contactor coil to form a freewheeling loop. The change in the contactor coil current is related to the freewheeling time t, the inductance L of the contactor coil, and the resistance R of the contactor coil. Follow the following formula:

[0041]

[0042] (in If is the current value of the contactor coil, I is the current value of the contactor coil after time t) Figure 6 It is the control part of the whole invention. The comparator is an open-drain output comparator. The hysteresis comparison circuit formed by the comparator U56, the resistor R50, the resistor R51, the resistor R53 and the resistor R54 sets the upper and lower limits of the comparison threshold of the voltage comparator superimposed on the resistor R51 according to the resistance value. When the sampled current signal is greater than the upper limit of the comparison threshold, Figure 6 The comparator 56 in the output is low level, Figure 8 After startup, when the sampling current is greater than the preset threshold, Figure 8 The N-channel MOSFET D74 is turned off, and the N-channel MOSFET D73 is freewheeling. Figure 1 The current of the sampling resistor R16 decreases to less than the comparison threshold. Figure 8 The N-channel MOSFET D74 in the middle is turned on and circulates continuously, forming a contact with the contactor coil, and the current value I changes very little, thus achieving a constant current modulation process.

[0043] Figure 5 It is the current regulation circuit. Figure 5 The resistor R41, resistor R47 and operational amplifier U46 form a hysteresis comparison circuit. Figure 5 The middle circuit outputs a high level voltage through resistor R48 and Figure 6 The middle resistor R51 forms a loop, and a larger threshold is superimposed on the resistor R51, in order to meet the initial startup, the contactor coil completes the large current modulation process. The resistor R42, the resistor R43, the capacitor C45, and the diode D45 form a charge and discharge circuit. Figure 4After the startup circuit is started, it outputs a high level, thus giving Figure 5 The capacitor C45 in the circuit is charged (the charging time can be determined by the capacitor value C45 and the resistor R43). When the voltage of the capacitor C45 is greater than Figure 5 When the threshold voltage of the positive terminal of the operational amplifier U46 is reached, the operational amplifier U46 outputs a low level and enters the pulse width modulation state after startup, thereby realizing the conversion from the initial startup large current to the holding current.

[0044] Figure 4 The hysteresis comparator composed of comparator R37, resistor R34, resistor R35 and resistor R36 outputs a low level when the input voltage is lower than the preset value at the initial power-on, thereby Figure 1 The diode D12 in Figure 1 In the circuit, the driving signal output by the pulse width modulation driving circuit is pulled to a low level. When the input voltage is higher than the preset value, a high level is output to complete the normal start-up of the contactor coil.

Claims

1. A contactor coil constant current pulse width modulation circuit, characterized in that: It includes an EMI circuit, a protection circuit, a power supply circuit, a current adjustment circuit, a start-up circuit, a pulse width modulation drive circuit, a coil control circuit, and a current acquisition circuit. The EMI circuit is connected to an external power supply, and the external power supply is respectively transmitted to the power supply circuit, the coil control circuit, and the contactor coil through the protection circuit. A diode D14 is connected between the protection circuit and the coil control circuit, and a diode D13 is connected between the contactor coil and the protection circuit. The power supply circuit converts the voltage into a reference voltage to supply power to the components in the circuit. The protection circuit is connected to the start-up circuit, and the start-up circuit is connected to the current adjustment circuit. The current adjustment circuit is connected to the pulse width modulation drive circuit through a diode D11, and the pulse width modulation drive circuit is connected to the current acquisition circuit and the coil control circuit. The coil control circuit is connected to the positive electrode of the contactor coil through a diode D15; The startup circuit includes a comparator U37, the positive electrode of the input end of the comparator U37 is connected to the resistor R34, the other end of the resistor R34 is connected in parallel with the resistor R31 and the resistor R33, the other end of the resistor R31 is connected to the protection circuit, and the resistor R33 and the capacitor C32 are connected in parallel to the ground; the negative electrode of the input end of the amplifier U37 is connected to the 2.5V power supply terminal in the power supply circuit, the output end of the amplifier U37 is connected to the negative electrode of the diode D12 and is connected to the 5V power supply terminal through the resistor R36, and the negative electrode of the diode D12 is connected to the resistor R42; The current regulating circuit includes an amplifier U46, the positive electrode of the input end of the amplifier U46 is connected to the 2.5V power supply terminal through a resistor R41, the negative electrode of the input end is connected to a capacitor C45 and a resistor R43 respectively, the other end of the resistor R43 is connected to a resistor R42, the other end of the resistor R42 is connected to the negative electrode of a diode D12, the resistor 43 is also connected in parallel with a diode D44, the other end of the capacitor 45 is grounded, and the output end of the amplifier U46 is connected to the positive electrode of a diode D11 through a resistor R48; The pulse width modulation drive circuit includes a comparator U56, wherein the positive electrode of the input end of the comparator U56 is respectively connected to the negative electrode of the resistor R50, the resistor R51, and the diode D11, the other end of the resistor R50 is connected to the 5V power supply terminal, the negative electrode of the comparator U56 is connected to the resistor R64, and is grounded to the resistor R51 through the capacitor C52, the output end of the comparator U56 is respectively connected to the resistor R55 and the resistor R54, the other end of the resistor R54 is connected to the 5V power supply terminal, and the other end of the resistor R55 is connected to the resistor R71; The current acquisition circuit includes an amplifier U60, the positive electrode of the input end of the amplifier U60 is connected to the source of the switch tube D74, the negative electrode of the input end of the amplifier U60 is grounded through a resistor R61, the output end of the amplifier U60 is connected to the positive electrode of the diode D63, the negative electrode of the diode D63 is connected to the negative electrode of the comparator U56 through a resistor R64, and the negative electrode of the diode D63 and the negative electrode of the input end of the amplifier U60 are also connected to a resistor R62; The coil control circuit includes a switch tube D73 and a switch tube D74. The gate of the switch tube D73 is connected to a resistor R67, a resistor R68, a cathode of a voltage-stabilizing diode D69, and a capacitor 70. The other end of the resistor R67 is connected to the cathode of a diode D14. The anode of the diode D14 is connected to the anode of a diode D19. The other end of the resistor R68, the anode of the voltage-stabilizing diode D69, and the other end of the capacitor C70 are connected in parallel to the source of the switch tube D73 and the drain of the switch tube D74. The drain and source of the switch tube D73 are respectively connected to the cathode of the contactor coil and the anode of the coil. The drain and source of the switch tube D73 are also respectively connected to the cathode and anode of a voltage-stabilizing diode D75. The gate of the switch tube D74 is connected to the resistor R55 through the resistor R71 and is grounded through the capacitor 72. The source of the switch tube D74 is grounded through the resistor R16.

2. The contactor coil constant current pulse width modulation circuit as claimed in claim 1, characterized in that: The protection circuit includes a diode D19, the anode of the diode D19 is connected to the EMI circuit, the cathode of the diode D19 is connected to the collector of the transistor T22, the emitter of the transistor T22 is connected to the power supply circuit and the startup circuit, the base of the transistor T22 is connected to the cathode of the voltage-stabilizing diode D21, the anode of the voltage-stabilizing diode D21 is grounded, and the base and collector of the transistor T22 are connected through a resistor R20.

3. The contactor coil constant current pulse width modulation circuit as claimed in claim 1, characterized in that: The power supply circuit includes a voltage regulator U25, whose input end is connected to the protection circuit and grounded through capacitor C26, and whose output end is connected to a 5V power supply terminal and a resistor R28, and the other end of the resistor R28 is connected to a 2.5V power supply terminal and a resistor R29, and the other end of the resistor R29 is grounded.

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