Control circuit of arc welding power supply powered by lithium battery

Abstract

The utility model discloses a control circuit of an arc welding power supply powered by a lithium battery. A control circuit of the control circuit board comprises a relay group, a normally open contact of the relay group, a relay control circuit, a switching power supply circuit, a driving circuit of an electronic switching tube group, the electronic switching tube group, a fast recovery diode group, an output control circuit, a capacitor C5, a resistor R6a, an output reactor DKQ1, a shunt FLQ and sockets CN1 to CN7; the control circuit board is used for controlling the working state of the conversion circuit under the action of an input given control signal and a current feedback detection signal of the current regulation potentiometer, so that the arc welding power supply realizes voltage and current conversion between input and output; the circuit is controlled to generate various DC working voltages by using a switching power supply circuit, so that the working state conversion of a relay group is realized, and the operation control of output current feedback control and the PWM pulse width adjustment control are realized; the device has the advantages of small size, light weight, portability, energy conservation and the like.

Description

Technical Field

[0001] This utility model discloses a control circuit for a lithium battery-powered arc welding power supply. It belongs to the field of arc welding power supply technology. Background Technology

[0002] Currently, arc welding power supplies on the domestic and international markets typically require connection to the power grid or a generator to perform arc welding. Arc welding power supplies requiring grid connection cannot be used when the power source is far from the power supply system. While generator-powered arc welding power supplies do not require grid power and can be used in areas with power shortages, they consume gasoline or diesel fuel, polluting the environment. Furthermore, the use of gasoline or diesel generators results in large and heavy arc welding power supply systems, wasting materials and hindering the development of a low-carbon economy. In recent years, lithium battery-powered devices, such as automobiles and power tools, have experienced rapid development. These devices are ready to use after charging, offering great convenience. Using lithium batteries to power arc welding power supplies offers numerous advantages over generator-powered systems, such as smaller size, lighter weight, material savings, and energy efficiency, demonstrating significant overall performance advantages. Therefore, this new type of arc welding power supply represents one of the development directions for arc welding power supplies.

[0003] Although new lithium battery-powered arc welding power supplies have made some progress, their design and control methods differ, resulting in significant variations in their structure, circuitry, and performance. Therefore, designing new lithium battery-powered arc welding power supplies and employing novel control methods to address certain issues is of practical significance and application value.

[0004] This utility model discloses a control circuit for a lithium battery-powered arc welding power supply, including a charging interface, a power switch, a lithium battery assembly, an overheat protection indicator light, a cooling fan, a lithium battery power and voltage display, a temperature controller, a current adjustment potentiometer, a welding button, a control circuit board, and positive and negative output terminals of the arc welding power supply. The electronic switching transistor group and fast recovery diode group in the control circuit board form a conversion circuit, which, under the action of the control circuit, realizes the output control of the arc welding power supply. Using this utility model, a lithium battery-powered arc welding power supply can be made, which has advantages such as small size, light weight, portability, energy saving, material saving, and energy efficiency, and is convenient for welding in places without power supply. It solves the problem that arc welding power supplies must be powered by mains electricity or gasoline / diesel generators to operate, and has good practical application value. Utility Model Content

[0005] This utility model discloses a control circuit for a lithium battery-powered arc welding power supply, characterized in that: the arc welding power supply includes a charging interface CDJK10, a power switch KG20, a lithium battery assembly 30, an overheat protection indicator OH40, a cooling fan Fan50, a lithium battery power and voltage display 60, a temperature controller 70, a current adjustment potentiometer 80, a welding button SB90, a control circuit board PCB100, and positive and negative output terminals of the arc welding power supply; a power supply from which the lithium battery is charged, such as 65VDC, is input to the charging interface CDJK10, whose I N1 is the positive terminal of the charging power supply, and IN2 is the negative terminal. During charging, it is connected to the corresponding output polarity terminal of the lithium battery charger. The charging interface CDJK10 is installed on the rear panel of the arc welding power supply and is used to connect the lithium battery charger to charge the lithium battery assembly 30 in the arc welding power supply. The output of the charging interface CDJK10 is connected to the power switch KG20 and the input terminal of the lithium battery assembly 30. The power switch KG20 is used to control the on / off state of the input of the circuit board PCB100. IN(+) and IN(-) control the circuit board respectively. The positive and negative input terminals of PCB100; the lithium battery assembly 30, after being charged by its charger, can provide the necessary power to the circuitry of the control circuit board PCB100, that is, to power the arc welding power supply; the overheat protection indicator light OH40, mounted on the front panel of the arc welding power supply, is connected to the CN1 socket of the control circuit board PCB100, and this indicator light is used to indicate whether the arc welding power supply has experienced overheating protection; the cooling fan Fan50, mounted on the side panel of the arc welding power supply, is connected to the CN7 socket of the control circuit board PCB100, and this cooling fan... The fan is used to cool the heat-generating components inside the arc welding power supply, such as the electronic switching transistor group and its heat sink, and the fast recovery diode group and its heat sink. The electronic switching transistor group and the fast recovery diode group form a conversion circuit. With this conversion circuit, DC-to-DC conversion control can be easily achieved under the action of the control circuit, and finally the output control of the arc welding power supply is realized. The lithium battery power and voltage display meter 60 is installed on the front panel of the arc welding power supply. It is connected to the CN4 socket of the control circuit board PCB100. This meter is used to indicate the power and voltage of the lithium battery inside the arc welding power supply during charging or welding.The temperature controller 70 is attached to the surface of the heat sink of the electronic switching transistor assembly installed inside the arc welding power supply. It is connected to the CN6 socket of the control circuit board PCB100 and is used to detect whether the heat sink and the electronic switching transistors mounted on its surface have overheated. When the temperature of the heat sink surface reaches the operating temperature of the temperature controller, it indicates overheating. At this time, the temperature controller changes from a normally open state to a normally closed state, and the control circuit in the control circuit board PCB100 stops the operation of the electronic switching transistor assembly, ultimately stopping the output of the arc welding power supply or welding, thus achieving overheat protection control. Simultaneously, it can activate the overheat protection indicator. When lamp OH40 illuminates, it indicates an overheating issue. The arc welding power supply can only resume output or welding when the temperature controller returns to its normally open state. The current adjustment potentiometer 80, mounted on the front panel of the arc welding power supply, is connected to the CN2 socket of the control circuit board PCB100. This potentiometer is used to adjust the output or welding current of the arc welding power supply. The welding button SB90, mounted on the front panel of the arc welding power supply, is connected to the CN5 socket of the control circuit board PCB100. This button is used for welding start control of the arc welding power supply. The positive output terminal (OUTPUT(+)) of the arc welding power supply... The welding torch and workpiece are connected to the negative polarity output terminal (OUTPUT (-)), which is the load during welding. The CN3 socket of the control circuit board PCB100 is connected to pin 2 of the charging interface CDJK10 through its plug and connecting wire. The control circuit board PCB100, under the input given control signal of the current adjustment potentiometer 80 and the current feedback detection signal Uif (note: will be mentioned in the following description, and will not be elaborated here), is used to control the working state of the conversion circuit composed of the electronic switching transistor group and the fast recovery diode group in the circuit board unit, so that the arc welding power supply can realize the voltage and current conversion between the input and output, that is, realize the welding or working output of the arc welding power supply. In addition, the circuit board also uses its switching power supply circuit to generate a variety of DC working voltages, realize the working state conversion of the relay group, realize the relay working state conversion of the lithium battery power voltage display table 60, realize the operation control of output current feedback control and PWM pulse width adjustment control, as well as overheat protection and indication functions. The output current of the arc welding power supply mainly depends on the battery power supply capacity of the lithium battery component 30 and the configuration of the electronic switching transistor group and the fast recovery diode group in the control circuit board PCB100. ;

[0006] The control circuit of the control circuit board PCB100 is characterized in that: this circuit includes a relay group and its normally open contact 110, a relay control circuit 120, a switching power supply circuit 130, a driving circuit 140 for the electronic switching transistor group, an electronic switching transistor group 150, a fast recovery diode group 160, an output control circuit 170, a capacitor C5, a resistor R6a, an output reactor DKQ1, a shunt FLQ, and sockets CN1 to CN7; the positive polarity input terminal IN(+) and the negative polarity input terminal IN(-) are connected to the power switch KG on the rear panel of the arc welding power supply, and through this power switch, they are respectively connected to the positive and negative polarity terminals of the lithium battery pack and the charging interface; IN(+) is respectively connected to... Pin 1 of the CN5 socket is connected to one end of two parallel normally open contacts in the relay group and its normally open contact 110. The other ends of these two parallel normally open contacts are connected to capacitor C5, the input terminal of the electronic switching transistor group 150, and the IN(+)-1 terminal. Pin 3 of the CN5 socket is connected to resistor R6a. The other end of R6a, IN(+)-1, is connected to the switching power supply circuit 130. The other end of capacitor C5, IN(-), is also connected to the switching power supply circuit 130, the positive terminal of the fast recovery diode group 160, the output control circuit 170, and one end of the shunt FLQ. The control terminal of the relay group and its normally open contact 110 is connected to the relay control circuit 120, and the input control signal terminal of this circuit is connected to the output control circuit. 170; The other end of the shunt FLQ is connected to the negative output terminal OUTPUT (-) of the arc welding power supply. The two ends of the shunt FLQ can obtain the current feedback detection signal Uif, which is connected to the output control circuit 170; The output terminal of the electronic switching transistor group 150 is connected to the other end (negative terminal) of the fast recovery diode group 160 and one end of the output reactor DKQ1. The other end of the output reactor DKQ1 is connected to the positive output terminal OUTPUT (+) of the arc welding power supply; The control terminal of the electronic switching transistor group 150 is connected to the drive circuit 140; The input control terminal of the drive circuit 140 is connected to the output control circuit 170; The input signals of the switching power supply circuit 130 are IN (+)-1 and IN (-). The outputs are +5V, +12V, +15V, +24V, Vcc1, and Vee, as well as ground power signals; the CN7 socket connects to the cooling fan Fan via its plug and control wire; the CN5 socket connects to the solder button SB via its plug and control wire, and when the button is pressed, pins 1 and 3 of the socket are connected; the CN1 socket connects to the overheat protection indicator OH via its plug and control wire; the CN4 socket connects to the lithium battery power and voltage display via its plug and control wire; the CN6 socket connects to the thermostat via its plug and control wire; the CN2 socket connects to the current adjustment potentiometer via its plug and control wire; and the CN3 socket connects to pin 2 of the charging interface CDJK via its plug and control wire.The output control circuit 170 of this invention includes a lithium battery power-voltage display conversion circuit. When the plug of the charger used to charge the arc welding power supply of this invention is inserted into the charging interface CDJK, pins 1 and 2 of the charging interface CDJK are connected, meaning the control line of CN3 is connected to the positive input terminal of IN1 or the positive terminal of the lithium battery. This activates the relay in the lithium battery power-voltage display conversion circuit, changing the connection method of the relay contacts to display the charging voltage on the lithium battery power-voltage display. Conversely, when the charger is not inserted into the charging interface CDJK, the relay in the lithium battery power-voltage display conversion circuit does not activate; in this case, the lithium battery power-voltage display only displays the voltage of the lithium battery in the arc welding power supply.

[0007] The electronic switch group 150 is composed of parallel electronic switch tubes, which can be IGBTs, MOSFETs, silicon carbide MOSFETs, or other similar devices.

[0008] The fast recovery diode group 160 is configured in parallel, and the fast recovery diodes can be of various types.

[0009] The relay control circuit 120 consists of a relay with normally open contacts connected in parallel, a diode, an N-channel MOSFET, a capacitor, a resistor, a transistor, an electrolytic capacitor, and a +24V power supply. The output signal from the output control circuit 170 controls the relay's operating state, thereby controlling the relay contact state. When the arc welding power supply's power switch KG is closed, pressing the welding button SB on the front panel of the arc welding power supply activates the relay under the action of the output control circuit 170, closing its normally open contacts. This allows the power or energy stored in the lithium battery to be supplied to the subsequent switching circuit composed of the electronic switching transistor group and the fast recovery diode group, thus starting the arc welding power supply. Furthermore, the parallel contact operation of the relay group ensures reliable operation.

[0010] The switching power supply circuit 130 consists of a switching power supply transformer, an optocoupler, diodes, an N-channel MOSFET, a PWM pulse width modulator, 7805, 7812, and 7815 integrated voltage regulators, capacitors, resistors, Zener diodes, and electrolytic capacitors. The switching power supply circuit 130 generates power signals of +5V, +12V, +15V, +24V, Vcc1, and Vee, as well as ground. Vcc1 and Vee power signals supply the drive circuit 140; the +24V power supply supplies the relay control circuit 120 and the output control circuit 170, as well as the cooling fan Fan; the +5V, +12V, and +15V power supplies supply the output control circuit 170. The switching power supply transformer is a power transformer with multiple working windings. Using the aforementioned components and IN(+)-1 and IN(-) input signals, multiple DC power outputs are constructed. Furthermore, since a switching power supply circuit is used, there is no need to control the power supply of a transformer. Therefore, while reducing costs and equipment weight, saving energy and materials, it also improves the adaptability of the DC power supply section to wide input voltage variations and the stability of the output DC power supply voltages.

[0011] The drive circuit 140 of the electronic switch group mainly consists of a high-speed optocoupler and a drive resistor connected to the control electrode of the electronic switch. Under the action of the output control circuit 170, the electronic switch can be driven and controlled through the drive resistor, so that the electronic switch is in a PWM pulse width modulation control state. Different PWM pulse widths can make the output of the conversion circuit different, and the size of the pulse width depends on the current setpoint signal of the aforementioned current adjustment potentiometer and the Uif current negative feedback signal.

[0012] The output control circuit 170 mainly consists of a relay JDQ1, a PWM pulse width modulator U1, an operational amplifier U2, CN1~CN4 and CN6 sockets, +5V, +12V, +24V, and some NPN transistors, PNP transistors, Zener diodes, resistors, capacitors, and electrolytic capacitors. This circuit can be further divided into a relay JDQ1 control circuit 171, a current setting circuit 172, a PWM pulse width modulator and its output control circuit 173, an overheat protection control and its indication circuit 174, a setting and negative feedback operation circuit, and a relay control circuit 175. The relay JDQ1 control circuit 171 is connected to IN(-), IN(+)-1, ground, and CN3 and CN4; the current setting circuit 172 is connected to +5V, ground, and the output current... The current given signal Ug; the PWM pulse width modulation and its output control circuit 173 is connected to +12V, ground, the output of the overheat protection control and its indicator circuit 174, the given and negative feedback operation and the input Uk control signal of the relay control circuit 175, and the drive resistor circuit; the output of the drive resistor circuit is connected to the control electrode of the switching transistor in the electronic switching transistor group; the overheat protection control and its indicator circuit 174 is connected to +12V, +24V, ground, CN1 and CN6, and the PWM pulse width modulation and its output control circuit 173; the given and negative feedback operation and relay control circuit 175 is connected to +12V, ground, IN (-), Uif current negative feedback signal, the output current given signal Ug of the current given circuit 172, and the output Uk and relay control signal of this part of the circuit.

[0013] The relay JDQ1 control circuit 171 consists of relay JDQ1, resistor R1, and sockets CN3 and CN4. The relay JDQ1 control circuit is used to display and control the switching between charging voltage and the internal lithium battery voltage of the arc welding power supply.

[0014] The current setting circuit consists of a +5V power supply, a variable potentiometer W1, a capacitor C29, resistors R21d and R27, and a CN2 socket. This part of the circuit is used to generate a current setting signal. Its output signal is the current setting signal Ug, which is connected to the current setting and negative feedback operation and relay control circuit 175. Changing the magnitude of the Ug signal changes the output signal Uk of the current setting and negative feedback operation and relay control circuit 175, thereby changing the pulse width of the output PWM pulse signal of the PWM pulse width modulation and its output control circuit 173, and ultimately changing the output current of the arc welding power supply.

[0015] The PWM pulse width modulation and its output control circuit consists of a PWM pulse width modulation chip (SG3525), an NPN transistor Q4, a PNP transistor Q3, resistors R42-R45 and R47-R49, capacitors C42-C44, a +12V circuit and its ground, diodes D41 and D42, and an electrolytic capacitor E8. This circuit section, under the action of the current negative feedback operational control signal Uk, generates a PWM pulse drive control signal for the electronic switching transistor group that controls the output of the arc welding power supply. Under the action of the soft-start control signal, it determines whether to generate the PWM drive signal output, ultimately determining whether the arc welding power supply outputs. The Uk signal is the output control signal resulting from the combined action of the current setpoint signal Ug and the current negative feedback signal Uif, processed by the operational amplifier control circuit. It is connected to the PWM control circuit and determines the pulse width of the PWM signal output by the PWM chip, ultimately determining the output of the arc welding power supply. For example, when the current setpoint signal Ug increases, the pulse width of the output PWM signal also increases, increasing the output current of the arc welding power supply; conversely, it decreases the output current. By controlling the output characteristics of the arc welding power supply, the requirements for arc welding power supply welding are ultimately met.

[0016] The overheat protection control and indication circuit consists of CN1 and CN6 sockets, +12V and +24V terminals, some resistors and capacitors, diodes, Zener diodes, and NPN transistors. One output signal of this circuit is connected to the soft-start pin 8 of the pulse width modulation chip (SG3525) in the PWM pulse width modulation and output control circuit. Pin 10 of this chip is grounded. When no overheating occurs, pin 8 of the chip is high, not affecting the output of the PWM pulse signal. When overheating occurs, pin 8 of the chip goes low, stopping the output of the PWM pulse signal. The temperature controller is attached to the surface of the heatsink of the electronic switching transistor assembly installed inside the arc welding power supply to detect whether the heatsink and the electronic switching transistors mounted on its surface have overheated. When the surface temperature of the heat sink reaches the operating temperature of the temperature controller, it indicates overheating. At this point, the temperature controller changes from its normally open state to its normally closed state. Through the overheat protection control and its indicator circuit, pin 8 of the pulse width modulation chip goes low, and the PWM pulse width modulation and its output control circuit stop outputting, thereby stopping the operation of the electronic switching transistor group 150, and ultimately stopping the output or welding of the arc welding power supply, thus achieving overheat protection control. Simultaneously, the overheat protection indicator light OH LED or OH40 will illuminate, indicating that overheating has occurred. Only when the temperature controller returns to its normally open state and pin 8 of the pulse width modulation chip goes high can the arc welding power supply resume output or welding. This achieves overheat protection and indication control.

[0017] The given and negative feedback operation and relay control circuit 175 consists of an operational amplifier, a current given signal Ug, a current negative feedback signal Uif, a +12V power supply and its ground, an IN (-) signal, diodes, an NPN transistor, and some resistors and capacitors; its function is: 1) to output a relay control signal to control the attached... Figure 2 The relay control circuit 120 in the middle ultimately realizes the control of the relay group. When attached Figure 2 When the relay group and its normally open contact 110 section operate, their normally open contacts become normally closed, thus preparing for the operation of subsequent circuits or the output of the arc welding power supply. 2) Output Uk control signal. The Uk signal is the output control signal resulting from the combined action of the current setpoint signal Ug and the current negative feedback signal Uif, processed by the operational amplifier control circuit. It is connected to the PWM control circuit and determines the pulse width of the PWM signal output by the PWM chip, ultimately determining the output of the arc welding power supply. For example, when the current setpoint signal Ug increases, the pulse width of the output PWM signal also increases, increasing the output current of the arc welding power supply; conversely, it decreases the output current. By controlling the output characteristics of the arc welding power supply, the requirements for arc welding power supply welding are ultimately met.

[0018] The control circuit and method of the lithium battery-powered arc welding power supply of this invention can be used to manufacture a lithium battery-powered arc welding power supply, which has the advantages of small size, light weight, portability, energy saving, material saving, and energy efficiency, and is convenient for welding in places without power supply. It solves the problem that arc welding power supplies must be powered by mains power or gasoline or diesel generators to operate, reduces the complexity of the system, and improves the stability of the system. Therefore, it has good practical application value. Attached Figure Description

[0019] Appendix Figure 1 This is a block diagram showing the composition and connection relationship of the arc welding power source of this utility model;

[0020] Appendix Figure 2 This is a block diagram showing the composition and connection relationship of the control circuit board PCB100 of this utility model;

[0021] Appendix Figure 3 This is a block diagram showing the composition and connection relationship of the output control circuit 170 of this utility model;

[0022] Appendix Figure 4 This is the schematic diagram of the control circuit of the relay JDQ1 of this utility model;

[0023] Appendix Figure 5 This is the schematic diagram of the current setting circuit of this utility model;

[0024] Appendix Figure 6This is a schematic diagram of the PWM pulse width modulation and its output control circuit of this utility model;

[0025] Appendix Figure 7 This is a schematic diagram of the overheat protection control and its indicator circuit of this utility model. Detailed Implementation

[0026] Appendix Figure 1This is a block diagram showing the composition and connection relationship of the arc welding power supply of this utility model. This utility model discloses a control circuit for an arc welding power supply powered by a lithium battery, characterized in that: the arc welding power supply includes a charging interface CDJK10, a power switch KG20, a lithium battery assembly 30, an overheat protection indicator OH40, a cooling fan Fan50, a lithium battery power and voltage display 60, a temperature controller 70, a current adjustment potentiometer 80, a welding button SB90, a control circuit board PCB100, and a positive output terminal (OUTPUT(+)) and a negative output terminal (OUTPUT(-)) of the arc welding power supply; the power supply is supplied from a power source for charging the lithium battery, such as 65VDC, etc. The power supply is connected to the charging interface CDJK10, where IN1 is the positive terminal of the charging power supply and IN2 is the negative terminal. During charging, it connects to the corresponding output polarity terminal of the lithium battery charger. The charging interface CDJK10 is installed on the rear panel of the arc welding power supply and is used to connect the lithium battery charger to charge the lithium battery assembly 30 in the arc welding power supply. The output of the charging interface CDJK10 is connected to the power switch KG20 and the input terminal of the lithium battery assembly 30. The power switch KG20 is used to control the on / off state of the input of the circuit board PCB100, IN(+) and IN... (-) are the positive and negative input terminals of the control circuit board PCB100, respectively; the lithium battery assembly 30, after being charged by its charger, can provide the necessary power to the circuit of the control circuit board PCB100, that is, to provide power to the arc welding power supply; the overheat protection indicator light OH40 is installed on the front panel of the arc welding power supply and is connected to the CN1 socket of the control circuit board PCB100. This indicator light is used to indicate whether the arc welding power supply has experienced overheat protection; the cooling fan Fan50 is installed on the side panel of the arc welding power supply and is connected to the CN7 socket of the control circuit board PCB100. The socket and cooling fan are used to cool the heat-generating components inside the arc welding power supply, such as the electronic switching transistor group and its heat sink, and the fast recovery diode group and its heat sink. The electronic switching transistor group and the fast recovery diode group form a conversion circuit. Under the action of the control circuit, the DC-DC conversion control can be easily realized, and finally the output control of the arc welding power supply is realized. The lithium battery power and voltage display meter 60 is installed on the front panel of the arc welding power supply. It is connected to the CN4 socket of the control circuit board PCB100. The meter is used to indicate the power and voltage of the lithium battery in the arc welding power supply during charging or welding.The temperature controller 70 is attached to the surface of the heat sink of the electronic switching transistor assembly installed inside the arc welding power supply. It is connected to the CN6 socket of the control circuit board PCB100 and is used to detect whether the heat sink and the electronic switching transistors mounted on its surface have overheated. When the temperature of the heat sink surface reaches the operating temperature of the temperature controller, it indicates overheating. At this time, the temperature controller changes from a normally open state to a normally closed state, and the control circuit in the control circuit board PCB100 can stop the operation of the electronic switching transistor assembly, ultimately stopping the output of the arc welding power supply or welding, thus achieving overheat protection control. Simultaneously, it can... The overheat protection indicator light OH40 illuminates, indicating an overheating event. The arc welding power supply can only resume output or welding when the temperature controller returns to its normally open state. The current adjustment potentiometer 80, mounted on the front panel of the arc welding power supply, is connected to the CN2 socket of the control circuit board PCB100. This potentiometer is used to adjust the output or welding current of the arc welding power supply. The welding button SB90, mounted on the front panel of the arc welding power supply, is connected to the CN5 socket of the control circuit board PCB100. This button is used for welding start control of the arc welding power supply. The positive output terminal of the arc welding power supply... The OUTPUT (+) and negative output terminals (OUTPUT (-)) connect to the welding torch and workpiece, which is the load during welding. The CN3 socket of the control circuit board PCB100 is connected to pin 2 of the charging interface CDJK10 via its plug and connecting wire. Under the action of the input given control signal of the current adjustment potentiometer 80 and the current feedback detection signal Uif, the control circuit board PCB100 is used to control the working state of the conversion circuit composed of the electronic switching transistor group and the fast recovery diode group in the circuit board unit, so that the arc welding power supply can realize the voltage and current conversion between the input and output, that is, realize the welding or working output of the arc welding power supply. In addition, the circuit board also uses its switching power supply circuit to generate various DC working voltages, realize the working state conversion of the relay group, realize the relay working state conversion of the lithium battery power voltage display 60, realize the operation control of output current feedback control and PWM pulse width adjustment control, as well as overheat protection and indication functions. The output current of the arc welding power supply mainly depends on the battery power supply capacity of the lithium battery assembly 30 and the configuration of the electronic switching transistor group and the fast recovery diode group in the control circuit board PCB100.

[0027] The control circuit and method of the lithium battery-powered arc welding power supply of this invention can be used to manufacture a lithium battery-powered arc welding power supply, which has the advantages of small size, light weight, portability, energy saving, material saving, and energy efficiency, and is convenient for welding in places without power supply. It solves the problem that arc welding power supplies must be powered by mains power or gasoline or diesel generators to operate, reduces the complexity of the system, and improves the stability of the system. Therefore, it has good practical application value.

[0028] The following section further explains the composition and connection relationships of the control circuit board (PCB) of the arc welding power supply of this utility model, as well as the function of each part:

[0029] Appendix Figure 2 This is a block diagram showing the composition and connection relationship of the control circuit board PCB100 of this utility model.

[0030] See attached Figure 2The control circuit of the control circuit board PCB100 of this utility model includes a relay group and its normally open contact 110, a relay control circuit 120, a switching power supply circuit 130, a driving circuit 140 for the electronic switching transistor group 150, an electronic switching transistor group 160, an output control circuit 170, a capacitor C5, a resistor R6a, an output reactor DKQ1, a shunt FLQ, and sockets CN1 to CN7; the positive polarity input terminal IN(+) and the negative polarity input terminal IN(-) are connected to the power switch KG on the rear panel of the arc welding power supply, and through this power switch, they are respectively connected to the positive and negative terminals of the lithium battery pack and the charging interface; IN(+) is connected to socket CN5. Pin 1 of the CN5 socket is connected to one end of two parallel normally open contacts in the relay group and its normally open contact 110. The other ends of these two parallel normally open contacts are connected to capacitor C5, the input terminal of the electronic switch group 150, and the IN(+)-1 terminal. Pin 3 of the CN5 socket is connected to resistor R6a. The other end of R6a, IN(+)-1, is connected to the switching power supply circuit 130. The other end of capacitor C5, IN(-), is also connected to the switching power supply circuit 130, the positive terminal of the fast recovery diode group 160, the output control circuit 170, and one end of the shunt FLQ. The control terminal of the relay group and its normally open contact 110 is connected to the relay control circuit 120, and the input control signal terminal of this circuit is connected to the output control circuit 170. The other end of the shunt FLQ is connected to the negative output terminal OUTPUT (-) of the arc welding power supply. The two ends of the shunt FLQ can obtain a current feedback detection signal Uif, which is connected to the output control circuit 170. The output terminal of the electronic switching transistor group 150 is connected to the other end (negative terminal) of the fast recovery diode group 160 and one end of the output reactor DKQ1. The other end of the output reactor DKQ1 is connected to the positive output terminal OUTPUT (+) of the arc welding power supply. The control terminal of the electronic switching transistor group 150 is connected to the drive circuit 140. The input control terminal of the drive circuit 140 is connected to the output control circuit 170. The input signals of the switching power supply circuit 130 are IN(+)-1 and IN(-). The outputs are +5V, +12V, +15V, +24V, Vcc1, and Vee, as well as ground power signals; the CN7 socket connects to the cooling fan Fan via its plug and control wire; the CN5 socket connects to the solder button SB via its plug and control wire, and when the button is pressed, pins 1 and 3 of the socket are connected; the CN1 socket connects to the overheat protection indicator OH via its plug and control wire; the CN4 socket connects to the lithium battery power and voltage display via its plug and control wire; the CN6 socket connects to the thermostat via its plug and control wire; the CN2 socket connects to the current adjustment potentiometer via its plug and control wire; and the CN3 socket connects to pin 2 of the charging interface CDJK via its plug and control wire.The output control circuit 170 of this invention includes a lithium battery power and voltage display conversion circuit. When the plug of the charger used to charge the arc welding power supply of this invention is inserted into the charging interface CDJK, pins 1 and 2 of the charging interface CDJK are connected, meaning the control line of CN3 is connected to the positive input terminal of IN1 or the positive terminal of the lithium battery. This activates the relay in the lithium battery power and voltage display conversion circuit, changing the connection method of the relay contacts to display the charging voltage on the lithium battery power and voltage display. Conversely, when the charger is not inserted into the charging interface CDJK, the relay in the lithium battery power and voltage display conversion circuit does not activate; in this case, the lithium battery power and voltage display only displays the voltage of the lithium battery in the arc welding power supply. The functions of the various parts connected to the other sockets are described in the appendix. Figure 1 The relevant part has already been explained, so I won't repeat it here.

[0031] See attached Figure 2 The electronic switch group 150 is composed of parallel electronic switch tubes, which can be IGBTs, MOS transistors, silicon carbide MOS transistors, etc.

[0032] See attached Figure 2 The fast recovery diode group 160 is configured to be connected in parallel, and the fast recovery diodes can be of various types.

[0033] See attached Figure 2 The relay control circuit 120 consists of a relay with normally open contacts connected in parallel, a diode, an N-channel MOSFET, a capacitor, a resistor, a transistor, an electrolytic capacitor, and a +24V power supply. The output signal from the output control circuit 170 controls the relay's operating state, thereby controlling the relay contact state. When the arc welding power supply's power switch KG is closed, pressing the welding button SB on the front panel of the arc welding power supply activates the relay under the action of the output control circuit 170, closing its normally open contacts. This allows the power or energy stored in the lithium battery to be supplied to the subsequent switching circuit composed of the electronic switching transistor group and the fast recovery diode group, thus starting the arc welding power supply. Furthermore, the parallel contact operation of the relay group ensures reliable operation. Since relay control circuits are relatively common, detailed descriptions of their composition and structure are omitted.

[0034] See attached Figure 2The switching power supply circuit 130 consists of a switching power supply transformer, an optocoupler, diodes, an N-channel MOSFET, a PWM pulse width modulator, 7805, 7812, and 7815 integrated voltage regulators, capacitors, resistors, Zener diodes, and electrolytic capacitors. The switching power supply circuit 130 generates power signals of +5V, +12V, +15V, +24V, Vcc1, and Vee, as well as ground. Vcc1 and Vee power signals supply the drive circuit 140; the +24V power supply supplies the relay control circuit 120 and the output control circuit 170, as well as the cooling fan Fan; the +5V, +12V, and +15V power supplies supply the output control circuit 170. The switching power supply transformer is a power transformer with multiple working windings. Using the aforementioned components and IN(+)-1 and IN(-) input signals, multiple DC power outputs are constructed. Furthermore, since a switching power supply circuit is used, there is no need for a control transformer. Therefore, while reducing costs and equipment weight, saving energy and materials, it also improves the adaptability of the DC power supply section to wide input voltage variations and the stability of the output DC power supply voltages. Given that switching power supply circuits are relatively common, detailed descriptions of their composition and structure will not be provided here.

[0035] See attached Figure 2 The driving circuit 140 of the electronic switch group mainly consists of a high-speed optocoupler and a driving resistor connected to the control electrode of the electronic switch. Under the action of the output control circuit 170, the electronic switch can be driven and controlled through the driving resistor, so that the electronic switch is in a PWM pulse width modulation control state. Different PWM pulse widths can make the output of the conversion circuit different, and the size of the pulse width depends on the current setpoint signal of the aforementioned current adjustment potentiometer and the Uif current negative feedback signal.

[0036] The output control circuit 170 mainly consists of a relay JDQ1, a PWM pulse width modulator U1, an operational amplifier U2, CN1~CN4 and CN6 sockets, +5V, +12V, +24V, and some NPN transistors, PNP transistors, Zener diodes, resistors, capacitors, and electrolytic capacitors. The circuit composed of these components can be further divided into a relay JDQ1 control circuit, a current setting circuit, a current setting and negative feedback operation circuit, and a relay control circuit (Note: the relay mentioned here is the attached...). Figure 2 The relays mentioned in the description section (hereinafter referred to as relays, and will not be repeated hereafter), PWM pulse width modulation and its output control circuit, and overheat protection control and its indicating circuit. The following is a further explanation of these control circuits:

[0037] Appendix Figure 3 This is a block diagram showing the composition and connection relationships of the output control circuit 170 of this utility model. See attached diagram. Figure 3 The output control circuit 170 of this utility model mainly consists of a relay JDQ1 control circuit 171, a current setting circuit 172, a PWM pulse width modulation and its output control circuit 173, an overheat protection control and its indication circuit 174, a setting and negative feedback operation circuit, and a relay control circuit 175. The relay JDQ1 control circuit 171 is connected to IN(-), IN(+)-1, ground, and CN3 and CN4. The current setting circuit 172 is connected to +5V, ground, and the output current setting signal Ug. The PWM pulse width modulation and its output control circuit 173 is connected to +12V, ground, and the overheat protection control and its indication circuit. The output, input, and negative feedback operation of circuit 174, the input Uk control signal of relay control circuit 175, and the drive resistor circuit are all connected. The output of the drive resistor circuit is connected to the control electrode of the switching transistor in the electronic switching transistor group. The overheat protection control and its indication circuit 174 is connected to +12V, +24V, ground, CN1 and CN6, and the PWM pulse width modulation and its output control circuit 173 is also connected. The input, negative feedback operation, and relay control circuit 175 is connected to +12V, ground, IN(-), Uif current negative feedback signal, the output current input signal Ug of current input circuit 172, and the output Uk and relay control signal of this part of the circuit. The parts connected to sockets CN1, CN3, CN4, and CN6, as well as IN(-), IN(+)-1, each power supply voltage and its ground, etc., have been explained in the relevant sections above and will not be described again here. The following is a further explanation of the composition and function of some main circuits in the output control circuit 170.

[0038] Appendix Figure 4This is a schematic diagram of the relay JDQ1 control circuit of this utility model. The relay JDQ1 control circuit 171 consists of relay JDQ1, resistor R1, CN3, and CN4 socket. The relay JDQ1 control circuit is used to realize the display and conversion control of charging voltage or the internal lithium battery voltage of the arc welding power supply. As mentioned earlier, the CN4 socket is connected to the lithium battery voltage display 60 mounted on the front panel of the arc welding power supply through its plug and control line; the CN3 socket is connected to pin 2 of the charging interface CDJK through its plug and control line. When the plug of the charger for the arc welding power supply of this utility model is inserted into the charging interface CDJK, pins 1 and 2 of the charging interface CDJK are connected, which connects the control line of CN3 to the positive input terminal of IN1 or the positive terminal of the lithium battery. At this time, the relay in the control circuit of relay JDQ1 will be activated. Through the change of the connection mode of the relay contacts, the lithium battery voltage display will show the charging voltage. Conversely, when the charger is not inserted into the charging interface CDJK, the relay in the control circuit of relay JDQ1 will not be activated. At this time, the lithium battery voltage display will only show the voltage of the lithium battery in the arc welding power supply. This realizes the voltage display conversion of the voltmeter.

[0039] Appendix Figure 5 This is a schematic diagram of the current setting circuit of this utility model. The current setting circuit consists of a +5V power supply, a variable potentiometer W1, a capacitor C29, resistors R21d and R27, and a CN2 socket. This part of the circuit is used to generate a current setting signal. Its output signal is the current setting signal Ug, which is connected to the current setting and negative feedback operation and relay control circuit 175. As mentioned above, the CN2 socket is connected to the current adjustment potentiometer through its plug and control line. +5V provides the operating power for the current setting circuit. The variable potentiometer is connected in series with the current adjustment potentiometer. The current adjustment potentiometer is used to adjust the output current of the arc welding power supply; the variable potentiometer is used for correction or fine adjustment to keep the output current of the arc welding power supply within a suitable range. Changing the magnitude of the Ug signal changes the output signal Uk of the current setting and negative feedback operation and relay control circuit 175, thereby changing the pulse width of the output PWM pulse signal of the PWM pulse width modulation and its output control circuit 173, and ultimately changing the magnitude of the output current of the arc welding power supply.

[0040] Appendix Figure 6This is a schematic diagram of the PWM pulse width modulation and its output control circuit of this utility model. The PWM pulse width modulation and its output control circuit consists of a PWM pulse width modulation chip (SG3525), an NPN transistor Q4, a PNP transistor Q3, resistors R42-R45 and R47-R49, capacitors C42-C44, a +12V circuit and its ground, diodes D41 and D42, and an electrolytic capacitor E8. This circuit, under the influence of the current negative feedback operation control signal Uk, generates the PWM pulse drive control signal for the electronic switching transistor group controlling the arc welding power supply output. Under the influence of the soft-start control signal, it determines whether to generate the PWM drive signal output, ultimately deciding whether the arc welding power supply outputs. Pin 8 of the pulse width modulation chip (SG3525) is the soft-start terminal, controlled by the output signal of the overheat protection control and its indicator circuit 174. When pin 8 of the PWM chip is high, it does not affect the output of the chip's PWM pulse signal; when pin 8 goes low, it stops the output of the chip's PWM pulse signal. The Uk signal terminal is controlled by the given and negative feedback operation and the relay control circuit 175; (The last sentence appears to be incomplete and possibly refers to a different circuit.) Figure 6 It can also be seen that the pulse signal output by the PWM chip is processed by the subsequent drive circuit to form a drive control signal, which is connected to the drive resistor. Since each drive resistor is connected to the control electrode of the electronic switch, the PWM drive control signal can control the working state of the electronic switch group, thereby controlling the output of the arc welding power supply. The Uk signal is the output control signal after the current setpoint signal Ug and the current negative feedback signal Uif are combined and processed by the operational amplifier control circuit. It is connected to the PWM control circuit and determines the pulse width of the PWM signal output by the PWM chip, which ultimately determines the output of the arc welding power supply. For example, when the current setpoint signal Ug increases, the pulse width of the output PWM signal also increases, increasing the output current of the arc welding power supply; conversely, it decreases the output current. By controlling the output characteristics of the arc welding power supply, the welding requirements of the arc welding power supply are ultimately met.

[0041] Appendix Figure 7This is a schematic diagram of the overheat protection control and indicator circuit of this utility model. The overheat protection control and indicator circuit consists of CN1 and CN6 sockets, +12V and +24V terminals, some resistors and capacitors, diodes, Zener diodes, and NPN transistors. One output signal of this circuit is connected to the soft-start pin 8 of the pulse width modulation chip (SG3525) in the PWM pulse width modulation and output control circuit. Pin 10 of this chip is grounded. When no overheating occurs, pin 8 of the chip is at a high level, which does not affect the output of the chip's PWM pulse signal. When overheating occurs, pin 8 of the chip goes low, stopping the output of the chip's PWM pulse signal. As mentioned above, the CN1 socket is connected to the overheat protection indicator light OH through its plug and control line; the CN6 socket is connected to the temperature controller through its plug and control line. The temperature controller is in close contact with the surface of the heat sink of the electronic switching transistor assembly installed inside the arc welding power supply, and is used to detect whether the heat sink and the electronic switching transistors mounted in close contact with its surface have overheated. When the surface temperature of the heat sink reaches the operating temperature of the temperature controller, it indicates overheating. At this point, the temperature controller changes from its normally open state to its normally closed state. Through the overheat protection control and its indicator circuit, pin 8 of the pulse width modulation chip goes low, and the PWM pulse width modulation and its output control circuit stop outputting, thereby stopping the operation of the electronic switching transistor group 150, and ultimately stopping the output or welding of the arc welding power supply, thus achieving overheat protection control. Simultaneously, the overheat protection indicator light OH LED or OH40 will illuminate, indicating that overheating has occurred. Only when the temperature controller returns to its normally open state and pin 8 of the pulse width modulation chip goes high can the arc welding power supply resume output or welding. This achieves overheat protection and indication control.

[0042] The given and negative feedback operation and relay control circuit 175 consists of an operational amplifier, a current given signal Ug, a current negative feedback signal Uif, a +12V power supply and its ground, an IN (-) signal, diodes, an NPN transistor, and some resistors and capacitors; its function is: 1) to output a relay control signal to control the attached... Figure 2 The relay control circuit 120 in the middle ultimately realizes the control of the relay group. When attached Figure 2When the relay group and its normally open contact 110 section operate, their normally open contacts become normally closed, thus preparing for the operation of subsequent circuits or the output of the arc welding power supply. 2) Output Uk control signal. The Uk signal is the output control signal resulting from the combined action of the current setpoint signal Ug and the current negative feedback signal Uif, processed by the operational amplifier control circuit. It is connected to the PWM control circuit and determines the pulse width of the PWM signal output by the PWM chip, ultimately determining the output of the arc welding power supply. For example, when the current setpoint signal Ug increases, the pulse width of the output PWM signal also increases, increasing the output current of the arc welding power supply; conversely, it decreases the output current. By controlling the output characteristics of the arc welding power supply, the requirements for arc welding power supply welding are ultimately met.

[0043] In summary, the control circuit and control method of this utility model can be used to manufacture an arc welding power supply powered by a lithium battery. Because it utilizes the parallel contact operation of the relay group, the reliability of the connected operation is guaranteed. Since a switching power supply circuit is used, there is no need for a control transformer, thus reducing costs and equipment weight, saving energy and materials, while also improving the adaptability of the DC power supply section to wide input voltage variations and the stability of the output DC power supply voltages. Because it uses a conversion circuit composed of an electronic switching transistor group and a fast recovery diode group, DC-to-DC conversion control is easily achieved under the action of the control circuit, ultimately realizing the output control of the arc welding power supply. Because it employs the relay JDQ1 control circuit 171, current setting circuit 172, PWM pulse width modulation and its output control circuit 173, overheat protection control and its indication circuit 174, setting and negative feedback calculation, and relay control circuit 175 in the output control circuit 170, it effectively achieves control of the relay JDQ1 and the relays in the main circuit; current setting and negative feedback control of the PWM pulse width modulation; and overheat protection control, etc. Meanwhile, this technology gives arc welding power supplies advantages such as small size, light weight, portability, energy saving, material saving, and ease of use in areas without power supply. It solves the problem that arc welding power supplies must be powered by mains electricity or gasoline / diesel generators, reducing system complexity and improving system stability. Therefore, it has good practical application value.

[0044] It is evident that the superior control circuit and method of the lithium battery-powered arc welding power supply are the advantages of this utility model. The scope of protection for this utility model patent application lies in protecting this arc welding power supply circuit and its control method.

[0045] The above description is a detailed explanation of the control circuit and control method of the lithium battery-powered arc welding power supply, and it should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the circuit and method of the present invention, and these should all be considered to fall within the scope of protection of the present invention.

Claims

1. A control circuit for a lithium battery-powered arc welding power supply, characterized in that: The control circuit of the arc welding power supply includes a charging interface, a power switch, a lithium battery assembly, an overheat protection indicator light, a cooling fan, a lithium battery voltage and charge display, a temperature controller, a current adjustment potentiometer, a welding button, a control circuit board, and positive and negative output terminals of the arc welding power supply. Power is input to the charging interface, and the output of the charging interface is connected to the power switch and the input terminal of the lithium battery assembly. The power switch controls the on / off state of the circuit board input. After being charged by its charger, the lithium battery assembly provides the necessary electrical energy to the circuitry of the control circuit board PCB100, i.e., provides power to the arc welding power supply. The overheat protection indicator light is mounted on the front panel of the arc welding power supply and is connected to the CN1 socket of the control circuit board. This indicator light is used to indicate whether an overheating protection event has occurred. The cooling fan is mounted on the side panel of the arc welding power supply and connected to the CN7 socket of the control circuit board. This cooling fan is used to cool the heat-generating components inside the arc welding power supply. The control circuit of the arc welding power supply also includes a conversion circuit composed of an electronic switching transistor group and a fast recovery diode group. This conversion circuit can realize DC-DC conversion control, ultimately achieving output control of the arc welding power supply. The lithium battery power and voltage display is mounted on the front panel of the arc welding power supply and connected to the CN4 socket of the control circuit board. It is used to indicate the power and voltage of the lithium battery during charging or welding. The temperature controller is attached to the surface of the heat sink of the electronic switching transistor group installed inside the arc welding power supply and connected to the CN6 socket of the control circuit board. It is used to detect whether the heat sink and the electronic switching transistors mounted on its surface are overheating. The current adjustment potentiometer is mounted on the front panel of the arc welding power supply and connected to the CN2 socket of the control circuit board. It is used to adjust the output current of the arc welding power supply or the welding current. The welding button is mounted on the front panel of the arc welding power supply. The current adjustment potentiometer is connected to the CN5 socket of the control circuit board for welding start control of the arc welding power supply. The positive and negative output terminals of the arc welding power supply are connected to the welding torch and the workpiece, respectively. The CN3 socket of the control circuit board is connected to the charging interface.

2. The control circuit for a lithium battery-powered arc welding power supply as described in claim 1, characterized in that: The control circuit of the control circuit board includes a relay group and its normally open contacts, a relay control circuit, a switching power supply circuit, a drive circuit for the electronic switching transistor group, the electronic switching transistor group, a fast recovery diode group, an output control circuit, a capacitor C5, a resistor R6a, an output reactor DKQ1, a shunt FLQ, and sockets CN1 to CN7. The positive and negative input terminals are connected to the power switch on the rear panel of the arc welding power supply, which in turn connects to the positive and negative terminals of the lithium battery pack and the charging interface, respectively. The positive input terminal is also connected to pin 1 of the CN5 socket and one end of two parallel normally open contacts in the relay group and its normally open contacts. The other end of the normally open contact in parallel is connected to capacitor C5 and the input terminal of the electronic switching transistor group; pin 3 of the CN5 socket is connected to resistor R6a, the other end of resistor R6a is connected to the switching power supply circuit, the other end of capacitor C5 is also connected to the switching power supply circuit, the positive terminal of the fast recovery diode group, the output control circuit, and one end of the shunt FLQ; the control terminal of the relay group and its normally open contact is connected to the relay control circuit, and the input control signal terminal of the relay control circuit is connected to the output control circuit; the other end of the shunt FLQ is connected to the negative output terminal of the arc welding power supply, and the two ends of the shunt FLQ can obtain a current feedback detection signal Uif, which is connected to the output control circuit; The output terminal of the electronic switch tube group is connected to the negative terminal of the fast recovery diode group and one end of the output reactor DKQ1. The other end of the output reactor DKQ1 is connected to the positive output terminal of the arc welding power supply. The control terminal of the electronic switch tube group is connected to the drive circuit of the electronic switch tube group; the drive circuit of the electronic switch tube group consists of a high-speed optocoupler and a drive resistor connected to the control electrode of the electronic switch tube. Under the action of the output control circuit, the electronic switch tube can be driven and controlled through the drive resistor.

3. The control circuit for a lithium battery-powered arc welding power supply as described in claim 2, characterized in that: The output control circuit includes a relay control circuit, a current setting circuit, a PWM pulse width modulation and its output control circuit, an overheat protection control and its indication circuit, a setting and negative feedback calculation circuit, and a relay control circuit. The relay control circuit includes relay JDQ1, resistor R1, socket CN3 and CN4. The relay JDQ1 control circuit is used to realize the display and conversion control of charging voltage or internal lithium battery power voltage of arc welding power supply. The current setting circuit includes a variable potentiometer W1, a capacitor C29, resistors R21d and R27, and a socket CN2. The current setting circuit generates a current setting signal, and the output signal is the current setting signal Ug. The current setting signal is connected to the current setting and negative feedback calculation and relay control circuits. The given and negative feedback operation and relay control circuit includes an operational amplifier, diodes, NPN transistors, resistors, and capacitors; The PWM pulse width modulation and its output control circuit includes a PWM pulse width modulation chip, an NPN transistor Q4, a PNP transistor Q3, resistors R42-R45 and R47-R49, capacitors C42-C44, diodes D41 and D42, and an electrolytic capacitor E8. Under the action of the current negative feedback operational control signal Uk, the PWM pulse drive control circuit generates a PWM pulse drive control signal for the electronic switching transistor group that controls the arc welding power supply output. Under the action of the soft-start control signal, it determines whether to generate the PWM drive signal output, ultimately determining whether the arc welding power supply outputs. The current negative feedback operational control signal Uk is the output control signal resulting from the combined action of the current setpoint signal Ug and the current negative feedback signal Uif, processed by the operational amplifier control circuit. The overheat protection control and its indicator circuit includes sockets CN1 and CN6, resistors, capacitors, diodes, Zener diodes, and NPN transistors; one output signal of the overheat protection control and its indicator circuit is connected to the soft-start terminal of pin 8 of the pulse width modulation chip in the PWM pulse width modulation and its output control circuit, and pin 10 of the pulse width modulation chip is grounded.

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