Large-current soft start circuit

Abstract

The utility model discloses a heavy current soft start circuit, which has a soft start function and comprises a current given primary unit, a current given detection unit and a current given secondary unit, and the current given primary unit provides given current according to preset current and outputs the given current; the current given detection unit detects an input given current signal and outputs a corresponding control signal to the current given secondary unit; the current given secondary unit performs comprehensive operation on signals input by the current given primary unit and the current given detection unit and outputs the signals; when the given current is smaller than the maximum given current, the output current is equal to the given current; when the given current is equal to the maximum given current, the output current is slowly increased to the maximum given current on the basis that the output current is smaller than the maximum given current. According to the utility model, segmented control can be carried out on the given large current, so that soft start can be successfully realized under the condition of sudden loading of the large current, and possible damage caused by over-impact on power during maximum power start is avoided.

Description

Technical Field

[0001] The utility model relates to a starting circuit, in particular to a high-current soft starting circuit with a function of reducing current and power during starting. Background Art

[0002] A generator welder is a machine integrating an engine and a welding machine. The generator generates current through rotation and directly drives the welding machine to work. Generally, there are two most commonly used types: gasoline-powered and diesel-powered, with a small-power auxiliary power supply that can drive small-power devices such as lighting. When the rated output current of the generator welder is suddenly increased under the premise of a small design margin of the engine, due to the large sudden power, the engine speed will drop sharply, the unit will emit black smoke, and in severe cases, the unit will even stall. Therefore, the current common methods for suddenly loading large current are as follows: 1. Reducing the capacitance of the filter capacitor. This method can reduce the inrush current at startup, ensure that the distribution board does not trip, and ensure the safe operation of the rectifier bridge, but it has a certain impact on the welding performance, especially not applicable to some welding methods that require precise control of the arc; 2. Using a series-connected unsaturated inductor. This method can reduce the inrush current at startup, but the effect is not obvious. When shutting down, a reverse electromotive force will be generated, posing a hidden danger to the safe operation of other circuits of the welding power supply. At the same time, the unsaturated inductor is large in volume and heavy in weight; 3. Using a negative temperature coefficient thermistor in series on the DC bus. When starting up, the resistance value of the thermistor is large, which can limit the inrush current at startup. Due to the action of the current, the temperature of the thermistor rises, and the resistance decreases until it is equivalent to a wire. This method can significantly reduce the inrush current at startup. However, if the machine is restarted immediately after shutdown, the temperature of the thermistor has not returned to room temperature, and the resistance value at this time is still very small, and the same large inrush current will be generated; 4. Using the method of soft start resistor plus relay delay connection. The power resistor and the relay are first connected in parallel and then in series on the DC bus. When starting up, the soft start resistor limits the inrush current at startup, and the relay is connected after a delay period. This method can well reduce the inrush current at startup. However, when the soft start resistor is open-circuited, the capacitor is not charged. When the relay is connected after the delay, the high voltage across the relay will also generate a very large inrush current, causing the relay to be damaged.

[0003] Among them, soft start means that the voltage is slowly increased from zero to the rated voltage, and the starting current of the motor during the starting process changes from the past uncontrollable overload inrush current to a controllable one, and the magnitude of the starting current can be adjusted according to needs. There is no impact torque throughout the starting process of the motor, but it starts and runs smoothly. For example, Chinese patent document CN204633590U discloses a soft start circuit for a welding power supply, including a three-phase rectifier bridge, a soft start resistor loop protection circuit, a power supply circuit, an over- and under-voltage detection circuit, a relay loop protection circuit, and a delay relay circuit.

[0004] The soft start circuit of the prior art greatly reduces the instantaneous impact current at startup. At the same time, after the power resistor is damaged, the relay cannot operate, avoiding more serious faults. An under-voltage and over-voltage protection function is also added to the circuit to make the welding power supply work more safely. However, the circuit is relatively complex. Summary of the Invention

[0005] The present invention provides a high-current soft start circuit with a simple circuit and a soft start function, which includes a current setting primary unit, a current setting detection unit, and a current setting secondary unit. The current setting primary unit provides a set current according to a preset current and outputs it. One path is input to the current setting secondary unit, and the other path is input to the current setting detection unit; the current setting detection unit detects the input set current signal and outputs a corresponding control signal to the current setting secondary unit;

[0006] The current setting secondary unit performs comprehensive operations on the signals input by the current setting primary unit and the current setting detection unit and outputs; when the set current is less than the maximum set current, the output current is equal to the set current; when the set current is equal to the maximum set current, the output current slowly rises to the maximum set current on the basis of being less than the maximum set current.

[0007] Preferably, the current setting detection unit includes a zener diode. When the set current is less than the breakdown current of the zener diode, the current fed into the current setting secondary unit is equal to the set current. When the set current is greater than the breakdown current of the zener diode, the current fed into the current setting secondary unit is less than the set current.

[0008] Preferably, the current setting detection unit further includes a switch SW1 for switching whether to enable the soft start function.

[0009] Preferably, the current reference detection unit includes a resistor R5, a voltage regulator ZD1, a switch SW1, a resistor R6, a resistor R7, a resistor R8, a triode T1, a triode T2, a resistor R12, a resistor R9, a triode T3, a resistor R10, and a resistor R4. One end of the resistor R5 is connected to the output end of the primary current reference unit, and the other end is connected to the negative electrode of the voltage regulator ZD1. The positive electrode of the voltage regulator ZD1 is respectively connected to the switch SW1, the resistor R6, and the base of the triode T1. The switch SW1 and the resistor R6 are grounded. The resistor R8 and the resistor R7 are connected in series and then connected to the collector of the triode T1. The emitter of the triode T1 is grounded. The base of the triode T2 is connected between the resistor R8 and the resistor R7. The collector of the resistor R8 and the triode T2 is connected to the welding current access terminal Ifb. When there is no welding current, Ifb is at a high potential. When there is welding current, Ifb is at a 0 potential. The emitter of the triode T2 is connected to the resistor R12. The resistor R9 and the resistor R12 are connected in series, and the other end of the resistor R9 is grounded. The base of the triode T3 is connected between the resistor R9 and the resistor R12, the emitter is grounded, and the collector is connected to the resistor R10. One end of the resistor R4 is connected to the output end of the primary current reference unit, and the other end is connected to the resistor R10 and then connected to the secondary current reference unit.

[0010] Preferably, the resistance value of the resistor R10 is 9 times that of the resistor R4.

[0011] Preferably, the primary current reference unit includes a potentiometer.

[0012] Preferably, the primary current reference unit further includes an operational amplifier IC1-1, a resistor R1, a resistor R2, and a resistor R3. After the resistor R1, the resistor R2, and the resistor R3 are connected in series, the resistor R3 is grounded, where the resistor R2 is a potentiometer. The operational amplifier IC1-1 is a negative feedback amplifier. The middle section of the resistor R2 is connected to the non-inverting input terminal of the operational amplifier IC1-1, and the output terminal is respectively connected to the current reference detection unit and the secondary current reference unit.

[0013] Preferably, the secondary current reference unit includes an operational amplifier IC1-2 and an RC slow-rise circuit. The operational amplifier is a negative feedback amplifier. The non-inverting input terminal of the operational amplifier IC1-2 is connected to the output terminal of the current reference detection unit. The output terminal of the operational amplifier IC1-2 is connected to the RC slow-rise circuit, and the other end of the RC slow-rise circuit is connected.

[0014] Preferably, one output of the primary current reference unit is also connected to a preset display circuit.

[0015] The utility model has the following beneficial effects:

[0016] 1. The utility model can perform segmented control on the large-current setting, ensuring the successful realization of soft start under the condition of sudden load addition of large current, and avoiding the damage that may be caused by the over-impact on power during starting at the maximum power.

[0017] 2. The soft start function in the utility model can be enabled or disabled, and users can enable the soft start function according to actual needs.

[0018] 3. In the utility model, when the engine suddenly adds ≤ 90% of the rated current and automatically adjusts to the rated current at a certain speed after the sudden addition is successful, the engine can work continuously and stably on the premise of ensuring that the welding generator can output the rated current. Description of the Drawings

[0019] Figure 1 It is the circuit diagram of an embodiment of a large-current soft start circuit of the utility model. Detailed Description of the Preferred Embodiments

[0020] The following is a further detailed description through specific embodiments:

[0021] 1. Definition

[0022] Resistor: It is a current-limiting component. After connecting the resistor in the circuit, the resistance value of the resistor is fixed, generally with two leads. It can limit the magnitude of the current passing through the branch it is connected to. A resistor with a variable resistance value is called a potentiometer or variable resistor.

[0023] Triode: The full name should be semiconductor triode, also known as bipolar transistor and crystal triode. It is a semiconductor device that controls current. Its function is to amplify a weak signal into an electrical signal with a larger amplitude value, and it is also used as a non-contact switch. The triode is one of the basic semiconductor components, with the function of current amplification and is the core component of electronic circuits. The triode is made by fabricating two PN junctions that are very close to each other on a semiconductor substrate. The two PN junctions divide the whole semiconductor into three parts. The middle part is the base region, and the two side parts are the emitter region and the collector region.

[0024] Zener diode: It refers to a zener diode. By using the phenomenon that the current can change within a large range while the voltage remains basically unchanged in the reverse breakdown state of the PN junction, a diode that plays a voltage stabilizing role is made. This diode is a semiconductor device that has a very high resistance until the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance drops to a very small value. In this low-resistance region, the current increases while the voltage remains constant. Zener diodes are classified according to the breakdown voltage. Because of this characteristic, zener diodes are mainly used as voltage regulators or voltage reference components. Zener diodes can be connected in series for use at higher voltages, and a higher stable voltage can be obtained through series connection.

[0025] Operational Amplifier: In an actual circuit, it usually combines with a feedback network to form a certain functional module. It is a circuit unit named from a functional perspective and can be implemented by discrete devices or integrated into a semiconductor chip. With the development of semiconductor technology, nowadays most operational amplifiers exist in the form of monolithic chips. There are a wide variety of operational amplifiers today and they are widely used in almost all industries.

[0026] 2. The embodiments are basically as shown in the appendix Figure 1 A high-current soft-start circuit has a soft-start function and includes a primary current-giving unit, a current-giving detection unit, and a secondary current-giving unit. The primary current-giving unit provides a given current according to a preset current and outputs it. One path is input to the secondary current-giving unit, and the other path is input to the current-giving detection unit; the current-giving detection unit detects the input given current signal and outputs a corresponding control signal to the secondary current-giving unit.

[0027] The secondary current-giving unit performs a comprehensive operation on the signals input from the primary current-giving unit and the current-giving detection unit and outputs; when the given current is less than the maximum given current, the output current is equal to the given current; when the given current is equal to the maximum given current, the output current ramps up to the maximum given current on the basis of being less than the maximum given current.

[0028] The primary current-giving unit includes a series of resistor R1, resistor R2, resistor R3, and operational amplifier IC1-1. Among them, resistor R2 is a potentiometer, and the operational amplifier IC1-1 is a negative feedback amplifier. The middle section of resistor R2 is connected to the non-inverting input terminal of the operational amplifier IC1-1, and the output terminal is respectively connected to the current-giving detection unit and the secondary current-giving unit.

[0029] The current reference detection unit includes resistor R5, voltage regulator ZD1, switch SW1, resistor R6, resistor R7, resistor R8, triode T1, triode T2, resistor R12, resistor R9, triode T3, resistor R10, and resistor R4. One end of resistor R5 is connected to the output terminal of the primary current reference unit, and the other end is connected to the negative electrode of voltage regulator ZD1. The positive electrode of voltage regulator ZD1 is connected to switch SW1, resistor R6, and the base of triode T1 respectively. Switch SW1 and resistor R6 are grounded. Resistor R8 and resistor R7 are connected in series and then connected to the collector of triode T1. The emitter of triode T1 is grounded. The base of triode T2 is connected between resistor R8 and resistor R7. The collector of resistor R8 and triode T2 is connected to the welding current input terminal Ifb. When there is no welding current, Ifb is at a high potential. When there is welding current, Ifb is at 0 potential. The emitter of triode T2 is connected to resistor R12. Resistor R9 and resistor R12 are connected in series, and the other end of resistor R9 is grounded. The base of triode T3 is connected between resistor R9 and resistor R12, the emitter is grounded, and the collector is connected to resistor R10. One end of resistor R4 is connected to the output terminal of the primary current reference unit, and the other end is connected to resistor R10 and then connected to the secondary current reference unit. Among them, the resistance value of resistor R10 is 9 times that of resistor R4, and switch SW1 is a DIP switch.

[0030] The secondary current reference unit includes operational amplifier IC1-2 and an RC slow-rise circuit. The operational amplifier is a negative feedback amplifier. The non-inverting input terminal of operational amplifier IC1-2 is connected to the output terminal of the current reference detection unit. The output terminal of operational amplifier IC1-2 is connected to the RC slow-rise circuit, and the other end of the RC slow-rise circuit is connected. The RC slow-rise circuit includes resistor R11 and capacitor C1.

[0031] The specific implementation process is as follows: Resistors R1, R2, and R3 form a voltage-dividing reference circuit. Resistor R2 outputs the current reference Ig0, and then the current reference Ig is output through operational amplifier IC1-1. The current reference Ig is output in three paths. One path is input to the preset display circuit, one path is input to the secondary current reference unit, and one path is input to the current reference detection unit.

[0032] The current reference detection unit consists of resistor R4, resistor R5, voltage regulator ZD1, resistor R6, switch SW1, triode T1, resistor R7, resistor R8, triode T2, resistor R9, resistor R12, triode T3, and resistor R10. When there is no welding current, Ifb is at a high potential. When there is welding current, Ifb is at 0 potential.

[0033] When not welded, the current Ig passes through the resistor R5 and the voltage regulator ZD1 in sequence. The resistor R6 acts on the base of the triode T1. When the current Ig is less than the breakdown current of the voltage regulator ZD1, the CE pole of the triode T1 is cut off, the CE pole of the triode T2 is cut off, and the CE pole of the triode T3 is cut off. Thus, the resistance value of the CE pole of the triode T3 is infinite. The current Ig is divided by the resistor R4 and the resistance value Rce of the resistor R10 + the CE pole of the triode T3. The current Ig1 is approximately equal to the current Ig. That is, when not welded and the current Ig is less than the maximum given current, the current Ig1 fed into the PID operation of the operational amplifier IC1-2 is approximately equal to the current Ig. When the current Ig is greater than a certain value, the voltage regulator ZD1 breaks down, the CE pole of the triode T1 is saturated and conducting, the CE pole of the triode T2 is saturated and conducting, and the CE pole of the triode T3 is triggered to be saturated and conducting. Thus, the resistance value Rce of the CE pole of the triode T3 approaches 0. The current Ig is divided by the resistor R4 and (the resistor R10 + the Rce of the CE pole of the triode T3). The resistance value of the resistor R10 is set to 9 times the resistance value of the resistor R4. Thus, the voltage division of the resistor R10 gives 0.9Ig, and the current Ig1 is equal to the current 0.9Ig. That is, when not welded and the current Ig is close to or equal to the maximum given current, the current Ig1 fed into the operational amplifier IC1-2 to participate in the PID operation is approximately equal to the current 0.9Ig.

[0034] In the case of sudden load or welding state: When the current Ig is less than the maximum given current, the current Ig1 fed into the operational amplifier IC1-2 to participate in the PID operation is approximately equal to the current Ig. The load current is equal to the given current value, and the load power is equal to the load power corresponding to the current Ig. When the current Ig is equal to the maximum given current, the current Ig1 fed into the operational amplifier IC1-2P to participate in the PID operation is approximately equal to the current 0.9Ig. The load current is equal to 0.9 times the given current value, and the load power is equal to the load power corresponding to 0.9 times the current Ig. Therefore, it has the effect of reducing the current and reducing the power.

[0035] When the load is successful, the welding current is established. At this time, the current Ifb is at 0 potential, the CE poles of the triode T2 and the triode T3 are cut off, and the Rce of the T3 triode is infinite. The current Ig is divided by the resistor R4 and (the resistor R10 + the Rce of the CE pole of the triode T3). The voltage division across (the resistor R10 + the Rce of the CE pole of the triode T3) is approximately equal to the current Ig. At this time, the voltage across the operational amplifier IC1-2 is only the voltage corresponding to the current 0.9Ig. The current Ig passes through the resistor R11 to charge the capacitor C1, causing the current Ig1 to rise exponentially to the current Ig slowly, that is, the voltage corresponding to the current Ig1 rises slowly from the voltage corresponding to 0.9Ig to 1 * Ig. The current Ig1 participates in the PID operation of the operational amplifier IC1-2, and the corresponding output current rises from 0.9Imax to 1 * Imax slowly. The corresponding output power rises from 0.81Pmax to Pmax.

[0036] In summary, after successful loading, the current slowly rises to the maximum output current. That is, when the maximum current is given, the soft-start circuit in this embodiment realizes the function of soft-start power reduction startup, avoiding the over-impact on the engine during maximum power startup.

[0037] The above are only embodiments of the present invention. Specific structures and common knowledge such as characteristics that are well known in the art are not described in detail here. Those of ordinary skill in the art know all the common general technical knowledge in the technical field to which the utility model belongs before the filing date or the priority date, can know all the existing technologies in this field, and have the ability to apply conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, combine their own abilities to improve and implement this solution. Some typical well-known structures or well-known methods should not become an obstacle for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. A large-current soft-start circuit with a soft-start function, characterized in that: It includes a primary current setting unit, a current setting detection unit, and a secondary current setting unit. The primary current setting unit provides and outputs a set current according to a preset current, with one path input to the secondary current setting unit and the other path input to the current setting detection unit; the current setting detection unit detects the input set current signal and outputs a corresponding control signal to the secondary current setting unit; the secondary current setting unit performs a comprehensive operation on the signals input from the primary current setting unit and the current setting detection unit and outputs; when the set current is less than the maximum set current, the output current is equal to the set current; when the set current is equal to the maximum set current, the output current slowly rises to the maximum set current on the basis of being less than the maximum set current, realizing soft start of large current.

2. The high-current soft start circuit according to claim 1, characterized in that: The current setting detection unit includes a zener diode. When the set current is less than the breakdown current of the zener diode, the current fed into the secondary current setting unit is equal to the set current. When the set current is greater than the breakdown current of the zener diode, the current fed into the secondary current setting unit is less than the set current.

3. The high-current soft start circuit according to claim 2, characterized in that: The current setting detection unit further includes a switch SW1 for switching whether to enable the soft start function.

4. The high-current soft start circuit according to claim 3, characterized in that: The current setting detection unit includes a resistor R5, a voltage regulator ZD1, a switch SW1, a resistor R6, a resistor R7, a resistor R8, a triode T1, a triode T2, a resistor R12, a resistor R9, a triode T3, a resistor R10, and a resistor R4. One end of the resistor R5 is connected to the output end of the primary current setting unit, and the other end is connected to the negative pole of the voltage regulator ZD1; the positive pole of the voltage regulator ZD1 is respectively connected to the switch SW1, the resistor R6, and the base of the triode T1. The switch SW1 and the resistor R6 are grounded; the resistor R8 and the resistor R7 are connected in series and then connected to the collector of the triode T1. The emitter of the triode T1 is grounded; the base of the triode T2 is connected between the resistor R8 and the resistor R7. The collector of the resistor R8 and the triode T2 is connected to the welding current access terminal Ifb. When there is no welding current, Ifb is at a high potential. When there is welding current, Ifb is at a 0 potential. The emitter of the triode T2 is connected to the resistor R12. The resistor R9 and the resistor R12 are connected in series, and the other end of the resistor R9 is grounded; the base of the triode T3 is connected between the resistor R9 and the resistor R12, the emitter is grounded, and the collector is connected to the resistor R10; one end of the resistor R4 is connected to the output end of the primary current setting unit, and the other end is connected to the resistor R10 and then connected to the secondary current setting unit.

5. The high-current soft start circuit according to claim 4, wherein: The resistance value of the resistor R10 is 9 times that of the resistor R4.

6. The high-current soft start circuit according to any one of claims 1-5, characterized in that: The primary current setting unit includes a potentiometer.

7. The high-current soft start circuit according to claim 6, wherein: The current reference primary unit further includes an operational amplifier IC1-1, a resistor R1, a resistor R2, and a resistor R3. After the resistors R1, R2, and R3 are connected in series, the resistor R3 is grounded. Among them, the resistor R2 is a potentiometer, the operational amplifier IC1-1 is a negative feedback amplifier, the middle section of the resistor R2 is connected to the non-inverting input terminal of the operational amplifier IC1-1, and the output terminal is respectively connected to the current reference detection unit and the current reference secondary unit.

8. The high-current soft start circuit according to claim 7, characterized in that: The current reference secondary unit includes an operational amplifier IC1-2 and an RC slow-rise circuit. The operational amplifier is a negative feedback amplifier. The non-inverting input terminal of the operational amplifier IC1-2 is connected to the output terminal of the current reference detection unit, the output terminal of the operational amplifier IC1-2 is connected to the RC slow-rise circuit, and the other end of the RC slow-rise circuit is connected.

9. The high-current soft start circuit according to claim 8, wherein: One output of the current reference primary unit is also connected to a preset display circuit.

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