Switching power supply and power equipment

Abstract

The utility model discloses a switching power supply and power equipment, the switching power supply comprises a controller and an overcurrent protection circuit, a first end of the overcurrent protection circuit is coupled with an error amplification output port of the controller, a second end of the overcurrent protection circuit is coupled with a reference voltage output port of the controller, and a third end of the overcurrent protection circuit is coupled with an oscillator control port of the controller; and when the voltage of the error amplification output port is greater than the preset voltage, the overcurrent protection circuit disconnects the access between the reference voltage output port and the oscillator control port. By adopting the scheme, the over-current protection of the switching power supply is realized, a complicated peripheral circuit does not need to be added, and the cost of the switching power supply is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to a switching power supply and electric power equipment. Background Art

[0002] Flyback switching power supplies are widely used in power equipment. For some flyback switching power supplies, when the output current is large, if an output short circuit occurs, there will be a large primary current, resulting in a large overall power consumption of the switch tube, which in turn leads to a high temperature of the switch tube, and there is a risk of thermal damage.

[0003] In a traditional flyback switching power supply, an additional current sampling circuit is usually provided at the output end to obtain the output current, and to perform overcurrent protection when an output short circuit fault is detected.

[0004] However, the additional provision of a current sampling circuit will result in a more complex structure and higher cost for the flyback switching power supply. Utility Model Content

[0005] The technical problem solved by the utility model is that the structure of the switching power supply for realizing overcurrent protection is relatively complex and the cost is relatively high.

[0006] To solve the above problems, the utility model provides a switching power supply, comprising: a controller and an overcurrent protection circuit, wherein: the overcurrent protection circuit has a first end coupled to an error amplifier output port of the controller, a second end coupled to a reference voltage output port of the controller, and a third end coupled to an oscillator control port of the controller; when the voltage of the error amplifier output port is greater than a preset voltage, the overcurrent protection circuit disconnects the path between the reference voltage output port and the oscillator control port.

[0007] An overcurrent protection circuit is provided at the reference voltage output port of the controller and the oscillator control port of the controller. When the output of the switching power supply is short-circuited, the voltage of the error amplifier output port of the controller increases. Therefore, when the voltage of the error amplifier output port is greater than the preset voltage, the overcurrent protection circuit disconnects the path between the reference voltage output port and the oscillator control port, thereby shutting down the controller. Therefore, overcurrent protection can be achieved without additionally providing a current sampling circuit, so the switching power supply has a simple structure and low cost.

[0008] Optionally, the overcurrent protection circuit includes: a current limiting unit, a first switch unit and a first filtering unit, wherein: the current limiting unit has an input end coupled to the reference voltage output port, and an output end coupled to the error amplifier output port; the first switch unit has a first end coupled to the reference voltage output port, and a second end coupled to the oscillator control port; the first filtering unit is coupled between the control end of the first switch unit and the error amplifier output port.

[0009] Optionally, the current limiting unit includes a first resistor.

[0010] Optionally, the switching power supply further includes: a second filtering unit coupled between the second end of the first switching unit and the oscillator control port.

[0011] Optionally, the second filtering unit includes: a third resistor and a second capacitor, wherein: the first end of the third resistor is coupled to the second end of the first switching unit, and the second end of the third capacitor is coupled to the oscillator control port; the first end of the second capacitor is coupled to the second end of the third resistor, and the second end of the third capacitor is grounded.

[0012] Optionally, the switch unit further includes: a clamping unit coupled to the second end of the current limiting unit and the error amplifier output port, and adapted to clamp the voltage of the error amplifier output port to the preset voltage.

[0013] Optionally, the clamping unit includes: a fourth resistor, a second switch unit and a third capacitor, wherein: the first end of the fourth resistor is coupled to the second end of the current limiting unit, and the second end of the fourth resistor is coupled to the control end of the second switch unit and the first end of the third capacitor; the first end of the second switch unit is coupled to the second end of the current limiting unit, and the second end of the second switch unit is grounded; the second end of the third capacitor is grounded.

[0014] Optionally, the switching power supply further includes: a power supply branch, coupled between a DC voltage source and a power port of the controller; the DC voltage source supplies power to the controller via the power supply branch.

[0015] Optionally, the power supply branch includes a fifth resistor and a fourth capacitor, wherein: the first end of the fifth resistor is coupled to the output end of the DC voltage source, and the second end of the fifth resistor is coupled to the first end of the fourth capacitor and the power port; the second end of the fourth capacitor is grounded.

[0016] The utility model also provides an electric power device, comprising: an AC power supply and any one of the switching power supplies described above; the switching power supply is coupled between the AC power supply and a load circuit, and is suitable for converting the AC power output by the AC power supply into an operating voltage required for the load circuit to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a switching power supply in an embodiment of the utility model;

[0018] Figure 2 It is a structural schematic diagram of another switching power supply in an embodiment of the utility model;

[0019] Figure 3 It is a structural schematic diagram of an electric power device in an embodiment of the utility model. DETAILED DESCRIPTION

[0020] In a traditional flyback switching power supply (hereinafter referred to as the switching power supply), an additional current sampling circuit is usually set at the output end to sample the output current of the switching power supply. When it is detected that the output current of the switching power supply exceeds a certain value, it is determined that an output short circuit fault occurs in the switching power supply, and the switching power supply is protected from overcurrent.

[0021] However, since an additional current sampling circuit is required, the structure of the switching power supply is more complicated and the cost is higher.

[0022] In an embodiment of the utility model, an overcurrent protection circuit is provided at the reference voltage output port of the controller and the oscillator control port of the controller. When the output of the switching power supply is short-circuited, the voltage of the error amplifier output port of the controller increases. Therefore, when the voltage of the error amplifier output port is greater than the preset voltage, the overcurrent protection circuit disconnects the passage between the reference voltage output port and the oscillator control port, thereby shutting down the controller. Therefore, overcurrent protection can be achieved without additionally providing a current sampling circuit, so the structure of the switching power supply is simple and the cost is low.

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] In the following embodiments of the present invention, the switching power supply may be a flyback switching power supply.

[0025] The embodiment of the utility model provides a switching power supply, including: a controller and an overcurrent protection circuit. The switching power supply may also include a main circuit power loop, which may include a power tube, a transformer, and the like.

[0026] In the embodiment of the utility model, the controller can output a driving signal to drive the switch tube of the switching power supply to conduct.

[0027] In a specific implementation, the driving signal may be a pulse width modulation (PWM) signal. The controller may adjust the duty cycle of the PWM signal based on the output voltage of the switching power supply to adjust the on-time of the switch tube, thereby achieving a stable voltage output.

[0028] The controller may include an error amplifier output port, a feedback voltage port, a primary current detection port, an oscillator control port, a reference voltage output port, a power supply port, a drive signal output port, a ground port, etc.

[0029] Specifically, the power port of the controller can be coupled to the output end of the DC voltage source, and the DC voltage source can power the controller. The feedback voltage port of the controller can be coupled to the output end of the switching power supply to obtain the feedback voltage of the output end of the switching power supply. When the controller is in a soft start state, the reference voltage port of the controller can output a reference voltage. The oscillator control port of the controller can control the oscillator module inside the controller based on the level of the input signal. The drive signal output port of the controller can output a drive signal. The primary current detection port of the controller can input the primary current. The error amplifier output port of the controller can output an error amplifier voltage, and the error amplifier voltage is associated with the difference between the reference voltage and the feedback voltage.

[0030] In some embodiments, the controller may be a PWM control chip, and specifically, the controller may be a PWM control chip of the UC2845 series or the UC2844 series.

[0031] In an embodiment of the utility model, the first end of the overcurrent protection circuit is coupled to the error amplifier output interface of the controller, the second end of the overcurrent protection circuit is coupled to the reference voltage output port of the controller, and the third end of the overcurrent protection circuit is coupled to the oscillator control port of the controller.

[0032] When the voltage of the error amplifier output port is greater than the preset voltage, the overcurrent protection circuit can disconnect the path between the reference voltage output port and the oscillator control port. As a result, the oscillator in the controller stops working, so the controller stops outputting the drive signal, and the power tube is in a disconnected state.

[0033] In a specific implementation, the above-mentioned preset voltage may be the maximum voltage at which the overcurrent protection circuit can form a path between the reference voltage output port and the oscillator control port when the switching power supply does not have a short circuit fault. Alternatively, the above-mentioned preset voltage may be the rated voltage output by the switching power supply. Alternatively, the above-mentioned preset voltage may also be set according to a specific application scenario.

[0034] In practical applications, it can be seen that when a short circuit occurs in the switching power supply, the output voltage at the output end of the switching power supply decreases. Accordingly, the feedback voltage obtained by the controller decreases. When the feedback voltage decreases, the difference between the reference voltage and the feedback voltage increases, which in turn causes the voltage of the error amplifier output port to increase. When the voltage of the error amplifier output port is greater than the preset voltage, the overcurrent protection circuit disconnects the path between the reference voltage output port and the oscillator control port, thereby stopping the oscillator in the controller from working, and then the controller stops outputting the drive signal, and the power tube is in a disconnected state.

[0035] Therefore, when a short circuit occurs in the switching power supply, the power tube enters a disconnected state, thereby being able to effectively protect the power tube and achieve overcurrent protection.

[0036] Reference Figure 1 , a schematic diagram of the structure of a switching power supply in an embodiment of the utility model is given. Figure 1 , the switching power supply provided in the embodiment of the utility model is described in detail.

[0037] like Figure 1 As shown, the controller U1 is a PWM control chip of the UC2845 series. The PWM control chip includes 8 pins, pin 1 is the error amplifier output port COMP, pin 2 is the feedback voltage port FB, pin 3 is the primary current detection port CS, pin 4 is the oscillator control port RT / CT, pin 5 is the reference voltage output port VREF, pin 6 is the power supply port VDD, pin 7 is the drive signal output port OUT, and pin 8 is the ground port GND.

[0038] In an embodiment of the utility model, the overcurrent protection circuit may include: a current limiting unit, a first switch unit and a first filter unit, wherein:

[0039] The input end of the current limiting unit is coupled to the reference voltage output port VREF, and the output end of the current limiting unit is coupled to the error amplification output port COMP;

[0040] A first terminal of the first switch unit is coupled to the reference voltage output port VREF, and a second terminal of the first switch unit is coupled to the oscillator control port RT / CT;

[0041] The first filtering unit may be coupled between the control terminal of the first switching unit and the error amplifying output port COMP.

[0042] In the embodiment of the utility model, the current limiting unit may be an impedance unit, or other electronic components or circuit structures capable of current limiting. In some embodiments, the current limiting unit may be a first resistor.

[0043] The first filtering unit may be an RC filter. Specifically, the first filtering unit may include a second resistor and a first capacitor, wherein: a first end of the second resistor is coupled to the error amplifier output port COMP, a second end of the second resistor is coupled to the control end of the first switch unit and the first end of the first capacitor; and a second end of the first capacitor is grounded.

[0044] In some embodiments, the first switch unit may include a first NPN transistor, the first end of the first switch unit is the emitter of the first NPN transistor, the second end of the first switch unit is the collector of the first NPN transistor, and the control end of the first switch unit is the base of the first NPN transistor.

[0045] In some other embodiments, the first switch unit may include a first NMOS transistor, the first end of the first switch unit is the source of the first NMOS transistor, the second end of the first switch unit is the drain of the first NMOS transistor, and the control end of the first switch unit is the gate of the first NMOS transistor.

[0046] It is understandable that the first switch unit may also be other devices or circuit structures that can realize the switch function, which will not be described in detail here.

[0047] Reference Figure 2 , a structural schematic diagram of another switching power supply in an embodiment of the utility model is given.

[0048] like Figure 2 As shown, the overcurrent protection circuit includes: a first resistor R1, a second resistor R2, a first NPN transistor Q1 and a first capacitor C1, wherein:

[0049] A first end of the first resistor R1 is coupled to the reference voltage output port VREF, and a second end of the first resistor R1 is coupled to the error amplifier output port COMP;

[0050] A first end of the second resistor R2 is coupled to the error amplifier output port COMP, and a second end of the second resistor R2 is coupled to the control end of the first NPN transistor Q1 and the first end of the first capacitor C1;

[0051] A first end of the first NPN transistor Q1 is coupled to the reference voltage output port VREF, and a second end of the first NPN transistor Q1 is coupled to the oscillator control port RT / CT;

[0052] A second terminal of the first capacitor C1 is grounded.

[0053] In a specific implementation, the switching power supply may further include a second filtering unit, which may be coupled between the second end of the first switching unit and the oscillator control port RT / CT of the controller U1. By setting the second filtering unit, the signal output by the collector of the first switching unit may be smoothed and filtered to avoid false triggering of the oscillator of the controller U1 by noise signals.

[0054] Reference Figure 1 or Figure 2 In some embodiments, the second filtering unit may include a third resistor R3 and a second capacitor C2, wherein:

[0055] A first end of the third resistor R3 is coupled to the second end of the first switch unit, and a second end of the third resistor R3 is coupled to the first end of the second capacitor C2 and the oscillator control port RT / CT of the controller U1;

[0056] A second terminal of the second capacitor C2 is grounded.

[0057] In a specific implementation, the switch unit may further include a clamping unit. The clamping unit may be coupled to the second end of the first resistor R1 and the error amplifier output port COMP of the controller U1. When the switching power supply is not short-circuited, the clamping unit may clamp the voltage of the error amplifier output port COMP of the controller U1 to a preset voltage.

[0058] Specifically, the clamping unit may include a fourth resistor R4, a second switch unit and a third capacitor C3, wherein:

[0059] A first end of the fourth resistor R4 is coupled to the second end of the first resistor R1, and a second end of the fourth resistor R4 is coupled to the control end of the second switch unit and a first end of the third capacitor C3;

[0060] A first end of the second switch unit is coupled to the second end of the first resistor R1, and a second end of the second switch unit is grounded;

[0061] A second terminal of the third capacitor C3 is grounded.

[0062] In some embodiments, the second switch unit may include a second NPN transistor Q2. The first end of the second switch unit is the emitter of the second NPN transistor Q2, the second end of the second switch unit is the collector of the second NPN transistor Q2, and the control end of the second switch unit is the base of the second NPN transistor Q2.

[0063] In some other embodiments, the second switch unit may include a second NMOS transistor, the first end of the second switch unit is the source of the second NMOS transistor, the second end of the second switch unit is the drain of the second NMOS transistor, and the control end of the second switch unit is the gate of the second NMOS transistor.

[0064] In a specific implementation, the switching power supply may further include a power supply branch. The power supply branch is coupled between the DC voltage source DCDC and the power port VDD of the controller U1. Thus, the DC voltage source DC may supply power to the controller U1 through the power supply branch.

[0065] Specifically, the power supply branch may include a fifth resistor R5 and a fourth capacitor C4, wherein:

[0066] A first end of the fifth resistor R5 is coupled to the output end of the DC voltage source DC, and a second end of the fifth resistor R5 is coupled to a first end of the fourth capacitor C4 and a power port VDD of the controller U1;

[0067] A second terminal of the fourth capacitor C4 is grounded.

[0068] In a specific implementation, the switching power supply may further include a main circuit power loop. The main circuit power loop may include a transformer T1, a first diode D1, a switch tube MOSFET, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a second diode D2, a fifth capacitor C5 and an output load RL.

[0069] The transformer T1 may include a primary winding, an auxiliary winding and an auxiliary winding, wherein: one end of the primary winding is coupled to the output end of the DC voltage source DC, and the other end of the primary winding is coupled to the first end of the switch tube MOSFET; one end of the auxiliary winding is coupled to the anode of the first diode D1, and the other end of the auxiliary winding is grounded; one end of the auxiliary winding is coupled to the first end of the fifth capacitor C5, the first end of the output load RL, and the first end of the seventh resistor R7, and the other end of the auxiliary winding is coupled to the anode of the second diode D2;

[0070] The second end of the switch tube MOSFET is coupled to the first end of the sixth resistor R6, and the control end of the switch tube MOSFET is coupled to the driving signal output port OUT of the controller U1;

[0071] A second end of the sixth resistor R6 is grounded;

[0072] The second end of the seventh resistor R7 is coupled to the first end of the eighth resistor R8 and the feedback voltage port FB of the controller U1;

[0073] A second end of the eighth resistor R8 is grounded;

[0074] The cathode of the first diode D1 is coupled to the second end of the fifth resistor R5 and the first end of the fourth capacitor C4;

[0075] A cathode of the second diode D2 is coupled to the second end of the fifth capacitor C5 and the second end of the output load RL.

[0076] The feedback voltage port FB of the controller U1 is coupled to the second end of the seventh resistor R7 and the second end of the eighth resistor R8. The voltage of the first end of the eighth resistor R8 is collected as the feedback voltage and output to the feedback voltage port FB of the controller U1. Thus, the controller U1 can output a control signal of a corresponding duty cycle to the control end of the switch tube MOSFET based on the feedback voltage to control the conduction time of the switch tube MOSFET.

[0077] The switch tube MOSFET may be an N-type MOSFET tube. The first end of the switch tube MOSFET may be a drain of the N-type MOSFET tube, the second end of the switch tube may be a source of the N-type MOSFET tube, and the control end of the switch tube may be a gate of the N-type MOSFET tube.

[0078] It should be noted that the specific circuit structure of the main circuit power loop mentioned above can also refer to the main circuit power loop in the traditional flyback topology switching power supply. Its specific working process, principle, etc. can all correspond to the main circuit power loop in the traditional flyback topology switching power supply, and will not be described in detail here.

[0079] Combine the following Figure 1 , the overcurrent protection process of the switching power supply provided in the embodiment of the utility model is described. The controller U1 is a PWM control chip.

[0080] The DC voltage source DC charges the fourth capacitor C4 through the fifth resistor R5, and the voltage at the first end of the fourth capacitor C4 gradually increases, and accordingly the voltage at the power port VDD of the controller U1 gradually increases. When the voltage at the power port VDD of the controller U1 reaches the start voltage of the controller U1, the controller U1 enters the soft start process.

[0081] The reference voltage output port VREF of the controller U1 outputs the reference voltage, and charges the third capacitor C3 through the first resistor R1, and the voltage at the first end of the third capacitor C3 gradually increases. When the voltage difference between the first end of the third capacitor C3 (that is, the base of the second NPN transistor Q2) and the emitter of the second NPN transistor Q2 is greater than the turn-on voltage (usually 0.6V to 0.7V), the second NPN transistor Q2 is turned on. In this scenario, the voltage at the error amplifier output port COMP of the controller U1 is clamped by the voltage at the first end of the third capacitor C3, and at the same time, the charge stored in the first capacitor C1 is released through the second resistor R2 and the second NPN transistor Q2.

[0082] When the switching power supply does not have an overcurrent, before the soft start ends, the voltage of the error amplifier output port COMP of the controller U1 is lower than the reference voltage, so the first NPN transistor Q1 is turned on.

[0083] If the switching power supply has an overcurrent, the voltage of the error amplifier output port COMP of the controller U1 will continue to rise. As the voltage of the error amplifier output port COMP increases, the first NPN transistor Q1 switches from the on state to the off state. When the first NPN transistor Q1 is turned off, there is no voltage input to the oscillator control port RT / CT of the controller U1, and the oscillator in the controller U1 stops working (that is, stops outputting the PWM signal). The charge in the fourth capacitor C4 is gradually consumed until the voltage of the power port VDD of the controller U1 is less than the chip undervoltage value, and the controller U1 is turned off.

[0084] When the controller U1 is turned off, the voltage of the reference voltage output port VREF of the controller U1 is 0, and the first capacitor C1 and the third capacitor C3 are discharged through the reference voltage output port VREF.

[0085] The DC voltage source DC continues to charge the fourth capacitor C4 through the fifth resistor R5, and the controller U1 re-executes the soft start process. If it is detected that there is still overcurrent, the controller U1 is turned off again. This cycle is repeated to effectively protect the switching power supply from overcurrent. If the short circuit fault disappears, after the soft start is completed, the voltage of the error amplifier output port COMP rises to the preset voltage, and the switching power supply works normally.

[0086] The utility model also provides an electric power device, comprising: an AC power supply and a switching power supply provided by any of the above embodiments.

[0087] In a specific implementation, the output end of the AC power supply can be coupled to a switching power supply, and the AC power supply outputs AC power. In some embodiments, the AC power supply can be a mains power supply.

[0088] The switching power supply is coupled between the AC power supply and the load circuit, and is suitable for converting the AC power into a corresponding working voltage and outputting it to the load circuit. The working voltage can be a DC voltage required for the load circuit to work, and the load circuit can be an electrical device.

[0089] Reference Figure 3 , a schematic diagram of the structure of an electric power device in an embodiment of the present invention is given. An AC power source 31 is coupled to a switching power source 32 , and the switching power source 32 supplies power to a load circuit 33 .

[0090] Although the utility model is disclosed as above, the utility model is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the utility model. Therefore, the protection scope of the utility model shall be subject to the scope defined by the claims.

Claims

1. A switching power supply, characterized in that: include: Controller and overcurrent protection circuit, wherein: The overcurrent protection circuit has a first end coupled to the error amplifier output port of the controller, a second end coupled to the reference voltage output port of the controller, and a third end coupled to the oscillator control port of the controller; when the voltage of the error amplifier output port is greater than a preset voltage, the overcurrent protection circuit disconnects the path between the reference voltage output port and the oscillator control port.

2. The switching power supply according to claim 1, characterized in that: The overcurrent protection circuit comprises: a current limiting unit, a first switch unit and a first filter unit, wherein: The current limiting unit has an input end coupled to the reference voltage output port and an output end coupled to the error amplification output port; The first switch unit has a first end coupled to the reference voltage output port and a second end coupled to the oscillator control port; The first filtering unit is coupled between the control terminal of the first switch unit and the error amplifying output port.

3. The switching power supply according to claim 2, characterized in that: The current limiting unit includes a first resistor.

4. The switching power supply according to claim 2 or 3, characterized in that: The first filtering unit includes a second resistor and a first capacitor, wherein: The second resistor has a first end coupled to the error amplification output port, and a second end coupled to the control end of the first switch unit and the first end of the first capacitor; A second terminal of the first capacitor is grounded.

5. The switching power supply according to claim 2, characterized in that: Also includes: The second filter unit is coupled between the second end of the first switch unit and the oscillator control port.

6. The switching power supply according to claim 5, characterized in that: The second filtering unit includes: a third resistor and a second capacitor, wherein: The third resistor has a first end coupled to the second end of the first switch unit and a second end coupled to the oscillator control port; The second capacitor has a first end coupled to the second end of the third resistor, and a second end grounded.

7. The switching power supply according to claim 2, characterized in that: Also includes: The clamping unit is coupled to the second end of the current limiting unit and the error amplifying output port, and is suitable for clamping the voltage of the error amplifying output port to the preset voltage.

8. The switching power supply according to claim 7, characterized in that: The clamping unit comprises: a fourth resistor, a second switch unit and a third capacitor, wherein: The fourth resistor has a first end coupled to the second end of the current limiting unit, and a second end coupled to the control end of the second switch unit and the first end of the third capacitor; The second switch unit has a first end coupled to the second end of the current limiting unit and a second end grounded; A second end of the third capacitor is grounded.

9. The switching power supply according to claim 1, characterized in that: Also includes: A power supply branch, coupled between a DC voltage source and a power port of the controller; The DC voltage source supplies power to the controller via the power supply branch.

10. The switching power supply according to claim 9, characterized in that: The power supply branch includes a fifth resistor and a fourth capacitor, wherein: The fifth resistor has a first end coupled to the output end of the DC voltage source, and a second end coupled to the first end of the fourth capacitor and the power port; The second end of the fourth capacitor is grounded.

11. An electric power device, characterized in that: include: An AC power supply and a switching power supply as claimed in any one of claims 1 to 10; The switching power supply is coupled between the AC power supply and the load circuit, and is suitable for converting the AC power output by the AC power supply into the working voltage required by the load circuit.

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