Over-temperature protection circuit and switching power supply using same

Abstract

In the over-temperature protection circuit disclosed by the invention, a temperature detection signal and a temperature reference voltage are set to be from the same voltage signal, so that the over-temperature protection threshold value can be flexibly adjusted under the condition of not increasing the number of chip pins, and the over-temperature protection threshold value can be flexibly adjusted no matter how the voltage of the same voltage signal changes. And the over-temperature protection threshold value is constant, so that the method is suitable for an application scheme with a wide voltage range.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and more specifically to an over-temperature protection circuit and a switching power supply using the same. Background Art

[0002] In switching power supply products, the control chip generally has an over-temperature protection function. Generally, the chip will stop working when the internal temperature exceeds a certain temperature, and resume working when the chip temperature drops to prevent the switching power supply from being damaged or catching fire.

[0003] In the design of power supply products, an external over-temperature protection function is usually required to facilitate the adjustment of the over-temperature protection threshold, such as 70-100°C. There are generally two common methods of external over-temperature protection on the market. One is to use a high-precision current source to achieve over-temperature protection. This method requires a high-precision current source, which is relatively expensive and requires a separate temperature detection pin OTP; the other is to use a high-precision voltage source to achieve over-temperature protection. This method cannot provide a constant over-temperature protection threshold. Therefore, the above two methods are either relatively expensive or only applicable to application conditions with fixed output voltages, and neither can meet the requirements of switching power supply products. Summary of the invention

[0004] In view of this, the present invention provides an over-temperature protection circuit. By setting the temperature detection signal and the temperature reference voltage to come from the same voltage signal, the over-temperature protection threshold can be flexibly adjusted without increasing the number of chip pins. Moreover, no matter how the voltage of the same voltage signal changes, the over-temperature protection threshold is constant, and is therefore suitable for applications with a wide voltage range.

[0005] In a first aspect, the present invention provides an over-temperature protection circuit, which is applied to a switching power supply, and includes a temperature detection circuit and a temperature reference voltage generation circuit connected in parallel, and a first comparison circuit;

[0006] Wherein, the temperature detection circuit is used to generate a temperature detection signal;

[0007] A temperature reference voltage generating circuit is configured to generate a temperature reference voltage, and the temperature detection signal and the temperature reference voltage are approximately in direct proportion to the same voltage signal;

[0008] The first comparison circuit is configured to receive the temperature reference voltage at a first end and receive the temperature detection signal at a second end, so as to generate a temperature protection signal indicating that an over-temperature protection threshold is reached when the temperature detection signal reaches the temperature reference voltage.

[0009] Preferably, the common node of the temperature detection circuit and the temperature reference voltage generating circuit includes a first node and a second node, and the temperature detection circuit includes an adjustment resistor and an over-temperature protection resistor coupled in series between the first node and the second end. When the temperature changes, the resistance of the over-temperature protection resistor changes accordingly to change the value of the temperature detection signal.

[0010] Preferably, the temperature detection circuit further includes a voltage dividing resistor coupled in series between the second end and the ground potential.

[0011] Preferably, the over-temperature protection threshold does not change with the change of the voltage signal.

[0012] Preferably, the over-temperature protection threshold is adjusted by changing the resistance of the adjusting resistor.

[0013] Preferably, as the resistance of the regulating resistor increases, the over-temperature protection threshold increases accordingly.

[0014] Preferably, the over-temperature protection resistor is a thermistor, and the thermistor has a negative temperature coefficient.

[0015] Preferably, the first node is a non-grounded end of an auxiliary winding coupled to an inductive device in the switching power supply.

[0016] Preferably, the temperature detection circuit further includes a first diode coupled in series with the adjustment resistor and the over-temperature protection resistor, wherein an anode of the first diode is coupled to the first node, and a cathode of the first diode is coupled to an output end of the temperature detection circuit.

[0017] Preferably, the output end of the temperature detection circuit is coupled to the current sampling pin of the control chip of the switching power supply. When the main power switch in the switching power supply is turned on, the signal at the output end of the temperature detection circuit is configured as a current sampling signal; when the main power switch in the switching power supply is turned off, the signal at the output end of the temperature detection circuit is configured as the temperature detection signal.

[0018] Preferably, the temperature reference voltage generating circuit is coupled between the first node and the ground terminal, and its output terminal is coupled to the voltage sampling pin of the control chip of the switching power supply. The first comparison circuit and the voltage detection circuit in the control chip both receive the voltage sampling signal, and the voltage detection circuit is used to obtain at least the output voltage information of the switching power supply according to the voltage sampling signal.

[0019] Preferably, the first node is a control terminal of a main power switch in the switching power supply.

[0020] Preferably, the output end of the temperature detection circuit is coupled to the temperature detection pin of the control chip of the switching power supply. When the main power switch in the switching power supply is turned on, the first comparison circuit compares the temperature detection signal with the temperature reference voltage to generate the temperature protection signal.

[0021] Preferably, the first node is an output end of a power supply voltage, and the power supply voltage is used to power a control chip of the switching power supply.

[0022] In a second aspect, the present invention provides a switching power supply, comprising:

[0023] power stage circuit, and

[0024] The over-temperature protection circuit mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 A schematic diagram of a schematic diagram of an over-temperature protection circuit of a comparative example;

[0027] Figure 2 is a schematic diagram of an over-temperature protection circuit according to a first embodiment of the present invention;

[0028] Figure 3 The operating waveform diagram of the switching power supply using the over-temperature protection circuit of the first embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of an over-temperature protection circuit according to a second embodiment of the present invention;

[0030] Figure 5 FIG. 4 is a schematic diagram of an over-temperature protection circuit according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. It is possible for a person skilled in the art to fully understand the present invention without the description of these details. In order to avoid confusing the essence of the present invention, known methods, processes, flows, components and circuits are not described in detail.

[0032] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes and are not necessarily drawn to scale.

[0033] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected between" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0034] Unless the context clearly requires otherwise, throughout the specification and claims, the words "include", "comprising" and similar words should be interpreted in an inclusive sense rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to".

[0035] In the description of the present invention, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0036] like Figure 1 FIG. 1 is a schematic diagram of a temperature protection circuit using a high-precision voltage source as a comparative example of the present invention. Figure 1 In the scheme shown, during the conduction period Ton of the main power switch M1, the auxiliary winding N AUX The voltage V AUX The voltage is negative, the diode D2 is reversely cut off, and there is no voltage drop on the resistor R4 (equivalent to a short circuit). Therefore, at this time, inside the current sampling pin CS, the voltage of the current sampling resistor R5 is compared with the peak reference voltage Vpk to achieve peak current control;

[0037] During the off period Toff of the main power switch M1, the main power switch M1 is turned off, and the auxiliary winding N AUX The voltage V AUX is high level, at this time, diode D2 is forward conducting, assuming its forward conduction voltage drop is 0.7V, then the voltage of the current sampling pin CS is:

[0038]

[0039] Normally, the auxiliary winding N AUX The voltage V AUX It is much larger than the forward voltage drop of diode D2, 0.7V, and R5 < 1Ohm, so the above formula can be simplified to:

[0040]

[0041] As the chip temperature increases, the resistance of thermistor R3 decreases, so the voltage at the CS terminal increases. When it is higher than the internal temperature reference voltage Vref of the chip, the over-temperature protection (OTP) is triggered. Therefore, the threshold of OTP protection meets the following requirements:

[0042]

[0043] In the above formula, the resistors R2 and R4, as well as the temperature reference voltage Vref are all fixed values. If the auxiliary winding N AUX The voltage V AUX is also fixed, so when the over-temperature protection threshold is reached, the resistance of thermistor R3 is also determined. AUX The voltage V AUX When the temperature changes, for example, when it decreases, the thermistor R3 also decreases when the voltage of the current sampling pin CS reaches the temperature reference voltage Vref, which means that the over-temperature protection threshold will increase accordingly. The control chip needs to reach a higher temperature to trigger the over-temperature protection. Therefore, for the auxiliary winding N AUX For applications with a wide voltage range, this method cannot provide a constant over-temperature protection threshold.

[0044] Figure 2 FIG. 1 is a schematic diagram of an over-temperature protection circuit according to a first embodiment of the present invention. Figure 2 As shown, the over-temperature protection circuit of this embodiment is applied to a switching power supply. Here, the switching power supply has an auxiliary winding N AUX The flyback converter topology is described as an example, but the present invention is not limited thereto. Figure 2 As shown, the main power switch M1 in the switching power supply is controlled by the driving signal V outputted from the DRV terminal of the control chip 21. DRV The main power switch M1 can be turned on and off so that the output voltage or output current of the switching power supply meets the requirements. In this embodiment, the main power switch M1 can adopt various existing electrically controllable switching devices, such as metal oxide semiconductor field effect transistor (MOSFET), bipolar junction transistor (BJT), or insulated gate bipolar transistor (IGBT), etc., and the present invention does not limit this.

[0045] In this embodiment, if Figure 2 As shown, the control circuit of the switching power supply at least includes a control chip 21 , and a temperature detection circuit 25 and a temperature reference voltage generation circuit 26 externally disposed on the control chip 21 .

[0046] Specifically, the temperature detection circuit 25 is coupled between the first node and the current sampling pin CS of the control chip 21, and is used to generate a temperature detection signal Vt according to the junction temperature; further, the temperature detection circuit 25 includes an adjustment resistor R2 and an over-temperature protection resistor R3 coupled in series between the first node and the second end, and also includes a first diode D2 coupled in series with the adjustment resistor R2 and the over-temperature protection resistor R3, the anode of the first diode D2 is coupled to the first node, the cathode is coupled to one end of the series structure including the adjustment resistor R2 and the over-temperature protection resistor R3, and the other end of the series structure is coupled to the current sampling pin CS. Here, the first node is an auxiliary winding N in the switching power supply for sampling voltage. AUX The non-grounded end of the auxiliary winding N AUX The voltage V AUX Preferably, the over-temperature protection resistor R3 is a thermistor, which has a negative temperature coefficient, and as the junction temperature of the chip increases, the resistance of the thermistor decreases accordingly.

[0047] The temperature reference voltage generating circuit 26 is coupled between the first node and the ground terminal, and includes a resistor R7 and a resistor R8 connected in series. The temperature reference voltage generating circuit 26 outputs a voltage sampling signal Vsen at a common node between the resistors R7 and R8. The voltage sampling signal Vsen is a voltage division signal of the first node voltage.

[0048] The temperature detection signal 25 and the temperature reference voltage generating circuit 26 are both coupled to the first node, so that the temperature detection signal Vt and the temperature reference voltage generating circuit are approximately in direct proportion to the voltage signal of the first node.

[0049] In the embodiment of the present invention, the current sampling circuit includes a resistor R5 connected in series with the main power switch M1, and a resistor R4 coupled between one end of the resistor R5 and the current sampling pin CS of the control chip 21, for obtaining a current sampling signal Isen representing the current flowing through the main power switch M1 during the conduction period of the main power switch M1. The temperature detection circuit 25 also includes a voltage dividing resistor coupled in series between the second end and the ground potential, where the resistors R4 and R5 are voltage dividing resistors.

[0050] In a preferred embodiment, the control chip 21 at least includes a first comparison circuit 23, a second comparison circuit 24 and a voltage detection circuit 22 built therein. The first comparison circuit 23 and the voltage detection circuit 22 both receive the voltage sampling signal Vsen output by the temperature reference voltage generation circuit 26. The voltage detection circuit 22 is used to obtain at least one of the input voltage information, the output voltage information or the valley information of the resonant voltage of the switching power supply according to the voltage sampling signal Vsen, wherein the voltage detection circuit 22 obtains the input voltage information of the switching power supply according to the voltage sampling signal Vsen during the conduction period of the main power switch M1; obtains the output voltage information of the switching power supply according to the voltage sampling signal Vsen during the first period during which the main power switch M1 is turned off; obtains the valley information of the resonant voltage according to the voltage sampling signal Vsen during the second period during which the main power switch M1 is turned off, and controls the on-off state of the main power switch M1 accordingly. The first comparison circuit 23 and the second comparison circuit 24 receive the temperature detection signal Vt and the current sampling signal Isen respectively through the current sampling pin CS.

[0051] In the switching power supply, the over-temperature protection circuit 20 is used to prevent the control chip from being damaged due to overheating. When the internal junction temperature of the control chip exceeds the over-temperature protection threshold (e.g., 150°C), the over-temperature protection circuit 20 will instruct the switching power supply to suspend operation or enter the shutdown mode and reset the internal logic. When the junction temperature drops to a certain temperature (e.g., 15°C), the switching power supply will resume normal operation. In an embodiment of the present invention, the over-temperature protection threshold of the over-temperature protection circuit 20 is constant, and it does not change with the voltage of the connection point of the temperature detection circuit 25, that is, the change of the first voltage.

[0052] Preferably, the over-temperature protection circuit 20 includes a temperature detection circuit 25, a first comparison circuit 23, and a temperature reference voltage generation circuit 26. Specifically, the non-inverting input terminal of the first comparison circuit 23 receives the temperature detection signal Vt generated by the temperature detection circuit 25 through the current sampling pin CS, and the inverting input terminal receives the voltage division signal of the voltage signal of the first node and uses it as the temperature reference voltage Tref. Specifically, the inverting input terminal receives the voltage sampling signal Vsen output by the temperature reference voltage generation circuit 26 through the voltage sampling pin VS as the temperature reference voltage Tref, so that the first comparison circuit 23 generates an effective temperature protection signal V indicating that the over-temperature protection threshold is reached when the temperature detection signal Vt reaches the temperature reference voltage Tref. OTP .

[0053] It should be noted that, in a switching power supply, there is generally a voltage detection circuit 22, and at the same time, there is also a temperature reference voltage generation circuit 26 that provides a voltage sampling signal Vsen for the voltage detection circuit 22. In fact, the temperature reference voltage generation circuit 26 and the voltage sampling pin VS are not added because of the improvement of the over-temperature protection function of this solution, but the voltage divider circuit of the voltage sampling circuit in the original control circuit is reused, and the first comparison circuit 23 can directly receive the voltage sampling signal Vsen inside the control chip 21. Therefore, compared with the prior art, the over-temperature protection circuit 20 of the embodiment of the present invention does not need to add additional pins. Only in order to make the function of the over-temperature protection circuit 20 more complete, the temperature reference voltage generation circuit 26 is divided into the over-temperature protection circuit 20.

[0054] Furthermore, in the over-temperature protection circuit 20, the over-temperature protection threshold can be adjusted by changing the resistance of the adjustment resistor R2 in the temperature detection circuit 25. In a preferred embodiment, the resistance of the adjustment resistor R2 corresponds to the over-temperature protection threshold one by one, so that the over-temperature protection circuit of this embodiment can be applied to occasions with different over-temperature protection thresholds. Furthermore, as the resistance of the adjustment resistor R2 increases, the over-temperature protection threshold increases accordingly.

[0055] The over-temperature protection circuit 20 of the embodiment of the present invention replaces the fixed temperature reference voltage Vref in the prior art with the output voltage Vsen from the temperature reference voltage generating circuit 26 which is the same source (first node) as the temperature detection circuit 25, so that the over-temperature protection threshold value is constant when the voltage signal of the first node changes. AUX After voltage division, a voltage sampling signal Vsen is obtained.

[0056] Next, combine Figure 3 The working waveform diagram of the switching power supply using the over-temperature protection circuit of the first embodiment of the present invention is shown to illustrate the working principle of the over-temperature protection circuit 20:

[0057] During the Ton period (t1-t2 period), the main power switch M1 in the switching power supply is turned on, and the current sampling pin CS is used for peak current control during this period. AUX The voltage V AUX is a negative voltage, the diode D2 is reversely cut off, and the resistor R4 is equivalent to a short circuit. Therefore, the current sampling signal Isen obtained by the current sampling circuit, which represents the current flowing through the main power switch M1, is transmitted to the current sampling pin CS, and the second comparison circuit 24 compares the current sampling signal Isen with the peak reference voltage Vpk to generate a peak current signal Vcs_pk, and then realizes peak current control through the peak current signal Vcs_pk;

[0058] During the Toff period (t2-t4 period), the main power switch M1 is turned off, and the current sampling pin CS is used for over-temperature protection control during part of this period. AUX The voltage V AUX is high level, at this time, the diode D2 is forward-conducted, and the temperature detection signal Vt representing the junction temperature generated by the temperature detection circuit 25 is transmitted to the current sampling pin CS. Preferably, the period t2 to t3 is set as the blanking time, and the blanking time is used to avoid the noise on the temperature detection signal Vt and the voltage sampling signal Vsen. After the time t3, the first comparison circuit 23 compares the temperature detection signal Vt and the voltage sampling signal Vsen. When the temperature detection signal Vt reaches the voltage sampling signal Vsen, it is determined that the over-temperature protection threshold has been reached. At this time, the first comparison circuit 23 outputs a valid temperature protection signal V OTP , used to indicate that the switching power supply enters a dormant state or a stopped state. Preferably, the value of the voltage sampling signal Vsen between the time t3 and before the resonance occurs is used as the effective temperature reference voltage Tref.

[0059] Assuming that the forward voltage drop of diode D2 is 0.7V, the voltage of the current sampling pin CS is:

[0060]

[0061] The voltage of the voltage sampling pin VS is:

[0062]

[0063] When the temperature detection signal Vt is equal to the voltage sampling signal Vsen,

[0064]

[0065] Normally, the auxiliary winding N AUX The voltage V AUX >>0.7V, and the resistance of resistor R5 is generally less than 1Ohm, so the above formula can be simplified to:

[0066]

[0067] The auxiliary windings N on both sides AUX The voltage V AUX Can be further simplified to

[0068]

[0069] As can be seen from the above formula, since the resistors R2, R4, R7 and R8 are all fixed values, the resistance of thermistor R3 is also fixed when the over-temperature protection threshold is reached, which means that the over-temperature protection threshold will not change with the auxiliary winding N AUX The over-temperature protection threshold of the embodiment of the present invention is independent of the voltage signal of the first node connected to the temperature detection circuit 25, and the over-temperature protection threshold does not change with the voltage signal of the first node. The reference temperature reference voltage Tref can be obtained through the voltage sampling pin Vsen of the control chip 41 without adding additional pins.

[0070] It can be seen that the over-temperature protection circuit proposed in the present invention, by setting the temperature detection signal Vt and the temperature reference voltage Tref to come from the same voltage signal, can achieve flexible adjustment of the over-temperature protection threshold without increasing the number of chip pins, and no matter how the voltage of the same voltage signal changes, the over-temperature protection threshold is constant, and is therefore suitable for applications with a wide voltage range.

[0071] Figure 4 Schematic diagram of an over-temperature protection circuit of a second embodiment of the present invention. The difference between the embodiment of the present invention and the first embodiment is that, on the one hand, the first node is no longer the auxiliary winding N in the switching power supply for sampling voltage. AUX The non-grounded end of the first node is set as the control end of the main power switch M1 in the switching power supply, and the voltage signal of the first node is the driving voltage V of the main power switch M1. DRV On the other hand, the control chip 41 requires a dedicated over-temperature protection terminal OTP.

[0072] refer to Figure 4In the embodiment of the present invention, the over-temperature protection circuit includes a temperature detection circuit 45, a first comparison circuit 43, and a temperature reference voltage generation circuit 46. Specifically, the non-inverting input terminal of the first comparison circuit 43 receives the temperature detection signal Vt generated by the temperature detection circuit 45 through the over-temperature protection terminal OTP of the control chip 41, and the inverting input terminal receives the signal obtained by dividing the voltage signal of the first node by the temperature reference voltage generation circuit 46 and uses it as the temperature reference voltage Tref. Specifically, the first node is the control terminal of the main power switch M1 in the switching power supply. The temperature reference voltage generation circuit 46 includes a seventh resistor R7 and an eighth resistor R8 connected in series, and generates a temperature reference voltage Tref at a common node of the seventh resistor R7 and the eighth resistor R8. One end of the temperature reference voltage generation circuit 46 is connected to the control ground, and the other end is connected to the control terminal of the main power switch M1 through the control signal output terminal DRV of the control chip 41. Preferably, the temperature detection circuit 45 also includes a voltage dividing resistor R6 coupled in series between the second end and the ground potential.

[0073] When the main power switch M1 in the switching power supply is turned on, the first comparison circuit 43 compares the temperature detection signal Vt with the temperature reference voltage Tref, thereby generating a valid temperature protection signal V indicating that the over-temperature protection threshold is reached when the temperature detection signal Vt reaches the temperature reference voltage Tref. OTP .

[0074] When the main power switch M1 is turned on, the temperature detection signal Vt of the over-temperature protection terminal OTP is:

[0075]

[0076] The output temperature reference voltage Tref of the temperature reference voltage generating circuit 46 is:

[0077]

[0078] When the temperature detection signal Vt is equal to the temperature reference voltage Tref,

[0079]

[0080] The driving voltage V DRV Cancel, further simplified to:

[0081]

[0082] As can be seen from the above formula, since the resistors R2, R6, R7 and R8 are all fixed values, the resistance value of thermistor R3 is also fixed when the over-temperature protection threshold is reached, which means that the over-temperature protection threshold will not change with the driving voltage V of the main power switch M1. DRVThe control chip 41 triggers the over-temperature protection at a constant temperature. Therefore, the over-temperature protection threshold of the embodiment of the present invention has nothing to do with the voltage signal of the first node connected to the temperature detection circuit 45, and the over-temperature protection threshold does not change with the voltage signal of the first node. The acquisition of the reference temperature reference voltage Tref can be achieved through the control signal output terminal DRV of the control chip 41, without adding additional pins.

[0083] Figure 5 Schematic diagram of an over-temperature protection circuit of the third embodiment of the present invention. The difference between the embodiment of the present invention and the first embodiment is that, on the one hand, the first node is no longer the auxiliary winding N used for sampling voltage in the switching power supply. AUX The non-grounded end of the first node is set as the output end of the power supply voltage VCC in the switching power supply, and the voltage signal of the first node is the power supply voltage VCC; on the other hand, the control chip 51 also needs a dedicated over-temperature protection terminal OTP.

[0084] The power supply voltage VCC is used to power the control chip 51 of the switching power supply. In a preferred embodiment, the power supply voltage VCC is provided by connecting the auxiliary winding N AUX The voltage V AUX Further, in the embodiment of the present invention, the auxiliary winding N is filtered by using the filtering circuit 57. AUX The voltage V AUX The filter circuit 57 includes a diode D1 and a resistor R1 connected in series, and a capacitor C1 connected between one end of the series module of the diode D1 and the resistor R1 and the control ground.

[0085] refer to Figure 5 In the embodiment of the present invention, the over-temperature protection circuit includes a temperature detection circuit 55, a first comparison circuit 53, and a temperature reference voltage generating circuit 56. Specifically, the non-inverting input terminal of the first comparison circuit 53 receives the temperature detection signal Vt generated by the temperature detection circuit 55 through the over-temperature protection terminal OTP of the control chip 51, and the inverting input terminal receives the signal obtained by dividing the voltage signal of the first node by the temperature reference voltage generating circuit 56 and uses it as the temperature reference voltage Tref. Specifically, the first node is the output terminal of the power supply voltage VCC in the switching power supply. The temperature reference voltage generating circuit 56 includes a seventh resistor R7 and an eighth resistor R8 connected in series, and generates a temperature reference voltage Tref at a common node of the seventh resistor R7 and the eighth resistor R8. One end of the temperature reference voltage generating circuit 56 is connected to the control ground, and the other end is connected to the output end of the power supply voltage VCC in the switching power supply through the power supply terminal VCC of the control chip 51. Preferably, the temperature detection circuit 45 also includes a voltage dividing resistor R6 coupled in series between the second end and the ground potential.

[0086] The first comparison circuit 53 compares the temperature detection signal Vt with the temperature reference voltage Tref, and provides a temperature protection signal V indicating that the over-temperature protection threshold is reached when the temperature detection signal Vt reaches the temperature reference voltage Tref. OTP .

[0087] The temperature detection signal Vt of the over-temperature protection terminal OTP is:

[0088]

[0089] The output temperature reference voltage Tref of the temperature reference voltage generating circuit 56 is:

[0090]

[0091] When the temperature detection signal Vt is equal to the temperature reference voltage Tref,

[0092]

[0093] By eliminating the supply voltage VCC on both sides, it can be further simplified to:

[0094]

[0095] It can be seen from the above formula that since the resistors R2, R6, R7 and R8 are all fixed values, the resistance value of thermistor R3 is also a fixed value when the over-temperature protection threshold is reached, which means that the over-temperature protection threshold will not increase or decrease with the change of the power supply voltage VCC in the switching power supply, and the control chip 51 triggers the over-temperature protection at a constant temperature. Therefore, the over-temperature protection threshold of the embodiment of the present invention is independent of the voltage signal of the first node connected to the temperature detection circuit 55, and the over-temperature protection threshold does not change with the change of the voltage signal of the first node. And the acquisition of the reference temperature reference voltage Tref can be achieved through the power supply terminal VCC of the control chip 41, without adding additional pins.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An over-temperature protection circuit, applied to a switching power supply, comprising a temperature detection circuit and a temperature reference voltage generating circuit connected in parallel, and a first comparison circuit; in, A temperature detection circuit, used to generate a temperature detection signal; A temperature reference voltage generating circuit is configured to generate a temperature reference voltage, and the temperature detection signal and the temperature reference voltage are approximately in direct proportion to the same voltage signal; The first comparison circuit is configured to receive the temperature reference voltage at a first end and receive the temperature detection signal at a second end, so as to generate a temperature protection signal indicating that an over-temperature protection threshold is reached when the temperature detection signal reaches the temperature reference voltage.

2. The over-temperature protection circuit according to claim 1, characterized in that: The common node of the temperature detection circuit and the temperature reference voltage generating circuit includes a first node and a second node. The temperature detection circuit includes an adjustment resistor and an over-temperature protection resistor coupled in series between the first node and the second end. When the temperature changes, the resistance of the over-temperature protection resistor changes accordingly to change the value of the temperature detection signal.

3. The over-temperature protection circuit according to claim 2, characterized in that: The temperature detection circuit further includes a voltage dividing resistor coupled in series between the second terminal and the ground potential.

4. The over-temperature protection circuit according to claim 1, characterized in that: The over-temperature protection threshold does not change with the change of the voltage signal.

5. The over-temperature protection circuit according to claim 2, characterized in that: The over-temperature protection threshold is adjusted by changing the resistance of the adjusting resistor.

6. The over-temperature protection circuit according to claim 5, characterized in that: As the resistance of the regulating resistor increases, the over-temperature protection threshold increases accordingly.

7. The over-temperature protection circuit according to claim 2, characterized in that: The over-temperature protection resistor is a thermistor, and the thermistor has a negative temperature coefficient.

8. The over-temperature protection circuit according to claim 2, characterized in that: The first node is a non-grounded end of an auxiliary winding coupled to an inductive device in the switching power supply.

9. The over-temperature protection circuit according to claim 8, characterized in that: The temperature detection circuit also includes a first diode coupled in series with the adjustment resistor and the over-temperature protection resistor, wherein an anode of the first diode is coupled to the first node, and a cathode of the first diode is coupled to an output end of the temperature detection circuit.

10. The over-temperature protection circuit according to claim 9, characterized in that: The output end of the temperature detection circuit is coupled to the current sampling pin of the control chip of the switching power supply. When the main power switch in the switching power supply is turned on, the signal at the output end of the temperature detection circuit is configured as a current sampling signal; when the main power switch in the switching power supply is turned off, the signal at the output end of the temperature detection circuit is configured as the temperature detection signal.

11. The over-temperature protection circuit according to claim 2, characterized in that: The temperature reference voltage generating circuit is coupled between the first node and the ground terminal, and its output terminal is coupled to the voltage sampling pin of the control chip of the switching power supply. The first comparison circuit and the voltage detection circuit in the control chip both receive the voltage sampling signal, and the voltage detection circuit is used to obtain at least the output voltage information of the switching power supply according to the voltage sampling signal.

12. The over-temperature protection circuit according to claim 2, characterized in that: The first node is a control terminal of a main power switch in the switching power supply.

13. The over-temperature protection circuit according to claim 12, characterized in that: The output end of the temperature detection circuit is coupled to the temperature detection pin of the control chip of the switching power supply. When the main power switch in the switching power supply is turned on, the first comparison circuit compares the temperature detection signal with the temperature reference voltage to generate the temperature protection signal.

14. The over-temperature protection circuit according to claim 2, characterized in that: The first node is an output end of a power supply voltage, and the power supply voltage is used to supply power to a control chip of the switching power supply.

15. The over-temperature protection circuit according to claim 14, characterized in that: The supply voltage is obtained by filtering the voltage across the auxiliary winding in the switching power supply.

16. The over-temperature protection circuit according to claim 2, characterized in that: The second node is connected to the ground terminal.

17. A switching power supply comprising: power stage circuit, and The over-temperature protection circuit according to any one of claims 1 to 16.

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