Switching power supply automatic derating circuit with over-temperature protection function

Abstract

The utility model provides a switching power supply automatic derating circuit with an over-temperature protection function, comprising a switching power supply circuit which comprises a switching power supply control module, an inductor, an output capacitor and a voltage feedback circuit, an input voltage end of the switching power supply control module is connected with a power supply, and a switching output end of the switching power supply control module is connected with an output end VOUT through the inductor; one end of the output capacitor is connected with the output end VOUT, and the other end of the output capacitor is grounded; the input end of the voltage feedback circuit is connected with the output end VOUT, and the output end of the voltage feedback circuit is connected with the feedback end of the switching power supply control module; the input end of the temperature detection circuit is connected with the output end VOUT, and the output end of the temperature detection circuit outputs bias voltage; the positive electrode of the unidirectional conduction device is connected with the output end of the temperature detection circuit, and the negative electrode is connected with the output end of the voltage feedback circuit. Compared with the prior art, the temperature of the system is detected through the thermistor, and when the temperature of the system exceeds a set threshold value, the output power of the switching power supply is reduced, so that power derating is realized.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially a kind of switching power supply automatic derating circuit with over-temperature protection function. BACKGROUND

[0002] Generally, the power supply for LED on market is switching power supply, and there are two kinds of over-temperature protection modes in general design: one kind of over-temperature protection is through over-temperature protection of switching power supply chip itself, but this over-temperature protection is disconnecting protection, that is, when temperature reaches over-temperature threshold, power supply is turned off, and after temperature drops, power supply outputs normally again; another kind of over-temperature protection is to monitor temperature value of whole power supply by MCU (Microcontroller Unit), and when temperature exceeds certain limit value, power supply temperature is reduced by adjusting output power, so that power supply can continuously output by derating mode. Over-temperature protection integrated in switching power supply chip is a fixed temperature value, and after reaching over-temperature protection point, power supply is turned off, so it is not suitable for some occasions with high ambient temperature, but output power can not be turned off. Temperature value of power supply can be collected by MCU, so that continuous derating requirement can be met, but because MCU and software development are needed, material and time cost cannot reach optimal scheme.

[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems. CONTENT OF UTILITY MODEL

[0004] One of the purposes of the utility model is to provide a kind of switching power supply automatic derating circuit with over-temperature protection function, and the working temperature of thermistor detection system is detected, and when system working temperature exceeds set threshold, the output power of switching power supply will be reduced, so that power derating is realized, and over-temperature protection is realized.

[0005] According to one aspect of the utility model, the utility model provides a switching power supply automatic derating circuit with overtemperature protection function, it includes: switching power supply circuit, it includes switching power supply control module, inductance L1, output capacitor and voltage feedback circuit, the input voltage end VIN of switching power supply control module is connected with power supply VS, its switch output end SW through inductance L1 with switching power supply automatic derating circuit's output end VOUT is connected, one end of output capacitor with switching power supply automatic derating circuit's output end VOUT is connected, its other end ground connection, the input end of voltage feedback circuit with switching power supply automatic derating circuit's output end VOUT is connected, its output end with switching power supply control module's feedback end FB is connected, temperature detection circuit, its input end with switching power supply automatic derating circuit's output end VOUT is connected, its output end exports bias voltage Vbias, the bias voltage Vbias is based on the voltage of switching power supply automatic derating circuit's output end VOUT produces, and the bias voltage Vbias increases with the rise of system temperature, unidirectional conducting device, its anode is connected with the output end of temperature detection circuit, its cathode is connected with the output end of voltage feedback circuit, the unidirectional conducting device can be from its anode to its cathode unidirectional conduction, and the unidirectional conducting device in the forward direction voltage drop of forward direction conduction state is Vf.

[0006] Further, when the system temperature is less than the overtemperature protection threshold, the unidirectional conducting device is turned off, the feedback voltage VFB output by the output end of the voltage feedback circuit reflects the voltage of the output end VOUT of the switching power supply automatic derating circuit, and the switching power supply control module adjusts the duty cycle of the switching power supply based on the feedback voltage VFB to make the output end VOUT of the switching power supply automatic derating circuit output a stable voltage; when the system temperature is greater than the overtemperature protection threshold, the unidirectional conducting device is forwardly conducted, the feedback voltage VFB output by the output end of the voltage feedback circuit reflects the size of the bias voltage Vbias, and the switching power supply control module adjusts the duty cycle of the switching power supply based on the feedback voltage VFB to make the voltage of the output end VOUT of the switching power supply automatic derating circuit less than the stable voltage.

[0007] Further, the temperature detection circuit includes a negative temperature coefficient thermistor R4 and a fixed value resistor R5, one end of the negative temperature coefficient thermistor R4 is connected to the output end VOUT of the switching power supply automatic derating circuit, and the other end is connected to node A; one end of the fixed value resistor R5 is connected to the node A, and the other end is grounded; the node A is the output end of the temperature detection circuit, and the voltage of the node A is the bias voltage Vbias.

[0008] Further, the voltage feedback circuit comprises a resistor R2 and a resistor R3, one end of the resistor R2 is connected with the output terminal VOUT of the automatic derating circuit of the switching power supply, and the other end thereof is connected with a node B; one end of the resistor R3 is connected with the node B, and the other end thereof is grounded; the node B is an output terminal of the voltage feedback circuit, and the voltage of the node B is the feedback voltage VFB.

[0009] Further, the switching power supply control module is a switching power supply chip; the unidirectional conducting device is a diode D1, and the Vf is a voltage drop of the diode D1.

[0010] Further, the switching power supply circuit further comprises a bootstrap capacitor C3, one end of the bootstrap capacitor C3 is connected with a bootstrap terminal BST of the switching power supply control module, and the other end thereof is connected with the switching output terminal SW.

[0011] Further, the switching power supply circuit further comprises an input capacitor and a resistor R1, the input capacitor is connected between an input voltage terminal VIN and a ground terminal of the switching power supply control module; one end of the resistor R1 is connected with the input voltage terminal VIN of the switching power supply control module, and the other end thereof is connected with an enable terminal EN of the switching power supply control module.

[0012] Further, the output terminal VOUT of the automatic derating circuit of the switching power supply supplies power for the LED lamp string.

[0013] Compared with the prior art, the output power of the switching power supply is reduced when the working temperature of the thermistor detection system exceeds the set threshold, so that the power derating is realized, and the over-temperature protection is realized. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0015] Figure 1 The circuit schematic diagram of the automatic derating circuit of the switching power supply with over-temperature protection function in one embodiment of the present application. DETAILED DESCRIPTION

[0016] In order to make the above-mentioned purpose, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0017] As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the technology. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The terms coupled, connected, connected together, connected with, connecting, connecting together, connecting with, or the like, as used herein, mean the joining of two members together for electrical purposes using a direct or indirect electrical connection unless indicated otherwise.

[0018] In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "right", "left", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0019] Please refer to Figure 1 As shown in the figure, it is a circuit schematic diagram of the automatic derating circuit of the switching power supply with over-temperature protection function in an embodiment of the present application. Figure 1 The automatic derating circuit of the switching power supply with over-temperature protection function shown in the figure includes a switching power supply circuit 110, a temperature detection circuit 120, and a unidirectional conduction device 130.

[0020] The switching power supply circuit 110 includes a switching power supply control module 112, an inductor L1, an output capacitor 114, and a voltage feedback circuit 116. Figure 1 In the specific embodiment shown in the figure, the switching power supply control module 112 is a switching power supply chip U1, the internal structure and working principle of which are well known to those skilled in the art, and therefore will not be described here. The input voltage end (or input voltage pin) VIN of the switching power supply control module 112 is connected with the power supply VS, the switching output end (or switching output pin) SW thereof is connected with the output end VOUT of the automatic derating circuit of the switching power supply through the inductor L1; one end of the output capacitor 114 is connected with the output end VOUT of the automatic derating circuit of the switching power supply, and the other end thereof is grounded; the input end of the voltage feedback circuit 116 is connected with the output end VOUT of the automatic derating circuit of the switching power supply, and the output end thereof is connected with the feedback end (or feedback pin) FB of the switching power supply control module 112.

[0021] The input terminal of the temperature detection circuit 120 is connected to the output terminal VOUT of the automatic derating circuit of the switching power supply. Its output terminal outputs a bias voltage Vbias, which is generated based on the voltage of the output terminal VOUT of the automatic derating circuit of the switching power supply, and the bias voltage Vbias increases with the increase of system temperature.

[0022] The positive terminal of the unidirectional conducting device 130 is connected to the output terminal (or bias voltage Vbias) of the temperature detection circuit 120, and its negative terminal is connected to the output terminal of the voltage feedback circuit 116. The unidirectional conducting device 130 can conduct unidirectionally from its positive terminal to its negative terminal, and the forward voltage drop of the unidirectional conducting device 130 in the forward conducting state is Vf. Figure 1 In the specific embodiment shown, the unidirectional conducting device 130 is a diode D1, and Vf is the diode voltage drop of diode D1.

[0023] When the system temperature is below the over-temperature protection threshold, the unidirectional conducting device 130 is turned off (or cut off). The feedback voltage VFB output by the voltage feedback circuit 116 reflects the voltage magnitude of the output VOUT of the automatic derating circuit of the switching power supply. The switching power supply control module 112 adjusts the duty cycle of the switching power supply based on this feedback voltage VFB to ensure that the output VOUT of the automatic derating circuit of the switching power supply outputs a stable voltage. When the system temperature is above the over-temperature protection threshold, the unidirectional conducting device 130 is forward-biased. The feedback voltage VFB output by the voltage feedback circuit 116 reflects the magnitude of the bias voltage Vbias. The switching power supply control module 112 adjusts the duty cycle of the switching power supply based on this feedback voltage VFB to ensure that the voltage VOUT of the automatic derating circuit of the switching power supply is less than the aforementioned stable voltage.

[0024] exist Figure 1 In the specific embodiment shown, the temperature detection circuit 120 includes an NTC (Negative Temperature Coefficient) thermistor R4 and a fixed resistor (whose resistance value does not change with temperature) R5. One end of the NTC thermistor R4 is connected to the output terminal VOUT of the automatic derating circuit of the switching power supply, and the other end is connected to node A. One end of the fixed resistor R5 is connected to node A, and the other end is grounded. Node A is the output terminal of the temperature detection circuit 120, and the voltage at node A is the bias voltage Vbias.

[0025] exist Figure 1In the specific embodiment shown, the voltage feedback circuit 116 includes a resistor R2 and a resistor R3, one end of the resistor R2 is connected with the output terminal VOUT of the switching power supply automatic derating circuit, and the other end is connected with a node B; one end of the resistor R3 is connected with the node B, and the other end is grounded; the node B is an output terminal of the voltage feedback circuit 116, and the voltage of the node B is the feedback voltage VFB.

[0026] In Figure 1 In the specific embodiment shown, the output capacitor 114 includes a capacitor C5 and a capacitor C6, one end of the capacitor C5 is connected with the output terminal VOUT of the switching power supply automatic derating circuit, and the other end is grounded; one end of the capacitor C6 is connected with the output terminal VOUT of the switching power supply automatic derating circuit, and the other end is grounded.

[0027] In Figure 1 In the embodiment shown, the switching power supply circuit 110 further includes a bootstrap capacitor C3, one end of the bootstrap capacitor C3 is connected with a bootstrap terminal (or bootstrap pin) BST of the switching power supply control module 112, and the other end is connected with a switching output terminal SW.

[0028] In Figure 1 In the embodiment shown, the switching power supply circuit 110 further includes an input capacitor 118 and a resistor R1, wherein the input capacitor 118 is connected between an input voltage terminal (or input voltage pin) VIN of the switching power supply control module 112 and a ground terminal; one end of the resistor R1 is connected with the input voltage terminal (or input voltage pin) VIN of the switching power supply control module 112, and the other end is connected with an enable terminal (or enable pin) EN of the switching power supply control module 112. Figure 1 In the specific embodiment shown, the input capacitor 118 includes a capacitor C1 and a capacitor C2, one end of the capacitor C1 is connected with the input voltage terminal (or input voltage pin) VIN of the switching power supply control module 112, and the other end is grounded; one end of the capacitor C2 is connected with the input voltage terminal (or input voltage pin) VIN of the switching power supply control module 112, and the other end is grounded.

[0029] In Figure 1 In the embodiment shown, the output terminal VOUT of the switching power supply automatic derating circuit supplies power to the LED lamp string 140, specifically, an input terminal (or an anode) of the LED lamp string 140 is connected with the output terminal VOUT of the switching power supply automatic derating circuit, and an output terminal (or a cathode) thereof is grounded. Figure 1 In the embodiment shown, the LED lamp string 140 includes LED1, LED2, …, LEDn connected in series.

[0030] The working principle of the switching power supply automatic derating circuit with over-temperature protection function shown will be specifically introduced below. Figure 1 The working principle of the switching power supply automatic derating circuit with over-temperature protection function shown will be specifically introduced below.

[0031] 1、System power on, switch power supply circuit 110 normal work, output voltage formula is: VOUT = VFB * (1 + R2 / R3). Switch power supply circuit 110 in normal work logic is: when the output voltage VOUT becomes larger, the feedback voltage VFB voltage value will become larger, switch power supply chip U1 detects the feedback voltage VFB value becomes larger, will reduce the duty cycle of switch power supply, thus the output voltage VOUT will become smaller, make feedback voltage VFB restore to normal voltage value; vice versa, when the output voltage VOUT becomes smaller, the feedback voltage VFB voltage value will become smaller, switch power supply chip U1 detects the feedback voltage VFB value becomes smaller, will increase the duty cycle of switch power supply, thus the output voltage VOUT will become larger, make feedback voltage VFB restore to normal voltage value, that is, in switch power supply circuit 110 normal work, switch power supply chip U1 according to the feedback voltage VFB voltage value changes, constantly adjust the duty cycle of switch power supply, thereby guarantee the voltage output of output terminal VOUT.

[0032] 2、Temperature detection circuit 120 output bias voltage Vbias = VOUT * (R5 / (R4+R5), because the resistance R4 is a NTC resistance, NTC resistance is negative temperature characteristic, that is, the higher the temperature, the smaller the resistance of NTC resistance, the lower the temperature, the greater the resistance of NTC resistance, when the temperature does not reach the set over temperature protection threshold, the voltage value of bias voltage Vbias is small, plus the diode D1 tube voltage drop Vf value, that is, Vbias + Vf < VFB, because the diode has unidirectional conductivity, so the diode D1 is off, temperature detection circuit 120 does not affect the normal work of switch power supply circuit 110, can drive LED lamp string 140 load output with full power.

[0033] 3、When the system works in the environment temperature is too high, the output load becomes larger, NTC thermistor R4 detects the temperature is getting higher and higher, the resistance of NTC thermistor R4 will become smaller and smaller, from the bias voltage Vbias = VOUT * (R5 / (R4+R5)) can be known, when the resistance of NTC thermistor R4 becomes smaller and smaller with the temperature is higher, the voltage value of bias voltage Vbias is getting larger and larger, when the voltage value of bias voltage Vbias satisfies: Vbias + Vf > VFB, diode D1 is forward biased, bias voltage Vbias will lift the voltage value of feedback voltage VFB, make the voltage value of feedback voltage VFB becomes larger, according to the working principle of switch power supply circuit 110 in step 1, when the voltage value of feedback voltage VFB becomes larger, the duty cycle of switch power supply will decrease, the output voltage value of output terminal VOUT will also decrease.

[0034] 4、Because the characteristic of LED lamp string 140 is that if the supply voltage is high, the current flowing through the LED lamp string 140 will become large, and if the supply voltage is low, the current flowing through the LED lamp string 140 will become small. It can be known from step 3 that when the temperature is too high, the output voltage value of the output end VOUT will become small, so that the current flowing through the LED lamp string 140 will also become small, and according to the power formula: P=U*I, it can be known that the final power P will become smaller, so the design meets the requirement that when the system temperature is too high, the output power can be automatically reduced to protect the product from being damaged due to over-temperature.

[0035] In summary, the automatic power reduction circuit of the switching power supply with over-temperature protection function has the following beneficial effects:

[0036] 1、The utility model discloses a switching power supply with over-temperature protection function has the following beneficial effects:

[0037] 2、The circuit design of the utility model is simple, can be applied to most switching power supply chips in the market, and the cost is extremely low.

[0038] 3、The utility model can set any over-temperature protection threshold point through adjusting the resistance value of resistance R4 and R5 according to the actual ambient temperature application scene of the product.

[0039] It should be pointed out that any modification made by the skilled person in the field to the specific embodiment of the utility model does not deviate from the scope of the claims of the utility model. Correspondingly, the scope of the claims of the utility model is also not limited to the foregoing specific embodiment.

Claims

1. An automatic derating circuit for a switching power supply with over-temperature protection, characterized in that, It includes: The switch power supply circuit includes a switch power supply control module, an inductor L1, an output capacitor and a voltage feedback circuit, the input voltage end VIN of the switch power supply control module is connected with the power supply VS, the switch output end SW is connected with the output end VOUT of the switch power supply automatic derating circuit through the inductor L1; one end of the output capacitor is connected with the output end VOUT of the switch power supply automatic derating circuit, and the other end is grounded; the input end of the voltage feedback circuit is connected with the output end VOUT of the switch power supply automatic derating circuit, and the output end is connected with the feedback end FB of the switch power supply control module; the input end of the temperature detection circuit is connected with the output end VOUT of the switch power supply automatic derating circuit, and the output end outputs the bias voltage Vbias, the bias voltage Vbias is generated based on the voltage of the output end VOUT of the switch power supply automatic derating circuit, and the bias voltage Vbias increases with the increase of the system temperature; The positive electrode of the unidirectional conduction device is connected with the output end of the temperature detection circuit, and the negative electrode is connected with the output end of the voltage feedback circuit, the unidirectional conduction device can be unidirectionally conducted from the positive electrode to the negative electrode, and the forward voltage drop of the unidirectional conduction device in the forward conduction state is Vf.

2. The switch power supply automatic derating circuit with over-temperature protection function according to claim 1, wherein When the system temperature is less than the over-temperature protection threshold, the unidirectional conduction device is turned off, the feedback voltage VFB output by the output end of the voltage feedback circuit reflects the voltage of the output end VOUT of the switch power supply automatic derating circuit, and the switch power supply control module adjusts the switch power supply duty cycle based on the feedback voltage VFB, so that the output end VOUT of the switch power supply automatic derating circuit outputs a stable voltage; When the system temperature is greater than the over-temperature protection threshold, the unidirectional conduction device is forwardly conducted, the feedback voltage VFB output by the output end of the voltage feedback circuit reflects the size of the bias voltage Vbias, and the switch power supply control module adjusts the switch power supply duty cycle based on the feedback voltage VFB, so that the voltage of the output end VOUT of the switch power supply automatic derating circuit is less than the stable voltage.

3. The switch power supply automatic derating circuit with over-temperature protection function according to claim 2, wherein The temperature detection circuit includes a negative temperature coefficient thermistor R4 and a constant value resistor R5, one end of the negative temperature coefficient thermistor R4 is connected with the output end VOUT of the switch power supply automatic derating circuit, and the other end is connected with a node A; one end of the constant value resistor R5 is connected with the node A, and the other end is grounded; the node A is the output end of the temperature detection circuit, and the voltage of the node A is the bias voltage Vbias.

4. The switch power supply automatic derating circuit with over-temperature protection function according to claim 3, wherein The voltage feedback circuit comprises a resistor R2 and a resistor R3, one end of the resistor R2 is connected with an output terminal VOUT of the switching power supply automatic derating circuit, and the other end is connected with a node B; one end of the resistor R3 is connected with the node B, and the other end is grounded; the node B is an output terminal of the voltage feedback circuit, and a voltage of the node B is the feedback voltage VFB.

5. The switching power supply automatic derating circuit with over-temperature protection function according to any one of claims 1-4, characterized in that, the switching power supply control module is a switching power supply chip; the unidirectional conduction device is a diode D1, and the Vf is a voltage drop of the diode D1.

6. The automatic derating circuit of a switching power supply with over-temperature protection function according to claim 5, characterized in that, the switching power supply circuit further comprises a bootstrap capacitor C3, one end of the bootstrap capacitor C3 is connected with a bootstrap terminal BST of the switching power supply control module, and the other end is connected with a switching output terminal SW.

7. The automatic derating circuit of a switching power supply with over-temperature protection function according to claim 5, characterized in that, the switching power supply circuit further comprises an input capacitor and a resistor R1, the input capacitor is connected between an input voltage terminal VIN and a ground terminal of the switching power supply control module; one end of the resistor R1 is connected with the input voltage terminal VIN of the switching power supply control module, and the other end is connected with an enable terminal EN of the switching power supply control module.

8. The switching power supply automatic derating circuit with over-temperature protection function according to claim 1, characterized in that, the output terminal VOUT of the switching power supply automatic derating circuit supplies power for an LED lamp string.

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