A control circuit, an overvoltage protection circuit, a control chip and a driving power supply

Abstract

The present application relates to a control circuit, an overvoltage protection circuit, a control chip and a driving power supply. The control circuit includes a reference voltage source for providing a reference voltage; a logic control module, based on the reference voltage and the sampling voltage of the driving MOS tube, turns off the driving MOS tube; when the driving MOS tube is turned off, the logic control module turns on the driving MOS tube based on the gate voltage of the driving MOS tube, wherein the reference voltage does not change with temperature. The control circuit provided in the present application can be used for controlling the driving power supply, and ensures that the overvoltage protection is not falsely triggered due to the influence of temperature.

Description

Technical Field

[0001] The present application relates to the field of driving power supplies, and in particular to a control circuit, an overvoltage protection circuit, and a control chip of an LED driving power supply. Background Art

[0002] LED driver power supply refers to the power supply that provides a constant output current for LED lamps. Usually, the input of LED driver power supply is connected to 220V mains or 110V mains, and LED lamps will select different numbers of LED lamp strings according to the brightness requirements. When the number of LED lamps is different, the forward voltage of the overall LED lamp will also be different. In order to reduce the current ripple flowing into the LED lamp, an output electrolytic capacitor is usually connected in parallel at both ends of the LED lamp. Because the electrolytic capacitor is connected in parallel at both ends of the LED lamp, if the voltage of the electrolytic capacitor is much higher than the forward voltage of the LED lamp, when the electrolytic capacitor touches the LED lamp and discharges, it will burn the LED lamp beads. In addition, if the rated voltage of the electrolytic capacitor is selected too low, the electrolytic capacitor will burn, and if the rated voltage is selected too high, the volume will be too large.

[0003] Therefore, while the LED driver power supply provides constant current output for the LED lamp, it also needs to consider limiting the output voltage, so that the output electrolytic capacitor can be selected to be only slightly higher than the forward voltage of the LED lamp, which is the most reasonable compromise between cost and performance.

[0004] In the prior art, the demagnetization time is detected and compared with the fixed time constant predetermined by the circuit. If the demagnetization time is shorter than the fixed time constant, it will be determined to trigger the output overvoltage protection. However, since most of the current LED driver power supplies are used in very high temperature environments, when the chip triggers the over-temperature protection, the chip will reduce the output current, so that the demagnetization time will also become shorter, and then shorter than the fixed time constant and mistakenly determined as overvoltage protection. On the other hand, the existing control circuit structure is complex, which increases the cost of the control chip. At the same time, if the ambient temperature changes, especially reaches a high value, and the corresponding limit value remains fixed (especially, remains high), it may cause harm to the power supply system.

[0005] Therefore, new technologies are currently needed to solve this problem that arises in circuit control. Summary of the invention

[0006] In view of this, the purpose of the present application is to provide a control circuit, an overvoltage protection circuit, a control chip and a driving power supply to solve the problems of misjudgment of overvoltage protection caused by temperature changes in the existing overvoltage protection circuit, the complex structure of the control circuit, and the possible harm of temperature to the power supply system.

[0007] The technical solution of this application is as follows:

[0008] In the first aspect, the present application provides a control circuit, comprising: a reference voltage source for providing a first reference voltage; a logic control module, based on the first reference voltage and the sampling voltage of the driving MOS tube, turning off the driving MOS tube; when the driving MOS tube is turned off, the logic control module turns on the driving MOS tube based on the gate voltage of the driving MOS tube; wherein, when the temperature reaches the over-temperature point, the first reference voltage decreases as the temperature increases. The control circuit of this solution provides an effective driving power supply control method, the control circuit is simple, effective, and the control cost is low.

[0009] Furthermore, the reference voltage source includes a reference module and an over-temperature protection module; the reference module is used to generate a reference voltage that does not change with temperature; the over-temperature protection module is used to directly output or process the reference voltage and output it; wherein, the voltage output by the over-temperature protection module is the first reference voltage. Providing a reference voltage that does not change with temperature, the various functions of the system can work normally and are not affected by temperature; on the other hand, the reference voltage of the reference module is output through the temperature protection module, for example, the over-temperature protection module outputs the received reference voltage after processing or not according to the over-temperature protection strategy (for example, the over-temperature point), and the output first reference voltage may be the received reference voltage, or it may be a reference voltage of different magnitude from the received reference voltage after processing, and the reference voltage (first reference voltage) is input into other modules of the control circuit as a reference voltage or reference voltage (for example, the input end of comparator U1 and U2). The voltage (first reference voltage) used as the reference voltage or reference voltage is related to the over-temperature protection strategy, which ensures that the control of the driving power supply can be related to the adaptability of the ambient temperature and protects the safety of the driving power supply. In addition, when the logic control module is in overvoltage protection, the reference voltage (first reference voltage) is output from the overtemperature protection module, and its value is based on the ambient temperature, which can avoid the chip from misjudging the chip and entering the overvoltage protection mode due to the ambient temperature of the chip.

[0010] Furthermore, when the temperature reaches the over-temperature point, the first reference voltage decreases linearly with the increase of temperature.

[0011] Furthermore, before the temperature reaches the over-temperature point, the first reference voltage is equal to the reference voltage.

[0012] Furthermore, the logic control module includes: a first comparator, a first input terminal of the first comparator inputs the sampling voltage of the driving MOS tube, and a second input terminal inputs the first reference voltage, when the sampling voltage of the driving MOS tube is greater than or equal to the first reference voltage, the output signal of the first comparator is flipped; a demagnetization detection module, the demagnetization detection module determines whether the system inductance is demagnetized by detecting the gate terminal voltage of the driving MOS tube, if the system inductance is demagnetized, the demagnetization detection module outputs a first signal; a logic processing unit, the flip level output by the first comparator triggers the logic processing unit to generate a shutdown signal to turn off the driving MOS tube; the first signal triggers the logic processing unit to generate a start signal to turn on the driving MOS tube.

[0013] The degaussing detection module detects the gate voltage of the driving MOS to determine whether the system's inductor current is zero. After the system's inductor current is zero (i.e., the inductor degaussing is completed), the degaussing detection module will trigger the logic function module to generate a signal to turn on the driving MOS; when the driving MOS is turned on, the sampling voltage is compared with the Vcs voltage (the first reference voltage). When it is greater than or equal to Vcs, the first comparator flips, triggering the logic function module to generate a signal to turn off the driving MOS, thereby turning off the MOS.

[0014] Furthermore, the driving MOS tube is connected to a sampling resistor. When the driving MOS tube is turned on, current flows through the sampling resistor to form the sampling voltage. It should be noted that the sampling voltage reflects the magnitude of the current flowing through the driving MOS. When the current reaches a peak value, the sampling voltage also reaches a maximum value. Since it can be obtained by collecting voltage at one end of the driving MOS, the sampling voltage in this application can be referred to as the sampling voltage of the driving MOS tube.

[0015] In the second aspect, the present application provides an overvoltage protection circuit, including: a current source, a capacitor, a second comparator, and a control circuit provided in the first aspect; the current source is used to provide current; the capacitor is charged based on the current provided by the current source to form a first voltage; the first voltage and the first reference voltage are input to the second comparator, and when the first voltage is greater than the first reference voltage, the second comparator output signal is flipped; the control circuit compares the length of time t1 and time t2, and when t2 is shorter than t1, the control circuit triggers the protection logic; wherein, the time t1 is the time for the capacitor to charge from 0 to greater than the first reference voltage; the time t2 is the system inductance demagnetization time. By judging the demagnetization time of the inductor and the length of time for the capacitor to charge to Vcs, it is judged whether it is overvoltage, the judgment method is simple, and the circuit is easy to implement. In this scheme, the first reference voltage output by the temperature protection module is input to the second comparator as a reference or reference voltage, and its value refers to the ambient temperature, which can avoid the ambient temperature of the chip causing the chip to misjudge and enter the overvoltage protection mode. Here, triggering the protection logic refers to triggering the overvoltage protection.

[0016] Furthermore, the current source includes an operational amplifier, a second resistor and a current mirror; a fixed current flows through the first resistor to form an overvoltage protection voltage; the operational amplifier clamps the overvoltage protection voltage to the second resistor to form a bias current, and the bias current serves as an input current of the current mirror; the output current of the current mirror is output to the capacitor for charging to form a first voltage.

[0017] Furthermore, when the driving MOS tube is turned on, the voltage of the capacitor is pulled down to zero; when the driving MOS tube is turned off, the current mirror outputs a current to charge the capacitor to form a first voltage.

[0018] Furthermore, the time t2 is obtained by detecting the gate terminal voltage of the driving MOS tube.

[0019] In a third aspect, the present application provides a control chip, wherein the control chip includes an overvoltage protection circuit provided in the second aspect.

[0020] In a fourth aspect, the present application provides a driving power supply, which includes a control chip provided in the third aspect.

[0021] Compared with the prior art, the present technical solution has a simple control circuit and low production cost on the one hand; on the other hand, the voltage provided to the system will not be affected by the ambient temperature; and, according to the over-temperature protection strategy, the reference voltages of the two comparators are adaptively changed, which ensures the safety of the driving power supply on the one hand, and ensures that the circuit does not accidentally trigger the over-voltage protection logic on the other hand. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work. As shown in the drawings, the above and other purposes, features and advantages of the present application will be clearer. The same reference numerals indicate the same parts in all the drawings. The drawings are not deliberately scaled to the actual size, and the focus is on showing the main purpose of the present application.

[0023] Figure 1 A schematic diagram of a control circuit structure provided by an embodiment of the present invention is shown;

[0024] Figure 2 A schematic diagram of a first reference voltage-temperature curve provided by an embodiment of the present invention is shown;

[0025] Figure 3 A schematic diagram of the structure of an overvoltage protection circuit provided by an embodiment of the present invention is shown;

[0026] Figure 4 A schematic diagram of a driving power supply structure provided by an embodiment of the present invention is shown;

[0027] 100-control circuit; 200-control chip; 1-reference voltage source; 2-logic control module. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0029] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it is not necessary to further define and explain it in the subsequent drawings. At the same time, in the description of this application, relational terms such as "first", "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements that are not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0030] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can also be an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0031] like Figure 1 As shown, this embodiment provides a control circuit 100, which is connected to a driving MOS tube M1. The control circuit controls the turning off and on of the driving MOS tube M1 based on a reference voltage (first reference voltage), a gate voltage of the driving MOS tube M1, and a sampling voltage of the driving MOS tube M1. In addition to being independent of the control circuit as described above, the driving MOS tube M1 can also be included in the above control circuit.

[0032] Optionally, the control circuit 100 includes a reference voltage source 1 and a logic control module 2, the reference voltage source is used to provide a reference voltage Vcs (first reference voltage), the logic control module 2 includes a first input terminal, a second input terminal, a third input terminal and an output terminal, the first input terminal of the logic control module is connected to the reference voltage source 1, and the first reference voltage Vcs provided by the reference voltage source is input, the second input terminal is connected to one end (e.g., source) of the driving MOS tube M1, and the sampling voltage (also called the sampling voltage of the driving MOS tube M1) is input, and the logic control module 2 is based on the first reference voltage and the driving MOS tube M1. The sampling voltage of the MOS tube M1 generates a control signal for closing the driving MOS tube M1; the third input end of the logic control module is connected to the gate of the driving MOS tube M1, and the gate voltage of the driving MOS tube M1 is input (detected). When the driving MOS tube M1 is in the closed state, the logic control module generates a control signal for opening the driving MOS tube M1 based on the gate (gate end) voltage of the driving MOS tube M1; the output end of the logic control module is also connected to the gate of the driving MOS tube, and the control signal is output to the driving MOS tube to control the closing or opening of the driving MOS tube M1.

[0033] Optionally, in this embodiment, the reference voltage source includes a reference module and an over-temperature protection module, the output end of the reference module is connected to the input end of the over-temperature protection module, the output end of the over-temperature protection module is connected to the first input end of the logic control module, the reference module generates a reference voltage VREF and inputs it to the over-temperature protection module, and then outputs it through the over-temperature protection module, such as a first reference voltage Vcs; specifically, the reference voltage VREF is processed into a voltage Vcs by the over-temperature protection module and then output to the logic control module as the reference voltage Vcs received by the logic control module. Specifically, the over-temperature protection module outputs the received reference voltage VREF with or without processing it according to the over-temperature protection strategy, and the output first reference voltage Vcs may be the received reference voltage VREF, or it may be a reference voltage of a different size from the received reference voltage VREF after processing, and the first reference voltage Vcs is input to other modules of the control circuit as a reference voltage or reference voltage (such as the input end of comparators U1 and U2). It ensures that the control of the driving power supply (such as the shutdown of MOS) can be related to the adaptability to the ambient temperature, thereby protecting the safety of the driving power supply. Figure 2 As shown, when the temperature reaches the over-temperature point, the voltage Vcs output by the temperature protection module forms a monotonically downward curve (which can also be considered as a monotonically downward negative temperature curve), that is, the first reference voltage Vcs output by the over-temperature protection module to the first input terminal decreases as the temperature increases. The negative temperature curve can be a straight line with a negative slope, that is, the first reference voltage Vcs output by the over-temperature protection module to the first input terminal decreases linearly as the temperature increases. In some embodiments, before the temperature reaches the over-temperature point, the voltage Vcs output by the temperature protection module is a constant value, and preferably, the constant value is the reference voltage VREF output by the reference module. That is, Vcs=VREF.

[0034] The reference voltage VREF provided in this embodiment does not change with temperature. Optionally, the reference module is a BANDGAP (bandgap reference).

[0035] Optionally, the logic control module includes a first comparator U1, a logic processing unit ( Figure 3The first comparator U1 is connected to the output terminal of the reference voltage source (such as the output terminal of the over-temperature protection module) and the demagnetization detection module, the second input terminal of the first comparator U1 is connected to the output terminal of the reference voltage source (such as the output terminal of the over-temperature protection module), receives the voltage Vcs, the first input terminal of the first comparator is connected to one end (such as the source) of the driving MOS tube, the output terminal of the first comparator is connected to the logic processing unit, the sampling voltage and the voltage Vcs are input through the first input terminal and the second input terminal of the first comparator respectively, the first comparator compares the voltage Vcs with the sampling voltage, when the sampling voltage is greater than or equal to the voltage Vcs, the output signal of the first comparator is flipped (such as flipped from a low level to a high level, or from a high level to a low level, how to flip is related to the specific situation of the two input signals being input to the in-phase terminal and the inverting terminal), triggering the logic processing unit to generate a shutdown signal, thereby turning off the driving MOS tube M1. That is to say, when the sampling voltage is greater than or equal to the voltage Vcs, the flip level output by the first comparator U1 triggers the logic processing unit to generate a shutdown signal to turn off the driving MOS tube. The input end of the degaussing detection module is connected to the gate of the driving MOS tube, and the output end is connected to the logic processing unit. When the driving MOS tube is turned off, the degaussing detection module detects the gate voltage of the driving MOS tube M1 to determine whether the system's inductance is degaussed (i.e., determine whether the system's inductance current is zero). If the system's inductance is degaussed (i.e., the system's inductance current is zero), the degaussing detection module outputs a first signal to the logic processing unit, triggering the logic processing unit to generate a start signal, thereby turning on the driving MOS tube. It can be understood that the first and second input ends of the first comparator U1 are the second input end and the first input end of the logic control module 2.

[0036] In a feasible embodiment, the driving MOS tube is connected to a sampling resistor Rcs, the other end of the sampling resistor is grounded, and when the driving MOS tube is turned on, current flows through the sampling resistor to form the sampling voltage described in this embodiment. Optionally, the source of the driving MOS tube is connected to the sampling resistor Rcs.

[0037] In a feasible embodiment, the logic processing unit specifically includes a logic module and a driver, such as Figure 3 The driver outputs a driving signal according to the control signal for driving the driving MOS.

[0038] like Figure 3As shown, this embodiment also provides an overvoltage protection circuit, which includes a current source, a capacitor C1, a second comparator U2 and the aforementioned control circuit 100. When the output end of the current source is connected to the capacitor C1, the current source outputs a current to charge the capacitor C1, thereby forming a first voltage on the capacitor C1. The first input end of the second comparator U2 is connected to the reference voltage source to receive the voltage Vcs output by the reference voltage source, and the second input end is connected to the capacitor C1 to input the first voltage. When the first voltage is greater than the voltage Vcs, the output signal of the second comparator U2 is flipped, and the output end of the second comparator is connected to the control circuit 100. The control circuit compares the length of time t1 and time t2. When t2 is shorter than t1, the protection logic (overvoltage protection) is triggered. Optionally, when the protection logic is triggered, the driving MOS tube is turned off, or the driving MOS tube is kept off, that is, it cannot be turned on. In other words, after the protection logic is triggered, the driving MOS tube is in a closed state and cannot be turned on until the overvoltage protection state is released. The time t1 is the time it takes for the capacitor to charge from 0 to a voltage greater than the first reference voltage Vcs; the time t2 is the demagnetization time (i.e. Figure 4 The demagnetization time of L1 in the circuit, or the freewheeling time of the freewheeling diode D1, specifically the time from when the driving MOS is turned off to when the current flowing through L1 is zero), can be obtained by detecting the gate terminal voltage of the driving MOS tube. Specifically, when the driving MOS tube is turned on, the voltage of the capacitor C1 is pulled down to zero; when the driving MOS tube is turned off, the current source outputs a current to charge the capacitor to form a first voltage. It can be understood that the control circuit records the time Tovp (ovp represents overvoltage protection) from when the driving MOS tube is turned off to when the second comparator U2 is flipped, and the logic processing unit in the control circuit compares the time Tovp with the demagnetization time Td. When the demagnetization time Td is longer than the time Tovp, the circuit (chip) works normally and the overvoltage protection logic is not triggered; when the demagnetization time Td is shorter than the time Tovp, the overvoltage protection logic is triggered. In one embodiment, the circuit (chip) works normally when the overvoltage protection logic is not triggered, and the driving MOS can be turned on normally. It can be understood that time t1 is actually time Tovp, that is, the time for the capacitor to charge from 0 to a voltage greater than the first reference voltage is actually equivalent to the time from the MOS driver being turned off to the time when the second comparator is flipped; and the time for the capacitor to charge to a voltage greater than the first reference voltage can actually be considered as the time to charge to the first reference voltage. The logic processing unit compares the length of time Tovp with the demagnetization time Td by performing a logic operation (such as AND operation) on the received signal output by the demagnetization detection module (such as outputting a high level when the D1 or L current is detected to be 0) and the signal output by the second comparator. When the demagnetization detection module outputs a high level, if the result of the AND operation is 0, the overvoltage protection is triggered; if not, it works normally.

[0039] The aforementioned time t2, i.e., the demagnetization time Td, can be obtained by detecting the gate voltage of the driving MOS tube. It can be understood that the demagnetization time Td is the time from when the MOS is turned off to when the system inductance ( Figure 4 The time when the current of the inductor L1 is zero can be detected by the demagnetization detection module. For example, when the demagnetization detection module detects that the system inductor ( Figure 4 When the current of the inductor L1 is 0, the output level flips, and the moment of flipping represents the moment when the inductor current is 0.

[0040] In an optional embodiment, the current source includes an operational amplifier U3, a second resistor Rb and a current mirror; the first input end of the operational amplifier U3 receives a voltage, the second input end of the operational amplifier U3 is connected to the first end of the second resistor Rb and the first end of the switch tube M4 (taking a MOS tube as an example, hereinafter referred to as MOS tube M4), and the second end of the second resistor Rb is grounded. The first end of the second resistor Rb is also connected to the input end of the current mirror. In one embodiment, Figure 3 As shown, the first end of the second resistor Rb is connected to the first end of the MOS tube M4, and the second end of the MOS tube is connected to the input end of the current mirror. The output end of the operational amplifier U3 is connected to the control end of the MOS tube. It should be noted that the MOS tube may not be needed. That is, the output of U3 is directly connected to the first end of Rb and the input end of the current mirror.

[0041] Optionally, the voltage received by the first input terminal of the operational amplifier U3 may be provided by a first resistor Rovp and a fixed current, such as Figure 3 It should be noted that the first resistor Rovp is usually set to be external, not included in the above-mentioned overvoltage protection circuit, outside the control chip, called the overvoltage protection setting resistor, used to adjust the voltage of the first end of U3; of course, it can also be included in the above-mentioned overvoltage protection circuit, or it can be set inside the chip.

[0042] Specifically, a fixed current Ib (which can be provided by a constant current source) flows through the first resistor Rovp to generate a voltage Vovp (ovp represents overvoltage protection), and the voltage Vovp is clamped to the second resistor Rb by the operational amplifier U3, thereby forming a bias current Vovp / Rb, which is used as the input current of the current mirror. The output current of the current mirror is output to the capacitor C1 to charge the capacitor C1 to form a first voltage. In addition, if Figure 3 As shown, the current mirror of this embodiment is composed of two MOS tubes. In practice, there are many ways to form a current mirror, and this application does not specifically limit it. It should be clear that the output current of the current mirror is proportional to its input current, and the proportionality coefficient is K (output to input), which is related to each selected MOS tube.

[0043] In order to realize that the output end of the current mirror can be selectively connected to the above-mentioned capacitor C1, or to realize the charge and discharge control of the capacitor C1. The present application adopts a switch module. The output end of the current source is connected to the first end of the switch module; the second end of the switch module is connected in common with the second end of the second comparator and the first end of the capacitor C1 (it can be understood that the term "connected in common" means that these three terminals are connected together); the third end of the switch module and the second end of the capacitor C1 are grounded; the control end of the switch module is connected to the control end of the driving MOS tube M1.

[0044] Alternatively, if Figure 3 As shown, the switch module includes a first switch tube M2 (for example, a MOS tube, such as an NMOS tube) and a second switch tube M3 (for example, a MOS tube); the control ends of the first switch tube and the second switch tube are connected to the control end of the driving MOS tube M1 (can also be considered to be connected to the output end of the logic control module of the aforementioned control circuit); the first end of the first switch tube is connected to the output end of the current mirror; the second end of the first switch tube, the first end of the second switch tube, the first end of the capacitor C1, and the second end of the second comparator are connected in common; the second end of the second switch tube is grounded. This solution proposes a specific switch module, which can judge the state of the driving MOS according to the gate terminal voltage of the driving MOS, thereby deciding whether to charge or discharge the above-mentioned capacitor C1.

[0045] Optionally, the first switch tube M2 and the second switch tube M3 are different types of MOS tubes, which receive the same control signal and present opposite on-off states. That is, M2 and M3 are not turned on or off at the same time, but one is turned on and the other is turned off. If M2 is PMOS, then M3 is NMOS; if M2 is NMOS, then M3 is PMOS. For example, M1 and M3 are selected as NMOS, and M2 is selected as PMOS; or, M1 and M3 are selected as PMOS, and M2 is selected as NMOS.

[0046] Combine the following Figure 3 The principle of overvoltage protection circuit is introduced.

[0047] Through the volt-second characteristics of inductance, we can know:

[0048] L*Ip=Vout*Td

[0049] Where, L is the inductance of L1, Ip is the peak current, Vout is the output voltage, and Td is the demagnetization time;

[0050] And Ip=Vcs / Rcs

[0051] thereby:

[0052] Vout=(L*Vcs) / (Rcs*Td)

[0053] Assuming that Td is a fixed time constant, the Vout voltage is also fixed. The smaller Td is, the larger Vout is. Therefore, the overvoltage protection logic of this application is: detect Td, compare Td with a parameter, and when the Td time is less than this parameter, trigger the logic processing unit to enter the protection state, thereby limiting Vout to a reference value.

[0054] When the driving MOS tube is turned on, the control terminals (gates) of M2 and M3 are connected to the gate of the driving MOS tube M1 (i.e., the output terminal of the logic control module of the aforementioned control circuit). Therefore, M2 is turned off and M3 is turned on. At this time, when M2 is turned off, the output terminal of the current mirror cannot output current to the capacitor C1 to charge it; when M3 is turned on, the capacitor C1 is discharged through M3, and the voltage of the capacitor C1 is pulled down to zero. When the driving MOS tube is turned off, M2 is turned on and M3 is turned off. At this time, the discharge loop of the capacitor C1 is disconnected, and the output terminal of the current mirror is connected to the capacitor C1 through M2, so that the current output by the current mirror charges the capacitor C1 to form a first voltage. When this voltage is greater than the Vcs voltage, the comparator flips. We record the time from the driving MOS turning off to the comparator flipping as Tovp. The chip logic function module will compare the time length of Tovp and Td. When Td is longer than Tovp, the chip works normally and will not trigger protection; when Td is shorter than Tovp, the chip triggers the overvoltage protection logic.

[0055] The output of the driving power supply of the present application is determined by the first resistor Rovp, and the principle is as follows (taking the ratio K of the current mirror input to output as 1 as an example):

[0056] Ib*Rovp / Rb=Ic1

[0057] C1*Vcs=(Ib*Rovp*Tovp) / Rb

[0058] Where, Ic1 is the charging current of capacitor C1, and C1 is the capacity of capacitor C1;

[0059] thereby:

[0060] Tovp=(C1*Vcs*Rb) / (Ib*Rovp)

[0061] When Tovp = Td, then we have

[0062] Vout=(L*Vcs) / (Rcs*Td)=((L*Vcs) / Rcs)*((Ib*Rovp) / (C1*Vcs*Rb))

[0063] Thus there is

[0064] Vout=(L*Ib*Rovp) / (Rcs*C1*Rb).

[0065] That is, in the present application, the voltage value of the output voltage Vout can be set by setting the resistance value of the first resistor Rovp, and other parameters are fixed parameters and have nothing to do with temperature.

[0066] This embodiment also provides a control chip, which includes the above-mentioned overvoltage protection circuit.

[0067] This embodiment also provides a control chip, which includes the above-mentioned control circuit.

[0068] like Figure 4 As shown, this embodiment further provides a driving power supply, which includes a rectifier bridge, a capacitor E1, a resistor R1, a capacitor E2, an inductor L1, a diode D1 and the above-mentioned control chip.

[0069] Specifically, in the present embodiment, the resistor R1 and the capacitor E1 are connected in parallel to form a filter circuit, and the output end of the rectifier bridge is connected to the filter circuit, specifically, the output end of the rectifier bridge is connected to the first end of the resistor R1, the first end of the capacitor E1, the second end of the resistor R1, and the second end of the capacitor E1 are grounded, and the filter circuit filters the voltage output by the rectifier bridge to a constant voltage. In addition, the output end of the rectifier bridge is also connected to the first end of the diode D1 and the first end of the capacitor E2, and the first end and the second end of the capacitor E2 are also used as the output end (VOUT+, VOUT-) of the driving power supply. The second end of the capacitor E2 is connected to the first end of the inductor L1, and the second end of the inductor L1 is connected to the second end of the diode D1 and the control chip. In one embodiment, the second end of the inductor L1 is connected to the control chip, specifically the drain of the driving MOS in the control chip.

[0070] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0071] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A control circuit, characterized in that: include: A reference voltage source, used for providing a first reference voltage; A first comparator, configured to output a first comparison signal when the sampling voltage driving the MOS tube is greater than or equal to the first reference voltage; A demagnetization detection module, which determines whether the system inductance has been demagnetized by detecting the gate terminal voltage of the driving MOS tube, and outputs a demagnetization completion signal when the demagnetization is completed; a logic processing unit, which turns off the driving MOS tube in response to the first comparison signal, and turns on the driving MOS tube in response to the demagnetization end signal; When the temperature reaches an over-temperature point, the first reference voltage decreases as the temperature increases.

2. A control circuit according to claim 1, characterized in that: The reference voltage source includes a reference module and an over-temperature protection module; The reference module is used to generate a reference voltage that does not change with temperature; The over-temperature protection module is used to directly output the reference voltage or output it after processing; wherein the voltage output by the over-temperature protection module is the first reference voltage.

3. A control circuit according to claim 2, characterized in that: When the temperature reaches the over-temperature point, the first reference voltage decreases linearly as the temperature increases.

4. A control circuit according to claim 3, characterized in that: Before the temperature reaches the over-temperature point, the first reference voltage is equal to the reference voltage.

5. A control circuit according to claim 1, characterized in that: The driving MOS tube is connected to a sampling resistor. When the driving MOS tube is turned on, current flows through the sampling resistor to form the sampling voltage.

6. A control circuit according to any one of claims 1 to 5, characterized in that: The logic processing unit is used to turn off the driving MOS tube when the demagnetization time is less than the time it takes for the capacitor to charge from 0 to the reference voltage.

7. A control circuit according to claim 6, characterized in that: Also includes: A current source, a capacitor, and a second comparator; The current source is used to provide current; The capacitor is charged based on the current provided by the current source to form a first voltage; The first voltage and the first reference voltage are input to the second comparator. When the first voltage is greater than the first reference voltage, the output signal of the second comparator is reversed.

8. A control circuit according to claim 7, characterized in that: The current source includes an operational amplifier, a second resistor and a current mirror; A fixed current flows through the first resistor to form an overvoltage protection voltage; The operational amplifier clamps the overvoltage protection voltage to the second resistor to form a bias current, and the bias current serves as an input current of the current mirror; The output current of the current mirror is output to the capacitor for charging to form a first voltage.

9. A control circuit according to claim 8, characterized in that: When the driving MOS tube is turned on, the voltage of the capacitor is pulled down to zero; When the driving MOS tube is turned off, the current mirror outputs a current to charge the capacitor to form a first voltage.

10. A control circuit according to claim 6, characterized in that: The demagnetization time is obtained by detecting the gate terminal voltage of the driving MOS tube.

11. A control chip, characterized in that: The control chip comprises a control circuit as described in any one of claims 1-10.

12. A driving power supply, characterized in that: The driving power supply includes a control chip as claimed in claim 11.

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