An externally adjustable inductor demagnetization detection and power detection circuit

Abstract

The present invention provides an externally adjustable inductor demagnetization detection and power detection circuit, comprising a discharge circuit, a power transistor M0, an inductor LAUX, and a voltage divider branch. The VIN voltage is connected to the drain of the power transistor M0 and the primary inductor L1 via the discharge circuit. The gate of the power transistor M0 is connected to the drive terminal of a switching power supply control chip, and the source of the power transistor M0 is connected to ground via a resistor RCS and to the current detection terminal of the switching power supply control chip. The inductor LAUX is grounded via a voltage divider branch, and a tap of the voltage divider branch is connected to the detection terminal of the switching power supply control chip. The voltage divider branch provides different voltages for the detection terminal of the switching power supply control chip. This circuit can provide an ideal compensation voltage for the switching power supply system, ensuring that the output overpower point of the switching power supply system remains consistent under high and low input voltage conditions, greatly increasing the flexibility of chip applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic circuits, and in particular relates to an externally adjustable inductance demagnetization detection and power detection circuit. Background Art

[0002] In a switching power supply system, there's a time delay between the activation of the system's overcurrent protection module and the shutdown of the output control power MOSFET. This causes the current in the power MOSFET to continue rising after reaching the internally set threshold. Furthermore, the switching power supply's inductor current rises at different rates under high and low input voltage conditions. At high input voltage, the power switch current rises faster, resulting in a higher output overpower point at high input voltage than at low input voltage. Summary of the Invention

[0003] In response to the defects in the existing technology, the present invention provides an externally adjustable inductor demagnetization detection and power detection circuit, which can provide an ideal compensation voltage for the switching power supply system, so that the output overpower point of the switching power supply system remains consistent under high input voltage and low input voltage conditions, greatly increasing the flexibility of chip application.

[0004] An externally adjustable inductor demagnetization detection and power detection circuit includes a discharge circuit, a power tube M0, an inductor LAUX and a voltage divider branch;

[0005] The VIN voltage is connected to the drain of the power tube M0 and the primary inductor L1 through the discharge circuit. The VIN voltage is obtained by rectifying and filtering the AC mains. The gate of the power tube M0 is connected to the drive terminal of the switching power supply control chip. The source of the power tube M0 is connected to the ground through the resistor RCS and to the current detection terminal of the switching power supply control chip.

[0006] The inductor LAUX is grounded through the voltage divider branch, and a tap of the voltage divider branch is connected to the detection terminal of the switching power supply control chip; the voltage divider branch provides different voltages to the detection terminal of the switching power supply control chip to realize inductor demagnetization detection or power detection of the main inductor L1.

[0007] Preferably, the discharge circuit includes a resistor R1, a capacitor C1 and a diode D1;

[0008] The VIN voltage is connected to the cathode of the diode D1 through the resistor R1. The VIN voltage is also connected to the cathode of the diode D1 through the capacitor C1. The anode of the diode D1 is connected to the drain of the power tube M0 and the same-name terminal of the main-stage inductor L1. The VIN voltage is connected to the opposite-name terminal of the main-stage inductor L1.

[0009] Preferably, the voltage dividing branch includes a resistor RZCD, a resistor RU, a resistor RL and a diode DU;

[0010] The opposite-name end of the inductor LAUX is grounded, and the same-name end of the inductor LAUX is connected in series with the resistor RZCD, the resistor RU and the resistor RL to ground. The positive electrode of the diode DU is connected to the middle node of the resistor RZCD and the resistor RU, and the negative electrode of the diode DU is connected to the middle node of the resistor RU and the resistor RL. The middle node of the resistor RU and the resistor RL serves as the tap and is connected to the detection terminal of the switching power supply control chip.

[0011] Preferably, the same-name end of the inductor LAUX is connected to the anode of the first diode, and the cathode of the first diode is connected to the VDD terminal of the switching power supply control chip through a resistor.

[0012] Preferably, the switching power supply control chip includes a first comparator, a second comparator, an adder and a drive circuit;

[0013] The detection terminal of the switching power supply control chip is respectively connected to the positive input terminal of the first comparator and one input terminal of the adder, the negative input terminal of the first comparator is connected to the internal first reference voltage, the other input terminal of the adder is connected to the internal second reference voltage, the output terminal of the adder is connected to the negative input terminal of the second comparator, the positive input terminal of the second comparator is connected to the DS terminal of the switching power supply control chip, the output terminals of the first comparator and the second comparator are both connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is connected to the drive terminal of the switching power supply control chip.

[0014] Preferably, the power tube M0 is a triode or a MOS tube.

[0015] It can be seen from the above technical solution that the externally adjustable inductor demagnetization detection and power detection circuit provided by the present invention can provide an ideal compensation voltage for the switching power supply system, so that the output overpower point of the switching power supply system remains consistent under high input voltage and low input voltage conditions, greatly increasing the flexibility of chip application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0017] Figure 1 This is a circuit diagram of an inductor demagnetization detection and power detection circuit provided by an embodiment of the present invention.

[0018] Figure 2for Figure 1 A partial enlarged view of . DETAILED DESCRIPTION

[0019] The following embodiments of the technical solution of the present invention are described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention. It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0020] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used in the specification and appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] As used in this specification and the appended claims, the term "if" can be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0023] Example:

[0024] An externally adjustable inductor demagnetization detection and power detection circuit, see Figure 1 、 2 , including discharge circuit, power tube M0, inductor LAUX and voltage divider branch;

[0025] The VIN voltage is connected to the drain of the power tube M0 and the primary inductor L1 through the discharge circuit. The VIN voltage is obtained by rectifying and filtering the AC mains. The gate of the power tube M0 is connected to the drive terminal of the switching power supply control chip (i.e. Figure 1 The source of the power tube M0 is connected to the ground through the resistor RCS and the current detection terminal of the switching power supply control chip;

[0026] The inductor LAUX is grounded through the voltage divider branch, and a tap of the voltage divider branch is connected to the detection terminal of the switching power supply control chip; the voltage divider branch provides different voltages to the detection terminal of the switching power supply control chip to realize inductor demagnetization detection or power detection of the main inductor L1.

[0027] Specifically, the power tube M0 is a triode or a MOS tube, for example, a PNP type can be used. The AC mains is rectified and filtered by a rectifier bridge to output a VIN voltage. The VIN voltage supplies power to the main inductor L1. Since the VIN voltage is a high voltage, if the VIN voltage is directly detected, losses will occur, affecting the standby power consumption and thus the efficiency. Therefore, in the detection circuit provided in this embodiment, when the power tube M0 is turned on, the voltage of the inductor LAUX and the voltage of the main inductor L1 are proportional: VIN / VAUX=Np / Naux, that is, the voltage ratio of the inductor LAUX to the main inductor L1 is equal to the ratio of the number of coil turns of the two. Therefore, the detection circuit provided in this embodiment can realize the power detection of the main inductor L1 by detecting the voltage of the inductor LAUX when the power tube M0 is turned on.

[0028] When power transistor M0 is on, the inductor LAUX has a negative voltage, and the voltage divider branch performs overpower detection on the main inductor L1. When power transistor M0 is off, the inductor LAUX has a positive voltage, and the voltage divider branch performs demagnetization detection on the main inductor L1. This circuit reuses the detection terminals of the switching power supply control chip to simultaneously perform demagnetization detection and overpower detection on the main inductor. The overpower detection function is externally adjustable, and the two functions of inductor demagnetization detection and power detection do not affect each other. It also utilizes the limited pins of the switching power supply control chip to achieve more functions.

[0029] This circuit can provide an ideal compensation voltage for the switching power supply system, so that the output overpower point of the switching power supply system remains consistent under high input voltage and low input voltage conditions, greatly increasing the flexibility of chip application.

[0030] Preferably, the discharge circuit includes a resistor R1, a capacitor C1 and a diode D1;

[0031] The VIN voltage is connected to the cathode of the diode D1 through the resistor R1. The VIN voltage is also connected to the cathode of the diode D1 through the capacitor C1. The anode of the diode D1 is connected to the drain of the power tube M0 and the same-name terminal of the main-stage inductor L1. The VIN voltage is connected to the opposite-name terminal of the main-stage inductor L1.

[0032] Specifically, the resistor R1 , the capacitor C1 , and the diode D1 form a discharge circuit for the primary inductor L1 , which can prevent the inductor current from being suddenly shut off and inducing high voltage breakdown that damages the device.

[0033] Preferably, the voltage dividing branch includes a resistor RZCD, a resistor RU, a resistor RL and a diode DU;

[0034] The opposite-name end of the inductor LAUX is grounded, and the same-name end of the inductor LAUX is connected in series with the resistor RZCD, the resistor RU and the resistor RL to ground. The positive electrode of the diode DU is connected to the middle node of the resistor RZCD and the resistor RU, and the negative electrode of the diode DU is connected to the middle node of the resistor RU and the resistor RL. The middle node of the resistor RU and the resistor RL serves as the tap and is connected to the detection terminal of the switching power supply control chip.

[0035] Specifically, when power transistor M0 is on, the inductor LAUX has a negative voltage. At this time, diode DU is reverse-biased, and over-power detection of the main-stage inductor L1 is achieved through the voltage divider of resistors RZCD, RU, and RL. When power transistor M0 is off, the inductor LAUX has a positive voltage. At this time, diode DU is forward-biased, limiting the voltage on resistor RU to a PN junction voltage. Demagnetization detection of the main-stage inductor L1 is achieved through the voltage divider of resistors RZCD, RL, and diode DU. The addition of diode DU enables a single resistor divider to perform two detection functions.

[0036] Preferably, the switching power supply control chip includes a first comparator, a second comparator, an adder and a drive circuit;

[0037] The detection terminal of the switching power supply control chip is respectively connected to the positive input terminal of the first comparator and one input terminal of the adder, the negative input terminal of the first comparator is connected to the internal first reference voltage, the other input terminal of the adder is connected to the internal second reference voltage, the output terminal of the adder is connected to the negative input terminal of the second comparator, the positive input terminal of the second comparator is connected to the DS terminal of the switching power supply control chip, the output terminals of the first comparator and the second comparator are both connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is connected to the drive terminal of the switching power supply control chip.

[0038] Preferably, the same-name end of the inductor LAUX is connected to the anode of the first diode, and the cathode of the first diode is connected to the VDD terminal of the switching power supply control chip through a resistor.

[0039] Specifically, the detection principle of the circuit is described below through an example.

[0040] Assuming that the number of turns of the primary inductor L1 is Np and the number of turns of the inductor LAUX is Naux, the over-power detection of the primary inductor L1 is performed when the power tube M0 is turned on. At this time, the inductor LAUX is a negative voltage, and VAUX is the voltage of the inductor LAUX. The calculation formula is:

[0041] VAUX=-(Naux / Np)*VIN (1)

[0042] The diode DU is reverse biased, and the voltage VOPP input to the detection terminal of the switching power supply control chip is:

[0043]

[0044] The switching power supply control chip adds the voltage received by the detection terminal to the internal reference voltage VREF_CS to obtain the power tube MO peak current detection threshold VCS(OPP), that is,

[0045] VCS(OPP)=VOPP+VREF_CS (3)

[0046] For example, assuming VREF_CS = 0.8V and VOPP = -0.15V, then VCS(OPP) = 0.65V. When the current flowing through resistor RCS causes the voltage at the current detection terminal of the switching power supply control chip to exceed 0.65V, the output of the second comparator flips, and the drive circuit controls the power transistor M0 to shut down. The larger the VIN voltage, the smaller the corresponding VOPP, that is, the smaller the voltage received by the detection terminal of the switching power supply control chip, the smaller the power transistor current, and overpower compensation is achieved. The resistance values of resistors RU, RL, and RZCD have the following relationship:

[0047]

[0048] As can be seen from the above formula, the resistance of resistor RL must be large enough to meet the requirements for zero-crossing detection of demagnetization of the primary inductor L1 during the off-state phase of the power tube M0 switch. In this case, the voltage at the detection terminal of the switching power supply control chip must generally be at least 8V. When the power tube MO is turned off, the inductor LAUX is at a positive voltage. At this time, the diode DU is forward-biased, limiting the voltage on the resistor RU to a PN junction voltage. The demagnetization detection of the primary inductor L1 is achieved through the voltage divider of resistor RZCD, resistor RL, and diode DU. VZCD is the voltage at the detection terminal after the power tube M0 is turned off. When it is less than the internal reference voltage VREF_ZCD, the output of the first comparator flips, and the drive circuit controls the power tube M0 to turn on. The resistance values of resistors RL and RZCD have the following relationship:

[0049]

[0050] Where VAUX is the voltage across the inductor LAUX when the power tube is off, VF is the forward bias voltage across the diode DU, and VZCD is the voltage across the detection terminal after the power tube is off. Assuming VAUX = 17V, VF = 0.7V, Naux / Np = 0.18, and VZCD = 8V, we can calculate using formula (5):

[0051]

[0052] Here, RL=1KΩ, then RZCD=1KΩ.

[0053] Assuming the overpower compensation voltage VOPP = -0.25V, substitute it into formula (4) to obtain

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. An externally adjustable inductor demagnetization detection and power detection circuit, characterized in that: It includes a discharge circuit, a power tube M0, an inductor LAUX and a voltage divider branch; The VIN voltage is connected to the drain of the power tube M0 and the primary inductor L1 through the discharge circuit. The VIN voltage is obtained by rectifying and filtering the AC mains. The gate of the power tube M0 is connected to the drive terminal of the switching power supply control chip. The source of the power tube M0 is connected to the ground through the resistor RCS and to the current detection terminal of the switching power supply control chip. The inductor LAUX is grounded through the voltage divider branch, and a tap of the voltage divider branch is connected to the detection terminal of the switching power supply control chip; the voltage divider branch provides different voltages to the detection terminal of the switching power supply control chip to implement inductor demagnetization detection or power detection of the main inductor L1; The discharge circuit includes a resistor R1, a capacitor C1 and a diode D1; The VIN voltage is connected to the cathode of the diode D1 through the resistor R1. The VIN voltage is also connected to the cathode of the diode D1 through the capacitor C1. The anode of the diode D1 is connected to the drain of the power tube M0 and the same-name terminal of the primary inductor L1. The VIN voltage is connected to the opposite-name terminal of the primary inductor L1. The voltage dividing branch includes a resistor RZCD, a resistor RU, a resistor RL and a diode DU; The opposite-name end of the inductor LAUX is grounded, and the same-name end of the inductor LAUX is connected in series with the resistor RZCD, the resistor RU and the resistor RL to ground. The positive electrode of the diode DU is connected to the middle node of the resistor RZCD and the resistor RU, and the negative electrode of the diode DU is connected to the middle node of the resistor RU and the resistor RL. The middle node of the resistor RU and the resistor RL serves as the tap and is connected to the detection terminal of the switching power supply control chip.

2. The externally adjustable inductor demagnetization detection and power detection circuit according to claim 1, characterized in that: The same-name end of the inductor LAUX is connected to the anode of the first diode, and the cathode of the first diode is connected to the VDD terminal of the switching power supply control chip through a resistor.

3. The externally adjustable inductor demagnetization detection and power detection circuit according to claim 1, characterized in that: The switching power supply control chip includes a first comparator, a second comparator, an adder and a driving circuit; The detection terminal of the switching power supply control chip is respectively connected to the positive input terminal of the first comparator and one input terminal of the adder, the negative input terminal of the first comparator is connected to the internal first reference voltage, the other input terminal of the adder is connected to the internal second reference voltage, the output terminal of the adder is connected to the negative input terminal of the second comparator, the positive input terminal of the second comparator is connected to the DS terminal of the switching power supply control chip, the output terminals of the first comparator and the second comparator are both connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is connected to the drive terminal of the switching power supply control chip.

4. The externally adjustable inductor demagnetization detection and power detection circuit according to any one of claims 1 to 3, characterized in that: The power tube M0 is a triode or a MOS tube.

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