Starting circuit and DC-DC converter
By using linear regulators and clamping units to control the output tubes in DC-DC power converters, the problem of starting difficulties at low input voltages is solved, voltage margin is increased and circuit design complexity is reduced, ensuring that under high voltages Works normally.
Patent Information
- Application Number
- CN202411268703.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2024-12-13
AI Technical Summary
The prior art is difficult to start the DC-DC power converter at low input voltages, resulting in an increase in chip area and an increase in circuit design complexity. When using NMOS tubes in the high voltage domain, the voltage drop loss of the threshold voltage Vth is large, which compresses Voltage margin of internal circuit.
Using a linear regulator and clamp unit to cooperate with the output tube, the linear regulator outputs the first voltage that changes with the input voltage when the input voltage rises, and outputs the second voltage that changes with the input voltage when the input voltage is less than the steady-state voltage. Voltage to control the opening and shutdown of the output tube, ensuring that the circuit can be started at low input voltage and self-shut down at high input voltage.
The voltage margin of the startup circuit at low voltage is improved, the internal circuit design difficulty is reduced, and the circuit working state is not affected under high voltage, and the chip working range is increased.
Smart Images
Figure CN119134880A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of integrated circuits, and in particular relates to a starting circuit and a DC-DC converter. Background Art
[0002] DC-DC power converters such as buck and flyback generally operate at high voltages (80V, 100V, etc.). Some applications also require normal startup at low input voltage VIN, such as PoE protocol detection.
[0003] If the internal startup circuit of the chip is built in the high voltage domain, each branch needs to use a high voltage tube, which greatly increases the area of the chip, and generally uses an NMOS tube as a high voltage resistant tube. This is because the NMOS tube has a better transient response, and if a PMOS tube is used, it is necessary to create a high voltage domain -5V voltage domain for it to generate its gate voltage, which increases the complexity of the circuit design. Therefore, in order to achieve high voltage resistance and reduce the chip area at the same time, the prior art often uses an NMOS tube with a gate clamped to about 5.5V as a voltage-resistant tube, and its source is used as the power supply of the internal startup circuit. However, this solution will directly lose the voltage drop of the threshold voltage Vth of a MOS tube under low input voltage VIN, further compressing the voltage margin of the internal circuit. For example, under an input voltage VIN of 2.5V, the solution requires that the internal circuit can work normally at about 2.5V-Vth=1.5V, which undoubtedly further increases the design difficulty of the internal startup circuit.
[0004] like Figure 1 As shown, under the existing high input voltage VIN, a high-voltage NMOS tube MN generates the power supply of the internal startup circuit. Its gate voltage Vg is generated by VIN through a resistor Rp and a voltage regulator D in series. When VIN < the clamping voltage of the voltage regulator D of 5.5V, Vg = VIN, and when VIN> 5.5V, Vg = 5.5V, which protects the high-voltage NMOS tube MN from working in the safe operating area SOA. The parallel capacitor C of the voltage regulator D is used to filter the ripple of the input voltage VIN. The power supply Vs of the internal startup circuit is Vg-Vth. When VIN < 5.5V, Vs = VIN-Vth. When VIN is 2.5V, Vs = 2.5V-Vth = 1.5V. Vth refers to the LDMOS tube, which is about 1V. The voltage margin loss introduced by Vth accounts for about 40% of the input voltage VIN. This requires that the internal startup circuit of the system must be established at a voltage of 1.5V, which increases the difficulty of circuit design.
[0005] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention
[0006] The object of the present invention is to provide a starting circuit and a DC-DC converter, which can enable an internal starting circuit to start even at low voltage, thereby improving the voltage margin at low voltage.
[0007] In order to achieve the above objective, a specific embodiment of the present invention provides a startup circuit, including: a linear regulator, a clamping unit and an output tube.
[0008] The linear regulator is connected to the input voltage, and when the input voltage rises from zero to a voltage interval, the linear regulator outputs a first voltage that varies with the input voltage based on a reference voltage and its own feedback voltage; the clamping unit is connected to the input voltage, and the clamping unit is used to output a second voltage that varies with the input voltage when the input voltage is less than a steady-state voltage; the control end of the output tube is connected to the output end of the clamping unit, the first end of the output tube is connected to the output end of the linear regulator, the output tube is turned off based on the control of the first voltage and the second voltage, and when the output tube is turned on based on the rise of the input voltage, a third voltage is generated at the first end of the output tube, and the linear regulator is turned off when the feedback voltage generated based on the third voltage is greater than the reference voltage.
[0009] In one or more embodiments of the present invention, the output tube generates a third voltage when the input voltage increases from a maximum voltage of the voltage interval and is turned on.
[0010] In one or more embodiments of the present invention, the startup circuit further includes: a voltage generating circuit connected to the first end of the output tube, for generating a reference voltage based on the voltage at the first end of the output tube when the output tube is turned on before the input voltage rises to the voltage interval, and for outputting a corresponding reference voltage based on the first voltage when the linear regulator outputs the first voltage.
[0011] In one or more embodiments of the present invention, the linear regulator includes a power tube, a feedback unit and a comparator, the first end of the power tube is connected to the input voltage, the first end of the feedback unit is connected to the second end of the power tube and the first end of the output tube to generate a feedback voltage, the feedback unit is connected to the first input end of the comparator to transmit the feedback voltage to the first input end of the comparator, the second input end of the comparator is used to receive a reference voltage, and the output end of the comparator is connected to the control end of the power tube.
[0012] In one or more embodiments of the present invention, the feedback unit includes a first resistor and a second resistor, the first end of the first resistor is connected to the second end of the power tube and the first end of the output tube, the second end of the first resistor is connected to the first end of the second resistor and the first input end of the comparator, and the second end of the second resistor is connected to the ground voltage.
[0013] In one or more embodiments of the present invention, the clamping unit includes a resistance unit and a Zener diode, the first end of the resistance unit is connected to the input voltage, the second end of the resistance unit is connected to the control end of the output tube and the cathode of the Zener diode, and the anode of the Zener diode is connected to the ground voltage.
[0014] In one or more embodiments of the present invention, the clamping unit further includes a capacitor, a first end of the capacitor is connected to the control end of the output tube, and a second end of the capacitor is connected to the ground voltage.
[0015] The present invention also discloses a starting method, comprising:
[0016] When the input voltage rises from zero to a voltage range, the linear regulator outputs a first voltage that varies with the input voltage based on the reference voltage and its own feedback voltage;
[0017] When the input voltage is less than the steady-state voltage, a second voltage that varies with the input voltage is output through the clamping unit, so as to turn off the output tube through the second voltage and the first voltage;
[0018] When the input voltage rises and the output tube is controlled to be turned on, a third voltage is generated at the first end of the output tube;
[0019] When the feedback voltage generated by the third voltage is greater than the reference voltage, the linear regulator is turned off.
[0020] In one or more embodiments of the present invention, the startup method further includes: when the output tube is turned on before the input voltage rises to the voltage interval, generating a reference voltage based on the voltage of the first end of the output tube by a voltage generating circuit.
[0021] The invention also discloses a DC-DC converter, comprising the starting circuit.
[0022] Compared with the prior art, the startup circuit and DC-DC converter of the present invention, by introducing a small linear regulator, increases the voltage margin of the startup circuit that needs to withstand high voltage by at least one threshold voltage, which is beneficial to reducing the voltage required when the circuit is started, increasing the working range of the chip, and is beneficial to some high-voltage circuits that require low voltage startup, and can greatly reduce the difficulty of designing the internal circuit. As the input voltage rises, by setting the steady-state voltage of the linear regulator, the circuit can automatically change with the input voltage when the input voltage is low, and the linear regulator will automatically shut down when the input voltage is high, without affecting the working state of the internal circuit under high voltage. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0024] Figure 1 The schematic diagram of the startup circuit in the prior art is shown in FIG.
[0025] Figure 2 FIG. 4 is a circuit schematic diagram of a startup circuit in an embodiment. DETAILED DESCRIPTION
[0026] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.
[0027] "Coupled" or "connected" or "connected" in the specification includes both direct connection and indirect connection. Indirect connection is a connection through an intermediate medium, such as a connection through an electrically conductive medium, which may have parasitic inductance or parasitic capacitance; indirect connection may also include connection through other active or passive devices on the basis of achieving the same or similar functional purposes, such as connection through circuits or components such as switches and follower circuits. In addition, in the invention, words such as "first" and "second" are mainly used to distinguish one technical feature from another technical feature, and do not necessarily require or imply that there is a certain actual relationship, quantity or order between these technical features.
[0028] In the detailed description of the specification, reference is made to the accompanying drawings forming a part thereof, wherein like reference numerals refer to like parts throughout, and wherein are shown by way of exemplary embodiments that may be implemented. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description should not be considered in a limiting sense.
[0029] The various operations in the specification may be described in turn as multiple discrete actions or operations in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be interpreted as implying that these operations must be order-dependent. Specifically, these operations may not be performed in the order presented. The described operations may be performed in an order different from the described embodiments. Various additional operations may be performed and / or the described operations may be omitted in additional embodiments.
[0030] For purposes of this disclosure, the phrase "A and / or B" means (A), (B), or (A and B). For purposes of this disclosure, the phrase "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).
[0031] Various components and devices may be referred to or shown in the singular form herein (e.g., "transistor," "transistor," "switch," etc.), but this is merely for ease of discussion, and any element referred to in the singular form may include multiple such elements in accordance with the teachings herein.
[0032] The specification describes the use of the phrases "in one embodiment" or "in other embodiments" or "in some embodiments", which may each refer to one or more of the same or different embodiments. In addition, the terms "including", "comprising", "having", etc. used in relation to the embodiments of the present disclosure are synonymous.
[0033] like Figure 2 As shown, a startup circuit in an embodiment of the present invention includes: a clamping unit 10, an output tube MN, a voltage generating circuit and a linear regulator 20.
[0034] The clamping unit 10 is connected to the input voltage VIN, the control end of the output tube MN is connected to the output end of the clamping unit 10, the first end of the output tube MN is connected to the output end of the linear regulator 20, the linear regulator 20 is connected to the input voltage VIN, and the voltage generating circuit is also connected to the first end of the output tube MN. In the process of powering on the input voltage VIN, each device plays a different role.
[0035] Specifically, before the input voltage VIN rises to a voltage interval, the clamping unit 10 outputs a second voltage Vg that changes with the input voltage VIN. The second voltage Vg rises with the input voltage VIN and turns on the output tube MN, thereby generating a control voltage at the first end of the output tube MN. The control voltage also rises with the input voltage VIN and the voltage Vg. When the control voltage rises to a certain value, the voltage generating circuit is turned on. At this time, the voltage generating circuit generates a reference voltage Vref based on the control voltage at the first end of the output tube MN.
[0036] When the input voltage VIN rises from zero to a voltage range, the linear regulator 20 outputs a first voltage Vs that varies with the input voltage VIN based on the reference voltage Vref and its own feedback voltage, that is, when the input voltage VIN is within the voltage range, the linear regulator 20 operates in the linear region. At this time, the voltage generating circuit generates a corresponding reference voltage Vref based on the first voltage Vs, and the linear regulator 20 generates a corresponding feedback voltage based on the first voltage Vs, thereby maintaining the linear regulator 20 in operation.
[0037] When the input voltage VIN is lower than the steady-state voltage, the second voltage Vg output by the clamping unit 10 will continue to change with the input voltage VIN until the input voltage VIN is equal to or greater than the steady-state voltage. The clamping unit 10 will then output a fixed voltage, which can be considered as the steady-state voltage. The steady-state voltage can be considered to be greater than the maximum voltage of the voltage range.
[0038] When the input voltage VIN is within the voltage range, that is, when the linear regulator 20 operates in the linear region, the first voltage Vs and the second voltage Vg both change with the input voltage VIN, and it can be considered that the first voltage Vs and the second voltage Vg are equal. At this time, the output tube MN is turned off under the control of the first voltage Vs and the second voltage Vg.
[0039] When the input voltage VIN continues to rise from the maximum voltage of the voltage interval, the output tube MN will be turned on, and a third voltage will be generated at the first end of the output tube MN. When the input voltage VIN is stable and the second voltage Vg is also stable as the clamping voltage of the clamping unit 10, the third voltage is also stable, and the stable third voltage can be considered as the final output voltage. At the same time, when the feedback voltage generated based on the third voltage is greater than the reference voltage Vref, the linear regulator 20 is turned off. The third voltage can be provided to the subsequent circuits for power supply, and the subsequent circuits include low voltage difference linear regulators, DC-DC power converters, etc.
[0040] like Figure 2As shown, the clamping unit 10 includes a resistor unit Rp, a voltage regulator tube D and a capacitor C. The first end of the resistor unit Rp is connected to the input voltage VIN, the second end of the resistor unit Rp is connected to the control end of the output tube MN and the cathode of the voltage regulator tube D, the anode of the voltage regulator tube D is connected to the ground voltage, the first end of the capacitor C is connected to the control end of the output tube MN, and the second end of the capacitor C is connected to the ground voltage. When the input voltage VIN is equal to or greater than the steady-state voltage, the output voltage of the clamping unit 10 can be clamped to the steady-state voltage of the voltage regulator tube D through the voltage regulator tube D, and the capacitor C is used for filtering the input voltage VIN.
[0041] like Figure 2 As shown, the linear regulator 20 includes a power tube MP, a feedback unit and a comparator CMP. The first end of the power tube MP is connected to the input voltage VIN, and the first end of the feedback unit is connected to the second end of the power tube MP and the first end of the output tube MN to generate a feedback voltage. The feedback unit is connected to the first input end of the comparator CMP to transmit the feedback voltage to the first input end of the comparator CMP, the second input end of the comparator CMP is used to receive the reference voltage Vref, and the output end of the comparator CMP is connected to the control end of the power tube MP. In one embodiment, the comparator CMP is powered by the input voltage VIN. The first input end of the comparator CMP is a positive input end, and the second input end of the comparator CMP is a negative input end. In its embodiment, the second input end of the comparator CMP can be a positive input end, and the first input end of the comparator CMP can be a negative input end.
[0042] In one embodiment, the feedback unit includes a first resistor R1 and a second resistor R2. A first end of the first resistor R1 is connected to a second end of the power tube MP and a first end of the output tube MN, a second end of the first resistor R1 is connected to a first end of the second resistor R2 and a first input end of the comparator CMP to generate a feedback voltage, and a second end of the second resistor R2 is connected to a ground voltage.
[0043] In one embodiment, the output tube MN is an N-channel MOS tube, and the power tube MP is a P-channel MOS tube. The first end of the output tube MN and the first end of the power tube MP are sources, the second end of the output tube MN and the second end of the power tube MP are drains, and the control end of the output tube MN and the control end of the power tube MP are gates. In the embodiment, the output tube MN is a P-channel MOS tube, and the power tube MP is an N-channel MOS tube.
[0044] Based on the above circuit, the present invention also discloses a starting method, including:
[0045] When the input voltage VIN rises from zero to a voltage range, the linear regulator 20 outputs a first voltage Vs that varies with the input voltage VIN based on the reference voltage Vref and its own feedback voltage.
[0046] When the input voltage VIN is less than the threshold voltage, the clamp unit 10 outputs a second voltage Vg that varies with the input voltage VIN, so as to turn off the output tube MN through the second voltage Vg and the first voltage Vs.
[0047] When the input voltage VIN rises and the output tube MN is turned on, a third voltage is generated at the first end of the output tube MN. Further, when the output tube MN is turned on before the input voltage VIN rises to the voltage interval, a reference voltage Vref is generated based on the voltage at the first end of the output tube MN by the voltage generating circuit.
[0048] When the feedback voltage generated by the third voltage is greater than the reference voltage Vref, the linear regulator 20 is turned off.
[0049] The specific method can be referred to the above description, and is described in detail below with a specific example.
[0050] Assuming that the steady-state voltage output by the clamping unit 10 is 5.5V, the output voltage of the linear regulator 20 when the input voltage VIN is stable is set to (R1+R2) / R2*Vref and is less than the third voltage of the first end of the output tube MN when the input voltage VIN is stable. The third voltage is the steady-state voltage output by the clamping unit 10 minus the voltage Vgs between the control end and the first end of the output tube MN. MN .
[0051] When the input voltage VIN rises from 0V until the comparator has working current, the input voltage VIN generally needs to rise to about 2V (it is necessary to consider the voltage Vgs between the control terminal and the first terminal of the output tube MN). MN and the voltage drop of the tube inside the voltage generating circuit) causes the voltage generating circuit to start and generate the corresponding reference voltage Vref, and the loop of the linear regulator 20 starts to work. Since the input voltage VIN is very small at this time, the power tube MP works in the linear stage, and the first voltage Vs is equal to the input voltage VIN, that is, the first voltage Vs changes with the input voltage VIN. At this time, since the second voltage Vg also changes with the input voltage VIN, the first voltage Vs is equal to the second voltage Vg, and the voltage Vgs MN =0V, the output tube MN does not work, at this time the voltage generating circuit and the subsequent circuits are powered by the first voltage Vs, that is, powered by the input voltage VIN, and the voltage received by the voltage generating circuit and other internal circuits and subsequent other circuits is at least increased by a threshold voltage Vth of the output tube MN compared to the prior art solution.
[0052] As the input voltage VIN increases slowly, the second voltage Vg gradually approaches 5.5V, the output tube MN starts to turn on, and the third voltage in steady state is greater than the voltage output by the linear regulator 20 when it is stable. Therefore, the linear regulator 20 automatically opens the loop, and the control end of the power tube MP is pulled to the input voltage VIN by the loop, turning off the power tube MP. At this time, other internal circuits in the startup circuit are powered by the third voltage.
[0053] In one embodiment, in the application scenario of the PoE (Power over Ethernet) protocol, in the detection (DETECTION) stage, the PSE (power supply equipment) needs to identify whether the device meets the Ethernet protocol, and thus sends a resistance detection signal to the PD (power device). According to the protocol requirements, two level signals with a voltage range of 2.7V to 10.1V will be given, and the current of the PD device will be measured at the same time. According to the voltage difference and current difference between the two, it is calculated whether the PD device can provide a characteristic resistance R, which is 24.9kΩ (23.7~26.3kΩ), which requires the PD device to be able to be almost stably completed when the input voltage VIN is the lowest at 2.7V. The solution proposed by the present invention can be applied to this architecture to solve the problem of low voltage instability, and the circuit working voltage margin is increased from 1.7V to 2.7V, reducing the complexity of the internal circuit design.
[0054] The invention also discloses a DC-DC converter, comprising the above starting circuit.
[0055] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.
[0056] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.
Claims
1. A starting circuit, characterized in that: include: A linear voltage regulator is connected to the input voltage, and when the input voltage rises from zero to a voltage interval, the linear voltage regulator outputs a first voltage that varies with the input voltage based on a reference voltage and its own feedback voltage; A clamping unit connected to the input voltage, the clamping unit being used to output a second voltage varying with the input voltage when the input voltage is less than the steady-state voltage; as well as An output tube, wherein a control end of the output tube is connected to an output end of the clamping unit, a first end of the output tube is connected to an output end of the linear regulator, the output tube is turned off based on control of a first voltage and a second voltage, when the output tube is turned on based on a rise in an input voltage, a third voltage is generated at the first end of the output tube, and the linear regulator is turned off when a feedback voltage generated based on the third voltage is greater than a reference voltage.
2. The starting circuit according to claim 1, characterized in that: The output tube generates a third voltage when the input voltage increases from the maximum voltage of the voltage interval and is turned on.
3. The starting circuit according to claim 1, characterized in that: The startup circuit also includes: a voltage generating circuit connected to the first end of the output tube, used to generate a reference voltage based on the voltage of the first end of the output tube when the output tube is turned on before the input voltage rises to the voltage interval, and output a corresponding reference voltage based on the first voltage when the linear regulator outputs the first voltage.
4. The starting circuit according to claim 1, characterized in that: The linear regulator includes a power tube, a feedback unit and a comparator. The first end of the power tube is connected to the input voltage, the first end of the feedback unit is connected to the second end of the power tube and the first end of the output tube to generate a feedback voltage, the feedback unit is connected to the first input end of the comparator to transmit the feedback voltage to the first input end of the comparator, the second input end of the comparator is used to receive a reference voltage, and the output end of the comparator is connected to the control end of the power tube.
5. The starting circuit according to claim 4, characterized in that: The feedback unit includes a first resistor and a second resistor, wherein the first end of the first resistor is connected to the second end of the power tube and the first end of the output tube, the second end of the first resistor is connected to the first end of the second resistor and the first input end of the comparator, and the second end of the second resistor is connected to the ground voltage.
6. The starting circuit according to claim 1, characterized in that: The clamping unit includes a resistor unit and a voltage regulator tube. The first end of the resistor unit is connected to the input voltage, the second end of the resistor unit is connected to the control end of the output tube and the cathode of the voltage regulator tube, and the anode of the voltage regulator tube is connected to the ground voltage.
7. The starting circuit according to claim 6, characterized in that: The clamping unit further comprises a capacitor, a first end of the capacitor is connected to the control end of the output tube, and a second end of the capacitor is connected to the ground voltage.
8. A startup method, characterized in that: include: When the input voltage rises from zero to a voltage range, the linear regulator outputs a first voltage that varies with the input voltage based on the reference voltage and its own feedback voltage; When the input voltage is less than the steady-state voltage, a second voltage that varies with the input voltage is output through the clamping unit, so as to turn off the output tube through the second voltage and the first voltage; When the input voltage rises and the output tube is controlled to be turned on, a third voltage is generated at the first end of the output tube; When the feedback voltage generated by the third voltage is greater than the reference voltage, the linear regulator is turned off.
9. The startup method according to claim 8, characterized in that: The startup method further includes: when the output tube is turned on before the input voltage rises to the voltage interval, a reference voltage is generated based on the voltage of the first end of the output tube by a voltage generating circuit.
10. A DC-DC converter, characterized in that: The invention comprises a starting circuit as claimed in any one of claims 1 to 7.