Current control circuit of switching tube and switching circuit applying current control circuit
By designing a current control circuit including multiple adjustment circuits and pull-up circuits, the problems of inaccurate current limiting of switch tubes and large capacitance occupancy in the prior art are solved, and the accurate current limiting and capacitance saving are achieved, while maintaining the voltage stability at high frequencies.
Patent Information
- Application Number
- CN202421167612.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-27
- Publication Date
- 2025-05-02
- Estimated Expiration
- 2034-05-27
AI Technical Summary
When the current limiting switch tube current is current, it is difficult to achieve accurate current limiting, and a large capacitance is required to stabilize the control terminal voltage of the switch tube, resulting in a large area of consumption and an increase in the total impedance of the system.
A current control circuit including a first adjustment circuit, a second adjustment circuit, a pull-up circuit and a switch switching circuit is designed. Through these circuit components, a driving voltage is generated according to the voltage of the switch tube to ensure that the current flowing through the switch tube is proportional to the reference current.
The accurate limit of the current of the switch tube is achieved, avoiding too large or too small current, reducing the capacitance area, and quickly stabilizing the control terminal voltage of the switch tube at high switching frequency.
Smart Images
Figure CN222827151U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of power electronics, in particular to a current control circuit of a switch tube and a switch circuit using the same. Background Art
[0002] In applications such as charge pumps and switching power supplies, it is often necessary to limit the current of the switches. The following two application scenarios are common: ① When the system is started or short-circuited, the switch will operate at saturation current. At this time, the power is relatively high and it is easy to damage the switch device. Therefore, it is necessary to limit the current flowing through the switch to protect the device itself; ② When the output of the system is current limited, since the on-time of the switch remains unchanged, it is necessary to limit the current each time the switch is turned on to limit the output current. At the same time, it is not desired that the current limiting of the switch affect the impedance during steady-state operation.
[0003] like Figure 1 As shown, a commonly used current control circuit is illustrated, which is used to limit the current of the switch tube NM1. The switch tube NM1 takes the NMOS tube as an example. The current control circuit 00 includes a sampling tube M1, a holding capacitor C1, a switch S1 and a switch S2. The gate and drain of the sampling tube M1 are connected, and its source is grounded. A reference current Iref is set to flow through the sampling tube M1. The holding capacitor C1 is connected to the control end of the sampling tube M1. The control end of the sampling tube M1 is connected to the control end of the switch tube NM1 through the switch S1, and the control end of the switch tube NM1 is also grounded through the switch S2. In some systems, such as a buck circuit and a charge pump circuit, the switch NM1 is also connected to the switch NM2.
[0004] When the switch control signal PWM is valid, the control switch S1 is turned on, and the gate voltage of the switch tube NM1 (the voltage at point B in the figure) is determined by the gate voltage of the sampling tube M1 (the voltage at point A in the figure). Since the parasitic capacitance of the gate of the switch tube NM1 is very large, a holding capacitor C1 with a large capacitance is required to stabilize the gate voltage of the switch tube NM1. The holding capacitor C1 occupies a large area. In addition, the sampling tube M1 always works in the saturation region. If the switch tube NM1 works in the linear region, since the voltage at point A cannot be adjusted, the current capacity of the switch tube NM1 will be reduced, resulting in a larger impedance of the switch tube NM1, thereby increasing the total impedance of the system. Summary of the invention
[0005] The purpose of the utility model is to provide a current control circuit of a switch tube and a switch circuit using the same, which can accurately limit the current flowing through the switch tube so that the current flowing through the switch tube reaches the expected current, avoiding the current flowing through the switch tube being too large or too small, and failing to achieve the ideal current limiting effect.
[0006] The utility model also provides a current control circuit of a switch tube, which is characterized by comprising:
[0007] a first adjustment circuit, wherein when the switch control signal is valid, the switch tube is turned on, and is used to obtain a first adjustment voltage according to the voltage at the first end of the switch tube;
[0008] a second adjustment circuit, wherein the second adjustment circuit is connected to the first adjustment circuit, and a given reference current flows through the first adjustment circuit and the second adjustment circuit;
[0009] A pull-up circuit, used for providing a pull-up current for the second adjustment circuit;
[0010] Among them, the second adjustment circuit generates a driving voltage for the switch tube according to the first adjustment voltage, and when the switch control signal is valid, the driving voltage is used to drive the switch tube so that the current flowing through the switch tube is proportional to the reference current.
[0011] Optionally, the current flowing through the switch tube is proportional to the reference current, and the proportionality coefficient is equal to a set value.
[0012] Optionally, when the switch control signal is valid, the first adjustment voltage is positively correlated with the voltage at the first end of the switch tube.
[0013] Optionally, the first adjustment circuit includes a sample-and-hold circuit, and when the switch control signal changes from valid to invalid, the sample-and-hold circuit is used to maintain the stability of the first adjustment voltage.
[0014] Optionally, the first adjustment circuit further includes:
[0015] A first adjustment tube, a first end of which receives a power supply voltage, a control end of which is connected to the first end, and a second end of which is connected to the first end of the switch tube when the switch control signal is valid;
[0016] A second adjustment tube, a first end of which receives a power supply voltage, a control end of which is connected to the control end of the first adjustment tube, and a voltage at a second end of which is the first adjustment voltage;
[0017] The sample-and-hold circuit is connected between the control end of the first adjustment tube and the control end of the second adjustment tube.
[0018] Optionally, the second adjustment circuit includes:
[0019] A sampling tube connected in series with the second adjustment tube, wherein the reference current flows through the second adjustment tube and the sampling tube;
[0020] The first resistor and the first capacitor are connected in parallel to the control end of the sampling tube.
[0021] Optionally, the pull-up circuit includes a pull-up switch tube, a first end of which receives a power supply voltage, a second end of which is connected to a control end of the sampling tube, and a control end of which is connected to the second adjustment tube.
[0022] Optionally, the sample-and-hold circuit comprises a sampling switch and a holding capacitor, the sampling switch is connected between the control end of the first adjustment tube and the control end of the second adjustment tube, and the holding capacitor is connected to the control end of the second adjustment tube;
[0023] When the switch control signal is valid, the sampling switch is turned on; when the switch control signal is invalid, the sampling switch is turned off.
[0024] Optionally, it further includes a switch switching circuit, including a first switch and a second switch;
[0025] The first end of the first switch is connected to the control end of the sampling tube, the second end of the first switch is connected to the first end of the second switch, and the second end of the second switch is grounded; the common connection end of the first switch and the second switch is connected to the control end of the switch tube;
[0026] When the switch control signal is valid, the first switch is controlled to be turned on and the second switch is controlled to be turned off; when the switch control signal is invalid, the first switch is controlled to be turned off and the second switch is controlled to be turned on.
[0027] The utility model also provides a switch circuit, comprising the switch tube and any one of the above-mentioned current control circuits, wherein the current control circuit is connected to the control end of the switch tube.
[0028] Compared with the prior art, the utility model has the following advantages: the utility model can accurately limit the current flowing through the switch tube to reach the expected current, avoid the current flowing through the switch tube being too large or too small, and at the same time, does not require a large capacitor to stabilize the control end voltage of the switch tube; in addition, the regulation loop bandwidth of the control end voltage of the switch tube can be made very low, even if the switching frequency is very high, the control end voltage of the switch tube can be quickly stabilized. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 It is a schematic diagram of a current control circuit of a switch tube in the prior art;
[0030] Figure 2 This is a block diagram of the current control circuit of the switch tube of the utility model;
[0031] Figure 3 This is a schematic diagram of a first embodiment of a current control circuit of a switch tube of the utility model;
[0032] Figure 4This is a schematic diagram of a second embodiment of the current control circuit of the switch tube of the utility model. DETAILED DESCRIPTION
[0033] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.
[0034] In order to enable the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, and those skilled in the art can fully understand the present invention without these detailed descriptions.
[0035] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and in non-precise proportions to facilitate and clearly illustrate the purpose of the embodiments of the present invention.
[0036] like Figure 2As shown, a block diagram of the switch tube current control circuit of the utility model is illustrated. In the figure, the switch tube NM1 takes an NMOS tube as an example. The current control circuit 00 is connected to the control end of the switch tube NM1, that is, the gate, to limit the current flowing through the switch tube NM1. In some systems, the switch tube NM1 is connected to the switch tube NM2. For example, in a boost circuit or a buck circuit, the switch tube NM1 and the switch tube NM2 are both power tubes for realizing power conversion of the system. The switch tube NM1 can also be used in power supply circuits such as charge pumps. The utility model is not limited to the specific application of the switch tube NM1. The current control circuit 00 includes a first adjustment circuit 01, a second adjustment circuit 02, a pull-up circuit 03 and a switch switching circuit 04. The first adjustment circuit 01 is connected to the first end of the switch tube NM1 through the switch k1. When the switch control signal PWM is at a high level and effective, the switch k1 is controlled to be turned on, and the first adjustment circuit 01 is connected to the first end of the switch tube NM1. The first adjustment circuit 01 obtains a first adjustment voltage V1 according to the voltage Vsw at the first end of the switch tube NM1; the second adjustment circuit 02 is connected to the first adjustment circuit 01, and a given reference current Iref flows through the first adjustment circuit 01 and the second adjustment circuit 02. Circuit 02; pull-up circuit 03 is connected to the control end of the second adjustment circuit 02, and is used to provide a pull-up current for the second adjustment circuit 02, so that the second adjustment circuit 02 can convert the first adjustment voltage V1 into the driving voltage V2 of the switch tube NM1; the switch switching circuit 04 is connected between the second adjustment circuit 02 and the switch tube NM1, receives the switch control signal PWM, and controls the gate of the switch tube NM1 to receive the driving voltage V2 when the switch control signal PWM is at a high level and effective, and controls the gate of the switch tube NM1 to be grounded when the switch control signal PWM is at a low level and invalid, so as to control the switch tube NM1 to be turned off. Among them, the driving voltage V2 drives the switch tube NM1 to turn on, so that the current flowing through the switch tube NM1 is proportional to the reference current Iref, preferably proportional, and the proportional coefficient is K. The utility model can make the proportional coefficient K reach the set value, and will not be too large or too small, that is, the current flowing through the switch tube NM1 can reach the expected current, and will not be too large or too small.
[0037] like Figure 3As shown, a schematic diagram of an embodiment of the current control circuit of the utility model is illustrated. In this embodiment, the first adjustment circuit 01 includes a first adjustment tube M1 and a second adjustment tube M2. The drain of the first adjustment tube M1 receives the power supply voltage VDD, and its gate and drain are connected. When the switch control signal PWM1 is valid, the source of the first adjustment tube M1 is connected to the drain of the switch tube NM1, and the gate of the second adjustment tube M2 is connected to the gate of the first adjustment tube M1. The drain of the second adjustment tube M2 receives the power supply voltage VDD. Since the second adjustment tube M2 and the first adjustment tube M1 share the same gate, the source voltage V2 of the second adjustment tube M2 follows the source voltage VDD of the first adjustment tube M1. , that is, when the switch control signal PWM is effective, the source voltage V1 of the second adjustment tube M2 follows the source voltage of the first adjustment tube M1, that is, the drain voltage Vsw of the switch tube NM1. Therefore, when the switch control signal PWM is effective, the first adjustment circuit 01 can obtain the first adjustment voltage V1 (that is, the source voltage of the second adjustment tube M2) according to the drain voltage Vsw of the switch tube NM1; the first adjustment circuit 01 also includes a first resistor R1, which is connected between the source of the first adjustment tube M1 and the ground terminal. When the switch control signal PWM is invalid, the source voltage of the first adjustment tube M1 becomes the voltage drop on the first resistor R1, and the first adjustment voltage V1 changes accordingly and returns to the initial voltage. The second adjustment circuit 02 includes a sampling tube M3, a second resistor R2 and a first capacitor C1. The sampling tube M3 and the second adjustment tube M2 are connected in series. A given reference current Iref flows through the sampling tube M3 and the second adjustment tube M2. The second resistor R2 and the first capacitor C1 are connected in parallel and then connected to the control end of the sampling tube M3. The pull-up circuit 03 includes a pull-up switch tube M4, the drain of which receives the power supply voltage VDD, the gate of which is connected to the drain of the second adjustment tube M2, and the source of which is connected to the control end of the sampling tube M3. After the system starts to generate the power supply voltage VDD, the pull-up switch tube M4 is turned on to provide a pull-up current for the sampling tube M3, so as to pull up the gate voltage V2 of the sampling tube M3. The first capacitor C1 is used to stabilize the gate voltage of the sampling tube M3, and the gate voltage V2 is used as the driving voltage of the switch tube NM1 to drive the switch tube NM1 to turn on. The switch switching circuit 04 is used to control the on and off of the switch tube NM1 by switching according to the switch control signal PWM, and includes a first switch S2 and a second switch S3. The first switch S2 is connected between the gate of the sampling tube M3 and the gate of the switch tube NM1, and the second switch S3 is connected between the gate of the switch tube NM1 and the ground terminal.
[0038] When the switch control signal PWM is high and effective, switches S1 and S2 are turned on, and switch S3 is turned off. The source voltage of the first adjustment tube M1 is equal to the drain voltage Vsw of the switch tube NM1. The source voltage V1 of the second adjustment tube M2 maintains a corresponding consistency relationship with the source voltage Vsw of the first adjustment tube M1, that is, after the voltage Vsw changes, the voltage V1 changes accordingly. The voltage V1 is positively correlated with the voltage Vsw, ensuring that the ratio between the current flowing through the switch tube NM1 and the reference current Iref reaches the expected value and remains unchanged regardless of whether the switch tube NM1 works in the linear region or the saturation region; the pull-up circuit 03 pulls up the gate voltage of the sampling tube M3 by pulling up the switch tube M4, so there is no need to set a large capacitor to stabilize the gate voltage V2 of the sampling tube M3. Figure 2 The capacitance C1 is much smaller than Figure 1 The capacitor C1 in the circuit has a small occupied area; at the same time, the current control circuit 00 can ensure the current capacity of the switch tube NM1 in different states by adjusting the gate voltage V2 of the sampling tube M3 so that the gate voltage V2 reaches the driving voltage required for the switch tube NM1 to be turned on, and can also ensure that in steady-state operation, when the drain voltage of the switch tube NM1 is particularly low, the gate voltage V2 of the sampling tube M3 can reach the power supply voltage VDD to obtain the minimum output impedance. When the switch control signal PWM changes from high level effective to low level invalid, the switch S3 is turned on, the switches S1 and S2 are turned off, the gate voltage of the switch tube NM1 is pulled to the ground voltage 0V, the switch tube NM1 is turned off, the source voltage of the first adjustment tube M1 becomes the voltage drop on the resistor R1, the first adjustment voltage V1 follows the source voltage of the first adjustment tube M1 to make corresponding adjustments, and the gate voltage V2 of the sampling tube M3 is also adjusted to the initialization voltage before the switch tube NM1 is turned on. Due to the limitation of loop bandwidth, each time the switch tube NM1 is turned on, the gate voltage V2 of the sampling tube M3 needs an adjustment time of us to adjust from the initialization voltage to the voltage required by the gate of the switch tube NM1. When the switching frequency is high, the adjustment time is long and may even be longer than the conduction time of the switch tube NM1, resulting in the actual current flowing through the switch tube NM1 being smaller than the expected current or the impedance being larger when the switch tube NM1 is required to be fully turned on; and if the loop bandwidth is increased, it is easy to cause the gate voltage V2 of the sampling tube M3 to overshoot each time the switch tube NM1 is turned on, resulting in the current flowing through the switch tube NM1 being larger than the expected current. The "loop" mentioned in this embodiment refers to the current control circuit.
[0039] like Figure 4 As shown, it illustrates the principle diagram of the second embodiment of the current control circuit of the switch tube of the utility model. Figure 3 Based on the schematic diagram, the first adjustment circuit 01 also includes a sampling and holding circuit 101, and the source of the first adjustment tube M1 does not need to be connected to the resistor R1. Figure 2The same parts are not repeated here. The sampling and holding circuit 101 is connected between the gate of the first adjustment tube M1 and the gate of the second adjustment tube M2. When the switch control signal PWM changes from valid to invalid, the sampling and holding circuit 101 can keep the gate voltage of the first adjustment tube M1 stable. The sampling and holding circuit 101 includes a sampling switch S4 and a holding capacitor C2. The sampling switch S4 is connected between the gates of the first adjustment tube M1 and the second adjustment tube M2. The first end of the holding capacitor C2 is connected to the gate of the second adjustment tube, and the second end thereof is grounded. When the switch control signal PWM is valid, the sampling switch S4 is turned on, and the voltage on the capacitor C2 / the gate voltage of the first adjustment tube M1 follows the drain voltage Vsw of the switch tube NM1, and the voltage on the capacitor C2 is kept equal to Vsw plus the turn-on voltage Vth of the MOS tube. When the switch control signal PWM changes from valid to invalid, the switch S4 is disconnected. Since the capacitor voltage cannot change suddenly, the gate voltage of the second adjustment tube M2 remains stable, so that during the shutdown period of the switch tube NM1, the current control circuit can still continue to work according to the state of the switch tube NM1 during the conduction period, and the gate voltage V2 of the sampling tube M3 will continue to adjust accordingly and will not be initialized again. When the switch control signal PWM becomes valid again, the gate voltage V2 of the sampling tube M3 no longer needs a considerable amount of adjustment time and can be used to drive the switch tube NM1. In this embodiment, the loop bandwidth of the current control circuit can be made very low. Even if the switching frequency is very high, the voltage V2 will be adjusted according to the voltage Vsw when the switch tube NM1 is turned on, and it can remain stable after several cycles. This not only ensures the stability of the current flowing through the switch tube NM1 (that is, the current limit is stable), but also enables the switch tube NM1 to be fully turned on in a specific steady state to obtain the minimum output impedance. Figure 3 The illustrated embodiment can also reduce the on-resistance of the switch tube NM1, so that the current flowing through the switch tube NM1 can be stabilized at the expected current in a relatively short time.
[0040] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.
[0041] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.
Claims
1. A current control circuit for a switch tube, which controls the on and off of the switch tube according to a switch control signal, characterized in that: include, a first adjustment circuit, wherein when the switch control signal is valid, the switch tube is turned on, and is used to obtain a first adjustment voltage according to the voltage at the first end of the switch tube; a second adjustment circuit, wherein the second adjustment circuit is connected to the first adjustment circuit, and a given reference current flows through the first adjustment circuit and the second adjustment circuit; A pull-up circuit, used for providing a pull-up current for the second adjustment circuit; Among them, the second adjustment circuit generates a driving voltage for the switch tube according to the first adjustment voltage, and when the switch control signal is valid, the driving voltage is used to drive the switch tube so that the current flowing through the switch tube is proportional to the reference current.
2. The current control circuit of the switch tube according to claim 1, characterized in that: The current flowing through the switch tube is proportional to the reference current, and the proportionality coefficient is equal to the set value.
3. The current control circuit of the switch tube according to claim 2, characterized in that: When the switch control signal is valid, the first adjustment voltage is positively correlated with the voltage at the first end of the switch tube.
4. The current control circuit of the switch tube according to claim 1, characterized in that: The first adjustment circuit includes a sampling and holding circuit. When the switch control signal changes from valid to invalid, the sampling and holding circuit is used to keep the first adjustment voltage stable.
5. The current control circuit of the switch tube according to claim 4, characterized in that: The first adjustment circuit further includes: A first adjustment tube, a first end of which receives a power supply voltage, a control end of which is connected to the first end, and a second end of which is connected to the first end of the switch tube when the switch control signal is valid; A second adjustment tube, a first end of which receives a power supply voltage, a control end of which is connected to the control end of the first adjustment tube, and a voltage at a second end of which is the first adjustment voltage; The sample-and-hold circuit is connected between the control end of the first adjustment tube and the control end of the second adjustment tube.
6. The current control circuit of the switch tube according to claim 5, characterized in that: The second adjustment circuit comprises: A sampling tube connected in series with the second adjustment tube, wherein the reference current flows through the second adjustment tube and the sampling tube; The first resistor and the first capacitor are connected in parallel to the control end of the sampling tube.
7. The current control circuit of the switch tube according to claim 6, characterized in that: The pull-up circuit includes a pull-up switch tube, a first end of which receives a power supply voltage, a second end of which is connected to a control end of the sampling tube, and a control end of which is connected to the second adjustment tube.
8. The current control circuit of the switch tube according to claim 5, characterized in that: The sample-and-hold circuit comprises a sampling switch and a holding capacitor, wherein the sampling switch is connected between the control end of the first adjustment tube and the control end of the second adjustment tube, and the holding capacitor is connected to the control end of the second adjustment tube; When the switch control signal is valid, the sampling switch is turned on; when the switch control signal is invalid, the sampling switch is turned off.
9. The current control circuit of the switch tube according to claim 6, characterized in that: Also included is a switch switching circuit, including a first switch and a second switch; The first end of the first switch is connected to the control end of the sampling tube, the second end of the first switch is connected to the first end of the second switch, and the second end of the second switch is grounded; the common connection end of the first switch and the second switch is connected to the control end of the switch tube; When the switch control signal is valid, the first switch is controlled to be turned on and the second switch is turned off; When the switch control signal is invalid, the first switch is controlled to be turned off and the second switch is controlled to be turned on.
10. A switch circuit, characterized in that: It comprises the switch tube and the current control circuit according to any one of claims 1 to 9, wherein the current control circuit is connected to the control end of the switch tube.