Bootstrap control circuit and voltage conversion device

Abstract

The invention provides a bootstrap control circuit and a voltage conversion device. The bootstrap control circuit comprises a current mirror, a diode string, a switch, a control voltage generator and a first transistor. The current mirror mirrors a bias current to generate a mirror current based on an input voltage. The diode string is coupled between the current mirror and a reference voltage terminal. The switch has a first end coupled to the diode string, a control end of the switch receives a first control voltage, and a second end of the switch provides a second control voltage. The first transistor generates an output voltage based on the input voltage according to a second control voltage.

Description

Technical Field

[0001] This invention relates to a bootstrap control circuit and a voltage conversion device, and more particularly to a bootstrap control circuit and a voltage conversion device that can stably maintain the output voltage under high duty cycle operating conditions. Background Technology

[0002] In the field of voltage conversion devices, a bootstrap control circuit is often required to generate a corresponding output voltage in response to the switching action of the voltage conversion device. The bootstrap control circuit can provide the output voltage to the upper driver of the voltage conversion device and use it as the power supply voltage for the upper driver.

[0003] In existing bootstrap control circuits, when the duty cycle of the voltage conversion device's switching action exceeds a threshold, the control terminal of the transistor generating the output voltage may fail to reach the default target voltage due to insufficient charging time during the period when the transistor is continuously off. Alternatively, during the period when the transistor is continuously on, the voltage at the control terminal may drop due to leakage current, causing the output voltage generated by the bootstrap control circuit to be unsustainable, resulting in insufficient output voltage and affecting the efficiency of the voltage conversion device. Summary of the Invention

[0004] This invention relates to a bootstrap control circuit and a voltage conversion device that can maintain a stable voltage output under high duty cycle conditions.

[0005] According to an embodiment of the present invention, a bootstrap control circuit includes a current mirror, a diode string, a switch, a control voltage generator, and a first transistor. The current mirror mirrors a bias current based on an input voltage to generate a mirrored current. The diode string is coupled between the current mirror and a reference voltage terminal. The switch has a first terminal coupled to the diode string, a control terminal receiving a first control voltage, and a second terminal providing a second control voltage. The first transistor generates an output voltage based on the input voltage and the second control voltage.

[0006] According to an embodiment of the present invention, the voltage conversion device includes a first power transistor, a second power transistor, a first driver, a second driver, an inductor, and a bootstrap control circuit as described above. The first power transistor and the second power transistor are connected in series between an input voltage and a reference ground voltage, or in series between an output voltage and a reference ground voltage. The first driver and the second driver are used to drive the first power transistor and the second power transistor, respectively. The inductor is coupled between the coupling terminals of the first power transistor and the second power transistor and the output or input terminal of the voltage conversion device. The bootstrap control circuit is coupled between the two ends of the first power transistor.

[0007] Based on the above, the bootstrap control circuit of the present invention, by setting a control voltage generator and a switch between the control terminal of the first transistor and the current mirror, allows the control terminal of the first transistor to be quickly charged during the first duty cycle by turning on the switch; and during the second duty cycle, the switch is turned off to prevent leakage current from occurring at the control terminal of the first transistor, thereby effectively maintaining the voltage value of the second control voltage. In this way, even under relatively high duty cycle operating conditions, the bootstrap control circuit can still maintain the correctness and stability of the output voltage, effectively improving the working efficiency of the voltage conversion device. Attached Figure Description

[0008] Figure 1 A schematic diagram of a bootstrap control circuit according to an embodiment of the present invention is shown.

[0009] Figure 2 A schematic diagram of a bootstrap control circuit according to another embodiment of the present invention is shown.

[0010] Figure 3 This invention is shown Figure 2 The waveform diagram of the operation of the bootstrap control circuit 200 in the embodiment.

[0011] Figure 4 A schematic diagram of a bootstrap control circuit according to another embodiment of the present invention is shown.

[0012] Figure 5 A schematic diagram of a voltage conversion device according to an embodiment of the present invention is shown.

[0013] Figure 6 A schematic diagram of a voltage conversion device according to another embodiment of the present invention is shown. Detailed Implementation

[0014] Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same element symbols are used in the drawings and description to denote the same or similar parts.

[0015] Please refer to Figure 1, Figure 1 A schematic diagram of a bootstrap control circuit according to an embodiment of the present invention is shown. The bootstrap control circuit 100 includes a current mirror 110, a diode string 120, a switch SW1, a control voltage generator 130, a transistor MDNBT, a diode DBT, a capacitor CB, and a current source IBT. The current mirror 110 is based on the input voltage VIN and is used to mirror a bias current IB1 to generate a mirrored current IM1. The diode string 120 is coupled between the current mirror 110 and a reference voltage terminal LX. The first terminal of the switch SW1 is coupled to the diode string 120; the control terminal of the switch SW1 receives a control voltage NGSW; the second terminal of the switch SW1 provides the control voltage NG. The first terminal of the transistor MDNBT has received the input voltage VIN through the diode DBT; the second terminal of the transistor MDNBT is coupled to the reference voltage terminal LX through the current source IBT. The capacitor CG is coupled to the control terminal of the transistor MDNBT and the reference voltage terminal LX, and the capacitor CB is coupled to the second terminal of the transistor MDNBT and the reference voltage terminal LX, serving as a voltage regulator for the output voltage VBT.

[0016] The control voltage generator 130 is coupled to the switch SW1 to generate a control voltage NGSW in response to the reference voltage VLX on the reference voltage terminal LX, and to control the on or off state of the switch SW1 by the control voltage NGSW.

[0017] The bootstrap control circuit 100 of this embodiment can be applied in a voltage conversion device. The reference voltage terminal LX can be coupled to the inductor of the voltage conversion device. Corresponding to the switching operation of the voltage conversion device, the reference voltage VLX can be pulled high or low. During the first duty cycle when the reference voltage VLX is pulled low, the control voltage generator 130 can generate a control voltage NGSW that turns on the switch SW1, corresponding to a reference voltage VLX substantially equal to the reference ground voltage. This allows the mirror current IM1 to pass through the switch SW1 to charge the capacitor CG, thereby raising the voltage value of the control voltage NG. Furthermore, during the second duty cycle when the reference voltage VLX is pulled high, the control voltage generator 130 can generate a control voltage NGSW that turns off the switch SW1, corresponding to a reference voltage VLX substantially equal to the input voltage VIN. This prevents the capacitor CG from discharging through the switch SW1, maintaining the stability of the control voltage NG.

[0018] Incidentally, in this embodiment, the current mirror 110 includes transistors MP1 and MP2, and a bias current source 111. Transistor MP1 and the bias current source 111 are connected in series and coupled between the input voltage VIN and the reference ground voltage GND. Specifically, the first terminal of transistor MP1 receives the input voltage VIN; the second terminal of transistor MP1 receives the bias current IB1 generated by the bias current source 111; and the control terminal of transistor MP1 is coupled to the second terminal. The first terminal of transistor MP2 receives the input voltage VIN; the second terminal of transistor MP2 generates a mirror current IM1; and the control terminal of transistor MP2 is coupled to the control terminal of transistor MP1. Notably, the substrate of transistor MP2 is coupled to the first terminal of transistor MP2.

[0019] The diode string 120 includes multiple diodes connected in series. In this embodiment, the diode string 120 includes three diodes constructed from transistors MN1 to MN3 respectively through a diode connection configuration. Specifically, the diodes formed by transistors MN1 to MN3 are forward biased between the second terminal of transistor MP2 and the reference voltage terminal LX. It is worth noting that the number of diodes in the diode string 120 can be adjusted by the designer according to actual needs. Figure 1 The three diodes shown are merely illustrative examples and are not intended to limit the scope of the invention.

[0020] Furthermore, switch SW1 can be a transistor switch. In this embodiment, switch SW1 includes transistor MSW. The first terminal of transistor MSW is coupled to the second terminal of transistor MP2 in current mirror 110 and is coupled to the substrate of transistor MSW; the second terminal of transistor MSW is coupled to the control terminal of transistor MDNBT; the control terminal of transistor MSW is coupled to control voltage generator 130 and receives control voltage NGSW.

[0021] In this embodiment, the transistor MSW can be an N-type transistor, and the switch SW1 can be turned on when the control voltage NGSW is greater than its turn-on voltage. Conversely, the switch SW1 can be turned off when the control voltage NGSW is not greater than its turn-on voltage.

[0022] Please refer to Figure 2 , Figure 2A schematic diagram of a bootstrap control circuit according to another embodiment of the present invention is shown. The bootstrap control circuit 200 includes a current mirror 210, a diode string 220, a control voltage generator 230, a switch SW1, a transistor MDNBT, a diode DBT, a capacitor CB, and a current source IBT. In this embodiment, the current mirror 210 includes a current source 211 and transistors MP1 and MP2. The diode string 220 includes transistors MN1 to MN3 connected in series. The current mirror 210 and the diode string 220 are respectively connected to… Figure 1 The current mirror 110 and the diode string 120 in the embodiment have similar circuit architectures, which will not be described in detail here.

[0023] In this embodiment, the control voltage generator 230 is constructed using transistor MN4. The first terminal and control terminal of transistor MN4 are coupled to transistor MP2 in the current mirror 210. The second terminal of transistor MN4 is coupled to the first terminal of switch SW1. The first terminal of switch SW1 is further coupled to diode string 220. The second terminal of switch SW1 is coupled to the control terminal of transistor MDNBT to generate control voltage NG. The control terminal of switch SW1 is coupled to the first terminal of transistor MN4 and receives the control voltage NGSW. Capacitor CG is coupled between the control terminal of transistor MDNBT and the reference voltage terminal LX. Current source IBT is coupled between the second terminal of transistor MDNBT and the reference voltage terminal LX. Diode DBT is located between the first terminal of transistor MDNBT and the input voltage VIN.

[0024] and Figure 1 Similarly, in this embodiment, switch SW1 is composed of transistor MSW. Transistor MSW is an N-type transistor. The first terminal of transistor MSW is coupled to the second terminal of transistor MP2 in current mirror 110 and is coupled to the substrate of transistor MSW; the second terminal of transistor MSW is coupled to the control terminal of transistor MDNBT; the control terminal of transistor MSW is coupled to control voltage generator 130 and receives control voltage NGSW.

[0025] For details regarding the operation of the bootstrap control circuit 200, please refer to [the relevant documentation / reference]. Figure 2 as well as Figure 3 ,in Figure 3 This invention is shown Figure 2 The waveform diagram of the operation of the bootstrap control circuit 200 in the embodiment. Figure 3 In the diagram, the horizontal axis is the time axis, and the vertical axis is the voltage axis.

[0026] During the first duty cycle DP1, the reference voltage VLX at the reference voltage terminal LX is pulled down to substantially equal to the reference ground voltage (e.g., 0 volts) because the power transistor at the low end of the voltage converter corresponding to the bootstrap control circuit 200 is turned on. Simultaneously, the current mirror 210 generates a mirrored current IM1 by mirroring the bias current IB1. The mirrored current IM1 flows through transistor MN4, correspondingly generating a control voltage NGSW at the first terminal of transistor MN4. For example, with an input voltage VIN of 6 volts, a bias current IB1 of 2 microamps, and a mirrored current IM1 of 8 microamps, a control voltage NGSW of, for example, 5.3 volts can be generated at the first terminal of transistor MN4.

[0027] During the first duty cycle DP1, switch SW1 can be turned on according to the control voltage NGSW received at the control terminal. Correspondingly, the mirror current IM1 can be passed through switch SW1 to charge capacitor CG and pull the control voltage NG at the control terminal of transistor MDNBT up to a voltage value (e.g., equal to 3.9 volts).

[0028] Please note that since switch SW1 is in the ON state, the voltage NGPRE at the coupling terminal of diode string 220 and switch SW1 is actually equal to 3.9 volts.

[0029] Furthermore, during the first duty cycle DP1, the control voltage NG has a relatively low voltage value, and therefore the output voltage VBT has a relatively low voltage value, for example, equal to 4.3 volts.

[0030] During the second duty cycle DP2, the reference voltage VLX at the reference voltage terminal LX is pulled up to be substantially equal to the input voltage VIN because the power transistor on the high end of the voltage converter corresponding to the bootstrap control circuit 200 is turned on. Correspondingly, the base diode of transistor MP2 can be turned on at this time, clamping the control voltage NGSW to a voltage value, for example, equal to 6 volts. At this time, the voltage value of the control voltage NGSW is not greater than the voltage value of the input voltage VIN.

[0031] Because the base of transistor MN4 is coupled to the reference voltage terminal LX, voltage NGPRE will not conduct to the control voltage NGSW through the base diode of transistor MN4. Therefore, voltage NGPRE can be higher than the input voltage VIN, for example, equal to 9.2 volts. Furthermore, the voltage difference between the control terminal (gate) and the first terminal (source) of transistor MSW (equal to the control voltage NGSW minus voltage NGPRE) is less than 0, therefore, transistor MSW is turned off, and switch SW1 is opened.

[0032] At this point, the control voltage NG, based on the boosting effect of the reference voltage VLX, can be, for example, equal to 9.8 volts, and will fully turn on the transistor MDNBT, producing an output voltage VBT, for example, equal to 10.3 volts.

[0033] With the switch SW1 disconnected, the potential leakage path of capacitor CG is effectively cut off. Under these conditions, the control voltage NG can be effectively maintained without dropping for a relatively long period. Correspondingly, the output voltage VBT generated by transistor MDNBT can be effectively maintained at a relatively high voltage value.

[0034] It is worth noting that the various voltage values ​​mentioned in the above embodiments are for the purpose of illustrating the operational details of the bootstrap control circuit 200 of the present invention, and do not imply that the bootstrap control circuit 200 of the present invention necessarily operates at these voltage values. Designers can set the parameters of each component of the circuit and generate corresponding voltage values ​​according to actual circuit requirements.

[0035] Please refer to Figure 4 , Figure 4 A schematic diagram of a bootstrap control circuit according to another embodiment of the present invention is shown. The bootstrap control circuit 400 includes a current mirror 410, a diode string 420, a control voltage generator 430, a switch SW1, a transistor MDNBT, a diode DBT, a capacitor CB, and a current source IBT. In this embodiment, the current mirror 410 includes a current source 411 and transistors MP1 and MP2. The diode string 420 includes transistors MN1 to MN3 connected in series.

[0036] This embodiment and Figure 2 The difference in the embodiment is that the control voltage generator 430 in this case is constructed using a diode D1. The anode of the diode D1 is coupled to the second terminal of the transistor MP2 in the current mirror 420, and the cathode of the diode D1 is coupled to the first terminal of the switch SW1.

[0037] The operational details of the bootstrap control circuit 400 are similar to those of the aforementioned bootstrap control circuit 200, and will not be elaborated upon here.

[0038] Please refer to Figure 5 , Figure 5 A schematic diagram of a voltage conversion device according to an embodiment of the present invention is shown. The voltage conversion device 500 includes power transistors PM1 and PM2, drivers DV1 and DV2, an inductor L1, and a bootstrap control circuit 510. Power transistors PM1 and PM2 are connected in series between the input voltage VIN and the reference ground voltage GND. Drivers DV1 and DV2 are a high-side driver and a low-side driver, respectively, used to drive power transistors PM1 and PM2.

[0039] A bootstrap control circuit 510 is coupled across the power transistor PM1. One end of the bootstrap control circuit 510 receives the input voltage VIN, and the other end is coupled to the reference voltage terminal LX. One end of the inductor L1 is coupled to the reference voltage terminal LX, and the other end of the inductor L1 is used to generate the output voltage VOUT.

[0040] The bootstrap control circuit 510 can be implemented using the bootstrap control circuits 100, 200, or 400 of the aforementioned embodiments. The output voltage VBT generated by the bootstrap control circuit 510 can be provided to the driver DV1 and used as the power supply voltage for the driver DV1.

[0041] Drivers DV1 and DV2 receive drive control signals NDRV_HS and NDRV_LS, respectively, and generate drive signals based on these signals to drive power transistors PM1 and PM2, respectively. In this embodiment, driver DV1 can receive a reference voltage VLX at the reference voltage terminal LX as a reference ground voltage. Driver DV2 can receive voltage VCCB as a power supply voltage, and its ground terminal can receive the reference ground voltage GND.

[0042] According to the foregoing Figure 3 The waveform diagram, in this embodiment of the invention, shows that the bootstrap control circuit 510 can be controlled by a set switch (such as...). Figure 2 The switch SW1 is used to make the generated output voltage VBT have a relatively high voltage value. In this way, the driver DV1 can provide a drive signal with a relatively high voltage value to drive the power transistor PM1, and the on-resistance of the power transistor PM1 can be effectively reduced.

[0043] Incidentally, the voltage conversion device 500 in this embodiment is a step-down voltage converter.

[0044] Please refer to Figure 6 , Figure 6 A schematic diagram of a voltage conversion device according to another embodiment of the present invention is shown. The voltage conversion device 600 includes power transistors PM1 and PM2, drivers DV1 and DV2, an inductor L1, and a bootstrap control circuit 610. Power transistors PM1 and PM2 are connected in series. One end of power transistor PM1 generates an output voltage VOUT, and one end of power transistor PM2 is coupled to a reference ground voltage GND. Drivers DV1 and DV2 are a high-side driver and a low-side driver, respectively, used to drive power transistors PM1 and PM2.

[0045] A bootstrap control circuit 610 is coupled across the power transistor PM1. One end of the bootstrap control circuit 610 receives the output voltage VOUT, and the other end is coupled to the reference voltage terminal LX. One end of the inductor L1 is coupled to the reference voltage terminal LX, and the other end of the inductor L1 is used to receive the input voltage VIN.

[0046] The bootstrap control circuit 610, by interchanged between the input voltage VIN and the output voltage VOUT, can be implemented using the bootstrap control circuits 100, 200, or 400 of the aforementioned embodiments. Figure 5 Similarly, in the embodiment, the output voltage VBT generated by the bootstrap control circuit 610 can be provided to the driver DV1 and used as the power supply voltage for the driver DV1.

[0047] Incidentally, the voltage conversion device 600 in this embodiment is a boost voltage converter.

[0048] In summary, the bootstrap control circuit of the present invention can control the on / off state of the switch between the control terminal of the transistor that generates the output voltage and the current mirror, and through a control voltage generator, based on the voltage at the reference voltage terminal. Thus, especially when the voltage conversion device operates under high duty cycle conditions (e.g., greater than or equal to 90%), when the switch is on, the capacitor at the control terminal of the transistor can be rapidly charged to boost the control voltage; when the switch is off, the leakage path at the control terminal of the transistor can be cut off, and the control voltage can be maintained at a certain value, thus maintaining the normal operation of the bootstrap control circuit.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bootstrap control circuit, comprising: A current mirror, based on an input voltage, mirrors a bias current to generate a mirrored current; A diode string is coupled between the current mirror and the reference voltage terminal; A switch having a first terminal coupled to the diode string, a control terminal of the switch receiving a first control voltage, and a second terminal of the switch providing a second control voltage; A control voltage generator is configured to generate the first control voltage in accordance with the voltage at the reference voltage terminal. as well as The first transistor generates an output voltage based on the input voltage and according to the second control voltage.

2. The bootstrap control circuit according to claim 1, wherein the control voltage generator comprises: A first diode has a first end coupled to the current mirror to receive the mirrored current and provide the first control voltage, and a second end of the first diode is coupled to the first end of the switch.

3. The bootstrap control circuit according to claim 1, further comprising: A capacitor is coupled between the control terminal of the first transistor and the reference voltage terminal.

4. The bootstrap control circuit according to claim 3, wherein during the first duty cycle, the switch is turned on, and the capacitor is charged by receiving the bias current through the switch, thereby pulling the second control voltage up to the first voltage value.

5. The bootstrap control circuit according to claim 4, wherein during the first duty cycle, the voltage at the reference voltage terminal is the reference ground voltage.

6. The bootstrap control circuit according to claim 5, wherein during the second duty cycle, the voltage at the reference voltage terminal is equal to the input voltage, and the switch is opened to cut off the discharge path between the control terminal of the first transistor and the second terminal of the first diode.

7. The bootstrap control circuit according to claim 6, wherein the current mirror comprises: The second transistor has a first terminal to receive the input voltage, a second terminal to receive the bias current, and a control terminal of the second transistor coupled to the second terminal of the second transistor. as well as A third transistor has a first terminal to receive the input voltage, a second terminal of the third transistor to generate the mirror current, a control terminal of the third transistor coupled to the control terminal of the second transistor, and a substrate of the third transistor coupled to the first terminal of the third transistor.

8. The bootstrap control circuit of claim 7, wherein during the second duty cycle, the base diode of the third transistor is turned on, and the first control voltage is clamped to a second voltage value, wherein the second voltage value is not greater than the voltage value of the input voltage.

9. The bootstrap control circuit according to claim 2, wherein the switch includes a second transistor, a first terminal of the second transistor is coupled to a second terminal of the first diode, a second terminal of the second transistor is coupled to a control terminal of the first transistor, the control terminal of the second transistor receives the first control voltage, and the substrate of the second transistor is coupled to the first terminal of the second transistor.

10. The bootstrap control circuit of claim 2, wherein the first diode is constructed from a second transistor, a first terminal of the second transistor is coupled to the current mirror, a second terminal of the second transistor is coupled to the first terminal of the switch, a control terminal of the second transistor receives the first control voltage, and a base of the second transistor is coupled to the reference voltage terminal.

11. The bootstrap control circuit according to claim 2, wherein the anode of the first diode is coupled to the current mirror, and the cathode of the first diode is coupled to the first terminal of the switch.

12. The bootstrap control circuit according to claim 2, further comprising: The second diode has an anode to receive the input voltage, and the cathode of the second diode is coupled to the first terminal of the first transistor; A current source is coupled between the second terminal of the first transistor and the reference voltage terminal; as well as A voltage-regulating capacitor is connected between the second terminal of the first transistor and the reference voltage terminal.

13. A voltage conversion device, comprising: The first power transistor and the second power transistor are connected in series between the input voltage and the reference ground voltage, or in series between the output voltage and the reference ground voltage. The first driver and the second driver are used to drive the first power transistor and the second power transistor, respectively; An inductor is coupled between the mutual coupling terminals of the first power transistor and the second power transistor and the output or input terminal of the voltage conversion device; as well as The bootstrap control circuit according to claim 1 is coupled between the two ends of the first power transistor.

14. The voltage conversion device according to claim 13, wherein when the first power transistor is coupled to the input voltage and the inductor is coupled to the output terminal of the voltage conversion device, the voltage conversion device is a buck voltage conversion device; and when the first power transistor is coupled to the output voltage and the inductor is coupled to the input terminal of the voltage conversion device, the voltage conversion device is a boost voltage conversion device.

15. The voltage conversion device of claim 13, wherein the output voltage generated by the bootstrap control circuit is provided as the power supply voltage for the first driver.

16. The voltage conversion device according to claim 13, wherein the station-to-air ratio of the power switching operation of the voltage conversion device is greater than a threshold.

17. The voltage conversion device according to claim 13, wherein both the first power transistor and the second power transistor are N-type transistors.

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