Switch circuit with soft start and switch control circuit and method thereof

Abstract

A switch control circuit is disclosed for controlling a path switch and a current sensing resistor connected in series between an input voltage and an output voltage. The switch control circuit includes: an amplifier that controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor for a smooth start-up with current limiting; a slope detection circuit coupled to the output voltage for monitoring the rising slope of the output voltage; and a pull-down switch coupled between the gate of the path switch and a disable potential. When the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, the pull-down switch is triggered to turn on, thereby turning off the path switch.

Description

[Technical Field]

[0001] This invention relates to a bidirectional power conversion and transmission system, particularly a bidirectional power conversion and transmission system with current limiting function. This invention also relates to a control circuit and control method for controlling the aforementioned bidirectional power conversion and transmission system. This invention relates to a switching circuit, particularly a switching circuit for hot-swappable applications. This invention also relates to its switching control circuit and control method. This invention enables efficient and smooth start-up operation and reduces the safe operating area (SOA) requirement of the path switches in the switching circuit. [Previous Technology]

[0002] In hot-swappable applications, implementing a smooth start-up mechanism is crucial for reducing interference with the backplane power supply and lowering the safe operating area (SOA) requirements of series power switches (typically N-type MOSFETs). By gradually charging the large output capacitor with a controlled, moderate current, heat dissipation can be effectively achieved using the MOSFET's heat sink and circuit board traces, thereby reducing the stress on the MOSFET.

[0003] Figures 1 and 2 show two main prior art methods for smooth start-up: gate voltage slope control method and current limiting method.

[0004] Figure 1 illustrates a multi-phase switching circuit using a gate voltage slope control smooth start method. The multi-phase switching circuit 100 includes multiple switching circuits (e.g., switching circuits 51 and 52) coupled in parallel between the input voltage VIN and the output voltage VOUT. Each switching circuit includes a path switch SP located between VIN and VOUT to control current flow. In this embodiment, smooth start is achieved by controlling the rising slope of the gate voltage VG of the path switch. Since SP is an NMOSFET, a charge pump 28 is configured to provide the required gate voltage, while a current source 38 supplies a constant charging current ICH. This configuration ensures that VG has a stable rising slope, thereby achieving the smooth start function.

[0005] In the gate voltage slope control method, the gate of the MOSFET is gradually charged by a constant current source, causing the source terminal (connected to the output capacitor Co) to rise with the gate potential and a threshold voltage offset. The smooth start-up current ISS flowing through the MOSFET and the current flowing into Co are given by the following formulas:

[0006] ISS = (dVOUT / dt) x Co

[0007] The smooth start-up current ISS is typically set below the current limit threshold to quickly terminate the smooth start-up operation when an output short circuit is detected. By immediately terminating the smooth start-up when the current reaches the threshold, MOSFET stress can be minimized, thereby reducing SOA requirements. However, threshold voltage variations of different MOSFETs can cause inconsistencies in current distribution when multiple devices are connected in parallel. Therefore, in this configuration, gate voltage slope control methods are limited in terms of current sharing accuracy.

[0008] Figure 2 shows a schematic diagram of another prior art switching circuit illustrating a current-limited smooth start-up method. The multi-phase switching circuit 200 includes multiple switching circuits (e.g., switching circuits 53 and 54). Each switching circuit, such as switching circuit 53, includes a path switch SP connected in series between VIN and VOUT and a current-sensing resistor RSNS. Each switching circuit also includes an amplifier 48 with an offset voltage VOS coupled across RSNS to sense the current in the path switch SP. The amplifier's output controls the gate voltage VG of the path switch SP, achieving a constant current during smooth start-up through feedback control to control the current flowing through RSNS.

[0009] In the current limiting method, the gate voltage VG is adjusted to maintain a constant current, typically set to a low level (e.g., 10% of the maximum load current) to reduce SOA requirements. By setting a longer smooth start-up time, the output capacitor can be fully charged, and margins are included for current limiting accuracy and capacitance tolerance variations. Compared to the gate voltage slope control method, this method offers higher current distribution accuracy in multi-device parallel applications and is unaffected by MOSFET threshold voltage variations.

[0010] However, the longer smooth start-up time poses some challenges in the event of a fault condition (such as an output short circuit). Because the current limit is active in both normal and fault conditions, the system cannot distinguish between these states and therefore cannot shorten the smooth start-up time. This can lead to continuous power loss and temperature rise at the path switch SP, increasing the risk of failure under sustained fault conditions.

[0011] In view of the above, in order to overcome the shortcomings of the prior art, the present invention proposes a method and circuit aimed at solving these problems. The switching circuit of the present invention can achieve high-precision current balance during smooth startup, while having the ability to quickly turn off path switches to prevent damage during output load failures and reduce SOA requirements. [Summary of the Invention]

[0012] In one viewpoint, the present invention provides a switch control circuit for controlling a path switch and a current sensing resistor connected in series between an input voltage and an output voltage. The switch control circuit includes: an amplifier that controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to perform a smooth start-up with current limiting; a slope detection circuit coupled to the output voltage for monitoring the rising slope of the output voltage; and a pull-down switch connected between the gate of the path switch and a disable potential; wherein, when the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

[0013] In a preferred embodiment, the switch control circuit further includes a charge pump that, after a smooth start-up, raises the gate voltage of the path switch to a high potential generated by the charge pump, thereby turning the path switch fully on.

[0014] In a preferred embodiment, the slope detection circuit includes an analog-to-digital converter (ADC) coupled to the output voltage to convert the output voltage into a digital signal; and a logic circuit that calculates the rising slope of the output voltage based on the digital signal and compares the rising slope with a preset slope threshold to generate a control signal for controlling the pull-down switch.

[0015] In a preferred embodiment, the switch control circuit allows the rise slope of the output voltage to be lower than a preset slope threshold within a preset time window, thereby achieving the de-jitter function.

[0016] In a preferred embodiment, when the rising slope of the output voltage is detected to be lower than a preset slope threshold and the path switch is turned off, the switch control circuit attempts to restart smoothly after a preset time delay.

[0017] In a preferred embodiment, the switch control circuit counts and records the number of retries for smooth start-up, and when the number of retries reaches a preset upper limit, the path switch is kept in the off state.

[0018] From another perspective, the present invention provides a switching circuit comprising: a path switch and a current sensing resistor connected in series between an input voltage and an output voltage; and a switching control circuit comprising: an amplifier that controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to perform a smooth start-up with current limiting; a slope detection circuit coupled to the output voltage for monitoring the rising slope of the output voltage; and a pull-down switch connected between the gate of the path switch and a disable potential; wherein, when the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

[0019] From another perspective, the present invention provides a method for controlling a path switch connected in series between an input voltage and an output voltage. The method includes: controlling the gate voltage of the path switch to perform a smooth start-up of current limiting on the output voltage; monitoring the rise slope of the output voltage; comparing the monitored rise slope with a preset slope threshold; and turning off the path switch when the rise slope is lower than the preset slope threshold.

[0020] In a preferred embodiment, the method further includes: during the smooth start-up process, allowing the rising slope to be lower than the slope threshold within a preset time window to achieve the de-jittering function.

[0021] In a preferred embodiment, when the path switch is turned off because the rising slope is lower than a preset slope threshold, the method further includes: retrying a smooth start after a preset time delay.

[0022] In a preferred embodiment, the method further includes: counting and recording the number of retries for a smooth start; and keeping the path switch off when the number of retries reaches a preset upper limit.

[0023] The following detailed description of specific embodiments will make it easier to understand the purpose, technical content, features and effects of the present invention.

Implementation Method

[0032] The drawings in this invention are all schematic and are mainly intended to illustrate the coupling relationships between circuits and the relationships between signal waveforms. The circuits, signal waveforms, and frequencies are not drawn to scale. For clarity, many practical details will be described in the following description, but this is not intended to limit the scope of the patent application of this invention.

[0033] Figure 3 shows a schematic diagram of a switching circuit according to an embodiment of the present invention. The switching circuit 300 includes a path switch SP and a current sensing resistor RSNS connected in series between the input voltage VIN and the output voltage VOUT, and includes a switching control circuit 60. The switching control circuit 60 includes an amplifier 62, a charge pump 63, a pull-down switch SPD, and a slope detection circuit 61. The amplifier 62 has an offset voltage VOS and is used to adjust the gate voltage VG of the path switch SP based on the voltage drop across the current sensing resistor RSNS and the offset voltage VOS, so as to perform a smooth start-up of the output voltage VOUT in a current-limited manner.

[0034] The output of charge pump 63 is connected to the gate voltage VG to raise the gate voltage VG to a higher level during the final stage of smooth startup, so that the path switch SP is fully turned on. Slope detection circuit 61: used to sense the rising slope dVOUT / dt of output voltage VOUT and generate pull-down control signal VPD. Pull-down switch SPD is set between gate voltage VG and ground potential. When the pull-down control signal VPD indicates that pull-down control is started, pull-down switch SPD pulls gate voltage VG to a disabled level (e.g., ground potential), thereby turning off path switch SP.

[0035] In one embodiment, when the slope detection circuit 61 senses that the rising slope dVOUT / dt of the output voltage VOUT is lower than a preset slope threshold Lth, it enables the pull-down control signal VPD, turns on the pull-down switch SPD, pulls down the gate voltage VG, and thereby turns off the path switch SP. Under current limiting conditions, if the current supplied to the output capacitor COUT and the load is insufficient to make the output voltage VOUT rise according to the preset slope, the slope detection circuit 61 can determine that a fault may have occurred, such as a short circuit in the load RL, and then trigger the pull-down switch SPD to turn off the path switch SP. It is worth noting that although this embodiment only shows one switching circuit, the present invention can also be used in applications where multiple switching circuits are connected in parallel, and can achieve accurate current balance among multiple path switches during smooth startup.

[0036] Figure 4 shows a more detailed embodiment of the switching circuit of the present invention corresponding to Figure 3. In this embodiment, the slope detection circuit 61 includes an analog-to-digital converter (ADC) 611 and a logic circuit 612. The analog-to-digital converter 611 is coupled to the output voltage VOUT and is used to convert VOUT into a corresponding digital signal reflecting the potential of the output voltage. The logic circuit 612 is used to calculate the rising slope dVOUT / dt of the output voltage VOUT based on the digital signal generated by the analog-to-digital converter 611 and the clock signal CLK, and compare it with a preset slope threshold Lth. When the logic circuit 612 detects that the slope dVOUT / dt of the output voltage VOUT is lower than the preset slope threshold Lth, it generates a pull-down control signal VPD, which in turn controls the pull-down switch SPD to turn off the path switch SP. This design can quickly respond when the rising slope of the output voltage is insufficient, preventing potential faults such as load short circuits.

[0037] Figure 5 shows an operation waveform diagram of an embodiment of the present invention, illustrating the normal state and the smooth start-up failure situation. The upper half of the waveform in Figure 5 shows the change of the output voltage VOUT under the normal state (CV1) and the fault state (CV2). The lower half of the waveform shows the rising slope of the corresponding output voltage VOUT, which is CV3 under the normal state and CV4 under the fault state.

[0038] Under normal conditions, the switch control circuit 60 starts smoothly at time t1, as shown by waveforms CV1 and CV3. During the smooth start-up period from t1 to t3, the output voltage VOUT rises steadily with a slope of LV1, and LV1 is greater than the preset slope threshold Lth. Therefore, the slope detection circuit 61 determines that this is a normal smooth start-up state. Furthermore, after the smooth start-up is completed at time t3, the output voltage has risen to the preset target value, and the switch control circuit 60 raises the gate voltage VG to a higher level, so that the path switch SP is fully turned on.

[0039] In the event of a fault, the switch control circuit 60 starts smoothly at time t1, as shown in waveforms CV2 and CV4. However, because the rising slope of the output voltage VOUT is too low, its slope value LV2 is lower than the preset slope threshold Lth. Therefore, the switch control circuit 60 pulls the gate voltage VG down to zero at time t2, turning off the path switch SP, so that after time t2, the output voltage VOUT also drops to a low level. It should be noted that the rising slope of the output voltage does not need to be detected outside of time points t1 to t3, and therefore is not plotted.

[0040] Figure 6 shows an operation waveform diagram of another embodiment of the present invention, illustrating a smooth start-up with debouncing function. Specifically, the upper half of Figure 6 shows the waveform CV5 of the output voltage VOUT, and the lower half shows the waveform CV6 of the corresponding output voltage rise slope. Starting from time point t1, the switching control circuit performs a smooth start-up. During the period from time point t1 to t2, the output voltage VOUT rises at a fixed slope LV1, which is higher than a preset slope threshold Lth, indicating that the smooth start-up is proceeding smoothly.

[0041] Starting from time point t2, the rising slope of the output voltage VOUT becomes a gentler LV2, which is lower than the slope threshold Lth. In the aforementioned embodiment shown in Figure 5, a slope lower than Lth may be judged as a fault, causing the smooth start-up to be interrupted. However, as shown in Figure 6, this embodiment introduces a deglitch function, allowing the switching control circuit to allow the slope to be lower than the slope threshold Lth for a short period of time.

[0042] Specifically, due to factors such as load changes, the slope LV2 of the output voltage VOUT may be temporarily lower than Lth during the period from time t2 to t2'. However, due to the de-jitter function, the switching control circuit allows the slope to be temporarily lower than Lth within a preset time window Tw. Therefore, the smooth start-up can continue.

[0043] Starting from time point t2', the rising slope of the output voltage VOUT recovers to LV3, which is higher than Lth, and continues until time point t3. At this time, the output voltage VOUT reaches the final highest level, and the smooth start-up is successfully completed.

[0044] In this embodiment, by introducing a debouncing function, the switch control circuit is insensitive to brief slope drops, avoiding misjudgments of faults due to momentary interference. This configuration enhances the system's stability and fault tolerance, ensuring the smooth completion of the smooth startup process.

[0045] Figure 7 shows the operation waveform diagram of an embodiment of the present invention with retry function. The upper waveform CV7 shows the change of output voltage VOUT over time, including the process of multiple retrying to start. The lower waveform CV8 shows the change of the rising slope dVOUT / dt of output voltage VOUT over time.

[0046] At time t1, the switch control circuit initiates the first smooth start-up of the switch circuit, and the output voltage VOUT gradually increases as the gate voltage VG of the path switch SP rises. However, at time t2, the slope detection circuit 61 detects that the rising slope dVOUT / dt of the output voltage VOUT is lower than the preset slope threshold Lth. The switch control circuit determines that a fault may exist, so it pulls the gate voltage VG down to zero, turns off the path switch SP, and causes VOUT to drop or remain at a low level.

[0047] In this embodiment, after a predetermined delay time Td, at time point t3, the switch control circuit automatically performs a second smooth start-up attempt, and the output voltage VOUT begins to rise again. Since the slope dVOUT / dt is detected to be lower than the threshold Lth again at time point T4, the switch control circuit repeats the above process.

[0048] The switch control circuit can be set with an allowed number of retries (e.g., three times); if the number of retries exceeds the set limit, the switch control circuit will remain in the off state.

[0049] As shown in Figure 7, when the rising slope of VOUT is lower than the threshold Lth, the switch control circuit of this embodiment can attempt to restart multiple times, with a predetermined delay time Td between each attempt. The retry mechanism can improve the reliability of the system, allowing temporary faults or erroneous messages to attempt automatic recovery without user intervention, thereby enhancing the fault tolerance of the switch circuit.

[0050] Figure 8 shows the operation flowchart of the present invention. Step S0: Start-up smoothly, wherein the switch control circuit 60 is activated, and the output voltage VOUT begins to rise as the gate voltage VG of the path switch SP rises. Next, proceed to step S1: Monitor the output slope, wherein the slope detection circuit 61 continuously monitors the rising slope dVOUT / dt of the output voltage VOUT.

[0051] Next, proceed to step S2: slope comparison, where the detected slope dVOUT / dt is compared with a preset slope threshold Lth. If the slope dVOUT / dt is higher than Lth, proceed to step S3. If the slope dVOUT / dt is lower than Lth, proceed to step S4. Step S3: Determine whether VOUT has reached the target value or has reached the preset smooth start time; if not, return to step S1 and continue the smooth start process. If yes, proceed to step S9, in the normal power supply procedure, maintain the path switch SP on to supply power to the load.

[0052] On the other hand, in step S4, the gate voltage VG is pulled down to zero, and the path switch SP is turned off. Next, proceed to step S5: check the number of retry attempts for smooth start. If the number of retry attempts has not reached the upper limit, proceed to step S6. Step S6: wait for a predetermined delay time Td, increment the retry counter n, and then return to step S0 to retry the start-up. If the number of retry attempts n has reached the upper limit, proceed to step S7. Step S7: enter protection mode, where the switch control circuit 60 remains off.

[0053] In one embodiment, some steps of the aforementioned process can be omitted, such as steps S5 and S6, that is, the retry function is not included. Once it is confirmed in step S4 that the output voltage slope dVOUT / dt is lower than the slope threshold Lth, the process directly jumps to step S7.

[0054] Furthermore, in one embodiment, the aforementioned step S2 can be replaced by step S2'. Step S2': Compare the detected slope dVOUT / dt with a preset slope threshold Lth, and incorporate a time window Tw. If the slope dVOUT / dt is higher than Lth: Proceed to step S3. If the time for which the slope dVOUT / dt is lower than Lth is longer than the time window Tw, proceed to step S4; otherwise, proceed to step S3.

[0055] Figure 8 illustrates in detail the decision-making and operation process of the switch control circuit 60 during startup. This embodiment corresponds to the waveform in Figure 7. When a fault is detected, multiple retries can be performed to improve the fault tolerance of the switch control circuit. In addition, the number of retries n and the delay time Td can be adjusted by the user according to the application requirements.

[0056] This invention has several advantages. First, by employing a current limiting method, the current is set to a fixed value through active control of the MOSFET's gate voltage. In applications where multiple switching circuits are connected in parallel to charge a large output capacitor for smooth startup, this provides better current sharing capability, unaffected by differences in MOSFET threshold voltages, achieving more accurate current distribution. Second, the switching control circuit continuously monitors the rising slope of the output voltage (dVOUT / dt), and can quickly stop the smooth startup when a fault is detected (such as an output short circuit). The response time can be shortened from hundreds of milliseconds to several milliseconds, significantly reducing the stress on the MOSFET, thereby reducing the requirement for a safe operating area (SOA) and saving system costs. Furthermore, by introducing debouncing functionality and a retry mechanism, the system has a certain degree of fault tolerance, allowing for brief slope drops and multiple startup attempts, improving system stability and reliability.

[0057] The present invention has been described above with reference to preferred embodiments. However, the above description is only for the purpose of enabling those skilled in the art to easily understand the content of the present invention and is not intended to limit the scope of the present invention. The various embodiments described are not limited to individual applications and can also be combined. For example, two or more embodiments can be used in combination, and some components in one embodiment can be used to replace corresponding components in another embodiment. Furthermore, under the same spirit of the present invention, those skilled in the art can conceive of various equivalent changes and combinations. For example, the present invention's statement of "processing or calculating based on a signal or generating an output result" is not limited to the signal itself, but also includes, when necessary, performing voltage-to-current conversion, current-to-voltage conversion, and / or proportional conversion on the signal, and then processing or calculating based on the converted signal to generate an output result. Therefore, under the same spirit of the present invention, those skilled in the art can conceive of various equivalent changes and combinations, and there are many combinations, which will not be listed here. Therefore, the scope of the present invention should cover the above and all other equivalent changes. [Simplified Explanation of the Diagram]

[0024] Figure 1 shows a schematic diagram of a prior art switching circuit.

[0025] Figure 2 shows a schematic diagram of another prior art switching circuit.

[0026] Figure 3 shows a schematic diagram of a switching circuit according to an embodiment of the present invention.

[0027] Figure 4 shows a more detailed embodiment of the switching circuit of the present invention corresponding to Figure 3.

[0028] Figure 5 shows an operation waveform diagram of an embodiment of the present invention, illustrating the normal state and the failure of a smooth start-up.

[0029] Figure 6 shows an operation waveform diagram of another embodiment of the present invention, demonstrating a smooth start-up with de-jitter function.

[0030] Figure 7 shows the operation waveform diagram of an embodiment of the present invention with retry function.

[0031] Figure 8 shows the operation flowchart of the present invention.

Claims

1. A switch control circuit for controlling a path switch and a current sensing resistor connected in series between an input voltage and an output voltage, the switch control circuit comprising: An amplifier controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to achieve a smooth start-up of the output voltage in a current-limited manner; a slope detection circuit is coupled to the output voltage to continuously monitor the rising slope of the output voltage; a pull-down switch is coupled between the gate of the path switch and a disable potential; wherein when the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

2. The switch control circuit as claimed in claim 1 further comprises: a charge pump that, after a smooth start-up, raises the gate voltage of the path switch to a high potential generated by the charge pump, thereby fully turning on the path switch.

3. The switch control circuit as claimed in claim 1, wherein the slope detection circuit comprises: An analog-to-digital converter is coupled to the output voltage and converts the output voltage into a digital signal; A logic circuit calculates the rise slope of the output voltage based on the digital signal and compares it with a preset slope threshold to generate a control signal for controlling the pull-down switch.

4. The switching control circuit as claimed in claim 1, wherein the switching control circuit allows the rise slope of the output voltage to be lower than the preset slope threshold within a preset time window, thereby achieving the debouncing function.

5. The switch control circuit as claimed in claim 1, wherein when the rise slope of the output voltage is detected to be lower than the preset slope threshold and the path switch is turned off, the switch control circuit re-attempts a smooth start after a predetermined time delay.

6. The switch control circuit as described in claim 5, wherein the switch control circuit counts and records the number of times a smooth start is retried, and when the number of retried attempts reaches a preset upper limit, the path switch remains in the off state.

7. A switching circuit comprising: a path switch and a current sensing resistor connected in series between an input voltage and an output voltage; and a switch control circuit as claimed in any one of claims 1 to 6.

8. A method for controlling a switching circuit, the switching circuit including a path switch connected in series between an input voltage and an output voltage, the method comprising: controlling the gate voltage of the path switch to smoothly start the output voltage in a current-limited manner; continuously monitoring a rising slope of the output voltage; comparing the monitored rising slope with a preset slope threshold; and turning off the path switch when the rising slope is lower than the preset slope threshold.

9. The method as described in claim 8 further includes: during the smooth start-up process, allowing the rising slope to be lower than the slope threshold within a preset time window.

10. The method as described in claim 8 further comprises: after the path switch is turned off when the rising slope is lower than the preset slope threshold, retrying a smooth start after a predetermined time delay.

11. The method as described in claim 10 further includes: counting and recording the number of times a smooth start is retried; and keeping the path switch off when the number of retried attempts reaches a preset upper limit.

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