Startup of a Switching Mode Power Supply

Abstract

Embodiments of the present disclosure relate to the startup of a switched-mode power supply. The following are used to perform a process for starting up a power circuit including a switched-mode power supply: a first stage, during which, if the output voltage of the switched-mode power supply is lower than a first voltage, the switched-mode power supply operates in a pulse-width modulation mode to increase its output voltage to the first voltage; and a second stage when the output voltage has reached the first voltage, during which the switched-mode power supply operates in a bypass mode.

Description

[0001] Citation of Related Applications

[0002] This application claims the benefit of priority of French Patent Application No. 1908288, filed on Jul. 22, 2019, the content of which is incorporated herein by reference in its entirety to the maximum extent permitted by law. Technical Field

[0003] The present disclosure generally relates to electronic circuits and devices, and more particularly, to power supplies for electronic circuits and devices. The present disclosure particularly relates to a power supply circuit including at least one switched-mode power supply (SMPS). Background Art

[0004] There are several types of power supply circuits that are capable of delivering a current / voltage pair to an electronic circuit, or device, or system, or more generally to a load. Linear power supplies and switched-mode power supplies are examples of power supply circuits.

[0005] The different types of power supply circuits each have specific characteristics, and it may be beneficial to combine several of them. The combination of a switched-mode power supply and a voltage regulator is a common combination in power supply circuits.

[0006] A switched-mode power supply is a power supply circuit configured to deliver a DC voltage from an input voltage. Although a switched-mode power supply is typically a DC / DC converter that receives a DC voltage as an input, certain switched-mode power supplies may include a rectification stage such that these switched-mode power supplies are capable of receiving an AC voltage (such as a mains line) as an input.

[0007] It is desirable to be able to at least partially improve certain aspects of known power supply circuits including switched-mode power supplies.

[0008] There is a need in the art for high-performance power supply circuits including switched-mode power supplies.

[0009] There is a more particular need in the art for power supply circuits having a faster start-up phase.

[0010] There is also a need in the art for power supply circuits having a start-up phase that consumes less power. Summary of the Invention

[0011] Embodiments overcome all or some of the drawbacks of known power supply circuits including switched-mode power supplies.

[0012] Embodiments provide a method for starting a power supply circuit including a switched-mode power supply, the method comprising: a first phase during which, if the output voltage of the switched-mode power supply is lower than a first voltage, the switched-mode power supply operates in pulse-width modulation to increase its output voltage to the first voltage; and a second bypass phase when the output voltage has reached the first voltage.

[0013] According to an embodiment, the first voltage is the voltage delivered by a switched - mode power supply during a bypass mode.

[0014] According to an embodiment, the first voltage is a DC voltage injected at the input of a switched - mode power supply.

[0015] According to an embodiment, the first voltage is a DC voltage injected at the input of a power supply circuit.

[0016] According to an embodiment, during a third stage before the first stage, the output voltage is compared with a second voltage that is lower than the first voltage.

[0017] Another embodiment provides a circuit for starting a switched - mode power supply, the circuit being configured to implement the foregoing method.

[0018] According to an embodiment, the circuit includes a comparator circuit configured to compare an output voltage with a third voltage.

[0019] According to an embodiment, during the first stage, the third voltage is equal to the first voltage.

[0020] According to an embodiment, during the third stage, the third voltage is equal to the second voltage.

[0021] According to an embodiment, the circuit further includes a state machine.

[0022] According to an embodiment, the comparator circuit is controlled by the state machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing and other features and advantages will be discussed in detail in the following non - limiting description of specific embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 The power supply circuit is schematically shown in block diagram form;

[0025] Figure 2 An embodiment of a switched - mode power supply is schematically shown in block diagram form;

[0026] Figure 3 An embodiment of a circuit for starting a Figure 2 switched - mode power supply is schematically shown in block diagram form;

[0027] Figure 4 A flowchart showing an embodiment of a method for starting the illustrated power supply circuit; and

[0028] Figure 5 showing Figure 3 the signal timing diagram and voltage curve of the starting circuit. DETAILED DESCRIPTION

[0029] In the different figures, the same reference numerals have been used to designate the same elements. In particular, structural and / or functional elements common to different embodiments may be designated by the same reference numerals and may have the same structure, dimensions, and material properties.

[0030] For clarity, only those steps and elements useful for understanding the described embodiments have been shown and described in detail. In particular, the general operation of the switching power supply has not been described in detail. The described embodiments and implementations are compatible with conventional switching-mode power supplies.

[0031] Throughout this disclosure, the term "connected" is used to specify a direct electrical connection between circuit elements with no intervening elements other than conductors, while the term "coupled" is used to specify an electrical connection between circuit elements that may be direct or may be via one or more other elements.

[0032] In the following description, unless otherwise specified, when referring to terms that define absolute positions (such as the terms "front", "rear", "top", "bottom", "left", "right", etc.) or relative positions (such as the terms "above", "below", "upper", "lower", etc.), or terms that define directions (such as the terms "horizontal", "vertical", etc.), the orientation of the drawings is being referred to.

[0033] The terms "about", "substantially", "essentially", and "approximately" are used herein to specify a tolerance of plus or minus 10%, preferably plus or minus 5%, of the value being discussed.

[0034] The signals referred to in this disclosure are analog signals that include a high state and a low state corresponding to the logic data "1" and "0", respectively. Unless otherwise mentioned, the high state represents a voltage level equal to the supply voltage. Unless otherwise mentioned, the low state represents a voltage level equal to the reference voltage (e.g., ground).

[0035] Figure 1 The power supply circuit 10 is schematically shown in block diagram form.

[0036] The circuit 10 includes a switching-mode power supply (SMPS) 100 and a voltage regulator circuit 110 (e.g., a low-dropout - LDO - regulator circuit) connected in series. The circuit 10 receives an input supply voltage Vin and a control signal ( Figure 1 not shown in the figure) as inputs, and outputs an output supply voltage Vout and, for example, other control signals ( Figure 1 not shown in the figure). The voltage Vin is more particularly received by the switching-mode power supply 100, and the voltage Vout is more particularly delivered by the voltage regulator 110. The switching-mode power supply 100 delivers a DC supply voltage VFB as an output to the input of the voltage regulator circuit 110.

[0037] A circuit of circuit 10 type can have multiple operating modes.

[0038] The normal operating mode of circuit 10 is as follows. The switched-mode power supply operates in pulse-width modulation and delivers a voltage VFB different from the voltage Vin received as input. Then, the voltage VFB is smoothed by regulator circuit 110.

[0039] Another operating mode of circuit 10 is the so-called bypass mode of switched-mode power supply 100, in which the switched-mode power supply 100 is bypassed. In other words, the switched-mode power supply delivers an output voltage VFB equal to the input voltage Vin to the input of regulator circuit 110. For this purpose, the switched-mode power supply does not operate in pulse-width modulation but is forced to output a voltage equal to the input voltage Vin. Thus, in this operating mode, the voltage VFB is equal to the input voltage Vin. This operating mode will be further described in Figure 2 further detail.

[0040] Figure 2 The structure of an embodiment of a switched-mode power supply 200 is schematically shown in block diagram form, and the switched-mode power supply 200 is configured for use in Figure 1 a power supply circuit of the type of circuit 10 shown in.

[0041] The switched-mode power supply 200 includes an N-channel MOS transistor 201N and a P-channel MOS transistor 201P. The transistors 201P and 201N are connected in series. More particularly, the drain of transistor 201N is coupled, preferably connected, to the drain of transistor 201P. The source of transistor 201P is coupled, preferably connected, to the terminal receiving the input voltage Vin. The source of transistor 201N is coupled, preferably connected, to the terminal receiving the low power supply voltage VSS_POWER. The low power supply voltage VSS_POWER is, for example, ground.

[0042] The switched-mode power supply 200 further includes an inductor coil and a capacitor Cext. The first terminal of the inductor coil is coupled, preferably connected, to the drains of transistors 201N and 201P. The second terminal of the inductor coil is coupled, preferably connected, to the first terminal of capacitor Cext. The second terminal of capacitor Cext is coupled, preferably connected, to the terminal receiving a reference voltage GND (such as ground). The reference voltage GND is, for example, equal to the low power supply voltage VSS_POWER. The second terminal of the inductor coil delivers the output voltage VFB of the switched-mode power supply 200.

[0043] The switched-mode power supply 200 further includes a state machine 203 (SM) that delivers signals GP and GN enabling the control of the gates of transistors 201P and 201N, respectively. The state machine 203 receives the control signals STARTUP_CMD and PWM_CMD, detailed hereinafter, as inputs.

[0044] The switched-mode power supply 200 further includes a pulse-width modulation circuit 205 (PWM) configured to implement the operation of the switched-mode power supply 200 in a pulse-width modulation mode. Circuit 205 receives, in particular, the output voltage VFB of the switched-mode power supply 200 and the control signal PWM_EN as inputs. Circuit 205 delivers at least the control signal PWM_CMD as an output to the state machine 203. It is common for a switched-mode power supply to operate in pulse-width modulation, and it will not be described herein further.

[0045] The switched-mode power supply 200 further includes a startup circuit 207 (STARTUP). Circuit 207 receives, in particular, the output voltage VFB and the control signal STARTUP_EN as inputs. Circuit 207 delivers the control signal STARTUP_CMD to the state machine 203 at its output. Figure 3 Circuit 207 is shown in more detail in

[0046] Figure 3 The structure of the startup circuit 207 of the switched-mode power supply 200 shown in Figure 2 is schematically shown in block diagram form.

[0047] Circuit 207 receives the output voltage VFB, the comparison voltage VCOMP, the supply voltage VDD, and the control signal STARTUP_EN of the switched-mode power supply 200 as inputs. The signal STARTUP_EN includes a signal ENA for enabling the startup circuit 207 and a signal BYPASS-EN for enabling the bypass mode of the switched-mode power supply 200.

[0048] Circuit 207 outputs a signal STARTUP_CMD that includes a status signal SD_RDY, a signal EN_SM for enabling the state machine 203, and a status signal BYPASS_RDY for enabling the bypass mode of the switched-mode power supply 200.

[0049] Circuit 207 includes two switches SW1 and SW2. Switch SW1 receives the voltage VFB at a first terminal and couples, preferably connects, a second terminal to node A. Switch SW2 receives the voltage VCOMP at a first terminal and couples, preferably connects, a second terminal to node A. Switches SW1 and SW2 are controlled by signals SW_CMD1 and SW_CMD2.

[0050] The circuit 207 further includes a switch SW3 and a current source 2071. The first terminal of the switch SW3 is coupled, preferably connected, to node A, and the second terminal of the switch SW3 is coupled, preferably connected, to the first terminal of the current source 2071. The second terminal of the current source 2071 receives the supply voltage VDD. The switch SW3 is controlled by the signal SW_CMD3.

[0051] The circuit 207 further includes a capacitor Cstart. The electrodes of the capacitor Cstart are coupled, preferably connected, to node A, and the second electrode of the capacitor Cstart is coupled, preferably connected, to a terminal receiving the reference voltage GND.

[0052] The circuit 207 further includes a comparator circuit 2072 (COMP). The circuit 2072 is configured to compare the voltage of node A (denoted as VSTART) with the voltage VCOMP. The circuit 2072 is controlled by the signal ENA_COMP and outputs a status signal CMP_RDY and an output signal OUT_CMP.

[0053] The circuit 207 further includes a state machine 2073 (SM) that receives the following signals as inputs: an enable signal ENA; a signal BYPASS_EN for enabling the bypass mode of the switched-mode power supply; the signal CMP_RDY; and the signal OUT_CMP.

[0054] The state machine 2073 outputs the following signals: signals SW_CMD1, SW_CMD2, and SW_CMD3 for controlling the switches SW1, SW2, and SW3; a signal ENA_COMP for enabling the comparator circuit 2072; a status signal SD_RDY; an enable signal EN_SM; and a status signal BYPASS_RDY.

[0055] In the bypass mode, the circuit 207 enables, in particular, the direct start-up of the switched-mode power supply 200. Figure 4 The operation and implementation mode of the circuit 207 are described in detail.

[0056] Figure 4 is a flowchart showing the implementation mode of the start-up circuit 207 in the context of starting the switched-mode power supply 200 in the bypass mode. Figure 3 The switched-mode power supply is considered to be in the bypass mode when the output voltage VFB of the switched-mode power supply is equal to the input voltage Vin and when the status signal BYPASS_RDY is at a high level.

[0057] At step 301 (BYPASS START), a request is made to start the switched - mode power supply 200 in bypass mode. To this end, the enable signal ENA is switched to a high level indicating the start of the power supply 200, and the signal BYPASS_EN is also switched to a high level indicating the triggering of the bypass mode of the switched - mode power supply 200.

[0058] At step 303 (VSTART = VFB), the state machine 2073 controls switch SW1 to the on state and switches SW2 and SW3 to the off state. Then, the voltage VSTART is equal to the voltage VFB, and the capacitor Cstart is charged by the voltage VFB. The comparator circuit 2072 is activated.

[0059] At step 305 (COMP READY), the signal COMP_RDY switches to a high level, and the comparator is ready for use. The state machine 2073 controls the three switches SW1, SW2, and SW3 to the off state. The comparison voltage VCOMP is first equal to the first low threshold voltage VREF. Then, the capacitor Cstart delivers the voltage VFB.

[0060] At step 307 (VSTART > VREF?), the comparator circuit compares the voltage VSTART with the voltage VCOMP, which still equals the voltage VREF. The result of this comparison is encoded in the output signal OUT_COMP of the comparator circuit. More specifically, if the voltage VSTART is lower than the voltage VCOMP (output N), the output signal OUT_COMP is in the low state, and the next step is step 309 (PWM MODE). If the voltage VSTART is higher than the voltage VCOMP (output Y), the output signal OUT_COMP is in the high state, and the next step is step 311 (RISE VCOMP).

[0061] At step 309, the switched - mode power supply is started in pulse - width modulation mode to increase its output voltage VFB until the voltage VFB is equal to the input voltage Vin. Then, the next step is step 313 (BYPASS READY), where the output voltage VFB of the switched - mode power supply 200 is equal to the input voltage Vin, and the signal BYPASS_RDY switches to a high level.

[0062] At step 311, the enable signal SD_RDY switches to a high state. The signal VCOMP increases to the value of the input voltage Vin. The comparator circuit 2072 stops, the signal COMP_RDY switches to a low state, and the comparator circuit is restarted.

[0063] At step 315 (COMP READY), the comparator is ready for use and the signal COMP_RDY switches to high level. The state machine 2073 controls the three switches SW1, SW2, and SW3 to the off state. The comparison voltage VCOMP is equal to the voltage Vin.

[0064] At step 317 (VSTART>Vin?), the comparator circuit compares the voltage VSTART, which is still equal to the output voltage VFB, with the voltage VCOMP, which then equals the voltage Vin. The result of this comparison is encoded in the output signal OUT_COMP of the comparator circuit. More specifically, if the voltage VSTART is greater than the voltage VCOMP (output Y), the output signal OUT_COMP is in the low state and the next step is step 319 (ALRDY BYPASS). If the voltage VSTART is lower than the voltage VCOMP (output N), the output signal OUT_COMP is in the high state and the next step is step 321 (PWM MODE).

[0065] At step 319, the output voltage VFB of the switched-mode power supply is already at a level greater than or equal to the level of the input voltage Vin. The state machine 2073 controls the switch SW1 and SW3 to the off state and the switch SW2 to the on state. By turning on the switch SW2, the capacitor Cstart is used as a coupling capacitor between the voltage VDD and the reference voltage GND. The signal BYPASS_RDY switches to high level. Then, the next step is step 313.

[0066] At step 321, the output voltage VFB is not high enough for the switched-mode power supply 200 to be in the bypass mode. Then, the switched-mode power supply 200 is started in the pulse-width modulation mode to increase its output voltage VFB until the voltage VFB equals the input voltage Vin. The voltage VFB follows a slow ramp to avoid damaging the transistor 201P of the switched-mode power supply 200 by sending too high a voltage to it too quickly.

[0067] Then, the state machine 2073 controls the switches SW1 and SW2 to the off state and the switch SW3 to the on state. By turning on the switch SW3, the capacitor Cstart is charged. Further, once the voltage VFB is the voltage Vin, the capacitor Cstart is charged and then the switch SW3 is turned off again. The signal BYPASS_RDY switches to high level. Then, the next step is step 313.

[0068] At step 313, the switched-mode power supply 200 has an output voltage VFB that is greater than or equal to the input voltage Vin. During its operation, the output voltage VFB will stabilize at the input voltage Vin, and then the switched-mode power supply will be in bypass mode.

[0069] Figure 5 is a diagram showing the timing diagram of the control signal and the voltage curve of the switched-mode power supply 200. More particularly, the shown timing diagram and curve diagram illustrate the startup method of the switched-mode power supply 200 ( Figure 2 as shown) when the output voltage VFB of the switched-mode power supply is higher than the first threshold voltage VREF and lower than the input voltage Vin. Figure 4 as shown).

[0070] Figure 5 The curve diagram more particularly shows: the timing diagram of the bypass mode enable signal BYPASS_EN; the timing diagram of the output voltage OUT_COMP of the comparator circuit 2072; the timing diagram of the status signal COMP_RDY of the comparator circuit 2072; the timing diagram of the signal ENA_COMP for enabling the comparator circuit 2072; the timing diagram of the status signal BYPASS_RDY of the bypass mode; the curve of the comparison voltage VCOMP; the curve of the output voltage VFB of the switched-mode power supply 200; and the voltage VSTART curve of node A of the startup circuit 207 of the switched-mode power supply 200.

[0071] Before the initial time t0, the comparator circuit 2072 is enabled and the signal ENA_COMP is in the high state. However, the comparator circuit 2072 is not yet ready to compare the signals it receives at its inputs, so the signal COMP_RDY is in the low state. The output signal OUT_COMP is arbitrarily in the low state or the high state. The switched-mode power supply 200 is not in bypass mode, so the signal BYPASS_RDY is in the low state, but it is also not in pulse width modulation mode. However, bypass mode is requested and the signal BYPASS_EN is in the high state. In the case illustrated herein, the output voltage VFB of the switched-mode power supply 200 is at a voltage level, for example, equal to 2V. The comparison voltage VCOMP is equal to the first threshold voltage, which, in Figure 5 the case illustrated, is lower than the voltage VFB, for example, equal to 1.2V. The voltage VSTART is equal to the output voltage VFB.

[0072] At the initial time t0, the comparator circuit 2072 is ready and compares the signal VFB with the comparison signal VCOMP ( Figure 4In steps 305 and 307), the signal COMP_RDY switches to the high state. As previously mentioned, the voltage VFB is greater than the comparison voltage VCOMP, and thus the output signal of comparator 2072 is in the high state.

[0073] At time t1, comparator circuit 2072 is reset, the signal ENA_COMP is successively switched to the low state and then to the high state. Then, the comparator circuit is no longer ready to perform a comparison, the signal COMP_RDY switches to the low state. The output signal OUT_COMP of comparator circuit 2072 switches to the low state. The level of the comparison voltage VCOMP is increased until it reaches the level of the input voltage Vin of the switched-mode power supply 200, which is equal to, for example, Figure 5 2.6V in Figure 4 step 311).

[0074] At time t2, comparator circuit 2072 is ready for use, the signal COMP_RDY switches to the high state. As previously mentioned, the voltage VFB is lower than the voltage Vin, so the output signal OUT_COMP is in the low state.

[0075] Then, the switched-mode power supply 200 enters the pulse-width modulation mode and gradually increases the output voltage VFB. Then, the voltage VSTART also increases according to a ramp.

[0076] At time t3, the voltage VSTART reaches the voltage Vin ( Figure 4 step 317), the output signal OUT_COMP of comparator circuit 2072 switches to the high state. The state machine 2073 deactivates comparator circuit 2072, whereby both the signals ENA_COMP and COMP_RDY switch to the low state.

[0077] Then, the switched-mode power supply 200 is in the bypass mode, and the signal BYPASS_RDY switches to the high state. The voltage VSTART in the pulse-width modulation mode is reduced to a low level, such as ground.

[0078] The advantage of this startup method is that it is faster and consumes less power than the conventional bypass-mode startup method. In fact, since the output voltage level of the switched-mode power supply is unknown at any time, the startup mode may have to wait until the output voltage of the switched-mode power supply reaches a low threshold voltage and then increase it back to the required voltage. This startup mode will be slower and consume more power.

[0079] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations can be combined, and other variations will occur to those skilled in the art. In particular, the input voltage of the switched-mode power supply can be an AC voltage, but in that case, the switched-mode power supply will include a rectification stage to convert the AC input voltage to a DC input voltage. In that case, once the output voltage of the switched-mode power supply equals the DC input voltage, the switched-mode power supply is in bypass mode.

[0080] Finally, based on the functional indications given above, the actual implementation of the described embodiments and variations is within the capabilities of those skilled in the art.

[0081] Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to fall within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The invention is limited only by the scope defined in the appended claims and their equivalents.

Claims

1. A method of starting a power supply circuit including a switched-mode power supply, comprising: Operating the power supply circuit in a first phase, wherein a bypass of the switched-mode power supply is requested to generate an output voltage from an input voltage; Setting a comparison voltage to a first level less than the input voltage during the first phase; Generating a start voltage equal to the output voltage; Then operating the power supply circuit in a second phase, wherein the switched-mode power supply is controlled to use pulse width modulation to cause an increase in the output voltage; During the second phase, increasing the start voltage according to a ramp; Comparing the ramp-increased start voltage with the comparison voltage during the second phase; And When the ramp-increased start voltage reaches the comparison voltage, then operating the power supply circuit in a third phase, wherein the switched-mode power supply is bypassed to generate the output voltage from the input voltage.

2. The method according to claim 1, further comprising: When operating the power supply circuit in the second phase, switching the comparison voltage to a second level equal to the input voltage.

3. A power supply circuit, comprising: A switched-mode power supply that receives an input voltage and generates an output voltage; And A circuit including a comparator circuit having an input that receives a comparison voltage, the circuit being configured to start the power supply circuit by: Operating in a first phase, wherein a bypass of the switched-mode power supply is requested to generate the output voltage from the input voltage; Generating a start voltage equal to the output voltage; Setting the comparison voltage to a first level less than the input voltage during the first phase; Then operating in a second phase, wherein the switched-mode power supply is controlled to use pulse width modulation to cause an increase in the output voltage; During the second phase, increasing the start voltage according to a ramp; During the second phase, comparing the ramp-increased start voltage with the comparison voltage; And When the ramp-increased start voltage reaches the comparison voltage, then operating in a third phase, wherein the switched-mode power supply is bypassed to generate the output voltage from the input voltage.

4. The power supply circuit according to claim 3, wherein the circuit includes a state machine.

5. The power supply circuit according to claim 4, wherein during the second phase, the comparison voltage is at a second level equal to the input voltage.

6. The power supply circuit according to claim 5, wherein the circuit includes a state machine, and wherein the comparator circuit is controlled by the state machine.

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