WO2020021821A1

WO2020021821A1 - Switching power supply device

Info

Publication number: WO2020021821A1
Application number: PCT/JP2019/019302
Authority: WO
Inventors: 隆志朝日
Original assignee: 株式会社デンソー
Priority date: 2018-07-25
Filing date: 2019-05-15
Publication date: 2020-01-30
Also published as: JP2020018090A

Abstract

In an embodiment according to the present disclosure, a switching power supply device 1 is provided with a low-side switch 6 which is disposed in a reverse flow path through which, when a short to power occurs at an output terminal VOUT, current flows reversely from the terminal to an inductor 3. The low-side switch 6 is used for performing synchronous rectification in association with a step-down switching operation. An input low-voltage detection unit 7 outputs an input low-voltage detection signal when a power supply voltage VIN becomes lower than a threshold voltage V1. An output high-voltage detection unit 8 outputs an output high-voltage detection signal when an output voltage VOUT becomes greater than a threshold voltage V2. A pulse generation unit 10 turns off the switch 6 to prevent the reverse flow of current when the input low-voltage detection signal or the output high-voltage detection signal has been output.

Description

Switching power supply

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2018-139391 filed on July 25, 2018, the contents of which are incorporated herein by reference.

The present disclosure relates to a switching power supply device that includes a series circuit of an energizing switching element and an inductor connected between a power supply and an output terminal to perform synchronous rectification.

(4) In a switching power supply device including a series circuit of a high-side switch and an inductor between a power supply and an output terminal, there is a switching power supply device that performs a synchronous rectification by providing a low-side switch, for example, as shown in Patent Document 1. The synchronous rectification method has an advantage that a loss caused by a forward voltage can be reduced as compared with a configuration in which rectification is performed by a freewheel diode.

On the other hand, when the output terminal is short-to-power, the low-side switch is turned on by feedback control, so that the current flows backward to the ground side, and an excessive current may flow through the inductor and the low-side switch.

JP 2009-171741 A

In order to prevent such a situation, for example, a configuration is conceivable in which a low-side switch is turned off when an excessive current flows by detecting a current flowing through an inductor via a shunt resistor. However, when the control unit of the switching power supply device is configured by an IC, there is a problem that a loss occurs in the shunt resistance, and an increase in external components and an increase in the number of terminals of the IC increase costs. .

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a countermeasure at the time of occurrence of short-to-power without increasing the number of external components and terminals at least when the control unit is integrated into an IC. A switching power supply device is provided.

The switching power supply device according to the present disclosure is arranged in a reverse flow path in which a current flows from the terminal to the inductor in a reverse direction when the output terminal is short-circuited, and at least one is used for performing synchronous rectification. Switching element. Hereinafter, the switching element is referred to as a backflow path switching element. The input low voltage detector outputs an input low voltage detection signal when the voltage of the power supply drops below the threshold voltage V1, and the output high voltage detector detects an output high voltage when the voltage of the output terminal rises above the threshold voltage V2. Outputs a detection signal. When the input low voltage detection signal or the output high voltage detection signal is output, the backflow prevention control unit turns off the backflow path switching element to prevent the backflow of the current.

(4) In a normal state, the voltage of the output terminal is controlled to a constant voltage by the operation of the error amplifier and the signal generator, so that the output high voltage detection signal is not output. Also, the power supply voltage may temporarily drop when supplying current to the load. At this time, when the power supply voltage falls below the threshold voltage V1, the input low voltage detection unit outputs an input low voltage detection signal. During that period, the synchronous rectification operation by the backflow path switching element is stopped.

On the other hand, if the output terminal is short-to-power, the voltage of the terminal changes in the same manner as the power supply voltage. Therefore, if the power supply voltage rises above the threshold voltage V2, the output high voltage detection unit outputs Is output. For example, in the process where the power supply voltage rises from a state lower than the threshold voltages V1 and V2, if V1 = V2, for example, the output high voltage detection signal is output following the output of the input low voltage detection signal. . Thereby, the synchronous rectification operation by the backflow path switching element is stopped by the backflow prevention control unit, so that the backflow of the current from the output terminal side to the ground can be prevented.

Here, it is assumed that the control unit excluding the switching element and the inductor is configured by an IC. In this case, the voltage of the output terminal needs to be detected by the error amplifier in order to generate the PWM signal, so that it is not necessary to increase the number of IC terminals. Therefore, the output high voltage detection unit can be configured inside the IC together with the input low voltage detection unit that detects the power supply voltage, and the same applies to the backflow prevention control unit. That is, the switching power supply device can be provided with a function to cope with short-to-power without adding external components to the IC and increasing the number of terminals of the IC.

In addition, in the switching power supply device of the present disclosure, the switching element that is turned off by the backflow prevention control unit is a synchronous rectification switching element that is connected between the common connection point of the series circuit and the ground. According to this configuration, at least in a configuration that performs a step-down switching operation, the switching element for synchronous rectification can be turned off to prevent a reverse current from flowing.

Further, the switching power supply device of the present disclosure is connected between the first boosting switching element connected between the output terminal and the inductor, and between the common connection point of the inductor and the first boosting switching element and the ground. A second boosting switching element. Then, by applying the PWM signal to the first and second boosting switching elements, the boosted voltage can be output. Therefore, in the configuration for performing the buck-boost switching operation, the reverse current path switching element is turned off to reverse the current. Can be prevented.

In the switching power supply of the present disclosure, the backflow prevention control unit turns off the first boosting switching element. Thus, in a configuration in which the step-up / step-down switching operation is performed, a reverse current can be prevented by turning off at least the first step-up switching element.

Further, since the switching power supply of the present disclosure sets the threshold voltage V1 to be higher than the threshold voltage V2, in the process in which the power supply voltage changes from a state lower than the threshold voltage V2 to exceeding the threshold voltage V1, the input low voltage The output period of the detection signal and the output period of the output high voltage detection signal surely overlap. Therefore, the backflow of the current can be more reliably prevented.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 2 is a diagram illustrating a configuration of a switching power supply device according to the first embodiment; It is a timing chart showing the operation at the time of short-to-power, It is a timing chart showing the operation at the time of normal, It is a timing chart showing the operation of only the output high voltage detection unit at the time of short-to-power, It is a timing chart showing the operation of only the input low voltage detection unit at the time of short-to-power, FIG. 9 is a timing chart showing an operation at the time of short-to-power in the second embodiment; FIG. 13 is a diagram illustrating a configuration of a switching power supply device according to a third embodiment; FIG. 14 is a diagram (part 1) illustrating a configuration of a switching power supply device and a response to occurrence of a short to power in the fourth embodiment; FIG. 11 is a diagram (part 2) illustrating a response when a short to power occurs.

(1st Embodiment)
As shown in FIG. 1, a switching power supply device 1 according to the present embodiment is mounted on, for example, a vehicle, and includes a control IC 2, an external inductor 3 and a capacitor 4. Inside the control IC 2, there is a series circuit of a high-side switch 5 and a low-side switch 6 connected between the power supply VIN and the ground. These

switches

5 and 6 correspond to switching elements, specifically, for example, MOSFETs, bipolar transistors, IGBTs and the like. In the present embodiment, these are all described as switches that are turned off when a high-level signal is supplied.

Although not shown, freewheel diodes are connected to both ends of the

switches

5 and 6, respectively. The common connection point of the

switches

5 and 6 is connected to ground via a series circuit of the inductor 3 and the capacitor 4. The common connection point of the inductor 3 and the capacitor 4 is the output terminal VOUT of the switching power supply 1. The high-side switch 5 corresponds to an energizing switching element, and the low-side switch 6 corresponds to a backflow path switching element and a synchronous rectification switching element.

{Circle around (2)} Inside the control IC 2, there are an input low voltage detection unit 7 and an output high voltage detection unit 8. The input low voltage detector 7 compares the power supply voltage VIN input to the inverting input terminal by the comparator 7a with the threshold voltage V1 applied to the non-inverting input terminal. The output high voltage detector 8 compares the output voltage VOUT input to the non-inverting input terminal by the comparator 8a with the threshold voltage V2 applied to the inverting input terminal. Output terminals of the

comparators

7a and 8a are connected to input terminals of the OR gate 9, respectively.

In this embodiment, since the power supply is a vehicle-mounted battery, the voltage VIN is, for example, about 12 to 14 V, and the set voltage of the switching power supply 1 is, for example, about 5 V. On the other hand, the threshold voltage V1 is set to, for example, about 10V, and the threshold voltage V2 is set to, for example, about 6V. That is, V1> V2 is set.

The output terminal of the OR gate 9 is connected to one of the input terminals of the pulse generator 10. The error amplifier 11 is an error amplifier that amplifies the difference between the output voltage VOUT and the set voltage, and the output voltage is input to another one of the input terminals of the pulse generator 10. The pulse generation unit 10 uses the error voltage input from the error amplification unit 11 as a PWM command, generates a PWM signal by comparing the PWM signal with a carrier, and outputs the PWM signal to the

switches

5 and 6, respectively. Basically, the PWM signal applied to the switch 6 is the inverse of the PWM signal applied to the switch 5. The switch 5 performs a step-down switching operation, and the switch 6 performs a synchronous rectification operation.

{Circle around (4)} When the signal level input from the OR gate 9 becomes high, the pulse generation unit 10 keeps the signal given to the low-side switch 6 at high level and turns off the switch 6. The pulse generation unit 10 corresponds to a backflow prevention unit.

Next, the operation of the present embodiment will be described. As shown in FIG. 3, if the output terminal VOUT is in a normal state where there is no short-to-power or the like, the output voltage VOUT is maintained at a substantially constant set voltage 5V even if the power supply voltage VIN fluctuates. The power supply voltage VIN fluctuates according to the state of current supply to the load. For example, when the engine is cranked, the power supply voltage VIN may drop to about 3V.

(4) When the power supply voltage VIN falls below the threshold voltage V1, the output signal of the input low-voltage detector 7 goes high. This high level signal corresponds to the input low voltage detection signal. As a result, the pulse generation unit 10 stops outputting the PWM signal to the low-side switch 6 and maintains the signal level at high. Then, the switch 6 maintains the off state, and the synchronous rectification operation stops. In this period, the return current flowing when the high-side switch 5 is turned off flows through the freewheel diode on the switch 6 side. “SW” in the figure indicates a period during which the switch 6 performs the synchronous rectification operation.

(4) On the other hand, when the output terminal VOUT is in the short-to-supply state, the voltage VOUT becomes equal to the power supply voltage VIN. Therefore, as shown in FIG. 2, the output voltage VOUT changes similarly to the power supply voltage VIN. When the power supply voltage VIN changes in the same manner as in the case shown in FIG. 3, in a process where the power supply voltage VIN rises from a state lower than the threshold voltage V1, V1> V2 is set, so that the input low voltage detection unit 7 The output signal of the output high voltage detector 8 changes to a high level at a timing before the output signal of the output high voltage changes to a low level. This high level signal corresponds to the output high voltage detection signal.

Further, in the process where the power supply voltage VIN decreases from a state higher than the threshold voltage V1, the output signal of the input low-voltage detector 7 is output at a timing before the output signal of the output high-voltage detector 8 changes to a low level. Change to high level. As a result, the signal supplied to the low-side switch 6 continuously goes to the high level, and the switch 6 continuously maintains the off state.

As a result, a short-to-power fault occurs, and the following current reverse flow path formed when the switch 6 is turned on is:
Power supply VIN → output terminal VOUT → inductor 3 → switch 6 → ground As shown in FIG. 1, the switch is turned off when the switch 6 is turned off. Therefore, the backflow of the current is prevented.

Here, for example, as shown in FIG. 4, when only the output high voltage detecting unit 8 is provided, when the power supply voltage VIN changes in the same manner as in the case shown in FIG. 2, the power supply voltage VIN exceeds the output set voltage. Synchronous rectification by the low-side switch 6 is performed until the voltage exceeds the threshold voltage V2. During that time, a reverse current flows. Further, when the power supply voltage VIN decreases, a reverse current similarly flows in a period from when the power supply voltage VIN falls below the threshold voltage V2 to below the output set voltage.

On the other hand, when only the input constant voltage detection unit 7 is provided as shown in FIG. 5, synchronous rectification by the low-side switch 6 is performed during a period when the power supply voltage VIN is higher than the threshold voltage V1, so that the reverse current Will flow. That is, in a configuration including only one of them, the backflow of the current cannot be appropriately prevented.

As described above, according to the present embodiment, when the output terminal VOUT is short-circuited to the switching power supply device 1, the switching power supply device 1 is disposed in the reverse flow path in which the current flows from the terminal to the inductor 3 in the reverse direction, and the step-down switching is performed. A low-side switch 6 used for performing synchronous rectification with operation is provided. The input low voltage detector 7 outputs an input low voltage detection signal when the power supply voltage VIN falls below the threshold voltage V1, and the output high voltage detector 8 outputs an output high voltage when the output voltage VOUT rises above the threshold voltage V2. Outputs a detection signal. When the input low voltage detection signal or the output high voltage detection signal is output, the pulse generation unit 10 turns off the switch 6 to prevent the current from flowing backward.

With this configuration, in a process in which the power supply voltage VIN rises from a state where the power supply voltage falls below the threshold voltage V2 when a short-to-power occurs, a period in which the voltage is higher than the threshold voltage V2 follows a period in which the voltage is lower than the threshold voltage V1. Continue. As a result, the output high voltage detection signal is output following the output of the input low voltage detection signal, so that the synchronous rectification operation by the switch 6 is stopped by the pulse generation unit 10, and the current flows backward from the output terminal VOUT to the ground side. Can be prevented.

{Circle around (2)} In the control IC 2, since the error amplifier 11 detects the output voltage VOUT to generate the PWM signal, it is not necessary to increase the number of terminals of the control IC 2. Therefore, the output high voltage detection unit 8 can be configured inside the control IC 2 together with the input low voltage detection unit 7 that detects the power supply voltage VIN, and the same applies to the pulse generation unit 10. That is, the switching power supply device 1 can be provided with a function to cope with short-to-power without adding external parts and without increasing the number of terminals of the control IC 2.

(2nd Embodiment)
Hereinafter, the same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Different portions will be described. The second embodiment shows a case where a hysteresis comparator is used for the input low-voltage detector 7 and the output high-voltage detector 8. Here, a higher voltage threshold V1 'is set for the threshold voltage V1, and a lower voltage threshold V2' is set for the threshold voltage V2. Then, the threshold voltage V1 ′ is set as a voltage detection threshold, and the threshold voltage V1 is set as a detection release threshold. The threshold voltage V2 is set as a high voltage detection threshold, and the threshold voltage V2 'is set as a detection release threshold. Further in this case,
V1 '> V2 and V1>V2' are set.

Next, the operation of the second embodiment will be described. Even when the comparators used in the detection units 7 and 8 have hysteresis characteristics in this manner, when a short-to-power occurs, the period during which the input low-voltage detection unit 7 outputs the input low-voltage detection signal and the output high-voltage detection signal are output. The period in which the voltage detection section 8 outputs the output high voltage detection signal surely overlaps. Therefore, it is possible to reliably prevent the backflow of the current when the short-to-power occurs.

(Third embodiment)
As shown in FIG. 7, the switching power supply device 21 of the third embodiment is configured as a control IC 22 in which the series circuit of the

switches

5 and 6 is removed from the control IC 2 of the first embodiment, and the series circuit is externally connected. It consists of the element of. With such a configuration, the same effect as in the first embodiment can be obtained.

(Fourth embodiment)
As shown in FIG. 8, the switching power supply device 31 of the fourth embodiment differs from the configuration of the third embodiment in that a high-side switch 35 is inserted between one end of the inductor 3 and the output terminal OUT. The low side switch 36 is connected between the power supply and the ground. The control IC 32 includes a pulse generation unit 33 instead of the pulse generation unit 10, and the pulse generation unit 33 outputs a PWM signal to the

switches

35 and 36. The

switches

35 and 36 correspond to first and second boosting switching elements, respectively. The switch 35 also corresponds to a backflow path switching element.

That is, if the

switches

5 and 6 are controlled in the state where the switch 35 is turned on and the switch 36 is turned off in the same manner as in the first to third embodiments, a step-down switching operation is performed. On the other hand, if the

switches

35 and 36 are switched while the switch 5 is turned on and the switch 6 is turned off, a step-up switching operation is performed. That is, the switching power supply device 31 has a buck-boost configuration.

With this configuration, when a short-to-power occurs, for example, as in the first to third embodiments, the switch 6 is turned off as shown in FIG. 8 to prevent a reverse current from flowing. Also, as shown in FIG. 9, turning off the switch 35 can similarly prevent the backflow of current.

As described above, according to the fourth embodiment, the switching power supply device 31 includes the high-side switch 35 connected between the output terminal VOUT and the inductor 3, the common connection point between the inductor 3 and the switch 35, and the ground. And a low-side switch 36 connected between them. Since the boosted voltage can be output by supplying the PWM signal to the

switches

35 and 36, the reverse flow path switching element can be turned off to prevent the current from flowing backward even in the configuration for performing the step-up / step-down switching operation.

Specifically, the pulse generator 33 turns off the switch 6 or the switch 35 when a short to power occurs. Accordingly, in a configuration in which the step-up / step-down switching operation is performed, the reverse current can be prevented by turning off at least the switch 35.

(Other embodiments)
The threshold voltages V1 and V2 do not necessarily need to be set to V1> V2, and may be set to at least V1 = V2.
The four switches of the fourth embodiment may be configured inside the control IC 32.
It is not limited to those mounted on vehicles.

Although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments and the structure. The present disclosure also encompasses various modifications and variations within an equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more or less, are also included in the scope and concept of the present disclosure.

Claims

A series circuit of an energizing switching element (5) and an inductor (3) connected between a power supply and an output terminal;
When the output terminal is short-to-supply, the output terminal is disposed in a reverse flow path in which current flows from the terminal in a reverse direction, and at least one of the output terminals includes one or more switching elements (6, 35) used for performing synchronous rectification. ,
An error amplifier (11) for outputting an error signal based on a deviation between the voltage of the output terminal and a target voltage;
A signal generation unit (10, 33) that generates a PWM signal based on the error signal and outputs the PWM signal to the energizing switching element;
An input low voltage detection unit (7) that outputs an input low voltage detection signal when the voltage of the power supply drops below a threshold voltage V1;
An output high voltage detection unit (8) that outputs an output high voltage detection signal when the voltage of the output terminal rises above a threshold voltage V2;
When the input low-voltage detection signal or the output high-voltage detection signal is output, a backflow prevention control unit (10, 33) that turns off a switching element disposed in the backflow path to prevent a backflow of current. A switching power supply device comprising:
The switching power supply according to claim 1, wherein the switching element turned off by the backflow prevention control unit is a synchronous rectification switching element (6) connected between a common connection point of the series circuits and a ground.
A first boosting switching element (35) connected between the output terminal and the inductor;
A second boosting switching element (36) connected between a common connection point of the inductor and the first boosting switching element and a ground, wherein the PWM signal is supplied to the first and second boosting switching elements. The switching power supply device according to claim 1, wherein a boosted voltage can be output by applying the boosted voltage to the switching element.
The switching power supply according to claim 3, wherein the switching element that is turned off by the backflow prevention control unit is the first boosting switching element.
The switching power supply device according to any one of claims 1 to 4, wherein the threshold voltage V1 is set higher than the threshold voltage V2.
A threshold value V1 'of a voltage higher than the threshold voltage V1 and a threshold value V2' of a voltage lower than the threshold voltage V2 are set, and the relationship between these threshold values is set to V1 '> V2, V1>V2'. And
The input low-voltage detection unit stops outputting the input low-voltage detection signal when the voltage of the power supply is equal to or higher than the detection release threshold V1 ′,
The switching power supply device according to any one of claims 1 to 5, wherein the output high voltage detection unit stops outputting the input high voltage detection signal when a voltage of the output terminal becomes equal to or less than the detection release threshold value V2 '. .