JP7388939B2 - switching power supply - Google Patents

Description

The present disclosure relates to a switching power supply having an overcurrent protection function.

Conventionally, a switching power supply device having an overcurrent protection function is known (see Patent Document 1). The switching power supply device 301 of Patent Document 1 includes a drive circuit 11, a feedback circuit 12, and a switching control IC 202. The switching control IC 202 outputs a rectangular wave signal to the drive circuit 11 from its OUT terminal. The feedback circuit 12 generates a feedback signal by comparing the divided voltage between the output terminals PO(+) and PO(G) with a reference voltage, and inputs the feedback signal to the feedback terminal FB of the switching control IC 202. A capacitor C4 and a Zener diode D4 are connected between the feedback terminal FB and the ground terminal GND. The Zener diode D4 is selectively connected, and the voltage at the feedback terminal FB changes depending on the presence or absence of the Zener diode D4. By detecting this voltage, it is possible to select whether the overcurrent protection operation will be a latch method or a hiccup method.

Japanese Patent Application Publication No. 2011-182537

Patent Document 1 does not take into consideration the time until the overcurrent protection operation is performed. Therefore, if the transition time to hiccup operation is long when the output current is excessive, such as during an output short circuit, it is necessary to select an inductor that takes heat generation due to overcurrent into consideration. Therefore, the inductor becomes larger and the switching power supply device may become larger.

The present disclosure has been made in view of the above circumstances, and provides a switching power supply that can reduce the size of the inductor included in the switching power supply, taking heat generation due to overcurrent into consideration.

One aspect of the present disclosure is a switching power supply, which includes a transistor for controlling an output voltage of the switching power supply, a control circuit for controlling on/off of the transistor, and a current detection circuit for detecting a current flowing through the transistor. , until the output voltage of the transistor starts an overcurrent protection operation to protect the switching power supply from the overcurrent based on the feedback voltage when the current is an overcurrent that is equal to or higher than a threshold current. and a protection circuit that performs the overcurrent protection operation by switching the transition time of the switching power supply.

According to the present disclosure, it is possible to reduce the size of an inductor included in a switching power supply by taking heat generation due to overcurrent into consideration.

A configuration diagram showing an example of a switching power supply in an embodiment Block diagram showing a first configuration example of the first protection control circuit Waveform diagram for explaining the first operation example of the first protection control circuit Waveform diagram for explaining the second operation example of the first protection control circuit Block diagram showing a second configuration example of the first protection control circuit Waveform diagram for explaining the third operation example of the first protection control circuit Waveform diagram for explaining the fourth operation example of the first protection control circuit Block diagram showing a third configuration example of the first protection control circuit

Hereinafter, an embodiment (hereinafter referred to as "this embodiment") specifically disclosing a switching power supply according to the present disclosure will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially the same configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

FIG. 1 is a configuration diagram showing an example of a switching power supply in an embodiment of the present disclosure.

The switching power supply 1 is a step-down switching power supply in which a coil L1, a Schottky barrier diode SBD1, and a capacitor _COUT are externally connected to a power supply IC5. In the step-down switching power supply 1, a coil L1 and a capacitor _COUT are connected in series to a terminal SW1. A resistor _RESR is connected between the coil L1 and the capacitor _COUT . A load 3 is connected to the coil L1. Resistors R _B1 and R _B2 are connected in series to the coil L1 in parallel with the load 3. A connection point between the resistor R _B1 and the resistor R _B2 is connected to the error amplifier 20 via a terminal FB1 serving as a feedback terminal of the power supply IC 5. The load 3 may be a non-inductive load such as a lamp or an inductive load such as a motor.

In the switching power supply 1, an input voltage _VIN is supplied from the DC power supply 2 to the terminal VIN1 of the power supply IC5 via the power line LN. A bypass capacitor _CIN is connected to the power line LN in parallel with the power supply IC5.

Switching power supply 1 converts voltage. The power supply IC 5 of the switching power supply 1 includes, for example, a transistor MP, a soft start circuit 10, an error amplifier 20, a PWM comparator 30, an FF (Flip-Flop) circuit 40, a first protection control circuit 50, and a logic circuit. It includes a circuit 60, a current detection circuit 70, a second protection control circuit 80, a slope compensation circuit 90, and an adder 95. The power supply IC 5 is an example of an integrated circuit. The first protection control circuit 50 and the logic circuit 60 constitute a protection circuit that determines information regarding overcurrent protection operation and executes the overcurrent protection operation. The soft start circuit 10, error amplifier 20, PWM comparator 30, FF circuit 40, and logic circuit 60 constitute a control circuit that controls on/off of the transistor MP.

The transistor MP is, for example, a PMOS transistor (also simply referred to as "PMOS"). The output voltage of the logic circuit 60 is applied to the transistor MP as a gate voltage. The transistor MP has a source connected to the terminal VIN1 and a drain connected to the terminal SW1. The source of transistor MP is connected to the back gate. When transistor MP is turned on, current from DC power supply 2 flows through transistor MP, coil L1, and capacitor C _OUT to charge capacitor C _OUT .

After the switching power supply 1 is started, the soft start circuit 10 controls the PWM comparator 30 to gradually increase the output voltage V _OUT . The operating period of the switching power supply 1 is divided into a soft start period and a steady period that continues after the end of the soft start period, depending on the output of the soft start circuit 10. In the steady period, steady PWM control is performed. The soft start circuit 10 limits the duty ratio for converting the voltage in the PWM comparator 30 during the soft start period. Soft start circuit 10 is connected to a non-inverting input terminal of error amplifier 20.

The error amplifier 20 is a differential amplifier that amplifies the difference between the reference voltage V _REF input to the non-inverting input terminal and the feedback voltage V _FB of the terminal FB1 input to the inverting input terminal. Therefore, the output voltage of the error amplifier 20 is proportional to the difference between the reference voltage V _REF and the feedback voltage V _FB . The reference voltage V _REF is set to be a voltage lower than the set voltage. The larger the difference between the reference voltage V _REF and the feedback voltage V _FB (that is, the closer the output voltage V _OUT is to the value 0), the larger the output voltage of the error amplifier 20 becomes. The smaller the difference between the reference voltage V _REF and the feedback voltage V _FB (that is, the closer the output voltage V _OUT is to the set voltage), the smaller the output voltage of the error amplifier 20 becomes. Since the error amplifier 20 operates as a negative feedback circuit, it controls the voltage so as to maintain the feedback voltage V _FB at the reference voltage V _REF , that is, to maintain the output voltage V _OUT at the set voltage. Furthermore, during the soft start period, the error amplifier 20 limits the output voltage of the error amplifier 20 by using the voltage of the SST signal from the soft start circuit 10 as the reference voltage V _REF . The SST signal is a signal for controlling the duty used in PWM during the soft start period.

Further, a phase compensation circuit may be arranged between the inverting input terminal and the output terminal of the error amplifier 20. The phase compensation circuit is, for example, a circuit in which a phase compensation capacitor 21 and a resistor 22 are connected in series. A phase compensation circuit is used to stabilize the voltage feedback loop.

The PWM comparator 30 inputs the output voltage of the adder 95 to its non-inverting input terminal, and inputs the output voltage of the error amplifier 20 to its inverting input terminal. The PWM comparator 30 determines the duty ratio for converting the voltage based on the output voltage of the adder 95 and the output voltage of the error amplifier 20. The PWM comparator 30 outputs an output voltage including the determined duty ratio to the FF circuit 40.

The FF circuit 40 receives a clock signal OSC from an oscillator (OSC) and the output voltage of the PWM comparator 30. The clock signal is used to determine the period of the PWM signal. The PWM signal is indicated by a high voltage and a low voltage. The High voltage and Low voltage of the PWM signal are based on the period and duty ratio of the PWM signal. The FF circuit 40 is set by the output voltage of the oscillation circuit (voltage of the clock signal OSC), reset by the output voltage of the PWM comparator 30, and outputs a PWM signal to the logic circuit 60. The FF circuit 40 is, for example, an RS flip-flop. For example, the higher the output voltage of the error amplifier 20, the greater the duty ratio of the PWM signal, and the greater the output voltage V _OUT of the switching power supply 1. The lower the output voltage of the error amplifier 20, the smaller the duty ratio of the PWM signal, and the smaller the output voltage V _OUT . The PWM signal is, for example, a pulse signal.

The first protection control circuit 50 performs processing related to overcurrent protection. The first protection control circuit 50 inputs the feedback voltage V _FB and performs various overcurrent protection operations based on the feedback voltage V _FB . This overcurrent protection operation includes hiccup operation, latch operation, and the like. The first protection control circuit 50 outputs a first protection control signal for performing an overcurrent protection operation to the logic circuit 60. The first protection control signal is indicated by a high voltage and a low voltage. The fact that the first protection control signal is at a high voltage corresponds to instructing the logic circuit 60 to stop the on/off control of the transistor MP.

In hiccup operation, when an excessively low feedback voltage V _FB (voltage below threshold voltage th1) corresponding to overcurrent is detected, on/off control of transistor MP is stopped, transistor MP is turned off, and after a certain period of time, the transistor MP is turned off. This is an operation of restarting on/off control of transistor MP and restarting voltage supply. The hiccup operation may be performed repeatedly, that is, the on/off control of transistor MP may be stopped and restarted repeatedly. The latch operation is an operation in which the on/off control of the transistor MP is stopped, the transistor MP is turned off, and the on/off control of the transistor MP is not resumed even after a certain period of time has elapsed.

Further, the first protection control circuit 50 determines detailed methods regarding hiccup operation and latch operation. In this detailed method, select hiccup operation or latch operation as overcurrent protection operation, transition time to hiccup operation or latch operation as overcurrent protection operation, and latch operation after hiccup operation. Decide whether to migrate or not. The transition time may be substituted by the count number of the PWM signal as a pulse signal. When measuring time, the first protection control circuit 50 may acquire the PWM signal from the FF circuit 40 and count by referring to the state of the PWM signal. Details of the first protection control circuit 50 will be described later.

The logic circuit 60 performs a level shift operation, a protection operation, a stop operation, and the like. In the level shift operation, the logic circuit 60 converts the PWM signal input to the logic circuit 60 into a signal at a level that drives the transistor MP, and outputs the level-shifted PWM signal to the transistor MP. In the protection operation, the logic circuit 60 protects the device (eg, transistor MP) by suppressing heating or the like to the device. In the stop operation, the logic circuit 60 stops the driver that drives the transistor MP and does not transmit the level-shifted PWM signal to the transistor MP. That is, in the stop operation, the logic circuit 60 stops the on/off control of the transistor MP, and turns the transistor MP into an off state.

Furthermore, in the protection operation or stop operation, the logic circuit 60 performs an overcurrent protection operation based on the output signal of the first protection control circuit 50 and the output signal of the second protection control circuit 80. In the overcurrent protection operation, on/off control of transistor MP is stopped, and transistor MP is turned off. This overcurrent protection operation may include a hiccup operation and a latch operation. When the output signal of the second protection control circuit 80 indicates an overcurrent, the logic circuit 60 performs a hiccup operation or a latch operation based on the first protection control signal output from the first protection control circuit 50. good.

The current detection circuit 70 detects a sense current corresponding to the drain current flowing through the transistor MP, and outputs a current detection signal indicating the detection result to the second protection control circuit 80 and the adder 95.

The second protection control circuit 80 outputs an OCP signal indicating the presence or absence of overcurrent to the logic circuit 60. The OCP signal is indicated by a high voltage and a low voltage. When the second protection control circuit 80 detects that the sense current is an overcurrent (also simply referred to as overcurrent detection), that is, the detection current detected by the current detection circuit 70 is a threshold current for detecting overcurrent. If it is greater than or equal to Ith, the second protection control circuit 80 sets the voltage of the OCP signal to High. When the second protection control circuit 80 detects that the sense current is not an overcurrent, the second protection control circuit 80 sets the voltage of the OCP signal to Low. Further, when the on/off control of the transistor MP is restarted in the hiccup operation after the voltage of the OCP signal becomes High, the second protection control circuit 80 sets the voltage of the OCP signal to Low (see FIG. 3, etc.).

Furthermore, when the second protection control circuit 80 detects that the sense current is an overcurrent, it instructs the logic circuit 60 to perform a pulse-by-pulse operation based on the sense current. The pulse-by-pulse operation is an operation in which the transistor MP is controlled to be turned off within the period of the overcurrent pulse among the pulses for performing PWM control. Then, when the PWM signal turns on according to the clock signal, the transistor MP is turned on again. The logic circuit 60 limits on/off control of the transistor MP to perform pulse-by-pulse operation in response to instructions from the logic circuit 60.

Further, the second protection control circuit 80 notifies the first protection control circuit 50 that overcurrent has been detected. This allows the first protection control circuit 50 to measure, for example, the time elapsed since overcurrent detection.

Slope compensation circuit 90 outputs a slope compensation signal for performing slope compensation to adder 95. The slope compensation signal is, for example, a signal with a predetermined ramp waveform. Adder 95 adds the slope compensation signal from slope compensation circuit 90 and the current detection signal from current detection circuit 70, and outputs the added signal to the non-inverting input terminal of PWM comparator 30. By adding an addition signal based on the slope compensation signal, it is possible to stabilize PWM control.

Next, a specific example of the configuration of the first protection control circuit 50 and an example of its operation will be described. Here, the first protection control circuit 50 of the first configuration example is also referred to as the first protection control circuit 50A, the first protection control circuit 50 of the second configuration example is also referred to as the first protection control circuit 50B, and the third configuration example The example first protection control circuit 50 is also referred to as a first protection control circuit 50C. Note that each configuration example and at least a portion of each operation according to each configuration example may be combined.

FIG. 2 is a block diagram showing a configuration example of the first protection control circuit 50A. FIG. 3 is a waveform diagram for explaining a first operation example of the first protection control circuit 50A. FIG. 4 is a waveform diagram for explaining a second operation example of the first protection control circuit 50A.

The first protection control circuit 50A performs a hiccup operation as an overcurrent protection operation. The first protection control circuit 50A changes the transition time until transition to hiccup operation based on the feedback voltage V _FB . Here, the operating range of the overcurrent protection operation differs depending on the voltage range of the feedback voltage _VFB . For example, the first overcurrent protection operating area (1st OCP area in FIG. 3) is an operating area when the feedback voltage V _FB is less than the reference voltage Vref1 and greater than or equal to the reference voltage Vref2. Reference voltage Vref1 is higher than reference voltage Vref2. The second overcurrent protection operating area (2nd OCP area in FIG. 4) is an operating area where the feedback voltage V _FB is less than the reference voltage Vref2. In the first overcurrent protection operation region, the transition time from detecting that the sense current is an overcurrent to transitioning to hiccup operation is set to transition time T1. Therefore, the transition time can also be said to be the elapsed time from the time of overcurrent detection. In the second overcurrent protection operation region, the above transition time is set to transition time T2. Transition time T2 is shorter than transition time T1.

The first protection control circuit 50A includes a comparator 51, a comparator 52, and a count control circuit 53. The count number is the number of pulses of the PWM signal from when an overcurrent is detected until an overcurrent protection operation (hiccup operation or latch operation) is performed.

The comparator 51 compares the feedback voltage V _FB and the reference voltage Vref1, and outputs a High voltage when the feedback voltage V _FB is greater than or equal to the reference voltage Vref1, and outputs a High voltage when the feedback voltage V _FB is less than the reference voltage Vref1. Outputs low voltage. The comparator 52 compares the feedback voltage V _FB and the reference voltage Vref2, and outputs a High voltage when the feedback voltage V _FB is greater than or equal to the reference voltage Vref2, and outputs a High voltage when the feedback voltage V _FB is less than the reference voltage Vref2. Outputs low voltage.

The count control circuit 53 receives the output voltages of the comparators 51 and 52 as input. The count control circuit 53 determines the count number of the PWM signal corresponding to the transition time until transition to hiccup operation based on the output voltages of the comparators 51 and 52.

The count control circuit 53 measures the elapsed time since overcurrent detection. In this case, the count control circuit 53 counts the number of pulses of the PWM signal corresponding to the elapsed time since overcurrent detection. The count control circuit 53 determines the voltage of the first protection control signal sent to the logic circuit 60 depending on whether or not the transition time has elapsed, and outputs the first protection control signal to the logic circuit 60. The first protection control signal has a low voltage until the transition time has elapsed, and has a high voltage after the transition time has elapsed. That is, when the count number of pulses of the PWM signal reaches a predetermined count number (the count number corresponding to the transition time), the count number control circuit 53 changes the voltage of the first protection control signal from Low to High.

The logic circuit 60 sets the logic signal to High voltage when the acquired first protection control signal is High voltage and the acquired OCP signal is High voltage. The logic signal here indicates whether or not to perform a stop operation for overcurrent protection operation. When the voltage of the logic signal is High, the logic circuit 60 operates to stop. When the voltage of the logic signal is Low, the logic circuit 60 does not stop.

In addition, since the overcurrent protection operation here is a hiccup operation, the count control circuit 53 measures the elapsed time from the stop operation instruction, and when a predetermined time has elapsed from the start of the stop operation, the first protection control circuit 53 outputs the first protection control signal. The voltage is changed from High to Low and output to the logic circuit 60. When the logic circuit 60 detects that the voltage of the first protection control signal is Low, it switches the voltage of the logic signal from High to Low. Then, the logic circuit 60 performs a restart operation to restart the transmission of the level-shifted PWM signal to the transistor MP in order to restart the on/off control of the transistor MP.

On the other hand, when the voltage of at least one of the acquired first protection control signal and the acquired OCP signal is a Low voltage, the logic circuit 60 sets the voltage of the logic signal to Low. In this case, the logic circuit 60 performs on/off control of the transistor MP and outputs a level-shifted PWM signal.

Specifically, when the output voltage of the comparator 51 is a High voltage and the output voltage of the comparator 52 is a High voltage, the count number control circuit 53 sets the first protection control signal to a Low voltage and outputs the logic circuit 60. send to In this case, the logic circuit 60 outputs a level-shifted PWM signal without performing an overcurrent protection operation.

Furthermore, when the output voltage of the comparator 51 is a low voltage and the output voltage of the comparator 52 is a high voltage, the count control circuit 53 instructs to perform the hiccup operation in the first overcurrent protection operation region. In other words, an instruction is given to perform the hiccup operation after a transition time T1 from overcurrent detection. In this case, the count control circuit 53 changes the voltage of the first protection control signal to High and sends it to the logic circuit 60 after a transition time T1 from overcurrent detection. In the voltage range included in the first overcurrent protection operation region, the transition time T1 may be constant regardless of the voltage. In this case, the logic circuit 60 outputs the level-shifted PWM signal until the transition time T1 elapses, then performs a stop operation, and then performs a restart operation.

Further, when the output voltage of the comparator 51 is a low voltage and the output voltage of the comparator 52 is a low voltage, the count control circuit 53 instructs to perform the hiccup operation in the second overcurrent protection operation region. In other words, an instruction is given to perform the hiccup operation after a transition time T2 from overcurrent detection. In this case, the count control circuit 53 changes the voltage of the first protection control signal to High and sends it to the logic circuit 60 after a transition time T2 from overcurrent detection. In the voltage range included in the second overcurrent protection operation region, the transition time T2 may be constant regardless of the voltage. In this case, the logic circuit 60 outputs the level-shifted PWM signal and operates until the transition time T2 has elapsed, then performs a stop operation, and then performs a restart operation.

In the hiccup operation, when restarting, for example, a soft start is performed. In the hiccup operation, after repeating the stopping and restarting operations of the logic circuit 60, that is, stopping and restarting the on/off control of the transistor MP, for a predetermined number of times, the on/off control of the transistor MP may be ended and the transistor MP may be turned off.

Note that in the first protection control circuit 50A, a latch operation may be taken into consideration instead of a hiccup operation. In other words, although the transition time until the hiccup operation is started in stages based on the feedback voltage V _FB is set, the transition time until the latch operation is started in stages based on the feedback voltage V _FB is set as an example. May be set.

Note that the transition time may exist in three or more stages instead of two stages. In this case, three or more comparators may be provided.

In FIG. 3, when the feedback voltage V _FB is included in the first voltage range that is the first overcurrent protection operating region, and the feedback voltage V _FB does not fall to the second voltage range that is the second overcurrent protection operating region. is shown. Note that "VFB" indicates the voltage at the terminal FB1 and corresponds to the feedback voltage _VFB . "VSW" indicates the voltage at terminal SW1. "ISW" indicates a current flowing through the terminal SW1, and corresponds to a sense current. This also applies to FIGS. 4, 6, and 7, which will be described later.

In FIG. 3, the second protection control circuit 80 detects that the current ISW corresponding to the sense current is an overcurrent equal to or higher than the threshold current Ith, and outputs the OCP signal to a high voltage to the logic circuit 60. The logic circuit 60 performs a pulse-by-pulse operation in response to the OCP signal being at a high voltage. Further, the time when the feedback voltage V _FB starts to decrease due to overcurrent (the time when the first overcurrent protection operation region starts) and the time when the overcurrent starts to be detected by the current detection circuit 70 are the same timing. I am assuming that. Note that these times do not have to be at the same timing. The pulse-by-pulse operation also lengthens the low voltage period of the PWM signal, so it can be expected that the output voltage V _OUT of the switching power supply 1, that is, the feedback voltage V _FB will decrease.

The first protection control circuit 50A measures a transition time T1 used in the first overcurrent protection operation region, and outputs the first protection control signal to a high voltage to the logic circuit 60 after the transition time T1 has elapsed. When the logic circuit 60 detects that the first protection control signal is High, it sets the logic signal to High voltage and starts a hiccup operation, that is, it temporarily stops the on/off control of the transistor MP and turns off the transistor MP for a certain period of time. Let it be.

The first protection control circuit 50A measures the elapsed time from the start of the hiccup operation, turns off the transistor MP for a certain period of time, and then outputs the first protection control signal to a low voltage to the logic circuit 60. When the logic circuit 60 detects that the first protection control signal is Low, it sets the logic signal to Low voltage and restarts the on/off control of the transistor MP by soft start.

The transition time T1 corresponds to, for example, a time corresponding to 20 cycles of the clock signal, that is, a time corresponding to a count of 20 pulses of the PWM signal (1/fsoc×20). In FIG. 3, the feedback voltage V _FB further decreases within the transition time T1 and does not reach the second overcurrent protection operating region. Therefore, the count number control circuit 53 of the first protection control circuit 50A does not reset the pulse counter of the PWM signal or change the transition time T1 to the transition time T2 (change the count number).

The transition time T2 corresponds to, for example, the transition time to the conventional hiccup motion. The transition time T1 is set longer than the transition time T2. Therefore, for example, in the case of a transient response of the load 3, it is considered that the decrease in the feedback voltage _VFB is eliminated within the transition time T1. In this case, the switching power supply 1 can suppress execution of a hiccup operation every time a load transient response occurs while realizing overcurrent protection.

In FIG. 4, the feedback voltage V _FB is included in the first voltage range that is the first overcurrent protection operating region, and the feedback voltage V _FB falls to the second voltage range that is the second overcurrent protection operating region. It is shown. Note that in FIG. 4, descriptions of items similar to those in FIG. 3 will be omitted or simplified.

The first protection control circuit 50A detects that the feedback voltage V _FB has decreased to the second voltage range before the transition time T1 used in the first overcurrent protection operation region has elapsed. In this case, since the output voltage of the comparator 51 is a low voltage and the output voltage of the comparator 52 is a low voltage, the count control circuit 53 changes the transition time until the hiccup operation from the transition time T1 to the transition time T2. change. In other words, the count control circuit 53 changes the transition time to T2 in accordance with the feedback voltage _VFB even if it is in the middle of counting the transition time T1. After the changed transition time T2 has elapsed, the first protection control circuit 50A starts the hiccup operation, that is, temporarily stops the on/off control of the transistor MP and turns off the transistor MP for a certain period of time.

The first protection control circuit 50A measures the elapsed time from the start of the hiccup operation, and outputs the first protection control signal to a low voltage to the logic circuit 60 after the transistor MP is turned off for a certain period of time. When the logic circuit 60 detects that the first protection control signal is Low, it sets the logic signal to Low voltage and restarts the on/off control of the transistor MP by soft start.

As in the case of FIG. 3, the transition time T1 corresponds to, for example, the time for counting 20 pulses of the PWM signal. The transition time T2 corresponds to, for example, a time corresponding to 15 periods of the clock signal, that is, a time corresponding to 15 pulse counts of the PWM signal (1/fsoc×15). Note that the change from the transition time T1 to the transition time T2 may be made by resetting the counter or changing the count number. In other words, the count control circuit 53 may continue counting until the changed transition time T2, taking into consideration the count counted up to the time of switching the transition time, or may continue counting until the transition time T2 is changed. The changed transition time T2 may be counted from the value 0 by resetting without considering the count number.

In this way, by changing (in this case shortening) the transition time to hiccup operation in stages, when the drop in feedback voltage V _FB is relatively small, the degree of overcurrent is relatively small, so coil L1 The amount of heat generated does not increase too much. Therefore, overcurrent protection can be achieved even if there is some time until the hiccup operation starts. On the other hand, when the decrease in the feedback voltage V _FB becomes relatively large, the degree of overcurrent is relatively large, and therefore the amount of heat generated by the coil L1 becomes large. Therefore, the switching power supply 1 can realize overcurrent protection by shortening the time until the start of hiccup operation. In this way, the switching power supply 1 can flexibly change the method of overcurrent protection operation according to the voltage range to which the feedback voltage _VFB , which can change over time, belongs.

Note that the switching power supply 1 may extend the transition time to the hiccup operation instead of shortening the transition time. For example, the switching power supply 1 may extend the transition time when the drop in the feedback voltage V _FB becomes smaller.

FIG. 5 is a block diagram showing a configuration example of the first protection control circuit 50B. FIG. 6 is a waveform diagram for explaining a first operation example of the first protection control circuit 50B. FIG. 7 is a waveform diagram for explaining a second operation example of the first protection control circuit 50B. Note that in FIGS. 5 to 7, descriptions of the same items as in FIGS. 2 to 4 will be omitted or simplified.

The first protection control circuit 50B performs a hiccup operation and a latch operation as overcurrent protection operations. The first protection control circuit 50B selects hiccup operation or latch operation based on the feedback voltage V _FB . The first protection control circuit 50B may switch between hiccup operation and latch operation based on the feedback voltage V _FB . Note that the hiccup operation is selected in the first overcurrent protection operation area (OCP area), and the latch operation is selected in the second overcurrent protection operation area (Latch area). Further, in the first overcurrent protection operation region, the transition time is set to T3, and in the second overcurrent protection operation region, the transition time is set to T4. Transition time T3 is shorter than transition time T4. Note that the transition times T3 and T4 may be the same length. The transition time T3 is an example of the transition time T1. The transition time T4 is an example of the transition time T2.

The first protection control circuit 50B includes a comparator 54, a comparator 55, and a mode selection circuit 56.

Comparator 54 compares feedback voltage V _FB and reference voltage Vref3, and outputs a High voltage when feedback voltage V _FB is greater than or equal to reference voltage Vref3, and outputs a High voltage when feedback voltage V _FB is less than reference voltage Vref3. Outputs low voltage. Comparator 55 compares feedback voltage V _FB and reference voltage Vref4, and outputs a High voltage when feedback voltage V _FB is greater than or equal to reference voltage Vref4, and outputs a High voltage when feedback voltage V _FB is less than reference voltage Vref4. Outputs low voltage. Note that the reference voltage Vref3 is higher than the reference voltage Vref4. Note that the reference voltage Vref1 and the reference voltage Vref3 may be the same, and the reference voltage Vref2 and the reference voltage Vref4 may be the same.

The mode selection circuit 56 inputs the output voltages of the comparators 54 and 55. The mode selection circuit 56 selects and determines an operation mode for overcurrent protection operation based on the output voltages of the comparators 54 and 55. The operating modes may include a hiccup mode of operation and a latching mode of operation.

Specifically, when the output voltage of the comparator 54 is a high voltage and the output voltage of the comparator 55 is a high voltage, the mode selection circuit 56 performs neither a hiccup operation nor a latch operation as an overcurrent protection operation. instruct them to do so. In this case, the mode selection circuit 56 makes the first protection control signal a Low voltage and outputs it to the logic circuit 60. Since the first protection control signal has a low voltage, the logic circuit 60 does not perform a stopping operation and outputs a level-shifted PWM signal.

Furthermore, when the output voltage of the comparator 54 is a low voltage and the output voltage of the comparator 55 is a high voltage, the mode selection circuit 56 performs a hiccup operation as an overcurrent protection operation in the first overcurrent protection operation region. instruct. In this case, the mode selection circuit 56 instructs to perform the hiccup operation after a transition time T3 from overcurrent detection. That is, the mode selection circuit 56 changes the voltage of the first protection control signal to High and sends it to the logic circuit 60 after the transition time T3 from overcurrent detection. In the voltage range included in the first overcurrent protection operation region, the transition time T3 may be constant regardless of the voltage. In this case, the logic circuit 60 outputs the level-shifted PWM signal until the transition time T3 has elapsed, then performs a stop operation, and then performs a restart operation.

Furthermore, when the output voltage of the comparator 54 is a low voltage and the output voltage of the comparator 55 is a low voltage, the mode selection circuit 56 performs a latch operation as an overcurrent protection operation in the second overcurrent protection operation region. Instruct. In other words, the mode selection circuit 56 instructs to perform the hiccup operation after the transition time T4 from overcurrent detection. That is, the mode selection circuit 56 changes the voltage of the first protection control signal to High and sends it to the logic circuit 60 after the transition time T4 from the overcurrent detection. In the voltage range included in the second overcurrent protection operation region, the transition time T4 may be constant regardless of the voltage. In this case, the logic circuit 60 outputs the level-shifted PWM signal until the transition time T4 has elapsed, and then performs a stop operation.

In FIG. 6, the feedback voltage V _FB is included in the first voltage range that is the first overcurrent protection operating region, and the feedback voltage V _FB falls to the second voltage range that is the second overcurrent protection operating region. It is shown. Further, the transition time T4 has a certain length. Note that in FIG. 6, descriptions of the same items as those in FIGS. 3 and 4 will be omitted or simplified.

The first protection control circuit 50B detects that the feedback voltage V _FB has decreased to the second voltage range before the transition time T3 used in the first overcurrent protection operation region has elapsed. In this case, since the output voltage of the comparator 54 is a low voltage and the output voltage of the comparator 55 is a low voltage, the mode selection circuit 56 changes the transition time until the hiccup operation from the transition time T3 to the transition time T4. do. Further, the mode selection circuit 56 changes the operation mode from hiccup operation to latch operation. That is, even if the transition time T3 is in the middle of counting, the mode selection circuit 56 changes the transition time to T4 according to the feedback voltage _VFB and also changes the operation mode. After the changed transition time T4 has elapsed, the first protection control circuit 50B starts the latch operation, that is, stops the on/off control of the transistor MP and turns off the transistor MP.

The transition time T3 corresponds to, for example, the time for counting 20 pulses of the PWM signal. The transition time T4 corresponds to, for example, a time corresponding to five cycles of the clock signal, that is, a time corresponding to five pulse counts of the PWM signal (1/fsoc×5). Note that the change from the transition time T3 to the transition time T4 may be made by resetting the counter or changing the count number.

When the decrease in the feedback voltage _VFB is relatively small, the degree of overcurrent is relatively small, so the amount of heat generated by the coil L1 does not increase very much. Therefore, the switching power supply 1 can suppress overcurrent even if the on/off control of the transistor MP is repeatedly stopped and restarted due to the hiccup operation. On the other hand, when the decrease in the feedback voltage V _FB becomes relatively large, the degree of overcurrent is relatively large, and therefore the amount of heat generated by the coil L1 becomes large. Therefore, by changing the hiccup operation to the latch operation, the switching power supply 1 does not restart the on/off control of the transistor MP, so that overcurrent can be further suppressed. In this manner, the switching power supply 1 can flexibly change the type of overcurrent protection operation according to the voltage range to which the feedback voltage _VFB , which can change over time, belongs.

Note that the switching power supply 1 may switch from the latch operation mode to the hiccup operation mode instead of switching from the hiccup operation mode to the latch operation mode based on the feedback voltage V _FB .

In FIG. 7, the feedback voltage V _FB is included in the first voltage range that is the first overcurrent protection operating region, and the feedback voltage V _FB falls to the second voltage range that is the second overcurrent protection operating region. It is shown. Further, the transition time T4 has a value of 0. Note that in FIG. 6, descriptions of items similar to those in FIGS. 3, 4, and 6 will be omitted or simplified.

The first protection control circuit 50B detects that the feedback voltage V _FB has decreased to the second voltage range before the transition time T3 used in the first overcurrent protection operation region has elapsed. In this case, since the output voltage of the comparator 54 is a low voltage and the output voltage of the comparator 55 is a low voltage, the mode selection circuit 56 changes the transition time until the hiccup operation from the transition time T3 to the transition time T4. and changes the operation mode from hiccup operation to latching operation. Here, since the transition time T4 has a value of 0, the voltage of the first protection control signal is made High and output to the logic circuit 60 immediately after the operation mode is changed to the latch operation. The logic circuit 60 operates to stop according to the acquired first protection control signal.

In this way, when the feedback voltage V _FB decreases significantly due to overcurrent, the transition time T4=0 allows the switching power supply 1 to quickly keep the transistor MP off, thereby preventing overcurrent protection. It can be expected that the effectiveness will improve.

FIG. 8 is a block diagram showing a configuration example of the first protection control circuit 50C. Note that in FIG. 8, descriptions of items similar to those in FIGS. 2 to 7 will be omitted or simplified.

The first protection control circuit 50C includes a timer 57. The timer 57 sets a transition time T5 until transition to hiccup operation based on the feedback voltage _VFB . Unlike the first protection control circuit 50A, the first protection control circuit 50C does not set a threshold voltage and change the transition time T5 in stages, but changes the transition time T5 smoothly without setting a threshold voltage. . Therefore, the timer 57 sets the transition time T5 longer as the feedback voltage V _FB is higher, and sets the transition time T5 shorter as the feedback voltage V _FB is lower. The transition time T5 may be set by the number of pulses of the PWM signal.

The timer 57 measures the elapsed time (for example, the number of pulses of the PWM signal) since the overcurrent detection, and instructs the hiccup operation to be performed after the set transition time T5 has elapsed. In this case, the logic circuit 60 outputs the level-shifted PWM signal until the transition time T5 has elapsed, then performs a stop operation, and then performs a restart operation. Note that when the feedback voltage V _FB is high, for example equal to the set voltage, the transition time T5 is maximum. The maximum transition time T5 may include not transitioning to hiccup motion. The minimum transition time T5 may include transitioning to hiccup operation with the transition time T5 having a value of 0.

In this way, in the switching power supply 1, for example, when the first protection control circuit 50 has the configuration of the first configuration example, when the amount of decrease in the feedback voltage _VFB is small, that is, when the degree of overcurrent is small, Increase the time it takes to stop during hiccup motion. Furthermore, when the amount of decrease in the feedback voltage V _FB is large, that is, when the degree of overcurrent is large, the time until the hiccup operation stops is shortened. Therefore, the amount of heat generated by the coil L1 in response to overcurrent can be reduced, and the size of the coil L1 can be reduced. Further, when a small overcurrent such as noise occurs, by lengthening the transition time, there is a possibility that the hiccup operation does not need to be stopped. Therefore, the period during which the output voltage VOUT drops unnecessarily can be reduced, and the output voltage VOUT can be stably supplied to the load 3.

Note that the present invention is applicable not only to the case where the timer 57 is used to shift to the hiccup operation, but also to the case where the timer 57 is used to shift to the latch operation.

As described above, the switching power supply 1 of the present embodiment includes a transistor MP for controlling the output voltage of the switching power supply 1, a control circuit for controlling on/off of the transistor MP, and a current detector for detecting the current flowing through the transistor MP. It includes a circuit 70 and a protection circuit. The protection circuit protects the switching power supply 1 from the overcurrent flowing through the transistor MP based on the feedback voltage _VFB to which the output voltage of the transistor MP is fed back when the current is an overcurrent that is equal to or higher than the threshold current Ith. The overcurrent protection operation is executed by switching the transition time until starting the overcurrent protection operation or the operation mode of the overcurrent protection operation. The protection circuit includes, for example, a first protection control circuit 50, a second protection control circuit 80, and a logic circuit 60. The control circuit includes, for example, a soft start circuit 10, an error amplifier 20, a PWM comparator 30, an FF circuit 40, and a logic circuit 60.

When an overcurrent occurs in transistor MP, feedback voltage V _FB may decrease. When the feedback voltage V _FB decreases, the switching power supply 1 performs an overcurrent protection operation to limit the on state of the transistor MP in order to protect from overcurrent. At this time, the switching power supply 1 can adjust the time until the on/off control of the transistor MP is stopped according to the feedback voltage V _FB . Alternatively, the switching power supply 1 can perform an overcurrent protection operation corresponding to the output voltage VOUT by switching the operation mode of the overcurrent protection operation, and can suppress overcurrent. Therefore, the switching power supply 1 can suppress the amount of heat generated by the coil L1 (inductor) due to overcurrent, the size of the coil L1 can be reduced, and the switching power supply 1 can be downsized when mounted on a board or the like.

Further, the protection circuit may perform an overcurrent protection operation that stops the on/off control of the transistor MP and turns the transistor MP into an OFF state.

Thereby, the switching power supply 1 can forcibly turn off the transistor MP, and can suppress overcurrent.

Furthermore, the higher the feedback voltage _VFB , the longer the transition time may be. The lower the feedback voltage _VFB , the shorter the transition time.

Thereby, when the amount of decrease of the feedback voltage V _FB from the set voltage is small, the switching power supply 1 can suppress, for example, noise or the like from being simulated as an overcurrent and stopping the on/off control of the transistor MP. In other words, it is possible to suppress unnecessary overcurrent protection operations from being performed. Furthermore, if the amount of decrease of the feedback voltage V _FB from the set voltage is large, it is assumed that there is a large overcurrent, which is a highly dangerous state. In this case, the switching power supply 1 can quickly escape from the highly dangerous state by quickly limiting the PWM control. Therefore, the switching power supply 1 can be adjusted so that the amount of overcurrent, taking time into account, is constant, for example, and the size of the coil L1 can be reduced.

In addition, when the feedback voltage V _FB is less than the reference voltage Vref1 (an example of the first threshold voltage) and greater than or equal to the reference voltage Vref2 (an example of the second threshold voltage) , the protection circuit sets the transition time to the transition time T1 (an example of the second threshold voltage). 1). The control circuit may set the transition time to transition time T2 (an example of a second time) when the feedback voltage V _FB is less than the reference voltage Vref 2 . Note that the reference voltage Vref2 is smaller than the reference voltage Vref1. The transition time T2 is shorter than the transition time T1.

Thereby, the switching power supply 1 can adjust the transition time until stopping the on/off control of the transistor MP in stages according to the feedback voltage V _FB .

Furthermore, if the feedback voltage V _FB is greater than or equal to the reference voltage Vref2 and less than the reference voltage Vref1, and the feedback voltage V _FB becomes less than the reference voltage Vref2 before the elapse of the transition time T1, the protection circuit is configured to control the transition time T2. An overcurrent protection operation corresponding to the transition time T2 may be performed depending on the progress of the transition time T2.

Thereby, when the feedback voltage V _FB changes over time, the switching power supply 1 can flexibly change the transition time according to the feedback voltage V _FB at each timing. Therefore, the switching power supply 1 can perform an appropriate overcurrent protection operation at each timing.

Furthermore, the transition time may be determined depending on the number of pulses for controlling on/off of the transistor MP.

Thereby, the switching power supply 1 can easily measure the passage of transition time by having a simple configuration such as comparators 51 and 52 for counting the number of pulses.

The protection circuit may also switch the transition time based on the feedback voltage and perform the hiccup operation after the transition time has elapsed.

Thereby, the switching power supply 1 can suppress the overcurrent flowing through the transistor MP while repeatedly stopping and restarting the on/off control of the transistor MP without completely stopping the switching power supply 1. Thereby, for example, it is possible to continue operation of a device (for example, a microcomputer, etc.) that can operate with small electric power while taking into account overcurrent. Therefore, for example, there is an advantage that communication functions and display functions can be secured through the microcomputer and monitoring can be continued. This also applies when performing pulse-by-pulse operation.

Further, the protection circuit may switch between hiccup operation and latch operation based on the feedback voltage V _FB .

Thereby, the switching power supply 1 can determine whether to restart the on/off control of the transistor MP after it has been stopped. Therefore, for example, when the amount of decrease in feedback voltage V _FB due to overcurrent is small, the overcurrent flowing through transistor MP can be suppressed while repeatedly stopping and restarting switching power supply 1 without completely stopping switching power supply 1 . On the other hand, if the amount of decrease in the feedback voltage V _FB due to overcurrent is large, the switching power supply 1 completely stops the on/off control of the transistor MP, thereby preventing the components inside the switching power supply 1 and the load. 3 failures can be suppressed. Therefore, maintenance of the switching power supply 1 becomes easy.

Further, when the current is an overcurrent, the control circuit may control the transistor MP to turn off within the period of the pulse that is an overcurrent among the pulses for performing on/off control of the transistor MP.

Thereby, when an overcurrent is detected, the switching power supply 1 can suppress the overcurrent by shortening the on period of the PWM signal for each pulse, that is, by reducing the duty ratio. Further, the switching power supply 1 can efficiently suppress overcurrent by combining pulse-by-pulse operation with overcurrent protection operation (hiccup operation or latch operation).

Although the embodiments of the switching power supply according to the present disclosure have been described above with reference to the drawings, the present disclosure is not limited to such examples. It is clear that those skilled in the art can come up with various changes, modifications, substitutions, additions, deletions, and equivalents within the scope of the claims, and It is understood that it naturally falls within the technical scope of the present disclosure.

In the embodiment described above, the first protection control circuit 50 determines the transition time for performing the overcurrent protection operation, measures the time and determines whether the transition time has elapsed, and the logic circuit 60 performs the stop operation. Although this is an example of instructing, the present invention is not limited to this. For example, the first protection control circuit 50 determines the transition time, notifies the determined transition time to the logic circuit 60, the logic circuit 60 measures the time, determines whether the transition time has elapsed, and stops the transition. You may make it work. Similarly, in the hiccup operation, the first protection control circuit 50 measures the time after the instruction to stop the operation, determines whether a predetermined time has elapsed, and instructs the logic circuit 60 to restart the operation. However, it is not limited to this. For example, in the hiccup operation, the logic circuit 60 may measure the time after the stop operation, determine whether a predetermined time has elapsed, and restart the operation.

In the above embodiment, when the feedback voltage V _FB is a voltage in the second voltage range from the start of detection of the feedback voltage V _FB , which is the second overcurrent protection operating region, the overcurrent protection operating region corresponds to the first overcurrent protection operating region. The overcurrent protection operation corresponding to the second overcurrent protection operation region may be performed from the beginning without performing the current protection operation.

In the above embodiment, the transistor MP is generated by a PMOS transistor, but the present invention is not limited to this. As long as the functions of the embodiments can be realized, the PMOS may be an NMOS or other transistors may be used.

The present disclosure is useful for switching power supplies and the like that can reduce the size of inductors included in switching power supplies, taking heat generation due to overcurrent into consideration.

1 Switching power supply 2 DC power supply 3 Load 10 Soft start circuit 20 Error amplifier 21 Phase compensation capacitor 22 Resistor 30 PWM comparator 40 FF circuit 50, 50A, 50B, 50C First protection control circuit 51, 52, 54, 55 Comparator 53 Count number control circuit 56 Mode selection circuit 57 Timer 60 Logic circuit 70 Current detection circuit 80 Second protection control circuit 90 Slope compensation circuit 95 Adder C _OUT capacitor L1 Coil MP transistor R _ESR , R _B1 , R _B2 resistance

Claims (10)

A switching power supply,
a transistor for controlling the output voltage of the switching power supply;
a control circuit that controls on/off of the transistor;
a current detection circuit that detects the current flowing through the transistor;
When the current is an overcurrent that is equal to or higher than a threshold current, the output voltage of the transistor is based on the feedback voltage fed back to start an overcurrent protection operation for protecting the switching power supply from the overcurrent. a protection circuit that performs the overcurrent protection operation by switching the transition time ;
A switching power supply equipped with The protection circuit performs an overcurrent protection operation for protecting the switching power supply from the overcurrent based on a feedback voltage obtained by feeding back the output voltage of the transistor when the current is an overcurrent that is equal to or higher than a threshold current. further switch the operating mode of
The switching power supply according to claim 1. The protection circuit executes the overcurrent protection operation of stopping the on/off control of the transistor and turning the transistor off.
The switching power supply according to claim 1 or 2 . The higher the feedback voltage, the longer the transition time;
The lower the feedback voltage, the shorter the transition time.
The switching power supply according to claim 3 . The protection circuit includes:
If the feedback voltage is less than a first threshold voltage and greater than or equal to a second threshold voltage that is smaller than the first threshold voltage , setting the transition time to a first time;
if the feedback voltage is less than the second threshold voltage , setting the transition time to a second time shorter than the first time;
The switching power supply according to claim 3 or 4 . The protection circuit is configured such that the feedback voltage is greater than or equal to a second threshold voltage and less than the first threshold voltage, and the feedback voltage becomes less than the second threshold voltage before the first time elapses. In this case, according to the passage of the second time, an overcurrent protection operation corresponding to the second time is performed.
The switching power supply according to claim 5 . The transition time is determined according to the number of pulses for controlling on/off of the transistor,
The switching power supply according to any one of claims 3 to 6 . The protection circuit includes:
switching the transition time based on the feedback voltage;
performing a hiccup motion after the transition time has elapsed;
The switching power supply according to any one of claims 1 and 3 to 6 . The protection circuit switches between hiccup operation and latch operation based on the feedback voltage.
The switching power supply according to claim 2 . When the current is the overcurrent, the control circuit controls the transistor to turn off within a period of the pulse that is the overcurrent among pulses for controlling on/off of the transistor.
The switching power supply according to any one of claims 1 to 9 .

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