Power circuit

Abstract

To provide a power supply circuit that can improve the efficiency of power supply to the load. [Solution] The power supply circuit according to the embodiment is a power supply circuit that generates an output voltage to be output to a load by switching control of a DC-DC converter by PWM control or PFM control, and has a controller. The controller switches from PWM control to PFM control when the number of Highs per unit time of the switching signal output from the switching element of the DC-DC converter exceeds a threshold during control by PWM control.

Description

Technical Field

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[0001] The present invention relates to a power supply circuit.

Background Art

[0002] Conventionally, a step-down DCDC converter has been widely used in a power supply circuit for controlling power supply to various loads mounted on a vehicle (see, for example, Patent Document 1). Further, the step-down DCDC converter has PWM (Pulse Width Modulation) control suitable for a case where the current supplied to the load (hereinafter, load current) is large and PFM (Pulse Frequency Modulation) control suitable for a case where the load current is small. Patent Document 1 discloses a technique in which, in a power supply circuit having both PWM control and PFM control, the load current is monitored by a sensor and PWM control and PFM control are switched according to the magnitude of the load current.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional technology, since it is necessary to provide a sensor for monitoring the load current in the power supply path to the load, the sensor becomes a resistance component, resulting in a decrease in the output voltage and a possible decrease in the power supply efficiency to the load.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a power supply circuit capable of improving the power supply efficiency to a load.

Means for Solving the Problems

[0006] To solve the above-mentioned problems and achieve the objective, the power supply circuit according to the present invention is a power supply circuit that generates an output voltage to be output to the load by switching control of a DC-DC converter by PWM control or PFM control, and includes a controller. The controller switches from PWM control to PFM control when the number of Highs per unit time of the switching signal output from the switching element of the DC-DC converter exceeds a threshold during control by PWM control. [Effects of the Invention]

[0007] According to the present invention, PWM control and PFM control are switched according to the number of High signals per unit time of the switching signal output from the switching element of the DC-DC converter. Therefore, in the present invention, there is no need to install a sensor to monitor the load current in the output path to the load, and thus no decrease in output voltage due to the sensor occurs. In other words, according to the present invention, the power supply efficiency to the load can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows the circuit configuration of the power supply circuit according to the embodiment. [Figure 2] Figure 2 is a timing chart showing the operating timing of the power supply circuit. [Figure 3] Figure 3 is a timing chart showing the operating timing of the power supply circuit. [Figure 4] Figure 4 is a timing chart showing the operating timing of the power supply circuit. [Modes for carrying out the invention]

[0009] The power supply circuit according to the embodiment will be described in detail below with reference to the attached drawings. However, the present invention is not limited to the embodiments shown below.

[0010] First, the configuration and operation of the power supply circuit according to the embodiment will be described using Figure 1. Figure 1 is a diagram showing the circuit configuration of the power supply circuit 1 according to the embodiment. The power supply circuit 1 shown in Figure 1 is, for example, mounted on a vehicle and steps down the power supply voltage Vin supplied from the vehicle battery and outputs it to the vehicle load 100. The load 100 is, for example, a control device used for vehicle control or vehicle electrical components.

[0011] As shown in Figure 1, the power supply circuit 1 comprises a controller 2, a DC-DC converter 3 (hereinafter referred to as DC-DC3), a first comparator 4, a second comparator 5, and a flip-flop circuit 6.

[0012] Controller 2 controls the switching of the DC-DC converter 3 to generate an output voltage that is output to the load 100 from the power supply voltage Vin. Specifically, Controller 2 comprises a PWM control unit 21, a PFM control unit 22, a changeover switch 23, and a mode switching unit 24.

[0013] The PWM control unit 21 performs PWM (Pulse Width Modulation) control by outputting a PWM signal to the DC-DC converter. Specifically, the PWM control unit 21 monitors the output voltage to the load 100 and performs feedback control to generate a PWM signal with adjusted pulse width so that the output voltage reaches the required value.

[0014] The PFM control unit 22 performs PFM (Pulse Frequency Modulation) control by outputting a PFM signal to the DC-DC converter. Specifically, the PFM control unit 22 generates a PFM signal in which the frequency of a pulse of a constant width is adjusted so that the output voltage becomes the required value by feedback control based on the output voltage to the load 100 using the signal output from the flip-flop circuit 6.

[0015] The changeover switch 23 switches whether the input to the DCDC3 is to the PWM control unit 21 or the PFM control unit 22, according to the control of the mode switching unit 24.

[0016] The mode switching unit 24 switches between a PWM mode for performing PWM control and a PFM mode for performing PFM control by performing switching control of the changeover switch 23. The operation of mode switching by the mode switching unit 24 will be described later.

[0017] DCDC3 is a step-down DCDC converter that steps down the power supply voltage Vin to generate an output voltage. DCDC3 includes a first switching element 31, a second switching element 32, a coil 33, and a capacitor 34.

[0018] The first switching element 31 is an N-channel type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The first switching element 31 is a switching element disposed on the high side, with its drain connected to a voltage source that supplies the power supply voltage Vin and its source connected to the drain of the second switching element 32. Also, the gate of the first switching element 31 is connected to the changeover switch 23.

[0019] The second switching element 32 is an N-channel type MOSFET. The second switching element 32 is a switching element disposed on the low side, with its drain connected to the source of the first switching element 31 and its source connected to the ground. Also, the gate of the second switching element 32 is connected to the changeover switch 23.

[0020] One end of the coil 33 is connected between the source of the first switching element 31 and the drain of the second switching element 32, and the other end is connected to the capacitor 34 and the load 100. One end of the capacitor 34 is connected to the coil 33 and the load 100, and the other end is connected to the ground. The coil 33 and the capacitor 34 generate an output voltage by smoothing the signals (switching signals) output from the first switching element 31 and the second switching element 32.

[0021] The first comparator 4 is a comparison circuit that compares the output voltage with the first reference voltage VTL which is the low voltage threshold. For the first comparator 4, the output voltage is input to the minus terminal and the first reference voltage VTL is input to the plus terminal. When the output voltage is less than the first reference voltage VTL (less than the low voltage threshold), the first comparator 4 outputs a High signal.

[0022] The second comparator 5 is a comparison circuit that compares the output voltage with the second reference voltage VTH which is the high voltage threshold. For the second comparator 5, the output voltage is input to the plus terminal and the second reference voltage VTH is input to the minus terminal. When the output voltage exceeds the second reference voltage VTH (exceeds the high voltage threshold), the second comparator 5 outputs a High signal.

[0023] The flip-flop circuit 6 has the first comparator 4 connected to the set terminal (S), the second comparator 5 connected to the reset terminal (R), and the PFM control unit 22 and the mode switching unit 24 connected to the output terminal (Q). When a High signal is output from the first comparator 4 and a Low signal is output from the second comparator 5, the flip-flop circuit 6 outputs a High signal from the output terminal. Also, when a Low signal is output from the first comparator 4 and a High signal is output from the second comparator 5, the flip-flop circuit 6 outputs a Low signal from the output terminal.

[0024] Next, an operation example of the power supply circuit 1 will be described with a focus on the switching operation of the mode switching unit 24.

[0025] In the present disclosure, during control by PWM control (during PWM mode), the mode switching unit 24 receives the input of the A signal (output signal before smoothing), measures the number of High times per unit time of the A signal, and when the number of High times becomes equal to or more than the threshold, switches from PWM control to PFM control. That is, the mode switching unit 24 switches from PWM mode to PFM mode and switches the switching switch 23 to switch the connection with the DCDC3 from the PWM control unit 21 to the PFM control unit 22.

[0026] According to this disclosure, the switching from PWM control to PFM control is performed by measuring the number of High cycles per unit time of the switching signal (A signal) output from the switching elements (first switching element 31 and second switching element 32) of the DC-DC converter 3. Therefore, in this disclosure, there is no need to provide a sensor to monitor the load current in the output path to the load 100 for switching from PWM control to PFM control, and thus no decrease in the output voltage to the load 100 occurs. In other words, according to this disclosure, the power supply efficiency to the load 100 can be improved.

[0027] Furthermore, in this disclosure, the mode switching unit 24 switches from PFM control to PWM control when, during control by PFM control (in PFM mode), the output voltage falls below a threshold when the off time of the PFM signal is below a threshold (when the C signal becomes a High signal). In other words, the mode switching unit 24 switches from PFM mode to PWM mode and switches the connection with the DCDC3 from the PFM control unit 22 to the PWM control unit 21 by switching the changeover switch 23.

[0028] According to this disclosure, when the off-time of the PFM signal is below a threshold, and the output voltage is also below a threshold (when the C signal is a High signal), a switch from PFM control to PWM control is performed. Therefore, in this disclosure, there is no need to provide a sensor to monitor the load current in the output path to the load 100 for the switch from PFM control to PWM control, and thus no decrease in the output voltage and output current to the load 100 occurs. In other words, according to this disclosure, the power supply efficiency to the load can be improved.

[0029] The following sections will provide a detailed explanation of switching between PWM control and PFM control, as well as switching between PFM control and PWM control.

[0030] (PWM control → PFM control) First, let's explain the switching operation from PWM control to PFM control. As described above, the mode switching unit 24 receives an A signal input while PWM control is in operation, measures the number of High signals per unit time of the A signal, and switches from PWM control to PFM control if the number of High signals is above a threshold.

[0031] Signal A is the switching signal after it is output from the first switching element 31 and the second switching element 32, but before it is input to the coil 33. In other words, signal A is the signal before it is smoothed by the coil 33 and the capacitor 34. Therefore, signal A is a signal in which High and Low are repeated according to the duty cycle of the PWM signal.

[0032] Here, if the load current output to load 100 is greater than or equal to the threshold, the number of Highs in signal A and the number of Ons in the PWM signal will be the same. In other words, if the current does not become zero during the Low period of signal A, the number of Highs in signal A and the number of Ons in the PWM signal will be the same. On the other hand, if the load current output to load 100 is less than the threshold, the number of Highs in signal A will be greater than the number of Ons in the PWM signal. In other words, if the current becomes zero during the Low period of signal A, the number of Highs in signal A will be greater than the number of Ons in the PWM signal. This is because the zero current during the Low period of signal A causes LC resonance in coil 33 and capacitor 34, resulting in a High judgment pulse for LC resonance in signal A. In short, if the load current is less than the threshold, signal A contains a pulse component (High) due to LC resonance, so the number of Highs will be greater than the number of Ons in the PWM signal.

[0033] This disclosure focuses on this point, and the mode switching unit 24 determines that the load current is less than the threshold when the number of Highs per unit time of signal A is equal to or greater than the threshold (number of ONs per unit time of the PWM signal), and switches from PWM control to PFM control. In other words, the mode switching unit 24 compares the number of ONs per unit time of the PWM signal (number of ONs of signal B) with the number of Highs, and switches from PWM control to PFM control when the number of Highs is greater than the number of ONs. As a result, the mode switching unit 24 can detect that the load current has fallen below the threshold and switch from PWM control to PFM control without measuring the load current with a sensor.

[0034] (PFM control → PWM control) Next, the switching operation from PFM control to PWM control will be explained. As described above, the mode switching unit 24 switches from PFM control to PWM control when the output voltage is below a threshold while the off time of the PFM signal is below a threshold during PFM control. The mode switching unit 24 detects the off time of the PFM signal using the A signal. Specifically, the mode switching unit 24 detects the time per Low of the A signal as the off time per PFM signal. The mode switching unit 24 directly receives the PFM signal from the PFM control unit 22 to detect the off time per signal. The mode switching unit 24 also determines whether the output voltage is below a threshold using the C signal. Specifically, the mode switching unit 24 determines that the output voltage is below a threshold (first reference voltage VTL) when the C signal is High, since the C signal becomes High when the C signal is High.

[0035] In other words, the mode switching unit 24 determines that the output voltage will not reach the target value under PFM control because the output voltage is below the threshold, even though the off time per PFM signal is below the threshold, meaning that there is little room for the output voltage to rise under PFM control. That is, the mode switching unit 24 detects that the load current is above the threshold and determines that PFM control cannot supply a load current above the threshold, so it switches to PWM control. As a result, the mode switching unit 24 can detect that the load current has exceeded the threshold and switch from PFM control to PWM control without measuring the load current with a sensor.

[0036] Furthermore, the mode switching unit 24 may switch from PFM control to PWM control if the output voltage remains below a threshold for a threshold time or longer while under PFM control. Specifically, the mode switching unit 24 switches from PFM control to PWM control if the output voltage remains below a threshold for a threshold time or longer when the off time of the PFM signal is below a threshold. This suppresses chattering, which occurs when the load current is near a threshold, by preventing repeated switching between PWM control and PFM control.

[0037] Furthermore, the mode switching unit 24 switches from PFM control to PWM control when the PFM signal is off for a period during PFM control in which the frequency of the PFM signal exceeds the frequency of the PWM signal. This allows the mode switching unit 24 to switch from PFM control to PWM control when the load current rises to a level that enables PWM control.

[0038] Next, the operating timing of power supply circuit 1 will be explained using Figures 2 to 4. Figures 2 to 4 are timing charts showing the operating timing of power supply circuit 1. Figure 2 shows the timing chart where the control switches from PWM control to PFM control at time t1, and then switches from PFM control to PWM control at time t2. Figure 3 shows a magnified view of the timing chart in Figure 2 just before time t1. Figure 4 shows a magnified view of the timing chart in Figure 2 around time t2. Figures 2 to 4 also show the "switching signal," "load current," "coil current," "A signal," "output voltage," and "C signal."

[0039] The "switching signal" is a signal output from the mode switching unit 24 to the changeover switch 23 to switch the switch state. The "load current" indicates the current supplied to the load 100. The "coil current" indicates the current flowing through the coil 33 (current before smoothing). The "A signal" indicates the A signal described above. The "output voltage" indicates the output voltage output to the load 100. The "C signal" indicates the C signal described above.

[0040] (PWM control → PFM control) As shown in Figure 2, when the load current drops below a threshold at time t1, the mode switching unit 24 outputs a High switching signal, switching from PWM control to PFM control.

[0041] Specifically, as shown in Figure 3, just before time t1, when the coil current falls below a threshold, LC resonance occurs, and the A signal begins to contain pulse components due to LC resonance. Specifically, the A signal contains square wave pulses caused by the PWM signal and triangular wave pulses caused by LC resonance immediately before each square wave. In other words, when the load current falls below a threshold, the number of Highs in the A signal becomes greater than the number of Ons (square wave pulses) of the PMW signal by the number of triangular wave pulses. Therefore, the mode switching unit 24 switches from PWM control to PFM control when the number of Highs in the A signal per unit time becomes twice the number of Ons of the PMW signal.

[0042] (PFM control → PWM control) Next, as shown in Figure 2, when the load current rises above a threshold at time t2, a Low switching signal is output from the mode switching unit 24, switching from PFM control to PWM control.

[0043] Specifically, as shown in Figure 4, if immediately before time t2 the off time of signal A (the value in the center of the graph corresponds to the off time) falls below the threshold and signal C is High (i.e., the output voltage is below the threshold), then at time t2, the control switches from PFM control to PWM control.

[0044] More specifically, in Figure 4, for signal A, the off-time is defined as the median time between one pulse set (considered as one set to be a square wave of a constant value and a waveform whose value is gradually subtracted to the median value) and the next pulse set. Also in Figure 4, signal C becomes High when the output signal falls below the first reference voltage VTL, and remains High until it reaches the second reference voltage VTH, at which point it becomes Low.

[0045] In other words, in Figure 4, the control switches from PFM to PWM when the C signal is High (i.e., the output voltage is below the threshold) at the third pulse set (time t2) after the off time of the A signal falls below the threshold. Alternatively, the control may switch from PFM to PWM after the fourth pulse set or later after the off time of the A signal falls below the threshold.

[0046] As described above, the power supply circuit 1 according to the embodiment is a power supply circuit that generates an output voltage to be output to a load 100 by switching control of a DC-DC converter 3 by PWM control or PFM control, and has a controller 2. When the controller 2 is controlling by PWM control, if the number of Highs per unit time of the switching signal (A signal) output from the switching element of the DC-DC converter 3 is greater than or equal to a threshold, the controller 2 switches from PWM control to PFM control.

[0047] According to this disclosure, PWM control and PFM control are switched according to the number of High signals per unit time of the switching signals output from the switching elements 31 and 32 of the DC-DC converter 3. Therefore, in this disclosure, there is no need to provide a sensor to monitor the load current in the output path to the load 100, and thus no decrease in output voltage due to the sensor occurs. In other words, according to this disclosure, the power supply efficiency to the load 100 can be improved.

[0048] Further effects and modifications can be readily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0049] 1 Power circuit 2 Controllers 3 DC-DC converter 4. First Comparator 5. Second Comparator 6. Flip-flop circuits 21 PWM Control Unit 22 PFM Control Unit 23 Changeover switch 24 Mode switching section 31 First switching element 32 Second switching element 33 coils 34 Capacitors 100 load

Claims

1. A power supply circuit that generates an output voltage supplied to a load by switching a DC-DC converter using PWM control or PFM control according to the amount of current supplied to the load, and having a controller, The aforementioned controller, During control by the PWM control, if the number of High signals per unit time output from the switching element of the DC-DC converter exceeds a threshold, the control switches from the PWM control to the PFM control. power circuit.

2. The aforementioned controller, During control by the PFM control described above, the number of times the PWM signal input to the switching element is turned on per unit time is compared with the number of times it is High. If the number of High signals is greater than the number of times it is turned on, the control switches from the PWM control to the PFM control. The power supply circuit according to claim 1.

3. The aforementioned controller, During control by the PFM control described above, if the output voltage falls below a threshold while the off-time of the PFM signal input to the switching element of the DC-DC converter is below a threshold, the control switches from the PFM control to the PWM control. The power supply circuit according to claim 1.

4. The aforementioned controller, If, during control by the PFM control, the output voltage remains below a threshold for a threshold time or longer, the system switches from PFM control to PWM control. The power supply circuit according to claim 3.

5. The aforementioned controller, If the frequency of the PFM signal exceeds the frequency of the PWM signal output during PWM control, the system switches from PFM control to PWM control. The power supply circuit according to claim 3.

6. A power supply circuit that generates an output voltage supplied to a load by switching a DC-DC converter using PWM control or PFM control according to the amount of current supplied to the load, and having a controller, The aforementioned controller, During control by the PFM control, if the output voltage is below a threshold when the off-time of the PFM signal input to the switching element of the DC-DC converter is below a threshold, the control switches from the PFM control to the PWM control. power circuit.

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