Automatic mode switching method and circuit for DC-DC converter

Abstract

The present invention discloses an automatic mode switching method for a DC-DC converter, comprising the following steps: (a) obtaining a first width of a duty cycle of a pulse-width modulation signal and a second width of a duty cycle of a pulse-frequency modulation signal, respectively, wherein the first width is related to an error voltage and the second width is related to a peak current; and (b) outputting a switching signal based on a comparison result of the first width and the second width to automatically switch the DC-DC converter between operating in a pulse-width modulation mode or a pulse-frequency modulation mode.

Description

Technical Field

[0001] The present invention relates to a DC-DC converter, and in particular to an automatic mode switching method and circuit for a DC-DC converter. Background Art

[0002] Generally speaking, a DC-DC converter usually has the following two different operating modes:

[0003] (1) Pulse Width Modulation (PWM) mode: Due to its high power consumption and small output ripple, it is more suitable for high current applications.

[0004] (2) Pulse Frequency Modulation (PFM) mode: Due to its lower power consumption and larger output ripple, it is more suitable for low current applications.

[0005] In the application of high-performance power integrated circuits (Power ICs), pulse frequency modulation (PFM) mode is used for light loads. When the load increases to a heavy load, it switches to pulse width modulation (PWM) mode to achieve high output efficiency and low output ripple.

[0006] However, in practical applications, when a heavy load transitions to a light load, the DC-DC converter can easily switch back and forth between pulse frequency modulation (PFM) mode and pulse width modulation (PWM) mode. This prevents the DC-DC converter from smoothly switching operating modes, resulting in large output ripple. This issue urgently needs to be addressed. Summary of the Invention

[0007] Therefore, the present invention proposes an automatic mode switching method and circuit for a DC-DC converter to effectively solve the above-mentioned problems encountered in the prior art.

[0008] A preferred embodiment of the present invention provides an automatic mode switching method for a DC-DC converter. In this embodiment, the automatic mode switching method includes the following steps: (a) obtaining a first duty cycle width of a pulse-width modulation signal and a second duty cycle width of a pulse-frequency modulation signal, respectively, wherein the first duty cycle width is related to an error voltage and the second duty cycle width is related to a peak current; and (b) outputting a switching signal to automatically switch the DC-DC converter between a pulse-width modulation mode and a pulse-frequency modulation mode based on a comparison result of the first duty cycle width and the second duty cycle width.

[0009] In one embodiment, step (b) includes: (b1) if the comparison result is that the first width is greater than the second width, automatically switching the DC-DC converter to operate in a pulse width modulation mode; and (b2) if the comparison result is that the first width is less than the second width, automatically switching the DC-DC converter to operate in a pulse frequency modulation mode.

[0010] In one embodiment, step (a) determines the first width according to a first rising edge and a first falling edge of the PWM signal and determines the second width according to a second rising edge and a second falling edge of the PFM signal.

[0011] In one embodiment, the first rising edge and the second rising edge both correspond to a first time, and the first falling edge and the second falling edge correspond to a second time and a third time, respectively. If the second time is later than the third time, the comparison result is that the first width is greater than the second width, and the DC-DC converter operates in a pulse-width modulation mode. If the second time is earlier than the third time, the comparison result is that the first width is less than the second width, and the DC-DC converter operates in a pulse-frequency modulation mode.

[0012] In one embodiment, the second time is determined by the intersection of the error voltage and the ramp signal and the third time is determined by the intersection of the peak current and the output inductor current.

[0013] In one embodiment, the error voltage is generated according to a reference voltage and a feedback voltage related to the output voltage.

[0014] Another preferred embodiment of the present invention is also a method for automatic mode switching of a DC-DC converter. In this embodiment, the method includes the following steps: (a) obtaining an error voltage and a threshold voltage of a pulse frequency modulation signal; and (b) outputting a switching signal to automatically switch the DC-DC converter between a pulse width modulation mode and a pulse frequency modulation mode based on a comparison result of the error voltage and the threshold voltage.

[0015] In one embodiment, step (b) includes: (b1) if the comparison result is that the error voltage is greater than the critical voltage value, automatically switching the DC-DC converter to operate in a pulse width modulation mode; and (b2) if the comparison result is that the error voltage is less than the critical voltage value, automatically switching the DC-DC converter to operate in a pulse frequency modulation mode.

[0016] In one embodiment, the error voltage is generated according to a reference voltage and a feedback voltage related to the output voltage.

[0017] In one embodiment, when the DC-DC converter operates in pulse-width modulation mode, the falling edge of the switching signal is determined by the intersection of the error voltage and the ramp signal; when the DC-DC converter operates in pulse-frequency modulation mode, the falling edge of the switching signal is determined by the intersection of the peak current and the output inductor current.

[0018] Another preferred embodiment of the present invention is an automatic mode switching circuit for a DC-DC converter. In this embodiment, the automatic mode switching circuit includes: a first comparator for providing a first width of a duty cycle of a pulse-width modulation signal, wherein the first width is related to an error voltage; a second comparator for providing a second width of a duty cycle of a pulse-frequency modulation signal, wherein the second width is related to a peak current; and a logic circuit, coupled to the first comparator and the second comparator, for outputting a switching signal based on a comparison result between the first width and the second width to automatically switch the DC-DC converter between operating in a pulse-width modulation mode and a pulse-frequency modulation mode.

[0019] In one embodiment, if the comparison result is that the first width is greater than the second width, the DC-DC converter operates in a pulse width modulation mode; if the comparison result is that the first width is less than the second width, the DC-DC converter operates in a pulse frequency modulation mode.

[0020] In one embodiment, two input terminals of the first comparator receive an error voltage and a ramp signal, respectively, and two input terminals of the second comparator receive a voltage generated by the output inductor current flowing through a resistor and a reference voltage, respectively. The error voltage is generated based on the reference voltage and a feedback voltage related to the output voltage.

[0021] In one embodiment, the first width is determined by a first rising edge and a first falling edge of the PWM signal, and the second width is determined by a second rising edge and a second falling edge of the PFM signal.

[0022] In one embodiment, the first rising edge and the second rising edge both correspond to a first time, and the first falling edge and the second falling edge correspond to a second time and a third time, respectively. If the second time is later than the third time, the comparison result is that the first width is greater than the second width, and the DC-DC converter operates in a pulse-width modulation mode. If the second time is earlier than the third time, the comparison result is that the first width is less than the second width, and the DC-DC converter operates in a pulse-frequency modulation mode.

[0023] In one embodiment, the second time is determined by the intersection of the error voltage and the ramp signal and the third time is determined by the intersection of the peak current and the output inductor current.

[0024] Another preferred embodiment of the present invention provides an automatic mode switching circuit for a DC-DC converter. In this embodiment, the automatic mode switching circuit includes an error amplifier for providing an error voltage; a pulse frequency modulation reference generator for providing a threshold voltage of a pulse frequency modulation signal; and a comparator coupled to the error amplifier and the pulse frequency modulation reference generator, respectively, for outputting a switching signal based on a comparison result between the error voltage and the threshold voltage to automatically switch the DC-DC converter between operating in a pulse width modulation mode or a pulse frequency modulation mode.

[0025] In one embodiment, if the comparison result shows that the error voltage is greater than the threshold voltage, the DC-DC converter operates in a pulse width modulation mode; if the comparison result shows that the error voltage is less than the threshold voltage, the DC-DC converter operates in a pulse frequency modulation mode.

[0026] In one embodiment, two input terminals of the error amplifier respectively receive a reference voltage and a feedback voltage related to the output voltage to generate an error voltage.

[0027] In one embodiment, when the DC-DC converter operates in pulse-width modulation mode, the falling edge of the switching signal is determined by the intersection of the error voltage and the ramp signal; when the DC-DC converter operates in pulse-frequency modulation mode, the falling edge of the switching signal is determined by the intersection of the peak current and the output inductor current.

[0028] Compared to the prior art, the automatic mode switching method and circuit for a DC-DC converter proposed in the present invention can achieve linear and smooth switching between pulse frequency modulation (PFM) mode and pulse width modulation (PWM) mode. This effectively solves the problem of conventional DC-DC converters frequently switching between PFM and PWM modes when switching from heavy load to light load, thereby reducing output ripple. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 4 is a flow chart of an automatic mode switching method for a DC-DC converter according to a specific embodiment of the present invention.

[0030] Figure 2 FIG. 4 is a schematic diagram of an automatic mode switching circuit for a DC-DC converter according to another embodiment of the present invention.

[0031] Figure 3 They are the timing diagrams of the output inductor current, ramp signal, pulse width modulation signal, pulse frequency modulation signal and switching signal respectively.

[0032] Figure 4 Graphs show the efficiency of the DC-DC converter when it operates in PWM mode or PFM mode at different load currents.

[0033] Figure 5 4 is a flow chart of an automatic mode switching method for a DC-DC converter in another embodiment of the present invention.

[0034] Figure 6 FIG. 4 is a schematic diagram of an automatic mode switching circuit for a DC-DC converter according to another embodiment of the present invention.

[0035] Figure 7 They are the timing diagrams of the output inductor current, ramp signal and switching signal respectively.

[0036] Description of main component symbols:

[0037] S10~S16…steps

[0038] S50~S56…steps

[0039] 2…Automatic mode switching circuit for DC-DC converter

[0040] 20…Error amplifier

[0041] 22…Current Source

[0042] 24…Compensation network

[0043] 26…Comparator

[0044] 28…Comparator

[0045] 30…Logic circuit

[0046] R…resistance

[0047] +…positive input terminal

[0048] -…Negative input terminal

[0049] VREF…reference voltage

[0050] FB…Feedback voltage

[0051] Verr…Error voltage

[0052] ILX…output inductor current

[0053] PFM_Ipeak…Pulse frequency modulation signal

[0054] Ipeak…peak current

[0055] SAW...Ramp signal

[0056] PWM_duty…Pulse width modulation signal

[0057] S1…Switching signal

[0058] GND…ground terminal

[0059] t1~t8…time

[0060] PFM…Pulse Frequency Modulation Mode

[0061] PWM…Pulse Width Modulation Mode

[0062] 6…Automatic mode switching circuit for DC-DC converter

[0063] 60…Error amplifier

[0064] 62…Pulse Frequency Modulation (PFM) Reference Generator

[0065] 64…Compensation network

[0066] 66…Comparator

[0067] PFM_TH…Threshold voltage of pulse frequency modulation signal DETAILED DESCRIPTION

[0068] A preferred embodiment according to the present invention is an automatic mode switching method for a DC-DC converter.

[0069] like Figure 1 , Figure 1 This is a flow chart of the automatic mode switching method for a DC-DC converter in this embodiment. Figure 1 As shown, the automatic mode switching method for a DC-DC converter in this embodiment may include the following steps:

[0070] Step S10: Obtaining a first width of a duty cycle of the PWM signal and a second width of a duty cycle of the PFM signal, respectively, wherein the first width is related to the error voltage and the second width is related to the peak current;

[0071] Step S12: comparing the first width and the second width;

[0072] Step S14: If the comparison result of step S12 is that the first width is greater than the second width, automatically switching the DC-DC converter to operate in a pulse width modulation mode; and

[0073] Step S16: If the comparison result of step S12 is that the first width is smaller than the second width, the DC-DC converter is automatically switched to operate in the pulse frequency modulation mode.

[0074] It should be noted that step S10 may determine the first width according to the first rising edge and the first falling edge of the PWM signal and may determine the second width according to the second rising edge and the second falling edge of the PFM signal, but is not limited thereto.

[0075] In one embodiment, it is assumed that the first rising edge and the second rising edge both correspond to a first time, and the first falling edge and the second falling edge correspond to a second time and a third time, respectively. If the second time is later than the third time, the comparison result of step S12 indicates that the first width is greater than the second width, and the method then proceeds to step S14 to automatically switch the DC-DC converter to pulse-width modulation mode. If the second time is earlier than the third time, the comparison result of step S12 indicates that the first width is less than the second width, and the method then proceeds to step S16 to automatically switch the DC-DC converter to pulse-frequency modulation mode.

[0076] In practical applications, the second time can be determined by the intersection of the error voltage and the ramp signal, and the third time can be determined by the intersection of the peak current and the output inductor current, but the present invention is not limited thereto. Furthermore, the error voltage can be generated based on a reference voltage and a feedback voltage related to the output voltage, but the present invention is not limited thereto.

[0077] Another preferred embodiment according to the present invention is an automatic mode switching circuit for a DC-DC converter.

[0078] Figure 2 This is a schematic diagram of an automatic mode switching circuit for a DC-DC converter in this embodiment. Figure 2 As shown, an automatic mode switching circuit 2 for a DC-DC converter includes an error amplifier 20, a current source 22, a compensation network 24, a comparator 26, a comparator 28, a logic circuit 30, and a resistor R. The output of the error amplifier 20 is coupled to the positive input terminal + of the comparator 28. The current source 22 is coupled to the resistor R and the positive input terminal + of the comparator 26. The resistor R is coupled between the current source 22 and the ground terminal GND. The compensation network 24 is coupled to the ground terminal GND. The outputs of the comparators 26 and 28 are both coupled to the logic circuit 30.

[0079] The error amplifier 20 receives a reference voltage VREF and a feedback voltage FB related to the output voltage of the DC-DC converter at its positive input terminal + and its negative input terminal -, respectively, to generate an error voltage Verr, which is then transmitted to the positive input terminal + of the comparator 28. The comparator 26 receives a voltage generated by the output inductor current ILX provided by the current source 22 flowing through the resistor R and the reference voltage VREF at its positive input terminal + and its negative input terminal -, respectively, to generate a pulse-frequency modulation signal PFM_Ipeak, which is transmitted to the logic circuit 30. The second duty cycle width of the pulse-frequency modulation signal PFM_Ipeak is related to the peak current Ipeak. The comparator 28 receives the error voltage Verr and the ramp signal SAW at its positive input terminal + and its negative input terminal -, respectively, to generate a pulse-width modulation signal PWM_duty, which is transmitted to the logic circuit 30. The first duty cycle width of the pulse-width modulation signal PWM_duty is related to the error voltage Verr.

[0080] The logic circuit 30 is coupled to the output terminals of the comparator 26 and the comparator 28, respectively, for receiving the pulse-width modulation signal PWM_duty and the pulse-frequency modulation signal PFM_Ipeak, and outputting a switching signal S1 based on a comparison result between a first duty cycle width of the pulse-width modulation signal PWM_duty and a second duty cycle width of the pulse-frequency modulation signal PFM_Ipeak, so as to automatically switch the DC-DC converter between operating in the pulse-width modulation mode or the pulse-frequency modulation mode.

[0081] In actual applications, if the comparison result is that the first width is greater than the second width, the switching signal S1 is used to automatically switch the DC-DC converter to operate in the pulse width modulation mode; if the comparison result is that the first width is less than the second width, the switching signal S1 is used to automatically switch the DC-DC converter to operate in the pulse frequency modulation mode.

[0082] Figure 3 They are timing diagrams of the output inductor current ILX, the ramp signal SAW, the pulse width modulation signal PWM_duty, the pulse frequency modulation signal PFM_Ipeak and the switching signal S1 respectively.

[0083] like Figure 3 As shown, at time t1, the ramp signal SAW rises to equal the error voltage Verr, and the pulse-width modulation signal PWM_duty output by the comparator 28 changes from a high level to a low level. The output inductor current ILX remains less than the peak current Ipeak, and the pulse-frequency modulation signal PFM_Ipeak output by the comparator 26 remains at a high level. At time t2, the ramp signal SAW continues to rise and becomes greater than the error voltage Verr. The pulse-width modulation signal PWM_duty output by the comparator 28 remains at a low level, and the output inductor current ILX rises to equal the peak current Ipeak. The pulse-frequency modulation signal PFM_Ipeak output by the comparator 26 changes from a high level to a low level.

[0084] Since the first rising edge of the PWM signal PWM_duty and the second rising edge of the PWM signal PFM_Ipeak occur at the same time, but the first falling edge of the PWM signal PWM_duty occurs earlier than the second falling edge of the PWM signal PFM_Ipeak, i.e., the first duty cycle width of the PWM signal PWM_duty is shorter than the second duty cycle width of the PWM signal PFM_Ipeak, the logic circuit 30 automatically switches the DC-DC converter to the PWM mode based on the comparison result, outputting a switching signal S1 in phase with the PWM signal PFM_Ipeak. The situations at times t3 and t4 are similar to those at times t1 and t2, and the DC-DC converter continues to operate in the PWM mode.

[0085] At time t5, the output inductor current ILX rises to equal the peak current Ipeak. The PWM signal PFM_Ipeak output by the comparator 26 transitions from a high level to a low level. The ramp signal SAW remains below the error voltage Verr, and the PWM signal PWM_duty output by the comparator 28 remains high. At time t6, the output inductor current ILX continues to rise and exceeds the peak current Ipeak. The PWM signal PFM_Ipeak output by the comparator 26 remains low. The ramp signal SAW rises to equal the error voltage Verr, and the PWM signal PWM_duty output by the comparator 28 transitions from a high level to a low level.

[0086] Since the first rising edge of the PWM signal PWM_duty and the second rising edge of the PWM signal PFM_Ipeak occur at the same time, but the first falling edge of the PWM signal PWM_duty corresponds to time t1 later than the second falling edge of the PWM signal PFM_Ipeak, meaning the first duty cycle width of the PWM signal PWM_duty is greater than the second duty cycle width of the PWM signal PFM_Ipeak, the logic circuit 30 automatically switches the DC-DC converter to PWM mode based on the comparison result by outputting a switching signal S1 in phase with the PWM signal PWM_duty. The situations at times t7 and t8 are similar to those at times t5 and t6, with the DC-DC converter continuing to operate in PWM mode. The remaining situations can be deduced similarly and are not further described here.

[0087] It should be noted that Figure 3 The times t1, t3, t6, and t8 are determined by the intersection of the ramp signal SAW and the error voltage Verr. Figure 3The times t2, t4, t5, and t7 are determined by the intersection of the output inductor current ILX and the peak current Ipeak, but are not limited thereto.

[0088] like Figure 4 As shown, the DC-DC converter operates in a pulse width modulation mode (PWM) or a pulse frequency modulation mode (PFM) under different load currents. When switching between the pulse frequency modulation (PFM) mode and the pulse width modulation (PWM) mode, the automatic mode switching circuit 2 of the present invention can effectively make the efficiency change of the DC-DC converter more linear and smooth, thereby avoiding the generation of large output ripples.

[0089] Another preferred embodiment according to the present invention is also an automatic mode switching method for a DC-DC converter.

[0090] Figure 5 This is a flow chart of the automatic mode switching method for a DC-DC converter in this embodiment. Figure 5 As shown, the automatic mode switching method for a DC-DC converter in this embodiment may include the following steps:

[0091] Step S50: Obtaining the error voltage and the critical voltage value of the pulse frequency modulation signal respectively;

[0092] Step S52: comparing the error voltage with the critical voltage value;

[0093] Step S54: If the comparison result of step S52 is that the error voltage is greater than the threshold voltage, the method automatically switches the DC-DC converter to operate in a pulse width modulation mode; and

[0094] Step S56 : If the comparison result of step S52 is that the error voltage is less than the threshold voltage, the method automatically switches the DC-DC converter to operate in the pulse frequency modulation mode.

[0095] In practical applications, the error voltage can be generated based on, but is not limited to, a reference voltage and a feedback voltage related to the output voltage of the DC-DC converter. When the method outputs a switching signal to automatically switch the DC-DC converter to operate in a pulse-width modulation mode, the falling edge of the switching signal can be determined by, but is not limited to, the intersection of the error voltage and the ramp signal. When the method outputs a switching signal to automatically switch the DC-DC converter to operate in a pulse-frequency modulation mode, the falling edge of the switching signal can be determined by, but is not limited to, the intersection of the peak current and the output inductor current.

[0096] Another preferred embodiment according to the present invention is an automatic mode switching circuit for a DC-DC converter.

[0097] Figure 6This is a schematic diagram of an automatic mode switching circuit for a DC-DC converter in this embodiment. Figure 6 As shown, the automatic mode switching circuit 6 for a DC-DC converter includes an error amplifier 60, a pulse frequency modulation (PFM) reference generator 62, a compensation network 64, and a comparator 66. The output of the error amplifier 60 is coupled to a positive input terminal (+) of the comparator 66. The pulse frequency modulation (PFM) reference generator 62 is coupled to the other positive input terminal (+) of the comparator 66. The compensation network 64 is coupled to the ground terminal GND.

[0098] The error amplifier 60 receives a reference voltage VREF and a feedback voltage FB related to the output voltage of the DC-DC converter at its positive input terminal + and negative input terminal -, respectively, to generate an error voltage Verr, which is then fed to a positive input terminal + of a comparator 66. A pulse frequency modulation (PFM) reference generator 62 provides a threshold voltage value PFM_TH of a PFM signal to the other positive input terminal + of the comparator 66. Comparator 66 receives the error voltage Verr and the threshold voltage value PFM_TH of the PFM signal at its two positive input terminals +, respectively, and receives a ramp signal SAW at its negative input terminal -. Comparator 66 outputs a switching signal S1 based on the comparison result between the error voltage Verr and the threshold voltage value PFM_TH of the PFM signal, automatically switching the DC-DC converter between pulse width modulation mode and pulse frequency modulation mode.

[0099] In actual applications, if the comparison result shows that the error voltage Verr is greater than the threshold voltage value PFM_TH of the pulse frequency modulation signal, the switching signal S1 is used to automatically switch the DC-DC converter to operate in the pulse width modulation mode; if the comparison result shows that the error voltage Verr is less than the threshold voltage value PFM_TH of the pulse frequency modulation signal, the switching signal S1 is used to automatically switch the DC-DC converter to operate in the pulse frequency modulation mode.

[0100] Figure 7 They are the timing diagrams of the output inductor current ILX, the ramp signal SAW and the switching signal S1. Figure 7 As shown, at time t1, the output inductor current ILX rises to equal the peak current Ipeak, while the error voltage Verr is less than the threshold voltage PFM_TH of the PWM signal. Switching signal S1 automatically switches the DC-DC converter to PWM mode, with the falling edge of switching signal S1 determined by the intersection of peak current Ipeak and output inductor current ILX. The situation at time t2 is similar to that at time t1, so the DC-DC converter continues to operate in PWM mode.

[0101] At time t3, the output inductor current ILX rises to equal the peak current Ipeak, and the error voltage Verr exceeds the threshold voltage PFM_TH of the pulse-frequency modulation signal. Switching signal S1 automatically switches the DC-DC converter to pulse-width modulation mode. The falling edge of switching signal S1 is determined by the intersection of error voltage Verr and ramp signal SAW (i.e., time t4). The situations at times t5 and t6 are similar to those at times t3 and t4, so the DC-DC converter continues to operate in pulse-width modulation mode. The remaining steps can be deduced similarly and are not further described here.

[0102] Compared to the prior art, the automatic mode switching method and circuit for a DC-DC converter proposed in the present invention can achieve linear and smooth switching between pulse frequency modulation (PFM) mode and pulse width modulation (PWM) mode. This effectively solves the problem of conventional DC-DC converters frequently switching between PFM and PWM modes when switching from heavy load to light load, thereby reducing output ripple.

Claims

1. A method for automatic mode switching of a DC-DC converter, characterized in that: The following steps are involved: (a) respectively obtaining a first width of a duty cycle of a pulse width modulation signal and a second width of a duty cycle of a pulse frequency modulation signal, wherein the first width is related to an error voltage and the second width is related to a peak current; as well as (b) Outputting a switching signal according to a comparison result of the first width and the second width to automatically switch the DC-DC converter to operate in a pulse width modulation mode or a pulse frequency modulation mode.

2. The automatic mode switching method according to claim 1, wherein: Step (b) comprises: (b1) if the comparison result is that the first width is greater than the second width, automatically switching the DC-DC converter to operate in the pulse width modulation mode; and (b2) If the comparison result is that the first width is smaller than the second width, the DC-DC converter is automatically switched to operate in the pulse frequency modulation mode.

3. The automatic mode switching method according to claim 1, wherein: Step (a) is to determine the first width according to the first rising edge and the first falling edge of the PWM signal and to determine the second width according to the second rising edge and the second falling edge of the PFM signal.

4. The automatic mode switching method according to claim 3, wherein: The first rising edge and the second rising edge both correspond to a first time, and the first falling edge and the second falling edge respectively correspond to a second time and a third time. If the second time is later than the third time, the comparison result is that the first width is greater than the second width, and the DC-DC converter operates in the pulse width modulation mode. If the second time is earlier than the third time, the comparison result is that the first width is less than the second width, and the DC-DC converter operates in the pulse frequency modulation mode.

5. The automatic mode switching method according to claim 4, wherein: The second time is determined by an intersection of the error voltage and the ramp signal and the third time is determined by an intersection of the peak current and the output inductor current.

6. The automatic mode switching method according to claim 1, wherein: The error voltage is generated according to a reference voltage and a feedback voltage related to the output voltage.

7. A method for automatic mode switching of a DC-DC converter, comprising the following steps: (a) respectively obtaining the critical voltage values ​​of the error voltage and the pulse frequency modulation signal; and (b) outputting a switching signal according to a comparison result between the error voltage and the threshold voltage value to automatically switch the DC-DC converter to operate in a pulse width modulation mode or a pulse frequency modulation mode; in, When the DC-DC converter operates in the pulse width modulation mode, the falling edge of the switching signal is determined by the intersection of the error voltage and the ramp signal; when the DC-DC converter operates in the pulse frequency modulation mode, the falling edge of the switching signal is determined by the intersection of the peak current and the output inductor current.

8. The automatic mode switching method according to claim 7, wherein: Step (b) comprises: (b1) if the comparison result shows that the error voltage is greater than the critical voltage value, automatically switching the DC-DC converter to operate in the pulse width modulation mode; and (b2) If the comparison result shows that the error voltage is less than the critical voltage value, the DC-DC converter is automatically switched to operate in the pulse frequency modulation mode.

9. The automatic mode switching method according to claim 7, wherein: The error voltage is generated according to a reference voltage and a feedback voltage related to the output voltage.

10. An automatic mode switching circuit for a DC-DC converter, comprising: A first comparator is used to provide a first width of a duty cycle of the PWM signal, wherein the first width is related to the error voltage; A second comparator for providing a second width of the duty cycle of the PWM signal, wherein the second width is related to the peak current; as well as The logic circuit is coupled to the first comparator and the second comparator respectively, and is used to output a switching signal according to a comparison result between the first width and the second width to automatically switch the DC-DC converter to operate in a pulse width modulation mode or a pulse frequency modulation mode.

11. The automatic mode switching circuit according to claim 10, wherein: If the comparison result shows that the first width is greater than the second width, the DC-DC converter operates in the pulse width modulation mode; if the comparison result shows that the first width is less than the second width, the DC-DC converter operates in the pulse frequency modulation mode.

12. The automatic mode switching circuit according to claim 10, wherein: The two input terminals of the first comparator receive the error voltage and the ramp signal respectively, and the two input terminals of the second comparator receive the voltage generated by the output inductor current flowing through the resistor and a reference voltage respectively. The error voltage is generated according to the reference voltage and a feedback voltage related to the output voltage.

13. The automatic mode switching circuit according to claim 10, wherein: The first width is determined by a first rising edge and a first falling edge of the PWM signal, and the second width is determined by a second rising edge and a second falling edge of the PFM signal.

14. The automatic mode switching circuit according to claim 13, wherein: The first rising edge and the second rising edge both correspond to a first time, and the first falling edge and the second falling edge respectively correspond to a second time and a third time. If the second time is later than the third time, the comparison result is that the first width is greater than the second width, and the DC-DC converter operates in the pulse width modulation mode. If the second time is earlier than the third time, the comparison result is that the first width is less than the second width, and the DC-DC converter operates in the pulse frequency modulation mode.

15. The automatic mode switching circuit according to claim 14, wherein: The second time is determined by an intersection of the error voltage and the ramp signal and the third time is determined by an intersection of the peak current and the output inductor current.

16. An automatic mode switching circuit for a DC-DC converter, characterized in that: include: an error amplifier for providing an error voltage; A pulse frequency modulation reference generator for providing a critical voltage value of a pulse frequency modulation signal; as well as a comparator, coupled to the error amplifier and the PWM reference generator, for outputting a switching signal according to a comparison result between the error voltage and the threshold voltage value to automatically switch the DC-DC converter to operate in a PWM mode or a PWM mode; When the DC-DC converter operates in the pulse width modulation mode, the falling edge of the switching signal is determined by the intersection of the error voltage and the ramp signal; when the DC-DC converter operates in the pulse frequency modulation mode, the falling edge of the switching signal is determined by the intersection of the peak current and the output inductor current.

17. The automatic mode switching circuit according to claim 16, wherein: If the comparison result shows that the error voltage is greater than the threshold voltage, the DC-DC converter operates in the pulse width modulation mode; if the comparison result shows that the error voltage is less than the threshold voltage, the DC-DC converter operates in the pulse frequency modulation mode.

18. The automatic mode switching circuit according to claim 16, wherein: Two input terminals of the error amplifier respectively receive a reference voltage and a feedback voltage related to the output voltage to generate the error voltage.

Images