Switching converter and control circuit and discontinuous conduction mode control method thereof
A switching converter includes: a power stage circuit configured to switch at least one switch of the power stage circuit according to a control signal, to convert an input voltage to an output voltage; and a control circuit configured to execute modulation on a pulse width according to a feedback voltage related to the output voltage, to generate the control signal in a heavy load status. In a light load status, and when the switching converter operates in a discontinuous conduction mode (DCM), after an inductor current flowing through the power stage circuit has already become a zero current, the control circuit ceases executing modulation on the pulse width according to the feedback voltage and keeps a compensation voltage correlate with the output voltage at a present level.
1 . A switching converter, comprising:
a power stage circuit, which is configured to operably switch at least one switch of the power stage circuit according to a control signal, to convert an input voltage to an output voltage; and
a control circuit, which is configured to operably execute modulation on a pulse width according to a feedback voltage related to the output voltage, to generate the control signal in a heavy load status;
wherein in a case where a light load status is in the presence and in a case where the switching converter operates in a discontinuous conduction mode (DCM), after an inductor current flowing through the power stage circuit has already become a zero current, the control circuit is configured to operably cease executing modulation on the pulse width according to the feedback voltage and keep a compensation voltage correlated with the output voltage at a present level;
wherein the control circuit includes:
a compensation voltage comparator, which is configured to operably compare the compensation voltage with a compensation threshold voltage, to generate a compensation comparison signal;
a pulse width decision circuit, which is configured to operably generate the control signal in accordance with the compensation comparison signal in the heavy load status;
a feedback voltage comparator, which is configured to operably compare a reference voltage and the feedback voltage, to generate a feedback comparison signal; and
a light load detection circuit, wherein after the inductor current flowing through the power stage circuit has already become the zero current, the light load detection circuit is configured to operably decide an occurrence time point of a zero current operation and the light load detection circuit is configured to operably decide a termination time point of the zero current operation based upon the feedback comparison signal.
2 . The switching converter as claimed in claim 1 , wherein the compensation threshold voltage is the reference voltage or a ramp voltage, wherein the ramp voltage is correlated with the control signal.
3 . The switching converter as claimed in claim 2 , wherein the control circuit further includes:
a compensator having:
a feedback voltage amplifier, wherein in the heavy load status, the feedback voltage amplifier is configured to operably amplify a difference between the reference voltage and the feedback voltage, so as to generate a feedback amplification voltage; and
a filter circuit, wherein in the heavy load status, the filter circuit is configured to operably execute an operation of filtering on the feedback amplification voltage to generate the compensation voltage, and wherein during the zero current operation, the filter circuit is configured to operably keep the compensation voltage correlated with the output voltage at the present level.
4 . The switching converter as claimed in claim 1 , wherein in the heavy load status, the switching converter operates in a constant ON time (COT) mode.
5 . The switching converter as claimed in claim 1 , wherein after the inductor current flowing through the power stage circuit has already become the zero current, the light load detection circuit is configured to operably decide the occurrence time point according to the feedback voltage or after the light load detection circuit has already conducted an operation of timing for a preset period, the light load detection circuit is configured to operably decide the occurrence time point.
6 . The switching converter as claimed in claim 1 , wherein the light load detection circuit is configured to operably decide the occurrence time point based upon a situation wherein each of the at least one switch is OFF.
7 . The switching converter as claimed in claim 1 , wherein the control circuit further includes:
a timer circuit, which is configured to operably conduct an operation of timing for a duplication period from the occurrence time point to a time point where the compensation comparison signal is a zero voltage, and then immediately continue timing for the duplication period to determine the termination time point.
8 . The switching converter as claimed in claim 7 , wherein the timer circuit includes: a digital timer or an analog timer.
9 . The switching converter as claimed in claim 8 , wherein the digital timer begins to count up for the duplication period at the occurrence time point, and subsequently begins to count down for the duplication period right after the digital timer finishing counting up for the duplication period to determine the termination time point.
10 . The switching converter as claimed in claim 1 , wherein subsequent to the termination time point, the control circuit adjusts the control signal, so as to turn ON a corresponding switch of the at least one switch for an additional ON time.
11 . A control circuit, which is configured to operably control a switching converter, wherein the switching converter includes: a power stage circuit, which is configured to operably switch at least one switch of the power stage circuit according to a control signal, to convert an input voltage to an output voltage;
wherein the control circuit is configured to operably execute modulation on a pulse width according to a feedback voltage related to the output voltage, to generate the control signal in a heavy load status;
wherein in a case where a light load status is in the presence and in a case where the switching converter operates in a discontinuous conduction mode (DCM), after an inductor current flowing through the power stage circuit has already become a zero current, the control circuit is configured to operably cease executing modulation on the pulse width according to the feedback voltage and keep a compensation voltage correlated with the output voltage at a present level;
the control circuit comprising:
a compensation voltage comparator, which is configured to operably compare the compensation voltage with a compensation threshold voltage, to generate a compensation comparison signal;
a pulse width decision circuit, which is configured to operably generate the control signal in accordance with the compensation comparison signal in the heavy load status;
a feedback voltage comparator, which is configured to operably compare a reference voltage and the feedback voltage, to generate a feedback comparison signal; and
a light load detection circuit, wherein after the inductor current flowing through the power stage circuit has already become the zero current, the light load detection circuit is configured to operably decide an occurrence time point of a zero current operation and the light load detection circuit is configured to operably decide a termination time point of the zero current operation based upon the feedback comparison signal.
12 . The control circuit as claimed in claim 11 , wherein the compensation threshold voltage is the reference voltage or a ramp voltage, wherein the ramp voltage is correlated with the control signal.
13 . The control circuit as claimed in claim 12 , further comprising:
a compensator having:
a feedback voltage amplifier, wherein in the heavy load status, the feedback voltage amplifier is configured to operably amplify a difference between the reference voltage and the feedback voltage, so as to generate a feedback amplification voltage; and
a filter circuit, wherein in the heavy load status, the filter circuit is configured to operably execute an operation of filtering on the feedback amplification voltage to generate the compensation voltage, and wherein during the zero current operation, the filter circuit is configured to operably keep the compensation voltage correlated with the output voltage at the present level.
14 . The control circuit as claimed in claim 11 , wherein the heavy load status, the switching converter operates in a constant ON time (COT) mode.
15 . The control circuit as claimed in claim 11 , wherein after the inductor current flowing through the power stage circuit has already become the zero current, the light load detection circuit is configured to operably decide the occurrence time point according to the feedback voltage or after the light load detection circuit has already conducted an operation of timing for a preset period, the light load detection circuit is configured to operably decide the occurrence time point.
16 . The control circuit as claimed in claim 11 , wherein the light load detection circuit is configured to operably decide the occurrence time point based upon a situation wherein each of the at least one switch is OFF.
17 . The control circuit as claimed in claim 11 , further comprising:
a timer circuit, which is configured to operably conduct an operation of timing for a duplication period from the occurrence time point to a time point where the compensation comparison signal is a zero voltage, and then immediately continue timing for the duplication period to determine the termination time point.
18 . The control circuit as claimed in claim 17 , wherein the timer circuit includes: a digital timer or an analog timer.
19 . The control circuit as claimed in claim 18 , wherein the digital timer begins to count up for the duplication period at the occurrence time point, and subsequently begins to count down for the duplication period right after the digital timer finishing counting up for the duplication period to determine the termination time point.
20 . The control circuit as claimed in claim 11 , wherein subsequent to the termination time point, the control circuit adjusts the control signal, so as to turn ON a corresponding switch of the at least one switch for an additional ON time.
21 . A control method for a switching converter operating in a discontinuous conduction mode (DCM), which is configured to operably control the switching converter, wherein the switching converter includes: a power stage circuit, which is configured to operably switch at least one switch of the power stage circuit according to a control signal, to convert an input voltage to an output voltage; the control method comprising following steps:
in a heavy load status, executing modulation on a pulse width according to a feedback voltage related to the output voltage, to generate the control signal;
in a case where a light load status is in the presence and in a case where the switching converter operates in the discontinuous conduction mode (DCM), after an inductor current flowing through the power stage circuit has already become a zero current, ceasing executing modulation on the pulse width according to the feedback voltage and keeping a compensation voltage correlated with the output voltage at a present level;
comparing the compensation voltage with a compensation threshold voltage, to generate a compensation comparison signal;
in the heavy load status, generating the control signal in accordance with the compensation comparison signal;
comparing a reference voltage and the feedback voltage, to generate a feedback comparison signal; and
after the inductor current flowing through the power stage circuit has already become the zero current, deciding an occurrence time point of a zero current operation and deciding a termination time point of the zero current operation based upon the feedback comparison signal.
22 . The control method as claimed in claim 21 , wherein the compensation threshold voltage is the reference voltage or a ramp voltage, wherein the ramp voltage is correlated with the control signal.
23 . The control method as claimed in claim 22 , further comprising following steps:
in the heavy load status, amplifying a difference between the reference voltage and the feedback voltage, so as to generate a feedback amplification voltage; and
in the heavy load status, filtering on the feedback amplification voltage to generate the compensation voltage, and wherein during the zero current operation, keeping the compensation voltage correlated with the output voltage at the present level.
24 . The control method as claimed in claim 21 , wherein in the heavy load status, the switching converter operates in a constant ON time (COT) mode.
25 . The control method as claimed in claim 21 , further comprising following steps:
after the inductor current flowing through the power stage circuit has already become the zero current, deciding the occurrence time point according to the feedback voltage or after timing for a preset period right after the inductor current becoming the zero current, deciding the occurrence time point.
26 . The control method as claimed in claim 21 , further comprising following steps:
deciding the occurrence time point based upon a situation wherein each of the at least one switch is OFF.
27 . The control method as claimed in claim 21 , further comprising following steps:
conducting an operation of timing for a duplication period from the occurrence time point to a time point where the compensation comparison signal is a zero voltage, and then immediately continuing timing for the duplication period to determine the termination time point.
28 . The control method as claimed in claim 27 , further comprising:
beginning to count up for the duplication period at the occurrence time point, and subsequently beginning to count down for the duplication period right after finishing counting up for the duplication period by a digital timer to determine the termination time point.
29 . The control method as claimed in claim 21 , further comprising following steps:
subsequent to the termination time point, adjusting the control signal, so as to turn ON a corresponding switch of the at least one switch for an additional ON time.