Control method, device, and system for synchronous buck circuit, and electronic device
A control method for a synchronous BUCK circuit is disclosed, including: obtaining an input voltage, an output voltage and an output current of the synchronous BUCK circuit; obtaining a current state of the synchronous switch transistor; obtaining a turn-off current threshold when the synchronous switch transistor is in an on state; switching the synchronous switch transistor to an off state when the output current is less than the turn-off current threshold; calculating a duty ratio of a main switch transistor according to the input voltage, the output voltage and the turn-off current threshold; and generating a corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit.
1. A control method for a synchronous BUCK circuit, comprising:
obtaining an input voltage, an output voltage and an output current of the synchronous BUCK circuit;
obtaining a current state of a synchronous switch transistor in the synchronous BUCK circuit;
obtaining a turn-off current threshold when the synchronous switch transistor is in an on state;
switching the synchronous switch transistor to an off state when the output current is less than the turn-off current threshold;
calculating a duty ratio of a main switch transistor in the synchronous BUCK circuit according to the input voltage, the output voltage and the turn-off current threshold; and
generating a corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit,
wherein the duty ratio of the main switch transistor is calculated according to the input voltage, the output voltage and the turn-off current threshold based on a first duty ratio formula; and the first duty ratio formula is:
D
=
V
out
V
in
-
V
out
2
L
·
I
x
V
out
·
T
s
,
wherein D is the duty ratio of the main switch transistor; V in is a currently sampled input voltage; V out is a currently sampled output voltage; L is an inductance value of an inductor in the synchronous BUCK circuit; I x is the turn-off current threshold; and T s is a switching cycle of the main switch transistor.
2. The method according to claim 1 , further including:
obtaining a turn-on current threshold when the synchronous switch transistor is in the off state;
switching the synchronous switch transistor to the on state when the output current is greater than the turn-on current threshold;
calculating the duty ratio of the main switch transistor according to the input voltage and the output voltage; and
generating the corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit.
3. The method according to claim 2 , wherein the duty ratio of the main switch transistor is calculated according to the input voltage and the output voltage based on a second duty ratio formula; and the second duty ratio formula is:
D
=
V
out
V
in
,
wherein D is the duty ratio of the main switch transistor; V m is a currently sampled input voltage; and V out is a currently sampled output voltage.
4. The method according to claim 2 , wherein the synchronous BUCK circuit further comprises a loop compensation module, and the loop compensation module is provided with a corresponding discrete domain difference equation so as to determine the duty ratio of the main switch transistor or an intermediate quantity for solving the duty ratio; and the method further comprises:
maintaining a current state of the synchronous switch transistor when the synchronous switch transistor is in the on state and the output current is greater than or equal to the turn-off current threshold;
calculating the duty ratio of the main switch transistor or the intermediate quantity for solving the duty ratio according to a deviation between the output voltage and a reference voltage and the discrete domain difference equation; and
generating the corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit, or generating the corresponding driving signal by using the duty ratio after the duty ratio is solved according to the intermediate quantity, to control the synchronous BUCK circuit.
5. The method according to claim 4 , wherein the method further comprises:
maintaining the current state of the synchronous switch transistor when the synchronous switch transistor is in the off state and the output current is less than or equal to the turn-on current threshold;
calculating the duty ratio of the main switch transistor or the intermediate quantity for solving the duty ratio according to the deviation between the output voltage and the reference voltage and the discrete domain difference equation; and
generating the corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit, or generating the corresponding driving signal by using the duty ratio after the duty ratio is solved according to the intermediate quantity, to control the synchronous BUCK circuit.
6. The method according to claim 4 , wherein an expression of the discrete domain difference equation is:
U ( n )= A 1 U ( n− 1)+ . . . + A i U ( n−i )+ B 1 E ( n )+ B 2 E ( n− 1)+ . . . + B j E ( n−j ),
wherein U represents the duty ratio or the intermediate quantity for calculating the duty ratio; n represents a current sample; n−1 represents a previous sample; E represents the deviation between the output voltage and the reference voltage; i and j are integers greater than or equal to 2; and A 1 , A i , B 1 , B 2 and B j represent gain coefficients of corresponding terms respectively.
7. The method according to claim 4 , wherein after the calculating the duty ratio of the main switch transistor according to the input voltage, the output voltage and the turn-off current threshold, the method further comprises:
adjusting a variable of the discrete domain difference equation according to the calculated duty ratio of the main switch transistor, so that an output value of the adjusted discrete domain difference equation is the duty ratio or the intermediate quantity for calculating the duty ratio.
8. The method according to claim 4 , wherein after the calculating the duty ratio of the main switch transistor according to the input voltage and the output voltage, the method further comprises:
adjusting a variable of the discrete domain difference equation according to the calculated duty ratio of the main switch transistor, so that an output value of the adjusted discrete domain difference equation is the duty ratio or the intermediate quantity for calculating the duty ratio.
9. The method according to claim 4 , wherein the loop compensation module comprises a loop controller adopting PI control, PD control or PID control.
10. A synchronous BUCK circuit system, comprising:
a synchronous BUCK circuit and a control device, wherein
the control device is configured to control the synchronous BUCK circuit; and the synchronous BUCK circuit comprises:
a main switch transistor, an inductor, a synchronous switch transistor, an energy-storage capacitor and a sampling circuit,
wherein:
the sampling circuit is configured to collect an input voltage, an output voltage and an output current of the synchronous BUCK circuit and output to the control device;
the main switch transistor has a first terminal connected to a positive electrode of a power supply, a second terminal connected to a first terminal of the inductor, and a control terminal connected to the control device;
the synchronous switch transistor has a first terminal connected to the second terminal of the main switch transistor and the first terminal of the inductor, a second terminal connected to a negative electrode of the power supply, and a control terminal connected to the control device;
a second terminal of the inductor is connected to a positive electrode of the energy-storage capacitor, a negative electrode of the energy-storage capacitor is connected to the negative electrode of the power supply, and both terminals of the energy-storage capacitor are further connected to a load in parallel, and
wherein the control device comprises:
an obtaining module, configured to obtain the input voltage, the output voltage and the output current of the synchronous BUCK circuit, obtain a current state of the synchronous switch transistor in the synchronous BUCK circuit, and further obtain a turn-off current threshold when the synchronous switch transistor is in an on state;
a switching module, configured to switch the synchronous switch transistor to an off state when the output current is less than the turn-off current threshold;
a calculating module, configured to calculate a duty ratio of the main switch transistor in the synchronous BUCK circuit according to the input voltage, the output voltage and the turn-off current threshold; and
a driving control module, configured to generate a corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit,
wherein the calculating module calculates the duty ratio of the main switch transistor according to the input voltage, the output voltage and the turn-off current threshold based on a first duty ratio formula; and the first duty ratio formula is:
D
=
V
out
V
in
-
V
out
2
L
·
I
x
V
out
·
T
s
,
wherein D is the duty ratio of the main switch transistor; V in is a currently sampled input voltage; V out is a currently sampled output voltage; L is an inductance value of an inductor in the synchronous BUCK circuit; I x is the turn-off current threshold; and T s is a switching cycle of the main switch transistor.
11. The synchronous BUCK circuit system according to claim 10 , wherein
the obtaining module is further configured to obtain a turn-on current threshold when the synchronous switch transistor is in the off state;
the switching module is further configured to switch the synchronous switch transistor to the on state when the output current is greater than the turn-on current threshold;
the calculating module is further configured to calculate a duty ratio of the main switch transistor according to the input voltage and the output voltage; and
the driving control module is further configured to generate a corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit.
12. The synchronous BUCK circuit system according to claim 11 , wherein the calculating module calculates the duty ratio of the main switch transistor according to the input voltage and the output voltage based on a second duty ratio formula; and the second duty ratio formula is:
D
=
V
out
V
in
,
wherein D is the duty ratio of the main switch transistor; V in is a currently sampled input voltage; and V out is a currently sampled output voltage.
13. The synchronous BUCK circuit system according to claim 11 , wherein the synchronous BUCK circuit further comprises a loop compensation module, and the loop compensation module is provided with a corresponding discrete domain difference equation so as to determine the duty ratio of the main switch transistor or an intermediate quantity for solving the duty ratio;
the switching module is further configured to maintain a current state of the synchronous switch transistor when the synchronous switch transistor is in the on state and the output current is greater than or equal to the turn-off current threshold;
the calculating module is further configured to calculate the duty ratio of the main switch transistor or the intermediate quantity for solving the duty ratio according to a deviation between the output voltage and a reference voltage and the discrete domain difference equation; and
the driving control module is further configured to generate the corresponding driving signal according to the duty ratio, to control the synchronous BUCK circuit, or generate the corresponding driving signal by using the duty ratio after the duty ratio is solved according to the intermediate quantity, to control the synchronous BUCK circuit.
14. The synchronous BUCK circuit system according to claim 13 , wherein an expression of the discrete domain difference equation is:
U ( n )= A 1 U ( n− 1)+ . . . + A i U ( n−i )+ B 1 E ( n )+ B 2 E ( n− 1)+ . . . + B j E ( n−j ),
wherein U represents the duty ratio or the intermediate quantity for calculating the duty ratio; n represents a current sample; n−1 represents a previous sample; E represents the deviation between the output voltage and the reference voltage; i and j are integers greater than or equal to 2; and A 1 , A i , B 1 , B 2 and B j represent gain coefficients of corresponding terms respectively.
15. The synchronous BUCK circuit system according to claim 13 , wherein the calculating module, after calculating the duty ratio of the main switch transistor according to the input voltage, the output voltage and the turn-off current threshold, or after calculating the duty ratio of the main switch transistor according to the input voltage and the output voltage, is further configured to:
adjust a variable of the discrete domain difference equation according to the obtained duty ratio of the main switch transistor, so that an output value of the adjusted discrete domain difference equation is the duty ratio or the intermediate quantity for calculating the duty ratio.
16. An electronic device, comprising a synchronous BUCK circuit system according to claim 10 .