Control circuit of buck converter, and server
View Patent ↗Provided is a control circuit of a buck converter, comprising three transistors, seven resistors and a comparator. Also provided is a server. In this solution, when a phase voltage of a buck converter changes, a controller in the buck converter is controlled to output a signal for turning off a lower MOS transistor, so that after the signal is transmitted through the line, the lower MOS transistor can be controlled to be exactly turned off just when the current is reversed. Such an accurate reverse current detection function can reduce the voltage loss of the buck converter, thereby improving the efficiency of a system in standby or having a light load.
1. A control circuit of a buck converter, comprising:
a first transistor, a base electrode of the first transistor receiving an output voltage of the buck converter;
a second transistor, a base electrode of the second transistor being connected to an emitter electrode of the first transistor;
a third transistor, a base electrode of the third transistor being connected to a collector electrode of the second transistor;
a first resistor, one end of the first resistor being connected to a collector electrode of the third transistor;
a second resistor, one end of the second resistor being connected to the other end of the first resistor;
a fourth transistor, a collector electrode of the fourth transistor being connected to the other end of the second resistor;
a third resistor, one end of the third resistor being connected to an emitter electrode of the third transistor, and the other end of the third resistor receiving a phase voltage of the buck converter;
a fourth resistor, one end of the fourth resistor being connected to an emitter electrode of the fourth transistor and the other end of the fourth resistor being connected to a collector electrode of the first transistor;
a fifth resistor and a sixth resistor, one end of the fifth resistor being connected to the base electrode of the third transistor, the other end of the fifth resistor being connected to one end of the sixth resistor, and the other end of the sixth resistor being connected to a base electrode of the fourth transistor;
a seventh resistor, one end of the seventh resistor being connected to an emitter electrode of the second transistor and the other end of the seventh resistor being connected to a collector electrode of the first transistor; and a comparator, a positive input end of the comparator being connected to the collector electrode of the fourth transistor, a negative input end of the comparator being connected to the collector electrode of the third transistor, and an output end of the comparator being connected to a controller of the buck converter.
2. The control circuit according to claim 1 , wherein the comparator is configured to output a preset signal to the controller of the buck converter in response to voltages input at the positive input end of the comparator and the negative input end of the comparator being equal.
3. The control circuit according to claim 2 , wherein the controller is configured to generate a signal to control turning off of the lower MOS transistor in the buck converter in response to receiving the preset signal.
4. The control circuit according to claim 2 , wherein a resistance value of the first resistor is equal to a resistance value of the second resistor and a resistance value of the third resistor is equal to a resistance value of the fourth resistor.
5. The control circuit according to claim 1 , wherein the voltages input at the positive input end of the comparator and the negative input end of the comparator are equal when a phase voltage of the buck converter satisfies the following condition:
V
phase
=
R
5
R
7
V
out
R 5 being a resistance value of the fifth resistor, R 7 being a resistance value of the seventh resistor, V out being the output voltage of the buck converter.
6. The control circuit according to claim 1 , wherein the controller is configured to generate a signal to control turning off of the lower MOS transistor in the buck converter in response to receiving the preset signal.
7. The control circuit according to claim 1 , wherein a resistance value of the first resistor is equal to a resistance value of the second resistor and a resistance value of the third resistor is equal to a resistance value of the fourth resistor.
8. The control circuit according to claim 1 , wherein the magnitude of the current flowing through the first resistor is:
I
1
=
1
2
β
1
(
V
a
-
V
thn
1
-
I
a
R
5
-
I
1
R
3
-
V
phase
)
2
wherein V thn1 is a voltage drop when the third transistor is conducting, β 1 is a parameter of the third transistor.
9. The control circuit according to claim 8 , wherein magnitude of the current flowing through the second resistor is:
I
2
=
1
2
β
2
(
V
a
-
V
thn
2
-
I
2
R
4
-
V
gnd
)
2
wherein V thn2 is a voltage drop when the fourth transistor is conducting, β 2 is a parameter of the fourth transistor.
10. The control circuit according to claim 9 , wherein parameters of the third transistor are the same as parameters of the fourth transistor.
11. A server comprising a control circuit of a buck converter, the control circuit of a buck converter comprising:
a first transistor, a base electrode of the first transistor receiving an output voltage of the buck converter;
a second transistor, a base electrode of the second transistor being connected to an emitter electrode of the first transistor;
a third transistor, a base electrode of the third transistor being connected to a collector electrode of the second transistor;
a first resistor, one end of the first resistor being connected to a collector electrode of the third transistor;
a second resistor, one end of the second resistor being connected to the other end of the first resistor;
a fourth transistor, a collector electrode of the fourth transistor being connected to the other end of the second resistor;
a third resistor, one end of the third resistor being connected to an emitter electrode of the third transistor, and the other end of the third resistor receiving a phase voltage of the buck converter;
a fourth resistor, one end of the fourth resistor being connected to an emitter electrode of the fourth transistor and the other end of the fourth resistor being connected to a collector electrode of the first transistor;
a fifth resistor and a sixth resistor, one end of the fifth resistor being connected to the base electrode of the third transistor, the other end of the fifth resistor being connected to one end of the sixth resistor, and the other end of the sixth resistor being connected to a base electrode of the fourth transistor;
a seventh resistor, one end of the seventh resistor being connected to an emitter electrode of the second transistor and the other end of the seventh resistor being connected to a collector electrode of the first transistor; and a comparator, a positive input end of the comparator being connected to the collector electrode of the fourth transistor, a negative input end of the comparator being connected to the collector electrode of the third transistor, and an output end of the comparator being connected to a controller of the buck converter.
12. The server according to claim 11 , wherein the comparator is configured to output a preset signal to the controller of the buck converter in response to voltages input at the positive input end of the comparator and the negative input end of the comparator being equal.
13. The server according to claim 11 , wherein the controller is configured to generate a signal to control turning off of the lower MOS transistor in the buck converter in response to receiving the preset signal.
14. The server according to claim 11 , wherein a resistance value of the first resistor is equal to a resistance value of the second resistor and a resistance value of the third resistor is equal to a resistance value of the fourth resistor.
15. The server according to claim 11 , wherein the voltages input at the positive input end of the comparator and the negative input end of the comparator are equal when a phase voltage of the buck converter satisfies the following condition:
V
phase
=
R
5
R
7
V
out
R 5 being a resistance value of the fifth resistor, R 7 being a resistance value of the seventh resistor, V out being the output voltage of the buck converter, and V phase being the phase voltage of the buck converter.
16. The server according to claim 11 , wherein the controller is configured to generate a signal to control turning off of the lower MOS transistor in the buck converter in response to receiving the preset signal.
17. The server according to claim 11 , wherein a resistance value of the first resistor is equal to a resistance value of the second resistor and a resistance value of the third resistor is equal to a resistance value of the fourth resistor.
18. The server according to claim 11 , wherein the magnitude of the current flowing through the first resistor is:
I
1
=
1
2
β
1
(
V
a
-
V
thn
1
-
I
a
R
5
-
I
1
R
3
-
V
phase
)
2
wherein V thn1 is a voltage drop when the third transistor is conducting, β 1 is a parameter of the third transistor.
19. The server according to claim 18 , wherein magnitude of the current flowing through the second resistor is:
I
2
=
1
2
β
2
(
V
a
-
V
thn
2
-
I
2
R
4
-
V
gnd
)
2
wherein V thn2 is a voltage drop when the fourth transistor is conducting, β 2 is a parameter of the fourth transistor.
20. The server according to claim 19 , wherein parameters of the third transistor are the same as parameters of the fourth transistor.