Bootstrap recharge system in dual-switch flyback converters
According to an embodiment, a converter includes a bootstrap capacitor, a high-side switch, a low-side switch, an auxiliary switch, and a controller. The bootstrap capacitor has a first terminal coupled to a floating ground node. The high-side switch has a source terminal coupled to the bootstrap capacitor through the floating ground node. The auxiliary switch has a drain terminal coupled to the bootstrap capacitor through the floating ground node. The controller provides a first control signal to a control terminal of the high-side switch, provides a second control signal to a control terminal of the low-side switch, and provides a third control signal to a control terminal of the auxiliary switch. The third control signal is based on a condition associated with the converter after the first control signal and the second control signal deactivate the high-side switch and the low-side switch respectively.
1 . A converter, comprising:
a transformer having a primary side and a secondary side;
a bootstrap capacitor having a first terminal coupled to a floating ground node;
a high-side switch having a source terminal coupled to the bootstrap capacitor through the floating ground node and a drain terminal coupled to the primary side of the transformer;
a low-side switch having a source terminal coupled to ground and a drain terminal coupled to the primary side of the transformer;
an auxiliary switch having a drain terminal coupled to the bootstrap capacitor through the floating ground node; and
a controller configured to:
provide a first control signal to a control terminal of the high-side switch,
provide a second control signal to a control terminal of the low-side switch, and
provide a third control signal to a control terminal of the auxiliary switch, wherein the third control signal activates the auxiliary switch for a current cycle based on a condition associated with the converter after the first control signal and the second control signal deactivate the high-side switch and the low-side switch, respectively.
2 . The converter of claim 1 , further comprising a control logic circuit configured to monitor a voltage across the bootstrap capacitor.
3 . The converter of claim 2 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is less than a threshold.
4 . The converter of claim 2 , wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is greater than a threshold.
5 . The converter of claim 1 , further comprising a control logic circuit configured to monitor a voltage at the floating ground node for a duration within a period immediately after the high-side switch is turned OFF.
6 . The converter of claim 5 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is greater than a threshold.
7 . The converter of claim 5 , wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is less than a threshold.
8 . A method of operating a converter, the method comprising:
generating, by a controller, a first control signal to a control terminal of a high-side switch of the converter, the high-side switch having a source terminal coupled to a bootstrap capacitor through a floating ground node and a drain terminal coupled to a primary side of a transformer;
generating, by the controller, a second control signal to a control terminal of a low-side switch of the converter, the low-side switch having a source terminal coupled to ground and a drain terminal coupled to the primary side of the transformer; and
determining, by the controller, whether to activate an auxiliary switch for a current cycle using a third control signal, the auxiliary switch having a drain terminal coupled to the bootstrap capacitor through the floating ground node, wherein the determining is based on a condition associated with the converter after the first control signal and the second control signal deactivate the high-side switch and the low-side switch, respectively.
9 . The method of claim 8 , further comprising monitoring, by a control logic circuit, a voltage across the bootstrap capacitor.
10 . The method of claim 9 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is less than a threshold.
11 . The method of claim 10 , wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is greater than the threshold.
12 . The method of claim 8 , further comprising monitoring, by a control logic circuit, a voltage at the floating ground node for a duration within a period immediately after the high-side switch is turned OFF.
13 . The method of claim 12 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is greater than a threshold.
14 . The method of claim 12 , wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is less than a threshold.
15 . A device comprising a converter, the converter comprising:
a transformer having a primary side and a secondary side;
a bootstrap capacitor having a first terminal coupled to a floating ground node;
a high-side switch having a source terminal coupled to the bootstrap capacitor through the floating ground node and a drain terminal coupled to the primary side of the transformer;
a low-side switch having a source terminal coupled to ground and a drain terminal coupled to the primary side of the transformer;
an auxiliary switch having a drain terminal coupled to the bootstrap capacitor through the floating ground node; and
a controller configured to:
provide a first control signal to a control terminal of the high-side switch,
provide a second control signal to a control terminal of the low-side switch, and
provide a third control signal to a control terminal of the auxiliary switch, wherein the third control signal activates the auxiliary switch for a current cycle based on a condition associated with the converter after the first control signal and the second control signal deactivate the high-side switch and the low-side switch, respectively.
16 . The device of claim 15 , wherein the converter further comprises a control logic circuit configured to monitor a voltage across the bootstrap capacitor.
17 . The device of claim 16 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is less than a threshold, and wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage across the bootstrap capacitor is greater than the threshold.
18 . The device of claim 15 , wherein the converter further comprises a control logic circuit configured to monitor a voltage at the floating ground node for a duration within a period immediately after the high-side switch is turned OFF.
19 . The device of claim 18 , wherein the third control signal is set to activate the auxiliary switch for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is greater than a threshold.
20 . The device of claim 19 , wherein the third control signal is set to keep the auxiliary switch deactivated for the current cycle in response to detecting, by the control logic circuit, that the voltage at the floating ground node for the duration within the period immediately after the high-side switch is turned OFF is less than the threshold.