Isolated DC/DC converter and power electronics system
An isolated DC/DC converter includes: a transformer having a primary side and a secondary side; an inverter configured to change a DC input voltage (Vin) to an AC current for energizing the primary side of the transformer; a capacitor in series with the primary side of the transformer; and a controller configured to operate the inverter in a first mode such that the capacitor pre-charges to |Vin| before the controller receives a turn ON command, the capacitor charges to X*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command where X>1, and the capacitor voltage resonates with a magnetizing inductance of the primary side of the transformer during a second part of the first switching cycle. A power electronics device that includes the isolated DC/DC converter is also described.
1. An isolated DC/DC converter, comprising:
a transformer having a primary side and a secondary side;
an inverter configured to change a DC input voltage (Vin) to an AC current for energizing the primary side of the transformer;
a capacitor in series with the primary side of the transformer; and
a controller configured to operate the inverter in a first mode such that the capacitor pre-charges to |Vin| before the controller receives a turn ON command, the capacitor charges to X*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command where X>1, and the capacitor voltage resonates with a magnetizing inductance of the primary side of the transformer during a second part of the first switching cycle.
2. The isolated DC/DC converter of claim 1 , wherein the inverter is a full-bridge inverter comprising a first leg and a second leg, wherein each leg comprises a high-side switch device in series with a low-side switch device, wherein the high-side switch device of the first leg and the low-side switch device of the second leg form a first phase of the inverter, wherein the high-side switch device of the second leg and the low-side switch device of the first leg form a second phase of the inverter, and wherein the controller is configured to operate the first and second phases in a complementary manner.
3. The isolated DC/DC converter of claim 2 , wherein before receiving the turn ON command in the first mode, the controller is configured to keep on the high-side switch device and the low-side switch device of one of the phases to pre-charge the capacitor to |Vin|.
4. The isolated DC/DC converter of claim 2 , wherein during the first part of the first switching cycle in the first mode, the controller is configured to deactivate the phase used to pre-charge the capacitor to |Vin| and then activate the complementary phase.
5. The isolated DC/DC converter of claim 2 , wherein during the second part of the first switching cycle in the first mode, the controller is configured to deactivate the phase used during the first part of the first switching cycle and then activate the complementary phase.
6. The isolated DC/DC converter of claim 1 , wherein the controller is configured to operate the inverter in the first mode for at least one additional switching cycle, wherein during a first part of each additional switching cycle, the controller is configured to operate the inverter to charge the capacitor to X*|Vin|, and wherein during a second part of each additional switching cycle, the controller is configured to operate the inverter such that the capacitor voltage resonates with the magnetizing inductance of the primary side of the transformer.
7. The isolated DC/DC converter of claim 1 , wherein the controller is configured to operate the inverter in a second mode that follows the first mode, wherein the inverter is operated at a lower switching frequency in the second mode than in the first mode.
8. The isolated DC/DC converter of claim 7 , wherein the controller is configured to control the switching frequency and the voltage across the capacitor in the second mode to generate a constant current source that is independent of Vin.
9. The isolated DC/DC converter of claim 7 , wherein the controller comprises:
a peak detector configured to determine when the capacitor voltage reaches a peak value; and
a delay-locked loop configured to maintain an on-phase for the inverter in the second mode.
10. The isolated DC/DC converter of claim 7 , wherein the controller is configured to trim an oscillator in the first mode to tune the switching frequency in the first mode, and wherein the controller is configured to use a minimum clock cycle in the second mode such that the capacitor fully pre-charges to Vin prior to charge transfer to the secondary side of the transformer.
11. The isolated DC/DC converter of claim 1 , wherein in the first mode, the controller is configured to determine when to transition from the first part of the first switching cycle to the second part of the first switching cycle based on the capacitor voltage.
12. The isolated DC/DC converter of claim 11 , wherein the controller is configured to transition from the first part of the first switching cycle to the second part of the first switching cycle when the capacitor voltage is at or near a peak value.
13. The isolated DC/DC converter of claim 1 , further comprising:
a rectifier coupled between the secondary side of the transformer and a gate of a power switch device,
wherein the power switch device is configured to turn on when the controller operates the inverter in the first mode.
14. The isolated DC/DC converter of claim 13 , wherein the controller is configured to operate the inverter in a second mode that follows the first mode, wherein the inverter is operated at a lower switching frequency in the second mode than in the first mode, and wherein the power switch device is configured to remain on when the controller operates the inverter in the second mode.
15. The isolated DC/DC converter of claim 14 , wherein the power switch device is a gate injection transistor having a non-isolated p-GaN gate structure, wherein the controller is configured to control the switching frequency of the inverter and the voltage across the capacitor in the second mode to generate a constant current source for energizing the primary side of the transformer, and wherein the rectifier is configured to convert energy transferred to the secondary side of the transformer from the constant current source in the second mode into a current that is injected into the non-isolated p-GaN gate structure to maintain the gate injection transistor in the on-state.
16. The isolated DC/DC converter of claim 13 , further comprising:
an additional transformer having a primary side and a secondary side;
a pulldown switch device configured to turn off the power switch device;
an additional rectifier coupled between the secondary side of the additional transformer and a gate of the pulldown switch device;
an additional inverter configured to change Vin to an AC current for energizing the primary side of the additional transformer; and
an additional capacitor in series with the primary side of the additional transformer,
wherein the controller is configured to operate the additional inverter in a first mode such that the additional capacitor pre-charges to |Vin| before the controller receives a turn ON command for the pulldown switch device, the additional capacitor charges to Y*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command for the pulldown switch device where Y>1, and the voltage of the additional capacitor resonates with a magnetizing inductance of the primary side of the additional transformer during a second part of the first switching cycle.
17. The isolated DC/DC converter of claim 16 , wherein the controller is configured to operate the additional inverter in a second mode that follows the first mode of the additional inverter, wherein the additional inverter is operated at a lower switching frequency in the second mode than in the first mode, and wherein the pulldown switch device is configured to remain on when the controller operates the additional inverter in the second mode.
18. The isolated DC/DC converter of claim 13 , further comprising:
an additional transformer having a primary side and a secondary side;
an additional rectifier coupled between the secondary side of the additional transformer and a gate of an additional power switch device connected in series with the power switch device;
an additional inverter configured to change Vin to an AC current for energizing the primary side of the additional transformer; and
an additional capacitor in series with the primary side of the additional transformer,
wherein the controller is configured to operate the additional inverter in a first mode such that the additional capacitor pre-charges to |Vin| before the controller receives a turn ON command for the additional power switch device, the additional capacitor charges to Z*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command for the additional power switch device where Z>1, and the voltage of the additional capacitor resonates with a magnetizing inductance of the primary side of the additional transformer during a second part of the first switching cycle.
19. The isolated DC/DC converter of claim 18 , wherein the controller is configured to operate the additional inverter in a second mode that follows the first mode of the additional inverter, wherein the additional inverter is operated at a lower switching frequency in the second mode than in the first mode, and wherein the additional power switch device is configured to remain on when the controller operates the additional inverter in the second mode.
20. The isolated DC/DC converter of claim 19 , wherein the additional power switch device is a gate injection transistor having a non-isolated p-GaN gate structure, wherein the controller is configured to control the switching frequency of the additional inverter and the voltage across the additional capacitor in the second mode of the additional inverter to generate a constant current source for energizing the primary side of the additional transformer, and wherein the additional rectifier is configured to convert energy transferred to the secondary side of the additional transformer from the constant current source in the second mode into a current that is injected into the non-isolated p-GaN gate structure to maintain the gate injection transistor in the on-state.
21. A power electronics system, comprising:
a power switch device;
a pulldown switch device configured to turn off the power switch device when the pulldown switch device is on;
a flyback converter configured to drive a gate of the power switch device; and
an isolated DC/DC converter comprising:
a transformer having a primary side and a secondary side;
a rectifier coupled between the secondary side of the transformer and a gate of the pulldown switch device;
an inverter configured to change a DC input voltage (Vin) to an AC current for energizing the primary side of the transformer;
a capacitor in series with the primary side of the transformer; and
a controller configured to operate the inverter in a first mode such that the capacitor pre-charges to |Vin| before the controller receives a turn ON command for the pulldown switch device, the capacitor charges to X*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command where X>1, and the capacitor voltage resonates with a magnetizing inductance of the primary side of the transformer during a second part of the first switching cycle.
22. The power electronics system of claim 21 , wherein the controller is configured to operate the inverter in a second mode that follows the first mode, wherein the inverter is operated at a lower switching frequency in the second mode than in the first mode, and wherein the pulldown switch device is configured to remain on when the controller operates the inverter in the second mode.
23. The power electronics system of claim 21 , further comprising:
a failsafe device configured to protect the pulldown switch device from overvoltage; and
an additional isolated DC/DC converter comprising:
an additional transformer having a primary side and a secondary side;
an additional rectifier coupled between the secondary side of the additional transformer and a gate of the failsafe device;
an additional inverter configured to change Vin to an AC current for energizing the primary side of the additional transformer; and
an additional capacitor in series with the primary side of the additional transformer,
wherein the controller is configured to operate the additional inverter in a first mode such that the additional capacitor pre-charges to |Vin| before the controller receives a turn ON command for the failsafe device, the additional capacitor charges to Y*|Vin| during a first part of a first switching cycle after the controller receives the turn ON command for the failsafe device where Y>1, and the voltage of the additional capacitor resonates with a magnetizing inductance of the primary side of the additional transformer during a second part of the first switching cycle.
24. The power electronics system of claim 23 , wherein the controller is configured to operate the additional inverter in a second mode that follows the first mode of the additional inverter, wherein the additional inverter is operated at a lower switching frequency in the second mode than in the first mode, and wherein the failsafe device is configured to remain on when the controller operates the additional inverter in the second mode.