Isolated DC-DC converter with an H-bridge circuit
Isolated DC-DC converters and methods for operating the same are described herein. DC-DC converters include a driver that drives a primary winding of a transformer to transmit power to a secondary winding of the transformer across an isolation barrier. In some embodiments, a pair of symmetrical serial capacitors are provided between the driver and the primary winding of a resonant DC-DC converter with an on-chip transformer to slow down variations of a common mode voltage on the primary winding during operation. This in turn can suppress radiation emissions related to time variation rates of the common mode voltage and, and can also improve electromagnetic interference (EMI) performance of the DC-DC converter.
1. A DC-DC converter, comprising:
a primary winding having first and second terminals;
a secondary winding separated from the primary winding by an isolation barrier;
a full bridge driver;
a first capacitor coupled between the full bridge driver and the first terminal of the primary winding;
a second capacitor coupled between the full bridge driver and the second terminal of the primary winding, wherein
the full bridge driver is an H-bridge circuit having a plurality of switches and wherein
the first capacitor is coupled between a common node of a first switch and a second switch of the plurality of switches and the first terminal of the primary winding, and
the second capacitor is coupled between a common node of a third switch and a fourth switch of the plurality of switches and the second terminal of the primary winding.
2. The DC-DC converter of claim 1 , wherein the primary winding and secondary winding are integrated on a same substrate.
3. The DC-DC converter of claim 1 , wherein the first capacitor and the second capacitor are of substantially the same capacitance value.
4. The DC-DC converter of claim 1 , further comprising a parallel capacitor in parallel with a switch of the plurality of switches.
5. The DC-DC converter of claim 1 , further comprising a current injection circuit coupled to the full bridge driver and configured to become active during a transition from an OFF state of the full bridge driver to an ON state of the full bridge driver.
6. The DC-DC converter of claim 1 , further comprising a bias resistor coupled between a terminal of the secondary winding and a voltage proportional to an output voltage of the DC-DC converter.
7. The DC-DC converter of claim 1 , further comprising a full bridge rectifier coupled to the secondary winding and a parallel capacitor coupled between a first terminal and a second terminal of the secondary winding.
8. A method of operating a DC-DC converter comprising a primary winding, a secondary winding and a full bridge driver, wherein the secondary winding is separated from the primary winding by an isolation barrier, the method comprising:
driving a signal from the full bridge driver through a serial current path through a first capacitor coupled to a first terminal of the primary winding, the primary winding and a second capacitor coupled to a second terminal of the primary winding, wherein
the full bridge driver is an H-bridge circuit having a plurality of switches and wherein
a first voltage node of the full bridge driver is a common node of a first switch and a second switch of the plurality of switches, and
a second voltage node of the full bridge driver is a common node of a third switch and a fourth switch of the plurality of switches.
9. The method of claim 8 , wherein the primary winding and secondary winding are integrated on a same substrate.
10. The method of claim 8 , wherein the first capacitor and the second capacitor are of substantially the same capacitance value.
11. The method of claim 8 , wherein the DC-DC converter further comprises a parallel capacitor in parallel with a switch of the plurality of switches.
12. The method of claim 8 , further comprising:
engaging a current injection circuit coupled to the full bridge driver to alter an amount of current passing through the primary winding during a transition from an OFF state of the full bridge driver to an ON state of the full bridge driver.
13. The method of claim 8 , further comprising:
coupling a terminal of the secondary winding with a voltage proportional to an output voltage of the DC-DC converter with a bias resistor.
14. The method of claim 8 , further comprising coupling a full bridge rectifier to the secondary winding, and coupling a first terminal and a second terminal of the secondary winding via a parallel capacitor.
15. A resonant DC-DC converter, comprising:
a transformer having a primary winding and a secondary winding integrated on a semiconductor substrate, wherein the secondary winding is separated from the primary winding by an isolation barrier;
a full bridge driver capacitively coupled to the primary winding with a first serial capacitor and a second serial capacitor, wherein
the full bridge driver is an H-bridge circuit having a plurality of switches and wherein
the first serial capacitor is coupled between a common node of a first switch and a second switch of the plurality of switches and a first terminal of the primary winding, and
the second serial capacitor is coupled between a common node of a third switch and a fourth switch of the plurality of switches and a second terminal of the primary winding;
a feedback loop coupled between an output of the DC-DC converter and an input of the full bridge driver.
16. The resonant DC-DC converter of claim 15 , wherein the second serial capacitor has substantially the same capacitance value as the first serial capacitor.
17. The resonant DC-DC converter of claim 15 , wherein the feedback loop comprises a pulse-width modulated signal generator configured to generate a pulse-width modulated signal representing an output signal of the DC-DC converter.
18. The resonant DC-DC converter of claim 15 , further comprising a parallel capacitor in parallel with a switch of the plurality of switches.
19. The resonant DC-DC converter of claim 15 , further comprising a bias resistor coupled between a terminal of the secondary winding and a voltage proportional to an output voltage of the DC-DC converter.
20. The resonant DC-DC converter of claim 15 , further comprising a full bridge rectifier coupled to the secondary winding and a parallel capacitor coupled between a first terminal and a second terminal of the secondary winding.