LED power source with over-voltage protection
View Patent ↗A resonant DC-DC converter used to drive an LED array includes a half-bridge converter configured to receive DC input power and produce a square wave voltage. A resonant tank circuit that includes an inductive element, a first resonance capacitor, and a second resonance capacitor, is coupled to the half-bridge converter to receive the square wave voltage such that a generally sinusoidal AC voltage is produced across the second resonance capacitor. An output transformer with a primary winding and one or more secondary windings, is coupled in parallel to the second resonance capacitor, and a clipping circuit is coupled to the primary winding such that the voltage across the primary winding does not substantially exceed the voltage of the DC input power. An output rectifier is coupled to the one or more secondary windings of the output transformer and is configured to produce a generally DC output voltage.
1. A resonant DC-DC converter, comprising:
a half-bridge converter configured to receive DC input power and produce a square wave voltage,
a resonant tank circuit comprising an inductive element, a first resonance capacitor, and a second resonance capacitor, wherein the resonant tank circuit is coupled to the half-bridge converter to receive the square wave voltage such that a generally sinusoidal AC voltage is produced across the second resonance capacitor,
an output transformer having a primary winding and one or more secondary windings, the primary winding coupled in parallel to the second resonance capacitor,
a clipping circuit coupled on an output side of the resonant tank circuit to the primary winding such that a voltage across the primary winding does not substantially exceed a voltage of the DC input power, and
an output rectifier coupled to the one or more secondary windings and configured to produce a generally DC output voltage.
2. The resonant DC-DC converter of claim 1 , wherein the clipping circuit comprises a first diode coupled between the primary winding and a supply of the DC input power, and a second diode coupled between the primary winding and a return of the DC input power.
3. The resonant DC-DC converter of claim 1 , wherein the output rectifier comprises an output filter capacitor, and two output diodes,
wherein the one or more secondary windings comprises two windings each coupled in opposite polarity to a respective one of the two output diodes such that a full-wave rectified output voltage is produced, and
wherein the output filter capacitor is coupled across the full-wave rectified output voltage to produce the generally DC output voltage.
4. The resonant DC-DC converter of claim 1 , wherein the half bridge converter further comprises a self-oscillating switch drive circuit magnetically coupled to the inductive element.
5. The resonant DC-DC converter of clam 4 , further comprising a controller, wherein the controller is coupled to the DC output voltage and magnetically coupled to the switch drive circuit, such that the controller is operable to adjust the frequency of the switch drive circuit based at least in part on the DC output voltage.
6. The resonant DC-DC converter of claim 1 , wherein a blocking capacitor is coupled in series with the primary winding.
7. The resonant DC-DC converter of claim 2 , wherein the resonant tank circuit further comprises a third resonance capacitor coupled between the supply and the second resonance capacitor.
8. The resonant DC-DC converter of claim 7 , wherein the primary winding is coupled in parallel with the third resonance capacitor.
9. The resonant DC-DC converter of claim 1 , wherein the first resonance capacitor is coupled in series with the inductive element which is coupled in series with the second resonance capacitor.
10. The resonant DC-DC converter of claim 1 , wherein the inductive element is coupled in series with the first capacitor which is coupled in series with the second capacitor.
11. A method for providing over-voltage protection in a resonant switch mode DC to DC converter, the method comprising:
converting a DC input voltage, having a supply and a return, to a square wave using a half-bridge converter;
converting the square wave to a generally sinusoidal AC bus voltage using a series-parallel LCC resonant tank circuit;
preventing the generally sinusoidal AC bus voltage from substantially exceeding the DC input voltage using a clipping circuit on an output side of the resonant tank circuit;
creating and electrically isolating an AC output voltage from the AC bus voltage via an output transformer; and
converting the AC output voltage to a DC output voltage using a rectifier and an output filter.
12. The method of claim 11 , further comprising regulating the output voltage at a generally constant value by adjusting the frequency of the half-bridge converter based at least in part on a measurement of the DC output voltage.
13. A power source for an LED array, the power source comprising:
an input rectifier configured to receive an input AC power and produce an initial DC voltage;
a boost regulator configured to receive the initial DC voltage and produce an intermediate DC voltage wherein the intermediate DC voltage is greater than the initial DC voltage;
a half-bridge converter configured to receive the intermediate DC voltage and produce a square wave voltage,
a resonant tank circuit comprising an inductive element, a first resonance capacitor, and a second resonance capacitor, wherein the resonant tank circuit is coupled to the half-bridge converter to receive the square wave voltage such that a generally sinusoidal AC voltage is produced across the second resonance capacitor,
an output transformer having a primary winding and one or more secondary windings, the primary winding coupled in parallel to the second resonance capacitor,
a clipping circuit coupled on an output side of the resonant tank circuit to the primary winding such that a voltage across the primary winding does not substantially exceed the intermediate DC voltage, and
an output rectifier coupled to the one or more secondary windings and configured to produce a generally DC output voltage.
14. The power source of claim 13 , wherein the clipping circuit comprises a first diode coupled between the primary winding and a supply of the intermediate DC voltage, and a second diode coupled between the primary winding and a return of the intermediate DC voltage.
15. The power source of claim 13 , wherein the output rectifier comprises an output filter capacitor, and two output diodes,
wherein the one or more secondary windings comprises two windings each coupled in opposite polarity to a respective one of the two output diodes such that a full-wave rectified output voltage is produced, and
wherein the output filter capacitor is coupled across the full-wave rectified output voltage to produce the generally DC output voltage.
16. The power source of claim 13 , wherein the half bridge converter further comprises a self-oscillating switch drive circuit magnetically coupled to the inductive element.
17. The power source of clam 16 , further comprising a controller, wherein the controller is coupled to the DC output voltage and magnetically coupled to the switch drive circuit, such that the controller is operable to adjust the frequency of the switch drive circuit based at least in part on the DC output voltage.
18. The power source of claim 13 , wherein a blocking capacitor is coupled in series with the primary winding.
19. The power source of claim 13 , wherein the half-bridge converter comprises two switches serially connected between a supply and a return of the intermediate DC voltage, and a microcontroller coupled to the two switches and configured to alternately turn each of the switches on and off such that the square wave voltage is produced at a circuit node between the two switches.
20. The power source of claim 19 , wherein the microcontroller is coupled to a feedback voltage wherein the feedback voltage is proportional to the DC output voltage, and
wherein the microcontroller is further configured to adjust the frequency of the square wave voltage based at least in part on the feedback voltage.