Frequency feedforward for constant light output in backlight inverters
View Patent ↗An inverter providing power to a load, the inverter receiving a direct current (DC) input. A plurality of switches included in the inverter are controlled by a plurality of control signals to generate an alternating current (AC) output in response to the DC input. A zero crossing of the AC output current provided by the plurality of switches is detected, and the controlling of the plurality of switches is delayed in response to the zero crossing. The amount of delay is adjusted responsive to a change in the DC input to effectively maintain a constant switching frequency of the inverter. The delayed AC output current of the plurality of switches may be filtered to provide power to the load.
1. An electrical inverter comprising:
an electrical pulse start device operable to receive a first input indicative of a primary alternating current, the electrical pulse start device generating a first output responsive to a zero crossing of the first input;
an electrical pulse duration device operable to receive a second input indicative of a load current and a third input indicative of a direct current (DC) input voltage, the electrical pulse duration device being operable to generate a second output responsive to the second and third inputs;
a time delay device operable to receive the first output and the DC input voltage, the time delay device introducing a time delay to generate a delayed first output;
a logic device operable to receive the delayed first output and the second output to generate a plurality of control signals; and
a plurality of switches operable to convert the DC input to the primary alternating current in response to receiving the plurality of control signals.
2. The inverter of claim 1 , further comprising:
a filtering device, wherein the filtering device includes a transformer having a primary section electro-magnetically coupled to a secondary section, wherein the primary alternating current flows through the primary section, and wherein the primary section is electrically coupled to the plurality of the switches and the secondary section is electrically coupled to the load.
3. The inverter of claim 1 , wherein the load is a cold cathode fluorescent lamp (CCFL).
4. The inverter of claim 1 , wherein the time delay is variable, a value of the time delay being selectable responsive to the DC input voltage.
5. The inverter of claim 4 , wherein the value increases as the DC input increases.
6. The inverter of claim 1 , wherein the logic device imposes the time delay to assert at least one control signal for controlling a corresponding switch following the zero crossover.
7. The inverter of claim 1 , wherein the plurality of switches are configured as a full-bridge.
8. The inverter of claim 1 , wherein an output of the full-bridge has a constant switching frequency caused by imposing the time delay.
9. The inverter of claim 1 , wherein each control signal of the plurality of control signals controls a corresponding switch by placing the switch in an ON or OFF state, and by controlling a time period in the ON state.
10. The inverter of claim 9 , wherein the time delay is imposed from the zero crossing to a change in the state of the switch.
11. The inverter of claim 9 , wherein the time delay causes an adjustment of the time period in the OFF state to maintain a constant switching frequency.
12. The inverter of claim 1 , wherein imposing the time delay causes a subsequent zero crossing of the first input to remain fixed relative to a previous zero crossing thereby generating a constant switching frequency.
13. A method for improving efficiency of an inverter providing power to a load, the method comprising:
receiving a direct current (DC) input;
controlling a plurality of switches to generate an alternating current (AC) output in response to the DC input;
detecting a zero crossing of the AC output; and
delaying the controlling of the plurality of switches to effectively maintain a constant switching frequency of the inverter in response to a change in the DC input.
14. The method of claim 13 , wherein the delaying is caused by setting a time delay, wherein the time delay has a variable time value.
15. The method of claim 14 , wherein the time delay varies as a predefined function of the DC input, wherein the variable time value increases as the DC input increases.
16. The method of claim 13 , wherein the controlling of the plurality of switches includes placing each switch in the plurality of switches to an ON or OFF state, and by adjusting a time period in the ON state.
17. The method of claim 16 , wherein the delaying imposes a time delay measured from the zero crossing to a change in the ON or OFF state.
18. The method of claim 16 , wherein the time delay causes an adjustment of the time period in the OFF state to maintain the constant switching frequency.
19. The method of claim 13 , wherein imposing the time delay causes a subsequent zero crossing of the AC output to remain fixed relative to a previous zero crossing thereby generating the constant switching frequency.
20. The method of claim 19 , wherein the subsequent zero crossing remaining fixed relative to the previous zero crossing generates the constant switching frequency.
21. The method of claim 13 , wherein the load is a cold cathode fluorescent lamp (CCFL).
22. A display device comprising:
a display panel;
an electrical inverter operable to provide power to the display device, the inverter including:
an electrical pulse start device receiving a first input indicative of a primary alternating current, the electrical pulse start device generating a first output responsive to a zero crossing of the first input;
an electrical pulse duration device receiving a second input indicative of a display device current and a third input indicative of a direct current (DC) input voltage, the electrical pulse duration device being operable to generate a second output responsive to the second and third inputs;
a time delay device receiving the first output and the DC input voltage, the time delay device introducing a time delay to generate a delayed first output;
a logic device receiving the delayed first output and the second output to generate a plurality of control signals; and
a plurality of switches converting the DC input to the primary alternating current in response to receiving the plurality of control signals.
23. The display device of claim 22 , wherein the display device includes a cold cathode fluorescent lamp (CCFL).
24. The display device of claim 22 , wherein the display panel is a liquid crystal display panel.
25. The display device of claim 22 , wherein the display device is coupled with an information handling system (IHS).
26. The display device of claim 25 , wherein the IHS is a notebook computer.
27. An information handling system (IHS) comprising:
a processor and a storage coupled to a display device; and
an inverter operable to provide power to the display device, the inverter including:
a electrical pulse start device operable to receive a first input indicative of a primary alternating current, the electrical pulse start device generating a first output responsive to a zero crossing of the first input;
a electrical pulse duration device operable to receive a second input indicative of a display device current and a third input indicative of a direct current (DC) input voltage, the electrical pulse duration device being operable to generate a second output responsive to the second and third inputs;
a time delay device operable to receive the first output and the DC input voltage, the time delay device introducing a time delay to generate a delayed first output;
a logic device operable to receive the delayed first output and the second output to generate a plurality of control signals; and
a plurality of switches operable to convert the DC input to the primary alternating current in response to receiving the plurality of control signals.