High-efficiency backlight driver
The disclosed devices may include a driver circuit including a voltage boost circuit, a pulse modulation controller, and optionally a headroom processor. The voltage boost circuit may be configured to receive a device input voltage (such as a battery voltage) and generate a backlight drive voltage. The pulse modulation controller may be configured to provide a pulse modulation signal to the voltage boost circuit, and may include a digital circuit or an analog circuit. Example devices may include a backlight unit receiving the backlight voltage. The optional headroom processor may provide a headroom signal to the pulse modulation controller based on a headroom voltage determined from the backlight unit. Devices may further include a backlight unit including an arrangement of light-emissive elements, and may include display devices such as head-mounted devices. Various other methods, systems, and computer-readable media are also disclosed.
1. A device, comprising:
a backlight unit comprising an arrangement of light-emissive elements; and
a driver circuit comprising:
a voltage boost circuit configured to receive a device input voltage and generate a backlight drive voltage; and
a pulse modulation circuit configured to provide a pulse modulation signal having a duty ratio to the voltage boost circuit, comprising:
a digital pulse width modulation controller;
a loop gain adjuster; and
an analog-to-digital converter configured to receive a headroom signal from a headroom processor and to provide a control signal to the loop gain adjuster thereby adjusting the digital pulse width modulation controller, wherein:
the device input voltage is between 3 V and 4.5 V;
the backlight drive voltage is between 20 V and 40 V;
the duty ratio is in a range of 5% to 20%;
the pulse modulation controller is configured to adjust the pulse modulation signal based on the headroom signal;
the device has an input power factor of greater than 0.9;
a loop gain of the pulse modulation controller is adjusted based on the headroom signal; and
the device is a head-mounted device.
2. The device of claim 1 , wherein:
the voltage boost circuit comprises a transistor; and
the transistor is configured to receive the pulse modulation signal having the duty ratio.
3. The device of claim 2 , wherein the voltage boost circuit further comprises at least one capacitor and at least one inductor.
4. The device of claim 2 , wherein:
the transistor is a MOSFET; and
the pulse modulation circuit is further configured to:
receive a soft-start signal based on a drain-source resistance of the MOSFET; and
reduce an input current ripple using the soft-start signal.
5. The device of claim 1 , wherein the arrangement of light-emissive elements comprises light-emitting diodes (LEDs).
6. The device of claim 5 , wherein:
the LEDs are arranged in a plurality of LED strings; and
the plurality of LED strings is arranged in a parallel electrical configuration.
7. The device of claim 6 , wherein each of the plurality of LED strings has an associated constant current driver.
8. The device of claim 1 , wherein the device further comprises a headroom processor configured to receive a plurality of headroom voltages from the backlight unit and to provide a headroom signal.
9. The device of claim 8 , wherein:
the headroom processor is further configured to select a lowest headroom voltage from the plurality of headroom voltages; and
the headroom signal is based on the lowest headroom voltage.
10. The device of claim 8 , wherein the pulse modulation circuit is configured to adjust the backlight drive voltage based on the headroom signal.
11. The device of claim 1 , wherein:
the device further comprises an electronic display associated with the backlight unit; and
the device is configured so that light from the backlight unit passes through at least a portion of the electronic display.
12. The device of claim 1 , wherein the device is a virtual reality device.
13. The device of claim 1 , wherein the device is an augmented reality device.
14. A method, comprising:
receiving a device input voltage;
boosting the device input voltage to obtain a backlight drive voltage; and
driving a backlight unit using the backlight drive voltage,
wherein:
the backlight unit comprises an arrangement of light-emitting diodes (LEDs); and
boosting the device input voltage comprises:
obtaining a pulse modulation signal from an analog pulse modulation circuit, wherein:
the analog pulse modulation circuit is configured to provide a pulse modulation signal having a duty ratio to a voltage boost circuit and comprises a pulse width modulation controller, a loop gain adjuster, and an analog-to-digital converter configured to receive a headroom signal from a driver circuit and to provide a control signal to the loop gain adjuster, thereby adjusting the analog pulse modulation circuit;
the device input voltage is between 3 V and 4.5 V;
the backlight drive voltage is between 20 V and 40 V;
the duty ratio is in a range of 5% to 20%;
the pulse modulation controller is configured to adjust the pulse modulation signal based on the headroom signal;
the device has an input power factor of greater than 0.9;
a loop gain of the pulse modulation controller is adjusted based on the headroom signal; and
the device is a head-mounted device.
15. The method of claim 14 , wherein the arrangement of LEDs comprises a plurality of LED strings, and the method further comprises:
obtaining headroom voltages from the plurality of LED strings;
determining a headroom signal based on a lowest headroom voltage of the headroom voltages; and
adjusting the pulse modulation signal based on the headroom signal.
16. The method of claim 14 , wherein receiving the device input voltage comprises receiving the device input voltage from a battery.