News Column

Patent Issued for Power Supply System for a Display Panel

September 3, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Kojima, Hidekazu (Kyoto, JP), filed on June 27, 2012, was published online on August 19, 2014.

The assignee for this patent, patent number 8810977, is Rohm Co., Ltd. (Kyoto, JP).

Reporters obtained the following quote from the background information supplied by the inventors: "FIG. 1 shows a layout diagram of a display panel and a power supply system for supplying the display panel with a power supply voltage. The display panel as shown in FIG. 1 may include a plurality of display panel elements. These display panel elements may include liquid crystal display elements or for example organic light emitting diode (OLED) elements. An organic light emitting diode is a light emitting diode (LED) in which an emissive electroluminescent layer is formed by a film of organic compounds which can emit light in response to an electric current. This layer of organic material is located between two electrodes wherein at least one of these electrodes is transparent. A display panel having OLED elements can operate without a back light. As shown in FIG. 1, the power supply circuit supplies the display panel elements within the display panel with a power supply voltage.

"FIG. 2 is a circuit diagram of the display panel and the power supply system shown in FIG. 1. The display panel in FIG. 2 includes a display panel element DPE. The display panel element DPE as shown in FIG. 2 within the display panel has an organic light emitting diode OLED which is supplied with a positive power supply voltage PVDD and a negative power supply voltage PVEE wherein the positive power supply voltage PVDD may typically range from +5 Volts to +6 Volts and the negative power supply voltage PVEE may be in a range from -5 Volts to -6 Volts. The display panel element that includes an OLED is driven by a display driver DD. The display driver DD receives a voltage PVDD as the positive supply voltage of the display panel element, and a voltage V.sub.SS (Ground voltage which normally has a potential of zero Volts) as the negative supply voltage. The supply voltage of the display panel elements within the display panel is provided by an external power supply regulator PSR which forms an external component and is controlled by a switching control circuit SWREG which may be integrated into an integrated power supply circuit chip. The integrated switching control circuit SWREG controls the power supply regulator PSR by applying control signals to transistors of the power supply regulator PSR as shown in FIG. 2. As can be seen in FIG. 2, the power supply regulator PSR includes two symmetrical power supply units PSU.sub.A, PSU.sub.B for regulating the positive power supply voltage PVDD and the negative power supply voltage PVEE of the display panel element DPE within the display panel. The negative power supply unit PSU.sub.A includes a transistor T.sub.A, a coil L.sub.A, a diode D.sub.A and a capacitor C.sub.A. The positive power supply unit PSU.sub.B includes a transistor T.sub.B, a coil L.sub.B, a diode D.sub.B and a capacitor C.sub.B. The transistors T.sub.A and T.sub.B of the power supply regulator PSR are controlled by switching control signals CRTL.sub.A and CRTL.sub.B output by the switching control circuit SWREG of the power supply circuit chip. The display panel element DPE as shown in FIG. 2 includes a selection transistor T.sub.SEL which is controlled by a selection signal CRTL-SEL to activate the display panel element. The selection transistor TSEL is switched in response to the switching control signals CRTL.sub.A and CRTL.sub.B when a driving voltage is applied to the gate of a switching transistor T.sub.SW of the display panel element which applies the positive power supply voltage PVDD to the organic light emitting diode OLED as shown in FIG. 2. The display panel element further includes a capacitance C.sub.DPE which may have a parasitic capacitance. The power supply regulator PSR regulates the positive power supply voltage PVDD and the negative power supply voltage PVEE of the display panel element DPE in response to the control signals CRTL.sub.A, CRTL.sub.B received from the switching control circuit SWREG. The power supply regulator PSR is connected to a battery as shown in FIGS. 1 and 2."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "The arrangement as shown in FIGS. 1 and 2 has several drawbacks. The power supply regulator PSR as shown in FIG. 2 includes two power supply units PSU, i.e. a power supply unit PSU.sub.B for the positive supply voltage PVDD and a power supply unit PSU.sub.A for the negative supply voltage PVEE. Since the components of the power supply regulator PSR are not integrated and because of the high number of components the power supply regulator PSR occupies a considerable amount of space and must be wired with the display panel element DPE, the power supply circuit chip and the battery. Another severe drawback of the arrangement as shown in FIGS. 1 and 2 is that the negative power supply unit PSU.sub.A providing the negative power supply PVEE of the display panel element DPE and consisting of transistor T.sub.A, coil L.sub.A, diode D.sub.A and capacitor C.sub.A operates with very low efficiency. Consequently, power consumption is increased. The low efficiency of the negative power supply unit PSU.sub.A within the power supply regulator PSR is partially caused by the fact that the negative power supply unit PSU.sub.A includes a P-MOSFET T.sub.A whereas the positive power supply unit PSU.sub.B includes an N-MOSFET T.sub.B.

"Accordingly, there is a need for a power supply system for a display panel that overcomes the above mentioned drawbacks and in particular to provide a power supply circuit with reduced power consumption which occupies a minimal area when integrated on a chip.

"In one embodiment, a power supply system for a display panel includes a power supply regulator configured to regulate a power supply voltage of a display driver connected to the display panel, and a protection circuit configured to protect the display driver against an overvoltage.

"In another embodiment, the power supply regulator has a supply terminal configured to supply the power supply regulator with a received loading current.

"In another embodiment, the power supply regulator includes a transistor having a control terminal connected to a switching control circuit, a first terminal connected via a coil to the supply terminal of the power supply regulator and having a second terminal to which a ground voltage is applied.

"In another embodiment, the second terminal of the transistor is connected via a diode to at least one capacitor which is loaded by the loading current via the coil and the diode in response to a control signal applied to a control terminal of the transistor by the switching control circuit depending on the monitored positive power supply voltage of the display driver.

"In another embodiment, the protection circuit of the power supply circuit is adapted to generate an intermediate reference voltage applied to the negative supply voltage terminal of the display driver to shift the positive power supply voltage of the display driver by a predetermined shift voltage.

"In another embodiment, the protection circuit of the power supply circuit includes a voltage comparator configured to compare the positive power supply voltage of the display driver with an internal reference voltage provided by an internal reference voltage source.

"In another embodiment, the protection circuit of the power supply circuit includes an impedance converter having an input connected to the voltage comparator.

"In another embodiment, the protection circuit of the power supply circuit includes a transistor having a control terminal connected to the output of the impedance converter, a first terminal connected to the negative power supply terminal of the display driver and a second terminal connected to the supply terminal of the power supply regulator.

"In another embodiment, a reactive current of the display panel flows under the control of the transistor of the protection circuit of the power supply circuit to the supply terminal of the power supply regulator.

"In another embodiment, the reactive current flows via the coil and the diode of the power supply regulator to the at least one capacitor of the power supply regulator to reduce the power consumption when the transistor of the power supply regulator is switched off in response to the control signal applied to the control terminal of the transistor by the switching control circuit.

"In another embodiment, the supply terminal of the power supply regulator is connected to the second terminal of the transistor of the protection circuit and is connected to a battery.

"In another embodiment, the transistor of the power supply regulator is formed by a MOSFET.

"The transistor of the power supply regulator in some embodiments is formed by an N-MOSFET. In another embodiment, the transistor of the protection circuit is also formed by a MOSFET.

"In some embodiments, this MOSFET is also formed by an N-MOSFET.

"The disclosure further provides a display panel including display panel elements connected to a power supply system. The power supply system includes a power supply regulator configured to regulate a power supply voltage of a display driver of the power supply system connected to the display panel and includes a protection circuit configured to protect the display driver against an overvoltage."

For more information, see this patent: Kojima, Hidekazu. Power Supply System for a Display Panel. U.S. Patent Number 8810977, filed June 27, 2012, and published online on August 19, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8810977.PN.&OS=PN/8810977RS=PN/8810977

Keywords for this news article include: Electronics, Rohm Co. Ltd, Light-emitting Diode.

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Source: Electronics Newsweekly


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