Display element drive device

• US 6,496,168 B1
• Filed: 10/02/2000
• Issued: 12/17/2002
• Est. Priority Date: 10/04/1999
• Status: Expired due to Fees

• Current Assignee: Autonetworks Technologies, Ltd. (Sumitomo Corporation)
• Original Assignee: Autonetworks Technologies, Ltd. (Sumitomo Corporation), Sumitomo Electric Industries Limited (Sumitomo Corporation), Sumitomo Wiring Systems Limited (Sumitomo Corporation)
• Inventors: Tomida, Takayuki
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Nguyen, Jimmy H.
• Application Number:
  US09/676,934
• Time in Patent Office: 806 Days
• Field of Search: 345/76, 345/77, 345/34, 345/35, 345/36, 345/44, 345/45, 327/108, 315/168, 315/169.1, 315/169.3, 348/800, 340/825.1
• US Class Current: 345/76
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 2330/04 Display protection
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

A transistor Q11 for supplying driving currents Ia to In to EL display elements 11a to 11n is provided in a stabilization voltage supply circuit 33. The transistor Q11 is connected to a current sensing resistor Ras for detecting a collector current of the transistor Q11. When a total current Ix for driving the EL display elements rises to a certain abnormal level, a bias suppressing element Qa is turned on to thereby reduce a base-emitter bias of the transistor 11.

Claims

1. A display element drive device for driving a single electro luminescent (EL) display element or a plurality of EL display elements parallel-connected to one another, comprising:

a single stabilization voltage supply circuit for applying a stabilization voltage to said EL display element;

a reference EL display element parallel-connected to said EL display element;

driving state detecting means for detecting a driving state and for changing an output signal according to the driving state;

a voltage control circuit for controlling a constant voltage by supplying a stabilization voltage adjustment signal to said stabilization voltage supply circuit according to the output signal of said driving state detecting means so that the driving state of said reference EL display element is constant; and

a switching circuit for switching between application and disapplication of the stabilization voltage to said EL display element, wherein

at least one of said stabilization voltage supply circuit and said switching circuit has a transistor for supplying a driving current to said EL display element, and wherein

said transistor is connected to a current detecting element for detecting a collector current of said transistor, and to a bias suppressing element for reducing a base-emitter bias of said transistor by on-switching when the current detected by said current detecting element rises to a certain abnormal level owing to leakage current of said EL display element.

2. A display element drive device for driving a single electro luminescent (EL) display element or a plurality of EL display elements parallel-connected to one another, comprising:

a single stabilization voltage supply circuit for applying a stabilization voltage to said EL display element;

a reference EL display element parallel-connected to said EL display element;

a control portion for detecting a driving state and for changing a control signal, which is used to control the stabilization voltage, according to the driving state;

a voltage control circuit for controlling a constant voltage by supplying a stabilization voltage adjustment signal to said stabilization voltage supply circuit according to the control signal outputted from said control portion so that the driving state of said reference EL display element is constant; and

a switching circuit for switching between application and disapplication of the stabilization voltage to said EL display element, wherein

said switching circuit is adapted to perform on-off switching according to a switching signal sent from said control portion, wherein

said stabilization voltage supply circuit has a stabilization voltage supply element for adjusting an output level of the stabilization voltage according to the stabilization voltage adjustment signal supplied from said voltage control circuit, and further has a current detecting element for detecting a current outputted from said stabilization voltage supply element, wherein

said control portion has a function of outputting to said switching circuit a switching signal for applying the stabilization voltage to said EL display element by on-switching of said switching circuit, wherein

 

said control portion further has a function of judging that leakage current of said EL display element abnormally increases, and changing the control signal to thereby limit the output level of the stabilization voltage outputted from said stabilization voltage supply element when the current detected by said current detecting element rises to an abnormally high level in comparison with a level of a driving current needed for driving said EL display element to emit light in a case that the on-switching of said switching circuit is performed in response to the switching signal.