CA1272818A - Electroluminescent display drive circuitry - Google Patents
Electroluminescent display drive circuitryInfo
- Publication number
- CA1272818A CA1272818A CA000528862A CA528862A CA1272818A CA 1272818 A CA1272818 A CA 1272818A CA 000528862 A CA000528862 A CA 000528862A CA 528862 A CA528862 A CA 528862A CA 1272818 A CA1272818 A CA 1272818A
- Authority
- CA
- Canada
- Prior art keywords
- electroluminescent display
- transistor
- display panel
- signal
- drive circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Electroluminescent Light Sources (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
Abstract
ABSTRACT OF THE INVENTION
An electroluminescent display drive circuit which compensates for the decrease in capacitance of the electroluminescent display panel that is experienced as the panel ages; this is accomplished by use of an RC time constant which will effectively increase the voltage presented across the electroluminescent display panel as the capacitive element of the RC time constant decreases with the age of the panel. Also presented is high frequency power supply to excite electroluminescent displays without a transformer such that the voltage across the display is in phase with the current through the display thereby reducing the effect of power factor and electromagnetic interference.
An electroluminescent display drive circuit which compensates for the decrease in capacitance of the electroluminescent display panel that is experienced as the panel ages; this is accomplished by use of an RC time constant which will effectively increase the voltage presented across the electroluminescent display panel as the capacitive element of the RC time constant decreases with the age of the panel. Also presented is high frequency power supply to excite electroluminescent displays without a transformer such that the voltage across the display is in phase with the current through the display thereby reducing the effect of power factor and electromagnetic interference.
Description
ELECTROLUMINESCENT DISPLAY DRIVE_RCUITRY
BACKGROUND ANV SUMMARY OF THE INVENTION
~ --Electroluminescent display drive circuits (drivers) are traditionally driven by transformers. Thc transformer driven excitation of ~he electroluminescent display panel is inheren~ly inefficient due to the capacitive load from the panel bein~ reflected back into the transformer. This causes an efficiency drop due to a power factor loss created by the existence of the inductance of the trans~ormer and the capacitance of the electroluminescent panel.
In addition, electroluminescent display devices have traditionally been driven by high power devices~ ùsually transformers. Although transformers may benecessary ~o generate high voltage, they are not necessary to drive the electroluminescent displays.
This discovery has far reaching conseguences on the art due to the possible reduction of the size and weight of electroluminescent display power supplies. It also has an additional benefit of making the desi~n less susceptible to electromagnetic interference (EMI). Now, the electroluminescent display can be designed to operate at a frequency which will minimize the EMI effects.
Typical of the electroluminescent displays driven by the subject circuitry can be found by referring to U.S. Patent No. 4,388,554 issued on June 14, 1983, to Suntola et al.
I ,.
Another type of electroluminescent display device for dashboards of an automobile is described in U.S. Patent No. 4,323~895 issued on April 6, 1982, toCoste.
Another electroluminescent display device is described in U.S. Patent ¦
No. 4,320,1~9 issued on March 16, 1982, to Yatabe et al.
~ ' ~ I
. 1.
It is a feature of the present invention to improve the efficiency of electroluminescent display drivers.
It is also a feature of the subject invention to improve the efficiency of electroluminescent display drivers by reducing or eliminating the effects of the power factor created in trans-former driven excitation circuits.
It is also a feature of the subject invention to reduce the si~e and weight of traditional electroluminescent display drive circuits. And it is still another object of the subject invention to eliminate the use of a transformer to drive electroluminescent display panels.
Specifically, the invention relates to an electrolumin-escent display drive circuit comprising: a high voltage source; an electroluminescent display panel; two signal transistors~ a source of two input signals presented to the base of each signal transis-tor where the input signals to one transistor is 180 degrees out of phase with the input signals to the second transistor; the electro-luminescent display panel being connected between the collectors of each transistor, and the electroluminescent display panel fur-ther being connected to each end of the high voltage source through two resistors such that the voltage generated across the electro-luminescent display panel is in phase with the current passing through the electroluminescent display panel.
DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present in-vention will become more fully apparent from the following detailed description of~the preferred embodiment, the appended claims and in the accompanying drawings in which:
'.
Fig. 1 shows an elementary embodiment of the electrolum-inescent display drive circuitry;
Fig. 2 shows another embodiment of the electrolumin-escent display drive circuitry;
Fig. 3 shows still another embodiment of the electro-luminescent display drive circuitry with a masking capacitor used to reduce the effect of the capacitance changes within the electro-luminescent display;
Fig. 4 is a timing diagram showing the input signals to the drive circuit;
Fig. 5 is a schematic diagram showing a prior art electroluminescent display driver;
-2a-~27~8 Fig. 6 is a graph showing the voltage across and current through the electroluminescent display as a function of time; and Fig. 7 is a graph showing the voltage across and current through the electroluminescent display as a function of time for the power supply according to the subject invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Fig. 1, the electroluminescent display panel is shown connected to a high voltage supply via two resistors R127 and R128.
The circuit is completed by way of two transistors Q105 and Q106, each connected to one of the resistors R127 and R128. The collectors of each of these transistors is connected to the electroluminescent display panel, one to each side.
The electroluminescent display panel is depicted as a capacitor connected between the collectors of the two transistors.
The emitters of each transistor, Qlû5 and Q106, are then connected to ground.
The bases of each ~ransistor, Q105 and Q106, are connected to a signal source. This signal source can be an individual oscillating circuit or it can be an output from a microprocessor. In any event, input A to Q105 is 180 degrees out of phase with input B to Q106. Both inputs are to the base of the transistors and are both square wave signals. The frequency of each input signal can be the same, just 180 degrees out of phase. However, it may be desirable to only turn one transistor on at a time. That is, keep the off time of one input signal slightly less than the on time for the other input signal. This creates a dead zone. It is designed to never allow the transistors Q105 or Q106 to be on at the same time. This keeps heat loss to a minimum and reduces stress on the transistors. There are many ways to accompllsh this; the ke~ Is never ~o turn them both on at once. This principle is :'.
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used for input A and input B with respect to Fig. 1, Fig. 2 and Fig. 3, although each would work with the signals at the same frequency but 180 degrees out of phase.
These signals are depicted in the timing diagram of Fig. l~, along with the wave form across the electroluminescent display.
In addition, varying the frequency of the input signal to increase the dead zone can be used to dirn the output of the display.
It can be seen that the subject invention will drive the electroluminescent display without the use of a traditional transformer. The emphasis of traditional designs is toward power and the use of power transistors. In contrast~ the subject invention utilizes transistors that operate at a much lower power and emit very little heat.
The design lends itself nicely to surface mounted devices and allows for a desi~n which lets the desi~ner select the resistor values for speclfic applications.
In other words, the resistor will correspond to the capacitance of the individual electroluminescent display panel used and the frequency that it is driven at.
There is also evidence that the subject design is less susceptiblc to electro-ma~netic interference (EMI) because it is run at a constant frequency or run at a frequency which will not interfere with the radio or other components in anautomotive environment.
All of these factors are of particular importance to almost any environment, but the subject design was developed for use in an automotive;
environment.
I .
In this environment, large temperature swings are usually present. In addition, size and wei~ht are of critical importance.
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l ~7Z8~ 1 Referring now to Fig. 2, another embodiment of the electroluminescent display drive circuitry is shown. The particular design calls for the inputs A and B
as in Fig. 1. Both inputs A and B are fed to the base of an NPN transistor, in this case input A fed to the base of NPN transistor Q109 and input B fed to the base of NPN transistor QllO. Both transistors Q109 and QllO are connected to ground via the emitter.
The collectors of each transistor are connected to one end of the electroluminescent display through resistors R135 and R136. As before, the electroluminescent display panel is depicted as a capacitance; this is done even though the display has inherent resistive losses.
However, in Fig. 2, the electroluminescent display is connected to the high voltage ~hrough two NPN transistors Q107 and Q108. The emitters of the drive transistors Q107 and Q108 are tied to the high voltage and each collector is tied to the electroluminescent display panel through a time constant resistor R133 for Q107 and R134 for Q108.
Driving each transistor Q107 and Q108 is a connection between the base of each transistor anq a resistor. The resistor R131 being connected to the base of Q107; and resistor R132 being connected to the base of Q108. Each resistor R131 and R132 is connected to the collector of the PNP transistors, Q108 and Q107, respectively, on the opposite side of the electroluminescent display. Each emitter of transistors Q107 and Q108 are connected to the high voltage supply and the base of each transistor is further biased by resistor R129 and R130 being connected between the bases of each transistor and the high voltage supply.
Referring now to Fig. 3, another embodiment shown in cut-away format illustrates the use of capacitor C112 hooked in parallel across the electroluminescent display, still depicted as a capacitor. The cut-away view of Fig.
3 is otherwi5e the sa--e s s`own in Fig. 2.
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All of the circuits shown in Figs. 1, 2 and 3 genera~e an A/C voltage across the electroluminescent display panel. For more efficient operation of the display, the peak-to-peak voltage across the electroluminescent display will be approximately twice the amGunt of the high voltaKe input. This amount might be less in Figs. 2 and 3 where the high voltage across the eJectroluminescent display will be slightly lower due to effect of an RC network.
The RC network is made up of the series combination of resistors R133 and R134 in series with the electroluminescent display panel shown in Fig. 2.
The RC network Is Fig. 3 comprises the resistors R13~ and R134 in series with the parallel combination of the eiectroluminescent display9 along with the capacitor C112.
The efficiency of the circu;ts shown in Figs. 1, 2 and 3 is very good ~ue to the fact that a power factor of one is ~enerated.
Electroluminescent displays are generally discussed in an article "D.C.
Electroluminescence for Automobile Instruments" published by the Institute of Electrical Engineers on July 6-9, 1976, and written by B. ~hepherd, R. N. Thomas and P. :1. ith.
Also discussing electrolurninescent displays is SAE Paper 810076, "Electroluminescent Instrumentation" by ~. Shepherd dated February 1981.
. I
. I
Referring to Fig. 5, shown is a typical excitation circuit for an electroluminescent display. Notice that a transformer is utilized such that the secondary of the transformer is connected directly across electroluminescent display. A power factor other then 1 is created due to the interaction between ~he inductance of the transformer and the capacitance of the electroluminescent display. In addition, the bulk and weight of a transformer is eliminated.
I .
~ 72~
Prior art power supplies to drive an electroluminescent display are run at low frequency since the displays run at low frequency. This means that large transformers must be used to generate the low frequency drive.
This is shown in Fig. 5 with a +V voltage supplied to the primary of transformer T. The collector of transistor Q is connected to the primary of T; the emitter to ground; the base to an input signal 1. The electroluminescent display panel is depicted as a capacitor connected across the secondary of transformer Q.
The circuits described in the subject invention run at high frequencies and create a voltage without a power factor to contend with.
Examples of waveforms in prior art power supplies and in the subject invention are shown in Fig. 6. Examples of waveforms for the power supplies of the present invention are shown in Fig. 7. Both Fig. 6 and Fig. 7 graph voltage and current as a function of time. It can be seen that the power factor is not an issue in Fig. 7 as the current through the electroluminescent display is in phase with the voltage across it.
The subject circuit does not introduce a transformer to the direct excitation of the display and, therefore, reduces the size and weight of the design.
In addition, the subject invention eliminates or reduces the effect of the power factor as no inductance is present in the direct excitation of the electroluminescent display drive circuit; this is because current and voltage are in phase.
Referring again to Fig. 4, capacitor C112 is shown connected in parallel across the capacitive electroluminescent display panel. The capacitor C112 is used to mask or reduce the effect of capacitance changes of the electroluminescent display panel.
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Over a period oi time, the electroluminescent display panel will change in its inherent capacitance due to age. In general, the electroluminescent display will decrease in capacitance over a period of time.
~ Ihen the capacitance of the electroluminescent display panel changes, the voltage across the paneJ increases due to the new and shorter RC time constant created by the changed capacitance; i.e., the RC charging time effects of resistors R133, R134 in series with the parallel combination of the electroluminescent display and capacitor C112. This shorter RC time constant provides for a constant output from the electroluminescent display panel. Therefore, the panel can be used for a longer period of time since the affects of aging are masked by the higher voltage input.
Typically, the capacitance of the electroluminescent display drops to about one-half of the capacitance of its original capacitance between 500 and 1,000 hours of operation. Therefore, if capacitor C112 is chosen to be approximately equal to the capacitance of the electroluminescent display when new, the above- j described increases in the voltage across the electroluminescent display will increase the peaks of the electroluminescent voltage waveform shown in Fig. 7.
If capacitor C112 is chosen to be much larger than the electroluminescent capacitance, i.e., such that the capacitance of Cl 12 is ten times or more greater than the capacitance of the electroluminescent display, then the effect of the capacitance change in the electrolurninescent display will be felt as the voltage across the panel will remain relatively constant due to the lack of change in the RC time constant.
Alternatively, if the capacitance of capacitor C112 is much smaller than the capacitance of the electroluminescent display, then the aging effects of the electroluminescent disl lay on its inherent capacitance will be exaggerated.
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While the present invention has been disclosed in connection with the preferred embodiment thereof, it should be understood that there may be other ¦
embodiments which fall within the spirit and scope of the invention and that theinvention is susceptible to modification, variation and chan~e without departin~l~ol the proper scope or lai~ meanin6 ol the lollowine claims.
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BACKGROUND ANV SUMMARY OF THE INVENTION
~ --Electroluminescent display drive circuits (drivers) are traditionally driven by transformers. Thc transformer driven excitation of ~he electroluminescent display panel is inheren~ly inefficient due to the capacitive load from the panel bein~ reflected back into the transformer. This causes an efficiency drop due to a power factor loss created by the existence of the inductance of the trans~ormer and the capacitance of the electroluminescent panel.
In addition, electroluminescent display devices have traditionally been driven by high power devices~ ùsually transformers. Although transformers may benecessary ~o generate high voltage, they are not necessary to drive the electroluminescent displays.
This discovery has far reaching conseguences on the art due to the possible reduction of the size and weight of electroluminescent display power supplies. It also has an additional benefit of making the desi~n less susceptible to electromagnetic interference (EMI). Now, the electroluminescent display can be designed to operate at a frequency which will minimize the EMI effects.
Typical of the electroluminescent displays driven by the subject circuitry can be found by referring to U.S. Patent No. 4,388,554 issued on June 14, 1983, to Suntola et al.
I ,.
Another type of electroluminescent display device for dashboards of an automobile is described in U.S. Patent No. 4,323~895 issued on April 6, 1982, toCoste.
Another electroluminescent display device is described in U.S. Patent ¦
No. 4,320,1~9 issued on March 16, 1982, to Yatabe et al.
~ ' ~ I
. 1.
It is a feature of the present invention to improve the efficiency of electroluminescent display drivers.
It is also a feature of the subject invention to improve the efficiency of electroluminescent display drivers by reducing or eliminating the effects of the power factor created in trans-former driven excitation circuits.
It is also a feature of the subject invention to reduce the si~e and weight of traditional electroluminescent display drive circuits. And it is still another object of the subject invention to eliminate the use of a transformer to drive electroluminescent display panels.
Specifically, the invention relates to an electrolumin-escent display drive circuit comprising: a high voltage source; an electroluminescent display panel; two signal transistors~ a source of two input signals presented to the base of each signal transis-tor where the input signals to one transistor is 180 degrees out of phase with the input signals to the second transistor; the electro-luminescent display panel being connected between the collectors of each transistor, and the electroluminescent display panel fur-ther being connected to each end of the high voltage source through two resistors such that the voltage generated across the electro-luminescent display panel is in phase with the current passing through the electroluminescent display panel.
DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present in-vention will become more fully apparent from the following detailed description of~the preferred embodiment, the appended claims and in the accompanying drawings in which:
'.
Fig. 1 shows an elementary embodiment of the electrolum-inescent display drive circuitry;
Fig. 2 shows another embodiment of the electrolumin-escent display drive circuitry;
Fig. 3 shows still another embodiment of the electro-luminescent display drive circuitry with a masking capacitor used to reduce the effect of the capacitance changes within the electro-luminescent display;
Fig. 4 is a timing diagram showing the input signals to the drive circuit;
Fig. 5 is a schematic diagram showing a prior art electroluminescent display driver;
-2a-~27~8 Fig. 6 is a graph showing the voltage across and current through the electroluminescent display as a function of time; and Fig. 7 is a graph showing the voltage across and current through the electroluminescent display as a function of time for the power supply according to the subject invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Fig. 1, the electroluminescent display panel is shown connected to a high voltage supply via two resistors R127 and R128.
The circuit is completed by way of two transistors Q105 and Q106, each connected to one of the resistors R127 and R128. The collectors of each of these transistors is connected to the electroluminescent display panel, one to each side.
The electroluminescent display panel is depicted as a capacitor connected between the collectors of the two transistors.
The emitters of each transistor, Qlû5 and Q106, are then connected to ground.
The bases of each ~ransistor, Q105 and Q106, are connected to a signal source. This signal source can be an individual oscillating circuit or it can be an output from a microprocessor. In any event, input A to Q105 is 180 degrees out of phase with input B to Q106. Both inputs are to the base of the transistors and are both square wave signals. The frequency of each input signal can be the same, just 180 degrees out of phase. However, it may be desirable to only turn one transistor on at a time. That is, keep the off time of one input signal slightly less than the on time for the other input signal. This creates a dead zone. It is designed to never allow the transistors Q105 or Q106 to be on at the same time. This keeps heat loss to a minimum and reduces stress on the transistors. There are many ways to accompllsh this; the ke~ Is never ~o turn them both on at once. This principle is :'.
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used for input A and input B with respect to Fig. 1, Fig. 2 and Fig. 3, although each would work with the signals at the same frequency but 180 degrees out of phase.
These signals are depicted in the timing diagram of Fig. l~, along with the wave form across the electroluminescent display.
In addition, varying the frequency of the input signal to increase the dead zone can be used to dirn the output of the display.
It can be seen that the subject invention will drive the electroluminescent display without the use of a traditional transformer. The emphasis of traditional designs is toward power and the use of power transistors. In contrast~ the subject invention utilizes transistors that operate at a much lower power and emit very little heat.
The design lends itself nicely to surface mounted devices and allows for a desi~n which lets the desi~ner select the resistor values for speclfic applications.
In other words, the resistor will correspond to the capacitance of the individual electroluminescent display panel used and the frequency that it is driven at.
There is also evidence that the subject design is less susceptiblc to electro-ma~netic interference (EMI) because it is run at a constant frequency or run at a frequency which will not interfere with the radio or other components in anautomotive environment.
All of these factors are of particular importance to almost any environment, but the subject design was developed for use in an automotive;
environment.
I .
In this environment, large temperature swings are usually present. In addition, size and wei~ht are of critical importance.
4_ . I
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-` '' -' ~ ' ', " ' ' ' .,, ' - ` "' ' ' ', ~ .: .' .
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l ~7Z8~ 1 Referring now to Fig. 2, another embodiment of the electroluminescent display drive circuitry is shown. The particular design calls for the inputs A and B
as in Fig. 1. Both inputs A and B are fed to the base of an NPN transistor, in this case input A fed to the base of NPN transistor Q109 and input B fed to the base of NPN transistor QllO. Both transistors Q109 and QllO are connected to ground via the emitter.
The collectors of each transistor are connected to one end of the electroluminescent display through resistors R135 and R136. As before, the electroluminescent display panel is depicted as a capacitance; this is done even though the display has inherent resistive losses.
However, in Fig. 2, the electroluminescent display is connected to the high voltage ~hrough two NPN transistors Q107 and Q108. The emitters of the drive transistors Q107 and Q108 are tied to the high voltage and each collector is tied to the electroluminescent display panel through a time constant resistor R133 for Q107 and R134 for Q108.
Driving each transistor Q107 and Q108 is a connection between the base of each transistor anq a resistor. The resistor R131 being connected to the base of Q107; and resistor R132 being connected to the base of Q108. Each resistor R131 and R132 is connected to the collector of the PNP transistors, Q108 and Q107, respectively, on the opposite side of the electroluminescent display. Each emitter of transistors Q107 and Q108 are connected to the high voltage supply and the base of each transistor is further biased by resistor R129 and R130 being connected between the bases of each transistor and the high voltage supply.
Referring now to Fig. 3, another embodiment shown in cut-away format illustrates the use of capacitor C112 hooked in parallel across the electroluminescent display, still depicted as a capacitor. The cut-away view of Fig.
3 is otherwi5e the sa--e s s`own in Fig. 2.
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All of the circuits shown in Figs. 1, 2 and 3 genera~e an A/C voltage across the electroluminescent display panel. For more efficient operation of the display, the peak-to-peak voltage across the electroluminescent display will be approximately twice the amGunt of the high voltaKe input. This amount might be less in Figs. 2 and 3 where the high voltage across the eJectroluminescent display will be slightly lower due to effect of an RC network.
The RC network is made up of the series combination of resistors R133 and R134 in series with the electroluminescent display panel shown in Fig. 2.
The RC network Is Fig. 3 comprises the resistors R13~ and R134 in series with the parallel combination of the eiectroluminescent display9 along with the capacitor C112.
The efficiency of the circu;ts shown in Figs. 1, 2 and 3 is very good ~ue to the fact that a power factor of one is ~enerated.
Electroluminescent displays are generally discussed in an article "D.C.
Electroluminescence for Automobile Instruments" published by the Institute of Electrical Engineers on July 6-9, 1976, and written by B. ~hepherd, R. N. Thomas and P. :1. ith.
Also discussing electrolurninescent displays is SAE Paper 810076, "Electroluminescent Instrumentation" by ~. Shepherd dated February 1981.
. I
. I
Referring to Fig. 5, shown is a typical excitation circuit for an electroluminescent display. Notice that a transformer is utilized such that the secondary of the transformer is connected directly across electroluminescent display. A power factor other then 1 is created due to the interaction between ~he inductance of the transformer and the capacitance of the electroluminescent display. In addition, the bulk and weight of a transformer is eliminated.
I .
~ 72~
Prior art power supplies to drive an electroluminescent display are run at low frequency since the displays run at low frequency. This means that large transformers must be used to generate the low frequency drive.
This is shown in Fig. 5 with a +V voltage supplied to the primary of transformer T. The collector of transistor Q is connected to the primary of T; the emitter to ground; the base to an input signal 1. The electroluminescent display panel is depicted as a capacitor connected across the secondary of transformer Q.
The circuits described in the subject invention run at high frequencies and create a voltage without a power factor to contend with.
Examples of waveforms in prior art power supplies and in the subject invention are shown in Fig. 6. Examples of waveforms for the power supplies of the present invention are shown in Fig. 7. Both Fig. 6 and Fig. 7 graph voltage and current as a function of time. It can be seen that the power factor is not an issue in Fig. 7 as the current through the electroluminescent display is in phase with the voltage across it.
The subject circuit does not introduce a transformer to the direct excitation of the display and, therefore, reduces the size and weight of the design.
In addition, the subject invention eliminates or reduces the effect of the power factor as no inductance is present in the direct excitation of the electroluminescent display drive circuit; this is because current and voltage are in phase.
Referring again to Fig. 4, capacitor C112 is shown connected in parallel across the capacitive electroluminescent display panel. The capacitor C112 is used to mask or reduce the effect of capacitance changes of the electroluminescent display panel.
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Over a period oi time, the electroluminescent display panel will change in its inherent capacitance due to age. In general, the electroluminescent display will decrease in capacitance over a period of time.
~ Ihen the capacitance of the electroluminescent display panel changes, the voltage across the paneJ increases due to the new and shorter RC time constant created by the changed capacitance; i.e., the RC charging time effects of resistors R133, R134 in series with the parallel combination of the electroluminescent display and capacitor C112. This shorter RC time constant provides for a constant output from the electroluminescent display panel. Therefore, the panel can be used for a longer period of time since the affects of aging are masked by the higher voltage input.
Typically, the capacitance of the electroluminescent display drops to about one-half of the capacitance of its original capacitance between 500 and 1,000 hours of operation. Therefore, if capacitor C112 is chosen to be approximately equal to the capacitance of the electroluminescent display when new, the above- j described increases in the voltage across the electroluminescent display will increase the peaks of the electroluminescent voltage waveform shown in Fig. 7.
If capacitor C112 is chosen to be much larger than the electroluminescent capacitance, i.e., such that the capacitance of Cl 12 is ten times or more greater than the capacitance of the electroluminescent display, then the effect of the capacitance change in the electrolurninescent display will be felt as the voltage across the panel will remain relatively constant due to the lack of change in the RC time constant.
Alternatively, if the capacitance of capacitor C112 is much smaller than the capacitance of the electroluminescent display, then the aging effects of the electroluminescent disl lay on its inherent capacitance will be exaggerated.
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~L272~
While the present invention has been disclosed in connection with the preferred embodiment thereof, it should be understood that there may be other ¦
embodiments which fall within the spirit and scope of the invention and that theinvention is susceptible to modification, variation and chan~e without departin~l~ol the proper scope or lai~ meanin6 ol the lollowine claims.
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Claims (15)
1. An electroluminescent display drive circuit comprising:
a high voltage source;
an electroluminescent display panel;
two signal transistors;
a source of two input signals presented to the base of each signal transistor where the input signals to one transistor is 180 degrees out of phase with the input signals to the second transistor;
the electroluminescent display panel being connected between the collectors of each transistor; and the electroluminescent display panel further being connected to each end of the high voltage source through two resistors such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel.
a high voltage source;
an electroluminescent display panel;
two signal transistors;
a source of two input signals presented to the base of each signal transistor where the input signals to one transistor is 180 degrees out of phase with the input signals to the second transistor;
the electroluminescent display panel being connected between the collectors of each transistor; and the electroluminescent display panel further being connected to each end of the high voltage source through two resistors such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel.
2. The electroluminescent display drive circuit of claim I where the emitters of each signal transistor are connected to ground.
3. An electroluminescent display drive circuit comprising:
a high voltage source;
an electroluminescent display panel;
a first and a second signal transistor for supplying input signals to the electroluminescent display, each transistor being connected such that the collector of each transistor is connected to alternate ends of the electroluminescent display panel through a resistor and where the base of each signal transistor is available for an input signal;
a source of two input signals presented to the base of each signal transistor, where the input signal to one of the signal transistors is 180 degrees out of phase with the input signal to the second signal transistor;
a first and second drive transistor;
the collector resistor of each signal transistor further being connected to the collector of each drive transistor with the emitter of each drive transistor being connected to the high voltage supply;
the collector of each drive transistor being connected to the electroluminescent display through a time constant resistor such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel;
a bias resistor being connected between the base of each drive transistor and the high voltage supply and a feedback resistor being connected between the base of each drive transistor and the collector of the other drive transistor;
the time constant resistors interacting with the capacitance of the electroluminescent display panel to increase the voltage across the electroluminescent display panel as the capacitance of the electroluminescent display panel decreases with age.
a high voltage source;
an electroluminescent display panel;
a first and a second signal transistor for supplying input signals to the electroluminescent display, each transistor being connected such that the collector of each transistor is connected to alternate ends of the electroluminescent display panel through a resistor and where the base of each signal transistor is available for an input signal;
a source of two input signals presented to the base of each signal transistor, where the input signal to one of the signal transistors is 180 degrees out of phase with the input signal to the second signal transistor;
a first and second drive transistor;
the collector resistor of each signal transistor further being connected to the collector of each drive transistor with the emitter of each drive transistor being connected to the high voltage supply;
the collector of each drive transistor being connected to the electroluminescent display through a time constant resistor such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel;
a bias resistor being connected between the base of each drive transistor and the high voltage supply and a feedback resistor being connected between the base of each drive transistor and the collector of the other drive transistor;
the time constant resistors interacting with the capacitance of the electroluminescent display panel to increase the voltage across the electroluminescent display panel as the capacitance of the electroluminescent display panel decreases with age.
4. The electroluminescent display drive circuit of claim 3 where the emitter of each signal transistor is connected to ground.
5. An electroluminescent display drive circuit comprising:
a high voltage source;
an electroluminescent display panel;
a first and a second signal transistor for supplying input signals to the electroluminescent display, each transistor being connected such that the collector of each transistor is connected to alternate ends of the electroluminescent display panel through a resistor and where the base of each signal transistor is available for an input signal;
a source of two input signals presented to the base of each signal transistor, where the input signal to one of the signal transistors is 180 degrees out of phase with the input signal to the second signal transistor;
a first and second drive transistor;
the collector resistor of each signal transistor further being connected to the collector of each drive transistor with the emitter of each drive transistor being connected to the high voltage supply;
the collector of each drive transistor being connected to the electroluminescent display through a time constant resistor such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel;
a bias resistor being connected between the base of each drive transistor and the high voltage supply and a feedback resistor being connected between the base of each drive transistor and the collector of the other drive transistor;
the time constant resistors interacting with the capacitance of the electroluminescent display panel to increase the voltage across the electroluminescent display panel as the capacitance of the electroluminescent display panel decreases with age;
a masking capacitor being connected in parallel across the electroluminescent display to control the change in voltage across the electroluminescent display as the capacitance of the electroluminescent display changes with age.
a high voltage source;
an electroluminescent display panel;
a first and a second signal transistor for supplying input signals to the electroluminescent display, each transistor being connected such that the collector of each transistor is connected to alternate ends of the electroluminescent display panel through a resistor and where the base of each signal transistor is available for an input signal;
a source of two input signals presented to the base of each signal transistor, where the input signal to one of the signal transistors is 180 degrees out of phase with the input signal to the second signal transistor;
a first and second drive transistor;
the collector resistor of each signal transistor further being connected to the collector of each drive transistor with the emitter of each drive transistor being connected to the high voltage supply;
the collector of each drive transistor being connected to the electroluminescent display through a time constant resistor such that the voltage generated across the electroluminescent display panel is in phase with the current passing through the electroluminescent display panel;
a bias resistor being connected between the base of each drive transistor and the high voltage supply and a feedback resistor being connected between the base of each drive transistor and the collector of the other drive transistor;
the time constant resistors interacting with the capacitance of the electroluminescent display panel to increase the voltage across the electroluminescent display panel as the capacitance of the electroluminescent display panel decreases with age;
a masking capacitor being connected in parallel across the electroluminescent display to control the change in voltage across the electroluminescent display as the capacitance of the electroluminescent display changes with age.
6. The electroluminescent display drive circuit of claim I where the input signals have a dead zone.
7. The electroluminescent display drive circuit of claim 2 where the input signals have a dead zone.
8. The electroluminescent display drive circuit of claim 3 where the input signals have a dead zone.
9. The electroluminescent display drive circuit of claim 4 where the input signals have a dead zone.
10. The electroluminescent display drive circuit of claim 5 where the input signals have a dead zone.
11. The electroluminescent display drive circuit of claim 6 where the dead zone is controlled to dim the display panel.
12. The electroluminescent display drive circuit of claim 7 where the dead zone is controlled to dim the display panel.
13. The electroluminescent display drive circuit of claim 8 where the dead zone is controlled to dim the display panel.
14. The electroluminescent display drive circuit of claim 9 where the dead zone is controlled to dim the display panel.
15. The electroluminescent display drive circuit of claim 10 where the dead zone is controlled to dim the display panel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000528862A CA1272818A (en) | 1987-02-03 | 1987-02-03 | Electroluminescent display drive circuitry |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000528862A CA1272818A (en) | 1987-02-03 | 1987-02-03 | Electroluminescent display drive circuitry |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1272818A true CA1272818A (en) | 1990-08-14 |
Family
ID=4134891
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000528862A Expired CA1272818A (en) | 1987-02-03 | 1987-02-03 | Electroluminescent display drive circuitry |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1272818A (en) |
-
1987
- 1987-02-03 CA CA000528862A patent/CA1272818A/en not_active Expired
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