US3543086A - Impedance controlling circuit for a load element - Google Patents

Impedance controlling circuit for a load element Download PDF

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Publication number
US3543086A
US3543086A US722755A US3543086DA US3543086A US 3543086 A US3543086 A US 3543086A US 722755 A US722755 A US 722755A US 3543086D A US3543086D A US 3543086DA US 3543086 A US3543086 A US 3543086A
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United States
Prior art keywords
voltage
impedance
transistor
secondary winding
primary winding
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Expired - Lifetime
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US722755A
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English (en)
Inventor
Hans G Blank
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Verizon Laboratories Inc
GTE LLC
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General Telephone and Electronics Corp
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B44/00—Circuit arrangements for operating electroluminescent light sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

  • An impedance-controlling circuit in which the impedance of the primary winding of a transformer is controlled by changing the effective load on the transformer secondary winding.
  • the primary winding is connected in series with an AC voltage source and a load element, so that the amount of voltage appearing across the load element depends on the primary winding impedance.
  • a transistor is used in conjunction with a pair of diodes to effectively open-circuit and short-circuit the secondary winding in response to external control signals applied to the base of the transistor.
  • This invention relates to impedance-controlling circuits and in particular to circuits for controlling high imped ance load elements such as electroluminescent devices.
  • an electroluminescent device comprises an electroluminescent phosphor interposed between two electrically conductive electrodes, at least one of which is transparent. When a varying voltage of appropriate magnitude and frequency is applied across the electrodes, the electroluminescent phosphor is excited and emits light. Groups of electroluminescent devices are often used to visually display information, and it becomes necessary to switch individual electroluminescent devices on and off in response to electrical control signals. These signals are typically DC voltage levels, of the order of a few volts, generated by logic circuitry. However, most electroluminescent devices require voltages of the order of hundreds of volts. At operating frequencies, a typical electroluminescent device has an impedance of the order of tens of thousands of ohms. Therefore, a relatively large AC voltage impressed across a high impedance load must be controlled with a relatively small DC control voltage.
  • the present invention is directed to an impedancecontrolling circuit in which an externally applied signal is used to control the impedance of an AC circuit element.
  • the impedance of the primary winding of a transformer is controlled by changing the effective load on the secondary winding.
  • the transformer primary winding is connected in series with a load element, such as an electroluminescent device, and an AC voltage source.
  • the AC voltage applied across the load is dependent upon the primary winding impedance, since the primary winding and the load divide the voltage supplied by the AC voltage source. Therefore, the voltage applied across the load can be controlled by changing the impedance of the primary winding.
  • first and second unidirectional current means poled in opposite directions, are connected in series across the transformer secondary winding.
  • a pair of diodes connected back-to-back may be used for this purpose.
  • a semiconductor switching element such as a transistor having conductive and non-conductive states, couples the junction of the diodes to an intermediate terminal on the secondary winding.
  • An externally applied signal is used to render the transistor conductive and non-conductive.
  • the AC signal applied across the primary winding induces voltages in the secondary winding.
  • the oppositely poled diodes prevent current from flowing in the secondary Winding.
  • the secondary winding is virtually open-circuited and the primary winding is, therefore, in a high impedance state.
  • the impedance looking into the primary winding of a transformer will assume its highest value when the transformer secondary is open-circuited, and its lowest value when the secondary is short-circuited.
  • voltages induced in the secondary winding cause current flow in part of the secondary since a current path is provided by one of the diodes in conjunction with the transistor.
  • the circuit arrangement allows the use of a conventional transistor, since the diodes restrict current flow to a direction compatible with the conductive direction of the transistor regardless of the polarity of the induced secondary voltage.
  • a transformer 10 is shown having primary Winding 11 and secondary winding 12.
  • An electroluminescent device 15 and voltage generating source 16 are coupled in series across primary winding 11.
  • the secondary winding 12 of transformer has an intermediate tap connection to a ground reference which divides secondary winding 12 into approximate half-windings.
  • First and second semiconductor diodes 20 and 21, poled in opposite directions, are connected in series across secondary winding 12.
  • Transistor 23, illustrated as of the NPN type, provides a controllable current path between junction point 27 and the intermediate tap of secondary winding 12.
  • Transistor 23 is shown in a common-emitter configuration, having its collector electrode connected to junction point 22, its emitter electrode connected to ground reference, and its base electrode connected to input terminal 14. Input signals applied at terminal 14 are measured with respect to ground reference.
  • the output of voltage generating source 16 is an AC voltage of the order of 100 volts R.M.S. at 2000 cycles per second.
  • the electroluminescent device requires a substantial AC voltage for excitation, for example 90 volts R.M.S. at 2000 cycles per second, and presents a high load impedance, of the order of 50,000 ohms, at said frequency.
  • the impedance of primary winding 11 is controlled by the signal at input terminal 14. The voltage applied across the electroluminescent device 15 is thereby controlled since electroluminescent device 15 and primary winding 11 divide the voltage supplied by voltage generating source 16.
  • Transistor 23 is operated as a switch being either conducting or cut-01f depending on the signal at input terminal 14.
  • transistor 23 is cut-off or nonconductive, secondary winding 12 is virtually open-circuited because oppositely poled diodes 20 and 21 prevent current flow in said winding.
  • the impedance looking into primary winding 11 is essentially determined by the primary inductance of transformer 10.
  • this primary inductance presents a high impedance, of the order of 150,000 ohms, to the AC voltage supplied by voltage generating source 16. Therefore, the portion of the supplied voltage which is applied across electroluminescent device 15 is relatively small, of the order of 25 volts R.M.S. At this voltage, the electroluminescent device is off, as it does not emit discernible light.
  • transistor 23 When transistor 23 is conductive, however, a current path is provided between junction point 27 and the intermediate tap of secondary winding 12. Diodes 20 and 21 conduct alternately as the polarity of the induced voltage changes every half-cycle, and a virtual short circuit exists continually across part of secondary winding 12. In this condition, the impedance looking into primary winding 11 is low, of the order of 2000 ohms, being essentially determined by the winding resistances and leakage inductance of transformer 10. Therefore, the voltage applied across the electroluminescent device is a large portion of the supply voltage, of the order of 96 volts R.M.S. At this voltage, the electroluminescent device is Transistor 23 is switched from cut-off to conduction and vice versa by relatively small DC voltage levels. The difference between the voltages required at terminal 14 to switch between conductive and non-conductive states is of the order of 1 volt.
  • the diodes 20 and 21 and the transistor 23 are subjected to maximum voltage stresses when transistor 23 is cut-off. These stresses are proportional to the magnitude of the voltages induced in secondary winding 12.
  • the magnitude of voltages induced in secondary winding 12 can be fixed at a desired level.
  • a stepdown ratio for transformer 10 of five primary turns to one secondary turn is preferred.
  • This ratio should be at least three to one to avoid unnecessary voltage stresses.
  • Transistor 23 Type 2N1605. Diodes 20 and 21 Type 1N536. Primary winding 11 200 turns. Secondary winding 12 turns. Electroluminescent device 15 40,000 ohms at 2000 c.p.s. AC voltage source 16 100 volts R.M.S. at 200 c.p.s.
  • transistor 23 may be of the PNP type if the polarities of diodes 20 and 21 as Well as the input signal polarity are reversed. Further changes and modifications may be made all within the scope of the appended claims.
  • An impedance-controlling circuit comprising:
  • first and second unidirectional current means connected in series between the first and second terminals of said secondary winding, said first and second unidirectional current means being connected at a junction point, said first and second unidirectional current means being poled in opposite directions,
  • a semiconductor switching element coupled between the said junction point and the intermediate terminal of said secondary winding, said semiconductor switching element having a conductive and a non-conductive state and being rendered con ductive and non-conductive by an externally applied signal, said primary winding being in its low impedance state when said semiconductor switching element is conductive and being in its high impedance state when said semiconductor switching element is non-conductive.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optics & Photonics (AREA)
  • Electroluminescent Light Sources (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
US722755A 1968-04-19 1968-04-19 Impedance controlling circuit for a load element Expired - Lifetime US3543086A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US72275568A 1968-04-19 1968-04-19

Publications (1)

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US3543086A true US3543086A (en) 1970-11-24

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US722755A Expired - Lifetime US3543086A (en) 1968-04-19 1968-04-19 Impedance controlling circuit for a load element

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US (1) US3543086A (enrdf_load_stackoverflow)
GB (1) GB1259358A (enrdf_load_stackoverflow)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5432015A (en) * 1992-05-08 1995-07-11 Westaim Technologies, Inc. Electroluminescent laminate with thick film dielectric

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3165640A (en) * 1960-12-15 1965-01-12 North American Aviation Inc D. c. controlled semiconductor switch for a. c. current
US3280341A (en) * 1963-03-11 1966-10-18 W W Henry Company Electroluminescent switching circuit
US3327163A (en) * 1965-11-02 1967-06-20 Gen Telephone & Elect Electroluminescent bar graph indicator
US3409876A (en) * 1965-05-28 1968-11-05 Navy Usa Electroluminescent grid control by voltage variable capacitors
US3432724A (en) * 1967-02-27 1969-03-11 North American Rockwell Electroluminescent crossed grid device for simultaneously displaying a plurality of points

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3165640A (en) * 1960-12-15 1965-01-12 North American Aviation Inc D. c. controlled semiconductor switch for a. c. current
US3280341A (en) * 1963-03-11 1966-10-18 W W Henry Company Electroluminescent switching circuit
US3409876A (en) * 1965-05-28 1968-11-05 Navy Usa Electroluminescent grid control by voltage variable capacitors
US3327163A (en) * 1965-11-02 1967-06-20 Gen Telephone & Elect Electroluminescent bar graph indicator
US3432724A (en) * 1967-02-27 1969-03-11 North American Rockwell Electroluminescent crossed grid device for simultaneously displaying a plurality of points

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Publication number Publication date
GB1259358A (enrdf_load_stackoverflow) 1972-01-05

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