Direct drive circuit for light emitting diodes

• US 3,925,690 A
• Filed: 09/30/1974
• Issued: 12/09/1975
• Est. Priority Date: 09/30/1974
• Status: Expired due to Term

• Current Assignee: John R. Spence
• Original Assignee: John R. Spence
• Inventors: Spence, John R.
• Primary Examiner(s): Heyman, John S.
• Assistant Examiner(s): Anagnos, L. N.
• Application Number:
  US05/510,254
• Time in Patent Office: 435 Days
• Field of Search: 307/270,297,311 323/21 340/173LS,166EL,324M,336 58/5R
• US Class Current: 326/83
• CPC Class Codes: G05F 3/24 wherein the transistors are of the field-effect type only G05F3/205, G05F3/26, G05F3/30 take precedence
• CPC Class Codes: G09G 3/14 Semiconductor devices, e.g. diodes

Abstract

A self-regulating circuit is disclosed for driving a load, such as an arithmetical calculator display using light-emitting diodes, directly from a single MOS calculator chip. A strobe driver, which may be a field effect transistor has its gate electrode connected to a regulated supply of dc voltage, its drain electrode connected to a supply of voltage subject to variation, and its source electrode connected at a common point to one terminal of each of the light-emitting diodes of the display in order that the light-emitting diodes may be driven thereby. A second field effect transistor is also provided and has the conduction path thereof connected between the other terminal of a respective light-emitting diode and a reference potential, e.g. ground, to selectively complete a current path including the respective light-emitting diode. Hence, a lightemitting diode may be illuminated at a particular time and according to a predetermined order as controlled by the application of signals at the gate electrode of the second field effect transistor.

Claims

1. A self regulating circuit for driving a load having first and second load terminals thereof, said circuit comprising a first field effect transistor having source, gate, and drain electrodes and a variable impedance thereof, said source electrode connected to the first of said load terminals, said gate electrode connected to a first source of regulated voltage so as to maintain the voltage at said gate electrode substantially constant, said drain electrode connected to a second source of voltage subject to variation, the impedance of said first field effect transistor adapted to vary a proportionate amount with a variation of said second source of voltage so as to maintain the supply of drive current to said load substantially constant, a second field effect transistor having source, gate, and drain electrodes, said gate electrode of said second field effect transistor connected to said first source of regulated voltage, and the source-drain conduction path of said second field effect transistor comprising a current regulating path selectively connected between the second of said load terminals and a reference potential supply to continuously control the supply of drive current to said load.

2. The invention of claim 1, wherein said load comprises at least one light-emitting diode.

3. The invention of claim 1, wherein said first and second field effect transistors are disposed upon a single metal oxide semiconductor-type chip.

4. The invention of claim 1, including impedance means additionally comprising said cUrrent regulating path, said impedance means connected in series with said source-drain conduction path of said second field effect transistor to continuously control the supply of drive current to said load.

5. The invention of claim 4, wherein said impedance means is a resistor.

6. The invention of claim 1, wherein the magnitude of said first source of regulated voltage is substantially larger than that of said second source of voltage subject to variation.

7. The invention of claim 1, said circuit further comprising a plurality of said second field effect transistors, each of said second field effect transistors having a source-drain conduction path thereof comprising a current regulating path, said load comprising a plurality of light-emitting diodes, the conduction path of each of said plurality of second field effect transistors connected between a respective one of said light-emitting diodes comprising said load and said reference potential supply to continuously control the drive current to each of said respective light-emitting diodes and simultaneously activate any of said light-emitting diodes according to a predetermined sequence of operation.

8. A driver circuit to drive a plurality of light emitting diodes, each having first and second terminals thereof, comprising a first three electrode transistor means including a control electrode and two electrodes having a conduction path formed therebetween, one of said first transistor means conduction path electrodes connected at a common point to the first terminal of each of said plurality of light emitting diodes, a supply of voltage subject to variation applied to the other of said conduction path electrodes of said first transistor means, a constant supply of voltage applied to the control electrode of said first transistor means, a plurality of second three electrode transistor means, each of said second transistor means including a control electrode and two electrodes having a conduction path formed therebetween, each of said conduction paths to be selectively connected to the second terminal of a respective light-emitting diode so as to comprise current regulating paths to continuously control the drive current to said plurality of light-emitting diodes and simultaneously activate any of said light-emitting diodes according to a predetermined sequence of operation, each of said control electrodes connected to selectively receive said constant supply of voltage, and a supply of reference potential applied to one electrode of each of said second transistor means.

9. The invention of claim 8, wherein said first three terminal transistor means is a field effect transistor having source, gate, and drain electrodes thereof.

10. The invention of claim 8, wherein at least one of said plurality of second three terminal transistor means is a field effect transistor having source, gate, and drain electrodes thereof.

11. The invention of claim 8, wherein said first and second three terminal transistor means are p-channel field effect transistors comprised of a layer of silicon on a sapphire substrate.

12. The invention of claim 8, wherein the supply of voltage subject to variation applied to the other of the conduction path electrodes of said first transistor means is a battery.

13. The invention of claim 8, wherein the supply of reference potential applied to the one electrode of each of said plurality of second transistor means is relatively positive with respect to the supply of voltage subject to variation applied to the other of the conduction path electrodes of said first transistor means.

14. The invention of claim 8, wherein each of said current regulating paths includes a respective impedance means connected in series with each of said second transistor means conduction paths to continuously control the drive current to each of said light-emitting diodes.