Transformerless electroluminescent lamp driver topology

• US 5,982,105 A
• Filed: 11/10/1997
• Issued: 11/09/1999
• Est. Priority Date: 11/10/1997
• Status: Expired due to Fees

• Current Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Original Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Inventors: Masters, John C.
• Primary Examiner(s): Le, Hoanganh
• Assistant Examiner(s): Malos, Jennifer H.
• Application Number:
  US08/967,652
• Time in Patent Office: 729 Days
• Field of Search: 315/169.3, 315/362, 315/291, 315/383
• US Class Current: 315/169.3
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A transformerless driver circuit for an EL device has a battery or other source of dc power, and a microcontroller that is suitably programmed with associated firmware, so that a first switch control signal appears at a first output and a second switch control signal appears at a second output. A flyback circuit is connected to the first microcontroller output and, through a diode, to a charge storage device, e.g., a capacitor. This charges the capacitor stepwise to a relatively high voltage. The flyback circuit includes an inductor having one end connected to a first terminal of the dc power source, and another end coupled to a transistor or similar switch element. The transistor is coupled to the second dc power terminal, and has a base or gate coupled to the first output of the microcomputer. A controlled discharge arrangement bridges across the charge storage device to discharge the same periodically, and create an alternating current to drive the EL device. A second transistor has its base or gate coupled to the microcontroller second output. An isolating capacitor can be positioned in series between the diode and the charge storage device to eliminate the dc offset to the EL element. In one alternative arrangement, two or more flyback circuits are gated on and off sequentially. In a power-saver arrangement, the discharge circuit returns charge back to the battery.

Claims

1. A transformerless driver circuit for creating a high voltage ac waveform suitable for powering an electroluminescent lamp device, comprising:

a source of dc power having a first and second terminals;

a microcontroller suitably programmed with associated firmware to output first and second signals at first and second microcontroller outputs, respectively;

a flyback circuit including an inductor having one end coupled to the first terminal of said dc source, and another end;

a first controlled switching element coupled between the other end of said inductor and said second terminal of said dc source, and defining a junction between the first switching element and said inductor, and having a control electrode coupled directly to the first microcontroller output to receive said first signal from said first microcontroller output; and

a diode having a first electrode coupled to said junction and a second electrode;

a charge storage retention means coupled to the second electrode of said diode to accumulate flyback voltage from said flyback circuit; and

a controlled discharge arrangement coupled across said charge storage retention means including a second controlled switching element having a control electrode coupled directly to said second microcontroller output to receive the second signal from the second microcontroller output.

2. The transformerless driver circuit of claim 1 wherein said first switching device comprises a switching transistor connected in series with said inductor.

3. The transformerless driver circuit of claim 1 wherein said charge storage retention means includes a discrete capacitor.

4. The transformerless driver circuit of claim 3 wherein an isolating capacitor is situated in series between the second electrode of said diode and said discrete capacitor.

5. The transformerless driver circuit of claim 1 wherein said first and second signals are pulse signals, and said first pulse signal is at a frequency in a range of ten to forty times the pulse frequency of said second signal.

6. The transformerless driver circuit of claim 5 wherein said first pulse signal is at a frequency of at least about twenty times the pulse frequency of said second signal.

7. The transformerless driver circuit of claim 1 wherein second pulse signal is on the order of 200 Hz to 1 KHz.

8. The transformerless driver circuit of claim 1 wherein said first signal is present as a pulse train when said second signal has one state, and is absent when said second signal has a second state.

9. A transformerless driver circuit for creating a high voltage ac waveform suitable for powering an electroluminescent lamp device, comprising:

a source of dc power having a first and second terminals;

a microcontroller suitably programmed with associated firmware to output a plurality of first signals at respective first microcontroller outputs and second signals at a second microcontroller output, respectively;

a plurality of flyback circuits, each including an inductor having one end coupled to the first terminal of said dc source, and another end;

a respective controlled switching element coupled between the other end of the inductor and the second terminal of said dc source, and defining a respective junction between the switching element and the inductor, and having a control electrode coupled to receive a respective one of said first signals from said first microcontroller outputs; and

a respective diode having a first electrode coupled to said junction and a second electrode;

a charge storage retention means coupled to the second electrodes of said diodes to accumulate flyback voltage from said flyback circuits; and

a discharge arrangement coupled across said charge storage retention means including a second controlled switching element having a control electrode coupled to receive the second signal from the second microcontroller output;

wherein said plurality of first signals are in the form of time-phased interleaved pulse trains, so that said flyback circuits are gated on and off alternately, and said respective flyback circuits act in sequence to charge said charge storage retention means.

10. The transformerless driver circuit of claim 9 wherein said first signals are applied directly from the first microcontroller terminals to the control electrodes of said respective controlled switching elements in time sequence.

11. A transformerless driver circuit for creating a high voltage ac waveform suitable for powering an electroluminescent lamp device, comprising:

a source of dc power having a first and second terminals;

a microcontroller suitably programmed with associated firmware to output first and second signals at first and second microcontroller outputs, respectively;

a flyback circuit including an inductor having one end coupled to the first terminal of said dc source, and another end;

a first controlled switching element coupled between the other end of said inductor and said second terminal of said dc source, and defining a junction between the first switching element and said inductor, and having a control electrode coupled to receive said first signal from said first microcontroller output; and

a diode having a first electrode coupled to said junction and a second electrode;

a charge storage retention means coupled to the second electrode of said diode to accumulate flyback voltage from said flyback circuit; and

a power-saver discharge arrangement coupled between said charge storage retention means and the first terminal of said dc power source for discharging accumulated electric charge from said storage retention means into said power source, and including a switching element coupled between said charge storage retention means and said first terminal, and gating means coupled to the second microcontroller output for gating said switching element on and off.

12. The transformerless driver circuit of claim 11, wherein said gating means includes a transistor having a control electrode coupled to the second output of said microcontroller and an output electrode coupled to a gating electrode of said switching element.