WO2001026430A1 - Circuit d'alimentation auto-oscillant - Google Patents

Circuit d'alimentation auto-oscillant Download PDF

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Publication number
WO2001026430A1
WO2001026430A1 PCT/GB2000/003835 GB0003835W WO0126430A1 WO 2001026430 A1 WO2001026430 A1 WO 2001026430A1 GB 0003835 W GB0003835 W GB 0003835W WO 0126430 A1 WO0126430 A1 WO 0126430A1
Authority
WO
WIPO (PCT)
Prior art keywords
self
power supply
fet
circuit
supply circuit
Prior art date
Application number
PCT/GB2000/003835
Other languages
English (en)
Inventor
Colin Julian Seymour
Original Assignee
Central Research Laboratories Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from GBGB9923392.6A external-priority patent/GB9923392D0/en
Application filed by Central Research Laboratories Limited filed Critical Central Research Laboratories Limited
Publication of WO2001026430A1 publication Critical patent/WO2001026430A1/fr

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Classifications

    • 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
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
    • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
    • H05B41/2806—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without electrodes in the vessel, e.g. surface discharge lamps, electrodeless discharge lamps
    • 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

Definitions

  • the present invention relates to a self-oscillating power supply circuit. It relates particularly, but not exclusively, to a self-oscillating power supply circuit for driving a discharge lamp, such as an inductively coupled electrodeless lamp.
  • Wound components there are 4, plus the lamp winding. These are all custom- made, except possibly LI, therefore introducing significant costs and PCB area requirements.
  • variable capacitor C adj The circuit must be adjusted by variable capacitor C adj .
  • This component is relatively expensive compared to a fixed capacitor, invokes production costs, and is susceptible to drift if, for example, contaminated by sealant. Eventually excessive ageing can occur, shortening the lifetime of the circuit. It is desirable to eliminate the variable capacitor or allow the use of a trimming resistor instead, which is less costly.
  • US 5,675,220 “Power supply for vehicular neon light” (ADAC Plastics) describes a DC-DC converter utilising a Royer inverter circuit at 30 kHz to drive a neon bulb so as to avoid electromagnetic interference radiation from the bulb.
  • High frequency devices e.g. fast switching, low distributed gate resistance power FETs.
  • the circuit must accommodate the reactive component of the gate impedance at the driving frequency - this is far more important at higher frequencies of operation.
  • a suitable phase shift response must be provided in the oscillator's feedback loop.
  • the circuit must generate a sufficiently large electric field to strike the plasma discharge, then maintain a sufficiently high (but controlled) current in the induction coil to maintain an inductive plasma discharge.
  • An aim of the present invention is to provide a self-oscillating power supply circuit for driving a discharge lamp.
  • Another aim of the present invention is to provide a self-oscillating power supply circuit for driving a discharge lamp which satisfies at least one of the five aforementioned general requirements of such a circuit.
  • Figure 1 shows a known circuit arrangement
  • Figure 2 shows a diagram of a circuit arrangement for driving a discharge lamp according to the first embodiment of the invention
  • Figure 3a and 3b show an inductively driven electrodeless lamp with inductive feedback loop
  • Figures 4 and 5 show the circuit of Figure 2 modified to have test outputs
  • Figure 6 shows a circuit diagram of another embodiment of the invention.
  • Figure 7 shows a circuit diagram of an oscillator
  • FIG. 8 shows a circuit diagram of a further embodiment of the invention. Detailed Description of Preferred Embodiments
  • the present invention is suitable for driving inductively coupled gas discharge lamps with air-cored coils. Due to the relatively low inductance and the frequency dependency of coupling between the magnetic field and plasma, the coils must be driven with frequencies of at least a few MHz. A frequency of 9-10 MHz has been found a good compromise between the coil-plasma response which improves with frequency, and the capability of present-day low cost transistors to supply power, which declines with frequency.
  • the circuit must handle the particular characteristics of inductively coupled discharge lamps. That is, a resonant circuit must generate a high order of voltage multiplication (Q) to strike the gas discharge, and must therefore be driven from a circuit which has a low source impedance throughout the full RF cycle, and not be damaged by the high voltages and currents present.
  • the circuit must also continue to supply drive power efficiently when the initial ⁇ ' mode shifts to ⁇ ' mode (power transferred by magnetic field to effective circulating current in the plasma) which results in an increase in effective loss resistance in the lamp resonant circuit.
  • any oscillator In any oscillator, assuming that a feedback loop can be identified and broken at some point in order to measure energy flow as flowing from an output node on one side of the break to an input node on the other side of the break, the phase shift through the whole network must be zero, (or n times 360 degrees where n is an integer), and the gain magnitude must be 1. These are the Barkhausen criteria. In practical circuits, the unity gain results from the amplitude of oscillation growing until non-linear compression causes the gain magnitude to fall to unity.
  • the circuit arrangement of the present invention uses an air-cored auto trans former (choke) to couple the two push-pull transistors together. It is made self-oscillating using an inductive feedback network.
  • Figure 2 shows an embodiment of the invention having the FET choke-coupled oscillator with inductive loop feedback.
  • a feedback loop suitable for use with an electrodeless lamp circuit is shown in Figure 3a.
  • This feedback loop is a rectangular wire loop 5 mm by 30 mm, with twisted pair connection to the gate circuit. The wire loop is placed close to the bulb with approximately 3mm axial separation from the end of the 12 turn winding.
  • Another feedback loop configuration is shown in Figure 3b.
  • This feedback loop is circular (rather than rectangular) and is positioned coaxially at the distal end of the lamp bulb.
  • the feedback loop can be located centrally within the main coil winding (not shown). This arrangement would give a more compact coil and is suitable for use with the circuit arrangement shown in Figure 8, whereas the feedback loops shown in Figure 3 are more suitable for use with the other circuit arrangements described herein.
  • the types of feedback loop shown in Figures 3a and 3b can be situated at either end of the main lamp resonator coil, but the feedback loop is usually placed at the opposite end of the lamp to which the light exits from the lamp. Both types of induction loop can be used with a single 0.47 microhenry inductor L2, as shown in Figure 2.
  • L2 tunes out (matches) the gate capacitance and ensures a good gate drive voltage level, without resistive loss.
  • the gate network resonance is expected to be sufficiently broadband to not require a tuneable component in production, since similar results are obtained for preferred value inductors either side of the value specified, provided the FET characteristics are sufficiently stable.
  • the circuits shown may use 1) a fixed inductor L2 with high-stability components Lla, Cl, L2, Ql and Q2, or 2) a selected L2 (which may be adjustable) with relaxed tolerance limits on the aforementioned components.
  • Transistors Q and Q 2 provide active gain in push-pull mode.
  • the resonant frequency is predominantly controlled by LI (electrodeless lamp coil) and Cl.
  • Diode Dl, D2, D3, D4 protect the gates against transient voltage spikes which must not exceed the Vgs absolute maximum limit. Transient voltage spikes may occur during switch-on or switch-off; but normally these diodes should not conduct.
  • DC is supplied to the oscillator through bifilar RF choke Tl and power supply decoupling is provided by C2, C3 and C4.
  • Tl couples the two FETs together such that the impedance seen at the drains is kept low throughout the cycle. Tl is air-cored to eliminate losses in ferrite. When Ql is off, the low impedance of Q2 (being on) is reflected via transformer coupling to Ql.
  • This is essential in order for sufficient voltage multiplication to occur in the high-Q resonant circuit of LI and Cl, to provide high E fields to initiate an E mode plasma in the lamp.
  • This circuit is shown with a pre-set bias circuit.
  • an autobias circuit including an RF output dependent bias feedback may be used.
  • An inhibit circuit may be connected to the gates of the FET transistors, as shown in Figure 2. This may, for example, use a transistor switch connected to the FET gates via diodes to control the FET bias. This allows the oscillator to be gated on and off under the control of an external pulse time modulation or pulse width modulation input (typically at 5 V logic levels). Such an input allows the lamp RF drive to be switched on and off or, by applying a variable duty cycle pulse at typically 100 Hz (this pulsation frequency being imperceptible to the human eye), the lamp brightness can be controlled over a continuous range of brightness.
  • Peak voltage to ground is lower than for a single capacitor-coil tuned circuit, hence alleviating insulation and HV clearance problems.
  • the capacitive divider pnnciple is used again in a different circuit arrangement descnbed later.
  • Figure 5 shows a circuit denved from either Figure 2 or 4, the circuit having an extra test pickup loop (Lie) and wound at the centre of Tl, as one turn overlaid on the pnmary winding.
  • the output voltage of this loop with no loading will be representative of what could be expected for a "notional oscillator" circuit having this pickup loop in its feedback mechanism.
  • the voltage on such a pickup loop was found to be 50V peak-peak with no load other than an oscilloscope probe (13 pF and 10 Megaohm, which constitutes a negligible load).
  • the phase relationship of this test loop is also representative of the notional oscillator.
  • phase of the Lie voltage was close to 90 degrees phase shifted (20ns) in advance of the normal gate waveform produced by the circuits of Figures 2 and 4.
  • the phase shift required can be provided by a suitable filter network; the simplest of which is a series inductor. This is precisely the function performed by L2 in the circuit of Figure 2 and Figure 4 (together with the FET gate capacitance).
  • a resistor may be used instead of an inductor, but this has been found to result in an extremely inefficient circuit.
  • variable resistor might, however, be a convenient method for 'tuning' the phase shift for optimum performance (maximum DC to light output efficacy at minimum Vdd).
  • a combination of a resistor and an inductor in series or parallel may be used, as shown in Figure 6.
  • the circuit arrangement shown in Figure 6 allows the phase / tuning of the gate circuit to be optimised by adjusting VR1 for peak light output or efficiency. In practice this method works, but it has been found to result in a less efficient oscillator compared to one tuned with the correct value of inductor alone. This circuit is also prone to instabilities, i.e., oscillations in amplitude on top of the intentional RF oscillation.
  • the principal advantage of using a weakly coupled feedback loop positioned away from one end of the lamp coil is that it forces oscillation to occur at the high-Q resonance frequency of the main lamp coil and HV capacitor. Only under these conditions does the main coil generate enough H field to induce sufficient feedback voltage in the feedback loop. Attempting to use feedback loops with tighter coupling, either magnetic or directly connected, risks oscillation at some other frequency. This oscillation could be only slightly offset from the high-Q resonance frequency, and yet lowers the voltage by a significant amount.
  • Another advantage of this circuit is that the combination of a variable resistor and a fixed inductor used for tuning the circuit for peak light output, or efficiency, may be advantageous due to the lower cost of variable resistors compared with the cost of variable inductors and capacitors.
  • Tl has a turns ratio between 3:1 and 6:1 wound on a suitable core, e.g. Philips TN9/6/3-4C65 (o.d. 9.5 +/- 0.3 mm), MMG-North America L01-BK5V-3K/1, or Neosid Pemetzrieder GmbH 05- 1342-00, which are all similarly-sized toroidal cores.
  • This circuit appears to be capable of running the lamp in H mode with reasonable efficiency and with a supply current of 0.7A at 12V.
  • the circuit of Figure 8 allows a tightly coupled feedback loop (located centrally within the main coil winding) to be used. This may be advantageous if there are metallic surfaces or EMC screens close to the lamp, in which case a loosely coupled feedback coil would not be effective.
  • the circuit shown in Figure 2 is considered to offer the best combination of efficiency and simplicity. In summary, the invention provides the following advantages:
  • Self-oscillating frequency is controlled by lamp tuned circuit and hence is more tolerant of drift in component values over time (compared with the sensitivity of the previous circuit to drift in the gate circuit tuning capacitor C ad) and related wound components L ad

Landscapes

  • Circuit Arrangements For Discharge Lamps (AREA)

Abstract

Ce circuit d'alimentation auto-oscillant sert à commander une lampe à décharge et comprend: un onduleur auto-résonnant comportant un premier (Q1) et un second (Q2) transistor à effet de champ -lesquels fonctionnent en opposition de phase- et conçu pour fournir une tension de commande à travers une charge couplée à l'onduleur, cette charge comprenant une impédance (L1a) à composante réactive, un transformateur (T1) destiné à coupler le premier transistor à effet de champ (Q1) au second (Q2), un circuit bouchon (C1) servant à annuler la composante réactive de l'impédance (L1a) de la charge, une bobine de rétroaction (L1b) couplée au champ magnétique de la lampe à décharge et conçue pour échantillonner une fraction de l'énergie de la fréquence radio à proximité de la lampe, des moyens correcteurs de phase servant à fournir la phase correcte au niveau de la grille du premier transistor à effet de champ et de la grille du second transistor à effet de champ, ainsi que des moyens de polarisation en courant continu (R3, R4) conçus pour démarrer l'oscillateur.
PCT/GB2000/003835 1999-10-05 2000-10-05 Circuit d'alimentation auto-oscillant WO2001026430A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB9923392.6 1999-10-05
GBGB9923392.6A GB9923392D0 (en) 1999-10-05 1999-10-05 A high frequency power oscillator
GB0009376A GB0009376D0 (en) 1999-10-05 2000-04-14 A high frequency power oscillator
GB0009376.5 2000-04-14

Publications (1)

Publication Number Publication Date
WO2001026430A1 true WO2001026430A1 (fr) 2001-04-12

Family

ID=26244118

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2000/003835 WO2001026430A1 (fr) 1999-10-05 2000-10-05 Circuit d'alimentation auto-oscillant

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WO (1) WO2001026430A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0016542A2 (fr) * 1979-02-21 1980-10-01 Westinghouse Electric Corporation Ensemble consistant en une lampe de décharge sans électrode et en un circuit oscillateur à radio-fréquence
WO1993026140A1 (fr) * 1992-06-05 1993-12-23 Diablo Research Corporation Lampe a decharge sans electrode contenant un amplificateur en montage push-pull de classe e et une bobine a enroulement bifilaire
GB2322019A (en) * 1997-02-07 1998-08-12 Central Research Lab Ltd Gas discharge lamp drive circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0016542A2 (fr) * 1979-02-21 1980-10-01 Westinghouse Electric Corporation Ensemble consistant en une lampe de décharge sans électrode et en un circuit oscillateur à radio-fréquence
WO1993026140A1 (fr) * 1992-06-05 1993-12-23 Diablo Research Corporation Lampe a decharge sans electrode contenant un amplificateur en montage push-pull de classe e et une bobine a enroulement bifilaire
GB2322019A (en) * 1997-02-07 1998-08-12 Central Research Lab Ltd Gas discharge lamp drive circuit

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