AU651368B2

AU651368B2 - Improvements in electronic ballasts

Info

Publication number: AU651368B2
Application number: AU83492/91A
Authority: AU
Inventors: Siew Ean Wong; Thien Siung Yang
Original assignee: Ultralite International Pty Ltd
Current assignee: Ultralite International Pty Ltd
Priority date: 1990-08-31
Filing date: 1991-08-29
Publication date: 1994-07-21
Anticipated expiration: 2011-08-29
Also published as: AU8349291A

Description

i UI1~e i: PATENTS ACT 1990 651368 COMPLETE SPECIFICATION

ORIGINAL

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: 4 Lapsed: Published: e Priority: et .*'',Related Art: i 'Name of Applicant: S.'Address of Applicant: .«'Address of Applicant: TO BE COMPLETED BY APPLICANT SIEW EAN WONG 13 Gowan Brae Avenue Mount Ousley NSW 2519 Actual Inventor: t Lt Address for Service: ANDERSON-TAYLOR ASSOCIATES, Registered Patent Attorneys of 10 Harrison Avenue BONNET BAY N.S.W. 2226 Complete Specification for the invention entitled: IMPROVEMENTS IN ELECTRONIC BALLASTS The following statement is a full description of this invention, including the best method of performing it known to me: JI- This invention relates to electrical apparatus and more particularly, although not exclusively to compact ballast circuits for fluorescent lamps of the type used as replacements for incandescent bulbs.

Because of their small size and cost constraints it is not feasible (as with larger fluorescent lamp circuits) to install a low-pass filter at the input of these circuits. As a result the .o compact ballast circuits presently available have 0 0 a very high current harmonic distortion and a very low power factor of between 0.45 and 0.6 A typical S° o circuit together with voltage I and current 2 waveforms 0 O for such existing ballasts is shown in figures 1 and 2. Because of these unfavorable characteristics power authorities in many countries such as Australia will not Fpprove these circuits for sale as separate 'items. Consequently the regulations can only be *complied with if the ballast circuit and fluorescent lamp are sold as a complete one piece unit. This however greatly adds to their cost and reduces consumer acceptance of the product.

It is therefore an object'of this invention to ameliorate the aforementioned disadvantages and accordingly a ballast circuit for a fluorescent lamp is disclosed, said circuit including a rectifier bridge coupled !f .1 to an AC source and providing a pulsating DC supply voltage, a mylar capacitor connected across the output of the rectifier bridge, a lamp drive capacitor connecting a junction of the mylar capacitor and the rectifier bridge with a first terminal of the fluorescent lamp load, a diode and smoothing capacitor means serially connected across the rectifier beidge whereby in operation of the circuit said mylar capacitor charges said smoothing capacitor means, an oscillator circuit coupled to the output of the rectifier bridge and an inductance connected between the output of .9 the oscillator circuit and the second terminal of the *9 0o o fluorescent lamp load wherein said diode is polarised so that during half cycles of the supply voltage when the supply voltage is less than the voltage on the smoothing capacitor means said diode blocks current from flowing from the smoothing capacitor means through the lamp drive capacitor to the fluorescent lamp load so that said fluorescent lamp load draws current directly from the rectifier bridge to thereby improve the power factor and reduce harmonic distortion of the ballast circuit.

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-7 that the lamp draws current from the rectifierbridge over substantially the whole of supply voltage waveform includ' eriods when this voltage ss than that across smoothing capacitor o0 9 0s QD 0 Qa 00 0 9 0 *i 0 9 One preferred form of this invention will now be described with reference to the attached illustrations in which: Figure 3 shows a schematic diagram of a circuit according to this concept, and Figure 4 shows the current waveform produced by the circuit of figure 3.

Referring first to figure 3 there is shown a ballast circuit :which at least in terms of power factor and size has substantial advantages over that of figure 1 and is suitable for use with compact fluorescent lamps of 9 to 18 watts such as those sold under serial numbers YDN13-2H, YDN13- 2U, PLC13/82, DULUX D13W and LYNX D13W. Typical non limiting values for the various components shown may be as follows: 0 0i @0 p 0.

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r L Cl 0.1 AF 250V AC C2 0.006 AF 250V AC C3 0.006 AF 220V AC C4 0.047 AF 400V DC 4.7 AF 400V DC C6 4.7 AF 400V DC C7 0.068 AF 100V DC Dl =Bridge Rectifier D2, D3, D5 D6 Diodes D4 Diac R1=820.0 ohms R2 20.0 ohms R3 3.3 ohms R4 3.3 ohms R5=330.0 qhms R6= 68.0 ohms R7= 68.0 ohms R8 5.1 ohms R9 5.1 ohms L1 =Filter Coil L3= Choke Coil L5, L2 L4=Core Coil I It

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4 *4 In this case it will be noted that a diode D2 (preferably of a high speed switching type such as FR104) is inserted into the circuit just after the full wave rectifier bridge D1 and before the smoothing capacitors C5 and C6.

Further, the single smoothing capacitor in figure 1 has been replaced by two capacitors C5 and C6 to reduce the physical size of the unit. The lamp drive capacitor C4 however remains directly connected to the rectifier bridge output.

-3A- I ~rP- The purpose of this diode is to ensure that the current used by the fluorescent lamp is not entirely supplied by capacitors C5 and C6 during portions of the half cycle when the supply voltage'3 is lower than the DC Voltage on C5., C6. During this period D2 blocks the supply from C5, C6 and allows the lamp to draw current directly from the rectifier bridge. Hence, the current waveform 4 becomes more even as shown in figure 4. Although this curve is still not sinusoidal, it does improve the power factor to better than 0.9, and reduce the current harmonic distortion to within the limits set for t i 4 t' even large electronic ballasts (as set out for exajmple in IEC 555/2 and AS3168).

The value of mylar capacitor C3 has to be modified to match the diode. With this particular embodiment when designed for use with a 13 watt fluorescent t lamp it may be 0.047 -IF 400 volts.

It will thus be appreciated that this invention at least in the form of the example disclosed e, provides a novel and useful improvement in ballast t i circuits for compact fluorescent lamps. Clearly however embodiment described is only the currently preferred form of this invention and a wide variety of modifications may be made which would be apparent to a person skilled in the art. For example the I: -4- 1 i values of the various components may be chnged to adapt the circuit for use with larger fluorescent lamps up to 125 watts and for other types of discharge lamps.

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Claims

2. The ballast circuit as claimed in claim 1 where said diode is a high speed switching diode.
3. The ballast circuit as claimed in claim 2 wherein the S power factor is improved to better than .9.
4. The ballast c;rcuit as claimed in claim 3 wherein the smoothing capacitor means comprises two capacitors to reduce the physical size of the circuit. Dated this t day of 1994 Siew Ean Wong By his Patent Attorney MICHAEL ANDERSON-TAYLOR 9 6 a 0 o £e00 4 -7- I! _i, n ABSTRACT A ballast circuit for a compact fluorescent lamp in which the power factor is increased by the insertion of a high speed switching diode D2 after the bridge rectifier D1 but before the smoothing capacitors (C5, C6) The switching diode operates to prevent the current used by the fluorescent lamp being entirely supplied by the smoothing capacitor(s) during those portions of the half cycle when the supply voltage is lower then the DC voltage on the smnoothing capacitor(s). *i 4444 4441 4.44 4. *I 4 Slit 54 II 55 I S 5