AU671545B2 - Improvements in electronic ballasts - Google Patents

Description

JjAUSTRALIAl PATENTS ACT 1990 COMPLETE SPECIFICATION FOR OFFICE USE Short Title: Int. CI: Application Number: Lodged: Complete Specification-Lodged: Accepted: S Lapsed: Published: Priority: Related At:

SEC.

TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: S5~ew -0 1 kj A +y C) e- e\v-onAannca k Fty ~5' "13 anoeii Brae Aveniee Na unk: NW 2519 62- (Cc'"-0v P( rcce Cc'l' rt4 2 PscnC 13 lu Actual Inventor: 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:

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This invention relates to electriual 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 compact ballast circuits presently available have a very high current harmonic distortion and a very low power factor of between 0.45 and 0.6 A typical circuit together with voltage I and current 2 waveforms 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 approve thase 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.

I-ts-- therefore an object of this- invention to ameliorate the aforementioned antages and accordingly an 'poved circuit is disclosed in addi-tinal diodo moano is provided to enure

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It is therefore an object of this invention to ameliorate the aforementioned disadvantages and accordingly an electronic ballast circuit for an electrical discharge lamp is disclosed, said circuit including a rectifier bridge coupled to an AC source and providing a pulsating DC supply voltage, a first capacitor connected ecross the output of the rectifier bridge, a lamp drive capacitor connecting a junction of the first capacitor and the rectifier bridge with a first terminal of the electrical discharge lamp load, a diode and smoothing capacitor means serially connected across the rectifier bridge whereby in operation uf the circuit said first capacitor charges o *said smoothing capacitor means, an oscillator circuit S. coupled across the smoothing capacitor means and an S* inductance connected between the output -f the oscillator circuit and a second terminal of the electrical discharge o *eo 00lamp 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 0electrical discharge lamp load so that said electrical discharge lamp load draws current directly from the 00 rectifier bridge to thereby improve the power factor and reduce harmonic distortion of the ballast circuit.

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Lhat the lamp draws current from the rectif bridge over substantially the whol the supply voltage waveform inclu j periods when this vol' qe is than that across smoothing capacitor One preferred form of this invention will 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: C1 0.1 F 250V AC C2 0.006 A F 250V AC C3 0.006 4tF 220V AC C4 0.047 A F 400V DC 4.7 ,AF 400V DC C6 4.7 a.F 400v DC C7 0.068 AF 100V DC D1 Bridge Rectifier D2, D3, D5 D6 Diodes D4 Diac 820.0 ohms 20.0 ohms 3.3 ohms 3.3 ohms 330.0 ohms 68.0 ohms 68.0 ohms 5.1 ohms 5.1 ohms L1 Filter Coil L3 Choke Coil L5, L2 L4 Core Coil 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 Dl 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.

U 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 even large electronic ballasts (as set out for example in IEC555/2 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 lamp it may be 0.047 AF 400 volts.

It will thus be appreciated that this invention at least in the form of the example disclosed provides a novel and useful improvement in ballast 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 values of the various components may be changed to adapt the circuit for use with larger fliorescent lamps up to 125 watts and for other types of discharge lamps. Also as an alternative to the mylar capacitor the following capacitors may be used for C3: ceramic, polycarbonate, polyester, polypropylene, polystyrene, aluminium and tantalum electrolytic.

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Claims (4)

1. 2. The electronic ballast circuit as claimed in claim 1 wherein said first capacitor is a mylar capacitor.
2. 3. The electronic ballast circuit as claimed in claim 1 wherein said electrical discharge lamp is a fluorescent lamp. S-7- I I
3. 4. The electronic ballast circuit as claimed in claim 1, 2 or 3 wherein said diode is a high speed switching diode. The electronic ballast circuit as claimed in claim 4 wherein the power factor is improved to better than 0.9.
4. 6. The electronic ballast circuit as claimed in any one of claims 1 to 5 where the smoothing capacitor means comprises two capacitors to reduce the physical size of the circuit. Dated this 6th day of July, 1994 Siew Ean Wong By his Patent Attorney MICHAEL ANDERSON-TAYLOR 4i II' 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 Dl 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 smoothing capacitor(s). o r