Philips Electromagnetic Lamp manual Capacitor ballasts, Inductive ballasts or chokes

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1.4 Types of ballasts

that the no-load voltage need be no more than 25 to 30 per cent higher than the lamp voltage.This is also the proportion of the power dissipated by the ballast compared to the total circuit power.

Fig. 103. Schematic diagram of a fluorescent lamp operated on a resistor ballast in a DC circuit.

‘TL’ R

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2 Capacitor ballasts

A capacitor used as a ballast causes only very little losses, but cannot be used by itself, as this would give rise to very high peaks in the lamp current wave form at each half cycle. Only at very high frequencies can a capacitor serve satisfactorily as a ballast.

3 Inductive ballasts or chokes

Choke coils are frequently used as current limiting devices in gas-discharge lamp circuits (see Fig. 104).They cause somewhat higher losses than a capacitor, but produce far less distortion in the lamp current at 50 Hz. Moreover, in combination with a switch starter, they can be made to produce the high voltage pulse needed to ignite the lamp.

In practice, a choke ballast consists of a large number of windings of copper wire on a laminated iron core. It operates on the self-inductance principle.The impedance of such a ballast must be chosen in accordance with the mains supply voltage and frequency, the lamp type and the voltage of the lamp, to ensure that the lamp current is at the correct value. In other words: each type of lamp requires for each supply voltage its own choke as a ballast with a specific impedance setting. Heat losses, occurring through the ohmic resistance of the windings and hysteresis in the core, much depend upon the mechanical construction of the ballast and the diameter of the copper wire.

The right ballast for a given lamp and supply voltage should be chosen by consulting documentation and/or ballast markings.

The Philips standard range of ballasts is for supply voltages of 220/230/240 V and for frequencies of 50/60 Hz.

	I b	+	B	+	Vl	-
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	+				La
	Vm				S
						Il
Fig. 104. Schematic diagram of a
fluorescent lamp operated on a choke	0
ballast in an AC starter circuit.	-

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