GB1584200A - Emergency lighting system with fluorescent lamps - Google Patents

Description

(54) EMERGENCY LIGHTING SYSTEM WITH FLUORESCENT LAMPS (71) We, THORN EMI LIMITED (formerly known as THORN ELECTRICAL INDUSTRIES LIMITED,) a British Company, of Thorn House, Upper St. Martin's Lane, London WC2H 9ED, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an emergency lighting system comprising an inverter for supplying power to one or more fluorescent lamps and is a modification of the invention of our co-pending British patent application No.

32761/74. (Serial No. 1,508,130).

In that application we claim an emergency lighting system comprising an inverter for supplying power to one or more fluorescent lamps, a mains supplied charging unit for keeping charged a stand-by storage battery for powering the inverter, the charging unit also providing a bias signal for inhibiting operation of the inverter while mains power is present, and a bright-up circuit for boosting the output of the inverter for a predetermined time after the mains fails.

In accordance with the present invention the system additionally comprises a timing capacitor charged by the mains and connected to the bright-up circuit to maintain the boost for a period determined by the discharge of the capacitor after mains failure. Conveniently the timing capacitor may form part of the charging unit and provide the said bias signal.

As described and claimed in Application No.

32761/74 (Serial No. 1,508,130) the inverter may be of the blocking oscillator type comprising a power transistor and a current transformer, the control electrode of the transistor being driven by the secondary of the transformer, the primary of which is in the collector circuit of the transistor, and the switching action of the inverter being effected by saturation of the core of the current transformer, and in which the bright-up circuit is arranged to regulate the voltage across the secondary of the current transformer of the inverter and thus its saturation time.

The bright-up circuit may comprise a regulating transistor connected to regulate the secondary voltage of the said current transformer, the regulator transistor being controlled by the voltage across the timing capacitor.

The invention will now be described in more detail with the aid of an example illustrated in the drawing accompanying the provisional specification, which is a circuit diagram of the circuit described in Application No. 32761/74 (Serial No. 1,508,130) with modifications in accordance with the present invention.

Parts of the circuit corresponding to those shown in the drawings accompanying Application No. 32761/74 (Serial No. 1,508,130) are given the same reference numerals. Thus there is a capacitor 16, charged from the mains by way of a transformer and rectifier, which supplies a hold-off bias by way of a line 36 to an inverter circuit as described in more detail in application No. 32761/74 (Serial No.

1,508,130). This inverter circuit includes a variable resistor 33 and a diode 34. As before the bright-up circuit 22 includes a pnp transistor 37 which controls the flow of current to the junction of the variable resistor 33 and the diode 34.

The present circuit differs in the manner in which the transistor 37 is controlled. The baseemitter circuit of the transistor 37 is connected across the capacitor 16 by way of a resistor 48 and an amplifying transistor 49. Thus the transistor 37 is held conducting to shunt the resistor 33 as long as the capacitor 16 is kept fully charged by the mains and until the capacitor is almost fully discharged after mains failure.

Supply of the lamp by the inverter commences as soon as the capacitor 16 begins to discharge following mains failure but the transistor 37 continues to be held conducting while the capacitor 16 discharges. In this way the supply from the inverter to the lamp is boosted for a period of two or three seconds after mains failure, which is sufficient to ensure full striking of the fluorescent lamp.

It will be apparent that it is convenient to use as the timing capacitor a capacitor which is already present in the circuit in order to provide the hold-off bias. However a quite separate timing capacitor could be provided if this proved more suitable in a particular case or if the hold-off bias were provided in some other way.

WHAT WE CLAIM IS: 1. An emergency lighting system comprising an inverter for supplying power to one or more fluorescent lamps, a mains supplied charging unit for keeping charged a stand-by storage battery for powering the inverter, the charging unit also providing a bias signal for inhibiting operation of the inverter while mains power is present, and a bright-up circuit for boosting the output of the inverter for a predetermined time after the mains fails, the system additionally comprising a timing capacitor charged by the mains and connected to the bright-up circuit to maintain the boost for a period determined by the discharge of the capacitor after mains failure.

2. An emergency lighting system as claimed in claim 1 in which the timing capacitor forms part of the charging unit and provides the said bias signal.

3. A system as claimed in claim 1 or 2 in which the inverter is of the blocking oscillator type comprising a power transistor and a current transformer, the control electrode of the transistor being driven by the secondary of the transformer, the primary of which is in the collector circuit of the transistor, and the switching action of the inverter being effected by saturation of the core of the current transformer, and in which the bright-up circuit is arranged to regulate the voltage across the secondary of the current transformer of the inverter and thus its saturation time.

4. A system as claimed in claim 3 in which the bright-up circuit comprises a regulating transistor connected to regulate the secondary voltage of the said current transformer, the regulating transistor being controlled by the voltage across the timing capacitor.

5. An emergency lighting system substantially as described with reference to the drawing accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. proved more suitable in a particular case or if the hold-off bias were provided in some other way. WHAT WE CLAIM IS:

1. An emergency lighting system comprising an inverter for supplying power to one or more fluorescent lamps, a mains supplied charging unit for keeping charged a stand-by storage battery for powering the inverter, the charging unit also providing a bias signal for inhibiting operation of the inverter while mains power is present, and a bright-up circuit for boosting the output of the inverter for a predetermined time after the mains fails, the system additionally comprising a timing capacitor charged by the mains and connected to the bright-up circuit to maintain the boost for a period determined by the discharge of the capacitor after mains failure.

2. An emergency lighting system as claimed in claim 1 in which the timing capacitor forms part of the charging unit and provides the said bias signal.

3. A system as claimed in claim 1 or 2 in which the inverter is of the blocking oscillator type comprising a power transistor and a current transformer, the control electrode of the transistor being driven by the secondary of the transformer, the primary of which is in the collector circuit of the transistor, and the switching action of the inverter being effected by saturation of the core of the current transformer, and in which the bright-up circuit is arranged to regulate the voltage across the secondary of the current transformer of the inverter and thus its saturation time.

4. A system as claimed in claim 3 in which the bright-up circuit comprises a regulating transistor connected to regulate the secondary voltage of the said current transformer, the regulating transistor being controlled by the voltage across the timing capacitor.

5. An emergency lighting system substantially as described with reference to the drawing accompanying the provisional specification.