GB2160723A

GB2160723A - Surge current suppressing adapter for an incandescent lamp

Info

Publication number: GB2160723A
Application number: GB08513417A
Authority: GB
Inventors: Kazumi Masaki
Original assignee: HAYASHIBARA KEN
Current assignee: HAYASHIBARA KEN
Priority date: 1984-06-01
Filing date: 1985-05-28
Publication date: 1985-12-24
Also published as: GB8513417D0; JPS60257099A; KR860000736A; GB2160723B

Abstract

The adapter has a series circuit of diodes D1, D2, D3 and a resistor R1 connected to the positive output of a bridge rectifier A, and an RC- integrating circuit R2, C2 connected in parallel to the series circuit. Either a thyristor SCR or an electromagnetic relay (Re) (Fig. 3) is arranged to short circuit resistor R1 when the voltage across the capacitor C2 of the integrating circuit reaches a predetermined level. The adapter is arranged to illuminate an incandescent lamp Z with a relatively high brightness, but also to significantly prolong the life of the lamp due to the absence of surge current. The adapter may be used to energise the lamp with a voltage of, for example, 1.3 times its rated voltage in order to obtain an increased luminous intensity. <IMAGE>

Description

SPECIFICATION Adapter for an incandescent lamp The present invention relates to an adapter for an incandescent lamp. For example, the adapter is arranged to prevent surge current in the incandescent lamp and yet to illuminate it with a relatively high brightness. The adapter can be arranged in the power supply for the incandescent lamp such that the luminous intensity of the lamp also the life of the lamp is increased.

According to the present invention there is provided an adpater for an incandescent lamp comprising: (a) a rectifier circuit; (b) a diode circuit and a resistive circuit both connected in series to the positive output of the rectifier circuit; (c) an RC-integrating circuit connected to the positive output of the rectifier circuit; and (d) means for switching the resistive circuit when the voltage across the integrating circuit reaches a predetermined level.

For example, an adapter of the invention may be provided in a power supply for a table lamp whereby the table lamp is initially supplied with a dc current of a limited magnitude upon switching on. Then when the filament is sufficiently preheated and after the lapse of a predetermined time, the lamp is supplied with the maximum output of the rectifier circuit.

Thus, the table lamp is illuminated with a relatively high-brightness, and its lamp life is prolonged due to the absence of surge current.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the circuit diagram of a first embodiment of an adapter in which a thyristor is used, Figure 2 is a graph illustrating the current curve of an incandescent lamp circuit, Figure 3 shows the circuit diagram of a further embodiment of an adapter in which an electromagnetic relay is used, Figure 4 shows the top plan view of a receptacle for housing an adapter, and Figure 5 shows the top plan view of a remote-type receptacle for an adapter of the invention.

Throughout the accompanying drawings, AC indicates an ac power supply; A a rectifier; C a capacitance; L an inductance; D a diode; R a resistance; S a switch; Z an incandescent lamp; SCR, a thyristor; Re an electromagnetic relay; 1 a receptacle; 2 and 3 plugs; 4 a plug socket; 5 a remote-type receptacle; and 6 a cord.

Reference is now made to Fig. 1 which shows an adapter to which ac current supplied by an ac power source AC. The ac current is first rectified by a rectifier A, e.g. a diode bridge, and is then smoothed by a capacitance C. An inductance L is connected in order to limit the current inflow into the capacitance C. The inductance can be replaced by a resistance. The positive output of the rectifier A is connected to a diode circuit D and to a resistive circuit which in the illustrated embodiment is a series resistance R,. The resistance R, is connected to one terminal of an incandescent lamp Z by way of a power switch S, and the other terminal of the incandescent lamp Z is connected to the negative output of the rectifier A to form the return circuit. As shown in Fig. 1, the diode circuit D comprises three or more diodes D1, D2, D3, which have been cascaded.

When the power switch S is turned on, a current of a limited magnitude flows into the circuit. If the resistances of the filament of the lamp Z under ambient temperature and of the series resistance R, are 10 ohms and 100 ohms respectively, then the total current I across the circuit will be 1.1 8 amperes (i.e.

1 = 130 volts/1 10 ohms), and this is indi- cated in Fig. 2 by the symbol "m". The switch S is turned off at point T,. At this time, the nonlinear voltage drop across the diodes D1, D2, and D3 is 2.1 volts (i.e. 0.7 volts X 3 = 2.1 volts), while the voltage drop across the series resistance R, is 118 volts (i.e. 1.18 amperes X 100 ohms = 118 volts).

These voltage drops are summed, and charged to resistance R2 in an integrating circuit, which is connected in parallel to the diode circuit D and the resistance R,, to charge a capacitance C2. When the time constant of the integrating circuit as determined by the resistance of resistance R2 and the capacitance of capacitance C2 is one-tenth of a second then the voltage across the capacitance C2 attains a level sufficient to trigger a thyristor SCR and to short-circuit the resistance R1 one-tenth of a second after switching-on. Within this one-tenth of a second, a filament temperature of the incandescent lamp Z attains 80% of that found in full-power illumination, and the filament resistance increases at T2 to a level which does not cause surge current.The current at this point is shown in Fig. 2 by the symbol "n" When ac power source is directly coupled to an incandescent lamp circuit without using an adapter of the invention, the incandescent lamp may receive a surge current up to 10 times larger in magnitude than its rate current, as shown in Fig. 2 by a broken line. This is one major cause of damage to lamp filaments.

The circuit shown in Fig. 3 is similar in construction to that of Fig. 1, except that the thyristor SCR is replaced by an electromagnetic relay Re comprised of an electromagnetic coil and a switch member. A predetermined time after the capacitance C2 in the integrating circuit is charged, the electromagnetic relay Re receives an energising current and acts to close the switch member and to short circuit the resistance R,.

In either case, ie using either the thyristor SCR or the electromagnetic relay Re, the voltage drop at the diode circuit D supplies a conduction energy to the triggering means, namely the thyristor SCR or the magnetic relay Re, after the series resistance R1 has been shorted.

When an incandescent lamp is supplied with a voltage 1.3 times higher than its rating from an adapter of the invention, the incandescent lamp attains an illumination having a spectrum similar to that of sunlight and luminous intensity of twice or much more than that attained with the rate voltage of the incandescent lamp.

Fig. 4 shows a receptacle 1 arranged to be equipped with circuits of the invention. The receptacle has both a plug 2 which can be connected to an ac wall socket, and a plug socket 4 to which, for instance, a plug 3 of a table lamp can be plugged.

Fig. 5 shows a remote-type receptacle 5 in which circuits of the invention can be housed.

The receptacle has both a plug 2 which can be connected to an ac wall socket by way of a cord 6, and a plug socket 4 to which, for example, a plug 3 of a table lamp can be plugged.

Claims

1. An adapter for an incandescent lamp comprising: (a) rectifier circuit; (b) a diode circuit and a resistive circuit both connected in series to the positive output of the rectifier circuit; (c) an RC-integrating circuit connected to the positive output of the rectifier circuit; and (d) means for switching the resistive circuit when the voltage across the integrating circuit reaches a predetermined level.

2. An adapter as claimed in Claim 1, wherein said switching means is a thyristor or an electromagnetic relay.

3. An adapter as claimed in Claim 1 or 2, wherein the adapter is housed in a receptacle.

4. An adapter as claimed in Claim 1 or 2, wherein the adapter is housed in a remotetype receptacle.

5. An adapter for an incandescent lamp substantially as hereinbefore described with reference to the accompanying drawings.