GB2146183A

GB2146183A - Lamp-dimmer unit

Info

Publication number: GB2146183A
Application number: GB08425595A
Authority: GB
Inventors: David John Martin
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-08-03
Filing date: 1984-10-10
Publication date: 1985-04-11
Also published as: GB8425595D0; GB2146183B

Abstract

A lamp-dimmer unit comprises a lamp (19) connected in series with the control triac of a control means (16) between mains supply terminals. A suppressor capacitor (C, 17) is connected across the supply terminals to form with the resistance of the lamp an RC filter attenuating the injection into the mains supply of potential radio frequency interference from the triac. A resistor (R, 18) may be connected between one supply terminal and one terminal of the capacitor to provide with the capacitor an RC filter for attenuating high frequencies or fast edges from the mains and/or to act as a surge current limiter. <IMAGE>

Description

SPECIFICATION Lamp-dimmer unit This invention relates to a lamp-dimmer unit.

In most countries there are statutory requirements for the permissible maximum levels or radio frequency interference (RFI) which can be injected back into the public AC mains supply by electrical apparatus. For triac controlled equipment in the U.K., British Standard specification BS 800 states the millivolt levels permitted at various frequencies and also the method of measurement.

The present invention is generally concerned with attenuation of potential RFI injected into a mains supply by a lamp-dimmer unit. It may also be desirable to protect the lamp-dimmer unit from high frequencies or fast edges arriving from the mains source. It may also be desirable to provide means for limiting surge current through the lamp.

Aspects of the present invention are set out in the claims of this specification.

The present invention will be further described with reference to embodiments thereof illustrated in the accompanying drawings, in which: Figure 1 illustrates an artificial mains unit; Figure 2 shows capacitor suppression of a lamp-dimmer unit; Figure 3 is an equivalent circuit of Fig. 2 for h.f. components; Figure 4 shows an RC circuit across the supply input to a lamp-dimmer unit; and Figure 5 shows a preferred embodiment of a lamp-dimmer unit.

Mention has already been made of British Standard Specification BS 800 and the method of measurement that it states for the stated millivolt levels permitted at various frequencies. An "artificial mains unit" as shown in Fig. 1 is used to make measurements.

Fig. 2 shows the circuit of one embodiment of the invention. It includes a pair of terminals to which the mains supply is connectable, a lamp 1 9 received in a lamp holder (not shown) and a control means 1 6 including a triac connected in series with the lamp between the supply terminals. Reference may be made to my copending application 8221959 (published under the number GB210545A) in which is illustrated a triac dimmer control of the kind thus far described which is an integral part of a lighting unit. The control means 1 6 is preferably that described and claimed in my U.K. Patent No. 1,410,351. With such a unit, sufficient attenuation of RFI can be obtained simply be placing a capacitor C across the supply terminals in the lamp-dimmer unit as shown in Fig. 2.This is because there is an RC filter formed by the bulb resistance and the suppressor capacitor which attenuates the high frequency components resulting from fast edges at the triac terminals. (Fig. 3 shows the equivalent circuit.) In addition to the problem of exported interference the lamp-dimmer can itself be adversely affected by transient interference coming from the supply. If fast edged interference arrives at the terminals of the lamp-dimmer (usually from a source electrically nearby), it causes the triac to trigger at spurious times.

In practice this gives rise to bright flashes from the controlled lamp when it should be at low level or off. The problem can be overcome by introducing a small amount of resistance between the input supply and the lamp dimmer suppressor capacitor described above.

An RC filter is then formed which attenuates high frequencies or fast edges arriving from the supply as shown in Fig. 4.

Having introduced a series resistor for transient suppression correct choice of value and peak current rating of this resistor can provide another very useful function. When a lamp bulb filament fails the arc formed between the two filament leads inside the bulb causes a very high peak current to flow for a very short time (typically 30 amps for part of half a cycle of the AC supply). This often causes failure of the triac control element if it is a comparatively low current device. Correct choice of series resistor will however limit the peak current caused by a lamp bulb failure to a value which does not damage the triac.Fig. 5 shows a preferred embodiment of a combined dimmer/lighting unit incorporating a control means 16, a suppressor capacitor 1 7 of 0.22 lif and a series resistor 1 8 of 33 ohms, 2 watt with a 40 watt lamp 1 9. Preferably. the control means 1 6 is that described and claimed in my aforementioned Patent No.

1410351, the content of which is included herein by reference thereto.

1. A lamp-dimmer unit comprising a lamp holder, a control unit having input terminals for connection to a voltage source and output terminals connected to said lamp holder. and an RC circuit connected to said input terminals to suppress radio frequency interference, said control unit comprising an electronic dimmer.

2. A lamp-dimmer unit comprising a lamp holder, a control unit having input terminals for connection to a voltage source and output terminals connected to said lamp holder, and an RC circuit connected to said input terminals to limit current surges resulting from lamp failure, said control unit comprising an electronic dimmer.

3. A lamp-dimmer unit comprising a lamp holder, a control unit having input terminals for connection to a voltage source and output terminals connected to said lamp holder, and an RC circuit connected to said input terminals to attenuate high frequencies or fast edges arriving from said voltage source, said

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Lamp-dimmer unit This invention relates to a lamp-dimmer unit. In most countries there are statutory requirements for the permissible maximum levels or radio frequency interference (RFI) which can be injected back into the public AC mains supply by electrical apparatus. For triac controlled equipment in the U.K., British Standard specification BS 800 states the millivolt levels permitted at various frequencies and also the method of measurement. The present invention is generally concerned with attenuation of potential RFI injected into a mains supply by a lamp-dimmer unit. It may also be desirable to protect the lamp-dimmer unit from high frequencies or fast edges arriving from the mains source. It may also be desirable to provide means for limiting surge current through the lamp. Aspects of the present invention are set out in the claims of this specification. The present invention will be further described with reference to embodiments thereof illustrated in the accompanying drawings, in which: Figure 1 illustrates an artificial mains unit; Figure 2 shows capacitor suppression of a lamp-dimmer unit; Figure 3 is an equivalent circuit of Fig. 2 for h.f. components; Figure 4 shows an RC circuit across the supply input to a lamp-dimmer unit; and Figure 5 shows a preferred embodiment of a lamp-dimmer unit. Mention has already been made of British Standard Specification BS 800 and the method of measurement that it states for the stated millivolt levels permitted at various frequencies. An "artificial mains unit" as shown in Fig. 1 is used to make measurements. Fig. 2 shows the circuit of one embodiment of the invention. It includes a pair of terminals to which the mains supply is connectable, a lamp 1 9 received in a lamp holder (not shown) and a control means 1 6 including a triac connected in series with the lamp between the supply terminals. Reference may be made to my copending application 8221959 (published under the number GB210545A) in which is illustrated a triac dimmer control of the kind thus far described which is an integral part of a lighting unit. The control means 1 6 is preferably that described and claimed in my U.K. Patent No. 1,410,351. With such a unit, sufficient attenuation of RFI can be obtained simply be placing a capacitor C across the supply terminals in the lamp-dimmer unit as shown in Fig. 2.This is because there is an RC filter formed by the bulb resistance and the suppressor capacitor which attenuates the high frequency components resulting from fast edges at the triac terminals. (Fig. 3 shows the equivalent circuit.) In addition to the problem of exported interference the lamp-dimmer can itself be adversely affected by transient interference coming from the supply. If fast edged interference arrives at the terminals of the lamp-dimmer (usually from a source electrically nearby), it causes the triac to trigger at spurious times. In practice this gives rise to bright flashes from the controlled lamp when it should be at low level or off. The problem can be overcome by introducing a small amount of resistance between the input supply and the lamp dimmer suppressor capacitor described above. An RC filter is then formed which attenuates high frequencies or fast edges arriving from the supply as shown in Fig. 4. Having introduced a series resistor for transient suppression correct choice of value and peak current rating of this resistor can provide another very useful function. When a lamp bulb filament fails the arc formed between the two filament leads inside the bulb causes a very high peak current to flow for a very short time (typically 30 amps for part of half a cycle of the AC supply). This often causes failure of the triac control element if it is a comparatively low current device. Correct choice of series resistor will however limit the peak current caused by a lamp bulb failure to a value which does not damage the triac.Fig. 5 shows a preferred embodiment of a combined dimmer/lighting unit incorporating a control means 16, a suppressor capacitor 1 7 of 0.22 lif and a series resistor 1 8 of 33 ohms, 2 watt with a 40 watt lamp 1 9. Preferably. the control means 1 6 is that described and claimed in my aforementioned Patent No. 1410351, the content of which is included herein by reference thereto. CLAIMS

3. A lamp-dimmer unit comprising a lamp holder, a control unit having input terminals for connection to a voltage source and output terminals connected to said lamp holder, and an RC circuit connected to said input terminals to attenuate high frequencies or fast edges arriving from said voltage source, said control unit comprising an electronic dimmer.

4. A lamp-dimmer unit as claimed in any one of Claims 1 to 3, wherein said control unit comprises control means as claimed in any one of the claims of Patent Specification No. 1410351.

5. A lamp-dimmer unit substantially as hereinbefore described with reference to any one of Figs. 2 to 5 of the accompanying drawings.