WO1990001247A1

WO1990001247A1 - Regulated ac controller

Info

Publication number: WO1990001247A1
Application number: PCT/AU1989/000305
Authority: WO
Inventors: Jon Andrew James Davis
Original assignee: The D & D Electrical Group Pty Limited
Priority date: 1988-07-22
Filing date: 1989-07-21
Publication date: 1990-02-08

Abstract

A regulated AC controller (16) wherein power to a lamp (10) is monitored and compared to a predetemined level (12) to generate a control signal representative of the difference, which control signal is used to reset the power level to the lamp (10) upon a difference from the predetermined level being registered. Power to the lamp (10) may be controlled by a triac (15) whose duty cycle is controlled at a desired level. Control pulses to the triac may be determined by comparison of an RMS measurement obtained at the lamp (10) with a stable reference voltage (12) determining a preset desired level.

Description

TITLE: "REGULATED AC CONTROLLER"

FIELD OF THE INVENTION This invention relates to a regulated AC controller for use with various types of incandescent light sources.

BACKGROUND OF THE INVENTION Over recent years there has been a dramatic increase in the use of low voltage lighting, in the form o "Low Voltage Dichroic Reflector Lamps" for domestic and commercial internal lighting.

This type of lamp allows the filament to run at higher temperatures (compared with conventional incandescent lamps) in a very small quartz envelope. The higher temperature shifts the spectral output curve to the shorter wavelengths providing increased output in the short wave blue end of the visible spectrum, thus producing a "whiter light". This, in conjunction with their small physical size, allows effective, yet discreet lighting systems to be installed in shops, showrooms, displays, foyers, etc.

It is now normal to find this style of lamp used in large numbers, particularly in commercial premises.

However, many owner/operators of such premises are finding that the lamps are not lasting anywhere near the manufacturers quoted life in hours. Due to the often large numbers of lamps installed, the costs involved in frequent lamp replacements are high. For instance, a typical medium sized shop installation may include 250 lamps, with a lamp replacement cost of $20 per lamp excluding labour.

An unfortunate characteristic of all quartz tungsten halogen and other incandescent lamps is their susceptibility to failure due to the following:- 1. At switch on, when the filament is cold, a large inrush current occurs while the filament heats up. This excessive current acts to stress the filament and its connections to a much greater degree than under normal stable operating conditions.

2. An increase of 6% in supply voltage reduces the operating rated life by 50%.

Although mains power distribution at the consumer level is supposed to be a fixed value, which varies from country to country (240V AC in Australia), in practice it can be found to vary considerably from location to location, and- even over a relatively small area (eg. a modern shopping centre complex) where due to load changes resulting from other electrical equipment such as lifts, freezers, air conditioners etc. switching in and out, the actual voltage appearing on a particular phase may be unpredictable. Fluctuations of 15% are commonplace.

Premature lamp failure is therefore caused by regular switching on of the lamp, and by power line surges and fluctuations. In addition, it has also been determined that a slight reduction in operating voltage, while having minimal effect on light output, can significantly increase bulb life.

OBJECT OF THE INVENTION It is an object of the present invention to provide a regulated AC controller for all incandescent lamps such as quartz tungsten halogen lamps, including low voltage dichroic reflector type lamps. Other objects, and various advantages of the invention will hereinafter become apparent.

NATURE OF THE INVENTION The invention achieves its object in providing a regulated AC controller for application with incandescent lamps to restrict excess operating voltages for the protection of lamp life in lighting circuits characterised in that it provides: a lamp level control means to be inserted, in use, in the active line of a lamp circuit; a set level means generating a first signal representative of a desired lamp power level; an actual level means applied to the output of the lamp level control means generating a second signal representative of the actual lamp power level; and a control means receiving the first and second signals, and, depending on their relative values, generating a control signal output to the lamp level control means to cause it to set the actual lamp power . level at the desired lamp power level.

In a preferred form of the invention, a 'soft start' is provided at switch on. DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to a preferred embodiment as shown in the accompanying figures wherein:

FIG. 1 is a schematic of a circuit in accordance with the present invention, shown in block form,

FIG. 2 shows the embodiment of FIG. 1 fitted to the power line to a lamp, and

FIG. 3 is a detailed diagram illustrating a preferred circuit for implementing a regulated AC controller in accordance with the invention.

FIG. 1 shows the basic circuits or sections used in an embodiment of this invention. These sections will be readily implemented by those familiar with industrial electronic circuits. Sections 11 to 14 might be implemented using conventional analogue techniques. However, it will be recognised by those in the art that alternative techniques may be employed to implement these sections. For instance, sections 11 to 14 may be implemented with digital techniques by using a microcontroller to perform the arithmatic computations necessary in each section. These sections would then exist solely as a set of software routines that perform an identical function as an analogue implementation.

With reference to FIG. 1, power to the load, a 5 tungsten halogen lamp, for example, is adjusted by controlling the firing point of an SCR/TRIAC device in the phase controller 14. This technique is referred to below as 'phase control' . It is commonly used in all forms of electronic light dimmers. It represents a low

10 cost method of changing power to a load.

To achieve an automatic and self-regulating system, some method of measuring the actual voltage or power being supplied to the load must be employed, so that the circuitry can compensate for change in mains

15 supply voltage or load requirements.

Conventional measuring techniques for AC waveforms are accurate only for undistorted εinewaves. The output waveform from a phase controller, such as those that may be employed in the regulated AC

20 controller of FIG. 1, is not a pure sinewave, and serious errors in measurement would result, if conventional measuring techniques were used, that is the system would be unable to maintain constant power to the load.

25 In the present invention, a method, referred to herein as 'true RMS to DC conversion' is used as is set out below. Such a technique is used in scientific equipment for the measurement of complex waveforms. It provides an accurate method of obtaining a true

30 measurement of the RMS voltage or power being supplied to the load.

The lamp voltage setpoint is established at 12 and is set to give the desired RMS voltage or power to be supplied to the lamp circuit. The RMS voltage to the

35 lamp circuit is maintained at a value established by the setpoint at 12 regardless of fluctuations in the mains input voltage or load. The lamp voltage setpoint at 1 may also incorporate the means for a 'soft' start b smoothly ramping the input to the rest of the system u to the desired set point voltage so as to ensure tha the inrush of current that would otherwise occur is limited while the filaments are cold.

The error amplifier 13 takes the error between the actual load RMS voltage and the desired lamp voltage and amplifies it to drive the phase controller 14. The phase controller 14 adjusts the firing point of an SCR/TRIAC device to maintain a constant RMS voltage or power to the lamp circuit. The phase controller can adjust the RMS voltage to be less than or equal to the mains input voltage 15. The RMS conversion 11 measures the true RMS voltage or power being supplied to the lamp circuit. This process is preferable because the voltage waveform supplied to the lamp circuit is not an undistorted sinewave and therefore other more conventional measuring techniques may not be suitable. The lamp circuit is any combination of, incandescent lamps, for example, standard quartz tungsten halogen lamps with their associated transformers.

The elements that perform the control operation, those elements in FIG. 1 that are within the area 16 inside the dotted perimeter, may be assembled together and supplied to users in a suitable heat disipative, mountable box, to be fitted into a lamp power circuit as shown in FIG. 2. The AC controller 16 is fitted into the power line to a lamp (not shown) , which lamp is connected at the output of FIG. 2 with the controller 16 downstream of the lamp power switch 17. Operation of the controller eliminates fluctuations at lamps 18.

The above described circuit is capable of achieving a tight regulation with a better than 6% variation in power levels. The circuit of FIG. 3 employs integrated circuits to. stablish certain functions as will become clear below and it will be apparent that a man skilled in the art is able to choose between a variety of off ^"5 the shelf chips to .perform the various functions, making, where necessary, any adjustments in peripheral circuitry to implement the requisite function. Only the broader circuit objectives are outlined in detail below. In FIG. 3 AC power is supplied across 0 terminals A and N. Current flows through the load via RF supreεsion devices FL1 and FL2, this current flow being controlled by switching device T2.

The voltage across the load is sensed at point FB and fed to the adjustable voltage divider R25, VR1, 5 R26.

The voltage waveform output from VR1 is fed to IC5 where the true RMS voltage of the waveform is converted_, to its equivalent DC value at IC5 pin 6. This signal is fed to 1/2 IC4 pin 5 where it is amplified at 0 pin 7, before being sent to Error Amplifier 1/2 IC4 pin 3. This signal is compared with the stable reference voltage developed across IC3 via R38, R16, R17, and fed to 1/2 IC4 pin 2. The resultant error voltage is output from 1/2 IC4 pin 1 and sent to IC2 where a voltage level 5 translation occurs which is necessary for the correct operation of phase controller IC1.

After passing through the voltage level translator, the error voltage which appears from IC2 at pins 5 and 8, is fed to Phase Controller IC1 pin 10. 0 The output of IC1 appears at pin 2. This output is a current pulse which turns on driver triac Tl, which then turns on the main current switching device triac T2.

Each time the AC supply waveform crosses through zero volts, IC1 delays the occurence of the 5 triac firing pulse by an amount related to the magnitude of the error voltage on pin 10 of IC1. For example, if the voltage across the load is too high, then the resultant error voltage causes IC1 to delay the switch- on pulse to the triacs resulting in an overall reduction of RMS voltage across the load, and a corresponding reduction in power.

IC4 pins 3, 2 and 1 compares the actual DC equivalent of the true RMS voltage across the load, with a stable voltage reference. The resultant error voltage is therefore used to maintain a regulated and constant true RMS voltage and power across the load.

By adjusting either signal level at pins 2 or . 3 of IC4, the output power of the load can be changed. The output voltage set point is controlled by adjusting VR1. R38, R16 and C17 form a network designed to gradually allow the reference voltage to increase, just after switch on, thereby providing the 'soft start' function.

Transistors Ql, Q2 are included to provide a short time delay before commencement of the soft start. This is necessary because IC1 requires a short stabilisation period immediately after switch on.

The above described circuit achieves a self- regulated AC output, that can be preset to any RMS voltage lower than or equal to the mains input voltage. This RMS voltage will then be maintained. Normally it will be set such that the lamps are operating on a slightly lower level than the quoted nominal lamp voltage.

In addition, a simple technique is employed that allows, at switch on, for the power to be gradually applied to the lamp thereby eliminating the high inrush current.

While the above has been described with reference to a preferred embodiment, any of the modifications and adaptations that will be apparent to a man skilled in the art may be made thereto within the scope and spirit of the invention herein set forth.

Claims

CLAIMS:

1. A regulated AC controller for application to incandescent lamps to restrict excess operating voltages for the protection of lamp life in lighting circuits characterised in that it provides: a lamp level control means to be inserted, in use, in the active line of a lamp circuit; a set level means generating a first signal representative of a desired lamp power level; an actual level means applied to the output of the lamp level control means generating a second signal representative of the actual lamp power level; and a control means receiving the first and second signals, and, depending on their relative values, generating a control signal output to the lamp level control means to cause it to set the actual lamp power level at the desired lamp power level.

2. A regulated AC controller as claimed in Claim 1 wherein the lamp level control means is a phase controller such as an SCR and the actual level means performs an RMS conversion to establish the second signal, the control signal being applied to the SCR to effect control of power levels to the lamp.

3. A regulated AC controller as claimed in Claim 2 wherein in the control means the first and second signals are compared and their difference is fed to an error amplifier to generate the control signal.

4. A regulated controller as claimed in Claim 3 wherein the set level means generates the first signal with a soft start that establishes the first signal's desired level after switch on with a steady rise from zero power to desired power.

5. A regulated controller as claimed in Claim 2 wherein the control means comprises an error amplifier receiving the first and second signal whose output is fed to a phase controller which introduces a delay of switch on in SCR firing pulses in proportion to the difference between the first and second signals.

6. A regulated controller as claimed in Claim 4 wherein the set level means is associated with circuit elements which delay the onset of the soft start.

7. A regulated controller as claimed in Claim 1 wherein the first and second signals are fed to an error amplifier whose output is buffered to a phase controller . which introduces a delay of switch on in SCR firing pulses in proportion to the difference between the first and second signals, the SCR firing pulses switching an SCR that controls a duty cycle of a mains power lamp level control means in the active line to a lamp being regulated.

8. A regulated controller as claimed in Claim 1 wherein the set level means comprises a stable voltage reference and generates the first signal with a soft start with a preset delay.