Electricity: power supply or regulation systems – Output level responsive – Phase controlled switching using electronic tube or a three...
Patent
1994-04-22
1996-02-06
Wong, Peter S.
Electricity: power supply or regulation systems
Output level responsive
Phase controlled switching using electronic tube or a three...
323235, G05F 112
Patent
active
054898390
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an A.C. power supply controller for a capacitive load, particularly an electroluminescent light source, and a waveform generator suitable for use in such a controller.
Electroluminescent (EL) lights have been used as formation lights for military aircraft. The lights are situated on the aircraft such that they are visible to other aircraft only. The lights must be bright enough for the aircraft's position to be safely identified by other aircraft flying in a formation but not so bright as to be seen by hostile aircraft flying some distance away. The light must therefore be variable to cope with varying formation separation and weather conditions.
The lights present a highly capacitive load to power supply controllers, causing a large difference in the relative phases of the voltage and current in an A.C. supply. Former power supply controllers have taken the form of a variable transformer supplying a sinewave the amplitude of which can be varied. Variable transformers suffer the disadvantages of large physical size, weight and cost. Further, adjustment is achieved by movement of a wiper over coils which produces electrical noise, upsetting sensitive aircraft avionics. The problem of noise increases with age as dust becomes entrapped within the transformer.
It is an object of the invention to provide a power supply controller that is inexpensive to manufacture, compact, lightweight and produces a low level of electrical noise.
According to the invention there is provided an A.C. power supply controller for a capacitive load comprising means for producing a pulsed switching waveform centred on the zero-crossing points of an applied alternating voltage waveform, powerswitch means for connecting an applied voltage waveform to the load in response to the pulsed switching waveform, and means for widening the pulse width of the switching waveform symmetrically about the zero-crossing points to vary the power applied to the load.
According to a second aspect of the invention, there is provided a waveform generator for producing a pulsed waveform centred about the zero-crossing points of an input alternating waveform comprising means to rectify the input waveform and means to determine when the rectified waveform is below a particular value and to generate a non-zero waveform level when the rectified waveform is below said value.
A specific embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which:
FIG. 1 shows a block diagram of a light controller in accordance with the invention;
FIGS. 2a, 2b, 2c, and 2d are waveforms representative of signal processes at 18, driver 16 and lights 1 (twice) used in the light controller shown in FIG. 1; and
FIG. 3 shows a circuit diagram of the A.C. power switch shown in FIG. 1.
With reference to FIG. 1, an array of eight electroluminescence formation lights 1 are controlled by a lighting controller 2 (within the broken lines). A 115 V, 400 Hz supply is connected to the input of the controller via supply and return ports 3 and 4, the lighting controller 2 and lights 1 being activated and controlled by a cockpit mounted 10K ohm linear potentiometer 5 incorporating a 5 amp switch 6.
The lighting controller 2 comprises a 115 V A.C. power rail 7 and a return rail 8 connected to the supply and return parts 3 and 4. A low voltage supply 9 provides a +15 V D.C. supply to the controller components.
A rectifier 10 rectifies the A.C. power waveform to give a full wave rectified output 11 of peak voltage 115 V. The zero crossing points of the voltage waveform are automatically derived in this rectification. The rectified output 11 is input to an attenuator 12 where it is reduced in amplitude before being passed to a comparator 13 where it is compared with a D.C. level set by the linear potentiometer 5.
The linear potentiometer 5 is supplied with a +5 V D.C. supply derived from the +15 V D.C. supply by a POT D.C. supply 14. Thus, by rotation of the potentiometer 5 the D.C. voltage level on input 15 to th
REFERENCES:
patent: 4904906 (1990-02-01), Atherton et al.
patent: 4935691 (1990-06-01), Lamar
patent: 5004969 (1991-04-01), Schanin
Burns David G.
Shannon Victor L.
Riley Shawn
Ultra Electronics Limited
Wong Peter S.
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