Parasitic power supply for traffic control systems
View Patent ↗A parasitic power supply provides for drawing power for an auxiliary device from a set of sequentially driven loads. A typical source of power is a traffic signal wherein the power may be sequentially applied to red, green and yellow lamps. The design provides isolation between loads so no two loads will be powered through any single-point failure of the power supply. The device may further contain control elements such as time delays to make the system compatible with requirements of safety devices used in traffic control systems to sense burned-out bulbs, and to sense conflicts between lighting patterns that are supposed to be mutually exclusive. The device may be configured as a separate component, or it may be integrated into a traffic signal head or into any selected device intended for connecting to a traffic signal head. The invention is particularly suitable for standard systems operating nominally at 115 VAC, though other AC voltages, and direct-current supplies, can also be used.
1. A parasitic power supply adapted to steal power from a multi-lamp traffic signal and supply power to an auxiliary device, comprising:
input connections from the respective incoming power lines of each of the lamps in said traffic signal, and from the common neutral of said lamps;
a plurality of redundant power supplies, one for each of said lamps in said signal, said power supplies further comprising switches for isolating them from one another;
a microcontroller configured to monitor the state of said traffic signal and actuate said isolation switches to engage a particular power supply when its respective signal lamp is receiving power;
output connections from said power supplies configured to deliver power to said auxiliary device; and,
an energy storage device connected to said outputs of said redundant power supplies.
2. The parasitic power supply of claim 1 wherein said traffic signal comprises at least two lamps, wherein at least one of said lamps is normally illuminated at any one time.
3. The parasitic power supply of claim 1 wherein each of said redundant power supplies comprises a device selected from the group consisting of: linear power supplies and switching power supplies.
4. The parasitic power supply of claim 1 wherein each of said redundant power supplies further comprises an output regulator.
5. The parasitic power supply of claim 1 wherein said isolating switches comprise devices selected from the group consisting of: SCRs; TRIACs; power MOSFETs; half-bridge rectifiers; and mechanical relays.
6. The parasitic power supply of claim 1 wherein said energy storage device is selected from the group consisting of: capacitors and batteries.
7. The parasitic power supply of claim 1 wherein said microcontroller delays the actuation of each of said isolation switches for a selected time interval after its respective signal lamp is energized.
8. The parasitic power supply of claim 7 wherein said selected time interval is in the range from about 0.25 to 1.0 second.
9. A traffic signal having an onboard parasitic power supply, comprising:
a substantially rigid housing;
at least two signal lamps contained within said housing, said lamps configured to be illuminated independently;
a parasitic power supply integral with said housing, said power supply comprising a plurality of redundant power supplies, one for each of said lamps in said signal, said power supplies further comprising switches for isolating them from one another, output connections from said power supplies configured to deliver power to said auxiliary device, an energy storage device connected to said outputs of said redundant power supplies, input power connections from each of said signal lamps and from the common neutral of said lamps, and a microcontroller configured to monitor the state of said traffic signal and actuate said isolation switches to engage a particular power supply when its respective signal lamp is receiving power; and,
output connections from said parasitic power supply configured to supply power to an auxiliary device.
10. The traffic signal of claim 9 wherein said isolating switches comprise devices selected from the group consisting of: SCRs; TRIACs; power MOSFETs; half-bridge rectifiers; and mechanical relays.
11. The traffic signal of claim 9 wherein said microcontroller delays the actuation of each of said isolation switches for a selected time interval after its respective signal lamp is energized.
12. The traffic signal of claim 11 wherein said selected time interval is in the range from about 0.25 to 1.0 second.
13. An electronic device configured to interface with a traffic signal head and draw power therefrom, comprising:
input connections adapted to be connected to the respective power circuits of each lamp in said signal head and to their common neutral;
a functional device configured to perform a selected electronic function; and,
a parasitic power supply configured to receive power from the respective lamp circuits and provide power to said functional device, said parasitic power supply comprising:
a plurality of redundant power supplies, one for each of said lamps in said signal, said power supplies further comprising switches for isolating them from one another;
a microcontroller configured to monitor the state of said traffic signal and actuate said isolation switches to engage a particular power supply when its respective signal lamp is receiving power; and,
an energy storage device connected to said outputs of said redundant power supplies.
14. The device of claim 13 wherein said microcontroller delays the actuation of each of said isolation switches for a selected time interval after its respective signal lamp is energized.
15. The device of claim 13 wherein said functional device comprises a device selected from the group consisting of: video sensors; chemical, biological, and radiological sensors; radar and other speed measurement devices; RF transmitters and receivers; and, audio annunciators and alarms.