Fail safe control circuit for traffic lights

Claim 2

A fail-safe circuit for preventing the simultaneous energization of a pair of signal lamps comprising, a source of supply voltage having first and second output terminals, first and second switching contacts, means for alternately closing said contacts in mutually exclusive time intervals, means connecting a first one of said lamps and said first switching contact in a first series circuit across said first and second output terminals in the order named and the second one of said lamps and said second switching contact in a second series circuit across said first and second output terminals in the order named and in parallel with the first series circuit, first and second diodes, a relay having a high value of resistance, means connecting said diodes in series opposition between the junction of said first lamp and the first contact and the junction of the second lamp and the second contact, and means connecting said relay between the junction of said diodes and said second output terminal of the voltage source, said diodes being polarized relative to the voltage at said output terminals so that when one contact is closed the relay is energized via the lamp that is in series with the open contact and its associated diode.

Claim 3

A circuit as claimed in claim 1 wherein one terminal of each said lamps is directly connected to said first output terminal and one terminal of each of said contacts is directly connected to the second output terminal, and one terminal of said relay is directly connected to the second output terminal so that the relay is in shunt with the seRies combination of one diode and one switching contact and the series combination of the other diode and the other switching contact.

Claim 4

A circuit as claimed in claim 1 wherein said relay is normally energized by a current flow from said voltage source via a first series circuit including said first lamp and the first diode when the second contact is closed or via a second series circuit including the second lamp and the second diode when the first contact is closed.

Claim 5

A circuit as claimed in claim 1 wherein said diodes are connected with their cathodes in common to one terminal of the relay.

Claim 6

A fail-safe circuit for preventing the simultaneous energization of a pair of signal lamps comprising, a source of supply voltage having first and second output terminals, first and second switching contacts arranged to close alternately in mutually exclusive time intervals, means connecting a first one of said lamps and said first switching contact in a first series circuit, means connecting the second one of said lamps and said second switching contact in a second series circuit, means connecting said first and second series circuits in parallel across said output terminals with one terminal of each lamp connected in common to said first output terminal and with one terminal of each switching contact connected in common to said second output terminal, first and second diode connected in series opposition between the junction of said first lamp and the first contact and the junction of the second lamp and the second contact, and a relay coil connected between the junction of said diodes and said second output terminal of the voltage source.

Claim 7

A fail-safe circuit for preventing the simultaneous energization of a pair of signal lamps comprising, a source of supply voltage having first and second output terminals, first and second switching contacts arranged to close alternately in mutually exclusive time intervals, means connecting a first one of said lamps and said first switching contact in a first series circuit, means connecting the second one of said lamps and said second switching contact in a second series circuit, means connecting said first and second series circuits in parallel across said output terminals with one terminal of each lamp connected in common to said first output terminal and with one terminal of each switching contact connected in common to said second output terminal, first and second diode connected in series opposition between the junction of said first lamp and the first contact and the junction of the second lamp and the second contact, and a relay coil connected between the junction of said diodes and said second output terminal of the voltage source.

Claim 8

A circuit as claimed in claim 5 wherein said relay coil is normally energized by said voltage source and includes a contact arranged to interrupt the supply of voltage from the output terminals to the lamps whenever the relay coil is deenergized.

Claim 9

A circuit as claimed in claim 5 wherein the resistance of said coil is chosen to have a value sufficient to develop a voltage drop that will back-bias the diode associated with a closed contact whereby the relay stays energized despite the closure of one of said contacts.

Claim 10

A fail-safe circuit for preventing the simultaneous energization of a pair of signal lamps comprising, a source of supply voltage having first and second output terminals, first and second switching contacts arranged to close alternately in mutually exclusive time intervals, means connecting a first one of said lamps and said first switching contact in a first series circuit, means connecting the second one of said lamps and said second switching contact in a second series circuit, means connecting said first and second series circuits in parallel across said output terminals with one terminal of each lamp connected in common to said first output terminal and with one terminal of each switching contact connected in common to said second output terminal, first and second diodes connected in series opposition between the junction of said first lamp and the first contact and the junction of the second lamp and the second contact, and a relay coil connected between the junction of said diodes and said second output terminal of the voltage source, said diodes being polarized relative to the voltage at said output terminals to provide an easy path for current to flow from said terminals to the relay coil via a series circuit comprising that lamp which is in series with the open one of said contacts and its associated diode, said current being of a magnitude to energize said relay independently of the state of the other one of said contacts.

Claim 11

A fail-safe circuit for preventing the simultaneous energization of a pair of signal lamps comprising, a source of supply voltage having first and second output terminals, first and second switching contacts arranged to close alternately in mutually exclusive time intervals, means connecting a first one of said lamps and said first switching contact in a first series circuit, means connecting the second one of said lamps and said second switching contact in a second series circuit, means connecting said first and second series circuits in parallel across said output terminals with one terminal of each lamp connected in common to said first output terminal and with one terminal of each switching contact connected in common to said second output terminal, first and second diodes connected in series opposition between the junction of said first lamp and the first contact and the junction of the second lamp and the second contact, and a relay coil connected between the junction of said diodes and said second output terminal of the voltage source, said diodes being polarized relative to the voltage at said output terminals to provide an easy path for current to flow from said terminals to the relay coil via a series circuit comprising that lamp which is in series with the open one of said contacts and its associated diode, said current being of a magnitude to energize said relay independently of the state of the other one of said contacts.

Claim 12

A circuit as claimed in claim 8 wherein the resistance of said coil is chosen to have a value sufficient to develop a voltage drop such that said relay coil can only be deenergized in the event that both contacts are closed at the same time or that a signal lamp burns out.