Relay contact protective circuit
AssigneeElectronic Specialty Corporation
InventorChester C. Hongel
Life of this patent
Estimating the term…
Abstract
A contact protective circuit for a relay detects a transient in the relay operating coil and turns on a low resistance power MOSFET in shunt relation with the contacts before the contacts close or open whereby arcing or deposition of metal on the contracts is avoided. Timing circuitry is provided for controlling the MOSFET to conduct large direct currents for short periods of time. In one embodiment, a ramp up circuit responds to a voltage level in a control signal to drive the operating coil and power a DC-to -DC converter and a timing circuit. The invention provides for hot side switching as well as cold side switching of a load.
Claims29
A contact protective circuit for a relay including a pair of contacts and an operating coil for changing the circuit-completing status of said contacts between an open circuit and a closed circuit condition, comprising:
- means for detecting a transient in said operating coil pursuant to a change in the energization of said operating coil prior to the resulting change in circuit-completing status of said contacts,
- a field effect transistor having a drain terminal, a source terminal and a gate terminal,
- means connecting said drain terminal and said source terminal respectively to contacts of said pair, and
- timing means responsive to said detecting means and coupled to said gate terminal of said field effect transistor for gating said field effect transistor to an on condition, shunting current around said contacts, starting at least as soon as the beginning of said change in circuit-completing status of said contacts.
A contact protective circuit comprising:
- a pair of contacts,
- means for detecting an expected change in the circuit-completing status of said contacts,
- a metal oxide semiconductor field effect transistor having a drain terminal, a source terminal and a gate terminal, said field effect transistor having an Rds On resistance of less than 0.5 volts divided by the DC current expected to flow between said contacts in the closed condition,
- means connecting said drain terminal and said source terminal respectively to the contacts of said pair, and
- timing means responsive to said detecting means and coupled to said gate terminal of said field effect transistor for gating said field effect transistor to an on condition during the entire period during which said change in the circuit-completing status of said contacts takes place such that substantially no arcing or metal deposition occurs.
A relay responsive to a control signal, the relay comprising:
- a pair of contacts;
- a field effect transistor having a drain terminal, a source terminal, and a gate terminal, said field effect transistor having an Rds On resistance of less than 0.5 volts divided by the DC current expected to flow between said contacts in closed condition;
- means connecting said drain terminal and said source terminal respectively to contacts of said pair;
- means for generating an activation signal in response to a given threshold level in the control signal, said last mentioned means having a hysteresis characteristic such that said activation signal is generated when said control signal increases to said threshold level and continues to be generated until said control signal drops to a second level lower than said threshold level;
- an operating coil responsive to the activation signal for changing the circuit completing status of said contacts between an open circuit condition and a closed circuit condition;
- and
- means responsive to said activation signal and coupled to the gate terminal of said field effect transistor for gating said field effect transistor to an on condition, shunting current around said contacts, starting at least as soon as the beginning of a change in the circuit completing status of said contacts.
A relay responsive to a control signal, said relay comprising:
- a pair of contacts;
- a field effect transistor having a drain terminal, a source terminal, and a gate terminal;
- means connecting said drain terminal and said source terminal respectively to contacts of said pair;
- means for generating an activation signal at a time when the control signal exceeds a given threshold;
- an operating coil responsive to the activation signal for changing the circuit completing status of said contacts between an open circuit condition and a closed circuit condition;
- a DC to DC converter powered by the control signal and supplying a source of DC power;
- and
- timing means powered by the source of DC power and triggerably responsive to the output of the DC power source, said timing means being coupled to the gate terminal of said field effect transistor for gating said field effect transistor to an on condition and shunting current around said contacts, starting at least as soon as the beginning of a change in the circuit completing status of said contacts.
A relay responsive to a control signal, said relay comprising:
- a first contact;
- a second contact;
- means responsive to said control signal for opening and closing said first and second contacts;
- means for shunting current around said contacts at times when said contacts are opening and closing, said shunting means requiring a source of power and having a power lead suitable for coupling to a power source;
- and
- means coupling said control signal and said power lead for deriving a power source for said shunting means from said control signal.
A relay responsive to a control signal, said relay comprising:
- a first contact;
- a second contact;
- an operating coil having a first terminal and a second terminal, said coil being responsive to said control signal for opening and closing said contacts;
- means responsive to a trigger input for shunting current around said contacts;
- a first diode having a first terminal and a second terminal, the first terminal of said first diode being connected to the first terminal of said coil;
- a second diode having a first terminal and a second terminal, the first terminal of said diode being connected to the second terminal of said coil, the second terminal of said second diode being connected to the second terminal of said first diode to form a trigger voltage terminal;
- and
- means coupling the trigger voltage terminal and the trigger input of said shunting means.
A contact protective circuit for a relay responsive to a control signal and including a pair of contacts and an operating coil for changing the circuit-completing status of the contacts between an open circuit and a closed circuit condition, the contact protective circuit comprising:
- means coupling the contacts and responsive to a shunt signal for shunting current around the contacts;
- and
- means for driving the operating coil and generating said shunt signal in response to said control signal reaching a given threshold level;
- said driving means comprising a Schmidt trigger for receiving the control signal and having an output responsive to a given voltage level of the control signal, the output being suitable for driving said operating coil;
- a DC-to-DC converter powered by the control signal and providing an isolated DC output when powered;
- and timing means responsive to the isolated DC output and coupled to said shunting means for bringing about the shunting of current around said contacts in response to the inception and termination of the isolated DC output.
Dependencies are inferred from the claim text.