Latching solid state relay
A latching relay coupled SSR circuit provides a simple means of achieving a true latching solid-state relay in both two or three input terminal configurations, with two output terminals switched by standard solid-state relay devices. The circuit does not require any additional power sources, and has true indefinite memory retention of the last state the output was in when all power is disconnected. The latching relay coupled SSR circuit can be configured for a “zero-cross” mode of turn-on style to synchronize with the AC waveform powering the load that cannot be done with electromechanical latching relays, in addition to the purely “random” style of load switching. A latching relay is utilized. The isolation of the input side to the output side is provided by the physical separation of the coil and switch, utilizing the magnetic field of the coil to actuate the switch.
1 . A method for circuit switching utilizing a solid state relay, the method comprising the steps of:
(a) providing an input circuit;
(b) isolating a solid state relay output circuit from said input circuit;
(c) coupling said input circuit to said solid state relay output circuit with a latching relay; and
(d) sending an input signal momentarily through said input circuit to switch said solid state relay output circuit.
2 . The method according to claim 1 wherein said latching relay is a magnetically operated latching relay.
3 . The method according to claim 1 wherein step (d) further comprises the steps of:
sending said input signal momentarily through a coil of said latching relay connected to said input circuit;
generating a magnetic field in said coil due to said input signal; and
actuating a switch of said latching relay in proximity to said coil with said magnetic field, wherein said switch is connected to said solid state relay output circuit.
4 . The method according to claim 3 wherein step (a) further comprises the steps of:
attaching a first input terminal to said coil; and
attaching a second input terminal to said coil, wherein said second input terminal serves as a common.
5 . The method according to claim 4 wherein step (d) further comprises the steps of:
sending said input signal with a first polarity momentarily through said first input terminal to open said switch; and
sending again said input signal with a second polarity momentarily through said first input terminal to close said switch.
6 . The method according to claim 4 wherein step (d) further comprises the steps of:
sending said input signal with a first polarity momentarily through said first input terminal to close said switch; and
sending again said input signal with a second polarity momentarily through said first input terminal to open said switch.
7 . The method according to claim 4 wherein step (d) further comprises the steps of:
sending said input signal with a first polarity momentarily through said first input terminal to open said switch; and
sending again said input signal with said first polarity momentarily through said first input terminal to close said switch.
8 . The method according to claim 4 wherein step (d) further comprises the steps of:
sending said input signal with a first polarity momentarily through said first input terminal to close said switch; and
sending again said input signal with said first polarity momentarily through said first input terminal to open said switch.
9 . The method according to claim 3 wherein step (a) further comprises the steps of:
attaching a first input terminal to said coil;
attaching a second input terminal to said coil; and
attaching a third input terminal to said coil.
10 . The method according to claim 9 wherein step (d) further comprises the steps of:
sending a first input signal momentarily through said first input terminal to open said switch; and
sending a second input signal momentarily through said second input terminal to close said switch;
wherein said third input terminal serves as a common to said first and second input terminals for said first and second input signals.
11 . The method according to claim 9 wherein step (d) further comprises the steps of:
sending a first input signal momentarily through said first input terminal to close said switch; and
sending a second input signal momentarily through said second input terminal to open said switch;
wherein said third input terminal serves as a common to said first and second input terminals for said first and second input signals.
12 . The method according to claim 1 wherein said solid state relay output circuit is a triac driver circuit.
13 . The method according to claim 1 wherein said solid state relay output circuit is a direct current solid state relay circuit.
14 . The method according to claim 1 wherein step (b) further comprises the steps of:
attaching a first output connection to said solid state relay output circuit;
attaching a second output connection to said solid state relay output circuit; and
connecting a load between said first and second output connections.
15 . The method according to claim 14 wherein a current rating for said load ranges between less than one amperes through several hundred amperes.
16 . The method according to claim 1 further comprising the step of:
configuring said solid state relay output circuit for a zero cross load switching style.
17 . The method according to claim 1 further comprising the step of:
configuring said solid state relay output circuit for a random load switching style.
18 . The method according to claim 1 further comprising the step of:
establishing a minimum possible potential difference between said input circuit and said solid state relay output circuit according to an isolation specification of said latching relay.
19 . The method according to claim 1 further comprising the step of:
applying said input signal for a minimum amount of time according to a specification of said latching relay in order to switch said solid state relay circuit.
20 . A latching solid state relay circuit comprising:
an input circuit;
a solid state relay output circuit isolated from said input circuit; and
a latching relay coupling said input circuit to said solid state relay output circuit;
wherein an input signal sent momentarily through said input circuit switches said solid state relay output circuit.
21 . The latching solid state relay circuit according to claim 20 wherein said latching relay is a magnetically operated latching relay.
22 . The latching solid state relay circuit according to claim 20 wherein said latching relay further comprises:
a coil connected to said input circuit; and
a switch connected to said solid state relay output circuit;
wherein said input signal sent momentarily through said coil generates a magnetic field which actuates said switch.
23 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a first input terminal connected to said coil; and
a second input terminal connected to said coil, wherein said second input terminal serves as a common;
wherein momentarily applying said input signal having a first polarity to said first input terminal opens said switch, and momentarily applying again said input signal having a second polarity to said first input terminal closes said switch.
24 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a first input terminal connected to said coil; and
a second input terminal connected to said coil, wherein said second input terminal serves as a common;
wherein momentarily applying said input signal having a first polarity to said first input terminal closes said switch, and momentarily applying again said input signal having a second polarity to said first input terminal opens said switch.
25 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a first input terminal connected to said coil; and
a second input terminal connected to said coil, wherein said second input terminal serves as a common;
wherein momentarily applying said input signal having a first polarity to said first input terminal opens said switch, and momentarily applying again said input signal having said first polarity to said first input terminal closes said switch.
26 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a first input terminal connected to said coil; and
a second input terminal connected to said coil, wherein said second input terminal serves as a common;
wherein momentarily applying said input signal having a first polarity to said first input terminal closes said switch, and momentarily applying again said input signal having said first polarity to said first input terminal opens said switch.
27 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a three terminal input connected to said coil;
wherein a first input signal that is momentarily applied to a first terminal of said three terminal input will open said switch, and a second input signal that is momentarily applied to a second terminal of said three terminal input will close said switch, and further wherein a third terminal of said three terminal input serves as a common to said first and second terminals for said first and second input signals.
28 . The latching solid state relay circuit according to claim 22 wherein said input circuit further comprises:
a three terminal input connected to said coil;
wherein a first input signal that is momentarily applied to a first terminal of said three terminal input will close said switch, and a second input signal that is momentarily applied to a second terminal of said three terminal input will open said switch, and further wherein a third terminal of said three terminal input serves as a common to said first and second terminals for said first and second input signals.
29 . The latching solid state relay circuit according to claim 20 wherein said solid state relay output circuit is a triac driver circuit.
30 . The latching solid state relay circuit according to claim 20 wherein said solid state relay output circuit is a direct current solid state relay circuit.
31 . The latching solid state relay circuit according to claim 20 wherein said solid state relay output circuit further comprises:
a first output connection;
a second output connection; and
a load connected between said first and second output connections.
32 . The latching solid state relay circuit according to claim 31 wherein a current rating for said load ranges between less than one ampere through several hundred amperes.
33 . The latching solid state relay circuit according to claim 20 further comprising:
a zero cross load switching style.
34 . The latching solid state relay circuit according to claim 20 further comprising:
a random load switching style.
35 . The latching solid state relay circuit according to claim 20 wherein a minimum possible potential difference between said input circuit and said solid state relay output circuit is established according to an isolation specification of said latching relay.
36 . The latching solid state relay circuit according to claim 20 wherein said input signal is present for a minimum amount of time according to a specification of said latching relay in order to switch said solid state relay circuit.