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Normally Closed Optoisolators
normally open or normally closed OptoMosSCR which can conduct 230V AC at Zero gate voltageSelf Latching RelayEfficient toggle switchConnecting a Camera Hot Shoe to a homemade strobechangeover normally closed to normally openhow to convert a PWM AC dimmer circuit from normally-closed to a normally-open one?Integrate residential hardwired alarm zone with modern wireless sensorReverse function optocoupler in series with physical NC switch?How to wire a normally open switch to a recoil start engine with no external battery?
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$begingroup$
I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for the failure state but also so that the opto's led doesn't have to be activated for 99% of the time.
How can this be done on the transistor side?
Failure states aside, should I be concerned with having the opto activated indefinitely (in a normally open circuit)?
relay opto-isolator normally-open
asked 8 hours ago
SpammySpammy
183 bronze badges
$endgroup$
add a comment |
$begingroup$
I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for the failure state but also so that the opto's led doesn't have to be activated for 99% of the time.
How can this be done on the transistor side?
Failure states aside, should I be concerned with having the opto activated indefinitely (in a normally open circuit)?
relay opto-isolator normally-open
asked 8 hours ago
SpammySpammy
183 bronze badges
$endgroup$
1
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago
add a comment |
$begingroup$
I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for the failure state but also so that the opto's led doesn't have to be activated for 99% of the time.
How can this be done on the transistor side?
Failure states aside, should I be concerned with having the opto activated indefinitely (in a normally open circuit)?
relay opto-isolator normally-open
asked 8 hours ago
SpammySpammy
183 bronze badges
$endgroup$
I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for the failure state but also so that the opto's led doesn't have to be activated for 99% of the time.
How can this be done on the transistor side?
Failure states aside, should I be concerned with having the opto activated indefinitely (in a normally open circuit)?
relay opto-isolator normally-open
relay opto-isolator normally-open
asked 8 hours ago
SpammySpammy
183 bronze badges
asked 8 hours ago
SpammySpammy
183 bronze badges
asked 8 hours ago
SpammySpammy
183 bronze badges
asked 8 hours ago
SpammySpammy
183 bronze badges
asked 8 hours ago
SpammySpammy
183 bronze badges
183 bronze badges
1
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago
add a comment |
1
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago
1
1
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.
However, note that if the opto fails short then that will open the transistor.
The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.
simulate this circuit – Schematic created using CircuitLab
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
$endgroup$
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
add a comment |
$begingroup$
Yes, there are DIP opto-MOS relays with depletion-mode MOSFETs on the output.
Or you can use a photovoltaic gate-drive optocoupler with a discrete depletion-mode transistor. Just remember to connect it to drive the gate negative.
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
$endgroup$
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.
However, note that if the opto fails short then that will open the transistor.
The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.
simulate this circuit – Schematic created using CircuitLab
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
$endgroup$
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
add a comment |
$begingroup$
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.
However, note that if the opto fails short then that will open the transistor.
The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.
simulate this circuit – Schematic created using CircuitLab
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
$endgroup$
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
add a comment |
$begingroup$
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.
However, note that if the opto fails short then that will open the transistor.
The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.
simulate this circuit – Schematic created using CircuitLab
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
$endgroup$
Instead of switching the actual load with the opto, use the opto to drive a transistor which switches the actual load.
However, note that if the opto fails short then that will open the transistor.
The risk could be potentially reduced by having two optos wired series on the output and parallel on the input so that both must close (or fail) for the transistor open.
simulate this circuit – Schematic created using CircuitLab
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
edited 7 hours ago
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
answered 8 hours ago
DKNguyenDKNguyen
5,1801 gold badge5 silver badges24 bronze badges
5,1801 gold badge5 silver badges24 bronze badges
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
add a comment |
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
Any thoughts on the second part of my question? Should I even bother - is it considered normal usage to just keep an opto activated for extended periods of time? I've ordered some 2N3904s and 2N3906s to add to my parts box anyway.
$endgroup$
– Spammy
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
$begingroup$
LEDs wear out, but then again, so do transistors while conducting so it's six of one or half a dozen of the other. The LED would also consumes mA though that might not matter depending on how much your load current is conducting when normally closed. I guess it matters how fail-safe your thing has to be.
$endgroup$
– DKNguyen
6 hours ago
add a comment |
$begingroup$
Yes, there are DIP opto-MOS relays with depletion-mode MOSFETs on the output.
Or you can use a photovoltaic gate-drive optocoupler with a discrete depletion-mode transistor. Just remember to connect it to drive the gate negative.
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
$endgroup$
add a comment |
$begingroup$
Yes, there are DIP opto-MOS relays with depletion-mode MOSFETs on the output.
Or you can use a photovoltaic gate-drive optocoupler with a discrete depletion-mode transistor. Just remember to connect it to drive the gate negative.
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
$endgroup$
add a comment |
$begingroup$
Yes, there are DIP opto-MOS relays with depletion-mode MOSFETs on the output.
Or you can use a photovoltaic gate-drive optocoupler with a discrete depletion-mode transistor. Just remember to connect it to drive the gate negative.
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
$endgroup$
Yes, there are DIP opto-MOS relays with depletion-mode MOSFETs on the output.
Or you can use a photovoltaic gate-drive optocoupler with a discrete depletion-mode transistor. Just remember to connect it to drive the gate negative.
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
answered 4 hours ago
Spehro PefhanySpehro Pefhany
220k5 gold badges175 silver badges457 bronze badges
220k5 gold badges175 silver badges457 bronze badges
add a comment |
add a comment |
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1
$begingroup$
Use an SSR instead, you can get isolated SSR's that are NO or NC
$endgroup$
– Voltage Spike
8 hours ago
$begingroup$
Can you recommend a part number? The circuit that needs to be NC is 12vdc
$endgroup$
– Spammy
7 hours ago
$begingroup$
Try CPC1117N. These normally closed relays are often called Form-B.
$endgroup$
– Steve G
6 hours ago