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Low-leakage triac or solid-state relay
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CodyDowling:
Absolutely- chasing down specs in data sheets is no biggie when you have 3 or 4 of them- but the staggering amount of components that fit the application every other way *but* a few super important ones makes rifling through data sheets a right "pain in the cunning linguist" as AvE says.
 
wraper:
For example this one has 3pF maximum. https://eu.mouser.com/ProductDetail/IXYS-Integrated-Circuits/CPC1966YX6?qs=sGAEpiMZZMsUriz2CNI3E27VrHTFQPrBI1CmPCUVKJJNRJywL0SmHw%3d%3d
CodyDowling:

--- Quote from: Hero999 on December 09, 2018, 09:46:54 am ---
They're just opto-couplers with an IR LED on the input and solar cell on the output. The peak forward current rating of the emitter is 1A, but the solar cell current is tiny.

The opto-coupler can't control the load circuit directly. The idea is to use it to drive a MOSFET. For an AC circuit, two MOSFETs are required.
--- End quote ---

 :palm: Yes, certainly- I missed that difference. I guess that a MOSFET with the set of parameters I'm interested in should be easier to identify since they tend to have Ciss and Coss values more readily available.


--- Quote ---You could use a TRIAC based opto-coupler. The capacitance isn't specified but it will be tiny, far below your requirements.
http://www.farnell.com/datasheets/97984.pdf

--- End quote ---

Great- I'll take a look. I probably should have attached this earlier in the thread, but here's a simplified block diagram what I'm aiming to do in the attachment.

As you can see, I have a ground referenced load driven by a  sort of push-pull / class-A output stage. The emitter resistors are large enough to handle the shunts to ground that will result from activating the triac (or mosfets). This will be only a momentary operating condition that occurs as a result of a fault condition. Soon after the shunt is applied the supplies will be turned off. Likewise when the supplies are turned back on, the shunt will release once the supplies and signal path are stable.
CodyDowling:

--- Quote from: wraper on December 13, 2018, 01:44:11 am ---SSR has triac optocoupler between input/output if it's AC type. Capacitance depends on that optocoupler and PCB/package. I just grabbed some random optocoupler and it has 3pF between input/output. I guess SSR in SIP package can do better.

--- End quote ---

Hi Wraper, thanks for the info. The 3pF sounds very reasonable- you mentioned that was from the triac's input to it's output, correct? I think in order to get the other leakage paths (input to ground, for example) I'll either have to get lucky with a data sheet or get some in and measure. As shown in the diagram I attached to Hero's response above, I would like to present as high of an impedance as possible- from say, 10Hz to 100kHz, to the node between the two 14 \$\Omega\$ resistors, so understanding the leakage paths better will really help I think.
CodyDowling:

--- Quote from: perieanuo on December 09, 2018, 12:39:03 pm ---Hi,
Do you mentioned frequency involved?
Regards,pierre
...


--- End quote ---

I didn't but, ideally, I'd like to be able to get very high impedance up to 100kHz. The RF components seem like they shouldn't start really leaking until much higher, so I thought that might be a good jumping off point.
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