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Old 14th April 2013, 04:50 AM   #81
nattawa is offline nattawa  Canada
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A PNP emitter follower probably works better than a resistor would in quickly discharging the gates of the MOSFETs. It might be non-desirable that R7 can bleed off the precious pv voltage. I have a MOFET relay built into my latest amp project. I got the MOSFET and the pv driver from avnet. I bench-tested the relay and it worked very well. The circuit is posted below if it helps. Q36 is the emitter follower:
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Old 14th April 2013, 05:16 AM   #82
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Hi,
Just in case you want to try it attached it is schematic of my solid state relay using an avago Dual Channel Photovoltaic MOSFET Driver. I have been using it in my LM3886 amplifier for about one year with no problems. You can see the scope open/close time signal in my thread Protecting the speaker output using a microprocessor
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Old 14th April 2013, 06:14 AM   #83
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Substituting a 2N5401/1N4148 per nattawa's diagram gave a longer turn-off time than the resistor in LTSpice. I got 65uS.

Using tauro0221's circuit, which looks a lot like one on Rod Elliott's site, required that I add another HCNR200 to the stack before it started to work. But once it did work in LTSpice, I got about a 5uS turn-off time. Not bad.

I'm not sure I understand these results. Maybe it has something to do with base/gate capacitance of the added PNP/NJFET.
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Old 14th April 2013, 06:28 AM   #84
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The relatively new Vishay VOM1271 opto-photovoltaic device seems to be the best device to use for driving a pair of mosfet relay switches. It includes a fast turn off circuit. The opto LED needs to be driven between 10mA and 20mA for best results.

See attachment for the mosfet relay concept, and the vom1271 datasheet at http://www.vishay.com/docs/83469/vom1271t.pdf

Note that I haven't tried this circuit yet, though I have bought the bits.

Paul Bysouth
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Old 14th April 2013, 07:05 AM   #85
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Paul, those switching times shown in the VOM1271 datasheet look good. But do I understand the waveform for the switching time test correctly? It appears that the output is inverted relative to the input. Is it an inverting device?

Vishay does not provide a Spice model that I can find. Too bad.
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Old 14th April 2013, 09:35 AM   #86
Bonsai is offline Bonsai  Taiwan
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That Vishay driver looks very good. Using a standard photo coupler, you can get turn off times down to about 100 to 200 us (2 in parallel). The integrated turn off circuit is neat, and means you can create a really fast solid state loudspeaker relay.
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Old 15th April 2013, 12:48 PM   #87
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I am Quite happy with the "old fashioned" PVI1050A .
Working great as a Songle 30A relay drop-in I made a while ago for my 5 channel HT amp with 5 LJM's L15D's .
very low RDsOn fast switch on an off , can't find scope pictures at the moment , but will keep looking .

Cheers ,

Rens

I know , some pins of the PV are not seated , but my rottie pinched my glasses from the bench before I took the picture of the PCB
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File Type: jpg SongleSSR.jpg (224.2 KB, 222 views)
File Type: jpg Songledropin1.jpg (180.0 KB, 367 views)
File Type: jpg Songledropin2.jpg (112.4 KB, 210 views)
File Type: png songle.png (9.2 KB, 79 views)
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Last edited by doctordata; 15th April 2013 at 01:06 PM. Reason: Pins
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Old 15th April 2013, 12:57 PM   #88
Mooly is online now Mooly  United Kingdom
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Very neat made to measure job
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Old 15th April 2013, 01:10 PM   #89
AndrewT is online now AndrewT  Scotland
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post87,
no resistor from gate to source?
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Old 15th April 2013, 02:17 PM   #90
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Quote:
Originally Posted by AndrewT View Post
post87,
no resistor from gate to source?
My compliments on reading the schematics AndrewT

Cheers ,

Rens
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