Electronics > Projects, Designs, and Technical Stuff
Mains switching research break out
temperance:
--- Quote from: oschonrock on August 02, 2020, 09:57:45 pm ---
I am trying to design a "breakout module" that does this "properly" and safely. It may/will ultimately need to come in a proper physical case, properly isolated, protected & appropriately fused etc so that people can do these things without killing themselves or the equipment.
--- End quote ---
-Perhaps the best place to start:
-EN/IEC 60950-1
-EN/IEC 61000-4-5
-EN/IEC 61000-4-4
For something you want to sell you don't want to settle for anything less.
Solutions for what you try achieve do exist and are called solid state relays. You will find some with MOSFET's made by Panasonic, IXYS, Omron,... But those are only used in well defined environments.
To give you an idea about what you might encounter in a not so well defines environment: a simple refrigerator can create an over voltage with enough energy under the right conditions to kill any MOSFET if it's not properly protected.
oschonrock:
--- Quote from: temperance on August 03, 2020, 01:29:05 am ---
--- Quote from: oschonrock on August 02, 2020, 09:57:45 pm ---
I am trying to design a "breakout module" that does this "properly" and safely. It may/will ultimately need to come in a proper physical case, properly isolated, protected & appropriately fused etc so that people can do these things without killing themselves or the equipment.
--- End quote ---
-Perhaps the best place to start:
-EN/IEC 60950-1
-EN/IEC 61000-4-5
-EN/IEC 61000-4-4
For something you want to sell you don't want to settle for anything less.
Solutions for what you try achieve do exist and are called solid state relays. You will find some with MOSFET's made by Panasonic, IXYS, Omron,... But those are only used in well defined environments.
To give you an idea about what you might encounter in a not so well defines environment: a simple refrigerator can create an over voltage with enough energy under the right conditions to kill any MOSFET if it's not properly protected.
--- End quote ---
Thanks. I am well familiar with SSRs. I used to work for Omron a long time ago ;-)
They can't turn off half half-way through the cycle to my understanding, so they cannot "duty cycle/ dim etc" , so this is a totally different application.
oschonrock:
--- Quote from: Monkeh on August 03, 2020, 01:13:59 am ---
--- Quote from: oschonrock on August 03, 2020, 01:08:41 am ---How mechanical relays are a solution I don't get. We want "half on" as well as off and on...and all points in between.
--- End quote ---
Up to this point you've never suggested you wanted a dimmer instead of a switch.
--- End quote ---
I am sorry. Not explicit enough. I thought the "zero cross trigger" would be a give away. If I just wanted to turn stuff on/off I would use an SSR.
Ian.M:
Errrr Guys . . . . . . .
Meanwell IRM-02-12S is a 12V power supply, not a bridge rectifier.
Now we've cleared up that confusion, there are three things I don't like about it.
1. No suppression of back-EMF spikes from inductive loads. Unless you use avalanche rated MOSFETs you *NEED* a beefy bidirectional TVS diode across the pair of MOSFETs. It may also benefit from a RC snubber to control dV/dt below the TVS breakover voltage.
2. Heavy load on the opto + limited CTRR at elevated temperature makes it too easy to get insufficient gate drive if your drive to the opto LED is weak. Unless you can guarantee sharp 10mA drive pulses, it would be a good idea to run the opto with a higher load resistor and add a Schmidt trigger input gate driver between it and the MOSFETs.
3. That simple ZC opto circuit is going to give a rather mushy ZC pulse. You may wish to consider using one of the many snap-action active ZC detector circuits, possibly separate ones for rising and falling zero crossing Their optoisolator phototransistors can always be paralleled if you don't want to discriminate between the crossing directions.
Adding load current monitoring could also be rather useful. It also opens up the possibility of protecting the MOSFETs by detecting over-current and rapidly driving the gates off, then locking out the drive till the next ZC pulse. Some additional inductance in series with the load may be required to give the over-current trip time to react.
oschonrock:
--- Quote from: BrianHG on August 03, 2020, 12:34:05 am ---photovoltaic optocouplers, each one
--- End quote ---
Actually these devices are new to me. You mean this yes?
https://www.vishay.com/docs/83469/vom1271.pdf
Not cheap, and not sooo available (yet?), but they look fab! I can ditch the whole annoying isolated 12V SMPS! Not sure of the limitations yet, ie I suspect that they top out at a certain size MOSFET? Too much energy required to switch efficiently - gate capacitance?
Thank you. That might really move it forward.
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