Electronics > Projects, Designs, and Technical Stuff
Mains switching research break out
oschonrock:
--- Quote from: BrianHG on August 03, 2020, 05:55:36 pm ---That virshay driver can do 100KHz if you look at the specs, but my head-room practice made me quote you the 25KHz figure. If you ever made anything down at 15KHz, I would never buy it because my ears would go nuts from coil-whine. Many old TVs drove me nuts & I already had a scan-doubled 31Khz large screen TV back in the early 90's when they were in they were over 15K$ (ouch to my pocketbook, but I had peace and silence). Though I can no longer hear 25KHz, I remember as a kid I could hear all the ultrasonic alarms in the shopping malls and it drove me nuts as my parents couldn't hear a thing. I have no interest in affecting children's hearing, so 25Khz is the absolute bottom I would allow in any of my designs.
--- End quote ---
I was starting with what is necessary to drive the load smoothly and without too many harmonics that don't get filtered by the inductors. So the industrial approach (which is my background). Small VSDs are generally 15kHz tops, that's why I picked that figure and since the amplitude is already modulated we wouldn't need even that. That's where my estimates came from. Humans didn't come into my thinking except for an afterthought. In a factory a bit of extra VSD whine just adds to ambiance!
Wow, you have some super good ears there. BUT, since you've been so super helpful, I promise if this ever turns into a product, it shall have nothing less than 25kHz switching frequency for the Mode3 PWM.
8)
BrianHG:
LOL, Future Electronics has the SMD version VOD3120AB available at 0.76$ each, or 0.58£.
hli:
If one needs a EU-style plug, Olimex has you covered: https://www.olimex.com/Products/Duino/Shields/PWR-SWITCH/
oschonrock:
--- Quote from: hli on August 04, 2020, 01:49:57 pm ---If one needs a EU-style plug, Olimex has you covered: https://www.olimex.com/Products/Duino/Shields/PWR-SWITCH/
--- End quote ---
That's a cool thing, and very well priced. Not much detail about "what mode of switching it supports" (see more verbose explanation of the "3 modes" in OP at top).
If I were to guess, it's probably mode1, ie that thing is an SSR in a cool box? And it can switch on zero cross only?
but yeah, I was mentally playing with how to make it physically convenient and safe. Various boxes with plugs did occur to me.
So thank you.
oschonrock:
--- Quote from: BrianHG on August 03, 2020, 06:14:42 pm ---LOL, Future Electronics has the SMD version VOD3120AB available at 0.76$ each, or 0.58£.
--- End quote ---
The prototype is working. I made a 2 channel version and that turned out to be a good thing...see below. Here is a pic...
I have connected it up to a pic18 and have it doing basic switching, leading edge and trailing edge dimming (ie modes 1 + 2, explained in OP above). Very good and very smooth. Currently working on mode3.
I had one major hickup in that the VOD3120 has a 12V UVLO and I used a floating 12V SMPS (because the 15V was out of stock :palm:). That didn't work, so I am currently letting my bench supply float up and being very careful. This is about to change anyway, see below..
Few improvements:
1. Changing it to switch the phase and not the neutral. This was a silly mistake and makes no difference if we are using fully isolated supply and driver anyway. ---
2. I realised that for switching significantly inductive loads (which was a major objective, see top) I need a free wheeling solution, and it's non trivial. Unlike in an H-Bridge where the body diodes naturally help you to create freewheeling paths, this back to back MOSFET topology doesn't help at all - it just blocks it all, so major spikes would ensue. I have only switched resistive loads so far for this reason, because I suspect that I would just blow up the MOSFETs or stress out the MOVs. Proposed design for solution below.
So for inductive load freewheeling, I have decided to try a second back-to-back MOSFET pair (directly across the load) and trigger it (carefully!) when the main pair is off. revised schematic is below.
Because I have 2 MOSFET pairs in my prototype I can just rewire this to the above, and use 2x mini 5V->15V isolated DC-DC converters https://uk.farnell.com/recom-power/roe-0515s/dc-dc-converter-15v-0-066a/dp/2846315 to generate the now 2 floating supplies we need. These, together, are actually cheaper and significantly smaller than the single 1W PCB mount SMPS in the picture below.
Looking around for cases and started ordering some samples. I am going for "lab use" here. So a robust, standards based and serviceable enclosure / termination. Suggestions very welcome. I am currently leaning towards one of these cases (my estimated power dissipation is ~10W at full 10A / 240 VAC load):
https://uk.farnell.com/hammond/1455nhd1201bk/enclosure-wall-mount-aluminium/dp/2904319
And these male and female IEC connectors for supply and load:
https://uk.farnell.com/bulgin/px0580-pc/iec-c14-inlet-pcb-10a-250v-flange/dp/313853
https://uk.farnell.com/bulgin/px0675-pc/outlet-iec-pcb/dp/151748
I thought these IEC connectors are tough enough and standard enough to work anywhere and on the load side people can cheaply buy a converter for their country: https://www.amazon.co.uk/Power-cable-IEC-plug-socket/dp/B005FWRHNQ , if they want a regular outlet.
The idea is to bolt the 4 MOSFETS to the floor of the case using the provided half-nut slots. Power inlet & outlet in the end plates and indicators,controls and low voltage interfaces (possibly canbus or similar), in the top panel. Does anyone know a safe way to provide HV probe points from outside the case, in case the user wants to hook up their oscilloscope..?
Any suggestions for better enclosures/solutions very welcome, this is the part I struggled with the most. There is work to do on EMC filtering too.
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