Electronics > Projects, Designs, and Technical Stuff
Linix Nursing Bed Actuator
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Dumpsterholic:
Excellent!

I gather that building up an H-bridge from separate MOSFETs, IGFETs or other transistors is not worth the effort. I just spent a bit of time Googling various motor driver ICs and kept being directed to the ubiquitous L293D and L298N, which though dirt-cheap apparently aren't rated for supply voltages above 35V or so. And I found quite a few ready-made complete motor controller boards in $50-$100 range, which seems a little spendy for my budget, considering what I paid for the LA....

So I dug around at Digi-Key, Jameco, and Mouser and became thoroughly bewildered; I then visited company websites for Infineon, International Rectifier, ST Microelectronics and Texas Instruments and spiraled further down the rabbit hole. I now have a bunch of data sheets and sales brochures in .pdf form saved on my laptop, plus a greater awareness of the vastness of the industrial-control market. I learned new vocabulary terms such as "gate driver" and "quadruple half-H bridge", but still find myself at sea.

So, I'm hoping somebody can point me in the direction of an IC that I can base a motor-control circuit on. I realize that without a current rating, it won't be realistic to start the design process, but let's just guess that my motor draws 10A @ 110VDC and go from there. Though-hole components would be preferable, but from what I've seen the kinds of ICs I'm looking for may only be available in SOIC packages. That's OK. There are plenty of people soldering these things onto PCBs by hand. Way back in the '90s I worked for a company whose lead engineer showed me some circuits he was building using with these flea-sized ICs; he warned me that the DIP packages I was used to might someday become obsolete, and he was most prescient indeed. FWIW, I am proficient enough at soldering, metalworking and reading application notes schematic diagrams that I feel confident that my circuit will eventually work. And if it doesn't, oh well. I will take full responsibility for my failures, and share the credit for my successes with those of you who have chimed in on this forum so far.
Zero999:
Actually, at this sort of power level and voltage, it makes sense to use discrete MOSFETs and a separate driver IC, to translate the logic levels into the drive signals for the MOSFETs. One thing you need to beware of is many of these drivers use bootstrapping capacitors, to drive the high side, which means the output can't go high for too long, as the capacitor needs time to recharge. This limits the duty cycle to below 100%. The only way to get 100% duty is with an isolated DC:DC converter for the high side, which increases complexity.

https://www.semicon.sanken-ele.co.jp/sk_content/sma2404m_ds_en.pdf
https://www.intersil.com/content/dam/Intersil/documents/an90/an9010.pdf
http://www.st.com/content/ccc/resource/technical/document/application_note/09/e6/1b/f4/72/7a/43/81/CD00200596.pdf/files/CD00200596.pdf/jcr:content/translations/en.CD00200596.pdf
http://datasheet.octopart.com/MD7120K6-G-Supertex-datasheet-11966372.pdf
https://cdn.anaren.com/product-documents/MSK/DiscontinuedProducts/bridges-gate-drive/MSK4227_DataSheet(Rev_E).pdf
http://www.ti.com/lit/ds/symlink/ucc27714.pdf
https://www.infineon.com/dgdl/irs2110.pdf?fileId=5546d462533600a40153567660ff27b0
https://www.infineon.com/dgdl/an-978.pdf?fileId=5546d462533600a40153559f7cf21200
Dumpsterholic:
Wow,  I just glanced over those application notes and data sheets, and I feel like the snake who swallowed the rabbit! Operative word here: "steep learning curve". I probably will not get around to tinkering with the linear actuator for awhile, but it's good to have some idea what kind of control circuitry is out there. Thanks for sourcing these documents.

I should note that the "10A @ 110VDC" I came up with above is a wild guess. As it happens, in the place where I scored the LA I also grabbed a pair of motors made by Shanghai Jugong Industry Co, Ltd. which have about the same size and heft but which came equipped with pulleys for driving belts. Grabbing one at random, I read this from the label:

   6ZY10002 DC MOTOR
   100VDC P080904
   0.58A 31W 1500 r/min

I suspect the motor on the LA has similar specs, so maybe the monster bridge rectifier I bought off of eBay was overkill. No matter. At least it didn't burst into flames when the LA was under test! Living in a part of Florida where nursing homes are about as common as liquor stores, I imagine that I will be finding more of these motors and linear actuators.... And at the very least, I now know how to safely test them for functionality.
arw:
By coincidence I found one the same DTG 110-92..  I tested the motor at 24 volts DC thinking it would not be sufficient however it did move slowly taking about 50 mAmps. Even worked down to 10volts. Almost certainly 110volts nevertheless seems to work OK at lower voltages. I did not test under load though so it might stall at the lower voltages. Armature resistance 95 ohms, possibly what the -92 means. I did not try the control wires but reversing the voltage changes direction.
arw:
Stall current at 24 volts would be around 250 mA so about 6 watts power required, which is probably enough to drive light loads, given the high gearing . Stall current at 100 volts would be over 1 Amp so 100 watts and enough for some serious motive force. A reasonable compromise might be to drive at 50 volts so stall current about 500mA or 25 watts depending on the load required.
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