| Electronics > Projects, Designs, and Technical Stuff |
| High voltage safety and design considerations |
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| magic:
--- Quote from: OM222O on June 28, 2019, 08:55:15 pm ---We finally settled on 3 7s and one 4s LiPo packs for a voltage range of 105-80V. --- End quote --- If such voltage is acceptable then I have seen ready to go, 12~30V in, up to 90V out, step-up converters on auction sites. Not sure if inverting ones are available, though. --- Quote from: OM222O on June 28, 2019, 08:55:15 pm ---The problem with the birdge approach is the high part numbers, especially needing 2 op amps. --- End quote --- Yeah, that circuit as drawn was quite bad cost-wise. It could be made much more elegantly with one differential output opamp (like OPA1632), but I doubt such parts exist for 100V operation. I wonder how difficult would those things be to build from discretes, probably not worth it as a first analog project. So perhaps PWM'd H-bridge as others suggest? People surely use them to drive DC motors at variable speed. Also, power efficiency of any linear solution will be quite crap. |
| max_torque:
How quickly do you need to be able to modulate the current through the voice coil? Given it's large inductance, the overall control bandwidth is going to be limited by that value and the supply voltage. Why not actually use a small OTS audio amplifier? Shouldn't be hard to find one with rails at around 100Vdc, and they are generally pretty robust and reliable. Easy to drive too, with a typical +-1V input with relatively high impedance? |
| OM222O:
--- Quote from: Zero999 on June 28, 2019, 10:35:33 pm ---Then don't use the ADHV. Use ordinary, cheap op-amps, run off <30V and some discrete devices to amplify the output voltage. Also note that it's very hard to protect semiconductors with fuses, normally the semiconductor blows first. Check that the fuse is rated for use with DC and that it has sufficient breaking capacity. --- End quote --- I had a look at voltage boost circuits for op amps, to be honest they are way above my level of understanding and each manufacturer recommends a different circuit (I had a look at TI, AD and ST micro app notes) so the ADHV with dual supplies is the simplest choice here. I will use HRC fuses which should be able to deal with this without any problems. --- Quote from: Someone on June 29, 2019, 12:59:32 am ---Until you get a short on their unfused side and then have 1kW or more fault to deal with. Batteries are much less safe than a current limited power supply here, you haven't discussed isolating the control signals or the actuator so the 100V supply will not be floating. You're in the range of operation where a H-bridge will likely work (I've never seen H-bridge used to describe a bridged linear amplifier). No linear mode devices, simple hard switching and a control loop. --- End quote --- batteries will always be floating with respect to ground (actual ground, not batteries mid point) :-// so if someone accidentally touches the robot during operation, it shouldn't be a problem. I was actually considering a current limiting circuit for the batteries, but couldn't come up with a decent idea. I thought about using a difference amplifier and some delay to open and close a mosfet. this way the circuit trips for a set amount of time and then tries again, but the robot would fall if the delay is too long which is dangerous, and it would be ineffective if the delay is too short. please give more feedback if you know about a suitable solution for current limiting rather than tripping. --- Quote from: max_torque on June 29, 2019, 09:48:10 am ---How quickly do you need to be able to modulate the current through the voice coil? Given it's large inductance, the overall control bandwidth is going to be limited by that value and the supply voltage. Why not actually use a small OTS audio amplifier? Shouldn't be hard to find one with rails at around 100Vdc, and they are generally pretty robust and reliable. Easy to drive too, with a typical +-1V input with relatively high impedance? --- End quote --- do you have any recommendations for a small one which also ends up being cheaper than the DIY approach? the full range response should be about 1 or 2ms (excluding oscillations). as I mentioned before, we have to drive 12 actuators. I think off the shelf amps would be way too expensive to use. |
| max_torque:
Any audio amp is going to manage 500Hz! (your 2m/s requirement) and given the fact i guess you are not making many of these devices (ie it's not a volume production run) then the cost of the integrated IC's is going to be far outweighed by the time and complexity of any DIY approach: Something like this: https://uk.farnell.com/stmicroelectronics/tda7293v/ic-amp-audio-120v-100w/dp/1366582 is about £4.50 in low volume from a reputable supplier, some time with google would probably find a chinese alternative for half the price or less. It has a 10V/us slew rate, so you can work out if that's good enough for your load...... You could buy one of those, fit a few support components around it (like some power rail caps for example) and be up and running ASAP with little risk of it "not working" or going BANG too many times, unlike any home-grown version. That just leaves you needed to sort out the +-50V DC supply, which if you are battery powered is a trivial issue because you can make the middle of the cell string your "zero" volts reference..... |
| OM222O:
don't forget that speaker drivers mostly care about resistance, since the inductance is usually very low. to achieve the 500Hz that you mentioned, the 100v supply is a requirement, like you mentioned before --- Quote from: max_torque on June 29, 2019, 09:48:10 am ---Given it's large inductance, the overall control bandwidth is going to be limited by that value and the supply voltage. --- End quote --- I had a look on digikey, mouser and farnell. mouser and digikey didn't have anything with +-100v and farnell only has outdated parts :-DD https://uk.farnell.com/w/c/semiconductors-ics/amplifiers-comparators/audio-amplifiers?amplifier-class=ab&supply-voltage-range=posneg-20v-to-posneg-100v unless there is something inherently wrong with my schematic and simulation, I think I'll stick to it for now. |
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