Electronics > Projects, Designs, and Technical Stuff
High voltage safety and design considerations
max_torque:
Not really, speaker drivers care about impedance, which for a speaker at high frequency is mostly about inductance... 100vdc into a 4 ohm speaker is 25amps, or 2.5 kW...... :bullshit:
max_torque:
At DC, 25mA through 1.5K requires 37Vdc.
At AC if you want a full scale current reversal, ie peak positive(+25mA) current to peak negative (-25mA) current, in 2ms, that's 25 A/Second
So as V = L di/dt with your 2H inductance,you'll need 50V to do that (50 = 2 * 25)
Add the two together and we get 87V which makes me think that with an OTS +-50V amplifier, you'll just about be able to meet your control bandwidth requirement. So the question becomes, how important is a full scale drive swing in 2ms? Is that a number that's estimated, picked from thin air /guessed, or established via validated simulation and calculation etc??
Assuming that the actual "project" is to make the robot do what you want to achieve, getting distracted down a rabbit hole of DIY amplifiers seems, well, like a massive distraction to me. Sure, it'll be fun and interesting but this is why many projects never get finished ime...... (you start a project to build a robot, you end up with a custom power amplifier for an application no one else needs...... :-DD ) Been there, bought that Tshirt....... :o
OM222O:
This is a university project, not a personal one ;D the actuators are combined with pressure sensors for force driven joints, the 2ms is worst case scenario where stability can be achieved, so I like to stay closer to the 1mS figure to have some headroom. I'm not building everything, just the driver for the actuators and adc to read the pressure sensors (they're analog, 0 to 5v proportional output).
max_torque:
In which case, a good option, one that allows the rest of the program to proceed is to build a basic prototype with off the shelf parts, which can be done quickly and cheaply (even if you only make a single channel test setup to start with) establish how that performs, and based on those results roll-your-own final solution. Chances are, what you'll learn using the prototype will steer your design optimisation and specification into areas that you probably haven't even thought of, or that are currently considered un-important. These days, i meet lots of young engineers, full of enthusiasm and great ideas, wanting to make complex systems, and yet they don't have the necessary experience to get a feel for "what works". In these cases, i send them away to "make a first prototype" and report back. In pretty much every case, the small delay in putting together than prototype is massively outweighed by the eventual time saving to the overall project from the early experience gained!
In this case, for probably £50 to £100, you could be up and running on the bench, with a basic actuator drive circuit, that enables to you test your control system code and servo loops etc, and one that allows you to establish the bandwidth of that basic solution as a bench mark to any eventual solution! Given the average power consumption of the system is reasonably low (25mA @ 100V is just 2.5W) a couple of cheap, low power isolated (floating) 48V switch mode supplies would see you up and running on the bench where you can begin to explore :-+
Zero999:
--- Quote from: max_torque on June 29, 2019, 01:13:47 pm ---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.....
--- End quote ---
The problem with that part is it uses bootstrapping capacitors and presumably he wants it to be work down to DC.
If the original poster is hell-bent on using dual power supply rails, then they should just use an ordinary op-amp, with a bootstrapped power supply. The op-amp just needs to be capable of outputting at least 25mA or pass transistors could be added.
Further reading:
https://www.proaudiodesignforum.com/images/pdf/Bootstrapping_Your_Op_Amp_Yields_Wide_Voltage_Swings_King_Watkins_EDN_May_13_1999.pdf
https://www.analog.com/media/en/technical-documentation/application-notes/AN-1593.pdf
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