low side current sense help

Im using a Low side current sense shunt(.1ohm) for the first time in a project, any suggestion on something easy to use preferably with minimal external components? The amps measured will be less than 2, though the high side voltage may be 500v which is why im opting for low side, most ics I saw only went up to 80v
its measuring the load of a Nchannel hbridge, with the resistor on the common vss of the two lower n channels
I don’t mind soic components and larger if it matters on what’s out there,
thx in advance

Oh, to clarify on the current resolution 1 ma would be nice, and the reading will probably be read by the arduino, probably with the internal reference
and while im posting here about this, if I wanted to have the supply cut off at a certain set current level how would I quickly trigger the circuit to cutoff power?

500 V and 2 Amp, that'll stop your heart in an instant!!

This sounds so dangerous you should not be asking about it around here, but
find an experienced professional engineer to design you something safe, and
then don't stand too close to it.

Naah it's just a kilowatt of power... Make a great Hot dog Exploder. AS to the sense resistor and High voltage the device sensing the over current condition should disable the HV supply with a latching relay...
REALLY 500V @ 2A - 1 KW of power handled by an H-Bridge??? and current sensed and all you are concerned about is that??? You had better sit yourself down and generate an accurate plan, schematic and
and proposed software first... there is the Generating that much voltage at that kind of current is going to make someone a very happy man selling you a transformer. (Try Hammond). At the voltage level
you are talking about it takes less that 100mA to be fatal... %00V and an H-Bridge... What kind of motor are you planning on driving. Did you ever see one of those generators that is supposed to make
earthworms come out of the ground? What you are discussing could KILL a 10 Acre farm of them... in about 5 seconds. 500V @ 2A or 1KW...? to a current sensed H Bridge. Better to use a different motor
and make a VFD (Variable Frequency Drive) for a 2KW AC motor, Vary the frequency and vary the speed. What were you going to do about the back emf this device is going to sense as well... If it's Even for a
motor. The prime issue is that in order for you to "reverse" this thing (What an H bridge does best) you have to do something with the energy present in the :System" you havve a Mass of so many units and in
motion it has stored kinetic energy... you have to deal with that before you can "Throw her into reverse" as to the sensing that can easily be part of an off the shelf Power supply and the H Bridge as well. It is
well beyond the expertise you have demonstrated in this Forum so far... For building the power supply there are several books I could recommend and The H Bridge is an off the shelf item. All of it is but you
are looking at about $900 to $1500.00 for the power supply... as surplus. It might be available as a 3 phase 440V device still I should think that a regulated (you didn't suggest otherwise) and that is usually
what sensing current is about, Would sell in the high $2000's possibly more and the H bridge is going to be a real surprise for you as well If all you want to do is change polarity 4 relays would do it and provide
dynamic braking Too and some kind of motion lockout would be trivial to do... U sure 500V @ 2A? 1KW and not 50V @ 2A??

At the voltage level
you are talking about it takes less that 100mA to be fatal


--- 100mA ---
extreme breathing difficulties
breathing upset
severe shock
muscular paralysis
painful shock
--- 10 mA ---

Luckily, the time I got across 1000V, it was only across my hand. As I recall,
my small finger tingled for about a week after that.

From another time, I can attest to the bit about muscular paralysis, that time
was from left hand [gripping metal] to right hand [gripping metal] to bare feet
on concrete. Couldn't let go. That was only 120VAC. The resistance of the concrete
probably limited the current flow.

Don't worry about me killing myself, im an electrician and work with decent voltages e eryday and have the ppe to protect myself
and those were maxs, definetly not 500v at the same time as 2A, more like 500v 40ma or 12v 2A, the input is meant to be changeable so I am designing it for the two extremes it may come across
Im not expecting to ever exceed like 35W under any circumstance,
I was planning on using a 600v nmosfet to kill the power,

The plan tho is to be able to adjust the trip level manually as the need arises, plus having the arduino monitor the supply and the current trip level so if it exceeds a certain wattage it wont even let it turn on for say if I upped the voltage nd forgot to change the trip level
the arduino will also monitor the current for display purposes, so multiple things will be going on at once and I need to figure out a sense hardware that can handle it
-the arduino monitoring the current flow from the sense resistor,
-an electronic circuit breaker type circuit to kill power as fast as possible if limitations are eexceeded

Plus it have to be turned on manually in the first place,

As for a kill circuit I was thinking to drive the main mosfet off as fast as possible could I have a properly sized capacitor, with a negative voltage of 10v, (mosfet can handle -30vgs) which I would use a smaller mosfet/or/transistor to connect it to the gate
normally the mosfet will be turned on by a mosfet or transistor circuit driven by an arduino pin, with probably a 1-10k resistor so it is easily driven low ffirst and fast by the negative surge, then kept low by the kill circuit

Most importantly tho if that sense circuit which would need tp be dependable for sure,

Ugghh I'm having flashbacks of a time I had just installed a new CDI ignition in a car. Hot coil and everything. Long story short, it was missing on two or more cylinders when I spotted that the cap was on a bit cock-eyed. I reached out to correct that situation. 50kv worth of blaster coil from my right arm to my left hand clutching the fender. Took more than a minute to shake that one off. A shocking lesson I suppose. Yet one I had to learn over and over. Anyone remember what would happen if you just tried to grab a WinModem out of a PC back in the day?

On topic. Any voltage sensing you do with the arduino is going to have to be at max 5v in. What is the max voltage you expect to see on the low side? You don't need a shunt. You can measure AC current with a non-contact device pretty reliably.

Its gonna basically be dc current, being the return of the hbridge, it will never go negative
I was figuring 2amps max so 2x.1=.2 volts max, which I figure with a reference of 1.1v it wouldn't be too bad but id like as much accuracy as I can get, also making it easier for the secondary safety circuit
also if I could get it in a 5v range that would be great since I also want to measure the higher supply voltage( so a pretty high ratio voltage divider with zener protection) and I was planning on a 5v reference for that

Use a hall sensor . Allegro has a whole range of them. You can get them from digikey


Super simple to use :
Connect the hall sensor in the current cirquit (will add virtually no resistance).
Apply 5V power supply
Read the voltage at the output via anolog inpyut pin on the Arduino.
Sensors include a 5A version.
Over 2 KV isolation.

I've used them to build a motor controller (24V with current limitation selectable between 10 and 100A)

Jan Huygh

~~A RTR opamp should get the job done. 25x gain. That will give you ~0-5v. out of 0-.2v. If you want opto-isolation you will need current to dive it. Opamps are generally terrible at delivering current and gain at the same time. You could use a power amplifier chip to avoid buffering. It wont be rail to rail though. It will require considerably more than 5v. LM386 could be used. ~~

A hall sensor is a way better idea. I thought about it for a second and my brain just dumped it out in favor of the totally convoluted crap above. Probably because those are things I have on hand. Well you know what they say about hammers and nails.

I really like that idea,
what would the practical resolution of that ic be?

Taking a look at it id have .37volts to detect the 2 amps with, so like .000185volts per m, which I think at 5v reference the resolution will be 20ma steps, bit innacurate especially when noise is taken into considerations
happen to know of any where the full range would be 2-3 amps? also the negative reading isn't really necessary
I tried looking on digikey, but couldn't find anything In my range and needs

Maybe check out the following SparkFun current sensor module. They also show links to the underlining sensor chip used for more detailed information.
SparkFun Current Sensor Breakout - ACS723 (Low Current) - SEN-14544 - SparkFun Electronics?


Do you think the LT1677 precision rail-to-rail opamp would work? Since the vottage at say 1ma would be .0001volts which isn't much
also would I have to use a dual supply?

Or would the OPA335 be better? It says 5ûv so that's well withing my needs and accounting for for noise

Hmm, I think the opa335 would be perfect, now the problem is Is to get the. 2v to 5 I need a 25x gain, which isn't too bad but with the arduinos resolution im only gonna get like 2ma resolution which is close to what I want but still wouldve been nice to get 1ma, I could even get much better but then. It wouldn't be able to get to 2a