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Hall Effect Current and Voltage Sensor

Thread starter #1
I am building a dc/dc boost converter and I need to sense currents and voltages. I am planning to buy some Hall Effect Sensors but I have no idea what are the parameters I have to look into before buying. Does the voltage and current rating (specified by manufacturer) changes with increase in temperature as it does in FETs. Also What should be the safer limit for Bandwidth if my switching frequency is 25KHz.
Also, Whether open loop or closed loop sensor would be perfect in terms of Cost, Power consumption and size.
Current to be sensed: 25A-75A dc
Voltages to be sensed 550V and 200V dc
Thankyou
 
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rjenkinsgb

Active Member
#2
That totally depends on the current & voltage ratings and if the control circuit is isolated from the power circuit or not.

There are dozens of possible sensing circuits or transducer types, each suited for different applications.
 

dr pepper

Well-Known Member
Most Helpful Member
#6
I have used current transformers before and recently used a Acs hall effect current sensor for something rather mundane.
Another couple of considerations for using a hall current sensor is frequency response and phase delay, frequency response you might be able to equalize depending on the circuit, delay could be a problem if your using current mode switching or cycle by cycle current limiting.
There are a couple of versions of hall current sensors, one senses the magnetic field around a wire directly and the other uses a core normally a torroid, an op amp then drives a winding around the core to null out the magnetic field sensed by the hall effect, this type can go to very high currents, despite having a core they can measure very low frequencies.
It'll be interesting to see if you do get something working.
 

dr pepper

Well-Known Member
Most Helpful Member
#10
I agree with Ron the voltage and currents involved demand some care in design.
Expect to have a bag of blown bits.
If I were to try this I'd power the thing from a dc supply preferably with a safe voltage that can only provide a small amount of energy till I was confident its working well, in fact I do that for small stuff too.
 

ronsimpson

Well-Known Member
Most Helpful Member
#11
It is my Master's Project.
Usually when some one asks for help on their master's project there is a request to have it done by Friday. LOL
I think you should start out by learning how this power supply works and then convert it to 600 volts. Later increase the power by 100x. I am not doing the work for you. There are people at school that get payed to help you.
upload_2018-8-8_15-14-22.png
 

crutschow

Well-Known Member
Most Helpful Member
#13
Hall effect sensors are used to detect current, not voltage.

For isolation, typically optocouplers are used for that purpose.
They are relatively inexpensive and reasonably simple to use.
Here's a simple example for the voltage feedback:
A similar scheme could be used for current feedback.
Note that a voltage reference (TL431) is used at the output before the signal is sent through the opto since optos generally have a wide tolerance on the transfer gain, making it difficult to use them to directly send an accurate voltage.

upload_2018-8-9_12-27-21.png
 
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#15
This is a typical closed-loop current transducer:
https://docs-emea.rs-online.com/webdocs/12ab/0900766b812ab2f3.pdf

They are current-output devices so you can scale the voltage you need by selecting an appropriate load or opamp feedback resistor, within a reasonable range for the specific device.

"Open loop" types tend to be cheaper but not as accurate; the close loop ones have a coil around the magnetic core that is used to cancel the magnetic field around the main conductor passing through the sensor.

If that's eg. 1000 turns for a single pass through "turn", the sensor output current will be exactly 1/1000th the primary current when the magnetic fields cancel out. The hall sensor only has to detect a precise null rather than be linear over a wide range, as with an open loop one.


For sensing AC input current, current transformers are still widely used.
https://inverterdrive.com/group/Spa...rker-CO500068-590-591-AC-Current-Transformer/

They are also current output, in the inverse ratio of their windings; a 200 turn secondary will give 1/200th the current of a single turn primary.
In electronic systems, they normally go to a bridge rectifier then an appropriate load resistor. The voltage across that resistor is proportional to the instantaneous current, with no extra power supply being needed and the whole thing inherently being isolated.

One thing you must note with a current transformer is the secondary must always be securely wired to a load resistance at all times.
Without a proper connection they try to emulate a tesla coil and produce extremely high voltages, normally destroying their own internal insulation...

Current transformers are also often used to connect directly to a low current ammeter and rated as input:eek:utput current rather than turns ratio.
eg. https://docs-emea.rs-online.com/webdocs/1499/0900766b81499bbe.pdf

Many sellers have ones with eg. 5A rated output rather than the milliamp range needed for electronic sensing; or you could scale the input and output ratings in proportion - eg. a 200:5 one could be used for 2A sensing with 50mA output.

This is more like the type for use with electronic control systems:
https://www.dhgate.com/product/hwct004-micro-precision-current-transformer/405151777.html
 

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