ac current sensing circuit design

[466576266]

hello, anyone.i am designing an ac current sensing circuit for my motor control. and my problem is: how to convert the ac current into dc voltage which can be processed by mcu?

can anyone give me some advice? by the way , i want to design the circuit with integrated ic ,such as isolation amplifier..

thanks in advance

 

[Windadct]

AC Current Sense

Hello 466576266

Difficult to answer without knowing how much current and at what voltage.

At low currents a shunt sensor is low cost - but getting the isolation in the electronics is more difficult.

For higher currents it is easier to get isolation while it is AC - CT ( current transformer) across a shunt, and you are working with voltage again.

The top end is a AC current sensor that has the electronis built in like a LEM - pricy, but does everything you need.

 

[466576266]

hello Windadct

thanks for ur reply.

the ac current maybe: 15Arms and the frequency is about 50hz.

and i want to design it with the ic hcpl-7840.

i just donnt understand the recommended application circuit. that is to say , i want to know the principle of the circuit.and the ic is from avago technology. pls see the circuit in the attachment.

 

[Laplace]

If you are sensing current for motor control, might you also be interested in the phase angle between the current and the voltage? Then a non-reactive sensor would be necessary, i.e., one able to sense DC current. In addition to the simple resistor current sensor, Hall effect and magnetoresistive effect sensors would be appropriate. The following documents may prove interesting:

The Universal Current Sensor - May 1, 2000
http://www.sensorsmag.com/sensors/electric-magnetic/the-universal-current-sensor-1029

AN6049 High-side Current Sensing Techniques for Power Manager Devices
http://www.latticesemi.com/dynamic/view_document.cfm?document_id=5940

 

[466576266]

dear laplace

thank u for the link u gave to me.

and i think this link "The Universal Current Sensor " will be a great help to me .

so many nice person here.

 

[466576266]

still confused

i am still a little confused.. the hcpl-7840 receive ac signal from the resistor, and how about the output of the ic? seems that it is ac signal which cannt be processed by cpu. so how to deal with it?

i mean : ac current equals to 0A, then the circuit maybe output 0V
ac current equals to 1A, then the circuit maybe output 0.5V
ac current equals to 15A, then the circuit should output 5V, and so on...

i just cannt imagine the principle.. pls help me ,thank u ...

 

[Windadct]

Datasheet has the answer - Pigure 9

Hello 466576266 (;-)

Your additional posts are quite different than you initial one - it seems you are asking about how to interface the output of an isolation amp to an MCU?

Regarding the HCPL-7840 - on the DS it shows V in -200 to +200mv -> Output of +1,29 to +3.8V - and suggest additional op amp to condition the signal, however there are a number of way to condition the signal for the MCU - but that is a signal problem not a current cense problem.

You need to figure out how best to take a +1.29 to + 3.8V Signal and have it readable by the MCU. If the MCU has it's own A/D converters - that is the spec you need to work with. If the MCY has a 0 to 5 V A/D input for example, it can read it directly - but you are giving up about half of the voltage range available.

B/R Paul