Author Topic: Transducer: current consumption from negative supply  (Read 2609 times)

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Offline onemilimeterTopic starter

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Transducer: current consumption from negative supply
« on: July 02, 2011, 01:58:28 pm »
LEM LA-55-P is a bi-directional current transducer which requires +/-15V power supply. According to the datasheet (see below), the current consumption is (10+Is)mA (or, (10+50)mA at Ipn=50A). If the primary current is a sinusoidal current, do you think the current consumptions from the +/-15V rails will be equal? Or, the positive rail tends to supply more current?

Cheers.
« Last Edit: July 02, 2011, 02:00:46 pm by onemilimeter »
 

Online Zero999

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Re: Transducer: current consumption from negative supply
« Reply #1 on: July 02, 2011, 02:50:18 pm »
The positive/negative current probably depend on the output voltage (which depends on the current being measured) and the load connected to the output.
 

Offline onemilimeterTopic starter

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Re: Transducer: current consumption from negative supply
« Reply #2 on: July 02, 2011, 03:06:00 pm »
Thanks.  I'm currently figuring out how much VA is required by a transformer to supply the +/-15V for four LA-55-P transducers. I believe there is an op-amp insides the LA-55-P. I might be wrong but I heard before that the negative rail of an op-amp usually consumes very little current.
 

Alex

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Re: Transducer: current consumption from negative supply
« Reply #3 on: July 02, 2011, 03:16:14 pm »
It is a current output device with a 1:1000 ratio of Isn:Ipn, therefore the supply current will vary with the output current.

The supply for the sensor is 10mA, and add (with sign) whatever the output current will be to that.

As the current output is flowing into 0V, when Ipn = say -50mA then the negative rail will be more heavily loaded.

If you spec both rails for 60mA and provide decoupling capacitors for each rail close to the sensor then you should be fine across the entire measurement range.
« Last Edit: July 02, 2011, 03:18:13 pm by Alex »
 

Online Zero999

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Re: Transducer: current consumption from negative supply
« Reply #4 on: July 02, 2011, 03:20:42 pm »
Don't forget that 50mA is the RMS output current so the power supply should be able to handle 71mA + 10mA = 81mA peak per transducer.
 

Alex

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Re: Transducer: current consumption from negative supply
« Reply #5 on: July 02, 2011, 03:22:48 pm »
Decoupling caps for an AC application.
 


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