Need help selecting an isolated voltage sensor

[~MJS]

Hello All,

I am looking for an isolated voltage sensor (or Transducer) to measure the DC Voltage on my output. My applications is a Full-Bridge DC/DC converter: Vin=30V, Vout= 0 - 60V, Pout = 800W, and fs=200 kHz. (Note: the response of my sensor does not need to be that fast)

Digikey has LEM LV 20P for $36.6 , but this seems way to expensive for this application. Does anyone know of a cheaper component that would work for this application?

I have thought about using a hall-effect current sensor, with a high resistance, both in parallel with my output. The problem seems to be finding an IC that will measure current in the mA range and is isolated.

Any suggestions would be appreciated.

 

[srizbf]

you can find the suitablity of any linear opto isolator , if you can search one.

srizbf
8thmay2010

 

[FvM]

LEM voltage transducers are basically using the same technique as their current transducers: closed loop (compensating) hall effect
sensors. Apart from these devices, that are popular for industrial and traction application, there are various methods for isolation
of analog signals, with quite different accuray and speed specification. For moderate accuracy requirements, linear optocouplers
can be an option, see e.g. the datasheet and application notes of Vishay IL300. Isolated ADC with digital coupling across the isolation
barrier are often replacing analog isolation in today's automation, drives and energy conversion designs.

 

[guitarboutique]

LEM voltage transducers are basically using the same technique as their current transducers: closed loop (compensating) hall effect
sensors. Apart from these devices, that are popular for industrial and traction application, there are various methods for isolation
of analog signals, with quite different accuray and speed specification. For moderate accuracy requirements, linear optocouplers
can be an option, see e.g. the datasheet and application notes of Vishay IL300. Isolated ADC with digital coupling across the isolation
barrier are often replacing analog isolation in today's automation, drives and energy conversion designs.

How do you compare the hall effect sensors to using sense resistors in your opinion?

Thanks.

 

[mtwieg]

I've tried linear optocouplers and have never gotten good linearity out of them. However if you use linearizing feedback on the isolated side then they can be very linear (but this requires an isolated power supply to operate an op amp on the output side).

It's very common to just use a simple diff amp with a low gain and very high input resistance (like 1Mohm is typical). If you use precise component tolerances, then it's very accurate and essentially isolated (though it has a finite common mode range, which can be adjusted as needed). And very cheap.