AMC1100: Transformerless mains sensing using isolated amplifier

Swanand Date

Part Number: AMC1100
Other Parts Discussed in Thread: AMC1301, AMC1200

Dear Sir,

Following circuit is from "Replacement of input mains transformer in inverter with isolated amplifier".

My question is : Does AMC1100 need differential signal shifted by 2.5V at input side with respect to input side ground ?

over 8 years ago

0 kai klaas69 over 8 years ago

Guru 140200 points

Hi Swanand,

I don't think so. The idea is to have the input signal/s swing arround input GND by +/-0.125V.

Kai

0 Tom Hendrick over 8 years ago

TI__Guru**** 182761 points

Hi Swanand (and Kai),

Welcome to our e2e Forum! The short answer to your question is no - the AMC1100 does not have to be biased to 2.5V. The AMC1100, AMC1200 and AMC1301 can all accept +/- 250 mV signals respective of their input side ground.

0 Swanand Date over 8 years ago in reply to Tom Hendrick

Prodigy 40 points

Ckt is from : AMC1100: Replacement of Input Main Sensing Transformer in Inverters with Isolated Amplifier

Why in this ckt differential input is shifted using R1& R2 divider ,is there any special purpose to do so ??

0 kai klaas69 over 8 years ago in reply to Swanand Date

Guru 140200 points

Hi Swanand,

you mean figure 32 of datasheet? R1 & R2 is just a voltage divider, to allow higher signal voltages to be interfaced to the AMC1100.

Kai

0 Tom Hendrick over 8 years ago in reply to kai klaas69

TI__Guru**** 182761 points

Hi Kai,

Swanand is referring to Figure 5 in AMC1100: Replacement of Input Main Sensing Transformer in Inverters with Isolated Amplifier

0 kai klaas69 over 8 years ago in reply to Tom Hendrick

Guru 140200 points

Thanks, Tom!

0 Tom Hendrick over 8 years ago in reply to Swanand Date

TI__Guru**** 182761 points

Hi Swanand,

The configuration shown in Figure 5 of that app note on the AMC1100 is basically setting VINN at positive 2.5V and then allowing the AC signal to swing +/- about that offset. I don't know the mindset of the authors at the time when the document was written so I'll ask them to provide some comment as to why they took this approach. I would have also liked to see them use the full dynamic range of the AMC1100 in this case by taking the full differential output and converting that to a single ended signal rather than only using VOUTP.

0 Swanand Date over 8 years ago in reply to Tom Hendrick

Prodigy 40 points

Thank you Tom & Kai

Tom let me know if you got info from authors.It will be very helpful to me.

Regards,
Swanand

0 Harmeet Singh over 8 years ago

TI__Intellectual 1520 points

Hi Swanand,

AMC1100 has been designed for measuring current across shunts.

You could give +/-250mV max. differential input to it.

In inverters 50HZ transformer is used to sense AC (Live - Neutral voltage) by stepping it down, rectifying it and then measuring with the ADC input of uC.

We proposed to replace this transformer with AMC1100.The AMC1100 is being used for measuring voltage ( resistor divider wrt ground) and not current.

Hence we can not short the Gnd pin with the VINN. Instead we have biased the VINN pin wrt to gnd at 2.5V. The bias voltage can be anything.

Hence you could scale down ac voltage to +/- 250mV wrt 2.5V.

I hope it answers your question.

Regards,

Harmeet

0 Swanand Date over 8 years ago in reply to Harmeet Singh

Prodigy 40 points

Thank you Sir

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AMC1100: Transformerless mains sensing using isolated amplifier