Interfacing to a 3.3V analog input 1

[HIPPMS]

So, our software guy has designed a PWM drive for our new 30kW Buck Regulator Design. Unfortunately, he has chosen an Arm Microcontroller that is powered with 3.3VDC, and the Analog inputs for voltage and current are also limited to 3.3VDC.

My current sensor is a LEM, with a nonimal output of 4V @ 100 Amps. (Hopefully, I won't see more than 60 Amps, but we all know better than to make that assumption.)

How do I safely limit the Analog Input to the microcontroller to 3.3V?

I was thinking of an Op Amp powered with 3.3V, and a Zener diode on the input...would this work?

I am a Pulse Power Engineer, usually dealing with high voltage and high current, so I could use some advice here.

Any comments or suggestions would be greatly appreciated. Thanks!

 

[VEBill]

If the internal ADC has enough bits, then you might be able to get away with just a resistive voltage divider. The extra bits give you some headroom for higher than expected input voltages due to various failure modes, with enough bits on the LSB end to provide the required resolution.

But you'd still clamp the input with diodes or equivalent. The voltage divider gives you two places to insert that function.

 

[HIPPMS]

Thanks for the reply VE1BLL....

Don't know the resolution of the Analog Input, but I don't want to sacrifice any resolution by wasting bits. (software guy will have a fit! HaHaHa.)

Just need a simple circuit to clamp the voltage so it never goes over 3.3V.

I was thinking about an Op Amp with a 3.3V supply, and clamping the input with a 3.3V Zener. Would this work?

 

[HIPPMS]

I just found this link!

 

[VEBill]

That's a fabulous reference.

Your approach is perfectly reasonable, I just like to think outside the box.

 

[HIPPMS]

VE1BLL......guess I should have "Googled" first. (Who have thunk that Google would become a verb...HaHaHa)

Are you in the Military now? (I am a grumpy old Vietnam Vet)

If so, I thank you and apperciate your service!

 

[VEBill]

No, it's just the field in which I work.

 

[HIPPMS]

You may not wear a Uniform.....but you at least have your priorities straight....so that deserves a "Thanks"