High-side current monitoring

[charliecoutas]

That's exactly what it is: Constant power control loop. The AD633 is an analog multiplier:

https://www.analog.com/media/en/technical-documentation/data-sheets/ad633.pdf

I tried this last year using a PIC but got into difficulties with timing and current measurement. So it's all analog now but who knows what the future may bring?

Charlie

[ken_k]

Ken:

What did you use to measure voltages to 7 figures?

Charlie

Hi Charlie
I apologise for not answering when you posted, a friend had a stroke in front of me, a week later we had a death and then funeral to deal with.

Regarding the voltage measurement it was a spice simulation only. I have often used voltage dividers to enable op-amps to operate within their allowable common mode ranges when high voltages are involved, the downside is the voltage division, often not a problem. The same goes for ADC inputs if 16 bits or more are available often a good solution.

I see you used an analogue solution, well done.
I looked at the price of some fast 16 bit ADC's not cheap, up to $100!

Ken K

[top204]

I cannot put into words how I feel for you and his/her family Ken.

My thoughts are with you.

As stated, it is still sometimes better to use an analogue method for control if it is possible to do so. The circuits and methods are tried and tested over decades and are very rugged if the correct components are used.

[midali]

A question...
It's poosible to use internal OP Amp from PIC for current monitoring ? Never I used it, but I  see that its unusually.

[ken_k]

I cannot put into words how I feel for you and his/her family Ken.
My thoughts are with you.

Les thank you very much for your kind words.

Midali, regarding your question about using the internap PIC opamps. I have never used this feature. Looking at Microchip Technical Bulletin TB3280 it seems one can access the inverting input, noninverting input and output so I would see no reason why it could not be used. I have no idea how good the opamps are compared to some of Microchips discrete opamps. There are so many cheap good SOT-23 opamps about I normally place them exactly where needed. For a commercial product where the cost or available PCB space is limited the in PIC device may be the best choice.

I would like to hear for somebody that has used the internal PIC opamps.

Ken K

[david]

Hi,
I've used one of the two op-amps in a 16F1783 but the application was not particularly demanding in terms of common mode range or output swing.  I used it as a 3rd order low pass filter for a 16 bit PWM filter to control an ovenised xtal in a Frac-N synthesizer.
Of greater concern was the noise on the internal reference voltage.  After much correspondence, Microchip did finally admit there was a bit of an issue with it and gave an unacceptable work-around.
Key thing is to understand the limits of your application and as Ken points out - you may not want an op-amp with limited capability sitting amongst all that digital noise.

Cheers,
David