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Modjo , 11-08-2018, 02:13 AM

Hi all, i have a question about a design that i have seen on a card. The designer use an AOP in voltage follower mode (yellow in picture). What is the utility of it ? Protect the micro ADC ? Otherwise, can you said me if the couple R1/C1 is really necessary in this mode? I ask this question because i would like to start a new design from this one but decrease the cost (if possible).

robertferanec , 11-08-2018, 05:00 AM

Here you can see the basic applications of OP AMP: https://en.wikipedia.org/wiki/Operat...r_applications

If you have a look, your application is combination of several circuits - depends what components you will fit, but basically, it is an Non-inverting amplifier (and without R3 fitted, output will just follow the input - from "voltage follower": "Used as a buffer amplifier to eliminate loading effects (e.g., connecting a device with a high source impedance to a device with a low input impedance)."). Because of the capacitor it will also have some Low Pass Filter capabilities: https://www.electronics-tutorials.ws.../filter_5.html

Modjo , 11-08-2018, 06:34 AM

Thanks a lot Robert for your explanation, it's very clear like in your course . Another question, there is another mean to protect ADC from hightvoltage (from exemple 24v in AIN1) ?

robertferanec , 11-12-2018, 01:06 AM

- it depends if you need to protect it from constant high voltage or just some pulses. For pulses you normally use some kind of diode protection (e.g. zener diodes), varistors or components specially designed for this purpose (in your schematic it is the PTVS12VS1UR). For high voltage applied by mistake you may need some kind of circuit which will disconnect the input, e.g. this is not exactly what you need, but we use something like this as overvoltage input power protection ( check out http://www.imx6rex.com/ ) - Full schematic here: http://www.imx6rex.com/wp-content/up...-Schematic.pdf

Modjo , 11-13-2018, 08:17 AM

Thanks a lot for your explanations !