Rail to Rail Op Amps - Advantages and Disadvantages

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Күн бұрын

The operational amplifier market has widely expanded with rail-to-rail devices that can operate with their input and/or output close to the rail. While this seems like a great thing to have, these rail-to-rail opamps have their drawbacks that need to be understood. Rail-to-Rail opamps do eliminate the terrible phase reversal effect that older opamps have when their specified common mode input voltage range is exceeded. An explanation of phase reversal is included.
00:00 Intro
00:18 Why Rail-to-Rail?
01:27 Common Mode Input Range
02:44 LF411 Input Voltage Range
03:20 Phase Reversal
04:01 Common Mode Input Voltage Range Spec
04:25 What Causes Phase Reversal
05:14 Common Mode Input Range Included One Rail or the Other
06:19 Complementary Pair Input
07:09 Distortion in a Rail-to-Rail Unity Gain Follower
08:14 Changes in Offset Voltage and Current
08:59 Rail-to-Rail Output Stage
09:28 Negative Power Supply Voltage Monitoring
11:20 High Side Current Sensing
13:40 Summary
Operational Amplifiers
Phase Reversal
Rail-to-Rail

Пікірлер: 11

@joejane9977 5 ай бұрын

information welcomed thank you

@oldhackee3915 5 ай бұрын

Thank you.

@TerryClarkAccordioncrazy Жыл бұрын

I learned a lot from this video. Thanks.

@oldhackee3915 Жыл бұрын

Thanks so much.

@kadamrohan16 Жыл бұрын

Nice informative post and catchy animations ! looking forward to more analog posts

@oldhackee3915 Жыл бұрын

Thanks very much.

@DaveEtchells 9 ай бұрын

Super informative and useful. I hadn’t expected the zero-crossing distortion, nor the wild shifts in offset voltage with common mode voltage. I’m a new subscriber, and filing this video away for reference, thanks!

@oldhackee3915 9 ай бұрын

Thanks for the comment. I’m glad you found it useful.

@dougbas3980 5 ай бұрын

Thank you. I am puzzled. On an MCP6002 rail to rail output amp using a differential amp with four 10K resistors, I can only get to 1.3v from rail (4.3vdc supply to get 3 volt output). I a m using a voltage ramp from 0-3vdc into 10K on + input. The output follows until within 1.3vdc of supply, then flattens. Just what I would expect with LM358 but not the rail to rail MCP6002. Can anyone tell me what is wrong with my thinking? BTW, I used SPICE of MCP 6002 with my circuit and it says it should work??? I tried with three MCP6002 chips with same result? In any case, thanks. Very good video.

@oldhackee3915 5 ай бұрын

Hi. Thanks for the comment. It’s sounds like it should work. What is the load on the output? Have you checked your 4.3v supply voltage to see that it’s not dipping during the positive peak?

@dougbas3980 5 ай бұрын

@@oldhackee3915Thanks for reply. This is my first rail-rail project, so I did a SPICE model with MCP6002 (1/2) and it worked for 3v out with 3.3vdc supply. Then I built the circuit (and tried 3 different MCP6002 DIPs). The circuit clipped at 2v with 3.3 supply and stopped clipping when supply was raised to 4.3vdc (1.3vdc head room). That would be expected with bipolar push-pull out put but not CMOS output stage. They are cheap chips from China (so???). At this time, I am not loading the output beyond the scope probe and 10K FB resistor. It seems like bad parts, but I could be doing something wrong (but what??). Thanks for your advise, Doug.👍