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I am using one op-amp of LM358 IC as a non inverting amplifier (Vcc-5V). Its input is from an IR proximity sensor. IR emitter used is SFH4350 and photodiode used is TEFT4300 also operating at 5V. I am pulsing my emitter at 15KHz using the second op-amp of LM358 IC as oscillator. Thus I also have to add a HPF (fc-11.5khz) at the input of amplifier part. I am feeding the output output of amplifier to an ADC which is reading values only up till 0 to 3.3V max. I am aware that LM358 is not a rail-to-rail op-amp, but I want my output voltage range to reach near 5V (+/- 0.5V). Is there some way out through which I could achieve the desired output voltage using the LM358 or some other IC but of the same price range?


Thank you all for your answers. I did a little research of my own and found the LMV358 which I think will do the job just fine. LMV358 is a Dual Low-Voltage Rail-to-Rail Output Operational Amplifier available at even a lower price than LM358.

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  • \$\begingroup\$ use a pull-up resistor \$\endgroup\$ – Jasen Feb 19 '18 at 7:04
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    \$\begingroup\$ Any reason not to use a rail-to-rail opamp when you need one? \$\endgroup\$ – Dmitry Grigoryev Feb 19 '18 at 7:59
  • \$\begingroup\$ @Dmitry Grigoryev rail to rail are expensive and not so easy to find. \$\endgroup\$ – Adam Smith Feb 19 '18 at 8:03
  • \$\begingroup\$ The TI LM358 Voh spec is listed as (Vcc-1.5), so use an analog Vcc of 6.5V to achieve a Voh of 5V. \$\endgroup\$ – Nedd Feb 19 '18 at 9:10
  • \$\begingroup\$ I was open to suggestions for a low cost rail-to-rail op-amp! \$\endgroup\$ – Kunal Gupta Feb 20 '18 at 6:32
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While you can get the output voltage of an LM358 up to +ve rail with a pull-up resistor, you can't get it down close to ground. The sinking current output has a follower configuration which limits you to around 1v when pulling any significant current.

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  • \$\begingroup\$ yes adding a pull resistor doesn't solve my problem. Any other way to do it? \$\endgroup\$ – Kunal Gupta Feb 19 '18 at 7:52
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You are looking for a LM393 comparator. When input offset is positive, the output goes to high impedance. You can then insert a pull up between output and VCC.

Be careful with the offset between VOL and zero. It is slightly larger than in the LM358 from my experience.

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  • \$\begingroup\$ Not looking for a comparator. \$\endgroup\$ – Kunal Gupta Feb 20 '18 at 6:28
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This is a common trap with cheap opamps such as LM358. You won't be able to bring the output voltage all the way up to the positive supply rail.

In some cases you may solve this by increasing the supply voltage. For example, if you really need the output voltage up to 10V then you might use the LM358 with a supply rail of 12V.

A comparator such as LM393 has an open-collector transistor output, so with a pull-up resistor it will swing essentially rail-to-rail assuming that the load impedance is high. (If a comparator is appropriate for your application.)

It's not really true that rail-to-rail opamps have to be expensive. (Of course, you do need to consider other factors such as the bandwidth needed, slew rate and other specifications for your application.)

As a cheap, basic example, there's the TLV271 (Digikey TLV271CW5-7DICT-ND) which is rail-to-rail and low cost.

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  • \$\begingroup\$ TLV271 is not as cheap as LM358. I don't need it to work as a comparator. Please read the question again. \$\endgroup\$ – Kunal Gupta Feb 20 '18 at 6:25
  • \$\begingroup\$ I did a bit of research of my own. and found the LMV358 which is even cheaper than LM358. I think it will do the job just fine. \$\endgroup\$ – Kunal Gupta Feb 20 '18 at 12:36
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LMV358 (rail-to-rail opamp) should be adequate for the purpose. Some ADCs I think allow you to scale the range with V ref, if it is possible to do that, you may be able scale vref to map the reduced range of perhaps capped at 0 to perhaps 1.8v (3.3v-1.5v)

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