For experimental - hobbiest purpose, I'm trying to control one 3-color led with the following circuit:

  • Power: single rail, 5v.
  • Signal generator: triangular 0-5v, 500 Hz (in next step, signal generator should be replaced by an op-amp circuit, could be a rectangular generator followed by integrator).
  • operational amplifier in comparator configuration. v- from signal generator; v+ from variable resistor (0-5v input).
  • red led with 160 ohms resistor at op-amp Vout (in next step it will be replaced by 3-color, using 3 op-amps and related variable resistors).

In this way, triangular signal is converted to rectangular with pulse width selectable via the variable resistor.

Problem: using a 741 op-amp (the one most used in the time when I studied electronics, a lot of years ago) its low and high limits restricts the valid margin to more or less 1.5v-4v.

Do you think MCP6004 is a better alternative for this application than 741 ?

Thanks a lot.


closed as off-topic by Andy aka, Wesley Lee, JRE, Olin Lathrop, JIm Dearden May 8 '17 at 12:10

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  • \$\begingroup\$ Shopping questions are off topic because any answers rapidly become superseded and are opinion based. There are plenty of rail-to-rail op amps around - use search engines provided by the main suppliers. Rules: electronics.stackexchange.com/help/on-topic \$\endgroup\$ – Andy aka May 8 '17 at 11:34
  • \$\begingroup\$ @Andyaka:please, when you quote, quote completely, end of the phrase is "Instead, describe your situation and the specific problem you're trying to solve.". I think the question fulfills this recommendation. \$\endgroup\$ – pasaba por aqui May 8 '17 at 11:45
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    \$\begingroup\$ But your specific problem is that your 741 can't work rail to rail, to which the answer would be "find one that can". You've already gone beyond that and are asking a shopping question. \$\endgroup\$ – Finbarr May 8 '17 at 11:51
  • \$\begingroup\$ @finbarr: thanks for your interest in the issue. The problem is have not enough knowledge to choice without a few help. By example, I do not know what means "rail to rail". It means an op-amp with null margins respect its power source? \$\endgroup\$ – pasaba por aqui May 8 '17 at 11:55
  • \$\begingroup\$ It's a subtle distinction, admittedly - especially if English isn't your first language - but "what sort of op-amp should I be looking for" is a design question, while "can you recommend an op-amp" is a shopping question. \$\endgroup\$ – Finbarr May 8 '17 at 12:02

You have very few constraints so there are a lot of rail to rail op amp that you could use. Look here for example: Texas Instruments rail to rail Op amps

  • \$\begingroup\$ Thanks a lot for your answer. In this manual it is said "Signal Input Terminals, Voltage(2) (V–) –0.3V to (V+) +0.3V". I do not understand it: it means v- and v+ can not exceed 0.3v ? in my application v- and v+ goes from 0 to 5v. \$\endgroup\$ – pasaba por aqui May 8 '17 at 11:51
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    \$\begingroup\$ No, the 0.3V is related to the V- and V+ supplies. In your application it would mean -0.3V to +5.3V \$\endgroup\$ – Finbarr May 8 '17 at 11:53

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