I did not really found anything on google to accomplish my idea, so try here to find out an answer:

My task is defined as follows: I need to check if the input voltage is in a specific range. Lets say, for example: 5V +/- 10% so Vmin=4.5V and Vmax=5.5V. If the input voltage is in the acceptable range then light up a LED and start a microcontroller else do nothing at all.

The problem: the voltage I want to check is the only voltage available, so I can't compare it to another for example.

I already came up with a solution but I don't think its perfect: use a simple zener diode in reverse and wait until it becomes conductive and then switch a transistor or so.

Is there a better and more professional way to do it?

EDIT: I just found a Voltage Detector IC (click) with a really low supply voltage, would that be an acceptable solution?

  • \$\begingroup\$ I just found a Voltage Detector IC... Part number? \$\endgroup\$ – tcrosley May 29 '15 at 16:57
  • \$\begingroup\$ Voltage detector- if you mean the one that keeps microcontroller in reset, than it's fine, but it usually only checks the undervoltage condition. Also it is actually integrated comparator with voltage reference and voltage divider. And also, if this is a homework, i bet your teacher expects to see zener reference and comparator. \$\endgroup\$ – Gregory Kornblum May 29 '15 at 16:59
  • \$\begingroup\$ How low can the voltage go, and still need to get a correct output? \$\endgroup\$ – The Photon May 29 '15 at 17:01
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    \$\begingroup\$ If correct behavior at low voltage (say below 2.5 V) is not required, then look for other q/a on the site about window comparators. \$\endgroup\$ – The Photon May 29 '15 at 17:02
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    \$\begingroup\$ Are you sure you need to detect voltage > 5.5? Assuming your supply is connected to the microcontroller, there's not much you can do about it. Otherwise, your linked IC is fine for what you need. Search for "voltage supervisor" circuits. \$\endgroup\$ – WhatRoughBeast May 29 '15 at 17:25

Zener is actually a good idea. Later you can replace it with voltage reference IC for better accuracy, but zener is just fine for your application.

You need two low voltage comparators, each will have a reference voltage set by a zener (with resistor in series! and a capacitor for cleaner signal...) and each will have a voltage divider (two resistors) with your input voltage on top. And- some basic logic on comparators outputs.

  • \$\begingroup\$ Are low voltage comparators comparators with a very low voltage supply? If so, that would be great! \$\endgroup\$ – d3L May 29 '15 at 17:15
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    \$\begingroup\$ Ok, define very low. LT6703 takes 1.4V, and actually incudes a voltage reference inside. You must remember, that any number is only valid in certain limits, which are usually defined by application. I mean, if you really really need to, you can design your own comparator that will work with VCC as low as 0.8V. Maybe you can find one like that. But for described application you just don't need it, because your microcontroller will not run with voltage lower than, say, 3V. So your problem is only relevant to voltages higher than 1.5V or 2V \$\endgroup\$ – Gregory Kornblum May 29 '15 at 17:20
  • \$\begingroup\$ You are right, I just thought of a solution without a microcontroller involved but that was not the question, so the comparator + zener diode solution seems like a good solution to me now \$\endgroup\$ – d3L May 29 '15 at 17:23
  • \$\begingroup\$ Oh, i thought you need to keep the MCU in reset. This is a very common application. google voltage supervisor. \$\endgroup\$ – Gregory Kornblum May 29 '15 at 17:24
  • \$\begingroup\$ Actually, that is exactly what I need, but why should this not be accomplishable with a low voltage comparator? \$\endgroup\$ – d3L May 29 '15 at 17:27

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