I am (still) learning about electronic and want to get a 555 timer. From a datasheet (page 5) it looks like when the input voltage is 5V, then the output voltage is only 3.3V.

Is that correct?

If this is correct, are there any 555 timers (or similar) that will operate on inputs on about 5V and give outputs also 5V

(or just the same as the input)?

  • 1
    I suspect that you are looking at the timing capacitor voltage. This input switches at 1/3 and 2/3 supply but the output switches between 0 V (GND) and V+ (5 V in your case). There must be a million 555 articles on the web because it is an old and very popular chip. Read on and if you need clarification on a point then ask another question. – Transistor May 20 '16 at 18:22
  • @transistor: Ok, so the output pin should give 5V in general? (I was probably just looking at something wrong then.) – John Doe May 20 '16 at 18:30
up vote 6 down vote accepted

For most 555's, the output-high voltage is whatever is provided as the supply voltage. So if you give the 555 9V it will output at 9V, if it give it 5V it will output at 5V.

This is with the stipulation that the supply voltage is within the ratings specified in the datasheet.

In the case of this TI 555 timer, the supply voltage range is 5-15V http://www.ti.com/lit/ds/symlink/lm555.pdf

The output voltage will never quite reach the supply voltage. From your datasheet:

enter image description here

With a 10mA load to +5 you'll see 100mV or more drop when sinking 10mA, and about 1.45V drop (meaning output voltage 3.55V typically) when sourcing 10mA (load to ground).

If you need more voltage than that when sourcing a low current (such as 1mA) you can use a CMOS 555 which only drops a couple hundred mV.

At high current you could add output transistors such as power MOSFETs that might drop a few mV for a big one at moderate current, but never zero.

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