comparators in IC 555

schreef in bericht news: snipped-for-privacy@googlegroups.com...

There are tons of stuff about the 555, including detailed descriptions of the inner workings. If you're only interested in a comparator, get the datasheet of the LM393.

petrus bitbyter

555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

All the stuff on the internet says there are two comparators but nowhere does it say what the comparators are! Unless you know somewhere where it says... Thx

IC 555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

The original 555 constructed the comparators on chip. They didn't give them a name. You can find the characteristics by doing what was suggested to you. Look at the data sheet.

snipped-for-privacy@btinternet.com wrote in news: snipped-for-privacy@googlegroups.com:

Comarator A trips when the generated sawtooth reaches 2/3 VCC, and toggles the internal flipflop,so the sawtooth goes down, comprator B trips when the saw tooth then reaches 1/3 VCC, and also toggles the flipflop, so the sawtooth goes up. All in all a voltage divider, 2 comparators and a flipflop, charging and draining a capacitor. Thats all.

IC 555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

Tom is correct. Internal to the 555, the "comparators" are simplistic diff stages driving latches... because there's no need for driving the outside world.

If you can find a circuit schematic of the 555 BIPOLAR version, you'll easily spot the diff pairs making up the "comparators". ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
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I love to cook with wine.     Sometimes I even put it in the food.

Its possible that macmanus has looked at the 555 schematic and failed to see much similarity between the one's on the chip & typical industry standard types.

Confusion can arise from the "shorthand" chip manufacturers use - like the far from standard representations of current mirrors, then there's the fact that the comparators in a 555 have much simpler structures than industry standard parts, they each only have to do one simple job - not be an all things to all circuits like the 393.

555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order?

Is it homework time already?

555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order?

IC 555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

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The schematic is on page 11-4 of Hans Camenzind's book,
"Designing Analog Chips", which can be downloaded for free at:

www.designinganalogchips.com

an IC 555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

Yup.

NPN's, Q1-Q4 make up one comparator

PNP's, Q10-Q13 make up the other ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Background - until 3 weeks ago I knew absolutely NOTHING about electronics, and even now I know very little. So I'm just starting out! Some of the responses to my origiinal post were helpful, but I still haven't been able to 'name' the comparators in the 555. All of the diagrams just seem to say 'comparator 1' or 'comparator 2'. Those that suggest I look at the data sheet are assuming I would know one end of a data sheet from the other.

New question: are the comparators in the 555 both 741s. If not, what 'number' is given to them, if at all? Maybe they don't have a number. Maybe the the only place you find these particular types of comparator are in the 555 in which case my question doesn't have the kind of answer I seek! As a for instance, say you were in a pub and someone said, 'The comaprators in the 555 are 741s, aren't they.?' You would reply, No they're not, they're 631s (or 456s or 2134s or whatever they are). This is not a homework question! It's just a curiosity question. Thanks!

There a thousands of variants of the 555, made by every manufacturer imaginable. Any one of them can have different components internally so long as the pinout doesn't change. There's low power variants, military variants...etc.

There's a big list on the wikipedia page I posted last time.

Some are low power.

Thanks fungus! Now it makes better sense what's going on.

s, and even now I know very little. So I'm just starting out! Some of the r= esponses to my origiinal post were helpful, but I still haven't been able t= o 'name' the comparators in the 555. All of the diagrams just seem to say '= comparator 1' or 'comparator 2'. Those that suggest I look at the data shee= t are assuming I would know one end of a data sheet from the other. New que= stion: are the comparators in the 555 both 741s. If not, what 'number' is g= iven to them, if at all? Maybe they don't have a number. Maybe the the only= place you find these particular types of comparator are in the 555 in whic= h case my question doesn't have the kind of answer I seek! As a for instanc= e, say you were in a pub and someone said, 'The comaprators in the 555 are =

741s, aren't they.?' You would reply, No they're not, they're 631s (or 456s= or 2134s or whatever they are). This is not a homework question! It's just= a curiosity question. Thanks!

Thanks fungus, now it makes a bit more sense!

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The comparators in a 555 are not commercially available models which
are assembled with other components to make a 555.

A 555 is an integrated circuit with all of the circuit elements and
connections fabricated from/on a tiny slice of silicon.

http://en.wikipedia.org/wiki/Semiconductor_device_fabrication

enig165BE7F593FFA3C4CC237EB2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

There doesn't need to be a name or model number. A comparator is just a functional block of components. You wouldn't name an amplifier section or a voltage divider section or an input section unless they were discrete components, sourced elsewhere.

mike

schreef in bericht news: snipped-for-privacy@n13g2000vby.googlegroups.com...

Well, with this explanation your question makes much more sense. Although many of us are in electronics for years, no one pretends to be a magician. Some may have crystal balls but they are always out of order :)

As for the question, a comparator is not an electronic device but an electronic circuit. You can build one with devices like transistors, (or even tubes) resistors and so on. A lot of comparators are designed to be placed in a chip. You can find components (packages) with up to four (FAIK) comparators in one chip. They are given a partnumber and called "comparators" as that are the circuits they contain.

The design of the 555 contains two comparators but only as parts of a more comprehensive circuit. So they are just the comparators (circuits) inside the 555 and have no other name or partnumber.

petrus bitbyter

555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order?

Yes, they are standard as far as being supported through out different venders if that is what you mean?

Also, 555 timers have and are used for comparator with latching function etc..

The trigger input acts on a sink signal or, any signal that is 1/3 or less in voltage of the rail.

THe threshold input works with souring voltage and that will trigger when the signal is 2/3 or more of the VCC(rail).

THe trigger will turn on the output when it gets active, which is when any signal at the trigger is 1/3 or less at that input. THis input is a PNP input so you actually need a sink related signal that is below 1/3 Vcc to trip it.

The threshold is a NPN input and only acts with source signals..

when Threshold is activated the discharge output pulls to common (open collector NPN)..

This gives you a number of things you can do with it..

I've used the 555 as a comparator in apps where a latching trigger was required due to an event and those inputs as comparators work very well for that.

Jamie

555. What are these two comparators? Are they 'standard'? What are they called? If you wanted a make an IC 555 what comparator would you order? Thanks, DAM

Yup, the Trigger and Threshold inputs are the comparators and they are set internally at 1/3 and 2/3 voltage..

Jamie