555 monostable circuit catches fire/blows up at 12v but works fine at 6v

AnalogKid

Joined Aug 1, 2013
10,987
Five posts from the TS and still no schematic; that little squiggle in post #4 doesn't count. Without a real schematic, we all are just reading bead crumbs. For example, the only resistor value mentioned is 10m. If that is 10 m (milliohms), that's a problem. If it is 10 M (megohms) and the 555 is the bipolar type, that is a different problem.

Please post your schematic of your circuit. To make things easier on the free help, please assign a reference designator to each component

ak
 

Daniel Sala

Joined May 28, 2015
65
Where did you learn to calculate power? Last I checked the NE555 uses a Darlington to source current, so the voltage is more like 1.5 not 12. So 1.5 times .2 = .3 watts.

After that it gets more complicated, having to account for frequency and duty cycle.
Hi,

Ohm's Law, P = V*I. Surely the NE555 output should be 12V* 0.2A, which passes through the top half of the totempole output pair, but as you say, that's not considering on-time and off-time (frequency and duty cycle) which hasn't been clarified yet. I suppose I'm wrong and it's only VCEsat and Iout that relate to PD.
 

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AnalogKid

Joined Aug 1, 2013
10,987
I suppose I'm wrong and it's only VCEsat and Iout that relate to PD.
Correct.

Also, Ohm's Law does not cover power in any way, For that you need

Joule's Law: P = I^2 x R

or

Watt's Law: P = E^2 / R

Ohm's Law can be used to convert one into the other, but they were discovered independently.

ak
 

Daniel Sala

Joined May 28, 2015
65
Ohm's Law does not cover power in any way, For that you need

Joule's Law: P = I^2 x R

or

Watt's Law: P = E^2 / R

Ohm's Law can be used to convert one into the other, but they were discovered independently.

ak
Hi,

Not sure what you mean there. The png seems to differ in that opinion. And, as you must know, P = V * I is the same as P * I^2 x R is the same as P = E^2 / R. They all give exactly the same result.

Suggest you contact endless websites, book publishers, schools and universities and professional engineers who use the formula P = V * I and correct them, too.

I assume you were being helpful and I feel a trifle pedantic about terms, while no William Shockley or Bob Pease, I'm not exactly a newbie either. I just left one forum after three years for a couple of reasons similar to your approach to interaction.

When I design my own pulse circuits I aim to reduce duty cycle to the minimum to reduce PD and not squander I^2 * R.

Anyway, thanks all the same.

Let's see if the thread returns to the original poster and their circuit issue, if they return. Threads shouldn't be hijacked and remain focussed on the problem, I would think. Any 555 that "blows up" at 12V but not 6V clearly has a design error issue, IMO possibly the irritating power-up turn-on the 555 has, unless the reset has a little POR RC incorporated. Let's see what Sharkbait says...
 

AnalogKid

Joined Aug 1, 2013
10,987
Not sure what you mean there. The png seems to differ in that opinion. And, as you must know, P = V * I is the same as P * I^2 x R is the same as P = E^2 / R. They all give exactly the same result.

Suggest you contact endless websites, book publishers, schools and universities and professional engineers who use the formula P = V * I and correct them, too.

I assume you were being helpful and I feel a trifle pedantic about terms, while no William Shockley or Bob Pease, I'm not exactly a newbie either. I just left one forum after three years for a couple of reasons similar to your approach to interaction.
Calm down there, sparky. If you re-read my post, you will see that there is nothing inappropriate with my approach. In fact, there was no "approach" at all

The png is fine; it is the title that is in error. Ohm's Law has been around since 1827 so it's pretty well understood (it even has its own Wikipedia page, which is longer than you might think). That's 13 years before Joule was born.

I didn't say anything about the equation P = V x I; I said it is not a part of Ohm's Law. In my experience, universities know and teach Ohm's and Joule's laws as separate entities for the simple reason that they are separate entities. As for the endless websites, your are correct - they are sloppy, lazy, and incorrect - some legendarily so. Welcome to the innergoogle.

I agree it is a minor point, but technical writing has value only if it handles the details well. A *lot* of the postings on this and other fora are more experienced persons cleaning up the language of less experienced persons who come here for guidance and advice. No insults, no attitude, no "approach", just pointing out 'here is the standard way to say that', here is how to clean up your schematic', 'that part doesn't work the way you think; it works like this', etc. For an attitude check, all of the postings from all of the more prolific users are available to peruse.

ak
 

Audioguru

Joined Dec 20, 2007
11,248
With no schematic we do not know what the resistor is connected to.
The photo from Jaycar does not show 10m ohms which is 10 milli ohms (0.001) and it also does not show 10M ohms which is 10 million ohms.
Jaycar shows 56 ohms.
 

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