(confession, I just dabble in 'lectrick stuff)
I need to take a 5v + pulse and make a 1-2sec + pulse from it, minimum parts count/weight/cost.
The load is a small motor; I'm guessing 1A with 4.2v. This circuit:
looks like it will work, and I can build it deadbug and heatshrink it in the control wiring.
Ignoring the load, it might work if you used a diode in series with the input pulse. They're using the /RESET input a bit unconventionally.
With the load, it's not happening. You already have 1.7V (typical) drop at only 100mA. Maybe you'll get 300mA or 400mA into the motor. You're supposed to use a series diode for inductive grounded loads (plus a flyback diode across the motor), so that would drop even more voltage. The dissipation in the 555 will be quite high but it might not fail right away with such short pulses. The motor won't get anywhere near full current. Stall current is going to be higher so unless it's almost unloaded (a fan maybe) the motor may not move at all.
Maybe a 555 switching a logic-level power MOSFET would work for you, not much more complex.
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
I don't think that the NPN transistor in the NE555 can sink anything like o ne ampere.
says +/-225mA is the absolute maximum rating, and anything over a few mA ta kes the transistor out of saturation.
I suspect you need to separate the timer function from the current driver - for wimpy currents the NE555 could be used for both jobs, but for your cur rent you more or less have to drive a biggish Darlington transistor or a lo w-on-resistance MOSFET. An NE555 can be used to do that job, but so can an y other monostable, though few are as cheap (or as nasty) as the NE555.
Adding a second transistor to the driver to make a two transistor monostabl e would probably offer the cheapest and simplest solution
but there are quite a few ways of getting wrong.
-- Bill Sloman, Sydney
Waht about just using the pulse to charge a cap, and the cap to turn on the mosfet, with a suitable bleed resistor? That's only three parts.
How about a solid state relay? They are slow... ~1ms max turn on times, but of 1 second pulses that should be OK.
George H.
The logic fet should be in the neighborhood of 2.5V switch on to drive the gate. Keep in mind this fet must act as a sink, the low side for your motor.
If you don't see enough (+) drive coming from output of the timer you can add a R from the Vcc (pin 8) over to the output to bring up the gate drive to the power supply level. The timer will simply pull it to common when the output is off.
Since you don't need any current except for the charge in the gate to turn on the gate, the pull up R is of high a value.
You can get mos fets in small packages that cover your needs, just glue it to the back of the timer after you snot the solder on it.
I'd also suspect you are using this 5 Volt pulse for making a one shot from it along with using it for power?
I can't help thinking this is some sort of devious device, I guess my amagination is working overtime.
Jamie
It's not devious at all. It's a bubble-machine, small enough to be carried by a quadcopter. The qaud I have has +, gnd, and pulse available; the bubble machine has + and gnd.
The smallest solid-state relay I saw with a quick google was 7g - too much weight.
Uh, nah! 1A is too much. add a logic level MOSFET to switch the current.
the MOSFET basically goes where the LED is.
-- \_(?)_
mosfet will get hot. heatsink adds a fourth part,
-- \_(?)_
That is about 5x its official absolute maximum rating of 200mA but you might get away with it for a while. Why not add a 2A rated transistor?
-- Regards, Martin Brown
7 grams? Here's one of many selected from digikey... I choose 2A to be safe
No weight, but I'd guess a fraction of a gram... George H.
ok, So what kind of conditioning are you trying to do?
Are you trying to extend the 5 volt pulse, shorten it or what ?
Jamie
The voltage drop across the NE555 output transistor is going to get pretty high above 200mA so the current probably won't get to 1 amp anyway - the 2A discrete transistor is much better idea.
-- Bill Sloman, Sydney
Day late and a dollar short..., as usual.
Jamie
Half-wit. It was my second contribution to the thread, and reiterated the point - made in passing in my first contribution - that the NE555's output transistor would be well out of saturation by the time you got to 1A.
Martin Brown didn't seem to have noticed ...
-- Bill Sloman, Sydney
Your posting history indicates I have "NO" wit, will you please make up your mind.
Jamie
:
minimum
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ink it in
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pretty high above 200mA so the current probably won't get to 1 amp anyway
- the 2A discrete transistor is much better idea.
he point - made in passing in my first contribution - that the NE555's out put transistor would be well out of saturation by the time you got to 1A.
The colloquial meaning of "half-wit" is that it applies to somebody who is cognitively challenged - as you certainly are. There's no implication that the wits that you have left are up to much.
Trying to extract a quantitative evaluation from an idiom - which "half-wit " certainly is - when an idiom, by definition, means something different fr om the naive interpretation of the word-cluster that forms the idiom - is p recisely the sort of dim-witted trick you pull all the time, because you do n't have the sense to know better.
-- Bill Sloman, Sydney
I wouldn't be so sure about that, at least I know how to word wrap my text so that most can read it with out scrolling horizontally, all the time!
Ever heard of the term "Too stupid to know any better"?
Jamie
You must have a pretty lame newsreader if it doesn't automatically word-wrap to the size of the window. Or maybe you haven't found the magic setting that turns it on? I use Windows Live Mail, which is pretty lame, but word-wraps with no problems.
Paul
He's the only one here that does it from what I can see. Just keeps on typing to the end of never land on the screen.
He has been told about it many times and simply ignores it, not by me but others.
The original system had a limited line length, he always ignores that and just keeps on typing.
Besides, he is never wrong about anything, even when he is contradicting himself.
Jamie
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