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

Thread Starter

sharkbait99

Joined May 11, 2019
5
Hi, I'm trying to build a simple delay circuit using a 555 timer in a monostable config, same as this one
The problem I'm having is every time power is applied to the circuit the 555 chip immediately blows up. Once literally (when using a 12v ac power brick) and once caught fire (running off a 12v car battery)
When using a 6v battery pack powered by AAA batteries the circuit works fine. But I need it to run off a 12v power source. I've been using 16v 4.7uf tantalum caps but then tried 4.7uf 50v electrolytic caps and it still blows. Resistor is 10m ohm.

Do I need to add some sort of power filter or a diode when running the 555 off 12v?
 

jpanhalt

Joined Jan 18, 2008
8,475
There are two versions of the "555". The NE555 in the video is rated for 18V, the low voltage CMOS version, e.g., TLC555, rated at only 6 V. Which version did you use?
 

Thread Starter

sharkbait99

Joined May 11, 2019
5

here's what I've got. I've got it soldered onto a perfboard and I've checked for shorts etc.

markings say ne555p 93m dn1719 Im pretty sure thats the higher voltage one. acording to the net it should work at 16v
 
Last edited by a moderator:

Thread Starter

sharkbait99

Joined May 11, 2019
5
ebay for the 555. local electronics store for everything else. I was thinking of buying a 555 localy to test. But local they are $2.50each compared to ebays $4 for 10 and i need 12 so its a major price difference. I might just buy 1 and see if it blows up.

this is the resistor im using. https://www.jaycar.com.au/10m-ohm-0-5-watt-metal-film-resistors-pack-of-8/p/RR0660

It works as far as expected on 6v for delay on time according to the online 555 delay timer calculators. barring capacitor tolerances. Which is why i went for the tantalum cap.

I've got it hooked up to the output of a 12v 24h programmable timer just one of the ebay cheapies similar to eBay auction: #192742533526 I haven't tested it straight from the car battery yet as the last one caught fire melting the dip socket. So i have to re solder it tomorrow.

I've also tested for surge on voltage with a normal multimeter. I dont see any spike, but im not sure if the multimemter would catch it if its to fast?
 

jpanhalt

Joined Jan 18, 2008
8,475
Connect pins 4&8. That's all. Then apply 12 volts to the proper pins (1 & 8). If it gets hot or "burns up" , you probably have a fake.
 

Thread Starter

sharkbait99

Joined May 11, 2019
5
Connect pins 4&8. That's all. Then apply 12 volts to the proper pins (1 & 8). If it gets hot or "burns up" , you probably have a fake.
So, i just tried that. Nothing happens. No fire, no exploding. so looks like the 555s should be good? Are their 2 pins I can measure voltage on in that config to confirm its working?
 

SamR

Joined Mar 19, 2019
1,626
12v ac power brick
Please tell me you didn't try to power it with 12VAC. TI rates it for up to 16VDC and MAX 18VDC so you should have no problems from a 12V car battery. It does have an output limit of 225mA so you may need a switching transistor on the output. You said you needed 12 chips so I assume this is not just for your own use? I buy Chinese chips for my own experiments, but if my reputation is in on it's reliability I would use a well know reliable source and pay more to protect myself. I also tend to use a trimmer potentiometer to tweak the timing to as close to the design value as possible if necessary.
 

Thread Starter

sharkbait99

Joined May 11, 2019
5
Its driving a 200ma load. But its still blowing immediately before the output pins even go high. So I doubt its the load thats killing it.
I ran it off a car battery and a 12v ac to dc power brick (laptop charger style with an adjustable voltage)
I also killed 2 chips attempting to solder directly onto them. I never had the iron on it for more than a few seconds, I thought they were pretty hardy chips? Or is it pretty easy to kill them with the iron?
I'm leaning towards having faulty chips, but I will have to confirm once the reputable local parts store opens on monday.
 

SamR

Joined Mar 19, 2019
1,626
I never solder chips. I always use a socket for them and never solder a socket with the chip in it. Where are you located? Australia? Arrow has worldwide sales but not sure about Australia. Or even Amazon or eBay... I buy cheap stuff from AliExpress and sometimes it bites me. Especially chips.
 

Daniel Sala

Joined May 28, 2015
60
Hi,

I'm no expert. You may find there's a "huge" current spike at power-up that a tester won't catch. If you don't have a decent oscilloscope (I don't either, mine's pretty rubbishy, all things considered), you could perhaps simulate it in LTSpice or TINA-TI or whatever simulator and get an idea of what happens at power-up and how battery/supply resistance could affect power-up behaviour. I would suggest a LPF(RC combination) to pin 8 to slow down turn on but I'm not sure that would eliminate a current spike but at least the spike would be for the capacitor and not the 555, I think.

Also, despite what you say about no output at power-up, I'd avoid running any 555 at 200mA, a little derating is never amiss, think of it like a transistors SOA chart - you can, but you probably shouldn't. I wouldn't drive a car at full speed just because it can do so. That's just my opinion.

Also, I'm missing or misunderstanding something here: An optimistic 12V output/0R10 = 1,200A?! Puzzled... Is that meant to be milli- or Mega-? Where is that 10 milli-/MegaOhm resistor in the circuit, please?
 

dendad

Joined Feb 20, 2016
3,254
As others have asked, please post a circuit of your aplication.
And, if you want 200mA from a 555, that could be your fire. On 6V, the output current to your load will be less, if the circuit is just the same, and on 12V, bang!
You need to drive a FET ot transistor from thw 555, not a 200mA load directly.

Do you have a multimeter?

I too am in Oz, a couple hours North of Melbourne.
 

Daniel Sala

Joined May 28, 2015
60
Hi,

As dendad has said, power dissipation may be (way) too high. 12V*0.2A = 2.4W. You might get away with a very brief millisecond-long pulse with a long off time at that wattage without it burning.

SA/SE/NE555 datasheet doesn't specify, just gives the formula to calculate max. PD which I doubt you'll want to have to do in all fairness.
LMC555 (CMOS timer with maximum output current of 100mA) claims ~1.2W for PDIP and 740mW for SOIC at 25ºC.
LM555 (basically, this part named replaces the parts named: SA/SE/NE555s) says 1180mW maximum PD for the PDIP and the SOIC.
 
As dendad has said, power dissipation may be (way) too high. 12V*0.2A = 2.4W.
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.
 
Top