Hi guys,

I built this simple little circuit which is powered with a 12vDC power supply.
But when I connect it up (without anything connected to the output) the 555 timer seems to be getting very hot.
Anyone know the reason?

 

Maybe the chip is in backwards, or something is mis-wired?

 

Likely a wiring error.

 

That and double-check your wiring. Does it work? Try using another one if all is correct and still getting hot. It shouldn't. The only reason would be too much current draw on the out pin 3 and from the schematic that doesn't seem to be the issue. Is it possible that you are using a CMOS version @ 12V?

 

Why not place the LED across the Mosfet load?
Replace with a 10k gate to GND.
Max.

 

What is the full part number of the IC?

 

Did ebay (or AliExpress or another Chinese online department store) send you a fake 555 IC?
I buy genuine Name-brand electronic parts from Digikey.

 

Maybe the chip is in backwards, or something is mis-wired?

Likely a wiring error.

No, it was working ok but then it failed and started to get hot.

Why not place the LED across the Mosfet load?
Replace with a 10k gate to GND.
Max.

I removed the MOSFET but it was still getting hot.

What is the full part number of the IC?

Did ebay (or AliExpress or another Chinese online department store) send you a fake 555 IC?

Not sure, I have had these 555's for several years, I am unsure where they came from.
Here is a photo of the 555.. Is it possible to identify if it's fake?

 

Deleted.

 

NE555P is the bipolar version. It can operate on supply voltages from 4.5V to 16V.
Have you tried replacing the IC with another NE555P?

 

? is your pin7 (discharge) floating as shown in the #1 (?pull it down) ... ups it's the 6 that shouldn't be floating = my bad
. . .
Option.2 :: the gate charge may cause current spikes over the 1 Ampere try a series resistor from pin-3 with the value around 60Ω or greater ... the Drain Gate capacity may also contribute to this (heating) so you may consider the value of 120Ω or greater

 

Hello,

There is no problem with pin 7 not being connected.
The circuit shown is a hysteretic oscillator:
https://www.allaboutcircuits.com/textbook/experiments/chpt-8/555-hysteretic-oscillator/

Perhaps lowering the value of the 220K will help, as the circuit is VERY slow now.



Bertus

 

NE555P is the bipolar version. It can operate on supply voltages from 4.5V to 16V.
Have you tried replacing the IC with another NE555P?

No, I haven't replaced the 555 IC and could be difficult because I didn't use a IC socket. I will make a new circuit board and try again.

There is no problem with pin 7 not being connected.
The circuit shown is a hysteretic oscillator:
https://www.allaboutcircuits.com/textbook/experiments/chpt-8/555-hysteretic-oscillator/

Perhaps lowering the value of the 220K will help, as the circuit is VERY slow now.

View attachment 215405

Bertus

True, as Bertus said, there is no problem with pin 7 not being connected.
My circuit has a 50% duty cycle with an equal mark/space ratio.
(Picture courtesy of Electronics Tutorials website)



Total time (T) = 2 x 0.693 x R x C
So in my circuit the total cycle time is T and so..
T = 2 x 0.693 x 220,000 x 0.0001
T = 1.386 x 220,000 x 0.0001
T = 1.386 x 22
T = 30.492 seconds
Ie. The output cycles about 30.492 seconds (LED is 15.246 off and 15.246 on).
I have disconnected the MOSFET but does not seem to make any difference..(the 555 is still getting hot).

I would not have thought lowering the resistor value would affect the 555 operation.

 

Breadboard your circuit first. This will allow you to make changes easily and test the 555-timer IC.

 

Hello,

Is the output of the 555 alternating with the 15 seconds interval?

Bertus

 

Is the output of the 555 alternating with the 15 seconds interval?

Bertus

Yes, it did until for some reason it suddenly it started getting warm then hot I don't quite understand why it's getting hot

 

I don't quite understand why it's getting hot

Try removing the FET from the circuit and check the 680 ohm resistor.
SG

 

Try removing the FET from the circuit and check the 680 ohm resistor.
SG

I have done this. When I connect the 12vDC supply the LED lights but after 5-7 seconds the 555 gets very hot.

I've decided I'm going to start again and try it on a breadboard first then if it's ok I will make a new board and put an IC socket on the board.

 

My solder sucker can easily "slurp" the solder off a solder joint in one second of time. Then a defective IC is quickly replaced.
Did you measure your 12V? I have a 9V wall wart that produces 18VDC when it has no load so yours might also have a voltage too high for the 555 when it does not have its rated load.

 

My solder sucker can easily "slurp" the solder off a solder joint in one second of time. Then a defective IC is quickly replaced.
Did you measure your 12V? I have a 9V wall wart that produces 18VDC when it has no load so yours might also have a voltage too high for the 555 when it does not have its rated load.

I'm seriously not going to bother replacing the 555. I could remove the capacitor and use it again but that's about it. It's only a simple circuit but not sure why it was working but now isn't.
I'm using a stabilised 12vDC power supply.