Did you replace the damaged 555 after adding the "snubber" diode?
Please post the schematic showing the location and polarity of the diode.

The 555 is missing the very important supply bypass capacitor as explained on the datasheet for the LM555.
An ordinary NE555 or LM555 is an old TTL device that causes a 400mA (!) supply current pulse each time the output switches. Without a supply bypass capacitor close to it then it probably oscillates at a high frequency and the millions of 400mA pulses overheats it. The messy wires on a solderless breadboard can also cause any IC to oscillate.

You should be using a Cmos 555 (LMC555, TLC555 or ICM7555) that draws an extremely low current then the resistor values can be higher and the battery will last much longer if the relay is replaced with a solid state one.

 

Probably because you're using a relay- which causes an inductive VOLTAGE spike. You need a snubber diode around your inductor.

Hi,
As a test, I also tried one more combination,
I replaced both R1 and R1 with 1K resisters keeping the capacitor the same, this gave me a High Time of about 7 seconds and Low Time of about 3.5 seconds. and then even if I connect the Relay directly between +Vcc and Pin-3 of the IC, it works fine without any issue. even without snubber diode.
But if I increase the delay, it breaks the IC.

 

Did you replace the damaged 555 after adding the "snubber" diode?
Please post the schematic showing the location and polarity of the diode.

The 555 is missing the very important supply bypass capacitor as explained on the datasheet for the LM555.
An ordinary NE555 or LM555 is an old TTL device that causes a 400mA (!) supply current pulse each time the output switches. Without a supply bypass capacitor close to it then it probably oscillates at a high frequency and the millions of 400mA pulses overheats it. The messy wires on a solderless breadboard can also cause any IC to oscillate.

You should be using a Cmos 555 (LMC555, TLC555 or ICM7555) that draws an extremely low current then the resistor values can be higher and the battery will last much longer if the relay is replaced with a solid state one.

Hi,
Thank you for the suggestion, I will try 7555 IC.

 

FWIW: I've never used this part, but there exists a software configurable '555" timer. http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555C_Spec.pdf

 

You said the '555 overheats. How warm does it get?

 

You said the '555 overheats. How warm does it get?

Hi,
It can burn finger if touched.

 

In that case if it is connected according to your schematic diagram and the component values are the same shown in the diagram, your NE555 has an internal fault. Accidents happen. Time to swap it out for a new one.

I hope you take heed to the aforementioned need for a capacitor across pins 8 and 4, and the damping diode across the relay coil before your fire up the new chip.

 

The datasheet for the CSS555 that has a built-in counter is 11 years old. I did a search at Digikey for it and the results were, "Huh?".

 

https://www.jameco.com/shop/StoreCa...Id=10001&search_type=jamecoall&freeText=cs555

http://www.customsiliconsolutions.com/products-for-ASIC-solutions/standard-IC-products.aspx

It might be available from them.

 

Jameco has CSS555.

 

I buy Name-Brand ICs. Since Digikey and I never heard of the CSS555 then I will not buy it.

 

the very discharge of the 4700µF is also adding to the thermal budget of 555 use CMOS v. of the 555 and lower capacity or external discharge NPN/MOSFET

 

Hi,
Thanks for your reply.
it overheats when it triggers, not when I power it.

That doesn’t make sense. The circuit you posted triggers when powered on.

eT

 

the very discharge of the 4700µF is also adding to the thermal budget of 555 use CMOS v. of the 555 and lower capacity or external discharge NPN/MOSFET

The discharge is done through a 1k resistor so I would not expect much heat. Being painful to the fingers suggest a more sever problem.

 

Hi,
I have attached the circuit diagram of my setup.
I want to drive the relay for about 3 seconds after about every half an hour, as per one of the online calculators I have selected components:
+VCC = 9V
R1 = 470K
R2/R4/R5 = 1K
R3 = 2.2K
C1 = 4700mf
Both Transistors are BC547 NPN Transistors.

Now, after I power the circuit, as soon as the IC triggers for the 1st time, it overheats and gets damaged. does anyone know why it happens?

Disconnect the output pin (pin 3) from the rest of the circuit. Power it on.

does it still overheat?

eT

 

the fly-back diode for the relay + perhaps "isolate" it from the 555's power of the vise versa
... check the pinout
... check the resistor values
... check the wiring
there does not seem to be any issues with the schematic
(i a bit modified to my own like ... but basically it's the same)

 

It hurts to look at your schematic. It is like looking at a solderless breadboard with a mess of wires all over the place.

 

It hurts to look at your schematic. It is like looking at a solderless breadboard with a mess of wires all over the place.

 

Try operating the circuit without the relay. I know that may seem pointless, but it will eliminate or identify the relay as the problem.
How did you measure the current? The measurement could have affected circuit parameters.

Hi,
it seems the relay was a problem.
I disconnected the relay and the circuit works properly.
I need some advice on the PNP transistor, would like to use 1 PNP transistor instead of 2 NPN's.
but I need a transistor that can handle about 400mA of collector current as I will be connecting a small water pump there.
will "2N6107" be a good choice? or should I use something else.

 

There seems to be general agreement here, and I concur, that you probably damaged the 555 when you originally had it connected to the relay.

You have been asked twice whether you have swapped out the likely damaged chip. You have not acknowledged or answered that question.

Don’t know why people are continuing to offer suggestions at this point.

Bob