IC 555 and 40106 heating up!!

[paddy_p]

Hi,

I have a circuit in which IC555 and 40106 used as a timer (for 25 seconds delay).
Circuit is working fine, but only problem is both the IC are heating when powered on.
Please have a look and suggest.

Thanks,
Paddy

 

[nandhu015]

The circuit seems good.

What is the voltage for VCC?

 

[tpetar]

Delay circuit can be made simple only with 555 timer IC.

What power source you use SMPS ?



Best regards,
Peter

 

[paddy_p]

Thanks for the prompt reply.

I have used SMPS of 12V.

 

[E-design]

Are you feeding an signal back into the output of U1/pin2?

 

[tpetar]

Thanks for the prompt reply.

I have used SMPS of 12V.

That's what I thought, replace SMPS psu with good psu and try. Probably you have very bad designed smps psu with high spikes. Respect maximum allowed supply voltage for IC.

Try with other power source such as battery or well designe psu, all will be good 100% I bet in that! This is school example.



Best regards,
Peter

;-)

 

[betwixt]

E-design has spotted the problem, you are back-driving the first inverter stage. With it's input left floating, it's output can be at either logic state or even oscillating and you are driving another signal against it. Try connecting your input signal to pin 1 instead of pin 2 of U1.

Also, the 1.2K resistor should be in series with the LED instead of the relay coil. You should be able to increase the value of the 1K resistor in TR22 base and remove the diode completely to reduce power consumption.

Brian.

 

[paddy_p]

Thanks a lot all of you for your suggestions.

I will check out with this and update the results.

Regards,
Paddy

 

[paddy_p]

Hi,

As suggested I removed the input signal from pin no.2 of 40106 and connected all unused inputs to ground. But still no progress.

When I isolate the pin no.4 of 40106 from IC 555 then there is no heating in 40106. Only 555 getting hot.

 

[Venkadesh_M]

Are you sure you are using 555IC. the pin 2 is input to a comparator and takes nothing...........
Check for short circuit or wrong connections.....


The reason for 555 heating up is finite connect 10k instead of 1k, its a good boy and It wont heat....

 

[E-design]

I think your 555 is faulty (hence the heating) and there is a DC level on pin 2 of the 555 driving back into pin 4 of the 40106.
As mentioned make sure you are not connecting the 555 pins up wrong. It should not heat up.

 

[paddy_p]

This problem is occurring on all boards.

I have replaced 1K resistor with 10K, but no effect.

Please find attached pics of circuit board.

Thanks,
paddy

 

[betwixt]

Pictures of the board don't really help when the problem is clearly in the electrical design. Can you power it up and measure the voltages at ALL the pins of the 555 and the 40106 with respect to ground and report them back to us. Both devices should be cold so clearly current is flowing where it shouldn't, perhaps knowing the voltages will help to find the path it is taking.

Brian.

 

[Venkadesh_M]

what is the input to not gate??

- - - Updated - - -

trigger is not the problem......... it is some where else

 

[schmitt trigger]

First, congratulations!! Your boards look beautiful and really well made.

Second: NEVER, ever spend time and expense fabricating boards on a circuit which you have not breadboarded, simulated and properly debugged.

In addition to the errors pointed out by other posters,
-an input of 7 volts is not a proper logic level for a gate which is supplied from 12 volt.
-The 1N4148 diode in the output of the 555 prevents the bases from having a proper bias level when it is in the low state. With the high gain of a discrete darlington, (with no base-emmiter resistor) noise can bias it slightly on.

And this is only a small circuit section.... there could be other wiring mistakes which are not shown. As you correctly mention: "trigger is not the problem......... it is some where else"

My advice: breadboard the circuit.

 

[Venkadesh_M]

Try this not gate instead of yours.....

- - - Updated - - -

This can be used for varying input signal also.........