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IC heating up!!

Discussion in 'General Electronics Discussion' started by paddy, Jun 29, 2013.

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  1. paddy

    paddy

    81
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    Sep 11, 2012
    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
     

    Attached Files:

  2. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Don't apply input signal to output pin2 of inverter IC. Your shorting output of 40106 pin2 when input signal goes hi or lo.

    Your NE555 circuit looks ok. But you did not place current limit resistor ( 1.2K) in series with LED. Causing it to overheat and also TR23. Place 1.2K resistor in series w/ LED as shown in my edited schematic diagram.
     

    Attached Files:

  3. paddy

    paddy

    81
    0
    Sep 11, 2012
    Hi Rleo6965,

    Thanks for your prompt reply.

    I removed pin no.2 from circuit and pin no.1 connected to ground.

    And I have drawn the schematic wrong. The current limiting resistor is placed in between supply and LED.

    But still there is no effect. Both the IC's are heating.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Firstly, ensure all the inputs of the 40106 are tied to valid logic levels (ground or Vcc is fine if they're unused).

    You are discharging the 10uF capacitor through the 555 without a current limiting resistor. You need a resistor between the cap and pin 7.

    I'm not sure that either of these are the real reason.

    How hot are the chips getting?

    Can you measure the current draw from the 12 volt supply to the 40106 and to the 555 and tell us what they are?

    Where does the 12V come from? Is it really 12V? Is it clean (it's not from a car electrical system for instance)?
     
  5. paddy

    paddy

    81
    0
    Sep 11, 2012
    Thanks a lot steve for your kind suggestions!!!!

    The unused inputs of 40106 are in floating condition. I have not tied them to ground.

    The 12 V supply is from SMPS.

    I will check out with your suggestions and update you once done.

    Thanks,
    Paddy
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    What voltage is the VCC rail? The 40106 and 555 are only specified up to 15V and will overheat if VCC is more than that. It's best to use 12V for safety.

    Your input signal seems to be connected to the output of the 40106 gate; it needs to be connected to the input.

    It's not good practice to drive a CMOS input negative; this will happen with the 10 uF / 100k arrangement that drives pin 3, when pin 2 goes low after previously being high. There are various fixes; a simple one would be to insert a resistor (e.g. 10k) between the junction of the capacitor and resistor, and pin 3 of the 40106.

    The inputs of the remaining four gates in the 40106 are not shown. Their inputs should be tied to 0V or VCC (it doesn't matter which). These are pins 5, 9, 11 and 13.

    The 1N4148 between pin 3 and the 1k resistor that feeds the base of TR22 isn't needed; you can connect that resistor straight to pin 3.

    LED9 and the 1.2k resistor aren't connected properly. The relay coil and D14 should connect directly to the
    +12V supply, not through the resistor; the resistor should be in series with LED9 only.
     
  7. paddy

    paddy

    81
    0
    Sep 11, 2012
    Hi,
    VCC is 12V for both the IC's.

    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.
     
  8. davenn

    davenn Moderator

    13,833
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    Sep 5, 2009
    OK ... time to show us some pix of your circuit sharp and well lit
    so it is easy to trace your wiring

    Dave
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    An input signal with a swing of 0V~7V will not reliably trigger a 40106 that's running from 12V.

    A simple voltage offset (which can be implemented with two resistors, or a zener diode and a resistor) could fix this, but whether it will work or not depends on the characteristics of the signal source.

    What is driving the input to the circuit?

    Also, as Dave said, please show us some sharp, well-lit pictures of your circuit.
     
  10. paddy

    paddy

    81
    0
    Sep 11, 2012
    Hi,

    Please find attached pics of circuit.

    The relay should be on for 25 seconds when there is alarm condition.

    So When the alarm condition is detected, the output of IC 4071(OR gate) goes high which is given to resistor capacitor network and then to NOT gate to generate a pulse for 555 timer IC.

    Earlier when the pin no.2 and pin no.3 of 40106 are shorted and at that time I am getting input swing of 0V-7V.

    Now I removed the pin no.2 from circuit and getting proper pulse of 12V at pin no.3. Circuit is working fine, only there is an issue of heating.

    Thanks,
    paddy
     

    Attached Files:

  11. davenn

    davenn Moderator

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    Sep 5, 2009
    ohhh dear ohhh dear

    you NEVER at any time told us all that this was part of a much larger and more complex commercial board

    I really wish people would give all the info up front. It saves so much time and "beating around the bush"

    So with the 555 unplugged, what is the voltage between pin 1 (0V) and pins 4 and 8 of the 555 socket ?
    what is the resistance on the socket between pin1 and pin 3 ie. 0V rail and the output pin ?

    and please show us an underside pic of the board in the same area

    Dave
     
  12. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    I hope that the design engineer did not forget to place traces on unused input pin of 40106. Can you post pcb side of the board. Showing traces on 40106. ic 40106 heats up if damage by static disharged.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    And does this occur on all boards, or is just this one affected?

    Or maybe just some revisions affected?

    And does it operate correctly despite the heating issue?
     
  14. paddy

    paddy

    81
    0
    Sep 11, 2012
    I am really sorry for the incomplete info.

    With the IC 555 unplugged, the voltage on pin no. 4 and 8 is 12V with respect to ground an resistance between pin no. 3 and pin no. 1 is infinite.

    This problem is occurring on all boards, but the circuit working correctly.

    Please find attached images.

    Thanks,
    paddy
     

    Attached Files:

  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You say that, but you still haven't explained very much about the situation.

    Have you heard the lateral thinking exercise about the man who lives on the 12th floor of an apartment block, and takes the elevator every morning, but every evening, takes the elevator to the 10th floor and takes the stairs for the last two floors, unless it was raining?

    Trying to figure out the full story can be fun if there's a clever twist, and if you can ask questions and receive quick replies. It isn't so much fun when there's no twist, and each question requires a separate post and takes a day or two to be answered, so one's train of thought cannot flow properly.

    That's how it feels with some problem descriptions, such as this one.

    We are not mind-readers. We know a lot about electronics, but we don't know anything about your specific situation.

    You need to imagine that we are strangers who are seeing your boards for the first time. You need to introduce the whole problem situation to us, starting from the beginning.

    I'm going to ask you some more questions. These are all starting points. Don't just give simple minimal answers to them; use them as cues about the sort of information you haven't given us yet, and fill out the answers with useful information.

    Are you sure that the board is exactly the same as the partial schematic diagram you posted? Is it possible there is a layout error, or a track that goes off somewhere else that you haven't told us about?

    Could it be faulty or damaged components? Have you replaced the 40106 and the 555 recently?

    What does this board do?

    What is it from?

    Do you know who designed it?

    How many of these boards do you have?

    Why do you have more than one board?

    When did the problem first occur?

    Does the WHOLE board still work perfectly, even though the ICs are getting hot? (You said yes in your first post, but I ask again to be sure.)

    Point from Steve that you didn't respond to: You are discharging the 10uF capacitor through the 555 without a current limiting resistor. You need a resistor between the cap and pin 7.

    Question from Steve that you didn't answer: How hot are the chips getting? (Tell us how long you can hold your finger on them, for example.)

    Question from Steve that you didn't answer: Can you measure the current draw from the 12 volt supply to the 40106 and to the 555 and tell us what they are? (Lift pin 8 out of the socket and put a multimeter on 200 milliamps range between the socket pin and the IC pin.)

    Point from me that you didn't respond do: It's not good practice to drive a CMOS input negative; this will happen with the 10 uF / 100k arrangement that drives pin 3, when pin 2 goes low after previously being high. There are various fixes; a simple one would be to insert a resistor (e.g. 10k) between the junction of the capacitor and resistor, and pin 3 of the 40106.

    Please imagine you're showing this board to someone who has never seen it before, and tell us everything about it that might be relevant.
     
  16. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    It looks like that unused input pin 1,5,9,11 and 13 have no connection to GND and VCC for static protection. Big mistake by the manufacturer.

    You can confirm the input pin of 40106 ic socket if connected to GND or VCC using Ohmmeter.Remove 40106 from the ic socket and test input pins if connected to GND and VCC using Ohmmeter. Place Black probe to GND and use RED probe to test pins 1,3,5,9,11 and 13 on ic socket. PIN 3 must read high resistance because its in use. Other pins must be low ohms if connected to ground. If its reads in megohm then its not connected to ground and therefore not protected.

    You must place wire on all unused input pin to either to GND or VCC to avoid damaged again for 40106.

    I'm still puzzled why the NE555 heating up. Replaced the 2 ic with new and test observe again.
     
    Last edited: Jul 3, 2013
  17. paddy

    paddy

    81
    0
    Sep 11, 2012
    Yes the board is exactly same as the schematic diagram. I have checked it physically on board.

    Yes I have replaced both the IC's. This problem is occurring on almost every board. So I don't think this is because of faulty component.

    This device accepts 4-20 mA signal from 8 different channels and displays on seven segment display.
    There are two different alarm levels set in the device. When process value rises above second alarm level for any channel, the output of OR gate (IC 4071) goes high(12 V). These 12 V signal is given to RC network which generates a pulse and then the pulse is inverted by IC 40106 which is connected to Trigger pin of IC 555 which turns on the relay for 25 seconds.

    No.This board is new to me and I found this problem during testing.

    I guess this problem exist from beginning but ignored as it is not affecting the circuit functionality.

    The complete board works perfectly in spite of this issue.

    I have placed 1K resistor in between pin no.7 and capacitor.

    Earlier the IC's are heating heavily.But now after connecting unused pins of 40106 to ground, the heating is reduced to great extent. But still it is not completely resolved.

    Current drawn from 12 volt supply to 555 is 8mA and for 40106 multimeter showing 0 mA. I have checked it on pin no.14 of 40106 and socket pin.

    As I mentioned earlier I have disconnected the pin no.2 of 40106 from the circuit. And also I have placed a 10K resistor between pin no.3 and junction of resistor and capacitor.

    thanks,paddy
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If the current to the 40106 is close to zero and the device is still heating up then my suspicion is that an input or an output is connected to a voltage higher than the Vcc for the chip.

    The same may be true for the 555.

    Measure the voltage between the Vcc pin on each chip and all other pins. Does any show a voltage higher than the Vcc pin?
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You still haven't given us a full and detailed introduction to your situation. In other words, tell us the FULL STORY. I can't ask the right questions because I don't know what to ask. You need to start from the beginning and explain the whole situation.

    I'll try one more time to work from your partial information.

    You said the board is new to you, and you found the problem during testing. Why are you testing these boards? Are you working for the company that manufactures them? Can you get a full schematic diagram? Why are there so many design errors on the board?

    We have identified several design errors with this board:

    1. 40106 pin 2 (output) fighting with the output from the 4071;
    2. 40106 input pins for unused devices were not grounded;
    3. 555 pin 7 should have a current limiting resistor;
    4. 40106 pin 3 should have a current limiting resistor.

    You have been patching the boards to fix these errors, right?

    What is your role? Are you testing these boards as part of a production process?

    You say with these corrections the heating is reduced but is "not completely resolved". How hot are the ICs getting now? Can you measure their temperatures?

    The current consumption figures you've given are reasonable for both ICs. The 555 is supposed to draw some current. At 8 mA and 12V it will be dissipating about 0.1W which could cause a temperature rise of as much as 10 degrees Celsius above ambient. That would be normal and acceptable. The 40106 should not be warmer than ambient temperature.
     
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I would be looking very closely at those boards where it DIDN'T occur.
     
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