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555 timer circuit

Dear All,

I have a 555 astable timer circuit as shown in the diagram.  Diode D2 is heating up significantly.  Ccan anyone offer any advice or mitigation for this issue?  Thanks in advance.


0 Votes


January 28, 2020 11:34

I am using 1K for both Ra and Rb and 100uF for C

0 Votes

January 28, 2020 11:35

What are the values you have used for RA and RB?
And C?
Even though D2 is getting hot is it functioning correctly?
My thoughts are RB is too low a value (assuming wired correctly). You may have to reduce the value of C and increase RA and RB.

0 Votes

January 28, 2020 11:34

@Boss I am using 10k resistors for Ra and Rb, C = 100uF.

January 29, 2020 10:15

@SalParadise Assuming the circuit is wired correctly, check the value of Rb with a meter or if you do not have one and it is on a breadboard try swapping Ra and Rb to see if that changes anything. You could try swapping the diodes after the above test. Do check the wiring though as I would not expect D2 to get significantly hot, make sure the resistor is in series and D2 is not going directly from pin 6 to pin 7. Also check it is not D1 getting 'significantly' hot, if it is it is likely to the wrong way round.

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