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Anik , 03-28-2024, 06:09 AM

I was made a astable multivibrator in breadboard, it was working. I was trying to make 1Hz. The bread board set up was working fine. But when I made it on PCB with SMD components then its speed increased too much. I think now its not in 1Hz. the value of the capacitor I used same.

Robert Feranec , 03-28-2024, 07:45 AM

do you have the 100k resistors also on your breadboard? r105 and r49

Anik , 03-28-2024, 10:41 AM

no sir, its just for the mosfet, I just used the led directly with the astable multivibrator. and on the PCB I have used the mosfet with R105 and R49 for powering up the output.
maybe its the discharging problem??

Robert Feranec , 03-28-2024, 11:27 AM

so, your circuit on the breadboard is different from your PCB. find what makes the difference

Anik , 03-28-2024, 11:28 AM

I will try to remove the 100K resistor from the gate pulll down.

QDrives , 03-28-2024, 04:12 PM

C1222 and C123 are class 2 ceramic capacitors on the PCB and electrolytic on the breadboard. The DC+AC bias changes the capacitance. Replace them with electrolytic or tantalum to solve your problem. Or make sure that the DC bias change will not be significant for the supplied voltage (ie. a 1210 package 100V capacitor and not a 16V 0603)

Anik , 03-28-2024, 04:14 PM

Ok sir, I will redesign the board again.
Thank you

QDrives , 03-29-2024, 04:34 PM

Test it before you do the redesign. It is easy. Take off the ceramic caps and solder the leads of the electrolytic on them. Test. If that works, then think of the new (correct) capacitors to use.

Anik , 03-30-2024, 04:51 PM

Sure sir,
Thank you.

QDrives , 03-30-2024, 09:32 PM

Le us know if that, or something else was the problem. Good luck.