Strobe Light / Police Light with 555 and 4017

Thread Starter

samuelsepfarman

Joined Oct 23, 2016
6
Strongly agree with dave.
Change Q1 and Q2 to n-channel power MOSFETs.
Delete R7 and R9
Increase R8 and R10 to 22 K each.

That fixes the circuit in terms of its output drive. Separate from that is doing whatever your LEDs require for current limiting.

ak
One more in agreement with using MOSFETs. Comment in #4 still stands.
it work with mosfet.. thanks for all your help,..

i try again my schematic (in the begininng of this thread) and just change the supply to 12v (no change to the led or transistor or anytihing), it doesn't work normally.. it blink randomly.. but when i use 9v and 3.7v, it work..
can you explain to me why this is happen??? why this circuit does't work with 12v supply???
* supply 12v from lighter jack in a car
* supply 9v and 3.7v from battery
* i use HCF4017 not CD4017 (i think it's similar)
* i am sorry for late respond..
 

Thread Starter

samuelsepfarman

Joined Oct 23, 2016
6
Was the car running when you tried this? A lot of noise on the power supply could cause your symptoms.
the engine of the car is on and park..

i am sorry, the 12v supply not only in car, i tried too with adaptor 12v (1A) (made in china, light weight, cheap) and still blink randomnly
 

wayneh

Joined Sep 9, 2010
18,133
Noise. If you want to use anything other than a battery, you'll need to design for noise. Decoupling capacitors at a minimum. (I don't see any in your schematic.) Maybe even a voltage regulator on the ICs. You could run them at 5V using a 7805. The power to the LEDs does not require filtering or regulation, just the ICs. Note that you would need logic level MOSFETs if you go down to 5V.
 

Thread Starter

samuelsepfarman

Joined Oct 23, 2016
6
Noise. If you want to use anything other than a battery, you'll need to design for noise. Decoupling capacitors at a minimum. (I don't see any in your schematic.) Maybe even a voltage regulator on the ICs. You could run them at 5V using a 7805. The power to the LEDs does not require filtering or regulation, just the ICs. Note that you would need logic level MOSFETs if you go down to 5V.
what is noise?? what the design for that??
and what is logic level MOSFETs ???

i am sorry, i am very beginner in elecronic
and english...
 

wayneh

Joined Sep 9, 2010
18,133
Noise is voltage fluctuations coming from outside your circuit (from your car) and from inside the circuit (switching of the ICs). This noise can cause unintended effects in your circuit. You can do things to reduce the fluctuation. Using a decoupling capacitor on each IC is a minimum. Search on that term at this site if you don't know what it means.

If that is not enough, there are additional options such as a low-pass filter on the power, or a voltage regulator. I think most people would choose a 5V regulator such as 7805.

But, that 5V would then be the highest voltage available for the gate of your MOSFET switch. A "logic level" MOSFET is one that can be turned fully on at 5V or less. A darlington transistor array is another low-voltage choice.

Another option would be to regulate your circuit to ~9V using a LM317 adjustable voltage regulator. You could get a little higher using a LDO (low drop out) regulator. With these higher voltages, you don't need a logic-level MOSFET.
 
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