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[Help] 555 IC Keeps Blowing Up

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Vimal Raj

New Member
Hi, I'm new to circuits and electronics stuff, so kindly help me to solve the issue.

I'm trying to add led DRL to my car, everything is working well if I power my circuit with 9V battery, but if I connect it to car battery after 3-5 seconds it getting blown. I have no idea why it's happening, I have attached schematic for reference.Capture.jpg

Thanks.
 

ronsimpson

Well-Known Member
Most Helpful Member
Hopefully you have pins 1 and 8 connected up.
Normally there is a capacitor across the supply. (0.1uF and maybe a large cap to)
The absolute maximum voltage on the LM555 is 16.
A car voltage is 12 (more or less) when stopped.
BUT
When operating the voltage is 14.5 volts. (could be as low as 12 or as high as 18)
My guess is that the supply voltage is too high.
 

chemelec

Well-Known Member
Does Pin 1 of the 555 go to battery Negative?
You should also put a 100 Ohm Resistor Between the Pin 3 Output and the Base of the Transistor.
 

Vimal Raj

New Member
Hopefully you have pins 1 and 8 connected up.
Normally there is a capacitor across the supply. (0.1uF and maybe a large cap to)
The absolute maximum voltage on the LM555 is 16.
A car voltage is 12 (more or less) when stopped.
BUT
When operating the voltage is 14.5 volts. (could be as low as 12 or as high as 18)
My guess is that the supply voltage is too high.
Ignition was off while testing out and I tested voltage of battery it was showing around 12.45. Doubt that leds draw more current despite having transistor.
 

Vimal Raj

New Member
Does Pin 1 of the 555 go to battery Negative?
You should also put a 100 Ohm Resistor Between the Pin 3 Output and the Base of the Transistor.
Yes, I connected both ground and supply, will try out adding resister between output and npn base.
 

chemelec

Well-Known Member
What Transistor is that? A Power Type?

And it would be better if your "LED's and Resistors part of the Circuit" was connected between the Battery and Collector.
Not from the Emitter to Battery Negative.
 

alec_t

Well-Known Member
Most Helpful Member
In an auto environment there will be load-dump spikes well above 18V. Suppression components would be advisable.
 

Vimal Raj

New Member
What Transistor is that? A Power Type?

And it would be better if your "LED's and Resistors part of the Circuit" was connected between the Battery and Collector.
Not from the Emitter to Battery Negative.
I'm using 13005A, and after connecting leds in collector part, I can see the increase in power slightly. Technically emitter should produce more power with collective of base and collector but why it's other way round?
 

chemelec

Well-Known Member
I'm using 13005A, and after connecting leds in collector part, I can see the increase in power slightly. Technically emitter should produce more power with collective of base and collector but why it's other way round?
In the Emitter, It changes the Base Bias and effectiveness to fully turn on.
 

chemelec

Well-Known Member
If you Need to have the LED's to Battery Negative, than you should use a PNP Transistor.
Emitter to Supply and LED's go Collector to Battery Negative
 

chemelec

Well-Known Member
Texas Instruments, NE555 and SE555, are rated to 18 Volt
 

crutschow

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Most Helpful Member
If you Need to have the LED's to Battery Negative, than you should use a PNP Transistor.
Emitter to Supply and LED's go Collector to Battery Negative
I see no problem with using an NPN emitter follower in this application.
The LEDs already need a resistor to control the current, so if the lower voltage from the emitter follower is a problem, you just need to reduce the resistor values to compensate.
 

chemelec

Well-Known Member
Yes you can do that, But not the best way.
Probably not a Problem but it adds a bit of heating to the transistor.
 

Vimal Raj

New Member
If you Need to have the LED's to Battery Negative, than you should use a PNP Transistor.
Emitter to Supply and LED's go Collector to Battery Negative
Either case I don't get as much brightness as I connect it to battery directly, may be I should try darlington to get more gain.
 

chemelec

Well-Known Member
Better Yet, Use a Power Mosfet.

Transistors have a 0.6 Volt Drop, Collector to Emitter.
Corrected: Mosfets have a Low Resistance between the Drain to Source.
 
Last edited:

ronsimpson

Well-Known Member
Most Helpful Member
Better Yet, Use a Power Mosfet.

Transistors have a 0.6 Volt Drop, Collector to Emitter.
Mosfets have a Low Resistance between the Gate to Drain.
1) Don't use a MOSFET as a emitter follower (source follower) like in the schematic.
2) Transistors can have very low C-E voltage drop. It is common for the C-E voltage to be less than 0.6V. Maybe you are thinking about B-E voltage.
3) MOSFETs have high resistance Gate to Drain or Gate to Source. Maybe you are thinking about the resistance of D-S.
 
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