555 timer keeps blowing up.

[Screech]

for you Kev.

 

[Kane2oo2]

urgh
ive made the timer circuit and it makes an led flash ..right....well if i replace the led with a transistorand then place the led before the collector the led no longer flashes....it just stays on constantly....
i was using a led to test before i use the coil!

any ideas?

 

[jonathand1000]

Referring back to the start of this thread, do the resistors *have* to be at least 5k? Obviously, I don't think they should be 0 as maximum discharge current is 200mA (? I think) and the comparators might blow up or something (again a guess...but I guess it could be dangerous) but I have sucessfully used 555s in the past with other values, eg 1k. is this bad?

Oh - and can someone explain to me what a schottky diode is?

thanks,
Jon

 

[Optikon]

The capacitors on the IC's are for bypassing purposes. Place on the IC supply pins and close to the chip itself. It is a good practice to do this. Use a high quality ceramic type and make sure the leads are VERY short. if you have just a little bit of inductance in that path due to long leads, you will completely defeat the bypassing function and have a worthless part in your design. I would do it here to help shunt some of the high voltage spikes that will invariable still make it back to your power supply via parasitic paths.. I would make sure the capacitor is rated for several thousand volts (easy to achieve with ceramic types)

 

[Screech]

here Kev.
pin 3 of 555 timer goes to "b"(binary input of transistor).
"c"of transistor goes to coil.
"e" of transistor goes to earth.
I can't make it any easier than that.
good luck.

 

[olorin]

Kane2002

For better understanding of what you are doing....
You are replacing the coil first with an led and it worked fine, and it should.
Then 2nd you replaced the led with another transistor and placed the led on the collector side of the transistor. This would make 2 transistors, right?

If this is correct my question then is this where are you connecting the base "B" side of this new transistor?

Think of the transistor as a switch completeley "on" or completeley "off". This is controlled by the current flowing through the base,oh and to some degree beta. It sounds like the current flowing through the base is keeping the transistor completeley on, which is keeping your led constantly on.

Olo

 

[olorin]

Kane2002

For better understanding of what you are doing....
You are replacing the coil first with an led and it worked fine, and it should.
Then 2nd you replaced the led with another transistor and placed the led on the collector side of the transistor. This would make 2 transistors, right?

If this is correct my question then is this where are you connecting the base "B" side of this new transistor?

Think of the transistor as a switch completeley "on" or completeley "off". This is controlled by the current flowing through the base,oh and to some degree beta. It sounds like the current flowing through the base is keeping the transistor completeley on, which is keeping your led constantly on.

Olo

 

[olorin]

oops sorry for the double post!

Olo

 

[Screech]

you can say that again.

 

[Kane2oo2]

Then 2nd you replaced the led with another transistor and placed the led on the collector side of the transistor. This would make 2 transistors, right?

not quite ...seems i didnt explain it clearly ....i had an led connected straight to the output of the 555 and then replaced this led with the transistor and put the led across the collector!

 

[olorin]

kane2002

Aaaah, ok that is better. Does the LED dim at all or is constantly the same brightness?

Sorry screech, I was trying to up my number of posts :lol:

Olo

 

[Kane2oo2]

it is still the same brightness ....which i thought was strange

but if i up the voltage then the LED jus dims (not flashing - prob because too much and so overloading LED)

Kane