Looks like 100 ohms to me.With only a 10 ohm resistor in series with it,
Yes. Smoke ensues! Check that it is 100R, not 10R as marked on your diagram.What is the zener and what is its power rating? What is the recommended current through it? With only a 10 ohm resistor in series with it, it will be drawing 330 mA and the zener will be dissipating almost 3 Watts. I think you need a much higher value for the resistor.
Oh, yes! I was seeing the Ω as a 0.Yes. Smoke ensues! Check that it is 100R, not 10R as marked on your diagram.
It is good practice to design the Zener regulator to handle the full current.The load must be connected to the output end to prevent zener from getting damaged. Series resistor 10 ohm is a current limiting resistor and when high current is drawn it has to pass that current through it, thus 5-watt resistor is necessary.
Yes, according to the datasheet, maximum supply is 16V which is plenty of headroom.Why is running the 555 circuit on 12 V such a big problem that it requires this? what is the problem?
ak