Hi Justin
The zener in your case will drop the voltage supplied to the ts7815. As you state in your quote, the zener will start to conduct only when the zener voltage is reach. This means that the supply voltage on the anode side of the zener will be 5.6V less than on the cathode side of the zener diode. With a 30V supply the 7815 will not see more than 24.6V on the input. This is done to make the headroom up to the 35V limit greater and allow for some voltage spikes, if present, without destroying the 7815.
Regarding the breakdown of the zener diode. This is a result of the power disipated in the zener. As a product of the voltage over the zener and the current through it, you should select at least a 1W zener for your design. This should support a current of up to 130 - 150mA, if necessary, but personally I would sett the limit to around 100mA continuous.
In my proposal I said the next diode(your 1N4002), should be a second zener of 30V. This would have protected the 7815 further, against both overvoltage and reversed spikes. As it is now the 1N4002 only protects against reversed voltage spikes.
Hopefully that is good enough.
Good luck.
TOK
The zener in your case will drop the voltage supplied to the ts7815. As you state in your quote, the zener will start to conduct only when the zener voltage is reach. This means that the supply voltage on the anode side of the zener will be 5.6V less than on the cathode side of the zener diode. With a 30V supply the 7815 will not see more than 24.6V on the input. This is done to make the headroom up to the 35V limit greater and allow for some voltage spikes, if present, without destroying the 7815.
Regarding the breakdown of the zener diode. This is a result of the power disipated in the zener. As a product of the voltage over the zener and the current through it, you should select at least a 1W zener for your design. This should support a current of up to 130 - 150mA, if necessary, but personally I would sett the limit to around 100mA continuous.
In my proposal I said the next diode(your 1N4002), should be a second zener of 30V. This would have protected the 7815 further, against both overvoltage and reversed spikes. As it is now the 1N4002 only protects against reversed voltage spikes.
Hopefully that is good enough.
Good luck.
TOK