The only thing changing that resistor does, is decrease the current and dissipation on the zener diode. It cannot change the voltage at the electrolytic capacitor however, it can stop that diode from heating the capacitor if they are close together. With the 68 ohm resistor, the zener diode is dissipating 700 milliwatts. The 150 Ohm resistor reduces this to 280 milliwatts, a significant reduction in heat.
This is the worst case no load condition on the output of the regulated zener diode. The interesting thing with this type of power supply is as you load the supply, the more current you draw, the less current flows through the zener diode and reduces the heat. The resistor basically controls the maximum amount of output current that can be supplied, while still maintaining regulation across the zener diode.
This is the worst case no load condition on the output of the regulated zener diode. The interesting thing with this type of power supply is as you load the supply, the more current you draw, the less current flows through the zener diode and reduces the heat. The resistor basically controls the maximum amount of output current that can be supplied, while still maintaining regulation across the zener diode.
