Fridgemagnet: Yea, a Zener will work. But it is much less efficient than an LM317. The adjustment pin on an LM317 only consumes 50 uA, while at least 5 mA are typically needed to bias a Zener. If this is a battery-operated device, then every milliamp is important.
Here’s an updated list:
1. Use a series resistor.
Advantages: The simplest and cheapest method. Efficiency is good (though certainly not as good as a switching converter).
Disadvantages: Very poor regulation. Will only work well when the load resistance doesn’t change and the source voltage doesn’t change.
2. Voltage divider.
Advantages: Simple – only 2 resistors needed. Better regulation than using a series resistor (#1 above).
Disadvantages: Input and output regulation can be good if you make a “stiff” voltage divider, i.e. if you choose low resistance values for the two resistors. But this has the drawback of significantly decreasing the efficiency of the circuit.
3. Shunt Zener regulator.
Advantages: Simple – only 2 components needed. Good input and output regulation. Better regulation than using a resistor-resistor voltage divider (#2 above).
Disadvantages: The Zener requires current to operate. So this solution is less efficient than using a series regulator.
4. Use 5 silicon diodes in series.
Advantages: Very simple. Very cheap. Good output regulation.
Disadvantages: No input regulation. Consumes quite a bit of board space.
5. Use a Zener diode in series.
Advantages: Very simple. Very cheap. Low parts count.
Disadvantages: No input regulation.
6. Use an adjustable voltage regulator.
Advantages: A fairly inexpensive and conventional approach. Even Radio Shack carries the LM317. Excellent input and output regulation. Temperature and over-current protection. Almost the same efficiency as using a series-regulator (#1, #4, and #5 above).
Disadvantages: You’ll need to add a couple “programming resistors,” plus a protection diode.
7. Use a 1.5 V regulator. One example is the National Semiconductor LP3992.
Advantages: Most precise; the regulator is trimmed to provide a precise 1.5 V. It does not require “programming resistors.”
Disadvantages: Availability may be a problem; you can’t buy this at Radio Shack. Input requirements are somewhat finicky. (The LP3992, for example, doesn’t want to see an input voltage above 5.2 V.) And the package might be surface mount, which means it will be difficult to solder.
8. Switched-mode boost converter.
Advantages: The most efficient approach.
Disadvantages: Complicated. High parts count. Noisy.