We're all spoiled by the ready availability and ease of use of the 78XX type voltage regulators, my self included. I generally stock a wide variety of 78LXX regulators, and 78MXX., as well as the LM317 types.
When I was working on the power supply for my general coverage receiver still in development, I decided to kill an afternoon making voltage regulators the old fashioned way - with a zener diode and a pass transistor.
The very simple circuit, likely in countless textbooks, is attached along with some of my practical observations. I do not advocate using this type of circuit in place of a 78LXX circuit, but with a sample book or assortment pack of zener diodes, one can cover pretty much every regulated voltage one might ever need. This can be important for someone like me, who travels between two houses, as it enables me to make maximum use of the limited number of parts I can carry with me to my second house, where I do most of my building these days.
I used this circuit for several weeks to power a Si5351 VFO and illuminated 1602 LCD, and it works reliably as long as heat from the pass transistor is adequately dissipated. In that regard, the transistors can survive running a lot hotter than you would ordinarily think. I expect a bigger transistor would pass more current, but all I had that afternoon were puny TO-92 and SOT-23 devices. You can get several hundred milliamps out of a TO-92, so they can bridge the gap between a 78LXX and the physically larger 78XX types if space is an issue.
Comments, criticisms, and suggestions welcome.
Normally, A smallish capacitor is placed across the zener in your circuit, this performs two functions. One, it shuts up the zener "shot" noise, and two, it allows the pass transistor to act as a capacitance multiplier. It is also common to place a series diode "backwards" across the collector/emitter junction, to protect the transistor from back voltages appearing at its output. A very interesting way to increase the power handling of these simple designs is by adding an SCR to the input side, the gate is connected to the output voltage via another zener diode. Here, the SCR will only switch on if the input voltage to the series pass transistor is equal to the zener gate voltage. That means the series pass transistor will only ever see the zener voltage across it, therefore its dissipation is much reduced. This is especially useful with variable power supplies, dissipation is at maximum when the output voltage is minimum. ... this technique will keep the dissipation constant independant of input voltage level. Heres a sketch of what i describe.
As you can see, a few parts can save on a bigger heatsink.