Do yourself a favor and mount...
Do yourself a favor and mount complex circuits to printed circuit board and cut them out. Metal mint tins make great project boxes because they're often cheaper than the real things and can also serve as the ground to the chassis. Just cut a hole for the heat sink.
We apologize up front for the next part as it's a bit confusing at first. Schematics for adjustable regulators flip the pins around. But it's not random; it's actually the simplest way to show what goes where. Like the fixed-regulator schematic, it reads from left (power in) to right (power out) and from top (positive) to bottom (negative). Here's how it looks:
Complementary Transistor
Regulators typically handle 1 to 5 amps. But some applications, especially heater fans and old tube radios, can draw more than even the most powerful regulator can handle. Technically, you could combine the outputs from several regulators but the following shows a more elegant way.
The following transistor complements the regulator's voltage output, only with a lot more current capacity to back it up. Even the inexpensive 2N3055 from Radio Shack can handle 15 amps. That's enough to run a full deck of gauges and a blower motor at full speed and a tube radio at full song with power to spare. Need more output? One regulator can feed many complementary transistors for amps aplenty.
Like the others, the complementary...
Like the others, the complementary transistor has three legs but only two have dedicated connectors; the transistor's case is the third (the input). That means the case is as electrically as "hot" as the battery when in use.
For simplicity's sake we haven't used the technically correct terms for transistor connection legs but they're sort of required to explain the complementary transistor's operation. The correct term for a transistor's input is the collector. The correct term for the transistor's output is the emitter. Transistors have what's called a base leg, only until now we referred to them as ground or adjust.
These base legs serve as a sort of reference for the regulator, only instead of referencing ground, the base leg in a complementary transistor references the voltage output of the regulator's emitter (output). In other words, instead of driving a device directly with its emitter (output) leg, the regulator drives the base leg of the complementary transistor.
Complementary transistors can mount as close to or as far away from the regulator. That's a good thing as these transistors usually require fairly big heat sinks; their capacity means they can generate lots of heat if asked to drive great current loads (fans and radios, for example). So long as their collectors (inputs) connect to the battery (preferably through an ignition switch), their emitters (outputs) connect to the devices, and their bases connect to the regulator's outputs (emitters), these complementary transistors can operate just about anywhere in a vehicle.
Here's what the symbol for...
Here's what the symbol for a complementary transistor looks like. We retained the technical transistor terms collector (1), base (2), and emitter (3), which we'll explain.
The only potential issue with complementary transistors is that they don't reproduce the regulator's output exactly; they "eat" about 0.7 V. So if you connect a 6V regulator to a complementary transistor, it will emit 5.3 V.
If using an adjustable regulator, tune it to emit roughly 0.7 or more additional V. But remember that we said that you can't alter a fixed-voltage regulator's output? Well we lied; resistance in a fixed regulator's base connection (ground) will fool it into increasing its voltage output. A diode usually reduces output by 0.7 V, so routing a fixed regulator's ground through one will increase its output by the same amount. Slick, eh?
Common Resistor Values And Regulator Voltages
The formula to calculate resistor values to achieve a particular voltage is easy:
V = 1.25(1 + [R2 ÷ R1])
That said, not everybody wants to go through the motions. The following values will get you close; however, with one exception, you'll have to calculate your own values to offset the voltage loss when using a complementary resistor:
| R1 |
R2 |
Voltage |
Application |
| 1,000 |
82 |
1.35 |
Sun tachometer sending unit power |
| 1,000 |
680 |
2.1 |
Most red, orange, yellow, and green LEDs |
| 820 |
1,500 |
3.53 |
Most blue and white LEDs (but verify first) |
| 330 |
1,000 |
5.03 |
USB-powered electronics (MP3 players, phones, etc.) |
| 1,200 |
4,700 |
6.15 |
6V components (gauges, fans, and radios) |
| 220 |
1,000 |
6.9 |
6V components when using a complementary transistor |
A fixed-output regulator circuit...
A fixed-output regulator circuit with a complementary transistor isn't necessarily more complex; it just requires some forethought ... and a diode in the regulator's ground leg (the triangle and line). Nearly any diode like will work so long as it can handle the voltage. Just make sure to orient the cathode (stripe side) to the ground.
Here's a complementary transistor...
Here's a complementary transistor in a circuit with an adjustable regulator. The voltage-dropping issue still stands, but as explained the regulator's output can be compensated by the resistors.
Complementary transistors...
Complementary transistors require considerably larger heat sinks than regulators do. Old car audio amplifier housings and processor heat sinks are perfect. The transistor's case is electrically "hot" but can be isolated from the heat sink by an insulating pad.
L-Com's handy panel-mount...
L-Com's handy panel-mount USB ports are inspiration enough to learn about transistors. They're designed to be full-function ports but we can use just the red (hot) and black (ground) wires to power USB devices. These sockets are waterproof and the company offers them in every USB plug style.
For the record, ammeters can't...
For the record, ammeters can't benefit from voltage regulation as they're not voltage sensitive; they work properly on nearly any voltage. They are, however, current sensitive so don't exceed their amperage rating (a 100-amp alternator replenishing a dead battery could toast this 30-amp ammeter).