Specifications

2.3.5 LM317 Adjustable Voltage Regulator

The LM317 offers a voltage regulation option unlike the ones previously looked

at. It is a package that can output a regulated voltage from 1.25Vdc to 37Vdc,

adjustable by applying a reference voltage to the third lead. It also has a

maximum current output of 1.5A, which should be sufficient for the purposes of

the other components on both the portable and car-based units.

The primary advantage of this unit is that it is a compact and complete package.

It has the ability to accept a wide variety of positive input voltages and output a

steady voltage. It also offers short circuit protection at the output leads, as well as

several other important protections. In addition, it is low cost ($1.95), and

compact to a sufficient degree.

The disadvantages are small. Reliability is a concern, as any failure cannot be

repaired as easily as with earlier circuits. With this unit, it does essentially act as

a black box – requiring replacement of the entire unit. However, due to cost, this

is not a large disadvantage. Another disadvantage is the ability to adjust the

voltage output. While this could be seen as an advantage, it becomes a

disadvantage for the purposes of our project due to the addition of cost and

complexity. A heatsink may be required depending on the eventual power

requirements of the entire circuit.

2.3.6 LD1117V33 3.3Vdc Voltage Regulator

This is very similar to the LM317 previously discussed, with the exception of a

fixed output voltage. No built-in adjustable output is available with this package. It

is capable of accepting input voltages up to 15Vdc. The maximum output current

is 800mA. Given the fact that most likely, logic components will be supplied by

this regulator, an 800mA maximum current output should suffice. If necessary, a

heatsink may be used to increase reliability for the regulator under heavy load.

It offers all the advantages of the LM317 while offering a lower cost ($0.88) due

to the lack of built-in output voltage adjustability. However, the The LD1117

series offers a variety of fixed voltages. The V33 is the 3.3Vdc version. The

temperature tolerance is also acceptable at -40°C to 150°C for storage (a likely

scenario as the device idles in its environment before being used). The circuit to

implement the device is shown in Figure 2.2.6-1.