0.1 Discrete components  (Page 6/6)

The diodes used in this way are power diodes, and the capacitor is usually an electrolytic or tantalum capacitor in the range of 10 to 200 µF (maybe more or less, depending on the variability and size of the load).

A second use of a diode in a power supply is to create a voltage reference. The type of diode used for this is a Zener diode. In its simplest form, the Zener diode controls the output voltage of a series pass transistor. Zener diodes generally run from about 2 V to about 200 V.

Remember that if you need a voltage reference below 2 V, using one or two signal diodes in series can be used for 0.7 V and 1.4 V, respectively. It is important on a Zener to stay within the power dissipation specification. The power can be estimated by multiplying the Zener voltage by the current load on the diode.

It is good to revisit the concept of reverse recovery time. When the AC voltage source is 50/60 Hz, a power diode generally works fine. (I first designed with a 1N4001.) But as this frequency goes up in a DC-to-DC converter, the reverse recovery time of the diodes in the rectifier bridge becomes a significant component in determining power efficiency. Depending on the power requirements of the overall circuit, a signal diode may be a better choice for the bridge.

Signals

Diodes can be used to alter the shape of a signal. They can clip a signal such that only the positive (or negative) part of the signal passes. This could be valuable when trying to capture a pulse riding on a large DC component.

Lighting

The term lighting is probably an understatement of what a diode can do in terms of creating light or capturing light. Light-emitting diodes (LEDs) have been used for years as indicator lights or display elements. They come in various colors and brightness. A whole new industry is happening using LEDs to replace conventional lights in our consumer and commercial applications.

Picking a diode for your design

Table 5 is a simple chart to give you a start on picking a diode for your design. It is separated into uses, with a couple of specifications that you need to consider. Included are a few of the key parameters for the devices.

Transistors

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is made up of semiconductor material, with at least three terminals for connection to an external circuit.

A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits [3].

Once again, I will leave theory out of this discussion, as you should already have learned it or can find many good sources with which to refresh your memory. With that said, let’s discuss how to pick the best transistor for your design.

Picking the right transistor

It is easy to get overwhelmed when picking the best transistor for your design. Table 6 is a quick chart to match your need to a device.

References

1. http://en.wikipedia.org/wiki/Inductor
2. http://en.wikipedia.org/wiki/Diode
3. http://en.wikipedia.org/wiki/Transistor