Art 317 Semiconductors Dr J Parker Semiconductors In

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Art 317 Semiconductors Dr. J Parker

Art 317 Semiconductors Dr. J Parker

Semiconductors In the 20 th century, electronics developed at a huge rate. Early on

Semiconductors In the 20 th century, electronics developed at a huge rate. Early on there was a need for a device that could act as an electronic switch: that is, a current (signal) at one input would allow current to flow between two others; no current or low voltage would prevent that current flow.

Semiconductors Like this:

Semiconductors Like this:

Semiconductors This could be used to control other electronic devices. Could also be used

Semiconductors This could be used to control other electronic devices. Could also be used in computers to be a ‘bit’, or binary digit. Can be on or off, 2 states.

Semiconductors We also needed a device that could amplify a signal. A small voltage/current

Semiconductors We also needed a device that could amplify a signal. A small voltage/current at one terminal can control a much greater voltage/current between two others.

Semiconductors

Semiconductors

Semiconductors Surely you can see the importance of this device. What is it?

Semiconductors Surely you can see the importance of this device. What is it?

Semiconductors The Vacuum tube.

Semiconductors The Vacuum tube.

Semiconductors It is unlikely that we will ever need one of these archaic devices,

Semiconductors It is unlikely that we will ever need one of these archaic devices, but they allowed the development of amplifiers, radios, and computers. The creation of semiconductor devices was an effort to mimic the function of tubes, but using less power and heat, and more reliably.

Semiconductors Semiconductor diode The most common function of a diode is to allow an

Semiconductors Semiconductor diode The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). This unidirectional behavior is used to convert alternating current to direct current, and to extract modulation from radio signals in radio receivers.

Semiconductor Diode Semiconductor diode – boring theory coming up! Conductors allow current (electrons) to

Semiconductor Diode Semiconductor diode – boring theory coming up! Conductors allow current (electrons) to move through them. Insulators (non-conductors) do not allow current (electrons) to flow. A semiconductor allows some current to flow.

Semiconductor Diode boring theory – boring theory - boring Silicon is a semiconductor, has

Semiconductor Diode boring theory – boring theory - boring Silicon is a semiconductor, has 4 electrons on outer shell. Makes nice crystals. All electrons are being used, so pure silicon is nearly a perfect insulator.

Semiconductor Diode boring theory – boring theory - boring If we add a little

Semiconductor Diode boring theory – boring theory - boring If we add a little Boron (3 outer electrons) then the crystal is no longer perfect, and there are ‘holes’ every once in a while. Called doping. This material conducts a little. P-type silicon

Semiconductor Diode boring theory – boring theory - boring If we add a little

Semiconductor Diode boring theory – boring theory - boring If we add a little Phosphorus (5 outer electrons) then the crystal is no longer perfect, and there are extra electrons every once in a while. This material also conducts a little.

Semiconductor Diode boring theory – boring theory - boring Placing some P-type silicon next

Semiconductor Diode boring theory – boring theory - boring Placing some P-type silicon next to N-type creates what’s called a P-N junction. The negative electrons in the Ntype silicon get attracted to the positive terminal of the battery. The positive holes in the P-type silicon get attracted to the negative terminal of the battery. No current flows across the junction because the holes and the electrons are each moving in the wrong direction.

Semiconductor Diode boring theory – boring theory - boring Current flows in one direction

Semiconductor Diode boring theory – boring theory - boring Current flows in one direction only through the P-N junction. We have a solid state (IE no gas, as in a tube) diode. .

Semiconductor Diode So, a diode conducts current in only one direction. One important use

Semiconductor Diode So, a diode conducts current in only one direction. One important use of this is in a power supply – taking AC into DC. .

Diode Rectifier This is a rectifier. A half-wave rectifier is simplest – it simply

Diode Rectifier This is a rectifier. A half-wave rectifier is simplest – it simply forbids the –ve part of the AC. The power signal is bumpy. .

Diode Rectifier Most electronic devices want current to flow through them in only one

Diode Rectifier Most electronic devices want current to flow through them in only one direction.

Diode Rectifier This is a rectifier.

Diode Rectifier This is a rectifier.

Diode Rectifier This will prevent current from flowing backwards during the negative voltage cycle,

Diode Rectifier This will prevent current from flowing backwards during the negative voltage cycle, but does have sections of low to 0 voltage. Something called a fullwave rectifier will have a positive voltage through both cycles. It’s a bit complex.

Diode Rectifier This circuit passes positive portion of the wave during that cycle, and

Diode Rectifier This circuit passes positive portion of the wave during that cycle, and the negative wave as positive during the negative cycle.

Diode Rectifier

Diode Rectifier

Diode Rectifier

Diode Rectifier

Diode Rectifier Pretty neat. But the voltagle is still bumpy. How to smooth it

Diode Rectifier Pretty neat. But the voltagle is still bumpy. How to smooth it out? ?

Diode Rectifier Good. A capacitor. It will store energy during the voltage rise and

Diode Rectifier Good. A capacitor. It will store energy during the voltage rise and supply it during the voltage drops. Bigger caps smooth better. Electrolytics can handle more power.

Diodes are useful for many other things, including: - Receiving radio signals Providing a

Diodes are useful for many other things, including: - Receiving radio signals Providing a stable voltage (regulation) Generating light, including laser. Temperature control and heat pumps Detecting light and converting light to voltage Acting as a variable capacitance

Photo. Diodes

Photo. Diodes