Semiconductors, Esd

Semiconductors, ESD/EMI, and On-board Computers

Diode Semiconductors Semiconductors are electronic devices, usually made from silicon sand or germanium. Simple semiconductors like diodes, LEDs (light emitting diodes), and Zener diodes are usually just improved switches.

Regular diodes operate much like oneway valves for current. That is, they switch ON if the polarity of the circuit is correct, and OFF if the Polarity is reversed.

A diode could be called a “smart” switch. When it detects the correct polarity, it turns ON; and when it detects a reverse polarty, it turns OFF. It also monitors pressure- if the pressure (voltage) is not high enough it will not turn ON.

Diode Operation is Similar to a Poppet Valve.

Regular Silicon Diodes Electricity and magnetism are much alike. This is true in the case of opposites attracting and likes repelling. In the case of magnets, opposite poles attract and like poles repel. In electricity, the same thing happens – like charges repel and opposite charges attract.

Regular Silicon Diodes Inside the diode are some small positive and negative areas. Both of these areas conduct current, but at the PN junction, they are separated by a thin boundary layer.

Regular Silicon Diodes When a diode is placed in a circuit ( with a lamp or some other load also in the circuit) in the correct (forward Bias) direction,the positive side of the circuit is applied to the positive side of the diode. Also, the negative side of the circuit is applied to the negative side of the diode.

Regular Silicon Diodes Remember, like electrical charges repel eacher other. The supply Voltage charges are much stronger than the diode P and N materials. The P conductive material is repelled toward the N and the N toward the P. This causes the PN junction to become a conductor, just like turning ON a switch. How does the diode “know” to switch OFF if the polarity is reversed? The similarity is in how magnets operate.

Diode Bias - Forward Bias This shows the battery negative terminal connected to the N-type material and the battery positive terminal connected to the P-type material – is known as a forward bias connection. This is the condition necessary for current flow through a diode. Diodes conduct when 0.6 to 0.7 volts are applied.

Forward Biased Diode

Diode Bias - Reverse Bias When battery connection are reversed, the positive battery potential effectively creates a very high electrical resistance at the PN junction of the diode. This is called reverse bias and causes the diode to block current flow.

Reverse Biased Diode

Note Peak Inverse Voltage is the highest reverse bias voltage that can be applied to a diode junction before damage occurs. 

The diode will always short before going open if reverse bias voltage is exceeded.

Diodes Protect Circuits The clamping diode, protects the circuit from surge currents developed when the current flowing through an electromagnetic device is abruptly interrupted. Any coil, such as a solenoid or a rely, when energized, will set up a magnetic field, similar to that of an ignition coil. When the electrons are passing through the coil, they don’t want to

Diodes Protect Circuits The coil tries to keep them going even if the circuit is opened. As the electrons pile up against the open in the circuit, they will try to jump the open. If this happens, a spark occurs and the resulting damage can take its toll on related components. The diode across the coil allows the electron pile-up to back up, bypassing the coil. This is like a pressure-relief valve in a pressure cooker

Clamping Diode Protects Against Surge Current

Zener Diodes Zener diodes are the voltage regulators of the diode family. Zener diodes are available in many voltage sizes, depending on the voltage level to be regulated. The rage is from 2 to 200 volts.

Zener Diodes Zener diodes are placed in a circuit “backwards” from regular diodes (the symbol pointing the wrong way). When the Zener voltage is reached, the Zener diode begins to conduct, but maintains the voltage drop across itself. This voltage drop is regulated at whatever the Zener diode is rated for. Zener diodes act like regular diodes when forward biased. If diode breakdown voltage is exceeded, permanent damage to the Zener does not occur

Zener Diodes Act as Voltage Regulators The Negatively mounted diodes in CS charging systems are Zener Diodes.

Transistors/Semiconductor s The most commonly used transistors are bipolar. Because of the advantages of digital electronics and computercontrolled devices, transistors are used more and more in place of relays and

Transistors/Semiconductor s Transistor are used because computer circuits do not have “fingers.” This may seem like a odd statement, but computers must be able to turn ON and OFF many circuits. The only way this can be done is with a small electrical signal (voltage). Transistors perform the functions of a switch without the need for a “finger”.

Transistor and Hydraulic Switch Equivalent.

Transistor Current Flow Transistor current flow is very much like a water faucet The more the faucet is turned ON, the more water will flow out of the spigot (collector/emitter path).

Transistor Current Flow

NPN and PNP Transistors For the NPN transistor, the arrow on the emitter is not pointing in (NPN). Looking at the PNP transistor, the arrow on the emitter is pointing in permanently (PNP). With an NPN transistor, the middle letter is “P,” and a positive voltage must be applied to the base to turn the collector/emitter circuit ON. With a PNP transistor, the middle letter is an “N,” and a negative (ground path) must be completed from the base to turn the emitter/collector circuit ON.

NPN and PNP Transistors Transistors have many advantages over the relays and switches they replace. Transistors are smaller, lighter, faster, and can be controlled with much lower current than traditional relays. In addition to these advantage, transistors have another advantage that is even more useful: transistors can be variable!

NPN and PNP Transistors

Transistor vs. Relay Operation With the relay, note the large current path of the controlled circuit. Also note the path of the “controlling” circuit, through the coil of the relay to ground. The main purpose for using a relay is to have a switch that can remotely control a larger (higher current) circuit.

Transistor vs. Relay Operation Notice that a small switch can be placed on either the positive or ground side of the relay’s coil circuit. The difference in where the switch for the coil circuit is placed explains the difference between NPN and PNP transistor. The main difference is in where the coil control is switched – on the positive side or the ground side.

Transistor vs. Relay Operation Examine the NPN transistor circuit, as compared with a similar relay circuit. The relay circuit is turned ON and OFF by closing and opening the switch in the positive side of the coil circuit. This turns the lamp ON and OFF in the larger controlled circuit.

Transistor vs. Relay Operation With a transistor, the same thing happens when the switch in the base circuit is opened and closed. The lamp turns ON and OFF as if it is being controlled by a relay. The most ever done with electricity is to turn it ON or OFF.

Switching Operation

Transistor Circuit

Transistor Circuit