TECHNOLOGIES ESO 4 UNIT 1: ELECTRICITY AND ELECTRONICS ANALOGIC ELECTRONICS (PART 1)

ANALOGIC ELECTRONICS 1.RESISTORS 1.1 FIXED RESISTORS 1.2 VARIABLE RESISTORS 2.RELAYS 3.CAPACITORS 4.SEMICONDUCTIVE MATERIALS 5.DIODES 6.TRANSISTORS

1. RESISTORS The first and most common electronic component is the resistor. The value of resistance, measured in Ohms is the primary parameter, and determines the current flow for any applied voltage. The resistance value is specified in ohms (Ω). Resistor values are often stated as "k“ or "M” for convenience. There are a few conventions that are followed: a resistor has a value of 2,200 Ohms, this may be shown as any of these... 2,200 Ohms 2,200 Ω 2.2k 2.2k Ω 2k2 (european, not commonly seen in the US or other countries)

1. RESISTORS The resistor value is color-coded with stripes. 1.1 FIXED RESISTORS There are two types of resistors: fixed and variable:

1. RESISTORS 1.1 FIXED RESISTORS (Continue) Fixed resistors impedes the flow of electric current. They have different sizes. The size of the resistor indicates the amount of power that it can dissipate in the form of heat. If they subjected to very high voltage or current they can burn.

1. RESISTORS 1.2 VARIABLE RESISTORS a) POTENTIOMETERS: These are resistors whose value can be adjusted, with a minimum value of 0 up to the maximum specified by the manufacturer. These resistors are used on circuits to control temperature, lighting, energy, speed or the volume of a radio receiver…

1. RESISTORS 1.2 VARIABLE RESISTORS (continue) b) RESISTORS THAT DEPEND UPON A PHYSICAL PARAMETER: Resistors can be controlled by physical parameters such as LIGHT and TEMPERATURE. b.1) LDR (LIGHT DEPENDENT RESISTOR): The resistance decreases as the luminous intensity increases.

1. RESISTORS 1.2 VARIABLE RESISTORS (continue) b.2) THERMISTORS (TEMPERATURE DEPENDANT RESISTOR): The resistance decreases or increases as the temperature changes. NTC (Negative Temperature Coefficient) PTC (Positive Temperature Coefficient)

2. RELAYS If we want to control much more powerful outputs such as even larger lamps or motors we can use a relay. A relay is just a type of switch, except that the position of the switch (on or off) is controlled by an electromagnet. When a coil is connected to a power supply it makes it work like a magnet. This magnetic force allows the contacts of the switch get pulled together.

2. RELAYS HOW RELAYS WORK: Normally the switch contacts are open. When the coil power supply is connected to a battery it turns into an electromagnet and attracts the metal arm. This are then pivots and pushes the two contacts together. The relay shown only has one SPST switch but relays can also contain a range of other switch types. EXAMPLES OF CIRCUITS WITH RELAYS: The relay allows very large currents or voltages to be safely controlled by low power circuits. An example of this is the standby button on a TV. You may notice that when you turn the power via the remote there is a little clicking noise in the TV, this is the relay turning on. Relay symbol

2. RELAYS TWO CIRCUITS: A useful property of relays is that the circuit powering the coil is completely separate from the circuit switched on by the relay. For this reason relays are used, for example, where a safe low-voltage circuit controls a high-voltage circuit. The symbol for a relay makes the separation of the two circuits clear by separating the coil symbol from the switch symbol. Relay

2. RELAYS MAKING CIRCUITS WITH RELAYS: Relays used in the school work with a voltage of 4.5 – 9V. They are normally SPDT (Single Pole Double Throw) or DPDT (Double Pole Double Throw “Doble contacto”):

3. CAPACITORS A capacitor is a component that can store an electrical charge. Capacitance is defined as the relation between the electric charge and the voltage: C = Q/V The larger the capacitance the more charge it can store. The unit of measurement of capacitance is the FARAD. Submultiples are often used: - microfarad (  F): 1  F = F - nanofarad (nF): 1nF = F - picofarad (pF): 1pF = F There are two types of capacitor: polarised or electrolytic capacitors non-polarised or non-electrolytic capacitors Q = electric charge (Coulombs, C) V = voltage (Volts, V)

3. CAPACITORS POLARISED OR ELECTROLYTIC CAPACITOR: These generally have larger capacitance values. Polarised capacitors have a positive pole and a negative pole, so they must be connected to a circuit the correct way round. They may be either axially mounted (on their side, connected at each end) or radially mounted (upright with both connections at the bottom). NON-POLARISED CAPACITORS: These are usually much smaller than the polarised type, and have smaller capacitance values. These might range from a few picofarads to a few microfarads. They don't have positive or negative poles so they can be connected to a circuit either way round.

3. CAPACITORS HOW DO CAPACITORS WORK? Capacitors are components that store electric charge (It is similar to a battery but it can’t produce new electrons, it only stores them). A capacitor consists of two conductors separated by a non-conductive region called the dielectric. The dielectric is an electrical insulator (glass, air, paper, vacuum …) When a capacitor is connected to a battery, the plate on the capacitor that attaches to the negative terminal of the battery accepts electrons that the battery is producing. The plate on the capacitor that attaches to the positive terminal of the battery loses electrons to the battery. Once it's charged, the capacitor has the same voltage as the battery (1.5 volts on the battery means 1.5 volts on the capacitor).

3. CAPACITORS Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Connected in series: The entire series acts as a capacitor smaller than any of its components. The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge. EXAMPLE OF CAPACITORS APPLICATION: Sometimes, capacitors are used to store charge for high-speed use. That's what a electronic flash on a camera does, it uses a capacitor instead of a battery - the battery charges up the flash's capacitor over several seconds, and then the capacitor dumps the full charge into the flash tube almost instantly.

3. CAPACITORS CHARGE AND DISCHARGE OF A CAPACITOR The rate at which a capacitor can be charged or discharged depends on: the capacitance the resistance of the circuit through which it is being charged or is discharging The resistor ONLY affects the TIME it takes for the capacitor to become fully charged or discharged and NOT the EVENTUAL POTENTIAL DIFFERENCE (VOLTAGE) ACROSS IT – this is always the same and equal to the potential difference across the supply.

3. CAPACITORS TIME CONSTANT: It is the time it takes for a capacitor to acquire 63% of the supply voltage. It is calculated as follows: TC = C·R Example: A 1K resistor in series with a 1,000 μF capacitor has a time constant of 1. This is the time it takes for a capacitor to acquire 63% of the voltage being supplied to it, if it starts with zero volts. Time(s)

3. CAPACITORS Time(s) In this circuit, charge and discharge takes the same time, as it happens through the same resistor. CHARGING: DISCHARGING: