Transcript Document
TRANSISTORS AS SWITCHES TRANSISTORS AS SWITCHES Common Formats Advantages: Size Efficiency Durability Cost Silicone Chips now contain over a million transistors for only a few pence each. How Transistors Work…….. The transistor is a bipolar device made up from 3 layers of semi conductor materials P type (good Conductor) N type (poor Conductor) P type How Transistors Work…….. The transistor layers are termed: P Collector N Base P Emitter How Transistors Work…….. C Apply Signal +0.6 [Volts] P B N Resistance of N type Semi-conductor Decreases P E How Transistors Work…….. C Apply Signal +0.6 [Volts] B P N P E The Transistor becomes an excellent conductor Across the collector and emitter How Transistors Work…….. The BC 108 is common general-purpose transistor. The diagram below shows the position of the legs when viewed from underneath the case. The transistor has to be connected into circuits correctly. The arrowhead on the emitter indicates the direction of ‘conventional’ current flow that is, opposite to the electron flow. How Transistors Work…….. Or apply Voltage Directly c If you apply Voltage Directly b e 0v How Transistors Work…….. c b e The Transistor must be protected from short circuit by placing loads at the base and the collector How Transistors Work…….. c b e Build the following circuit using crocodile clips How Transistors Circuits are built…. Transistor Circuit Group Using input transducer devices that convert a change in physical conditions into a change in resistance and voltage. This can then be processed in an electrical network based on a voltage divider circuit. How Transistors Circuits are built…. Voltage Divider Circuit Group Example 1: a simple voltage divider can be used to fine tune the signal to the transistor How Transistors Circuits are built…. Thermistor Divider Circuit Group Example 2: a thermistor in the voltage divider can be used to trigger the transistor at a given temperature How Transistors Circuits are built…. ‘LDR’ Divider Circuit Group Example 3: a LDR in the voltage divider can be used to trigger the transistor at a given light Level Build a circuit on a bread board Problem: Mr & Mrs Beverage go regularly to their local clubby. When coming home, usually too worse for drink. They stot and fumble in the dark trying to open the door for ages, causing him to swear loudly and wake up Mr Walker next door. Brief: Design Mr Beverage a system that will bring on a Light when it gets dark and has an adjustment that can alter for summer time- leaving Mr Beverage more money for drink. Investigate: LDR voltage divider configuration to provide a “darkness” sensor Design & Build: A proto type using a breadboard