1. TRANSISTORS AS SWITCHES

2. Durability TRANSISTORS AS SWITCHES Silicone Chips now contain over a million transistors for only a few pence each. SizeEfficiency Cost Common Formats Advantages:

3. How Transistors Work…….. The transistor is a bipolar device made up from 3 layers of semi conductor materials N type (poor Conductor) P type (good Conductor) P type

4. How Transistors Work…….. N P Base P Emitter Collector The transistor layers are termed:

5. How Transistors Work…….. N P Apply Signal +0.6 [Volts] Resistance of N type Semi-conductor Decreases P C B E

6. How Transistors Work…….. N P Apply Signal +0.6 [Volts] The Transistor becomes an excellent conductor Across the collector and emitter P C B E

7. 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……..

8. b c e 0v If you apply Voltage Directly Or apply Voltage Directly

9. How Transistors Work…….. The Transistor must be protected from short circuit by placing loads at the base and the collector b c e

10. How Transistors Work…….. b c e Build the following circuit using crocodile clips c b e

11. How Transistors Circuits are built…. 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. Transistor Circuit Group

12. How Transistors Circuits are built…. Example 1: a simple voltage divider can be used to fine tune the signal to the transistor Voltage Divider Circuit Group

13. How Transistors Circuits are built…. Example 2 : a thermistor in the voltage divider can be used to trigger the transistor at a given temperature Thermistor Divider Circuit Group

14. How Transistors Circuits are built…. Example 3 : a LDR in the voltage divider can be used to trigger the transistor at a given light Level ‘LDR’ Divider Circuit Group

15. 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