8572977
| Question | Answer |
| What is a transistor? | An active component, its an amplifier. It has an external power supply which it uses to generate gain |
| What happens to the base layer when a sufficient voltage is placed across it? | Effectively disappears as it is so thin compared to the other layers |
| Applying KCL to a transistor gives what equation? | I(E) = I(C)+ I(B) |
| What is another equation for I(C)? | I(C) = I(C,majority) + I(CO) |
| What is I(CO)? | Collector current measured with the emitter open, is termed the LEAKAGE current |
| What is the definition of "common base" configuration? | The two voltage sources share the base terminal |
| In the cut-off region what state are the junctions? | Both are fully REVERSE bias |
| In the saturation region what state are the junctions? | Both are fully FORWARD bias |
| What is ⍺(DC)? | ⍺(DC) = I(C) / I(E) It's the common base short circuit amplification factor Normally ranges from around 0.90 to 0.99, though the approximation is ⍺ = 1. |
| What is ⍺(AC)? | ⍺(AC) = ΔI(C) / ΔI(E) The values of alpha are approximately equal for AC and DC |
| What is the definition of "common emitter" configuration? |
The two voltage sources share the emitter terminal
Image:
Common Emitter (image/png)
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| How does common emitter vary from common base? | The output characteristic lines of I(C) are much more sloped, the effect of the source used for gain is much greater |
| What is β? | β = I(C) / I(B) Its the common-emitter forward amplification factor Typically has a value between 50-400 |
| What is β often listed as on transistor data sheets? | h(fe) |
| How are ⍺ and β linked? | β = ⍺ / (1 - ⍺) ⍺ = β / (β + 1) |
| What is the Quiescent point or 'Q' point? | Refers to the DC biasing, so that the AC amplification occurs within the active region of the output characteristics |
| What two currents does β link together? | I(C) = β * I(B) |
| What is the emitter current in a common emitter amplifier in terms of base current and β? | I(E) = (1 + β) * I(B) |
| What is the definition of a "common collector amplifier" | |
| What is the difference between common collector and common emitter? | The output curves differ as I(E) = ⍺ * I(C) |
| What limits the curves in the active region? | Transistors have a maximum power dissipation so I(C) * V(CE) must be less than that value |
| How to use derating info? | It is used to calculate the max power when ambient air or case temperatures can't be met. As this value will be lower |
| What are load lines? | They are used to graphically solve problems where a non-linear circuit element is connected to a linear one |
| What does a fixed bias transistor circuit look like? | |
| What does a voltage divider bias transistor circuit look like? | |
| What are the steps for finding bias voltages and currents? | 1. Simplify circuit for DC analysis 2. Simplify input using Thevenin's theorem 3. Calculate base current 4. Infer collector current 5. Calculate V(CE) from the 'load line' equation |
| What is the assumption given for the voltage across the emitter resistor? | It is one tenth of the supply voltage |
| What is the assumption made for the current through the potential divider and why is this assumption made? | In order to maintain the bias, by maintaining I(B), the current through the potential divider must be greater than the base current. Say 10 times as an assumption |
| What is the problem with class A amplifiers? | Even when not amplifying the active device and series resistor(s) consume power. The theoretical efficiency is 50% at best |
| What is linearity? | The output increases exactly in proportion to the input. If this does not happen the signal is distorted, leading to harmonics. |
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