Electronics Flashcards
saturation (define, transistor)
transistor acts like a short circuit (current flow freely from collector to emitter). Being driven so hard that there is no longer any amplification
cut-off (define, transistor)
transistor acts like an OPEN CIRCUIT (no current flows from collector to emitter)
why would you use a transistor as a switch?
- switches faster
- less mechanical wear
- less “noise” (switch bounce) - better at higher freq.
what are some design factors when using a transistor as a switch?
make sure it’s at saturation (e.g. set correct operating point)
astable (define, 555)
555 acts as a rectangular-wave generator
monostable (define, 555)
555 acts as a “one-shot timer” - when an input voltage is applied, it goes from low to high
Basic op-amp operation
Switches from one maximum output to another when there’s a voltage difference between it’s inputs.
Negative feedback
When voltage is fed back to inverting terminal, gain can be controlled.
Basic op-amp rules
1) v(out) = A0(V+ - V-)
2) A0 is infinity (open loop)
3) R(in) is infinity (therefore no current can flow into op-amp)
Advantages and disadvantages of centre-tapping transforming/rectifier set-up.
Advantages: need only 2 diodes instead of full wave bridge
Disadvantages: centre-tapping means half of the secondary voltage as output
What is ‘duty cycle’?
Fraction of the time output is high
= t(high)
mark-space ratio concept
Literally mark (time high, or active) divided by space (time low)
t(high) for a 555 astable
0.693R2C2
t(low) for a 555 astable
0.693(R1 + R2)C1
duty cycle
fraction of time the output is high.
duty cycle = t(high) / t(high) + t(low)
