notes on diodes

uni/mmme/2051_electromechanical_devices/diodes.md

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+---
+author: Akbar Rahman
+date: \today
+title: MMME2051 // Diodes and Rectifiers
+tags: [ diodes, rectifier ]
+uuid: 21cf8e5b-d808-412c-bb71-d298cdb02b4f
+lecture_slides: [ ./lecture_slides/MMME2051EMD_Lecture8.pdf ]
+lecture_notes: []
+exercise_sheets: []
+---
+
+Diodes are like one way valves for electricity --- they allow current to flow in the forward
+direction but not in the reverse.
+
+Pure semiconductors are often intentionally doped by specific impurity to alter
+its electrical properties.
+
+The most basic thing you can produce with this is the PN junction (or, a diode):
+
+![A PN Junction (diode) with its circuit symbol.](./images/vimscrot-2023-03-23T12:04:26,471475256+00:00.png)
+
+
+![Real diode behaviour in orange, ideal in red.](./images/vimscrot-2023-03-23T12:06:05,423779641+00:00.png)
+
+- $I_\text{leak}$ is the current that is able to flow in the reverse direction.
+  It is a very small amount.
+- Forward voltage, $V_f$, is the voltage required to move current forward.
+- Forward bias impedance, $Z_f$, shows that the diode has a low resistance until a certain point.
+- At a certain point a diode will fail to block the reverse voltage (DC blocking voltage)
+
+![A real diode can be approximated with this this of ideal components.](./images/vimscrot-2023-03-23T12:09:18,426229668+00:00.png)
+
+# Rectification
+
+![ElectroBOOM <3](./images/full_bridge_rectifier.gif)
+
+How the rectifiers work are stepped through in lecture slides (pp. 32-44)
+
+The most basic rectification is very wasteful:
+
+![](./images/vimscrot-2023-03-23T12:12:41,250590501+00:00.png)
+
+This produces a waveform like this:
+
+![](./images/vimscrot-2023-03-23T12:13:04,564941427+00:00.png)
+
+This is a step in the right direction but it is still very wasteful and not a smooth
+voltage at all.
+
+A H-Bridge (full bridge) rectifier allows the negative cycle to be harnessed as well:
+
+![H-Bridge Rectifier](./images/vimscrot-2023-03-23T12:14:18,334219094+00:00.png)
+
+This produces a voltage like:
+
+![](./images/vimscrot-2023-03-23T12:15:03,479660034+00:00.png)
+
+Capacitors can be added to smooth out the voltage:
+
+![H-Bridge Rectifier with capactior](./images/vimscrot-2023-03-23T12:15:29,203766582+00:00.png)
+
+This produces a voltage like:
+
+![](./images/vimscrot-2023-03-23T12:16:11,795530248+00:00.png)

uni/mmme/2051_electromechanical_devices/transformers.md

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+---
+author: Akbar Rahman
+date: \today
+title: MMME2051 // Transformers
+tags: [ transformers, alternating_current, ac ]
+uuid: 486f441f-14ec-41e5-94f9-06f25c534086
+lecture_slides: [ ./lecture_slides/MMME2051EMD_Lecture8.pdf ]
+exercise_sheets: [ ./exercise_sheets/Exercise Sheet 11 - Transformers.pdf ]
+---
+
+Transformers are used to convert between AC voltages.
+
+Transmission is always done at very high voltage to reduce copper losses (heat loss, $E = i^2R$).
+
+![](./images/how.png)
+
+A current carrying coil induces a magnet inside the core.
+Another coil is wrapped around the core.
+This coil has a current induced in it by induced magnetic field.
+
+![](./images/vimscrot-2023-03-23T11:15:40,310863581+00:00.png)
+
+$$\frac{i_s}{i_p} = \frac{v_p}{v_s} = \frac{n_p}{n_s} = \text{turns ratio}$$
+
+**Note that the current fraction is s over p, not p over s like the others.**
+Transformers have very high efficiency so will not be considered for this module and
+has been left out of the equation above.
+Derivation in lecture slides (pp. 12-15).
+
+Transformers are usually described as having a ratio $p:s$, where $p$ is the number of primary coils
+and $s$ the number of secondary coils.
+
+![Symbol of an "Isolaton Tranformer". The dot indicates polarity.](./images/vimscrot-2023-03-23T11:17:40,931099514+00:00.png)
+
+## Referred Impedance
+
+$$\frac{Z_P}{Z_S} = \left(\frac{n_p}{n_s}\right)^2$$
+
+Derivation in in lecture slides (pp. 19-21).