Handy Electronics Youtube Videos

! Reactive Components
!! Inductors
[Electroluminescent Backlight (Or, how to get 100V AC @ 150 Hz from 5V DC)|http://www.youtube.com/watch?v=NRnqGBisKY8]
* Video starts at 1:14 and ends at 2:00, or just skip straight to [their web site|http://www.nerdkits.com/videos/backlight/]
* Inductors resist change, so if their output is suddenly cut off (as in when the first MOSFET is switched off, controlled by the AVR microcontroller's internal timer), a voltage spike occurs while the inductor "tries to keep the current flowing".
* When this happens, the monster diode passes the kick-back voltage into the capacitor (I don't fully understand that storage part. Capacitors hold a charge, but how exactly does that relate to a high voltage?). The reverse-bias of the capacitor works as a peak detector.
* As the other MOSFET oscillates (at a much lower rate, also controlled by the AVR), the negative terminal of the electroluminescent device is pulled low and current flows through it. 
* A higher frequency for the first MOSFET gives less time for the inductor to build its magnetic field, so the resulting voltage spike is smaller.
* Driven by [this C code|http://www.nerdkits.com/videos/backlight/backlight.c]
[All-American 5 Radio---Transformer Basics|http://www.youtube.com/watch?v=UvHCQswnjEg]
* Current in primary flows opposite the secondary
* Lowering voltage in primary (or moving the two further apart) causes secondary to flow with primary
* Factors: # of turns, how wound, gauge of wire
* Collapsing magnetic field reverses current
* Cores:
** Air core: More in high-frequency (such as Radio Frequency)
** Iron core: More in low-frequency (audio and power). Can transfer much more power
* Step-down transformer, e.g. AM radio to use high-impedance circuit to drive 8Ω speaker
* Step-up transformer, higher voltage on secondary (but lower current, of course)
* Both step-up and step-down
* At 7:02, he shows two air-cores on an oscilloscope.
* Side-by-side:
** Windings in same direction = AC out of phase
** Windings in opposite directions = AC in phase
* One inside other
** Windings same = AC in phase
** Windings opposite = AC out of phase
[Olympic College|http://www.youtube.com/watch?v=8_dvelvJIrA]
* Fewer turns in the primary means: secondary current less, voltage more
* V{sub}in{/sub} * I{sub}in{/sub} = V{sub}out{/sub} * I{sub}out{/sub} (power of both is roughly equal)
* V{sub}out{/sub}/V{sub}in{/sub} = I{sub}out{/sub}/I{sub}in{/sub} = Coils{sub}out{/sub}/Coils{sub}in{/sub} (mechanical advantage)
[How It's Made---Pole Transformer|http://www.youtube.com/watch?v=tUO3o5JTGhQ]
* Not terribly informative, but mesmerizing as all industrial manufacturing videos are.
!! Capacitors
[Animated Capacitor Charging @ 2ns, 1ps/frame|http://www.youtube.com/watch?v=FJZKm5khaAA]
[Images of Bad Capacitors (e.g., capacitor plague)|http://www.youtube.com/watch?v=oDGjWOabJ2E]
* I had a motherboard that had this problem
[Scope of Bad Capacitor (info in comments)|http://www.youtube.com/watch?v=yjq0CXEI_q8]
[My favorite High-voltage Cap Guy, bobdavis321|http://www.youtube.com/watch?v=2M3rzx6jtnk]
[Discharging a DC Filter Capacitor (wa2kwl)|http://www.youtube.com/watch?v=oCnQsvcvEp4]
* Had bleeder resistor, removed.
* Then he pops it with a screwdriver.
* I guess he's just showing what caps charged to 170V can do.

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Handy Electronics Youtube Videos