Unit 6 in four lessons

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Unit 6 in four lessons
Controlling changing current
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Current
There are two types of current
Direct current (dc) in which the current travels
in one direction only
Alternating current (ac) in which the current
alternates (changes direction) 50 times a second
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Transformers How they work
Iron core
Secondary coil
Primary coil
An alternating current in the primary coil
Induces a magnetic field through the core which
Induces an ac current in the secondary coil
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Transformers changing voltage current
Primary side
Secondary side
More turns on the secondary coil means it is a
step up transformer VOLTAGE UP, CURRENT DOWN
100 turns
50 turns
More turns on the Primary coil means it is a
step down transformer VOLTAGE DOWN, CURRENT UP
50 turns
100 turns
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Same number of turns on each side Means..
It is an isolating transformer. Example would be
a shaver. If water gets on the mains side it
stops you getting a shock as the wires aren't
touching
50 turns
50 turns
The live parts will not touch the Earth so a
large current cant flow through you
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Calculations easy if you follow the steps
You are always given three of the four variables
Vp 12V
Vs ?
Primary side
Secondary side
Tp50 turns
Ts150 turns

1. Voltages one side, number of turns on the other

Vs Ts Vp Tp

2. Put in the numbers
Vs 150 12 50
150 x 12 36V 50

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This time you need to find VP
You are always given three of the four variables
Vp ?
Vs 12
Primary side
Secondary side
Tp50 turns
Ts150 turns

1. This time you put the primary side on the top

Vp Tp Vs Ts

2. Put in the numbers
Vp 50 12 150
50 x 12 4V 150

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Diodes Capacitors
A diode changes alternating current into direct
current
?
A.C turns into
This is called half wave rectification
This wastes half the current
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Four diodes connected the correct way result in
full wave rectification
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Charging a capacitor

-
Charge can be stored on a capacitor The capacitor
has a voltage across it

-
When connected the capacitor discharges
The current will be large at first but drop
quickly
Because the voltage across the capacitor drops
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Capacitors and diodes in a circuit together
What do they do??????????
Smooooooooooth out the current