NEVER been described before, so read carefully.
The 240v AC (called the "mains") consists of two wires, one is called the ACTIVE and
the other is NEUTRAL. Suppose you touch both wires. You will get a shock. The neutral
is connected to an earth wire (or rod driven into the ground or connected to a water
pipe) at the point where the electricity enters the premises and you do not get a shock
from the NEUTRAL.
But the voltage on the active is rising to +345v then goes to -345v at the rate of 50
times per second (for a complete cycle).
345v is the peak voltage of 240v. You never get a 240v shock. (It is a 345v shock.)
In other words, if you touch the two wires at a particular instant, you would get a
POSITIVE 345v shock and at another instant you would get a negative 345v shock.
This is shown in the diagram below.
We now transfer this concept to the output of a transformer. The diagram shows an AC
waveform on the output of the secondary.
This voltage is rising 15v higher than the bottom lead then it is 15v LOWER than the
bottom lead. The bottom lead is called "zero volts." You have to say one lead or wire is
not "rising and falling" as you need a "reference" or starting-point" or "zero point" for
voltage measurements.
The diode only conducts when the voltage is "above zero" (actually when it is 0.7v
above zero) and does not conduct (at all) when the voltage goes below zero.
This is shown on the output of the Power Diode. Only the positive peaks or the positive
parts of the waveform appear on the output and this is called "pulsing DC." This is
called "half-wave" and is not used in a power supply. We have used it to describe how
the diode works. The electrolytics charge during the peaks and deliver energy when
the diode is not delivering current. This is how the output becomes a steady DC
voltage.
Power supplies use FULL WAVE rectification and the other half of the AC waveform is
delivered to the output (and fills in the "gaps") and appears as shown in "A."
DAMPER
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