|
Start,
Tools and equipment,
Voltage,
Current,
Resistor, Power,
Capacitor,
Inductor,
Diode,
LED,
Transistor,
OP-Amp,
Linear Integrated Circuits,
Digital Integrated Circuits,
Microprocessor,
Relay,
Thyristor,
Transformer
<- Previous
Next ->
Power
Page 2:2
<-Previous Page:
1 2
Power matching
Power matching is a term that is used when we want to get as
much power into a load (a loudspeaker, for example) as possible
and the driving output has an internal resistance (which it
always has). It can be shown that when the load has the same
resistance as the internal resistance of the source, as much
power as possible is developed into the load. If the load
resistance is higher or lower, the power in the load becomes
lower. When we have maximum power in the load, we can say that
the power is matched and that happens when the resistance in the
load is equal to the internal resistance of the source.
The circuit above shows a voltage source (Usource) with an
internal resistance (Ri) which is connected to a load (Rload).
We can set the value for Usource to 10V and the value for Ri to
20Ω for this example.
The highest current in the load is if the Rload resistor is 0Ω
which equals 0.5A. However, since the resistance is 0Ω there is
no voltage over Rload which means that the power in Rload = 0W
(P = U * I). In this case all the voltage is over Ri.
The highest voltage over Rload
is when there is no current in the circuit which is when Rload
has an infinite resistance, that is when Rload is an open
circuit. In this case the whole of Usource is over Rload. Since
there is no current, the power is also 0W.
This indicates that we must be
somewhere in between these extreme values for Rload to use the
most power. If we plot a diagram with Rload between 0Ω and 40Ω
on the X-axis and the power in Rload on the Y-axis we can see
that maximum power in Rload is when it's resistance is 20Ω.
The power in the above example can be calculated in several
way. I have choosen to first calculate the current, which equals
Usource / (Ri + Rload), and then calculate the power with the
formula P = R * I2. Another way would be to calculate
the voltage over Rload and then use P = U2 / R.
We can also see that the resistor value for Rload when power
is matched into it, is independent of the voltage for Usource
which means that Usource could be an AC voltage or a complex
signal, like an audio or video signal, and the power matched
Rload resistance would still be the same as the internal
resistance.
<-Previous
Page: 1 2
Start,
Tools and equipment,
Voltage,
Current,
Resistor, Power,
Capacitor,
Inductor,
Diode,
LED,
Transistor,
OP-Amp,
Linear Integrated Circuits,
Digital Integrated Circuits,
Microprocessor,
Relay,
Thyristor,
Transformer
<- Previous
Next -> |
