- Some electronic circuits are sensitive
and their components can be easily damaged
if they receive too large of an input signal,
much like how loud noises can hurt my sensitive ears.
If somebody is speaking to me at a reasonable volume -
- Hey Ben, how are ya?
- I'm doing fine Ray, thanks -
that's fine.
But if Ray's yelling in my ears,
- Who are you talking to?!
- that's too loud and can damage my ears,
so I need a way to protect myself
from those loud noises,
like earmuffs.
- I still don't know who you're talking to!
- [Ben] When working with electronics,
a clipper circuit can be used to protect sensitive equipment
by limiting the amplitude of input signals.
The clipper will remove any parts of a signal
that are above or below a certain threshold voltage.
For example, the equipment I'm using right now
to record this video,
uses an amplifier to boost the audio signal
coming from my microphone,
and then it sends that amplified signal
to an analog-to-digital converter
connected to my computer.
If for some reason the output voltage
from the amplifier was too powerful,
maybe I talked too loud into the microphone,
I could potentially damage
the analog-to-digital converter chip.
So, to protect this sensitive converter chip
from the amplifier,
I can insert a clipper circuit between them.
The clipper will limit the signal from the amplifier
to keep it within a safe voltage range.
If I was only concerned about protecting my circuit
against negative voltages,
then I could use this simple circuit
with the diode and a resistor
to clip out negative voltages below a certain threshold.
When the input voltage from the signal source is positive,
the diode will act like an open circuit,
so current will flow passed it
and the output voltage will basically be unchanged.
But if the input voltage turns negative
and drops below the forward voltage of the diode
which is around point six volts,
then current will flow through the diode
and back through the resistor to the signal source.
At the output of the clipper circuit,
the voltage will only drop as low
as that forward voltage of the diode.
So the output will never drop below negative 0.6 volts.
To demonstrate that,
I've built a clipper circuit to remove negative voltage
on my breadboard using a 1N4148 diode
and a one kilo ohm resistor,
and I've configured my function generator
to provide a 10 volt peak-to-peak sine wave
as the input signal.
My oscilloscope is displaying the input signal
from the function generator on channel one in yellow,
and the output signal from the clipper circuit
on channel two in blue.
I can see that this circuit allows
the positive parts of the AC signal to pass through
more or less undisturbed,
but it limits the output voltage
from ever dropping below negative 0.6 volts,
which is the forward voltage of the diode.
If instead of clipping off the negative parts
of the input signal,
I want to keep those and cut out the positive parts,
all I need to do is switch the direction of the diode
by turning it around.
Now the clipper circuit is limiting the voltage
from ever rising above point six volts,
but it allows the negative part
of the AC signal to pass through it freely.
If I wanted to limit the positive
and the negative output voltage from my clipper circuit,
from ever going above or below certain thresholds,
I can do that by using two diodes -
one in each direction.
In this arrangement,
if the input voltage ever goes above the forward voltage
of the diode on the left,
that diode will turn on and drain current to ground,
thus limiting the output to always be
less than 0.6 volts.
And a similar thing will happen in the negative direction.
If the input voltage ever drops
below negative point six volts,
the diode on the right will turn on
allowing current to flow through it,
and ensuring that the output voltage
remains above negative 0.6 volts.
When I send a small input signal shown in yellow
through the dual-direction clipper,
the output voltage, shown in the blue,
will be more or less that small.
But if I increase the amplitude of the input signal
to be much larger,
the clipper circuit will restrict the output
to stay within plus or minus 0.6 volts.
The range in my clipper circuit
doesn't have to be limited by the forward voltage
of the diodes I'm using.
I can adjust the range of the clipper circuit
by incorporating other circuit elements
to provide reference voltages to bias those diodes.
In the example shown here,
the 1.4 volt source on the left branch
combined with the diodes forward voltage of 0.6 volts,
will prevent the output voltage of this clipper circuit
from ever rising above two volts.
And on the other branch,
a negative 2.4 volt source,
along with the upward pointing diode,
will prevent the output voltage
from ever dropping below negative three volts.
Keep in mind that the circuit shown here
is simplified by showing three different voltage sources
to illustrate the concept.
In practice, those reference voltages would be generated
using some combination of other circuit elements
that act as a voltage regulator.