components by restricting the flow of current when voltage increases.
require resistors in series for the same reason so that they can be operated at
voltages higher than the specified rating. Other active components like
transistors, mosfets, triacs, SCRs also incorporate resistors for the same
stores a certain amount of electric charge or simply the applied voltage/current,
when its leads are connected across the relevant supply points.
is basically rated with a couple of units, microfarad and voltage. The "microfarad" decides the amount of current it can store and the voltage defines
how much maximum voltage may be applied across it or stored in it. The voltage rating is
critical, if it exceeds the marking, the capacitor will simply explode.
energy becomes usable, therefore these are used as filters where the stored
voltage is used for filling the blank spaces or voltage depressions in the
source supply, thus filling up or smoothing the ditches in the line.
slowly through a restricting component like a resistor. Here, the time consumed
by the capacitor to charge fully or discharge fully becomes ideal for timer
applications, where the capacitor value decides the timing range of the unit.
Therefore these are used in timers, oscillators etc.
refuses to pass any more current/voltage and stops the flow of the current
across its leads, meaning the applied current passes across its leads only in
the course of charging and is blocked once the charging process is completed.
particular active component momentarily. For example if a triggering voltage is
applied to the base of a transistor via a capacitor, it would get activated
only for a particular fragment of time, until the capacitor gets fully charged,
after which the transistor stops conducting. The same thing may be witnessed
with an LED when powered through a capacitor; it illuminates for a fraction of
a second and then shuts off.
three leads or legs. The legs can be wired such that one leg becomes a common
outlet for the voltages applied to the other two legs.
legs are named as base and the collector. The base receives the switching
trigger with reference to emitter and this enables relatively huge voltage and
current for passing from collector to emitter.
load connected at the collector can be switched ON or OFF with relatively tiny
potentials at the base of the device.
reach the common destination through the emitter. The emitter is connected to
ground for NPN type and to positive for PNP types of transistor. NPN and PNP
are complementary to each other and operate exactly in the same manner but by
using the opposite directions or polarities with voltages and currents.
is also used as a switch in electronic circuits. The three leads or legs are
specified as the gate, the anode and the cathode. The cathode is the common terminal
which becomes the receiving path for the voltages applied at gate and the anode
of the device.
connected to anode across the common leg of cathode.
higher amount of voltage and current and moreover the device can be used for
switching exclusively AC across its anode and cathode. Therefore it becomes
useful for switching AC loads in response to the triggers received at its gate;
but the gate will need purely a DC potential for implementing the operations.
above components in a practical circuit:
How to Configure Resistors, Capacitors and Transistors in Electronic Circuits......?
electronic circuits is the ultimate thing that any electronic hobbyist intends
to learn and master. Though it’s easier said than done, the following couple of
examples will help you to understand regarding how resistors, capacitors,
transistors can be set up for building a particular application circuit:
will be discussing only a single circuit comprising transistor, capacitor,
resistors and LED.
circuit, while the passive components perform the supporting role.
transistor is the main active component, must take the center stage. So we
place it right at the center of the schematic.
required setting up via the passive parts.
we are using an NPN type of transistor, the emitter must go to the ground, so
we connect it to the ground or the negative supply rail of the circuit.
this input needs to be connected to the sensor element. The sensor element here
is a pair of metal terminals.
the other terminal needs to be connected to the base of the transistor.
moment raining begins; the water droplets bridge the two terminals. Since water
has a low resistance, starts leaking the positive voltage across its terminals,
to the base of the transistor.
the course reaches the ground through the emitter. The moment this happens, as
per the property of the device, it opens the gates between the collector and
the collector, it will be immediately connected to the ground via its emitter.
positive, however we do this via the load so that the load operates with the
switching, and that’s exactly what we are looking for.
positive supply leaks through the metal terminals of the sensor, touches the
base and carries on its course to finally reach the ground completing the base
circuit, however this operation instantly pulls the collector voltage to the
ground via the emitter, switching ON the load which is a buzzer here. The
corrections and also can be modified in many different ways.
include a base resistor because the water itself acts as a resistor, but what
happens if the sensor terminals are accidentally shorted, the entire current
would be dumped to the base of the transistor, frying it instantly.
of the transistor. However the base resistor value decides how much triggering
current can enter across the base/emitter pins, and therefore in turn affects
the collector current. Conversely, the base resistor should be such that it
allows sufficient current to be pulled from collector to the emitter,
permitting perfect switching of the collector load.
value to be 40 times less than the collector load resistance.
we measure the resistance of the buzzer which amounts to say 10K. 40 times 10K
means the base resistance must be somewhere around 400K, however we find that
the water resistance is around 150K, so deducting this value from 400K, we get
250K, that’s the base resistor value we need to select.
instead of a buzzer. We cannot connect the LED directly to the collector of the
transistor because LEDs are also vulnerable and will require a current limiting
resistor if the operating voltage is higher than its specified forward voltage.
collector and positive of the above circuit, replacing the buzzer.
resistor in series with the LED may be considered as the collector load
So now the base resistance should be 40 times this value, which
amounts to 40K, however the water resistance itself is 150K, means the base
resistance is already too high, meaning when rain water bridges the sensor, the
transistor won’t be able to switch ON the LED brightly, rather will illuminate
it very dimly.
What do we need to do now?
another transistor to aid the existing one in a Darlington configuration. With
this arrangement the transistor pair becomes highly sensitive, at least 25 times
more sensitive than the previous circuit.
resistance that may be 25+40 = 65 to 75 times the collector resistance; we get
the maximum range of about 75 into 10 = 750K, so this can be taken as the total
value of the base resistor.
that’s the base resistor value we can choose for the present configuration.
Remember the case resistor can be any value as long as it’s fulfilling two
conditions: it’s not heating up the transistor and it’s helping to switch the
collector load satisfactorily. That’s it.
transistor and the ground. The capacitor, as explained above will store
initially some current when raining begins through the leakages across the
Now after the rain stops, and the sensor bridge leakage is
disconnected, the transistor still keeps conducting sounding the buzzer…how?
The stored voltage inside the capacitor now feeds the transistor base and keeps
it switched ON until it has discharged below the base switching voltage. This
shows how a capacitor might serve in an electronic circuit.