REPORT ON: APPLICATION of semiconductor
devices and optoelectronic devices in MOBILE CHARGER
Briefing application of semiconductor devices
pn junction diode in rectifier
Diodes only allow current to flow in one direction. In first half cycle of AC
diode two 1st ALTERNATE are forward biased and two 2nd ALTERNATE
are reversed biased, and in the second half cycle (negative half) 2 2nd
ALTERNATE Diode are forward biased and 2 1st ALTERNATE are
reversed biased. This Combination converts the negative half cycle into
positive.
4 pn juction diodes as rectifier.Rectification is the process of removing
the negative part of the Alternate Current (AC), hence producing the
partial DC
fluctuating DC filters from the capacitor and becomes almost pure DC.
The capacitor then give that as high voltage DC input to oscillator
Npn transistor in oscillator
This is an oscillator circuit. This converts DC back to high-frequency AC of 15 to
50 KHz.
These consist two NPN transistors.NPN transistors in a mobile charger oscillator
work to generate a high-frequency AC signal that is used to drive the
transformer.
Now, this current passes from the 2M ohm resistor to the base of the 1st
transistor to turn it on. This transistor isn’t fully turned on, because of the
resistance it turns on partially. Due to the partial turning on of the transistor, a
low current passed from the primary winding of the transformer. This induces a
low voltage in the auxiliary winding.
The induced voltage now charges the capacitor and then the capacitor fully turns on
the transistor. As the transistor is now fully on, it allows the current to flow through
itself. Now, this turns on the transistor 2, this shunts the base of the 1 transistor
turning it off. As the 1 turns off the flow of current to the 2 is cut off. Now the current
flows to the base of the 1 and the cycle repeats
The induced voltage now charges the capacitor and then the capacitor fully turns on
the transistor. As the transistor is now fully on, it allows the current to flow through
itself. Now, this turns on the transistor 2, this shunts the base of the 1 transistor
turning it off. As the 1 turns off the flow of current to the 2 is cut off. Now the current
flows to the base of the 1 and the cycle repeats.
Zener diode
A zener diode is used in mobile chargers to provide a stable reference voltage
for the optocoupler. The optocoupler is a feedback device that helps to regulate
the output voltage of the charger.
When the output voltage of the charger is too high, the zener diode will start to
conduct current. This current will flow through the optocoupler, turning it on.
The optocoupler will then send a signal to the oscillator circuit, telling it to
reduce the output voltage.Conversely, when the output voltage of the charger
is too low, the zener diode will not conduct current. This will turn off the
optocoupler, which will send a signal to the oscillator circuit, telling it to
increase the output voltage.
In this way, the zener diode helps to ensure that the output voltage of the
charger remains stable, even if the input voltage varies.
Photo diode in Optocoupler
optocoupler uses a photodiode to convert light from an LED into an electrical
signal. When the input signal is applied to the LED, it turns on and emits light.
The light from the LED is received by the photodiode. The photodiode converts
the light into an electrical signal. The electrical signal from the photodiode is
amplified and used to control the output of the optocoupler.
CIRCUIT DIAGRAM AND PRINCIPLE OF OPERATION
A mobile charger works on the principle of converting AC (alternating current) to
DC (direct current). This is because mobile phone batteries require DC power to
operate
1. The AC input voltage is applied to the primary winding of a transformer.
2. The transformer steps down the voltage to a lower level.
3. The stepped-down voltage is rectified to DC voltage by a diode bridge.
4. The DC voltage is filtered by a capacitor to remove any AC ripple.
5. The filtered DC voltage is then regulated to a constant voltage by a
voltage regulator.
6. The regulated DC voltage is then output to the mobile phone battery
OUTPUT AND INFERENCE
I tried simulation of diode using online matlab due to some some issues in
Online matlab Graph was not running .
INFERENCE
I have learnt about application of pn junction in rectifiers and npn transistor in
switching application to generate ac voltage .on a whole I have used my
knowledge of semiconductor and optoelectonic device to understand and make
a report on how a modern charger works.
I have learnt how to do simulation in Simulink in matab.