How does a mobile charger work? SMPS with Opto-Coupler.

We use our smartphone every day.  But, have you ever wondered how  your smartphone charger works?  You would know that charger converts AC  to DC, but it's not that straightforward.  First, It converts AC to DC then again  back to AC and then finally to DC.  Today we are going to see how the charger does  this, and why are there intermediate steps.  This is a normal charger that  converts 220 volts AC to 5 volts DC.  Let's see what's inside. Now we can see all the electronic components used in it. There are diodes, capacitors, transistors and resistor, also  there are resistors below the PCB.  This is a transformer, and this is an optocoupler. Once power is supplied it turns on.  To understand it better  let's rearrange the circuit.  Now we can see all the components and connections. This red wire is phase wire and the black is neutral. First we have is a resistor. By observing the color bands and reference  table we can see it's 260 kilo ohms (2.6 ohm). (It's a golden band and not yellow band) This is a fusible resistor which  prevents damage from overloading.  Then there is a bridge rectifier made by four  of one n4007 diodes and a filter capacitor of 450 volts and 2.2 microfarad. This circuit converts AC to DC.  This is an oscillator circuit this converts DC  back to high frequency ac of 15 to 50 kilohertz.  We can see the values of the components.  This is transistor s8050,  this is its pin configuration.  And this is transistor 13001,  this is its pin configuration.  This is a diode, It looks like Zener diode  but it's a fast switching diode 1n4148 and   a capacitor of 50 volts 22 micro farad. This is AC to DC converter for the photo   transistor in optocoupler,  I t forms a circuit like this. This is the transformer, it has  three windings primary, secondary,   and auxiliary winding wrapped around the core. It is used to step down the voltage.  The auxiliary winding is used  to run the oscillator circuit.  Then we have a Schottky diode 1n5819 with  a capacitor of 10 volts 470 microfarad to   convert AC to DC and a led for indication. Also, there is a feedback circuit that consists of an optocoupler pc817c and 4.2 volt Zener diode. This is an optocoupler.  It is used for transmission  of signal without contact.  On the right side we have is an infrared  led and on the left is photo transistor.  When the led turns on its light turns on  the base of photo transistor turning it on.  This capacitor is of 102 nano  farad used for safety purposes.  It is connected between primary and secondary  grounds to stop electromagnetic interference.  Let's turn it on and see in action. The green wires carry the positive voltage and the blue wires carry the negative voltage or ground. Also, we can see the voltage in the circuit on the graphs. We have the input of 220 volts 50(60) hertz AC.  This is a bridge rectifier, it  converts AC to fluctuating DC.  As we can see this fluctuating DC filters  from the capacitor and becomes almost pure DC.  We can see we have as DC in the circuit.  Now this current passes from the 2 mega ohm  resistor to the base of T1 turning it on.  This transistor isn't fully turned on, because  of the resistance it turns on partially.  Due to 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 T2, this  shunts the base of the T1 turning it off.  As the T1 turns off the flow of  current to the T2 is cut off.  Now the current flows to the base  of the T1 and the cycle repeats.  This happens at 15 to 50 kilohertz which is  thousand times faster than the rectifier circuit.  Hence, you would see that the  rectifier circuit is stopped.  At the same time the voltage from  the auxiliary also turns the diode   on and charges the capacitor  and flows to the optocoupler.  This diode and capacitor convert the AC from  the auxiliary coil to DC for the optocoupler.  The current is also induced  in the secondary winding.  This is converted to DC by a Schottky  diode and a filter capacitor.  It is indicated by the led. But what if the voltage is more than 5 volts.  Hence, we have as a feedback circuit. As we reach 4.2 volts the Zener diode turns on allowing current to flow to the optocoupler. It also drops the voltage by 4.2 volts hence the led of the optocoupler doesn't turn on. The led requires 0.8 volt to turn on.  When the voltage reaches more than 5 volts  this turns on the led of optocoupler.  The light of the led turns on the  phototransistor of the optocoupler allowing   the current to flow to the transistor T2. This turns on the transistor T2 shunting   the first and stopping the flow  of current in the primary winding.  Also, the voltage in the secondary side  of transformer drops below 5 volts,   turning off the Zener diode and optocoupler  and the circuit continuous to run normally.  Now you would have the question why not  directly convert AC to DC than this?  This is because for the normal power  supply which is at 50(60) hertz.  The size of transformer and  the capacitors are large.  They cannot be mounted in  a small charger like this.  Hence in the charger the 50(60) hertz  frequency is converted to 50 kilohertz.  This reduces the size of the transformer  and capacitor required in the circuit.  So to change the frequency of AC first we have  to convert it to DC and then again back to AC.  Now you know how the charger  that we use daily works.  Thank you for watching.

Channel: Explorer

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Keywords: how mobile charge works, how mobile charger works animation, mobile charger smps, mobile charger circuit diagram, Electronic circuit, fast charging, electronics engineering, Circuit Diagram, Smartphone, charger, mobile, ac to dc, adaptar, animation, smps, mobile charger, charging, wireless charging, 3d animated, 3d animation, switch mode power supply, smps power supply

Id: 2N_T7VFymFg

Length: 6min 30sec (390 seconds)

Published: Sun Sep 20 2020