Saturday, 18 October 2014

How to make a 12v 5Amp transformerless or electronic power supply which is Switched Mode Power Supply (SMPS) based

How to make a 12v 5Amp transformerless or electronic power supply which is Switched Mode Power Supply(SMPS) based.

Making a 12v 5A Transormerless electronic power supply is really a complicated task and if we made it the resulting circuit will become a bulky circuit. Don't worry about it, Now we are going to solve it together.

In this post, We are going to take advantage of High frequency method over a small transformer or inducuctors coupled together over a ferrite core, This method also known as Flyback Converter type design. As we all know at High frequency, we can make a small transformer conduct even much higher current or power far above the rated...
specification without damaging it. So just use this property to exploit the small transformer to get high amperage from a little ferrite transformer. Simply switch mode power supply simply the property of inductor that it always opposes the rate of change of current flowing through. So simply by switching on and off the inductor will result in boosted output across the inductor with opposit polarity. The simplest switch mode power supply (smps) are boost converter circuit but it is not a isolated power supply from mains so today we are going to make a flyback converter power supply (smps based) to get a highly regulated output by using a beedback by optocoupler to tightly regulate output and is also isolated from the mains supply also for our 12 volt 5 ampere electronic supply which is switch mode power supply ( smps based) to be stable tightly regulated and isolated like we need .


So lets get started without wasting our Precious time:

The 12v 5Amp SMPS power supply circuit uses a flyback converter method which will yield the result in the required 12v 5A Transformerless electronic power supply which will be SMPS based having High Current (5Amp), compact and Safely isolated from mains supply (220v 60Hz).

Circuit diagram of 12v 5amp transformerless power supply. (Here the input EMI coil is for stability and is optional.)

Here a high power Mosfet is playing the role of switching component ( to be safe with high reverse voltages and can handles high current easily) and this is used for triggering the primary winding of ferite cored transformer which sets the high frequency of mains rectified DC which we get from rectification of mains.

When Mosfet is switched ON, then 470kohm resistor charges the Mosfet gate to start conduction and start's the switching action.

Above action induces voltage across the Auxillary winding of ferrite cored transformer which will result in a feedback voltage across the voltage Gate though 2n2 100v capacitor, Which makes or force the mosfet to conduct even Higher power.

As soon as this happens, the primary winding of ferrite cored transformer gets connected to the full 310V DC, which is the rectified voltage via the mosfet drain/source terminals.

During this process, the voltage across the 0.22 ohm 1Watt resistor connected to the mosfet source tends to cross the 0.6 Voltage level, which then instantly triggers the transistor BC546, which shorts the gate of the mosfet to ground makes it's state switched OFF.

This ensures the cutting-off the auxillary feedback voltage at Auxillary winding of transformer and restoring the entire primary section of transformer(ferrite cored) to its original state switched OFF.

Now thecycle begins Afresh and this is switched on-off continuously at Approx. 60kHz rate which can be varied by increasing or decreasing the values of 2n2 feed back capacitors and 100pF base capacitor of transistor BC546 NPN, Although it is not recommended.

During the period of switched OFF state of the primary winding of transformer, an induced equivalent back emf(electro-motive force) is transferred to the secondary winding of transformer which translates it to the pre specified stepped down low voltage and high current secondary winding's output. 

Now, the secondary winding's output is appropriately rectified and also filtered by filter condenser.\

Now a feedback stage across the secondary and the primary stages is implemented through a opto-coupler, which determines the required stable and regulated output voltage so that we can use it safely.

The zener diode here associated with the opto-coupler which may be changed or altered for getting different stabilized outputs we need.

Here, it is fixed to about 14.4 Volt, which becomes the optimum level for producing 12 V output. 

Here the current output value of this transformerless electronic power supply is @ 12V & 5 amp smps based can be changed by two different methods.

                1. By modifying the wire thickness of secondary winding of the transformer so that it can carry high currents value without burning or overheating it.
                2. By altering the value of 0.22 ohm resistor connected across the source and ground terminals of mosfet. 

Click here to learn How to wind the Ferrite core transformer used in above diagram.

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