Power Supply Modules

Power supply modules are easy to do instead of assembling one. If you assemble you may have a power supply to your taste / requirement and may cost more or less the same as a ready made one.      So lets see how may types of power supplies are present
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Linear Power supply modules:

LDO Module

You can assemble a linear power supply module or buy one. Linear power supply are cheap, easy to assemble and easy to work. These power supply will have very less / no electrical noise on the output.

These power supply module or regulator are good if you are powering up a 5V / 3.3V micro-controller with LED, keypad connected to its pins and in general current is less than 100mA at 12V input. The problem is the voltage across the regulator times the current is the power dissipated in the regulator.

Example if you use a 12V adapter and need only 5V output the voltage drop across the regulator is 7V and the current about 0.1A. Power dissipated by the regulator will be 7V x 0.1A = 0.7W. This wattage should be properly dissipated else if the regulator has thermal shut down feature it will shut down.
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Switching power supply.

Switching power supply are used when higher power > 1W drop is observed across the voltage regulator. Example you have 12V power supply and want to drive GSM modem,  LED array etc then you may consider using buck converter.
Obviously if you need to convert 5V to 12V then you have to go with the boost converter, which is a switching converter.
All switching converters will have a minimum one inductor, one switch (BJT / MOSFET) and few capacitors to smoothen the output ripple.
Switching power supply will have EMI associated, suppose if you have a radio near to these converters the radio will catch up the switching noise and the sound from radio will be distorted, higher the switching current  higher the magnitude of disturbance. In order to reduce the EMI it is necessary to place the filter inductor /common mode choke & ferrite beads at the input and the output side of the converter along with filter capacitors.

Buck converter

Buck converter module

Buck converter circuit

Buck converter converts high DC voltage to Low DC voltage; this does not mean current will also be reduced - output power = input power - converter efficiency. A 12V 1A(12W) input can power 5V 2.4A (12W) if the converter efficiency is 100%.

Usually it is possible to achieve full load efficiency > 95% in these converters. No Load efficiency will be very low; because the  converter consumes little power even when no output is present.

In boost converter the switch(MOSFET) is in series with the input and output. The output voltage of this circuit is dependent on the duty cycle in which the MOSFET (S) is driven; higher the duty cycle; higher the voltage output. output voltage Vo = Vin x duty cycle.

Boost converter

Boost Converter

Boost Converter Circuit

Boost converter increases the input voltage to a desired output voltage which is greater than the input voltage (Vo > Vin). Here the switch(MOSFET) is in parallel to the supply bus after the inductor. Once the switch closes current flows thru the inductor and builds voltage

VL = L x di/dt. when the switch opens the inductor voltage will become in series with the voltage source and the net output voltage = Vin + VL. It should be noted that the switch has time period for which it should be closed; beyond which the inductor current will become infinite and damage the switch. In practice the switch should be opened before the inductor voltage has reached desired voltage level / the inductor current gets saturated.

Boost converters find application in driving LED lights, Fluorescent tubes, motors etc.

Fly-back converter (AC to DC)

Flyback converter AC DC supply

Flyback converters are mainly used for AC to DC conversion. The principle of operation is when the switch (MOSFET) turns ON energy is stored in the transformer primary coil; when the switch turns OFF the stored energy in the inductor is transferred to the secondary coil. voltage induced in the secondary coil is rectified and filtered. Secondary voltage is measured and a opto-coupler feedback is present to keep the output voltage constant. Flyback converter is a simple topology which can be applied for power supplies up to 100W; has minimum components and costs less compared to other type of AC to DC converters.

Brick / Sugar cube AC to DC modules:

Sugar Cube power supply.

Brick / sugar cube modules also referred to closed frame power supply makes any application design look good, simple and more robust in operation as they are sealed within a plastic enclosure which protects against the humidity, dust. But these are costly and were only available for industries as it was to be brought in bulk. Currently these modules are available in retail. 

Sugar cube power supplies are available in 3W, 5W and maximum up to 10W. These require external EMI filter, input Fuse and  capacitors at the output to filter the voltage ripple.