Does using voltage regulator in power supply further reduces the rippling?

Question

I want to build a 12 V DC power supply. Which one is a better approach?

1. If I have a step down transformer 220/12 volt and after doing its full wave rectification and smoothing its wave using capacitor, place the load in parallel to the capacitor.

or

2. I should rather get a 220/15 volt transformer and after doing its full wave rectification and using smoothing capacitor i should use a 7812 voltage regulator at the rectified output along with capacitors recommended to use with voltage regulator? and after doing all that I should place my load to the output of voltage regulator?

Because I heard that voltage regulators reduces the rippling. Is it true?

Answer 1

Adding a linear regulator will significantly reduce the ripple, but it has its downsides.

1) The regulator has a minimum "dropout" voltage, in this case about 1-2V depending on current. To account for this, your first stage needs to have an output voltage greater than 12V by at least the minimum dropout voltage - so, maybe 14V.

This means you're dissipating some power (V_dropout * I_load) in the linear regulator. In addition to power loss, you may have to pay attention to heat sinking it appropriately.

2) Depending on the ripple before the regulator, you may have to increase that "drop out" voltage even further, because you have to do the dropout calculation based on the minimum value of the ripple waveform (not the average "DC" value).

The advantage of the linear regulator is that the final waveform will be perfectly clean - the final ripple will be plenty low enough for almost any load.

So, what's the right approach? Depends on your load. If you're powering, say, a heater, the ripple probably doesn't matter. If you're powering a circuit with a secondary power conversion (IE, it takes your 12V and converts it to 5V), you're probably ok with high ripple, depending on the quality of that 12V to 5V converter. If you're directly powering something sensitive (say, an amplifier or other analog circuitry), you probably want to use the regulator.

Answer 2

I will not say anything extra about ripple reduction. Others have already made the necessary explanations.

I just want to warn you about the other things more important than ripple reduction.

Heat dissipation: Selvek has made a good explanation in his/her answer.

Size: If you use a 220V-to-12V step-down transformer then the output voltage will be around 16VDC after FW rectification. So you can directly place a 7812 regulator right across the smoothing capacitor (Remember the power dissipation here). BUT the RMS current drawn from the secondary winding will be twice (or even higher) the DC output current due to the need of a big smoothing capacitor. For example, if you're planning to make a 12V/1A power supply then the secondary winding should handle at least 2A_RMS. For this reason the required transformer can be "bigger" than you imagined.

I just want to recommend you to make an offline SMPS but it looks that you don't have enough experience about the topic.