hi,

I am First Time Design SMPS Circuit Through Power Integration Software.
i attached my SMPS Power Design.
i have one Doubt in this Design whether i need 7805,7812 and 7824 Regular Circuit after smps output or not??

 

It depends upon what output voltage variation and ripple voltage your loads can tolerate.

 

hi crutschow,

Thanks for Reply.

is that smps gives steady output like 78xx series?? Because i searched on google.none of circuit has 78xx series ic.

 

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is that smps gives steady output like 78xx series?? Because i searched on google.none of circuit has 78xx series ic.

The output regulation will be determined by the transformer winding resistance (except for the bottom output which is in the regulation loop).
If you want better regulation then that, than you need to add some linear regulators on the output.
That means the transformer output voltage will need to be increase by the dropout voltage of the regulator.
For best efficiency you should use LDO type regulators, not the 78xx series which have a dropout of a couple volts or so.

 

An Smpsu doesn't use linear regulators, they use an opto coupler and usually a Tl431 precision zener, to regulate one of the outputs, they use a tight feedback loop that alters the pwm, this controls all the outputs, and is not limited by current or power wasting.

 

hi,

I am First Time Design SMPS Circuit Through Power Integration Software.
i attached my SMPS Power Design.
i have one Doubt in this Design whether i need 7805,7812 and 7824 Regular Circuit after smps output or not??

Quite a lot of early SMPSU designs used 78xx post regulators - PC PSUs in particular have adopted tight coupling between the secondary windings. Originally only the 5V rail was sensed for regulation, but I think the 3.3V rail is more critical since its introduction. An ATX PSU I stripped and hand traced, had a resistor summing network to combine the 3.3 & 5V into the TL431 circuit.

In some high end network hubs, they use completely separate 5 & 12V SMPSUs.

If you don't have tight coupling between secondaries - you may have to use post regulation on all but the regulated rail. this means higher secondary voltages to cover the 3-terminal regulator's drop out voltage.