AC/DC Conversion - Transformer+Rectifier Vs Rectifier+DC/DC Conversion ?

[Hatimoooo]

Hello everyone!
I just wanted to know some advantages and disadvantages for both solutions.
I believe that Rectifier + DC/DC Conversion is more efficient and less expensive, but a bit difficult.
But why is Transformer + rectifier solution still used?
Please, I need some arguments.
Thanks

PS: The DC output will be used for a RL + battery charging

 

[ehsanelahimirza]

DC/DC conversion is more expensive in case you need much power
you need more parts in your circuit for a Rectifier+DC/DC converter
but Transformer+Rectifier doesnt need more circuitry. simple circuit and reliable in this case.
but in other case complex circuit, and specialized parts to be used, you will need switch mode circuitry and non-conventional transformers.

if you need very low power like for charging a mobile, then Rect+DC/DC is good, it will use simple components like zener and those too of low power ratings,
and you need to step down voltage so Regulator ICs work instead of transformers.
so Rect+DC/DC is good for low power applications, because at this stage cost of DC circuit is reduced as compared to AC transformer
hope this helps

 

[tpetar]

Hello everyone!
I just wanted to know some advantages and disadvantages for both solutions.
I believe that Rectifier + DC/DC Conversion is more efficient and less expensive, but a bit difficult.
But why is Transformer + rectifier solution still used?
Please, I need some arguments.
Thanks

PS: The DC output will be used for a RL + battery charging

Transformer based PSU will always be used. Thise PSU can be simplified, but often needs more space and this PSUs are heavier then switchers. Price is discutabile if we speak about quality switcher PSU, we all know that you can buy PC PSU for 7eur and better for over 50eur and up. About price of specialized and finest lab switchers PSUs for higher currents I dont even want to talk about, its like small wealth. DC/DC converters in modules are not cheap and can be even more expensive then transformer.

Switcher often have lots of ripple on output and need additional filtering if this is not done already inside of device. Transformer have good and clean current, and dont need some special filtering. Finest current goes out from transformers PSU.

Transformer based PSU if transformer is calculated and made good, can work many many years, but average chinese switcher PSU dont have that luck.

Usually switchers require permanent presence of minimal load, and this is not the case with transformer based PSU.


You can count always on transformer based PSU reliability, this is my personal opinion, and we assume that trafo is correctly calculated and that its maded on right way with good materials.

For your smaller projects for power source needs you can use MC34063 to adjust required voltage (this IC just as one example, there is more ways and ICs for this).

By the way, transformers is used in both types of PSUs, but on different frequencies and with different construction and materials.


You can search existing threads on EDABoard, I'm sure there is threads about this.


;-)

 

[Hatimoooo]

Hello again!
Thank you for your answers. You pointed some points I really didn't know to be honest .
For a 2.5kVA and 0.5% voltage ripple in the output. I think I'm going to choose reliability for my UPS.
Thank you again.