# PCB Heaven

## General Category => Analog discussion => Topic started by: Mercury on April 05, 2008, 12:37:43 PM

Title: Switching power supply
Post by: Mercury on April 05, 2008, 12:37:43 PM
I see everywhere the switching mode power supplies and all insist that the are much more efficient than the classic linear power supplies. I wonder if someone knows how the SMPS works. I mean the principal of their operation and why they are more efficient than the linear PSUs.

Thank you

Gab
Title: Re: Switching power supply
Post by: Andre on April 06, 2008, 14:00:06 PM
for example you have a power supply that uses 10 volts as input. if you connect a circuit that uses 1A@5 volts, there is a remaining power that goes out of the psu as heat. The efficiency is calculated by Pout/Pin. Pin=10W, Pout=5W, so the efficiency is 50%.

The SMPS uses another way. They store the remaining energy in inductors and capacitors. In the previous examle, in case of stepping down voltage, the connected circuit requires 5W. The psu does not take constantly 10W, but it takes 10W in average by switching on and off. The output is standard 5W as the capacitors and inductors keeps it alive. With this way, an efficiency of 80-95% can be achieved.

There are also step up SMPS. These can for example supply you of 15volts with an input of 10. This of course cannot be done with a linear psu.
Title: Re: Switching power supply
Post by: Mercury on April 06, 2008, 15:31:14 PM
thank you Andre
Title: Re: Switching power supply
Post by: SiEger on April 10, 2008, 20:53:01 PM
The computer PSUs are switching?
Title: Re: Switching power supply
Post by: kam on April 11, 2008, 00:27:12 AM
The computer PSUs are switching?

Yep. The new age psu are switching.
Title: Re: Switching power supply
Post by: Erkeli on April 12, 2008, 01:12:25 AM
In an SMPS the are several different topologies. The buck topology is where the input is greater than the output. The boost topology is used when you want the output to be higher than the input. The trade off is current output. This magic happens because of the way energy is stored in the inductor.

After you get comfortable with those topologies there are the CUK, FLYBACK, and the SEPIC topologies to get your arms around. The main differences are about input power (voltage and current) and output power(voltage and current). Always remember that you can't get something for nothing. In all the Switch Mode Power Supplies that you will ever see, besides all the ones that you won't, the ouput power will always be strictly less than the input power. With quick and dirty design you should be able to get 80% efficiency. With skillful and careful design you might get to 96%.
Title: Re: Switching power supply
Post by: Mercury on April 14, 2008, 18:53:56 PM
Thank you people! You really impress me in your forum!
Title: Re: Switching power supply
Post by: SiEger on June 05, 2008, 08:37:05 AM
Thank you people! You really impress me in your forum!

;) Lol mercury, are you friend of the admins?  ;D ;D ;D
Title: Re: Switching power supply
Post by: spic0m on June 05, 2008, 21:46:59 PM
You don't have to be friends as long he pays good money!  ;D  ;D  ;D
Title: Re: Switching power supply
Post by: kam on July 18, 2008, 16:52:11 PM
;) ;) ;)
Title: Re: Switching power supply
Post by: Mercury on August 06, 2008, 02:29:55 AM
Nooooooo it's not that much....  ;D ;D      :P :P :P :P :P :P :P
Title: Switching power supply
Post by: D.woorp on November 14, 2009, 07:48:56 AM
What does "Switching Power Supply" mean? Are they talking about the switch in the back that lets you decide what AC voltage to run it on or something else?
Thanks
Title: Re: Switching power supply
Post by: kam on November 14, 2009, 08:48:03 AM
What does "Switching Power Supply" mean? Are they talking about the switch in the back that lets you decide what AC voltage to run it on or something else?
Thanks

The switching power supply is a technique that allow power supplies to run much more efficient than the classic power supplies. Instead of regulating the voltage in a continuous line, it send PWM pulses. The more the duty cycle, the higher the voltage output. Read more in the PWM theory article (http://pcbheaven.com/wikipages/PWM_Modulation/), at section 4.1 Voltage and power control