I have a 5 V 3 A SMPS which says that it can take input voltages between 100 V and 240 V AC and frequencies between 50 Hz and 60 Hz.

  • How do these work?
  • How can they take such a large range of input voltage and provide a constant output voltage and current?

I know the basic working of the SMPS Technology. But all the articles I read suggest a fixed DC input voltage to produce a desired voltage below this input. How can such a wide range AC produce a fixed DC input voltage to the SMPS IC?

  • 3
    \$\begingroup\$ The miracle of feedback control. \$\endgroup\$ – pericynthion Nov 3 '18 at 2:40
  • \$\begingroup\$ A bit of explanation would help..! \$\endgroup\$ – Sagar Nov 3 '18 at 2:44
  • \$\begingroup\$ smps.us/power-supply.html \$\endgroup\$ – TimWescott Nov 3 '18 at 2:56
  • \$\begingroup\$ You call that wide? Oh, please ;) Look at universal input range. \$\endgroup\$ – Long Pham Nov 3 '18 at 3:00
  • \$\begingroup\$ moved to answer, by analogsystemsrf \$\endgroup\$ – analogsystemsrf Nov 3 '18 at 5:21

You may as well ask "when water is poured from a bottle into a glass why is it that the glass is always filled (assuming there is sufficient water) regardless of the size of the bottle or how much water is in it?" The answer here is that the person filling the glass is watching the water level in the glass.

The power supply monitors the output voltage, comparing it with a reference and if the output is high enough it sends a signal back to the controller to reduce or shut off the flow.

"that is the magic of feedback"

The reference is often a Zener diode or a TL431 and the signal usually goes though an opto-coupler.


Energy is stored at HIGH VOLTAGE at the input capacitor C1; using a buck regulator, energy is transferred into an inductor L1; then switches alter the topology, and the energy in L1 is transferred into the output capacitor C2. Even as ripple on C1 (from 50 or 60Hz rectification) causes the voltage into the inductor to vary, the feedback circuit adjusts the ON TIME of the switch, with this variable ON TIME resulting in a constant amount of energy loaded into L1 each time.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.