A few years back, if you take a power adapter designed for 110v and plug it in 220 v; you end up with a burnt adapter ( fuses etc never worked for some reason or another) but this is NOT related to this post.
Now every adapter has TWO things:
1. 110-240 tolerance
2. use switched power supply concept

Can someone explain to me, how such a circuit adapt itself "Magically" to accept 100-240 range without blowing a fuse !!!!!

 

Fast active switching electronics allows an adapter to control the amount of power it TAKES from a source as well as the amount is DELIVERS to a load.

The older power adapters used passive componentry to control power demand and delivery (resistances and inductances) and these were designed to operate at specific voltages.

 

BTW, N.A. standard has been 120v/240v for some decades now.

 

The switching power supply in the adapter is both an AC to DC converter and a regulator. The transformer has a fixed turns ratio, so that part is similar to older linear adapters. but the switcher has ab input-side circuit that varies the amount of time energy is moving through the transformer.

*** NOTE TO PEDANTICS: This is a reduced and simplified explanation, not a tutorial on isolated flyback design.

By varying the time, it varies how much energy moves through the circuit. The time periods are shorter for high input voltages, and longer for lower inputs, because for x amount of energy it takes less time at high voltages. The output side regulator sends a signal back to the input side telling it to increase or decrease the energy flow, whatever it takes to hold the output voltage constant when the output current varies.

ak

 

BTW, N.A. standard has been 120v/240v for some decades now.

The TS is older than both of us, and in Egypt. People of a certain age (me) still think of it as 110. I think 110/220, but write 120/240.

Residential power in Egypt is listed as 220.

https://en.wikipedia.org/wiki/Mains...ble_of_mains_voltages,_frequencies,_and_plugs

ak

 

The switching mode supply uses the rectified mains voltage as an input, and there is a diode/transistor switching scheme that creates the required higher input voltage when the lower mains voltage is present. So the changing arrangement is on the input. But the fact that the input circuit can adapt is only useful because the switching inverter can use the DC voltage input.

 

https://www.sunpower-uk.com/glossary/what-is-universal-input/

 

Usually it's a flyback converter.
The mains is rectified to produce either 325V or 162V.
This voltage is switched across an inductor. The energy stored in the inductor is \(E=\frac{V^2 t^2}{2L}\). Every cycle, the inductor energy is transferred to the output.
The electronics vary t to keep the output voltage constant.

 

Pulse adapters use pulse-mode transistors that operate at higher voltages at higher input voltages. The technology has evolved and high-voltage transistors are now cheaper. Therefore, adapters for an extended range of input supply voltages have become quite cost-effective. In addition, microcircuits with a built-in high voltage transistor appeared. And the old adapters for the USA used relatively low-voltage transistors (due to lower cost).

 

The TS is older than both of us, and in Egypt. People of a certain age (me) still think of it as 110. I think 110/220, but write 120/240.

Residential power in Egypt is listed as 220.

https://en.wikipedia.org/wiki/Mains...ble_of_mains_voltages,_frequencies,_and_plugs

ak

I am Egyptian too...And you know a

https://www.sunpower-uk.com/glossary/what-is-universal-input/

For not knowing the principle behind the "flyback converter "; I agree and I will do the check-up soon (;
few years for us could be 100 years!!! easily (;

 

The switching power supply in the adapter is both an AC to DC converter and a regulator. The transformer has a fixed turns ratio, so that part is similar to older linear adapters. but the switcher has ab input-side circuit that varies the amount of time energy is moving through the transformer.

*** NOTE TO PEDANTICS: This is a reduced and simplified explanation, not a tutorial on isolated flyback design.

By varying the time, it varies how much energy moves through the circuit. The time periods are shorter for high input voltages, and longer for lower inputs, because for x amount of energy it takes less time at high voltages. The output side regulator sends a signal back to the input side telling it to increase or decrease the energy flow, whatever it takes to hold the output voltage constant when the output current varies.

ak

very well explained. Thank you.
The keyword is the "feedback" that is where the "Magic" starts.

 

For not knowing the principle behind the "flyback converter

Take an inductor with two windings on the same core.
Every 10us, connect DC to one winding for a time t. The current increases linearly, and the energy stored is proportional to the square of the current.
Switch off the DC. The inductor requires that current must continue to flow and it does so in the secondary winding. The current charges a capacitor through a diode.

 

OK, the initial versions of the dual input voltage power supplies had a scheme that altered the rectification scheme so that the spread of DC input voltages was not so very broad. Something like a voltage doubler for the ow range and just a pain half wave rectifier for the higher input voltage range. Even now there can be range switching to improve efficiency, athough it will be a bit more complex.

 

Back when, SGS had a TRIAC and control chip combination targeted at making a power supply input stage auto-ranging. It monitored the input voltage (with noise filtering and hysteresis) and drove the TRIAC to switch between the two modes by grounding (or not) the centertap of two large bulk filter capacitors in series.

Found it. Still an active part. Page 5 of the datasheet has the circuit.

https://www.st.com/resource/en/datasheet/avs08cb.pdf

https://www.st.com/en/thyristors-scr-and-ac-switches/triacs.html

ak

 

Thanks for providing the link, AK! That is the sort of circuit that I read about when the universal supplies were big news. And I recall the confusion among some of the less technical folks when they then started to assume that any "switching" power supply would also switch mains voltage range. They did not pay attention to the range switches on the power supplies, and so popped many fuses.
Really, that change-over scheme in the app note is brilliant in both function and simplicity.
The wide input range units that do not change modes are an interesting alternative, and it is interesting to consider the compromises that must be made to provide a constant output with the input variable over such a wide range..
And with either type of input scheme, providing an AC output anything close to a sine wave will still be an interesting effort.

 

Way back, Zenith had an open-frame 400 W switcher that moved the price/performance bar. We negotiated an excellent volume price, and put them in a bunch of mid-sized VME and other systems. It was a 110/220 device, not universal input and not auto-ranging. It had a 2-pin removable shunt very much like the little 0.1" guys on computer boards, except this one was 0.312" wide and rated for 10 A. It plugged onto a 3-pin 0.156" header with the center pin removed (for UL spacing). I still have some of the shunts somewhere.

Gold star to Zenith for using an industry-standard header. I got a demo kit from SGS, plugged it onto the header pins, and the little puppy actually worked. Even though there were no cuts, jumpers, or any other modifications of the pc board, Zenith wouldn't sanction this adaptation so we never shipped anything with it installed.

ak