Transformerless power supply

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Thread Starter


Joined Aug 29, 2008
hi all during searching for files talking about Transformerless power supply
i found this good files

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i hope to be active member
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Joined Apr 5, 2008

In my oppinion, transformerless powersupplies are pretty dangerous.
They are directly connected to the mains.
If a series capicitor fails and makes a short the mains will get on the output.



Joined Sep 14, 2008
Thanks Hany! I have been looking for something of this nature for some time now.

I would have to agree with bertus that these types of power supplies can be dangerous. However figures 10 and 11 do try to address those saftey concerns a some degree.



Joined Aug 21, 2008
Be careful -that application note shows a 470 uF capacitor connected between the Line and Ground! A sure fire way to cause a fire, or at least blow a fuse (you are going to use a fuse or two, aren't you?).

I suspect that L and N got reversed, but I leave it to the experts to explain.


Joined Jul 17, 2007
These are VERY DANGEROUS circuits, and should NOT be built! They are not correct!
Figures 1, 5, 10, 11 and 12 are all in error!

L1, or 120VAC, will be connected directly to the output, and the "virtual ground" will be floating at about 5v less.

It is not simply a matter of reversing the L and N inputs to correct the errors.

This is the worst application note I have ever read in my entire life.

I have put in a technical request ticket on Microchip's website, requesting them to withdraw the application note pending review.
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Joined May 16, 2005
From the very first page of the document under discussion:
Warning: An electrocution hazard exists during experimentation with transformerless circuits that interface to wall power. There is no transformer for power-line isolation in the following circuits, so the user must be very careful and assess the risks from line-transients in the user’s application. An isolation transformer should be used when probing the following circuits
Is your life and safety really worth less than the cost of a transformer?


Joined Dec 19, 2007
Did you happen to notice the load values in the Index.

Like "Figure 2: Vout at Startup with a 10kW Load" :eek:

Similar for Figures 3., 4, 6, 7, and 8. The text at least is correct...load values in Ohms.



Joined Jul 17, 2007
I haven't had time to analyze every word of the AN yet. Just quick glances at the schematics were enough for me to realize that they were absurdly dangerous.

Take Figure 1 for example. Line voltage is connected directly from the input to the output, and the "ground" is isolated from the Neutral line via R1 and C1. This means that VOUT will be at a 120VAC potential, and the "ground" will be riding about 4.3v to 4.9v below VOUT, depending upon what kind of diode is used for D2.

R1, C1 and D2 need to be moved from the Neutral line to L, and D2 turned around. However, there will still be some voltage on the N line, depending on whatever other loads are using N for a power return. This can cause great problems if attempting to connect a circuit powered by such a supply to another circuit.

See the attached.

Schematics removed by moderator

Corrected Figure 5 attached; similar problems still exist.
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