Are you using sufficient inductance in series with the primary? (ie the "primary" that the vendor meant to be the secondary)
Is you primary current looking sinusoidal?
The primary consists of many turns of thin wire. Normal usage has a power transformer designed to offer high impedance to the electric company.
Raw math calculates as 97 ohms when drawing 500 Watts at 220 VAC.
970 ohms when drawing 50W.
So when operating it in reverse direction, you're driving a new load from an unknown impedance inside the transformer. We should expect meager current flow when a load is in place of the electric company .
View attachment 181122
This is where I am unclear, also my second post was little confusing to you. Well I know, ideally it should keep it at 8.4v, but whats then voltage feedback pin for?Hi,
12V / sqrt(2) = 8.48 V
What output voltage do you expect?
Klaus
Would be really helpful to see a sketch of the setup, e.g. how you connected the feedback.
Obviously it can't regulate more than 8.4V, thus it just can regulate downwards., but whats then voltage feedback pin for?
Upper limit of 8.4 and regulation below sound logical, however in reality it doesn't do any downward regulation, i checked. It simply stops when VFB cross a threshold on either side, in between voltage stays flat 8.4vHi,
Obviously it can't regulate more than 8.4V, thus it just can regulate downwards.
Maybe 6V...8.4V.
--> thus use a transformer with a higher voltage ratio.
Klaus
You used a 220V --> 12V transformer.
Now the "12V" is at nominal load. To compensate for the voltage drop caused by the load current the transformer was designed for a higher output voltage at no load. Maybe 13.5V (winding ratio 220 : 13.5)
Now if you connect this transformer to 12V RMS (which is impossible in your configuration)..
It would output 195V on no load, and even less when load is applied.
With 8.4V RMS input you could expect 137V @ no load. Les with load.(example values)
Klaus
Feedback i now take from LC filter output, which earlier went into transformer. I changed resistance from 2x100k ohm to 1x10kohm in series. VFB is now maintained about 3v and board works fine as long as no load connectedHi,
if you remove the transformer ... how can the feedback be "as usual"?
Makes no sense to me.
What is the expected V_FB?
And what is the measured/tested V_FB range?
Klaus
Ok, now some improvementsHi,
I don´t hink this is correct:
--> I expect a "fixed" voltage for V_FB not a range of 2.75V ... 3.1V
* No information about the measured/tested voltage range.
* No schematic/draft about the FB wiring.
Now post#14 ... I´m about to leave.
Klaus
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