Smps Output Voltage Drops underload

[hamid159]

Smps Output Voltage Drops under load

Hi guyz,
i have made half Bridge 27V,26A..but output voltage is not constant..it is decreasing continuously with load current.1A decreses 1V approx. .what should be the reason behind it?..
Any help would be appreciated.
Thanks in advance.

 

[syenidogan]

Re: Smps Output Voltage Drops under load

Hi guyz,
i have made half Bridge 27V,26A..but output voltage is not constant..it is decreasing continuously with load current.1A decreses 1V approx. .what should be the reason behind it?..
Any help would be appreciated.
Thanks in advance.

did you use inductor at the output? yep you did i have seen your schematic later.

do you have a real curcuit or are you just simulating it?

 

[chuckey]

The impedance of C8, and L1 is in series with the output and the diode voltage drops and the DC drops in the primary of the transformer and its wiring. Also any ringing or spikes on the waveform will give an artificially high voltage at low currents. So load it up to 10% of its rated current , this give the nominal output voltage.Now load it up by an extra X amps to gets the output impedance.
Frank

 

[hamid159]

Thanks for your suggestion.
i have loaded it upto 18A...and the same behaviour.At 18A,11V drops approx. is there any way to keep the voltage constant by some method?
yes syenidogan,it is real circuit not simulated.

 

[chuckey]

The thing to do is to go around the circuit and see exactly where the DC voltage drops are and then any AC ripple due to insufficient decoupling or even excessive leakage inductance in the transformer reducing the voltage applied to the active part of the windings.
Frank

 

[hamid159]

i checked the voltage across bulk capacitors..thery also decreasing with load..at no load it is 250V but at 15A,it is 200V about 50V drops.what will be the reason?

 

[chuckey]

They could be too small, have too high an impedance or the AC input voltage drops.
Frank

 

[dick_freebird]

Do not neglect the possibility of ground rise, if your load
current gets into the reference ground significant error
can accrue. I would begin with looking at the Vref and
its reference ground point, vs load current. Be sure your
voltage feedback divider returns to the same prime reference
point, physically - on paper / screen, you get a free pass.

 

[goldsmith]

Hi guyz,
i have made half Bridge 27V,26A..but output voltage is not constant..it is decreasing continuously with load current.1A decreses 1V approx. .what should be the reason behind it?..
Any help would be appreciated.
Thanks in advance.

Hi
In addition to other guy's statements , your Gate driver is not optimum ! you need at least an RCD network before your gates after your Pulse transformer .

You know why ?


Best Wishes
Goldsmith