Problem With SMPS

[xyz9915]

Hello All,
The attached circuit I found in a forum and it is working satisfactorily with Mains AC 100 to 150 Volt & 175 to 230Volts. But I noticed a problem that from the voltage range 151V to 175VAC this circuit stops working. Why? I do not know... Can someone explain me what happens among this voltage span


I am using variable transformer at mains AC input to observe its working voltage range

 

[Sorento]

could be that 7812 VDD regulator falls out of regulation ...
check VCC / VDD supply and compare to undervoltage lockout spec

 

[sreten]

Hi,

I'd guess it essentially has two modes of operation being relatively high power.

One for around 115 VAC and the other for around 230VAC would make a
lot of sense. Somewhere inbetween, far too high for 115 VAC and far too
low for 230VAC it doesn't try, both modes won't work makes a lot of sense.

I can't tell how it does that or surmise the difference between the modes.
(Though it clearly would be a switch from bridged to parallel somewhere.)

rgds, sreten.

It might be typical of SMPS's, that claim 100VAC to 275VAC compatibility,
two modes, knowing the overlap range is basically not a real practical issue.
That makes a lot more sense than a single mode for 100VAC to 275VAC.

 

[nigelwright7557]

It clearly says 220VAC on the diagram.
Are you sure it is supposed to work with other voltages ?

 

[sreten]

Hi,

If it has two modes the switch has to be near the input where it matters.

rgds, sreten.

 

[xyz9915]

In my opinion a typical switch mode power supply works over a wide range of voltage, error amplifier controls the pulse width to maintain the voltage at output, and I also mentioned in the post that this circuit works but only a voltage range 151vac to 174vac inhibits it to stop working.

 

[nigelwright7557]

What does the spec say on the label.
They will often have on 85-240VAC input if they work with full supply range.

If it doesn't have this then its likely just 240VAC or 110VAC in which case who knows how it will behave at in between voltages.

 

[xyz9915]

What does the spec say on the label.
They will often have on 85-240VAC input if they work with full supply range.

If it doesn't have this then its likely just 240VAC or 110VAC in which case who knows how it will behave at in between voltages.

I agree with you. But I need solution because only it stop working among a short range of voltage

 

[nigelwright7557]

I am not convinced it is a wide range mains input SMPS.

1/ It clearly says 220VAC on the circuit diagram.

2/ The 12 volt regulator needs at least 18 volts to function. So if it is 18 volts at 110VAC then at 240VAC it will be 39 volts which is out of spec for the regulator.

3/ The circuit has voltages marked on it that can only occur with 240VAC.

 

[sreten]

In my opinion a typical switch mode power supply works over a wide range
of voltage, error amplifier controls the pulse width to maintain the voltage
at output, and I also mentioned in the post that this circuit works but only
a voltage range 151vac to 174vac inhibits it to stop working.

Hi,

The only sensible reason that would happen is if it has two modes.

Its not a problem if its normal operation.

rgds, sreten.

 

[xyz9915]

I am not convinced it is a wide range mains input SMPS.

1/ It clearly says 220VAC on the circuit diagram.

2/ The 12 volt regulator needs at least 18 volts to function. So if it is 18 volts at 110VAC then at 240VAC it will be 39 volts which is out of spec for the regulator.

The 12v transformer power separately from 230vac to maintain voltage at regulator (not shown in the schematic)

 

[xyz9915]

Hi,

The only sensible reason that would happen is if it has two modes.

Its not a problem if its normal operation.

rgds, sreten.

I want this circuit to work with a wide range of voltage (100v to 240v)

 

[xyz9915]

The Problem has been solved by replacing 0.1uF capacitor with 10uF capacitor at Pin9 (Compensation) of SG3525. Now the smps works from 100vac to 240vac.

Thanks to Everyone

 

[dmills]

That circuit is clearly not a univeral input supply, and I am somewhat surprised that it works at all at very low input voltage.

The canonical way to do universal input (And at 900W it is not a bad idea anyway) is to start with a power factor correction stage (a boost converter) to produce somewhere around 400V on the storage caps irrespective of the applied input voltage, then follow that with the standard isolated switcher curcuit. Note that PFC voltage control loops can get a bit tricky when the load is audio....

This is all non isolated power electronics so rapidly gets behond the proper scope of these forums.

73 Dan.

 

[xyz9915]

Although the smps works satisfactorily but can someone explain how a big capacitor fixed the problem because a big capacitor capacitor at Pin9 (Compensation) is not usual.