Problem With SMPS voltage

[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

 

[ronsimpson]

I can't see the wave forms!! LOL
You have a little transformer to make 12V for the ICs to live from. Do you do something to switch from 110 to 220? These transformers often have a 110 and a 220 input winding. What is the voltage at the input of the LM7812 over the 110 to 22 range.

 

[xyz9915]

The 12v transformer operate separately from 220vac, only the smps input provided with a variable transformer which delivers 80VAC to 240VAC so I can change input voltage as i desire

 

[cowboybob]

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

What are the voltage readings across the listed "310V" and "Float" points of the circuit as you vary the input?

 

[xyz9915]

Voltage level listed at 310v is dependent upon input mains voltage. for 230VAC it may be around 325VDC & for 115VAC it is near 165VDC. The voltage at Float point is half of the volt at Flag (310V).

 

[ronsimpson]

First, you have done well to get power from a off line supply. Many people on the forum bread board a switcher and fight noise. You have done farther than many.

The 1uF 400V cap seems small. I would have chosen that value if I was running resonant, but I don't think you are.

What does the bottom FET gate look like then it is working and not working. Maybe 25% on and 75% off???

 

[xyz9915]

I think capacitor value 1uF is not much important, because it works below 150vac and also works above 175vac

I did not checked status at FET gate. It will be checked after weekend (Monday)

 

[cowboybob]

Voltage level listed at 310v is dependent upon input mains voltage. for 230VAC it may be around 325VDC & for 115VAC it is near 165VDC. The voltage at Float point is half of the volt at Flag (310V).

xyz9915,

Not the voltage from ground to "310v" (and then "float"): the voltage from "float" to "310v" (across those two) as you vary the input voltage.

Since you say that the output of the SMPS disappears as you vary the input from 151VAC to 175VAC, it would seem wise to discover what becomes of the voltage(s) being supplied by the "310v" and "float" nodes to the SMPS.

 

[xyz9915]

xyz9915,

Not the voltage from ground to "310v" (and then "float"): the voltage from "float" to "310v" (across those two) as you vary the input voltage.

OK, I will check the voltage from Float to 310V to discover what happens from 151vac to 175vac

 

[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

 

[cowboybob]

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

Good catch, xyz9915!

How did you arrive at that fix?

From this?:



Or something else?

If you leave your input at, say, 170VAC, for an extened period of time, does the output stay steady, or eventually shut down (as a result of the cap finally discharging)?

Just curious.

 

[xyz9915]

The voltage remain stable t any input voltage from 100vac to 240vac and does not eventually shuts down as a result of capacitor discharging. This function is available with Pin8 (soft start) which slowly increase duty cycle to prevent from inrush current at start-up.