switching powee supply problem using NE5561

[erif]

Need help to solve problem in start-up in a switching power supply using NE5561, this circuit use a circuit to get 12VDC from the 300VDC main, using a PTC and transistor.

It still working only 5 second and shutdown, all components seems OK in NE 5561 circuit, I test this circuit with and external 12VDC and work OK.

When work for this 5 second or more, all DC output voltages are OK.

Pleas need urgent help, thanks erif

 

[E-design]

Do you have the schematic of the start-up circuit?

 

[schmitt trigger]

Schematics, please. Waveforms and/or voltage readings also.

We try to help, but without meaningful info, it is only a guessing game.

 

[erif]

Need help to solve problem in start-up in a switching power supply using NE5561, this circuit use a circuit to get 12VDC from the 300VDC main, using a PTC and transistor.

It still working only 5 second and shutdown, all components seems OK in NE 5561 circuit, I test this circuit with and external 12VDC and work OK.

When work for this 5 second or more, all DC output voltages are OK.

Pleas need urgent help, thanks erif

[B]That is one of the problem, don´t have start-up circuit[/B]

Is impossible to get technical specifications for PTC C887

 

[schmitt trigger]

So if you have no startup circuit, how are you starting the NE5561 from 300 volts?????

Show us what you have done so far. What topology are you planning to use?

But I can tell you one thing already.....To reduce from 300 to 12 volt you will require either a flyback or forward topology. And in those topologies, the NE5561 is not a suitable controller.

 

[rvionics]

Check the support winding filter capacitor (once IC starts working through 300V line it needs a continuous dc supply for working which generally is fed through a separate winding + diode & filter capacitor)
Most of the time failure happens to this small filter capacitor due to stress.

if power supply is older than 4~5 years this is very common.

 

[erif]

Dear, thanks for your cooperation, after a long time I found problem, was "PTC", I replace for a normal R and power supply work fine.-
Thanks to all that support the help.-