Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Auxiliary output and poor cross-regulation, Flyback converter

Status
Not open for further replies.

strape81

Junior Member level 3
Joined
Dec 16, 2011
Messages
25
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,283
Activity points
1,558
Hi all,

I am currently working on a 65W flyback converter which is controlled by a NCP1217A PWM controller.

The problem is the auxiliary output which supplies the PWM controller. When the main outputs are not loaded, I measure a 12,8V voltage at the auxiliary one but when they are fully loaded then the auxiliary output is measured at 22Volt which is unacceptable (datasheet NCP1217A: Vccmax=16V).

I have two questions:

1) Is a Zener diode the best solution in order to clamp the Vcc-voltage at 15V or should I work more on something else, for example transformer?

2) Can this cross regulation problem cause problems to the short-circuit-protection function of the controller? The converter at no circumstance enters the protection mode when a short occurs.

some infos:

The flyback transformer has a sandwich winding in order to reduce leakage inductance: (from bottom to upper layer) PrimA - Sec1 - Sec2 - PrimB - Vcc
Lprim=930uH , Lpleak=10uH , Nprim=58turns, Nsec1=10turns, Nsec2=14turns, Nvcc=10turns

The auxiliary circuit is quite known: Resistor - Diode - el.Capacitor
R=10ohm, C=47uF


Thanks in advance,

Efstratios
 

Attachments

  • NCP1217-D.pdf
    286 KB · Views: 3

goldsmith

Advanced Member level 5
Joined
Dec 14, 2010
Messages
3,986
Helped
739
Reputation
1,482
Reaction score
725
Trophy points
1,413
Location
Tehran - IRAN
Activity points
24,529
Hi Efstratios
It seems a bit strange . but you can use a zener diode across the vcc pin of your driver . or a resistor in parallel with auxiliary winding . but i think a simple zener will be better . ( 15 volts ) ( by the way i hope that you know a flyback converter shouldn't be without load ! )
Best Wishes
Goldsmith
 

strape81

Junior Member level 3
Joined
Dec 16, 2011
Messages
25
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,283
Activity points
1,558
Thanks goldsmith for answering my question...about the load u are right...normally I have a light load of 150mA at the outputs
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top