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.
How to determine the current relationship between primary side winding and secondary side winding when considering auxiliary winding, such as the top of sgp100 below.
Hi,
The auxilliary winding is in intimate contact with the secondary winding as it is wound on the same core, therfore any load current variation on the secondary output will cause a proportional voltage drop, which will reflect through the transformer and cause a corresponding voltage drop in the auxilliary winding which is sensed by the voltage feedback input of the IC and a rapid correction will be made to the PWM switching waveform to compensate. The overall system pulse current is monitored by the current sense resistor in the source of the switching FET which again will sense the increased load and allow for it. The turns ratio of the auxilliary winding to the primary winding will generate the correct voltage to run the IC, this will be proportional to the main secondary output winding as they have the same turns per volt ratio, so a 10% drop on the secondary will create a 10% drop in the auxilliary winding, which will be compensated for by the IC as explained above.
I hope that makes sense and is not to much of an over-simplification.
Best regards,
Bob.
Hi,
The auxilliary winding is in intimate contact with the secondary winding as it is wound on the same core, therfore any load current variation on the secondary output will cause a proportional voltage drop, which will reflect through the transformer and cause a corresponding voltage drop in the auxilliary winding which is sensed by the voltage feedback input of the IC and a rapid correction will be made to the PWM switching waveform to compensate. The overall system pulse current is monitored by the current sense resistor in the source of the switching FET which again will sense the increased load and allow for it. The turns ratio of the auxilliary winding to the primary winding will generate the correct voltage to run the IC, this will be proportional to the main secondary output winding as they have the same turns per volt ratio, so a 10% drop on the secondary will create a 10% drop in the auxilliary winding, which will be compensated for by the IC as explained above.
I hope that makes sense and is not to much of an over-simplification.
Best regards,
Bob.
Is / turns ration = Ip (Aslo applicable for peak currents) this is gross relation
Exact primary current depends upon Efficiency of the converter
The turns ration is derived from Voltage requirement at Secondary & the primary current is reflection of Secondary power (Vsec X Isec) / Efficiency = Primary Wattage & Primary wattage/ Primary Voltage = I avg Primary.
Hi,
To go a little further than rvionics, the gif I have attached may help, it is part of a design calculation sheet that I used recently, it is not for that IC though but it gives a good approximation of the relationship that you want, I hope it is useful to you.
Regards,
Bob
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
