Transfering power through a transformer - Page 1
Forum section: electronics / projects

author: nihial
author_rank: Regular Contributor
timestamp: December 13, 2022, 10:57:16 pm
content: Hi,I'm currently trying to transfer power to an isolated load which is a simple resistive load but with unknown value (could be open or shorted) with the simplest circuit possible.The goal is to transfer current to the load but of course without going over some limit (10-20A max in the primary) since that load could fail either in short or open.The circuit that came up is the one attached (don't mind the part numbers) :The issue with the load being unkown is that I cannot simply use a defined command pwm signal on the mosfet or I will either saturate the transformer or not transfer enough current to the load.So I think I need something that would adjust the duty cycle by monitoring the current going through the primary of the transformer.Since there's an IC for almost everything, does someone know if there is an IC for this kind of function ?I would prefer to avoid a flyback or similar controller but if nothing more or less straight forward exists I will look for one.Best regards

author: Terry Bites
author_rank: Super Contributor
timestamp: December 14, 2022, 01:36:24 pm
content: You seem to be going for an "isolated flyback" converter.The world's your oyster with respect to ic choices. You might start with everyone's favourite 40 cent jellybean the TL494.You'll find tons of app notes and design guides for thgis ic eg SLVA666 from TIMaybe check out the UCC2808 for a simple to use device.Heres great design toolboxwww.ti.com/design-resources/design-tools-simulation/webench-power-designer.html

author: nihial
author_rank: Regular Contributor
timestamp: December 17, 2022, 12:29:44 am
content: Quote from: Terry Bites on December 14, 2022, 01:36:24 pmIt's really like an isolated flyback controller, except that I don't want to regulate an output voltage but I want to regulate the current going through the primary to inject as much as I can to the other side.I will look at your references thank you for taking some time to reply

author: uer166
author_rank: Super Contributor
timestamp: December 17, 2022, 12:31:55 am
content: Quote from: nihial on December 17, 2022, 12:29:44 amA DCM flyback output is simply a current source set by primary current times turns ratio, minus losses. A peak current controlled DCM flyback would be trivial to implement and inherently stable. Just make sure to not get an open load or the output will blow up with high voltage!

author: nihial
author_rank: Regular Contributor
timestamp: December 19, 2022, 07:19:43 pm
content: Hi all,I continued to work on it and I came with the following principle that achieves what I want, components are not necessarily those in the schematicAn IC that could do the trick is uc2845 or the UCC2808 proposed here above but I need to confirm

author: Kleinstein
author_rank: Super Contributor
timestamp: December 19, 2022, 07:34:33 pm
content: Withpout a load on the secondary, the voltage can go up quite high. One would either need a rather sturdy snubber (essentially burning the power on the primary to a big zener or similar) or some kind of voltage regulation to limit the voltage and this way the power going to the snubber.