Re: Switched Mode Power Supply
Posted: Tue Jul 18, 2017 2:20 pm
Niels,
I have been following this thread from the start, and I feel it is time to chip in.
My background is in the special full bridge converter that you will find in a DualResonantSolidStateTeslaCoil, where I have come up with a couple of engineering "firsts", as well as produced several units for museum, art and television shows. I have also built a handfull of the most common DC-DC converter topologies.
1. About driving mosfets with an Arduino:
Take a look at the datasheet of a IRFP250
https://www.google.dk/url?sa=t&rct=j&q= ... uw&cad=rja
on page 4 you will see this diagram: This diagram shows how the Drain-Source voltage relates to the charge you transfer to it (the gate). As you will see, the voltage stops rising momentarily when it reaches 6.5 volts, and this horisontal line on the graph is called the miller plateau, this is where the mosfet starts to turn on. You have to drive the gate higher to turn the mosfet properly on, and you can not do this with the output of an arduino, which only puts out 5 volt.
The arduino can also not deliver enough current to turn the mosfet on properly, and that is why there are gate driver chips. You need a totem pole driver with a bootstrap capacitor to also turn the top mosfet on.
2. Topology
There is no need to invent a new topology, as the one you show in your last post. Read a good application note on topologies
https://www.google.dk/url?sa=t&rct=j&q= ... SA&cad=rja
and choose one that is suitable for a high power supply. You will see that most of the topologies stop at around 500W, and from there, there are only the resonant converters that come through. My own pet is the series resonant converter, because it is easy to build and understand, it supports zero current switching, and with that, a lot is gained. If you have ever tried to design snubber circuits for a hardswitching converter you will follow me here. Zero voltage switching is even better, but then you have to build a LLC converter, which is harder to construct.
As a note to topology: My advice, ditch the arduino and get a proper dedicated converter chip that is designed to do just that job. A good old fasioned chip for an entry level converter is the TL494, but there are newer ones also.
3.Layout
When it comes to building power electronics, proper layout practices are key, and along that note, I will encourage you to post actual pictures of your work, because in that case we will probably be able to point at obvious mistakes.
These are the most obvious points I will point at, you have a lot of gumption and that is commendable, and needed, if you are going to see this project to the end with success. The most important advice I can give you is: read the application notes from TI, Linear, etc. They have covered this subject in great detail, and often the notes are written by authors who have exceptionally great command of written language, so that it is well suited for even a lay person studying on his own.
I wish you good luck on this journey, there are a lot of frustrating moments ahead, but there is also a lot of satisfaction to be gained.
Cheers, Finn Hammer
I have been following this thread from the start, and I feel it is time to chip in.
My background is in the special full bridge converter that you will find in a DualResonantSolidStateTeslaCoil, where I have come up with a couple of engineering "firsts", as well as produced several units for museum, art and television shows. I have also built a handfull of the most common DC-DC converter topologies.
1. About driving mosfets with an Arduino:
Take a look at the datasheet of a IRFP250
https://www.google.dk/url?sa=t&rct=j&q= ... uw&cad=rja
on page 4 you will see this diagram: This diagram shows how the Drain-Source voltage relates to the charge you transfer to it (the gate). As you will see, the voltage stops rising momentarily when it reaches 6.5 volts, and this horisontal line on the graph is called the miller plateau, this is where the mosfet starts to turn on. You have to drive the gate higher to turn the mosfet properly on, and you can not do this with the output of an arduino, which only puts out 5 volt.
The arduino can also not deliver enough current to turn the mosfet on properly, and that is why there are gate driver chips. You need a totem pole driver with a bootstrap capacitor to also turn the top mosfet on.
2. Topology
There is no need to invent a new topology, as the one you show in your last post. Read a good application note on topologies
https://www.google.dk/url?sa=t&rct=j&q= ... SA&cad=rja
and choose one that is suitable for a high power supply. You will see that most of the topologies stop at around 500W, and from there, there are only the resonant converters that come through. My own pet is the series resonant converter, because it is easy to build and understand, it supports zero current switching, and with that, a lot is gained. If you have ever tried to design snubber circuits for a hardswitching converter you will follow me here. Zero voltage switching is even better, but then you have to build a LLC converter, which is harder to construct.
As a note to topology: My advice, ditch the arduino and get a proper dedicated converter chip that is designed to do just that job. A good old fasioned chip for an entry level converter is the TL494, but there are newer ones also.
3.Layout
When it comes to building power electronics, proper layout practices are key, and along that note, I will encourage you to post actual pictures of your work, because in that case we will probably be able to point at obvious mistakes.
These are the most obvious points I will point at, you have a lot of gumption and that is commendable, and needed, if you are going to see this project to the end with success. The most important advice I can give you is: read the application notes from TI, Linear, etc. They have covered this subject in great detail, and often the notes are written by authors who have exceptionally great command of written language, so that it is well suited for even a lay person studying on his own.
I wish you good luck on this journey, there are a lot of frustrating moments ahead, but there is also a lot of satisfaction to be gained.
Cheers, Finn Hammer