matt09
Newbie level 4
Hi all,
I wish to build a variable lab style SMPS with output voltage from around 1V up to 100V and variable current from 0-10A. I have quite a lot of experience from doing electronics as a hobby for many years as well as studying the subject. I haven't tried anything like this before though. I am building this as part of a university project so this will actually happen and hopefully this thread will be open the next year or so as I progress.
First of all does anyone know of any existing designs which can be modified to achieve the output I want (I've checked I am allowed to do this). I haven't been able to find any so far?
Failing this I have already been looking into designing my own from scratch. I am struggling in choosing a topology, I know flyback is more suited to variable voltage but not suitable for high power and ideally I want to achieve 1KW or at least 500W. At the moment I am going with half bridge but could anyone tell me if this is good idea for variable voltage? I need to have isolation as it will be mains powered.
I have various ideas so far on how to achieve such a wide voltage range from an SMPS with pulse width limitations. So far I am looking at doing one of the following after reaching my lower voltage limit, presumably of 5-10V.
1. Have a second converter running in series off the output of the first which will rechop the waveform a second time and easily reach down to 0V
2. The same about but have two running in parallel.
3. Have a linear regulator stage running from the SMPS secondary which cuts in at a given voltage which will then go down to almost 0V
4. Lower the switching frequency once a given voltage is reached so that a higher mark-space ratio can be realised.
5. Feed the disable pin of a driver chip with a clock signal so that i get a duty cycle of the duty cycle, effectively missing out some pulses.
If anyone could advise which direction to go on with this element that would be great.
I am also struggling with choosing a base switching frequency as I want it to be as low as possible so that I can get the narrowest possible pulses, could anyone advise a starting point?
I also have no idea if any of the 5 suggestions will be needed? It has been suggested that it will not be possible to achieve a 1% duty cycle to give a down to nearly 0V at any reasonable frequency. From my initial calculations this seems likely as I would need a td + tr of around 100nS at a low 40KHz switching freq. There are many Mosfets around this speed or faster, but I'm assuming I would never be able to reach this and get proper pulses in reality?
I haven't looked into it yet but a head start on the best way to have a variable current limit from 0-10A would be great.
I'd really appreciate any help as these questions are really holding me up from making progress with calculations and have done for some time. I probably already have most of the components and a suitable core from being a hobbyist for so many years but I will get on to this later.
As the post is so long I have made questions bold to make it much more readable.
Many Thanks,
Matt.
I wish to build a variable lab style SMPS with output voltage from around 1V up to 100V and variable current from 0-10A. I have quite a lot of experience from doing electronics as a hobby for many years as well as studying the subject. I haven't tried anything like this before though. I am building this as part of a university project so this will actually happen and hopefully this thread will be open the next year or so as I progress.
First of all does anyone know of any existing designs which can be modified to achieve the output I want (I've checked I am allowed to do this). I haven't been able to find any so far?
Failing this I have already been looking into designing my own from scratch. I am struggling in choosing a topology, I know flyback is more suited to variable voltage but not suitable for high power and ideally I want to achieve 1KW or at least 500W. At the moment I am going with half bridge but could anyone tell me if this is good idea for variable voltage? I need to have isolation as it will be mains powered.
I have various ideas so far on how to achieve such a wide voltage range from an SMPS with pulse width limitations. So far I am looking at doing one of the following after reaching my lower voltage limit, presumably of 5-10V.
1. Have a second converter running in series off the output of the first which will rechop the waveform a second time and easily reach down to 0V
2. The same about but have two running in parallel.
3. Have a linear regulator stage running from the SMPS secondary which cuts in at a given voltage which will then go down to almost 0V
4. Lower the switching frequency once a given voltage is reached so that a higher mark-space ratio can be realised.
5. Feed the disable pin of a driver chip with a clock signal so that i get a duty cycle of the duty cycle, effectively missing out some pulses.
If anyone could advise which direction to go on with this element that would be great.
I am also struggling with choosing a base switching frequency as I want it to be as low as possible so that I can get the narrowest possible pulses, could anyone advise a starting point?
I also have no idea if any of the 5 suggestions will be needed? It has been suggested that it will not be possible to achieve a 1% duty cycle to give a down to nearly 0V at any reasonable frequency. From my initial calculations this seems likely as I would need a td + tr of around 100nS at a low 40KHz switching freq. There are many Mosfets around this speed or faster, but I'm assuming I would never be able to reach this and get proper pulses in reality?
I haven't looked into it yet but a head start on the best way to have a variable current limit from 0-10A would be great.
I'd really appreciate any help as these questions are really holding me up from making progress with calculations and have done for some time. I probably already have most of the components and a suitable core from being a hobbyist for so many years but I will get on to this later.
As the post is so long I have made questions bold to make it much more readable.
Many Thanks,
Matt.
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