DC DC Step Up/Down - How it Works?

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Phrazemaster said:
True but...isn't that cheating? Fun to learn stuff.

I appreciate all the thoughts gang.
Learning is always good... As I've shared before, back in the 60's I had a technician gig working on a switching PS but back then there were no canned IC solutions.  The design I worked on was based around a linear regulator, tricked into being a switcher.  ;D

Now several decades later there are many IC switcher solutions to pick from. They almost all come with extensive application notes that can help you size inductors and associated parts. Some even include preferred layouts in the application notes. Perhaps start with a search of available switchers then narrow that search based on your application. Then download some app notes and read them...

JR
 
Who knew you guys were such genius at SMPSs? Wow, thanks for the wealth of knowledge and tips - I can see it's a science unto itself. Especially the bits about layout to avoid frequency switching in the audio band.

Thanks much; greatly appreciated!
 
There are lots of "boost" / step-up flyback smps chips. LM2577 looks like a fairly popular one. There are modules are Ebay that use it (that go up to 42V but you might be able to hack one to get to 48V).

However, note that to get a high output voltage depends on the input voltage and load. There is usually a formula in the datasheet that describes the rules. So you might have to supply 12V instead of only 5V or the load may not be more than 20mA or so on. Ultimately you might have to just play around with the chip to see what you can actually get.

Also high frequency switchers are very fickle about layout. It's not the sort of thing you can do on a bread board. You'll have to actually have PCBs made just to try it out.
 
saint gillis said:
Anyone knows a good chip to get 48V out of lower DC supplies ?
https://uk.rs-online.com/web/p/isolated-dc-dc-converters/1228156/
 
go to TI.com and use the webtools on there to input requirements and get solutions optimised for various parameters - pcb size , cost. component count etc.
And second Squarewave's advice that  you need a pcb (with low impedance planes) or at least some clever prototyping and not your typical
stripboard.
 
I'm also trying to make a 48V phantom power from 12VDC.
I've made tests with a cheap chip called MC34063A, the spikes were huge, unusable.

I also tried several voltage multipliers from a ne555 oscillator, a bit like here : https://befaco.org/docs/Instrument_Interface/I4_Schematic.pdf
I was possible to get low spikes with good filtering and by smoothing the initial square wave from the ne555, but with 5 multipliers the voltage drops to about 30v with 1mA, so not perfect.

I tried to find a cheaper solution than the aforementioned LM2577  (good example here https://sound-au.com/project193.htm ), that I still didn't test, but for now I don't find.
 
saint gillis said:
I'm also trying to make a 48V phantom power from 12VDC.
I've made tests with a cheap chip called MC34063A, the spikes were huge, unusable.

I also tried several voltage multipliers from a ne555 oscillator, a bit like here : https://befaco.org/docs/Instrument_Interface/I4_Schematic.pdf
I was possible to get low spikes with good filtering and by smoothing the initial square wave from the ne555, but with 5 multipliers the voltage drops to about 30v with 1mA, so not perfect.

I tried to find a cheaper solution than the aforementioned LM2577  (good example here https://sound-au.com/project193.htm ), that I still didn't test, but for now I don't find.
The spikes may be related to layout or inadequate filtering.

The 555 example is a variant on classic cap doubler/tripler. You could use smaller capacitors if you increased the switching frequency. Most doublers us AC from mains power 50-60Hz so require decent sized capacitors. I added a 48V output to an existing dc to dc switcher using tiny SMD caps but switching at 100kHz +.

The latter example is a proper switcher using an inductor to store energy and then deliver same at higher voltage.

Any of these approaches can be made to work effectively. If rolling your own switcher, I repeat my advice from years ago, check out IC manufacturers data sheets and application notes for advice.

JR
 
JohnRoberts said:
The 555 example is a variant on classic cap doubler/tripler. You could use smaller capacitors if you increased the switching frequency. Most doublers us AC from mains power 50-60Hz so require decent sized capacitors. I added a 48V output to an existing dc to dc switcher using tiny SMD caps but switching at 100kHz +.
So the idea with smaller caps would be to add more multiplier stages (6 or 7) to be able to deal with the voltage drop?
 
saint gillis said:
So the idea with smaller caps would be to add more multiplier stages (6 or 7) to be able to deal with the voltage drop?
No, it's that the impedance of the caps drops at higher frequency, so smaller caps can charge the output in the same time at higher frequency.
 
saint gillis said:
So the idea with smaller caps would be to add more multiplier stages (6 or 7) to be able to deal with the voltage drop?
This topology is basically a charge pump where a capacitor alternately gets charged up then discharged into another capacitor by driving the bottom of the first capacitor positive. By cycling at a much higher frequency a much smaller amount of charge can be passed with every cycle to accumulate to the same net current output. In that old 48V supply I made I used something like tiny 0.1uF SMD caps, but I only needed enough phantom supply current for one mic input. You still need to stack several stages in series to get up to 48V, exactly like charge pumping (doubling) at mains frequency.
=======
A true DC-DC switcher can use less parts, for my old application I didn't want to add yet another switcher to an existing switching supply to avoid clock interference.

JR
 
It would be worthwhile for someone to make some DIY SMPS supplies for common audio scenarios. Something to make +15, -15 and +48 from one transformer would be a great project. I'm surprised that we don't see that around here more often. SMPS are tricky but they're not that tricky.

But if you really just need one +48V supply, that happens to be a common SMPS voltage that you can buy off the shelf units for $20. Or less depending on power rating. And they are small encapsulated units. It is not that common in engineering to find an off the shelf part that is such an obviously great solution. Building audio gear with a supply that uses a doubler or tripler circuit is like building a car with a steam engine. Just get the right part and spend your time learning about other more interesting things.
 
squarewave said:
It would be worthwhile for someone to make some DIY SMPS supplies for common audio scenarios. Something to make +15, -15 and +48 from one transformer would be a great project. I'm surprised that we don't see that around here more often. SMPS are tricky but they're not that tricky.
I used to operate a kit business so pass.... but tag you're it.

If you want to connect directly to mains power you will need agency approval (like UL/CSA). I guess you could finesse that by stipulating that it only takes a DC input.

Have fun...

JR 


But if you really just need one +48V supply, that happens to be a common SMPS voltage that you can buy off the shelf units for $20. Or less depending on power rating. And they are small encapsulated units. It is not that common in engineering to find an off the shelf part that is such an obviously great solution. Building audio gear with a supply that uses a doubler or tripler circuit is like building a car with a steam engine. Just get the right part and spend your time learning about other more interesting things.
 
JohnRoberts said:
If you want to connect directly to mains power you will need agency approval (like UL/CSA). I guess you could finesse that by stipulating that it only takes a DC input.
Oh, definitely. For vaguely small devices it's customary to just have a DC barrel connector for whatever mains to 12V brick. And I would make them small like 5W or so. That would handle 90% of DIY projects and help keep it out of hiccup mode (although if you're DIY-ing it, it might be possible to configure the IC to simply not use hiccup mode). For larger products you just use more and maybe arrange them to be stackable with a link to the oscillator caps.

But I'm definitely not "it" because I need to dedicate my life to writing Java code right now. All my E stuff is packed away in a closet.
 
I've seen step up circuits that pull 5V from USB ports.

The cheap (chinese) lump power supply these days are 5V phone chargers/USB supplies.

Sorry I was just giving you a hard time... selling kits is a PIA (at least my recollection).

JR
 
squarewave said:
Building audio gear with a supply that uses a doubler or tripler circuit is like building a car with a steam engine. Just get the right part and spend your time learning about other more interesting things.

I agree, but we also need to use parts that will be available in decades to come if we want our devices to be reparable in the future, ne555 will be available in 20 years (if the world has not collapsed too much). Working with smps chips also implies choosing an easiely available chip.
 
saint gillis said:
I agree, but we also need to use parts that will be available in decades to come if we want our devices to be reparable in the future, ne555 will be available in 20 years (if the world has not collapsed too much). Working with smps chips also implies choosing an easiely available chip.
I think you have this exactly backwards.
 
saint gillis said:
Maybe, let's choose then a smps chip that is already produced and available in big quantities.
I first messed with DC to DC switchers back in 60s before there were dedicated switching ICs. Now these several decades later these are widely available and commonly used.

I am not smart enough to tell you which switcher IC will still be available 20 years from now, I wouldn't bet big money on the 555 timer either.

Maybe roll your own switching supply using a fast microprocessor, those will likely still be around 20 years from now. But that would be more design effort...

Maybe use an AC supply and go really old school with conventional capacitor doubler/tripler.

JR 
 

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