Author Topic: Help Me Design my SMPS  (Read 5521 times)

0 Members and 1 Guest are viewing this topic.

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Help Me Design my SMPS
« on: May 30, 2017, 12:56:48 pm »
Hi everyone! Lately I have been interested in designing my own 0 - 30V 10A SMPS. I understand the basics of how a SMPS works but this helps very little and I cant seem to find a schematic that fits my design anywhere. I want to keep the power electronics very simple so I don't want to mess with any switching transformers and figuring out how to wind the primary etc. I first was considering using an ATTiny 216 as a controller for the MOSFETS but the programming was just too much and I got completely lost. So I turned to using an all-in-one controller IC. I settled on the TL594 becuase all of the other ones that I would love to use are SMD and I want to use as little SMD parts as possible.

In my design I want to use an arduino to take the input of a potentiometer and then activate either a Boost or Buck converter. Im doing this so that I can get the absolute highest efficiency out of both the boost and buck converters instead of combining them. It might not be the best way of doing it but it's the way I'm interested in doing it.

My real frustration starts with the TL594. I have spent countless hours trying to get a simple boost converter to work using it and it just never works. Im constantly blowing up MOSFETS and I can't figure out how to controll the output voltage. I'm also confused on how to use the error amps and feedback on the TL594 in the boost converter so that the pulse width changes based on the current drawn. I'm also having a tough time figuring out the components I should use. I have looked at the Data sheet for the TL594 but it hasn't helped me much (maybe because I dont understand it that well).

Anyway I'm just curious if this is even a half decent design, what I'm doing wrong, how I would go about designing this power supply, and what IC I could use to replae the TL594 because it's really annoying me.

Thanks
 

Offline mdszy

  • Supporter
  • ****
  • Posts: 230
  • Country: us
  • pixie wrangler in training!
    • szy.io
Re: Help Me Design my SMPS
« Reply #1 on: May 30, 2017, 12:58:50 pm »
So you want to design a 300W power supply... with no experience whatsoever, while just looking for already-done schematics that will fit the bill? I'd suggest you tone back your expectations a bit and start simpler. Dealing with that much power isn't easy, and it seems like you think it will be.
 
The following users thanked this post: debininja

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #2 on: May 30, 2017, 01:15:09 pm »
That’s my final goal, to make a 300W power supply. In the meantime I do want to work with MUCH lower power designs to first learn what I need to. Also I'm looking for schematics so that I have examples to work off of to make my own power supply. I just can’t find any that help me design the one I have in mind.
 

Offline Someone

  • Super Contributor
  • ***
  • Posts: 1941
  • Country: au
Re: Help Me Design my SMPS
« Reply #3 on: May 30, 2017, 03:38:10 pm »
That’s my final goal, to make a 300W power supply. In the meantime I do want to work with MUCH lower power designs to first learn what I need to. Also I'm looking for schematics so that I have examples to work off of to make my own power supply. I just can’t find any that help me design the one I have in mind.
The problem is a simple (single) boost or buck stage doesn't scale up to larger power very well if at all. Also trying to make buck convertors work across a wide output range is difficult, so you're adding in multiple difficult requirements. If its a bench supply there is a wealth of information out there already, but why add the complexity of different switching stages if you only need 0-30V? Almost every design will start with a higher rail and buck down from there, because its simpler.
 

Offline strawberry

  • Regular Contributor
  • *
  • Posts: 151
  • Country: lv
Re: Help Me Design my SMPS
« Reply #4 on: May 30, 2017, 04:14:34 pm »
https://www.onsemi.com/pub/Collateral/TL594-D.PDF  in page 10.
reason why you are blowing MOSFETS is inproper gate drive.. over 15V or too slow gate pulse rise/fall time
MOSFET cant be used as source/emiter folover in switching aplications , because of drain to source voltage drop aprox 3V
it is better sinhronous BUCK converter to go in this power level. you can use 2xMOSFET and IR2104(deadtime) insted of transistor and diode
feedback is always negative
to change output voltage/current need to change reference voltage or feedback network
 

Offline P90

  • Frequent Contributor
  • **
  • Posts: 646
Re: Help Me Design my SMPS
« Reply #5 on: May 30, 2017, 04:19:02 pm »
I was interested reading until I got to the arduino part...  LOL
 

Online blueskull

  • Supporter
  • ****
  • Posts: 10197
  • Country: cn
  • Power Electronics Guy
Re: Help Me Design my SMPS
« Reply #6 on: May 30, 2017, 04:33:52 pm »
I won't even touch 494/594. There are so many modern controllers with integrated gate driver and some even with integrated power FETs, and the latest trend is to even put the inductor inside.
I can't see a reason why you want to use such a primitive controller unless you are counting beans.
BTW, pure digital is too hard to do and I don't recommend it, but a hybrid of digital and analog, as you've described, is a good way to go unless you want absolute best performance.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 

Offline strawberry

  • Regular Contributor
  • *
  • Posts: 151
  • Country: lv
Re: Help Me Design my SMPS
« Reply #7 on: May 30, 2017, 10:33:40 pm »
and the latest trend is to even put the inductor inside.
I can't see a reason why you want to use such a primitive controller unless you are counting beans.
you mean insulated gate drives with integrated insulation transformer?
FPGA is right direction or dedicated arm'ish processor
Microcontroller ADC is too slow to go above something 10W
 

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #8 on: May 30, 2017, 11:27:26 pm »
Ok so the TL494/594 is off the table. I still don't want to use a mircocontroller to switch the MOSFETS because programming is definitely not my strong point but if I really have to then I'll just have to learn the programming. Do you have any recomonedation for a through hole IC that is relatively easy to use and actually works well that I can use to switch the MOSFETS. I definitely want to use a controller that lets me use an external switch so that it can handle more current. Also I have decided to use an audio amp transformer for my first low power revision and just use a buck converter to convert the transformers 45v output to a 0-30V output at 1A.
 

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #9 on: May 30, 2017, 11:37:39 pm »
@strawberry
What happens to the MOSFET is that when I'm driving them with the TL594 I use a small transistor to convert the low power signal from the TL594 to a stronger 9v signal for the main power MOSFET (for some reason the output square wave disappears when I connect it to the MOSFET). The boost converter will work for about 30 seconds but I cant controll the output and the voltage instantly jumps to something like 55v. After that the output if the TL594 dies on my ocilliscope and the MOSFET pulls 5A and then blows.
 

Offline strawberry

  • Regular Contributor
  • *
  • Posts: 151
  • Country: lv
Re: Help Me Design my SMPS
« Reply #10 on: May 31, 2017, 12:44:30 am »
MOSFET gate capacitance is reason why driver square signal disapear. you can adjust driver first with 2nF capacitor insted of blowing MOSFET's

In BOOST converter you should be using higher voltage N-MOSFET than output voltage
In BOOST converter can't be used pwm more than 50% duty cycle

Why voltage jump up, Feedback loop might be pozitive/wrong

Integrated chips usualy come below 30V something about
 

Offline diyaudio

  • Frequent Contributor
  • **
  • Posts: 645
  • Country: za
Re: Help Me Design my SMPS
« Reply #11 on: May 31, 2017, 12:47:27 am »
Ok so the TL494/594 is off the table.
:palm:
 
The following users thanked this post: debininja

Offline debininja

  • Contributor
  • Posts: 41
  • Country: us
Re: Help Me Design my SMPS
« Reply #12 on: May 31, 2017, 02:07:06 am »
I'm actually doing something with the TL494 (less capable brother of the 594) myself, but my topology is different from yours: step-down, flyback, with isolated feedback. It's low powered, 5Watts (5Volt, 1Amp). I wanted to start off small and build up, but I'm interested in how your project will turn out. It's very ambitious, that's for sure.

As of right now, I have a cheap, $3 buck-boost PCB from eBay which has a range of 2V to 32V at 2Amps max recommended current. Even drawing 1Amp and 30V (30Watts) from it, using my 12V ATX PSU as the input, the PCB gets quite hot from the switching inductors and ICs, which get to around 95C. And you are wanting 10Amps at 30Volts  :scared:. Depending on your frequency, maximum PWM width (45% for the 494/594), inductors and switching mosfets/bjts, your circuit will be affected in terms of efficiency, dimensions, and so on.

You say you don't want to "mess with any switching transformers and figuring out how to wind the primary etc," but I think that's not a good way of going about when working with SMPS. As someone completely new to building SMPS myself, I often struggle to understand many of the design equations for the different topologies around, but I don't limit myself by saying "oh, I don't want to use calculations."

Anyways, I think I get what you mean when you say buck-boost using a TL594, but I don't think a microcontroller is required. It's apparently called a non-inverting 4-switch buck-boost converter. I don't know if this schematic will even work well, but here's what someone came up with:
 
The following users thanked this post: John_Hofmeyr

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #13 on: May 31, 2017, 04:09:16 am »
@debinninja

Thanks for the reply, really helpful! I am curious though what the difference is between the TL494 and 594. I have both but they seem to be the exact same. Now that I know what I have been doing wrong with the TL494/594 I'll try to use them again but I'm still open to using different IC's.  With regards to the output power that I'm aiming to get I have realized that 30v at 10A is WAY too much. I do still want a 10A output capability but I want the total output power to be around 90 - 120 watts instead of 300 to lower the "danger factor". Now I just need to find the right topology. I'm planning on using this power supply as a second supply for projects because my current one only has one output and it can be really annoying to power projects that need different voltages. So should I go with an Isolated or non-isolated converter. I like non-isolated converters because they seem to be much simpler to make but I'm open to trying to make an Isolated converter and making my own transformer if I need to for the amount of power I'm working with. Im also confused with what topology of Isolated or non-isolated converter I should use. Oh and BTW I'm going to be using a buck converter to step down the 45v from an audio transformer down to 0-30v.

Thanks.


« Last Edit: May 31, 2017, 04:23:05 am by John_Hofmeyr »
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 15263
  • Country: nl
    • NCT Developments
Re: Help Me Design my SMPS
« Reply #14 on: May 31, 2017, 04:19:08 am »
I'd go for a synchronous DC-DC converter controller with integrated MOSFET drivers. The trick to selecting the right MOSFETs is finding ones with the smallest gate capacitance which meet the worst case voltage (short cricuit) and current (SOA graph). Also have an 8V power supply to drive the MOSFETs as this will usually be a good trade-off between RDSon and switching speed. The PCB layout is the most tricky part of these kind of designs so it is a good plan to start with an evaluation board of the DC-DC controller. For now forget about the boost configuration.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #15 on: May 31, 2017, 05:11:49 am »
@nctnico

Is it possible to use an external MOSFET driver along with the TL494/594 or is it best to just buy an all in one chip that just needs the external MOSFETS and other parts. Also I have been using IRFZ48N MOSFETS from an old inverter, are they any good?
 

Offline Hero999

  • Super Contributor
  • ***
  • Posts: 11083
  • Country: gb
Re: Help Me Design my SMPS
« Reply #16 on: May 31, 2017, 05:40:41 am »
You've omitted what range of input voltages this needs to work off, from your specification. Please don't say you're planning to power this directly off rectified mains.  :palm:

Start off with 12VDC.

Is this intended as a bench power supply?

If so, to achieve low noise/ripple it may be better to use a linear regulator on the output of the SMPS, although it will reduce the efficiency.
 

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #17 on: May 31, 2017, 05:51:59 am »
@Hero999
 
Are you crazy?? I would never power it from rectified 120VAC. No for the final supply I'm thinking of using a transformer to step down mains voltage to something like 45V, for now I'm just going to use 30VDC from my current power supply to test my design. I would like the supply to run off of 35 - 45V DC so that my max output voltage of the supply is 30V DC. Also I can’t think of any linear regulator that will be ok with passing 90 - 120 watts through it (9v @10A or 12v @10A) .
 

Offline Hero999

  • Super Contributor
  • ***
  • Posts: 11083
  • Country: gb
Re: Help Me Design my SMPS
« Reply #18 on: May 31, 2017, 06:05:12 am »
@Hero999
 
Are you crazy?? I would never power it from rectified 120VAC.
Good. We've had crazier people than that here before, so I had to check. lol

Quote
No for the final supply I'm thinking of using a transformer to step down mains voltage to something like 45V, for now I'm just going to use 30VDC from my current power supply to test my design. I would like the supply to run off of 35 - 45V DC so that my max output voltage of the supply is 30V DC.
So you're intending to use a buck converter? That will work fine for the higher any of the voltage range but will become challenging at low voltages. Why not shoot for a voltage half way between the two, about 12V to 15V, then use buck-boost? Despite the extra complexity it'll make achieving the large range of voltages easier.

Quote
Also I can’t think of any linear regulator that will be ok with passing 90 - 120 watts through it (9v @10A or 12v @10A).

The point is to use the switcher, as a pre-regulator, to reduce the voltage to a few volts above the linear regulator's output, so the power dissipation will be no more than 30W.
 

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #19 on: May 31, 2017, 06:14:58 am »
@Hero999

I'm kinda confused. What difficulty will the buck converter have with lower voltages, and also could you clarify a bit on the linear regulator, sounds interesting I just don't understand exactly what you mean. Also if I were to use a buck and boost converter would it be a good idea to have two completely separate converters and then use a micro controller to look at the requested voltage and output voltage and then either activate or deactivate the buck or boost converter.

thnaks
 

Offline strawberry

  • Regular Contributor
  • *
  • Posts: 151
  • Country: lv
Re: Help Me Design my SMPS
« Reply #20 on: May 31, 2017, 07:48:54 am »
non-isolated coupled inductor SEPIC topology
 
The following users thanked this post: John_Hofmeyr

Offline MagicSmoker

  • Frequent Contributor
  • **
  • Posts: 752
  • Country: us
Re: Help Me Design my SMPS
« Reply #21 on: May 31, 2017, 08:49:03 am »
Looks like it is time to go through this thread like a scythe through wheat...

non-isolated coupled inductor SEPIC topology

Bad suggestion. High stress on semiconductors and coupling capacitor. Prone to high circulating current and oscillation/ringing from coupling capacitor resonating with inductor. Very difficult to stabilize due to right half plane zero and a non-linear input/output transfer function.


So you're intending to use a buck converter? That will work fine for the higher any of the voltage range but will become challenging at low voltages. Why not shoot for a voltage half way between the two, about 12V to 15V, then use buck-boost? Despite the extra complexity it'll make achieving the large range of voltages easier.

The buck-boost (aka non-isolated flyback) also subjects the semiconductors, input and output capacitors to high stresses, and also suffers from the right half plane zero if the inductor current goes continuous. Without a transformer the output polarity is inverted as well.

Getting a buck converter to go down to near 0V isn't a problem, either *if* the PWM controller can skip pulses (usually this is intended for maintaining regulation at very light load but it can apply to very high step-down ratios as well).

The point is to use the switcher, as a pre-regulator, to reduce the voltage to a few volts above the linear regulator's output, so the power dissipation will be no more than 30W.

This, however, is good advice - the best in this thread, in fact. I would just reiterate that a buck converter would be the best to use as the pre-regulator, not a buck-boost or SEPIC or Cuk or whatever. Note to OP: Linear Technology has an App Note on doing just this with, IIRC, the LT1074. I can't remember the number but it should be easy enough to find with google.


I'd go for a synchronous DC-DC converter controller with integrated MOSFET drivers.

I agree in principle, but this is the first SMPS for the OP and so I wouldn't recommend a synchronous topology which is more challenging to get working because of shoot-through and operating in forced continuous conduction mode all the time.


...
FPGA is right direction or dedicated arm'ish processor
Microcontroller ADC is too slow to go above something 10W

I have no words... No one in their right mind is going to use an FPGA or an ARM to control a 0-30V/10A power supply. And the speed of a MCU's ADC is not the limiting factor for how much power can be controlled; if there is sufficient inductance present (regardless of topology) and the loop bandwidth doesn't need to be too high (ie - more than a few kHz) then even a crappy 8b PIC or AVR can perform acceptably quickly in multi-kW converters (I know, I've designed and built them). Just don't use an Arduino fercryingoutloud...

MOSFET gate capacitance is reason why driver square signal disapear. you can adjust driver first with 2nF capacitor insted of blowing MOSFET's

In BOOST converter you should be using higher voltage N-MOSFET than output voltage
In BOOST converter can't be used pwm more than 50% duty cycle

Yes, yes, NO.

Duty cycle can definitely go above 50% in a boost converter. The transfer function does get a bit twitchy as duty cycle exceeds 80%, and 100% duty is verboten, but pretty much every PFC stage on the planet needs to go to at least 95% duty near the zero crossings of the mains to achieve distortion requirements.


I won't even touch 494/594. There are so many modern controllers with integrated gate driver and some even with integrated power FETs, and the latest trend is to even put the inductor inside.
I can't see a reason why you want to use such a primitive controller unless you are counting beans.
BTW, pure digital is too hard to do and I don't recommend it, but a hybrid of digital and analog, as you've described, is a good way to go unless you want absolute best performance.

I mostly agree with this, except to reiterate once again that this will be the OP's first SMPS and so he probably shouldn't mess with MHz class switchers which is what an integrated inductor implies. Nor should he be messing with a hybrid digital and analog controller. A simple circuit using well-established controller ICs like, e.g., the SG3525A, would be much more appropriate and deliver excellent performance.


The problem is a simple (single) boost or buck stage doesn't scale up to larger power very well if at all. Also trying to make buck convertors work across a wide output range is difficult, so you're adding in multiple difficult requirements. If its a bench supply there is a wealth of information out there already, but why add the complexity of different switching stages if you only need 0-30V? Almost every design will start with a higher rail and buck down from there, because its simpler. 

I agree with most of what you wrote except* that single stage buck and boost converters scale just fine up to nearly any power level. It is true that it is difficult to cover a very wide range of input/output voltage conversion ratio with a single stage unless pulse-skipping is employed, but that is where Hero999's suggestion of using a switcher as a pre-regulator for a linear regulator comes into fore.

* - forgot to insert this word in original post
« Last Edit: May 31, 2017, 07:48:21 pm by MagicSmoker »
 
The following users thanked this post: John_Hofmeyr

Offline John_Hofmeyr

  • Contributor
  • Posts: 17
  • Country: us
Re: Help Me Design my SMPS
« Reply #22 on: May 31, 2017, 10:35:04 am »
Whoa! So much info, thanks! Just to make sure I understand what's been said:

So if the non-isolated coupled inductor SEPIC topology and non-isolated flyback converter impose stresses on the components, then what is a better topology that I should use? Also, I'm still not quite sure how to use the linear regulator. If I'm not mistaken, you are saying that the output of the switching regulator is set a few volts higher than the desirred output, and then finally filtered by a linear regulator to get a smoothe output at the required voltage.

 

Offline debininja

  • Contributor
  • Posts: 41
  • Country: us
Re: Help Me Design my SMPS
« Reply #23 on: May 31, 2017, 03:38:47 pm »
Quote
you are saying that the output of the switching regulator is set a few volts higher than the desirred output, and then finally filtered by a linear regulator to get a smoothe output at the required voltage

Exactly. The power lost as heat, following that method, becomes: (VoltageIn - VoltageOut)*CurrentOut. Say you had a 10V fixed output and you wanted 1V out to power some widget. If you used a linear regulator by itself, it would have to drop 9V. You multiply that by the current, say 1Amp. So that poor linear regulator has to dump 9Watts as heat. You would need a beefy heatsink.

Compare that to if you have an adjustable SMPS, you can set the voltage at 1V plus a little more than the maximum voltage drop (usually 2.5V at worst, but there are linear regulators that are "low dropout", which have 0.5V or so of drop). So, you set the SMPS to 4V on the output, and the linear regulator drops 3V, at 1A for example. The power loss as heat is now only 3Watts. You can put on a tiny heatsink and it'll work just fine. See here for the calculations.
 
The following users thanked this post: John_Hofmeyr

Offline strawberry

  • Regular Contributor
  • *
  • Posts: 151
  • Country: lv
Re: Help Me Design my SMPS
« Reply #24 on: May 31, 2017, 05:55:24 pm »
@MagicSmoker
50% is max boost ratio ( x 2 )at max output power
double stress but you can use one MOSFET insted of two

slow 8bit microcontroller will give delay in feedback loop (it resoult in output voltage overshoots..instability) to process all (digital voltage adjust, monitoring, false modes..USB) instructions  and hard to implement current protection..
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf