Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: aruna1 on May 16, 2011, 01:32:14 AM
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Hi, I want to make a power supply that will reduce 230V AC voltage to 5V DC voltage. Do do this I want to use a buck converter. Easiest buck converter I can get is MC34063. it has input up to 40V.
what I want to know is how to reduce 230V rectified DC voltage to 30V DC voltage so I can use MC34063 to drop 30V to 5V.
I have added a diagram below. my question is to solve the middle box named as "voltage dropper". I'm looking for a simple circuit for this. since i dont know current requirement of the load I guess i cant use a resistive dropper. any idea would be great.
EDIT: cant use a transformer due to space constraints.
thank you
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how to reduce 230V rectified DC voltage to 30V DC voltage
There are several ways to reduce DC voltage, but I am going to suggest a different approach.
Use a transformer on the mains and reduce the AC voltage to a safe (and isolated) level and then rectify the AC voltage.
A small 230 to 24V AC transformer will give you a little better than 30DC after the rectifier.
Please be aware that using line voltage is dangerous if you're not trained to do so. The wall plug in your home is likely capable of providing many hundreds of amps if not into the thousands if you short the two lines together. There is a good risk of starting a fire or electrocuting yourself or spraying yourself with molten copper.
Can you purchase a small power supply (aka wall wart) for your project? Perhaps much safer.
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Hi
for my circuit I cant use a transformer because of space constraints.
I wonder how they do this on mobile phone chargers.it reduce 230v to 5v using switching regulator. i tried but couldnt reverse engineer that circuit
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It really depends on your power needs... You can do that with a simple voltage divider...
But don't expect much...
Most designs I have seen somehow incorporate a transformer... Or else expect heavy power loses...
Which you don't like do you...
But to get to your question, give a look at 1200P60 or anything from the series (ON Semi)...
You will still need a transformer, but maybe much reduced on size... generally... Transformers are
rated in VA (looks like Watt to be, but for some reasons they insist on VoltAmpere, of course it happens to know the reason, but it comes a little complicated for now).....
Typically a low rated VA with be smaller than a high rated VA....
But as I said... you're gonna need a transformer to get serious in Amps (if not mA at first)
Best Regards, Lefteris
Greece
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I'm ok with small transformers like ones we can see in mobile phone charger circuits. Not sure i could find one with a model number though.
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In mobile phone and other charges they probably use a DC-DC switching power supply to reduce the voltage.
It is important is provide isolation from the AC mains for safety.
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In mobile phone and other charges they probably use a DC-DC switching power supply to reduce the voltage.
It is important is provide isolation from the AC mains for safety.
yes they are. I wonder where I can find a schematic of one of those chargers
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5.2V out switch mode power supply for cell phone charger
(http://www.coilws.com/images/Switch%20Mode/3R6W_ckt.gif)
http://www.coilws.com/index.php?main_page=page&id=66 (http://www.coilws.com/index.php?main_page=page&id=66)
http://www.powerint.com/en/products/product-documents/data-sheets (http://www.powerint.com/en/products/product-documents/data-sheets)
Transformerless Power Supplies: Resistive and Capacitive
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf (http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf)
Don't mess with main voltage unless you know exactly what you are doing !!
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Hi,
for my circuit I cant use a transformer because of space constraints.
I wonder how they do this on mobile phone chargers.it reduce 230v to 5v using switching regulator. i tried but couldnt reverse engineer that circuit
Be very careful!
When making an off-line switcher, as they're called, first you need to rectify the AC to DC. Then you chop the DC at a high frequency to make a square wave DC that only needs a (relatively) small pulse transformer for isolation.
Usually, an optocoupler is used to control the primary side switching from the low voltage side, but I have seen some where the feedback is coupled via the transformer.
If you make one, the entire liability is on you, if anything goes wrong.
Most large companies buy their switchers to avoid this liability and this is why we all have far too many wall warts.
My advice is to pay your way around of making one - no risk, no liability, just spend all your time on making the main circuit awesome.
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hi soeren;
to tell you the truth power supply is for my final year project.
in this project what we do is using ultrasonic sensor system for robot localization.
to do this we use lot of wall mount ultrasonic receivers.
these receivers need to be light weight and small, thats why I remove the option of using a 50Hz transformer looked for a SMPS system.
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And if you want to calculate the coils use this program, extremely helpful.
If calculates everything, from the number of turns to the length of the wire you are gonna need ;-)
http://www.dl5swb.de/html/mini_ring_core_calculator.htm (http://www.dl5swb.de/html/mini_ring_core_calculator.htm)
A side note... You can also build your own transformer with toroids.
A must note... Be careful, if you are gonna use a switching HV IC, you MUST take into consideration the frequency of the PWM...
Iron cores will NOT work at frequencies above 60 ~ 70 Hz... (Maybe 100Hz but don't push it)
This is due to Eddie currents. So even if your frequency is 100Hz, better use Ferrite or something else that can work there.
(Ok ferrite maybe an overkill... but still... they are not expensive and you can sleep well at night ;) )
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And if you want to calculate the coils use this program, extremely helpful.
If calculates everything, from the number of turns to the length of the wire you are gonna need ;-)
http://www.dl5swb.de/html/mini_ring_core_calculator.htm (http://www.dl5swb.de/html/mini_ring_core_calculator.htm)
A side note... You can also build your own transformer with toroids.
A must note... Be careful, if you are gonna use a switching HV IC, you MUST take into consideration the frequency of the PWM...
Iron cores will NOT work at frequencies above 60 ~ 70 Hz... (Maybe 100Hz but don't push it)
This is due to Eddie currents. So even if your frequency is 100Hz, better use Ferrite or something else that can work there.
(Ok ferrite maybe an overkill... but still... they are not expensive and you can sleep well at night ;) )
[/quote
hi
is it possible to use a toroid to make 50Hz transformer? If so it will be great coz i can convert 230 to 30v with toroid transformer.
and can we use a ferrite toroid with 50Hz?
thank you
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hi
is it possible to use a toroid to make 50Hz transformer? If so it will be great coz i can convert 230 to 30v with toroid transformer.
Of course ;)
and can we use a ferrite toroid with 50Hz?
thank you
For that one I'm not sure, Most ferrite cores will work well from 40Hz to their peak frequency.
But to be sure you must look into it. That's why datasheets exist :)
PS: Common pal! put some effort to place the quotes right... I'm loosing track of what you say...
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PS: Common pal! put some effort to place the quotes right... I'm loosing track of what you say...
sorry my bad :)
and new question
so i need to 230V to 30V
so that means turn ratio is
Np/Ns = 230/30
so how do i calculate number of turns for primary and secondary?
i mean i can use 230 turns for primary and 30 turns for secondary
or
i can wind 23 turns for primary and 3 turns for secondary?
how to select proper number of turns?
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The more turns you use the power your transformer will deliver, cause of the greater magnetic field that is produced.
The more magnetic field the more energy will be stored at the toroid material, so you will be able to draw more energy out
with the secondary.
Generally speaking the more turns the more VA, but expect higher core losses (which may be negligible) (which occur cause of paramagnetic core hysteresis and Eddie currents)...
I suspect that a primary with ~100 turns will be good enough... But I have yet to study for electromagnetism,
so I can't be sure...
Remember when placing the turns into the ring core to space them evenly, for less losses.
Also, I suggest that you first place the secondary and then the primary, suspecting that you are gonna use larger diameter wire for the primary.
Best Regards, Lefteris
Greece
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hi
I think secondary wire will have larger diameter than primary wire, because secondary current is greater than primary
Vp*Ip = Vs*Is and Vp > Vs
and when winding primary and secondary what method should i use?
1. wind primary and then wind secondary on top of that
or
2 wind primary and secondary seperately on two halves of same toroid?
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Switching power supply design can be a bit tricking. A good starting app note is AN19 from Linear Tech.
http://search.linear.com/search?filter=p&getfields= (http://search.linear.com/search?filter=p&getfields=)*&output=xml_no_dtd&sort=date%3AD%3AL%3Ad1&site=english_full&ie=UTF-8&oe=UTF-8&client=default_frontend&proxystylesheet=default_frontend&numgm=5&q=AN19
LinTech and other manufactures of switching PS ICs have app notes that are helpful.
The best books I have that give practical design information are by Marty Brown.
http://www.amazon.com/Power-Supply-Cookbook-Design-Engineers/dp/075067010X (http://www.amazon.com/Power-Supply-Cookbook-Design-Engineers/dp/075067010X)
http://www.amazon.com/Practical-Switching-Supply-Motorola-Electronics/dp/0121370305/ref=pd_sim_b_5 (http://www.amazon.com/Practical-Switching-Supply-Motorola-Electronics/dp/0121370305/ref=pd_sim_b_5)
He does cover many types of switching PSs as well as the calculation for core material, #turn, wires size, etc.
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It's a matter of watts not a matter of current necessarily.
You are always gonna get less wattage on the secondary than the primary.
Keep in mind that coils have also an inevitable ohmic resistance and that you are not going to use all
the energy that is available...
Sometimes, you use thicker wire for the secondary, sometimes thicker for the primary...(see fly-back transformers)
What currents are you expecting...???
I get you aren't going to use more than some mA though.
Anyhow,
You want the secondary on the inside, to be as close as it can get, to the ring.
But generally, you want both coils evenly distributed around the ring, as close to it as the can get.
The less air in between the ring and the coils the better, cause less magnetic flux will escape.
But don't use much thicker wire for the inside. It's a matter of practicality not necessity.
Best regards, Lefteris
Greece
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@waltr
thank you for the info. I will check it
@nitro
my final required output is about 500mA. so transformer output of 300mA will be enough if possible.
230 --> 30V 300mA
30V --> 12V 500mA
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I just saw that the Linear Tech link I posted is partly broke. So just type 'AN19' into LinTech's search box.
30V @ 300ma is 9Watts. That should not be too hard to do.
30V -> 12V @500mA? Are you going to linear regulate the 30V output for the switcher to 12V? If so then you need much more power out of the switcher. You will need 30V x 500mA = 15Watts. There would be a loss of (30-12)x500mA = 9Watts in the linear regulator (remember to heatsink).
Or are you going to use a DC-DC switcher (Buck regulator) to get 12V from the 30V?
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@waltr
I'm going to use MC34063 buck converter for converting 30V to 12V so i would be able to get 12V 500mA
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The efficiency of the MC34063 Step-down circuit is listed as 83.7% but I'll use 80% (could be higher or lower) for 'off the cuff' calculations. 12V at 500mA is 6Watts output plus the power to run the MC34063 is 4mA x 30V = 0.12W. At 80% the input power is 7.65Watts so this should work from the 30V, 300mA supply (9Watts).
Do follow the layout guide in the data sheet and read the app notes referenced in the data sheet.
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If I were you I would just step it down to ~16V with the transformer and then use a 7812...
Much much easier and fail prof.
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@ it will be bulkier ;D
this is my final year project so it has to be superb if I want to save my second upper :-\
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this is my final year project so it has to be superb if I want to save my second upper :-\
Can't imagine how well I can understand you.... Next year for me , too, is the final year and I'm going to Germany for the final project....
But still....Best of all is something that will work under any conditions. I guess you also have your time limited.
And because in electronics you never know what may go wrong, (best that nothing goes wrong, I wish you that but still
may not happen) Don't waste all your time only in one part.
Have something that it's elegant but also that it's fail proof and doesn't waste much of your time, if it isn't the main ingredient...
Best Regards, Lefteris
Greece
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@nitro.
Your point is correct.
but then question arises about the offline converter ICs available in market. aren't they reliable? I just contacted a local shop and they told me TEA1507 and MC44608 ICs are available (flyback converters)
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I don't say that... They obviously make them and market them for a reason.
I just say that using a lineal regulator, it's gonna be much more fail proof and gonna help you, if you know that
you are constricted in time... That's all...
If you have time, it's a lot more flashy to use the switching regulator. It means that you can actually understand and build it,
and more things. Like you can debug problems quickly, your designs are based on correct calculations etc etc etc....
But if the power supply isn't the base of what you're building. It's best to concentrate on the latter then work out the power supply problem.
Just get something that works. Get the hard part working, then consider spending time on the peripherals.
I think you told you were working on Ultrasonic. These little blighters can be quite a big pain in the a$$...
Just, I want to remind you that you should first work on your schedule.... ;)
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@ nitro
actually ultrasonic part is finished and doing minor adjustments like range adjustments etc. but all the circuits were powered using lab power supplies and now we need to make seperate power supply systems for them, which is I'm working on now :)
My idea is to drop voltage using a switch mode and then use a lin regulator to smooth things up
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My idea is to drop voltage using a switch mode and then use a lin regulator to smooth things up
That's exactly what I have proposed you above ;-)
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ok
I checked TEA1507 and MC44608 datasheets and application notes
and I'm completely lost. ???
I have no idea what they did can you help me to design a smps using any above IC
230V in 15V 500mA out flyback?
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Hmm that's a little bit bad.
I can help you but I don't have the time to do so (I got exams in 3 weeks or so)
And it'll take me a week or so to have it ready and working.
It's basically calculations, I did give a look at MC44608, cause it's quite a popular IC, and it's not that hard.
It depends a lot on what you want (feedback or not and other stuff)
Of course, I don't know how well it may work without feedback (it may drift with time)
Still, what I can do is to help you out wherever you don't get something.
What are you studying exactly? Give a look at the schematics on the last page of MC44608 datasheet.
And let's start with what you don't understand there.
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what I dont understand is how to calculate number of turns in transformer (in all coils)
i found this calculator in internet
http://www.daycounter.com/Calculators/Flyback-Transformer/Flyback-Design-Calculator.phtml (http://www.daycounter.com/Calculators/Flyback-Transformer/Flyback-Design-Calculator.phtml)
problem to use this calculator is I dont know the Al values of cores. I went to the local shop,they had these ferrite transformer cores (no model numbers as always), so I cant figure out Al value
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As I said Switching power supplies are not trivial. I made many mistakes when I first started designing them and it has taken several years to get to a point where I almost know what I'm doing.
Try to get one of the Marty Brown books I linked to above. His books are much, much more clear in explaining SMPS than any other book or app note.
I did a quick look at the typical application circuit for the MC44608 (figure 18) found in the data sheet. That circuit is fairly typical of a SMPS using a transformer. Any thing in particular you don't understand or are you just totally overwhelmed?
Try reading the data sheet piece by piece and relation each to the example circuit.
SMPS do seem to have a bit of 'black magic' in their design but can be understood.
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what I dont understand is how to calculate number of turns in transformer (in all coils)
i found this calculator in internet
http://www.daycounter.com/Calculators/Flyback-Transformer/Flyback-Design-Calculator.phtml (http://www.daycounter.com/Calculators/Flyback-Transformer/Flyback-Design-Calculator.phtml)
problem to use this calculator is I dont know the Al values of cores. I went to the local shop,they had these ferrite transformer cores (no model numbers as always), so I cant figure out Al value
You must know the un-gapped core's AL. Does your school have an inductance meter? If so then wind 10 turns on the core and measure the inductance. Then calculate the AL.
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oh thats too bad, school has no inductance meter. however i ordered one from ebay about two weeks ago but it seems delayed. ???
until I get it;
is it possible to use dimensions of unknown core and use Al value of a known core (from a manufacturer core list) with a similar dimension
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problem to use this calculator is I dont know the Al values of cores. I went to the local shop,they had these ferrite transformer cores (no model numbers as always), so I cant figure out Al value
Hmm, that's not hard at all... What RL circuits are good for... Even better what RLC circuits are good more...
Wound up 50 turns and build a simple Resistor - Coil filter circuit (high pass would be better)...
Better precision can be achieved with a Resistor Capacitor and Coil band pass filter.
The lower the resistance, the more narrow the band will be. Current delivery capabilities of your function generator not be a problem.
But do NOT forget the resistor... Or else you will be shorting the function generator every time your frequency is different from the oscillation frequency.
So... you can see what the inductance is... you already know the number of turns, and then go ahead a calculate anything else...
I don't remember the formula... But it won't be hard to find... google around ;)
SMPS do seem to have a bit of 'black magic' in their design but can be understood.
Ahh, there is no black magic, just knowing what the heck you are doing ;)
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You must know the un-gapped core's AL. Does your school have an inductance meter? If so then wind 10 turns on the core and measure the inductance. Then calculate the AL.
Inductance meter? Shame on you! Just a capacitor and a resistor...
Cause, his school just can't fail at having a function generator... ;)
Edit: Uuupss... you are gonna need a scope too, but generally, where there is a function generator, there is a scope too ;)
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@nitro,
Thank you for the advice, I guess I will have to wait till next week as university starts on next monday.
anyway what is your idea about using Al value from known core with similar dimension to unknown one
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If I can figure this out I'm definitely going to write a tutorial on "flybacks for dummies" so dummies like me will have less hedache over these :-\
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anyway what is your idea about using Al value from known core with similar dimension to unknown one
Dimensions really don't play a major role in this (they do...but)
That's cause a core with relevant permeability of 4300 will have let's say an inductance of 4mH with 48 turns
and a core with relevant permeability of 2300 will need 65 turns to have the same inductance.
Since you are switching the coil on a certain frequency, that's gonna affect the current through your coil.
And the current in your coil is gonna affect the strength of your magnetic field in the core.
Note that you can't impose a current on a coil, as you can't impose a voltage on a capacitor.
Further more the less current the less power stored in the core, and the less can be extracted from it on the other side.
So it's not all that of black magic in the end. It's what you need and what you get...
In the end, it's a golden ratio that you should keep. As from what you get the energy at the second coil is the magnetic field in the core
and depends on both the current that runs the first coil, but also the number of turns...
Best Regards, Lefteris
Greece
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oh i see :)
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ok I made a flyback converter using MC44608
40KHZ speed
applied power, and booooom Ic blew ;D
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applied power, and booooom Ic blew Grin
Yep, been there.
Try again but go step by step
Start with a lower voltage to only power the MC44608 and use a resistor instead of a MOSFET.
The goal is to get the MC44608 to free run without feed-back and then measure the gate drive output with a scope. Ensure that the wave form is at the correct (calculated frequency) and the duty cycle looks correct.
Then add the MOSFET and use a resistor instead of the transformer. Ensure with a scope that the gate and Drain waveforms are correct.
Keep adding in parts and measure at each stage until the the PS is working.
Start with a high value current sense resistor, MOSFET Source to ground and keep the ground path very short and close the the IC's ground reference pins.
As you proceed keep us posted with what you find and hopefully some of us can help out.
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well power supply has to wait. I was able to find a 50Hz transformer small enough for the proect, so I'm working on otherparts of the project. hopefully in future I will try this again