Author Topic: voltage dropper help (Read 13316 times)

aruna1 · « **on:** May 16, 2011, 01:32:14 AM »

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

Billy · « **Reply #1 on:** May 16, 2011, 02:05:51 AM »

Quote from: aruna1 on May 16, 2011, 01:32:14 AM

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.

aruna1 · « **Reply #2 on:** May 16, 2011, 02:10:33 AM »

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

TrickyNekro · « **Reply #3 on:** May 16, 2011, 02:46:34 AM »

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

aruna1 · « **Reply #4 on:** May 16, 2011, 02:52:02 AM »

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.

waltr · « **Reply #5 on:** May 16, 2011, 07:56:39 AM »

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.

aruna1 · « **Reply #6 on:** May 16, 2011, 09:18:14 AM »

Quote from: waltr on May 16, 2011, 07:56:39 AM

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

billhowl · « **Reply #7 on:** May 16, 2011, 09:53:15 AM »

5.2V out switch mode power supply for cell phone charger

http://www.coilws.com/index.php?main_page=page&id=66

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

Don't mess with main voltage unless you know exactly what you are doing !!

Soeren · « **Reply #8 on:** May 16, 2011, 01:15:45 PM »

Hi,

Quote from: aruna1 on May 16, 2011, 02:10:33 AM

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.

aruna1 · « **Reply #9 on:** May 16, 2011, 07:30:29 PM »

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.

TrickyNekro · « **Reply #10 on:** May 17, 2011, 05:30:16 AM »

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

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

)

aruna1 · « **Reply #11 on:** May 17, 2011, 05:33:28 AM »

Quote from: TrickyNekro on May 17, 2011, 05:30:16 AM

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

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

TrickyNekro · « **Reply #12 on:** May 17, 2011, 05:42:52 AM »

Quote from: aruna1 on May 17, 2011, 05:33:28 AM

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

Quote from: aruna1 on May 17, 2011, 05:33:28 AM

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...

aruna1 · « **Reply #13 on:** May 17, 2011, 06:01:41 AM »

Quote

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?

TrickyNekro · « **Reply #14 on:** May 17, 2011, 07:40:54 AM »

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

aruna1 · « **Reply #15 on:** May 17, 2011, 07:55:49 AM »

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?

waltr · « **Reply #16 on:** May 17, 2011, 09:02:16 AM »

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=*&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/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.

TrickyNekro · « **Reply #17 on:** May 17, 2011, 09:14:34 AM »

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

aruna1 · « **Reply #18 on:** May 17, 2011, 09:22:56 AM »

@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

waltr · « **Reply #19 on:** May 17, 2011, 09:33:08 AM »

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?

aruna1 · « **Reply #20 on:** May 17, 2011, 11:32:50 AM »

@waltr
I'm going to use MC34063 buck converter for converting 30V to 12V so i would be able to get 12V 500mA

waltr · « **Reply #21 on:** May 17, 2011, 01:35:29 PM »

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.

TrickyNekro · « **Reply #22 on:** May 18, 2011, 07:35:56 AM »

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.

aruna1 · « **Reply #23 on:** May 18, 2011, 07:40:42 AM »

@ it will be bulkier

this is my final year project so it has to be superb if I want to save my second upper $:-\$

TrickyNekro · « **Reply #24 on:** May 18, 2011, 07:50:19 AM »

Quote from: aruna1 on May 18, 2011, 07:40:42 AM

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

aruna1 · « **Reply #25 on:** May 18, 2011, 07:53:24 AM »

@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)

TrickyNekro · « **Reply #26 on:** May 18, 2011, 10:31:38 AM »

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....

aruna1 · « **Reply #27 on:** May 18, 2011, 10:35:24 AM »

@ 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

TrickyNekro · « **Reply #28 on:** May 18, 2011, 03:38:43 PM »

Quote from: aruna1 on May 18, 2011, 10:35:24 AM

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 ;-)

aruna1 · « **Reply #29 on:** May 19, 2011, 08:01:37 AM »

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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Author Topic: voltage dropper help (Read 13316 times)