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multiple SMPS Voltages

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muhammadali_16

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Hiz.

how r u all?

i want some help regarding SMPS. im using PUSH-PULL terminology to make 12Volts.

i want multiple output voltages. +12V, 5V and 3.5V.

kindly tell me any terminology to do this.

thx
 

Dear Muhammad
Hi
More information needed about what you want to do exactly , to earn best guidance . for example , how much current do you need and how much ripple for current and voltage is acceptable for you , and how much is your input voltage .
Best Wishes
Goldsmith
 

muhammadali_16 said:
Hiz.

how r u all?

i want some help regarding SMPS. im using PUSH-PULL terminology to make 12Volts.

i want multiple output voltages. +12V, 5V and 3.5V.

kindly tell me any terminology to do this.

thx
Click to expand...

One way to accomplish creating multiple voltages from a single power converter would be to use a flyback topology. If you use multiple secondary coils, you can make multiple output voltages from a single input voltage. Beware, you generally set up one output voltage to be your reference, and all of the others will track it as the duty cycle changes w/ load.

flyback-smps-dc-bus-feed-back.png
 
@ Goldsmith
Thx for ur reply. my input is 24VDC and output is 12VDC - 15A with 5VDC and 3.3VDC of 100mA for some ICs.

basically i have no problem in making 12VDC - 15A. the main problem is to make other voltages.

hope u understand my problem
 

Dear Muhammad
Hi again
well , it is possible and very simple .
I can suggest you a fly back converter for this low power . it will be simple and economic . you can use a uc3844 or uc3845 driver ic to build your aim !
Best Wishes
Goldsmith
 

For simplicity you'd probably want a single controller and
inductor (transformer). However that scheme has the issue
of "cross-regulation" (one supply, or a summed product of
them, at most can close the loop meaning the control is
going to be sloppy for some).

The other approach is to consider the highest voltage
supply to be both a primary, and a "distribution" supply.
Here the 12V would be that. The 5V and 3.3V you may
call "point of load" supplies, and at the low currents
called out, these might be simple linear regulators or
very small DC-DCs.

You might end up at roughly parity, using this scheme,
because 24V - 3.3V is going to be a big ratio and many
DC-DCs don't fare so well at high step-down ratios, in
efficiency. Integrated buck ICs capable of >12V input
and 1A output are not that expensive, and their size
will be dwarfed by the switching components and the
magnetics for your 12V, 15A primary conversion I expect.
 

muhammadali_16 said:
@ Goldsmith
Thx for ur reply. my input is 24VDC and output is 12VDC - 15A with 5VDC and 3.3VDC of 100mA for some ICs.

basically i have no problem in making 12VDC - 15A. the main problem is to make other voltages.

hope u understand my problem
Click to expand...

Use a SMPS to convert 24V to 12V efficiently, then use a linear regulator to take 12V down to 5V, and another LDO to take 5V down to 3.3V. With that topology, you just have one switching stage to contend with and minimal power dissipation in your linear regulators.
 

goldsmith said:
Dear Muhammad
Hi again
well , it is possible and very simple .
I can suggest you a fly back converter for this low power . it will be simple and economic . you can use a uc3844 or uc3845 driver ic to build your aim !
Best Wishes
Goldsmith
Click to expand...

mr, i had a problem with my ferit trafo.
it's not generated a voltage in the secondary trafo?
what it's cause it?
 

Dear pol
Hi
How much is your frequency ? and how did you test it ? and what are the number of turns ?
Best Wishes
Goldsmith
 

enjunear said:
Use a SMPS to convert 24V to 12V efficiently, then use a linear regulator to take 12V down to 5V, and another LDO to take 5V down to 3.3V. With that topology, you just have one switching stage to contend with and minimal power dissipation in your linear regulators.
Click to expand...
Yeah I have to agree here. If the 5V and 3.3V rails each only need 100mA, compared to the 12V rail at 15A, then using a multiple output SMPS is probably much more trouble than it's worth. Using linear regulators off the 12V rail would barely put a dent in your overall efficiency, and you wouldn't have to worry about cross regulation.
 

after a long research, i will wind three winding on transformer. 1st input, 2nd 12v (high current) and 3rd for the regulators for 5 and 3.5V.

i know the science of transformer but dont know fly back converter.
Can u post any application note with some real calculations and design guidelines, which could really help me
 

muhammadali_16 said:
after a long research, i will wind three winding on transformer. 1st input, 2nd 12v (high current) and 3rd for the regulators for 5 and 3.5V.

i know the science of transformer but dont know fly back converter.
Can u post any application note with some real calculations and design guidelines, which could really help me
Click to expand...

I'd avoid the multiple-output power converter... it could be more of a headache than you realize (especially if the 12V current changes a lot... the 5V and 3.3V will change voltages as the PWM changes to compensate for a wide range of 12V current; cross-regulation, @mtwieg).

For a design-from-scratch approach, check out TI.com and use the WebBench tool. Use the suggested designs as a baseline. If you go with a 24V-to-12V converter, google for buck converter design guides and you'll find lots of websites that talk about that kind of converter. I don't have a direct link to articles, but others might.
 

Hi , for information about flyback converters see , below , please :
**broken link removed**

**broken link removed**
Best Wishes
Goldsmith
 

    V

    Points: 2
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@enjuner
Thx for ur kind reply but it is possible by doing the calculation only regarding to 12V supply (High Current Output) and i think i can do it easily by using the inductors regarding to frequency and the difficulty removers, YES LM78XX and LM79XX.......lol :)

@goldsmith
thx for ur reply
ur material is beneficial for me

can u also tell me the Snubber calculations??? kindly plz tell me the exact formula and others. i dont wana do PHd in SNUBBERS LOL

Thx
 

can u also tell me the Snubber calculations??? kindly plz tell me the exact formula and others. i dont wana do PHd in SNUBBERS LOL
Click to expand...
Hi again
For snubbers , there are many ways , but i want tell you a simple way :
build your circuit without snubber and then see the overshoots ( oscillations ) and measure the frequency of those damped oscillations , and then use an RCD or RC network , the has an Fo=1/2*pi*R*C and F0 should be about the frequency of those oscillations and you can select the capacitor randomly and then you'll find the R , simply ( remember that R should have high wattage , but not very high , it require a bit higher wattage that you can calculate it simply .)
Best Wishes
Goldsmith
 

goldsmith said:
Dear pol
Hi
How much is your frequency ? and how did you test it ? and what are the number of turns ?
Best Wishes
Goldsmith
Click to expand...


i had return the ferrit trafo,i take it from apart of PC the power supply,with the pri:sec 12:10. with wire gauge 1.25,to generated 12 v:3 A.
how to test the trafo that i had return good or not??????

i had to measure it with the osciloscope, i gave the primer 12 voltage, but there is no voltage in the secondary or the output the ferrit trafo.

Could you help me,please...
 

what i would like to check of transistor, THE CURRENT OF basis,
OR the voltage of transistor or what????
 

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