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Regulated DC power supply

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skyymanz

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Hi all,

i am trying to design a regulated DC power supply board. From 230V ac i will have to step down and rectified it. any idea wat other extra circuit do i need to make it reliable before feeding it into the regulator? Filter after the rectifier?

Cheers!
skyy
 
You have not specified the output voltage that u require.
U need a step down transformers,two capacitors(one across the rectifier and the other across the IC that u will use for the desired output voltage).U will also need a bridge rectifier at the output of the transformer.The capacitors will do the required filtering.
Just try it out.
Byeeeee,
Peeyush
 
If you plan to power something specific you would need to know the voltage and current requirements. Additional things that might be relevant are ripple and regulation requirements.

A google search on Linear Power Supply Design yeilded a site or two on the first page that might be worth reading. A linear power supply and a switched mode power supply (SMPS) are different.

My amateur radio handbook and "Practical Electronics for Inventors", among other references, has some great basic explanations of many of the design considerations for power supplies. Most any electronics handbook is likely to have a decent discussion.
 
Hi, thanks for the reply. so i will need a capacitor at the output of the rectifier to filter off the ripples. any ideal wat value should i use? should i need a resistor to form a RC LPF. the input to the full bridge rectifier will be a 48V 50Hz signal. Any protection circuit should i use to protect my regulator IC ?

cheers!
skyy
 
skyymanz said:
Hi, thanks for the reply. so i will need a capacitor at the output of the rectifier to filter off the ripples. any ideal wat value should i use? should i need a resistor to form a RC LPF. the input to the full bridge rectifier will be a 48V 50Hz signal. Any protection circuit should i use to protect my regulator IC ?

cheers!
skyy

No a resistor will just cause wasted power and voltage drops.

Your bulk capacitance can be chosen sufficiently large to reduce your ripple down to sufficient levels. If it is higher frequency noise you are concerned about, snubbers on the rectifier diodes can help. But you havnt said what all you care about for your design.

Also, most newer regulator IC's have built in protection circuits for overvoltage. Look at its schematic from the datasheet.
Otherwise, you can use a zener diode to protect from occasional high line voltage conditions that might over voltage the input.

If you are seriously concerned about protection, it is best to just make sure you get that built into the regulator. The vendors know how to protect their own devices best.
 
Hi,

i am concerned for a good regulated dc signal. i have source for the regulator and its quite ok. but wat value of capacitor should i use to minimised the ripple from the output of the amplifier? a value of 1000uF good enough??

cheers!
SKyy
 
With 48V ac input the bridge rectifier output with capacitor give - without load - almost 70V dc. Regulator chips with HV suffix accept only 60V input.
Still need the required regulated output voltage and current for proper answer.
 
skyymanz said:
Hi,

i am concerned for a good regulated dc signal. i have source for the regulator and its quite ok. but wat value of capacitor should i use to minimised the ripple from the output of the amplifier? a value of 1000uF good enough??

cheers!
SKyy

For a FULL WAVE rectification scheme
A first order approximation to what you should use is:

Vripple (p-p) = (Vpeak) / [ 2 * F * Cmin * Req ]

Where,

Vripple is peak to peak ripple voltage.
Vpeak is peak voltage of the sinewave (not RMS!)
F is frequency of operation i.e. 50Hz
Cmin is minimum value of capacitor for the given ripple voltage.
Req is equivalent resistance (load) seen by capacitor. Iload etc.. Estimate maximums.

The equation doesn't account for diode drops but it won't affect your answer too much. In this equation set your desired ripple voltage and solve for the Cmin. Then add 10% margin to that value then pick the nearest standard value. As you can see, higher load current => higher ripple voltage. Lower Capacitance => higher ripple. Lower frequency of operation => higher ripple.
 
to calculate capacitor value: 20000/(V X I). this is for a full wave rectifier. if u r using a single diode (not this case i know) then double it. naturally u can use higher values but this is the minimum.
 
Thunderchild said:
to calculate capacitor value: 20000/(V X I). this is for a full wave rectifier. if u r using a single diode (not this case i know) then double it. naturally u can use higher values but this is the minimum.

This doesnt make any sense to me whatsoever. The units arent even right.
Capacitance is not 1 / Watts.
 
never said it was but that was the formula i was told is there another way to work it out ?
btw what r the output specifications of this thing
 
Eh...not always you have to work it out (unless its that important). Most of the time if you look at your regulator datasheet it will give you a a basic schematic hook up and tell you what kind of capacitor you need. Just make sure the voltage rating is high enough.
 
err rectification on the formula i posted the other day. i have just come across my old note book and found it again and it is NOT 20000/(V X I) but 20000/(V/I) and do not ask why it is not 20000/V/I because i have never tried to verify it is the same but common sense tells me it is :lol
 
Thunderchild said:
err rectification on the formula i posted the other day. i have just come across my old note book and found it again and it is NOT 20000/(V X I) but 20000/(V/I) and do not ask why it is not 20000/V/I because i have never tried to verify it is the same but common sense tells me it is :lol

It is still not a capacitance and it has no basis at all. I'm sorry, but unless you can show us by derivation, it is simply wrong. If that's what you have in your notes, scratch it out! :)
 
wel ys it ould be wrong i mean i read it in a magazine and allhould know that sometimes hey ome out with some weird stuff theor wise ut if my formul i rong then i too now ask: how do you calculate the capacitance needed.
btw the result of myformula should give uF (miro farads) directly.
 
skyymanz said:
Hi,

i am concerned for a good regulated dc signal. i have source for the regulator and its quite ok. but wat value of capacitor should i use to minimised the ripple from the output of the amplifier? a value of 1000uF good enough??

cheers!
SKyy

Hi there,
Ya, a capacitor of 1000uF with a voltage rating of 35V will b good enough.
 
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