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AC - DC rectification

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surjit

New Member
what is the difference between 1) Step down Transformer + Bridge rectifier and 2) Bridge rectifier + DC - DC converter ??
 
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4pyros

Well-Known Member
Most Helpful Member
The two really are not related.
You don't need a bridge rectifier for a DC to DC converter, you need a DC power source.
These are the proper arrangements;
AC power in to Step down Transformer, bridge rectifier, Filter, DC out.
DC in to DC - DC converter, DC out.

You can use a DC - DC converter after a DC power supply to change the voltage if you want.
 

surjit

New Member
Thank you . Actually my input is 12 V AC . I want to convert into 3 V DC . may be i should use Rectifier + DC DC converter , since my input is low . am i correct ??
 

4pyros

Well-Known Member
Most Helpful Member
Depends on cost and efficiency needs as well as power demands.
A traditional full wave power supply may be cheaper, and easier to get higher currents out of.
A DC/DC converter is more efficient but harder to get higher currents out of.

A traditional full wave power supply is easy to make your self.
A DC/DC converter can be complicated with harder to find parts.

What voltage and current do you need out of your 12 volt AC supply?

Hope this helps.
 

surjit

New Member
my supply is variable voltage between 6 - 12 V AC , different frequency but less than 200 Hz , current 10 - 100 nA and I want to convert it in to DC 3V , cost is not an issue .
 

4pyros

Well-Known Member
Most Helpful Member
For nano amps you could use one diode, a cap a resister and a zener.
 

4pyros

Well-Known Member
Most Helpful Member
Read here about zener diodes;

Use a single diode and a cap as a half wave power supply off your AC voltage, then add the zener regulater.
 

cowboybob

Well-Known Member
Most Helpful Member
what is the difference between 1) Step down Transformer + Bridge rectifier and 2) Bridge rectifier + DC - DC converter ??
Thank you . Actually my input is 12 V AC . I want to convert into 3 V DC . may be i should use Rectifier + DC DC converter , since my input is low . am i correct ??
sorry....can you plz explain in detail ? or with a diagram if possible

If I may ask, are you looking for explanations, or are you looking for a solution?

Explanations are readily available by googling.

As per 4pyros (this is simplest):
AC-DC-Reg PS.JPG

There is a little noise on the output.
 

kubeek

Well-Known Member
Most Helpful Member
Thank you i will try this circuit , and can i also try Flyback converter to step down DC ??
No, 10 - 100 nA is not enough current to power anything, so anything that requires its own power like a step down is completely out of question.
 

surjit

New Member
If I may ask, are you looking for explanations, or are you looking for a solution?

Explanations are readily available by googling.

As per 4pyros (this is simplest):
View attachment 89370
There is a little noise on the output.

Thank you its really helpful . I am looking for both because i have doubt weather to implement DC - DC buck converter or use Step down transformer ? your solution is perfect , Ty
 

surjit

New Member
No, 10 - 100 nA is not enough current to power anything, so anything that requires its own power like a step down is completely out of question.

Yeah thats what i think , thn i need some switching regulator for low current application .
 

kubeek

Well-Known Member
Most Helpful Member
No exactly the opposite. Any active ciruitry such as switching regulator needs about a thousand times more power to operate than what you have available. You need a completely passive solution with as little leakage as possible. Stick with a single low leakage diode as a rectifier, and a second zener diode to clamp the voltage. Fedd the result into a very low leakage capacitor.

I have no idea what are you trying to power, but I dont think your source will be able to power anything. Can you give more details about what is that mysterious power source and what you are trying to do with it?
 

4pyros

Well-Known Member
Most Helpful Member
Ok now I am really confused.
Where is the 14 volts AC coming from?
What are you trying to power wit 3 volts DC/
 
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