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Step-Down Converters
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Project_Nightmare
HG Master


Joined: 12 Oct 2007
Posts: 119
Location: Gig Harbor, WA

PostPosted: Sun Oct 28, 2007 2:20 am    Post subject: Step-Down Converters Reply with quote

This post is for the people new to electronics and don't know how to control the voltage in a simple circuit. It is going to be quick and dirty so for those who want to learn more about what I wrote about, wikipedia.org is a great resource at explaining how these circuits work. (Sorry about the big pictures, I didn't know the size that they would be in the post)

The most commonly used converter is the Linear Regulator. It's cheap and works well at keeping a constant voltage. They usually are made for particular voltages, but there are adjustable versions. The down side is that they are limited to a specific current rating, they use a lot of current, and generate a lot of heat.

Another option is a Zener Diode. All diodes have a unique aspect that prevents them from allowing current to pass through them till it reaches a particular voltage, this is know as bias. Zeners have an unusual ability to allow voltage to run the opposite way a normal diode would and has a very accurate voltage constant. The down side of Zeners is that you are restricted to the zenerís voltage rating, have to avoid going over the resistorís wattage threshold, and the resistor wastes energy in the form of heat.

An option is an op-amp and voltage divider. Voltage dividers, as seen in the picture, are two or more resistor used to drop the voltage to a specific desired value. If you want it to be adjustable, you can buy a trimmer or a potentiometer. These devices cannot take much load so they are often used as voltage references for buffers (the op-amp). I included a transistor in the picture of the buffer, because of the limited current output of the op-amps. This circuit will not filter any fluctuations in the power supply because voltage divide's voltage reference would change from changes in voltage fluctuations. The circuit is also limited in current output the transistor can handle.

The last common option is the buckpuck (aka buck converter). It works by using Pulse Width Modulation (PWM) using a switch (mosfet or transistor) to run current over the inductor and capacitor. The purpose of the inductor and capacitor is their filtering abilities to soften the PWM to a constant DC current. They are incredibly efficient at saving power, but they are limited to certain current ranges, are complex in how they operate, and expensive to make or buy.


Last edited by Project_Nightmare on Fri Dec 07, 2007 9:41 am; edited 4 times in total
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Turd
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Joined: 18 Aug 2007
Posts: 274
Location: Saskatchewan, Canada

PostPosted: Sun Oct 28, 2007 1:53 pm    Post subject: Reply with quote

Good info, Project_Nightmare! Very Happy


eric
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Project_Nightmare
HG Master


Joined: 12 Oct 2007
Posts: 119
Location: Gig Harbor, WA

PostPosted: Sun Oct 28, 2007 5:54 pm    Post subject: Reply with quote

Thanks Smile , I would have included a bunch more info and converters (not just some of the step-down), but people can find that looking online Cool
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Turd
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Joined: 18 Aug 2007
Posts: 274
Location: Saskatchewan, Canada

PostPosted: Sun Oct 28, 2007 6:47 pm    Post subject: Reply with quote

I suppose you could use a Zener Diode and a resistor for the reference voltage on the op-amp circuit, eh? Very Happy


eric
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Oct 28, 2007 7:51 pm    Post subject: Reply with quote

Nice info. Smile Great addition to the forum for people to reference!
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Project_Nightmare
HG Master


Joined: 12 Oct 2007
Posts: 119
Location: Gig Harbor, WA

PostPosted: Sun Oct 28, 2007 8:56 pm    Post subject: Reply with quote

Turd wrote:
I suppose you could use a Zener Diode and a resistor for the reference voltage on the op-amp circuit, eh? Very Happy


eric


Yep, I've seen circuits that do that exact thing Razz
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melstav
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Joined: 27 Nov 2007
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PostPosted: Tue Nov 27, 2007 9:23 am    Post subject: Reply with quote

I've heard that a zener can generate a bit of a noisy output, and heard suggestions that if you're using a zener as a step-down converter, that you should parallel it with a capacitor to provide some filtering.

Can anyone speak to that statement?
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Project_Nightmare
HG Master


Joined: 12 Oct 2007
Posts: 119
Location: Gig Harbor, WA

PostPosted: Fri Dec 07, 2007 9:35 am    Post subject: Reply with quote

Well it is always good to have a capacitor in dc circuits, so that might get rid of the noise. The only reason that i can think of that would make it generate noise is if the power supply is oscilating or changes in load Rolling Eyes
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Reverend Jones
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Joined: 15 Aug 2007
Posts: 39
Location: Jonestown, Guyana

PostPosted: Fri Dec 07, 2007 12:12 pm    Post subject: Reply with quote

melstav wrote:
I've heard that a zener can generate a bit of a noisy output, and heard suggestions that if you're using a zener as a step-down converter, that you should parallel it with a capacitor to provide some filtering.

Can anyone speak to that statement?

That is true. Zener diodes are commonly used as the noise source in white/pink noise generators. When used as a voltage regulator they should be paralleled by a small capacitor.
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Project_Nightmare
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Joined: 12 Oct 2007
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PostPosted: Sun Feb 03, 2008 11:15 am    Post subject: Reply with quote

Umm, Alan can you delete goodfriend's post on this forum topic, it appears that they accidentally posting here and in other places looking at the other topics created by them (and how they all say the same thing) Rolling Eyes
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Alan
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Joined: 29 Jan 2006
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PostPosted: Sun Feb 03, 2008 12:58 pm    Post subject: Reply with quote

Thanks, post deleted...
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steve0
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Joined: 18 May 2008
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PostPosted: Wed May 28, 2008 1:34 am    Post subject: Reply with quote

Good info, Project_Nightmare!
________
sc2 replay


Last edited by steve0 on Thu Feb 03, 2011 5:33 pm; edited 1 time in total
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Benny
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Joined: 17 Oct 2008
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PostPosted: Fri Oct 17, 2008 5:28 am    Post subject: Hello Reply with quote

I like this side very much because it has good information about electronic components and please give me more information about electronics and circuit

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friendlyzookeeper
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Joined: 26 Apr 2009
Posts: 10
Location: USA

PostPosted: Sun Apr 26, 2009 4:12 pm    Post subject: Reply with quote

Hello everyone,

This is my first reply.
Here is a example of an dc-dc step-up converter.
This will step-up 2 X 1v5 batteries to a steady 5v power
source.

http://www.ladyada.net/make/mintyboost/

I like step-up converters, because there is not so much heat
at all. Very Happy

Thanks,
Friendlyzookeeper.
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Apr 26, 2009 4:25 pm    Post subject: Reply with quote

friendlyzookeeper wrote:
Hello everyone,

This is my first reply.
Here is a example of an dc-dc step-up converter.
This will step-up 2 X 1v5 batteries to a steady 5v power
source.

http://www.ladyada.net/make/mintyboost/

I like step-up converters, because there is not so much heat
at all. Very Happy

Thanks,
Friendlyzookeeper.


Step ups are quite interesting! Welcome. Smile
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