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Help needed

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woodstock

New Member
hello everybody I need help. I can´t find LM2931A 5.0 anywere. its a Semi low-dropout 5V regulator. Is it posible to use another one instead of this one.Itś only part what I need. I really need your help
 

jbeng

Member
Apparently, you didn't try www.digikey.com, because a search on their site turned up THOUSANDS of them IN STOCK.
JB

*edit* You didn't try www.mouser.com either, because they have them in-stock, too.
 

chemelec

Well-Known Member
Well I'm not sure about that regulator, but the Shipping cost to buy just that will be expensive.

However, if it will Help and If you Email me I can supply you with a "TL750M05CKC" Low Drop out Regulator. Totally FREE including Postage to you.

No Catch to this, I have a Surplus of them.
 

woodstock

New Member
what does LM means.I have a thousands of 7805CV REG IC 50 S 1450.On other forum they told me that it can be used.It´s in the same TO-92 packaga and the voltage is same. But I´m a little suspiciouc about that. What is your opinion
 

audioguru

Well-Known Member
Most Helpful Member
Hi Woodstock,
Your "ordinary" 7805CV regulators are guaranteed to have an output from 4.75V to 5.25V that is regulated, when their input voltage is 8V or higher. They can supply 1A or more of output current. They have a fairly high operating current. They are in a monster TO-220 case.

For your project that is powered by a little 9V battery, you need a low-dropout regulator that continues to work as the battery voltage drops over its life. You don't need 1A output with its high operating current. You don't need a wide 1/2V tolerance. You don't need the big case.

The voltage of a little 9 alkaline battery quickly drops to 7.2V then drops slower to 6V over its life. See my graph.

The LM2931AZ 5.0 is guaranteed to have an output from 4.81V to 5.19V that is regulated, when its input voltage is only 6V. Typically it operates well when its input voltage is only about 5.3V. Its max output current is limited to 100mA. It has a low operating current. It is in a small TO-92 case like a BC547 or 2N3904 small transistor. It is perfect for circuits powered by a 9V battery and all semiconductor manufacturers make low-dropout 5V regulators like this.

Low dropout regulators must have a pretty big output capacitor. The LM2931 needs at least 22uF but I use 100uF to be safe. :lol:
 

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woodstock

New Member
what if I use a transformator to get a stable 9V source. But then I would have to rid of a noise I guess.And to me it´s not problem if it´s in TO-220 package.Could this work with this source???
 

audioguru

Well-Known Member
Most Helpful Member
A 9VDC AC adapter will blow-up your circuit because its output is far from being stable. It will be about 15V to 18V (for a little 100-300mA adapter) with the low current of your project.

If you want to use an AC adapter then you'll need a 9V regulator for it, then you could use an ordinary 5V regulator for the other part of it.
 
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