×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Low battery voltage - automatic shutdown

Low battery voltage - automatic shutdown

Low battery voltage - automatic shutdown

(OP)
4.8-5.2Vdc, 150mAh device is powered by 4-AA nimh batteries in series.  

Looking for a simple (few extra components needed) i/c component to regulate voltage in the range of 4.8-5.2Vdc (fully charged, 4-AA nimh can be 6.0Vdc, which might be too much for the device), and, to shutoff device (open the 5.0Vdc 150mAh circuit) when voltage drops below 4.8Vdc (3.3 min. to 4.5 range),

I found LDO linear regulators with integrated reset (e.g. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3494) and http://focus.ti.com/docs/prod/folders/print/tps7325.html

But, I didn't see an application diagram for my situation.

Mick

RE: Low battery voltage - automatic shutdown

(OP)
Thanks Keith,
I looked and read, but I still don't get it.  I don't have enough electronics savy.

Linear Technologies LM1121 series shows some circuit diagrams in their pdf data sheet (1121fc.pdf) showing how to connect pins. but:

In the case of adjustable regulator, what value of resistors will give output of 4.8 volts?  Input is 4-AA nimh. maybe 6.0 volts when fully charged.

I see automatic shutdown pin SHTDN, but I don't know what to connect to this pin, to cause the input to shutdown when battery voltage drops below 4.8V.  


RE: Low battery voltage - automatic shutdown

There is almost always an equation listed in the datasheet specifying how to choose the resistor values (or at least their ratio)... figure a few tens of kohm to put them in the proper range.  Depending upon the current requirements of the SHTDN pin, you may be able to get away with a series zener diode appropriately sized, or you could combine the diode with a transistor for a more hardcore shutoff.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Low battery voltage - automatic shutdown

your looking for a supervisory circuit. Google and you'll find a ton.

RE: Low battery voltage - automatic shutdown

Look at these parts as an example:  National LP2986 as the regulator.  To drive the shutdown pin take a look at the LM3701.

I agree with Keith, something has gone wrong with National's website.  I wonder what machines or what software their web developers are using, but it shows really bad on my Opera browser.

RE: Low battery voltage - automatic shutdown

(OP)
Dear felixc.
Thanks for your suggestion.  I may try to figure how to use LP2986 and LM3701 if this (below) doesn't work.

Couple of days ago, I found a simple low battery cutoff circuit at <http://www.edn.com/archives/1998/091198/19di.htm>

It uses a Panasonic MN13812-Q-ND (TO92) voltage detector IC set to trip at 3.8 volt and an Internal Rectifier IRLZ14S-ND (D3PAK) MOFSET to open and close the circuit.

I will add a Microchip MCP1700-5002E (TO92) 5V LDO voltage regulator with 1mfd ceramic capicators in Vin and Vout.  

Does this combination seem ok?
Mickey



RE: Low battery voltage - automatic shutdown

I was afraid at the 1.2mA figure in the text but it was a typo error.   At 1.2uA of leakage when off, it looks like a good circuit.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources