Low battery voltage - automatic shutdown

[mick43]

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

 

[itsmoked]

Perhaps:

http://datasheets.maxim-ic.com/en/ds/MAX6329-MAX6349.pdf

They have a truck load - run thru their parametric search.

Linear Technology also has these devices as does National. However National's web site has gone from very good to supreme suckedness in recent months.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[mick43]

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.

 

[MacGyverS2000]

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

 

[IRstuff]

Sounds like you need more than a regulator:

http://para.maxim-ic.com/cache/en/results/4645.html

Undervoltage shutdown is something that laptops have to have.

TTFN

 

[automatic2]

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

 

[felixc]

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.

 

[mick43]

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

 

[felixc]

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.