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9V Battery and 7404 and 7408

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fantasymick

New Member
I have a circuit that uses two types of chips. One set uses 9V, perfect for a 9V battery, and the others use 5V, namely the 74LS04 inverter and the 74LS08 NAND. I want to use resistors to adjust to 5V so all chips can use the 9V battery.

I don't know the internal resistance of the chip, and so am unsure what value of resistor to use.
 

amadeus

New Member
I=V/R

You could use this formula, but if you don´t know the I parameter, then will be a little dificult. I think you should test with 333 ohms or 270 ohms.
 

John Sorensen

New Member
If you're running off a 9V battery a 7805 will kill it quick. Try a low Iq regulator like a MAX603. I have a project that I calculated would run for 1 week on a 9v battery (with the MAX603). It has been like three weeks with no sign of letting up.

j.
 

Scubasteve

New Member
Skyknight said:
A suggestion: Maybe you can use a 7805. It does all the job itself. :idea:
Resistors are very capricious with humidity and temperature. You won't get accurate results.

We where chating about the 7805 days ago in this forum, if you don't know how it works, you can check the picture:

http://www.electro-tech-online.com/threads/computer-clean-up.1426/
Resistors are not used in these circuits because of the load changing the voltage. Temperature change is not as big as a concern. The no-load current would also be ridiculous.

I would take the suggestion of using a low Iq current 5v regulator for this circuit. Or perhaps you can change to CMOS and get lower power consumption. The only real reason one would use TTL is for a bit more speed.

Steve
 

john1

Active Member
Hi fantasymick,

Check this out:
http://www.romanblack.com/a00.htm

claims:

5v, smallest size + lowest cost
Specs:
* 80% efficiency (from 30mA to 90mA out)
* very tiny Rf inductor
* very cheap circuit (under 50 cents in parts!)
* good 5v regulation
* input: 8v to 20v
* output: 5v @ 150mA maximum

Worth a look.

John
 

John Sorensen

New Member
I'll put this ckt to the test tomorrow, but it looks risky. If it works as advertised I'll thank you for the link; if not, I hope it is a nice day so I can open the windows and let the smoke out.

For a no brainer solution, look at the Maxim MAX603 (free samples available :) ).

j.
 
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