digital logic gate power suppy

david90

merged with the other thread by enigma

david90

Will ICs work if I power it with 3 or 4 1.5 volt bat connected in series? I read that you need to use a power regulator to regulate it to 5 volt but what if you don't? Will it still work?

I guess my question is, is 5 volts from just batteries the same as 5 volts from a regulator. I tried with batteries but didn't work. Just want to confirm.

chroot

Virtually all IC's (with the exception of those that use bandgap references or PLL's, etc.) will "work" when powered by the wrong supply voltage; the problem is that they won't work exactly according to the performace specifications on the manufacturer's data sheet. Since making sure a product works according to its datasheet is a huge concern for a semiconductor company, from a liability standpoint, they don't encourage users to use them at different voltages.

If you undersupply a digital part, it'll most likely not switch as fast as it says it will on the datasheet, for example. If you oversupply it, it might get a bit too warm and degrade a noise specification. In general, though, your IC will work just fine as long as your design does not depend on being right on the edge of a specification. (Good designs don't do this anyway!)

- Warren

chroot

5V is 5V is 5V. I don't know how you got 5V from "3 or 4 1.5V batteries," though, or maybe my arithmetic is slipping.

- Warren

david90

at school, my ICs (7400,32 etc.) works fine but when I use batteries at home, it doesn't seem to follow the truth table. I thought i might be the power supply fault.

chroot

The 74 series is very linear, and should work at just about any supply voltage. According to Fairchild, the 7404 can be operated up to 7V, with 2V to 6V the recommended range.

- Warren

david90

I think your arithmetic is slipping. 4=1.5 = 5.

Anyway, my 7400 ICs doesn't work! it is so weird. it works at school when I use the power supply from those big box.
























jk about your arithmetic. but it should somewhat work with 6 volts.

chroot

Well, since you're saying it doesn't work, what exactly doesn't it do? What exactly is different about its behavior?

- Warren

david90

I used the OR gate chip and hooked up power to pin 14 and ground to pin 7. Then I hooked led to pin 3 and make pin 1 "high" by connecting it to pin 14. Nothing light up... I'm pretty sure the led is hook up right. cathrode to pin 3 and anode to ground. Resistor is between the led and cathrode. nohting light.

dduardo

Are you sure you have the led in the right direction? Maybe the led went bad. Do you have a voltmeter to check to see if there is any output on pin 3?

[edit] Why are you saying you are using an OR gate. The 7400 is a NAND gate

david90

problem solved. I re did my circuit. THanks all.

Cliff_J

For future reference, you could use a 1k resistor, 47uF cap, and 5V Zener to make a simple power supply with a low idle current cost. Also you could tie the Zener to a linear regulator to handle more current as well.

I've had 15V rated 555 chips literally go up in smoke when my unloaded PS (cheapie wall transformer) would go up to 17V and I hadn't bothered to wire them up with a 12V Zener. At least it was very obvious when it happened. :)

Super cheap way to get a stable 5V source with a few amps of capacity: an old computer power supply. I picked up a couple 250W on sale for $14.99 brand new just a couple weeks ago.

Cliff