IC FAMILIES OF DIGITAL GATE

dl324

Joined Mar 30, 2015
11,551
74AC can sink or source about 20mA with a 5V supply while maintaining valid logic levels. You should pay attention to maximum power dissipation.

If you use high brightness LEDs and drive at low currents, most logic families will be sufficient.
 

ronsimpson

Joined Oct 7, 2019
940
ic family of digital gate
There are many kinds of logic.
CD40xx and MC140xx family that can run at 12 volts. (15max)
There are many types like the 74LSxx that works at 5 volts.
Then there are some built for 3.3 V or 2.5V to 1.8V and ECL has a signal less than one volt.

LEDs also come is different kinds. White LEDs often need 3 volts to work and will not do well with 2.5V logic. A red LED turns on at 1.8 to 2.2 volts.

You will have good luck of you choose 5V logic. Remember to add a current limiting resistor. Many logic types can pull down better than they can pull up. So build your circuit so a "0" or low level turns on the LED and a "1" or high level is LED off.
 

Papabravo

Joined Feb 24, 2006
14,446
Driving any LED without a current limiting resistor is courting disaster, at least for the LED, if not for the surroundings as well.

You don't tug on Supeman's cape.
You don't spit into the wind.
You don't tear the mask
Off the old Lone Ranger
And you don't drive a LED without a reisitor
 

Audioguru again

Joined Oct 21, 2019
1,926
I use CD4xxx gates and counters (a CD4017 makes a good 10 LEDs chaser) with a 6V supply and no series current-limiting resistor on most of my LED decorations.
For 3V to 5V supplies I use 74HC4xxx gates and counters with a series resistor to limit the current.

The datasheets from Texas Instruments show graphs of current like this:
 

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MisterBill2

Joined Jan 23, 2018
7,035
I also have driven red and yellow LEDs directly with 4000 series CMOS gates, but I may have used a series resistor to limit the current. That was 25 years ago so I do not recall all of the details, other than I was using what Digikey called "high intensity" LEDs at that time. But now I recall that the gates had a 12 volt supply.
 

MisterBill2

Joined Jan 23, 2018
7,035
My point was intended to be that the 4000 series of CMOS CAN drive an LED to a useful intensity.. I doubt that the current was even close to 20 mA, but because they were "high brightness" devices the light at 5mA was bright enough.
 

Audioguru again

Joined Oct 21, 2019
1,926
My point was intended to be that the 4000 series of CMOS CAN drive an LED to a useful intensity.. I doubt that the current was even close to 20 mA, but because they were "high brightness" devices the light at 5mA was bright enough.
The Texas Instruments datasheet I posted shows that with a 10V supply, the output current is typically 16mA into two 2V red LEDs in series without a current limiting resistor.
 

Thread Starter

aragon1971

Joined Apr 7, 2008
54
thank you ! the behavor of led depedent from the logic familly
i think in 74LSxx maybe need a external supply volatage with a serie resistor to protect LED..1603467802504.png
 

dl324

Joined Mar 30, 2015
11,551
thank you ! the behavor of led depedent from the logic familly
i think in 74LSxx maybe need a external supply volatage with a serie resistor to protect LED..
What you mean by LED behavior is dependent on logic family? An LED behaves the same regardless of the logic family you're using.
 
What you mean by LED behavior is dependent on logic family? An LED behaves the same regardless of the logic family you're using.
Different logic families are able to sink or source vastly different amounts of current and output different voltages. And an LED behaves differently depending on how much current is passing through it, and that current often depends on the voltage pushing it.
 

Thread Starter

aragon1971

Joined Apr 7, 2008
54
Different logic families are able to sink or source vastly different amounts of current and output different voltages. And an LED behaves differently depending on how much current is passing through it, and that current often depends on the voltage pushing it.
Yes this i mean... if the the IC family sink a current of μΑ led cant open and in this case need an external dc voltage
 

Thread Starter

aragon1971

Joined Apr 7, 2008
54
according TO FLOYD BOOK (digital fundanental)

When driving a load such as an LED with a logic gate, consult the manufacturer’s data sheet for
maximum drive capabilities (output current). A regular IC logic gate may not be capable of handling
the current required by certain loads such as some LEDs. Logic gates with a buffered output, such
as an open-collector (OC) or open-drain (OD) output, are available in many types of IC logic gate
configurations. The output current capability of typical IC logic gates is limited to the mA or relatively
low mA range. For example, standard TTL can handle output currents up to 16 mA but only when the
output is LOW. Most LEDs require currents in the range of about 10 mA to 50 mA.
 
You will find many LED's today that work well with currents of 0.5 mA to 2 mA . Digikey shows 628 hits for that range and that number douobles if you increase the range to 5 mA.
Certainly this is true. Quite a while back I was using the high brightness yellow LEDs driven by the CMOS low output one-shot gates and they were not loading the outputs very much at all. So some LEDs can work on a very low current. The light will not be as much as at the rated max current, but still, they are working.
 

dl324

Joined Mar 30, 2015
11,551
Most LEDs require currents in the range of about 10 mA to 50 mA.
Most LEDs don't require 10-50mA to emit light. When used as indicators, high brightness LEDs can sometimes be operated at 1mA or less; even standard LEDs will light with 1mA. They won't be very bright, but they will turn on.

LED characteristics don't change when used with different logic families. You're limited by the current sink/source capabilities of the logic family, but the LEDs still function the same.
 
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