Dual Line driver

Sid 03 wrote:


What exactly are you trying to do?   You might look at prebiased  
transistors for the LED driving job, or for a through-hole approach,  
2N7000s with one resistor each.

Cheers

Phil Hobbs

On Wednesday, January 20, 2021 at 2:48:20 PM UTC-6, Phil Hobbs wrote:

What LEDs are you driving?
What are the LEDs doing or indicating?
A schematic would help.

I've seen many mistakes with something as simple as driving an LED.
There's thinking that some expensive driver chip has to be used.
There's thinking that an open collector/drain output has to be used.
There's thinking that a pullup resistor is needed in addiditon to the LED  
series resistor.
A single transistor and one or two resistors can drive an LED and depending  
on where you put your resistor it can keep the LED current reasonably  
constant over a wide suppy range.

If we don't know exactly what you're trying to achieve then this thread  
could easily get longer than the 741 thread.

On Wednesday, January 20, 2021 at 3:32:57 PM UTC-6, Edward Rawde wrote:


I am just trying to drive a couple of LEDs and also supply that output to another logic board and/or relay.
Looking at the specs from the chips that have a max output current of < 10mA, I thought that using a simple  
chip to drive the LEDs and relays would be simple, but if its not then I need that answer as well.
Thank You.

wrote:



Most LEDs these days are blinding at a mA or two. We run maybe 100 uA
for test led's on pcb's, so we can see around them to probe. Most LEDs
are visible in office light at 1 uA.

I tested one green LED up at the cabin on a moonless night, dark
adapted at 2AM, and I could just make out light at about 1 nA.

Are we allowed to see those specs?
I found the spec of the 75121N like this:
https://www.google.com/search?q75%121N



My answer, without knowing more, is one transistor and one resistor for each  
LED. The resistor goes in the transistor's emitter circuit.

Sid 03 wrote:


A hex inverter sounds like the ticket.  74HC04 or its brethren.

For a DIP package see e.g.

<https://www.digikey.com/en/products/detail/nexperia-usa-inc/74HC04D652/333139>

Cheers

Phil Hobbs

On Wednesday, January 20, 2021 at 4:29:05 PM UTC-6, Phil Hobbs wrote:


I may have found a possibility, TI has a chip 'SN75451BP',  The NAND gate version.
Specs:  https://www.ti.com/lit/ds/symlink/sn75452b.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts16%11160841430

On Wednesday, January 20, 2021 at 5:49:33 PM UTC-6, Sid 03 wrote:


I thought about using a inverter or even just a quad AND gate, but if I can find a chip that was designed and intended for this function would be a better option.

>> I may have found a possibility, TI has a chip 'SN75451BP', The NAND  
gate version.


I'm curious why you think that a "chip that was designed and intended for  
this function would be a better option" for driving an LED.

Does moving a fridge require an individual that was designed and intended  
for this function or can anyone do it?  

On Wednesday, January 20, 2021 at 3:51:43 PM UTC-8, snipped-for-privacy@gmail.com wrote:



That's the germ of a TERRIBLE plan.   Every chip manufacturer has a sales force that wants to
convince you that your intention fits their chip.   But the intention that matters is YOURS,
the designer's, not the chip manufacturer's.

logic gates are generally suitable for driving indicator LEDs
describe the task in more detail. Quantify your requirements.

There are specialised LED driver chips, but seeing as you only have
one or two LEDs they seem like probably overkill

On Wednesday, January 20, 2021 at 6:49:33 PM UTC-5, snipped-for-privacy@gmail.com wrote:


Huh?  If you thought the 75451 was power hungry....  

ICCL Supply current, outputs low VCC= MAX, VI= 0V SNx5451B52   65 mA

What's wrong with a FET like the 2N7002?  Good up to 20V on the gate and more on the drain.  100's of mA.  If you are driving a relay protect from kickback with a diode across the relay.  

Sid 03 wrote:



Congratulations on picking a 53-year-old part.  There aren't that many  
of those around. ;)  (At least it isn't super-expensive.)

Driving a few LEDs and shipping around 10-mA-level binary signals really  
doesn't require this level of drama, though.  Why not pick something  
less current-hungry such as the above, or (if you need HV open-collector  
outputs) a prebiased (or 'digital') transistor array such as

<https://www.digikey.com/en/products/detail/nexperia-usa-inc/PUMH4115/1157880>?


Cheers

Phil Hobbs

 Edward Rawde wrote:
 ==================


** Characters like " sidw...."  posting via gmail.com are never going to tell you that.  
Cos then you would know their "secret" and likely not help any more.  

Mostly their project is either crazy, illegal or dangerous - sometimes all three.  

IMO:  if you do not know what the poster is up to,  DO NOT HELP !!  

BTW:    
Q. Why is "gmail " so bad ?

A.  Because several years ago "Google Groups" began and opened the flood gate to every stinking troll on the internet to access usenet.

Ever since,  usenet has fallen into decline and disrespect.
Hardly anything left now.  



.......  Phil  

On Wednesday, January 20, 2021 at 5:01:04 PM UTC-5, snipped-for-privacy@gmail.com wrote:


True, mostly these groups are full of whiny old men decrying the loss of their domain.  

On Wednesday, January 20, 2021 at 5:01:04 PM UTC-5, snipped-for-privacy@gmail.com wrote:


He's probably someone with a recent master's degree in EE from the university of California system...
It ends up ripping off a lot victims, people lucky to get a job at the night desk in a hotel afterwards.



LOL- other than myself, I don't see a lot of trolling of usenet coming out of gmail. Get over it. Don't what makes you think having a newsreader makes the process more selective somehow.

On Thursday, January 21, 2021 at 6:43:11 AM UTC-6, Fred Bloggs wrote:



Thanks to everyone who provided input.
I ordered the 'PUMH4,115' from DigiKey.   $0.20

:

ther circuits. Found this on Newark: 'SN75121N' [Line Driver, Dual, TTL, 4.
75V to 5.25V Supply, DIP-16] But I don't like that its TTL and probably a c
urrent hog.  


If 5.5V operation is good enough how about this?  

https://www.ti.com/lit/ds/symlink/sn74lvc2g241.pdf?ts16%11107237435

The AC product line gives the current you are asking for.   If you are tryi
ng to drive a line without any specific specs on timing, what's wrong with  
a simple transistor.  Use the LED as your pullup/down with a current limite
r resistor in series with the LED and a resistor in parallel with them to a
ssure pull to the rail.