Driver/Buffer datasheet voltages

Discussion in 'General Electronics Chat' started by SPQR, Feb 17, 2013.

1. SPQR Thread Starter Member

Nov 4, 2011
379
49
Hello again,

I'm going through a "driver/buffer" stage, and have purchased some representative samples of about 20 different types.

Before I start building circuits, I'd like to learn a bit more about each one.
I'm building a spreadsheet with a series of variables regarding each buffer, and I'm stumped on some voltages:

SN74HC125 -
Introduction - "Wide operating voltage range of 2-6V"
Page 2 - "supply voltage range - -0.5-7V"
Page 3- "VCC supply voltage - 2-6V"
Why the difference?

SN7417 -
"open collector" - I understand the implications of this
"sinking 40mA" - this I understand
Page 2&3 - "supply voltage Vcc = 7V"
__________"output voltage = 15V"
Don't think that this is a voltage amplifier, so does the output voltage mean that you can attach up to 15V to the open collector? Like a 15V motor?

Thanks again.

Last edited: Feb 17, 2013
2. StayatHomeElectronics AAC Fanatic!

Sep 25, 2008
1,021
71
On the sn74hc125: the -0.5 v to 7 v number is the absolute maximum supply range that would probably not damage the chip. The 2 v to 6 v range is the recommended operation range over which many of the other parameters are measured. So, although you could put 1 v on the supply, since it will not damage the part, you are not supplied with any guaranteed characteristics for the chip outputs...

3. StayatHomeElectronics AAC Fanatic!

Sep 25, 2008
1,021
71
On the sn7417: the open collector output means there is a BJT transistor with no connection to its collector inside the chip. The output load can be connected between the collector and a voltage as high as 15 v, so a 15 v motor would be one option. When there is no current flowing through the load, the voltage at the collector would be 15 v, the maximum allowed by this part before the transistor collector can be damaged.

4. SPQR Thread Starter Member

Nov 4, 2011
379
49
Very, very nice - Thank you!

I've read many datasheets over the last few months and I marvel at such a fantastic, organized, engineering profession,
that can have such variation in nomenclature.

So for the 125
Introduction - "Wide operating voltage range of 2-6V"
Page 2 - "supply voltage range - -0.5-7V"
Page 3- "VCC supply voltage - 2-6V"

Two different concepts with three different names.
So I'm going to label the columns with MY names:

Supply Voltage = Sup V
Tolerable Supply Voltage Range = Tol Vcc

In terms of the 7417, it's what I figured - that would make sense.
So my new name:
Maximum Applied Voltage to Collector Output - Max Coll Volt

Thanks again! Very helpful!

5. w2aew Active Member

Jan 3, 2012
219
64
The key is to look at the headings above each of the tables. On page 2, it says "absolute maximum ratings". This are the ratings, which if exceeded, will damage the part. On page 3, these are the "recommended operating conditions". Self explanatory.

SPQR likes this.
6. SPQR Thread Starter Member

Nov 4, 2011
379
49
Yep, just noted those!
I'll have to be REALLY carefull in future.
Thanks!

7. ScottWang Moderator

Aug 23, 2012
6,459
1,001
How is the current of 15V motor?

8. StayatHomeElectronics AAC Fanatic!

Sep 25, 2008
1,021
71
I think the motor example was just to try to understand the concept of a 15 volt output on the part. The OP stated he knew the part on could sink 40 mA. So, motor specifications were not questioned.

9. ScottWang Moderator

Aug 23, 2012
6,459
1,001
The motor specifications maybe not the question, but when a load needed 40mA connecting to the 40mA sink could be caused a problem.

10. SPQR Thread Starter Member

Nov 4, 2011
379
49
Exactly!

In terms of the open collector output, I usually think of motors/LEDs/solenoids being connected and "doing something".
It was a random example that I understand, at my level.