Why do we use a darlington sink driver?

Thread Starter

blue6x

Joined Apr 6, 2005
38
does anyone here knows why we have to pass positive rectangular pulse to a darlington sink driver??? I'm just wondering why because the output in an oscilloscope is quite different in that of the rectangular pulse I sent to that darlington sink driver. Anyone please share your thoughts. Thanks....
 

Thread Starter

blue6x

Joined Apr 6, 2005
38
the input to this darlington sink driver came from a microprocessor, i used an oscilloscope to check it out and the input is a rectangular wave. The output of the darlington is then sent to a seven segment display. The output signal as viewed from an oscilloscope is somewhat similar to decaying signal just like in capacitor discharging, with some spikes though.. How is it explained.... Thanks by the way.
 

Thread Starter

blue6x

Joined Apr 6, 2005
38
I'm sorry but i don't have a soft copy of the circuit, i'll be attaching the data sheet of the microprocessor though nd the darlington sink driver. The darlington's pins 7 down to 1 except pin 2 are connected to the pin segments 60 to 65.The darlington's output is then connected to a seven segment display. Hope you could still help me with this. Thanks

PS. input to the microprocessor is at pin 6, which is actually a rectangular wave based on my analysis using an oscilloscope, also, the output of the microprocessor being fed to the darlington sink driver is a rectangular pulse also, but as what i have said the output of the darlington sink driver has changed, but still it is a positive pulse. Thanks for your time taking this.
 

Thread Starter

blue6x

Joined Apr 6, 2005
38
By the way, the application of this one is for a tachometer, that part i mentioned is for the display segment. thanks
 

David Bridgen

Joined Feb 10, 2005
278
Originally posted by blue6x@Apr 20 2005, 03:06 AM
the output of the darlington sink driver has changed, but still it is a positive pulse.
[post=7094]Quoted post[/post]​
The darlington stages are inverting so with a positive-going input pulse you should be getting a negative-going output, i.e. the collector should be going from some positive voltage down to 0V.
 

Thread Starter

blue6x

Joined Apr 6, 2005
38
I'm currently looking on the output pulse on the oscilloscope of the darlington, you were right, a rectangular pulse input turne to an almost zero output, and the zero input has gone high, then decreasing until the next rectangular pulse (i mean high input) is received.

but wait, this could be my last question, but why is it necessary to use this darlington sink driver, i'm thinking of this because why we just don't accept that rectangular pulse as our input to the seven segment directly.

Important: I've said that because there are also sink drivers that are non inverting. What are their purpose. Thanks for your time.... You were really of great help.
 

David Bridgen

Joined Feb 10, 2005
278
Originally posted by blue6x@Apr 20 2005, 04:39 AM
why is it necessary to use this darlington sink driver, i'm thinking of this because why we just don't accept that rectangular pulse as our input to the seven segment directly.

Important: I've said that because there are also sink drivers that are non inverting. What are their purpose. Thanks for your time.... You were really of great help.
[post=7097]Quoted post[/post]​
The outputs from the uP can neither source (provide) nor sink (switch to ground) much current. The drivers can sink much more.

The display will have its positive supply line permanently connected and this is common to all segments.

For a segment to be lit it must have its other end connected to 0V ("ground".)

As the outputs from the uP are positive-going you need an inverting driver.

A non-inverting driver would be used where the driven device requires a voltage applied across it rather than connecting the device to ground as is done in your application.
 

Thread Starter

blue6x

Joined Apr 6, 2005
38
thank you. now i think so much have been said and it helps me lot. i hope you could answer my further questions in the near future. Thanks.....
 
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