November 15, 2007
why do we put pull up resistors before connecting to a darlington pair?
tul asked:
when we place a connection between a microcontroller and a darlington pair ,in between we connect some pull up resistors.why is it so?
Sign Language For Babies And Beyond
when we place a connection between a microcontroller and a darlington pair ,in between we connect some pull up resistors.why is it so?
Sign Language For Babies And Beyond
Written by: John
Filed Under: Microcontrollers
Tags: Darlington Pair, Microcontroller, Resistors
Trackback URL: http://roboticstechnologycenter.com/421/why-do-we-put-pull-up-resistors-before-connecting-to-a-darlington-pair/trackback/
Farhad K
November 17, 2007 at 9:52 pm
To drive a darlington pair, the connected output should go High (+5V).and sink sufficient current,
There is four different modes for a microcontroller I/O port to be configured in:
1-input-only(tristated)
2-full CMOS output
3-open-drain output
4-quasi-bidirectional ( as in classic 8051)
CMOS output can easily drive a darlington pair.
Open-drain output cannot go high(+5V) so you need pull up resistor..
Quasi-bidirectional port has an internal pull up resistor, but it’s more than 100K ohms. To make the sink current sufficient, you may need another parallel pull-up resistor.