h bridge control problems
i have an h bridge set up with four transistors to the motor.· I use PNP transistors so bringing their base leads low via the i/o pins on the stamp should turn them on.· When I bring them low a certain amount of current is sunk into the i/o pin.· However, when it is brought high, their is still a smaller but significant amount of current being sunk into the stamp.· Is this because·I didn't use pullup resistors on the i/o pins?
Comments
Post Edited (Obiwan) : 6/7/2005 6:00:44 PM GMT
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
modified version of what you described. I might point out that to turn a PNP transistor "ON" you need a negative
voltage difference of .6V across the B-E junction. This is the opposite for NPN transistors.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Think of it this way...
Assume that a LOW signal on the BASE of a PNP transistor relative to the Emitter turns the transistor on.
If the Stamp Pin is LOW (0V), the PNP turns "on"
If the Stamp pin is HIGH (5V), the PNP turns "on"
Why does the transistor stay "on" you ask? Even though the Stamp is supplying 5V, there
is still a 4V difference between the B-E junction of the PNP transistor.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.