At 01:00 PM 3/7/2005, Gordon Williams wrote: >Hi, > >I have a small DC motor (max 300 mA) and I have made up a small H-Bridge >with PNP transistors on the top (2N2907) and NPN on the bottom (2N2222). >This will be run off a 5v battery. I will be using flyback diodes. > >I will be using PWM to control the motor speed with a freq of about 300 Hz. >Should I be using the PNP or the NPN for the speed control? Does one turn >on/off faster or are there other issues? I will be using a PIC for the PWM. You've chosen a supply voltage such that all 4 transistors can be driven directly by PIC pins. As such, it doesn't matter much whether you apply the PWM to the upper or lower devices. The challenges come when your motor voltage is much larger than the PIC supply. Now you have to get into level translation issues - the simple and cheap level translators are often fairly slow. In those cases, it is easier to PWM the lower devices and switch the upper devices only for direction changes. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 21 years of Engineering Innovation (1984 - 2005) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist