Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Problem in design?

Status
Not open for further replies.
The simpler circuit will need base resistors on the PNP transistors to keep them turned off as the bases are floating at the moment.
The 10uH choke will not be needed as it will not have any effect in this situation. The 25R (27R) resistor will reduce the back emf from the relay coil.

The series inductor-resistor combo is the relay coil equivalent. At first glance, large value resistors from the PNP bases to 5V would seem necessary to keep them turned off, but not much of anything can happen until deliberate turn-on of one of the NPNs occurs, after which niether base is floating.
 
After the relay has been pulsed in one direction (either direction) the base of each PNP transistor is connected in such a way that any leakage from them will turn them on more. This is basically called "floating."
 
Status
Not open for further replies.

New Articles From Microcontroller Tips

Back
Top