jal@pandora.cs.wayne.edu (Jason Leigh) (11/14/90)
Ok, hope some ee major can answer this. I am a cs major with enough know-how to design and build logic using simple MSI parts, but I don't know much about electronics in general. What I need to know is, given a CMOS or TTL output how can I amplify the output so as to be able to drive a small relay (5VDC, 20mA, 250ohm)? I've been glacing at relay drivers in my CMOS book and wasn't sure if I was looking at the right chip or how I was to use it correctly. Thanx. Jason Leigh jal@cs.wayne.edu -- :^) :^) :^) :^) :^) :^) :^) :^) ;^) O^: (^: (^: (^: (^: (^: (^: (^: :^) Where the telescope ends, the microscope begins. (^: :v) Which of the two has the grander view? - Victor Hugo (v: :v) :v) :v) :v) :v) :v) :v) :v) :v( $v: (v: (v: (v: (v: (v: (v: (v:
cgordon@vpnet.chi.il.us (Crash Gordon) (11/16/90)
Probably the neatest way to pull this off is to use something like the ULN2003 (Motorola MC1413). This IC contains an array of seven darlington power switches, with biasing resistors and protection diodes included to allow low-side swithing of inductive loads. (I think there's also a ULN2803, which has 8 drivers.) One pin is connected to ground, and one to the relay power supply. Then, the common side of the relay(s) is/are connected to the relay supply, and the other side(s) go to the IC. Applying a logic high to the switch input pin will pick up the relay. (The data sheet makes this all pretty obvious) The chip can switch 500 mA. ----------------------------------------------------- Gordon S. Hlavenka cgordon@vpnet.chi.il.us Disclaimer: Yeah, I said it. So what?