Transistor as a relay vs mechanical relay

Just a very basic question:

Can anyone share with me what's the benefit of using transistor as an
electrical relay compared to mechanical relay when the incoming signal
is from a computer?

Is it related to pricing, input voltage/current, power rating and etc?

Pls help.

Thanks.

Albert

 

[Chris]

Rich Grise wrote:

On Sat, 21 May 2005 12:19:50 -0700, albertleng wrote:

Just a very basic question:

Can anyone share with me what's the benefit of using transistor as
an
electrical relay compared to mechanical relay when the incoming
signal
is from a computer?

Is it related to pricing, input voltage/current, power rating and
etc?


No moving parts.

Cheers!
Rich

Yup.

A basic question, indeed. Let's count the ways.

* Tranistors switch in microseconds, relays in milliseconds.

* Transistors switch directly on without contact bounce, relay
contacts smack and bounce together for a millisecond or so, causing
intermittent on/off for that time until the contacts settle in.

* Relays are mechanical devices with moving parts -- they will wear
out. A typical relay is rated for somewhere between 10 thousand and 10
million operations before failure. And relay contacts usually wear out
first, if they're swicthing at anywhere near rated load. Actually,
they're supposed to.

* Relay contact bounce can cause EMI which can cause problems.
Although you generally have to be more careful with transistors when
switching inductive loads, there isn't a spark being created with
switching like with relays. That EMI can cause the computer to spit
up.

* A typical high current transistor will usually cost much less than a
relay rated to switch equivalent current.

* A transistor will typically require much less power to operate than
a relay coil, especially if you use a darlington transistor or a
MOSFET.

I guess there are more reasons, but these are the ones that come to
mind first.

Good luck
Chris

 

[Nikolas Britton]

albertleng@gmail.com wrote:

Just a very basic question:

Can anyone share with me what's the benefit of using transistor as an
electrical relay compared to mechanical relay when the incoming
signal
is from a computer?

Is it related to pricing, input voltage/current, power rating and
etc?

Pls help.

Thanks.

Albert

Read the the intro, pages 1-6, for this book:
http://www.amazon.com/gp/reader/0521478790/ref=sib_dp_pt/103-2146462-2957458#reader-link