Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

What is the power rating of this 120R resistor?

Status
Not open for further replies.
tony_lth

tony_lth

Advanced Member level 5
Joined
Jul 28, 2010
Messages
2,088
Helped
377
Reputation
756
Reaction score
368
Trophy points
1,363
Location
Beijing
Activity points
12,635
Hi, ALL,
In the following RS422 converter circuit, diff RS422 signal is converted to un-banlanced.
According to def of RS422, + signal may be +2V~+6V, and vice versa.
1. So R415 voltage may be 12V, then R415 power rating is 12^2/120=1.2W. Right?
2. What function is the circuits of R415/R413/R419?
Thanks.
Tony Liu
 

Attachments

  • 捕获.JPG
    捕获.JPG
    51.3 KB · Views: 93

You are confusing common mode and differential line voltage. The maximum RS-485 differential driver level is +/- 5V, typically +/- 3V with termination. 1/4 W rating is barely sufficient, 1/2 W suggested.

The pull-up and pull-down resistor are referred as "Idle-line failsafe bias circuit" in EIA RS-485 application note.
The developer of a system using 485 drivers, receivers, or transceivers should consider the situation in which all drivers may be in the passive state.
Click to expand...

Without this circuit, the idle level is undefined and bus receivers may sense a break state.
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top