Electrical and electronics sample problem 109

[qiudogcool]

Hi. I need some help with sample problem 109. What is the R in the chart? R=4C/W. Is this problem in the electronics topic? How does a regulator function?

 

[jimbo7825]

Not sure if you still need help with this, but for anybody else this what i did to solve the problem. Its different than how its explained in the solution area. I didnt understand how they got the equation. But anyway we know the Vin=15, VRload=5 so VReg =9 by KVL. Rload=5ohm so ILoad=5/5=1A. Since the current in the ground connection of the regulator is 0, Ireg=ILoad=1A. Preg=V*I=9*1=9W.

now this where i went different than the solution, from the graph we have the following points (90,15) and (150,0) find the slope m = -0.25, b = 37.5 so PD=-0.25*Tc+37.5. setting this equal to 9 and solving for Tc the answer is 114.