# Car Tire Pressure. Zener

#### Car Tire Pressure

Prior to a street venture you verify the tire pressure on every one of the 4 tires worn out on your auto. You discover each is at 32 psig. The surrounding temperature is 60F. You start riding and get to be in the a forsaken road inside the focal point of the day. Because of the top surrounding temperature and the warming of the tires as a result of the reliable flexing of the fabric, the tire temperature achieves 120F. In the event that the surrounding pressure stays steady at 14.7 psia, please find the gauge psia inside the warm tires.

Total initial absolute pressure in the tire $P1 =32 +14.7 =46.7 psia =321985 N/m^2$ Initial temperature $T1 = 60 F =15.56 Celsius = 15.56+273.15 K =288.71 K$ Final Temperature $T2 =120 F =48.89 Celsius =322.04 K$ The transformation of the air inside the tire is at constant volume $P1/T1 =P2/T2$ $P2 = P1*T2/T1 = 321985*322.04/288.71 =359156.4 N/m^2 = 52.09 Psia =$

$=(52.09-14.7) psig =37.39 psig$

#### Zener Regulator

Please design a standard Zener regulator for voltage. Find the ratings of all components. Explain your choice of transistor, Zenner diode and resitors used.

The schematics of the simplest Zener regulator is show.

$I(C) = \beta*IB$

$IB(max) = I(C)max/\beta =3.947/75 =0.05263 A =52.63 mA$

$I(R) = I(B)+Iz =52.63 +1.5 = 54.13 mA$

Zenner voltage is

$Vz = V(L)+V(BE)open = 5+0.7 =5.7 V$

Maximum theoretical value of resistor R is

$R = (Vsmin-Vz)/I(R) = (12-5.7)/54.13 m =116.38 ohm$

In practice it is taken

$R = (Vsmin -Vz)/(I(B) +1.5*Iz) =(12-5.7)/(52.63+1.5*1.5) m =114.79 ohm$

(http://en.wikipedia.org/wiki/Linear_regulator#Simple_series_regulator)

The diode is 1N4734 with standard $Vz=5.6 V$ and 1 W power (1N752 with $Vz =5.6 v$ and $P =0.4 W$), and the standard value for resistor is 110 ohms.

The power rating for diode is $Pz =Iz*Vz =5.7*1.5 m =8.55 mW$

The power rating for resistor is

$P(R) = U^2/R = (16-5.7)^2/114.8 =0.924 W =1W$

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