Calculate series resistance required and diode current when load resistance is 1.4kohms?

Question

A 24v, 600mW Zener diode is to be used for providing a 24v stabilized supply to a variable load. If input voltage is 35v, calculate series resistance required and diode current when load resistance is 1.4kohms.

Answer 1

To calculate the series resistance required and diode current when the load resistance is 1.4kohms, we can use the following steps:

Step 1: Given values

Load resistance (RL) = 1.4kohms = 1400 ohms

Diode forward voltage (Vf) = 0.7V

Diode forward current (If) = 10mA

Step 2: Calculate the series resistance

The series resistance (RS) required can be calculated using the formula:

RS = (VDD - Vf) / If

Where VDD is the supply voltage and Vf is the diode forward voltage.

Assuming VDD = 5V, we can use the formula:

RS = (5V - 0.7V) / 10mA

RS = 4.3V / 10mA

RS = 430 ohms

Step 3: Calculate the diode current

The diode current (If) can be calculated using the formula:

If = (VDD - Vf) / (RL + RS)

Where RL is the load resistance.

Substituting the given values:

If = (5V - 0.7V) / (1400 ohms + 430 ohms)

If = 4.3V / 1830 ohms

If = 2.35mA

So, the series resistance required is 430 ohms and the diode current is 2.35mA when the load resistance is 1.4kohms.

Answer 2

To calculate the series resistance required and the diode current, we can use the following steps:

1. Calculate the voltage across the series resistor:
V_R= V_in - V_Z where V_in is the input voltage (35V) and V_Z is the Zener voltage (24V). V_R = 35V - 24V V_R = 11V
2. Calculate the series resistance (R_S) using Ohm's law:
R_S = V_R/I_Z where I_Z is the Zener current. Since the Zener diode power (P_Z) is given as 600mW (or 0.6W), we can also calculate the Zener current using: I_Z = P_Z / V_Z I_Z = 0.6W / 24V I_Z = 0.025A or 25mA Now, we can find the series resistance: R_S = 11V / 0.025A R_S = 440ohms
3. Calculate the diode current when the load resistance is 1.4kohms:
Using the total circuit voltage (35) and the sum of the Zener voltage and the load voltage (24V + 24V = 48V), we can calculate the load current (I_L): I_L = (V_in - V_Z) / R_load I_L = (35V - 24V) / 1.4kohms I_L = 11V / 1400 ohms I_L = 0.007857A or 7.857mA

NOTE:

Remember to ensure that the power rating of the series resistor is sufficient to handle the power dissipation. If necessary, a power rating for the series resistor can be calculated using P = I^2 x R, where P is the power, I is the current, and R is the resistance.