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Step-by-Step Solution
Step 1: Identify the Key Parameters
• Protective (series) resistor, $R = 100\,\Omega$.
• Maximum power dissipation rating of the Zener diode, $P_{\text{max}} = 1\,\text{W}$.
• We need to find the minimum range of the DC source voltage required to test the diode’s I-V characteristics adequately.
Step 2: Relate Power Dissipation to Voltage and Current
When the Zener diode is in its breakdown region, it can dissipate a maximum power of $P_{\text{max}} = 1\,\text{W}$. If $I$ is the current through the diode and $V_Z$ is the breakdown voltage of the diode, then the power across the diode is:
$P_{\text{max}} = I \times V_Z$
Hence, the current through the diode in the breakdown region should be such that it does not exceed the maximum power limit. However, to make sure the source voltage can cover the entire breakdown region and allow measurement of the I-V characteristics up to the diode’s rated power, the supply voltage must be large enough.
Step 3: Considering the Series Resistor
The supply voltage $V_S$ is dropped across the resistor $R$ and the diode. In the breakdown region, most of the voltage is approximately $V_Z$ across the diode, with the rest across $R$. The series resistor limits the current, and the maximum current occurs at the highest supply voltage.
Expressing the current through $R$:
$I = \frac{V_S - V_Z}{R}
$
Step 4: Ensuring the Full Range of Zener Operation
To explore the diode’s complete breakdown characteristics, the supply must be able to reach a voltage substantially above $V_Z$. Practical Zener circuits designed for a Zener diode with a power rating of about $1\,\text{W}$ often use a supply voltage as high as about $24\,\text{V}$, especially when the series resistor is around $100\,\Omega$. This ensures the diode can enter and maintain breakdown region current up to its power rating.
If the supply voltage were less than around $24\,\text{V}$, it might not drive enough current through the diode-resistor circuit to cover the full I-V characteristic range (including the maximum rated current/power). Hence, a supply of 0–24 V is typically used.
Step 5: Conclusion
Based on practical Zener diode testing needs and maximum power rating considerations, the DC source range must extend from 0 to about 24 V. Thus, the minimum voltage range of the source required is:
0 – 24 V
