Temperature Dependence in Circuit Components

Steps:

• Identify components with known temperature coefficients, such as diodes (Vbe decreases ~ -2 mV/°C) or resistors (PTC increases resistance with temperature).
• Analyze Vout expression for each circuit, substituting temp-dependent terms.
• Determine dVout/dT sign: positive for increasing Vout with temperature.
• Select circuit where overall coefficient yields positive dVout/dT.

Why C is correct:

• Circuit C uses a PTC resistor in a configuration where rising resistance increases voltage drop across it, directly raising Vout per Ohm's law (V = IR, with I constant).

Why the others are wrong:

• A: Fixed resistors yield constant Vout, independent of temperature.
• B: Diode-based drop decreases with temperature, lowering Vout.
• D: NTC thermistor decreases resistance with heat, reducing Vout.

Final answer: C