In the comparator circuit CR1, CR1 conducts as a zener and rectifier diode.

In the comparator circuit CR1, CR1 conducts as a zener and rectifier diode.

• A. Normal diode
• B. Zener and rectifier diode
• C. Transistor
• D. Capacitor

Answer: (B)

The key idea is that a diode in this role can conduct in two ways depending on polarity. In forward bias, it behaves like a normal rectifier diode, allowing current to pass with a small forward drop (about 0.6–0.7 V for silicon). In reverse bias, if it’s a Zener diode, it can conduct when the voltage reaches its breakdown (Zener) voltage, effectively clamping or setting a reference level. So CR1 is used both as a forward-conducting rectifier and as a Zener diode that conducts in reverse at a defined voltage. That combination is what makes the description “Zener and rectifier diode” the best fit for CR1 in the comparator circuit. A normal diode wouldn’t take advantage of Zener breakdown, a transistor isn’t a diode, and a capacitor isn’t a diode at all.

The key idea is that a diode in this role can conduct in two ways depending on polarity. In forward bias, it behaves like a normal rectifier diode, allowing current to pass with a small forward drop (about 0.6–0.7 V for silicon). In reverse bias, if it’s a Zener diode, it can conduct when the voltage reaches its breakdown (Zener) voltage, effectively clamping or setting a reference level.

So CR1 is used both as a forward-conducting rectifier and as a Zener diode that conducts in reverse at a defined voltage. That combination is what makes the description “Zener and rectifier diode” the best fit for CR1 in the comparator circuit. A normal diode wouldn’t take advantage of Zener breakdown, a transistor isn’t a diode, and a capacitor isn’t a diode at all.