AC, DC, and TTL are the three most common types of which circuits used in controller output modules?

• A. Input circuits
• B. Output circuits
• C. Power circuits
• D. Signal circuits

Answer: (B)

Controllers deliver energy or signals to the outside world through their output circuits, so AC, DC, and TTL describe the kinds of outputs you can have. An AC output is used to switch or feed AC power to a load, typically through relays or solid‑state switches designed for AC. A DC output does the same for DC-powered loads, using transistors or relays to switch the DC. TTL outputs provide a digital logic‑level signal (usually 0 to 5 volts) used to drive other digital devices or optocouplers, not high‑power loads. All of these are core ways the controller sends something to the outside, which is why they’re categorized as output circuits. The other terms describe sensing or supplying power rather than the act of driving the external load.