An open-collector output is a standard digital interface used to signal the power supply's status, such as alarms or operation modes. This circuit acts as a switch, allowing the unit to communicate with external devices like PLCs, relays, or indicators. Conversely, external control inputs (e.g., Output ON/OFF) are often designed to be driven by open-collector signals or contact closures.
Internal Structure
The open-collector output exposes the collector and emitter terminals of an internal transistor to the external circuit. It is crucial to distinguish between the two main transistor types, as their wiring requirements differ:
- NPN (Sinking): Connects the load to the ground.
- PNP (Sourcing): Connects the load to the power source.
Difference between NPN and PNP transistors
Matsusada Precision's Configuration
Most Matsusada Precision power supplies utilize NPN open-collector outputs for status signals on the analog remote control connector. The operation logic is as follows:
- Active State (Signal ON): The internal NPN transistor turns ON, connecting the output pin to the ground (Low level / Logic "0").
- Inactive State (Signal OFF): The transistor turns OFF, leaving the output pin in a high-impedance (floating) state.
To generate a logic "High" signal (Logic "1") during the inactive state, an external pull-up resistor is required. This configuration allows the user to match the signal voltage level (e.g., 5V, 12V, or 24V) to their specific system requirements.
Connection diagram of NPN open-collector output
For reference, a connection diagram of PNP open-collector output is shown below.
Connection diagram of PNP open-collector output
Isolation and Regional Standards
To ensure safety and reliability, these circuits often employ optocouplers (photocouplers). Optical isolation protects the power supply's internal control logic from external electrical noise, ground loops, and potential surge damage.
Global Standards:
- NPN (Sink logic): Widely used in Japan and the United States for sensors and PLC interfaces.
- PNP (Source logic): Common in Europe due to safety considerations regarding ground faults.
While open-collector is the most common interface, some models or applications may utilize TTL or CMOS logic levels. Please refer to the specific product datasheet for details.
Power supply analog remote control internal circuit example