FAQ

What is an open collector in a power supply?

Category
How to Use Power Supply

The open-collector output of a power supply is a method of control circuitry used to output the state (status) and other information of the power supply. The output of a power supply is controlled by an open collector to turn it on and off externally.
With open-collector output, an external circuit is connected to the collector and emitter terminals, but the circuit is different between NPN open-collector output and PNP open-collector output, so it is necessary to pay attention to which output is being connected.

Difference between NPN and PNP transistors

Difference between NPN and PNP transistors

Many of Matsusada Precision's power supply devices have NPN open-collector output at the remote terminal.

connection diagram of NPN open-collector output

connection diagram of NPN open-collector output

For your information, the connection diagram of PNP open collector output is shown below.

PNP open collector output

PNP open collector output

The transistors used in open-collector input/output circuits are often photocouplers (also known as optocouplers) to prevent equipment malfunction and reduce the risk of failure.
In Japan, the NPN type is mainly used for the output of sensors and PLCs. In Europe, however, the PNP type is often used to prevent malfunctions in case of disconnection or short circuit to the enclosure.
Besides the open-collector type, there is also the transistor-transistor logic (TTL) type.

Power supply internal circuit

Power supply internal circuit