NPN and NPN open collector

This type of electronic output is composed by a NPN transistor and a pull-up resistor used to match the output voltage to the power supply when the transistor is off. It has low saturation levels at 0 Vdc and close to 0 at the positive. It is proportionally influenced by the cable length, pulses frequency and by the load, so these factors should be considered to meet the application’s needs.

The open collector variant differs since it has no pull-up resistor, therefore the collector of the transistor is free from the constraint of the encoder power supply, allowing to obtain signals with different voltage.

NPN scheme	NPN open collector scheme

PNP and PNP open collector

Main characteristics and limitations of the PNP interface are the same as for NPN electronics. The main difference lies in the transistor, which is a PNP type. The resistor, if present, is a pull-down one. Therefore, it is connected between the output and 0V.

PNP scheme	PNP open collector scheme

Push-pull

In NPN or PNP electronics the major limitations are caused by the resistor, which works with a much higher impedance than a transistor. To overcome this issue, the Push-Pull circuit uses a complementary transistor, so the impedance is lower for commutation to positive and to zero. This solution increases frequency performances allowing longer cable connections and an optimal data transmission even at high working speed. Saturation signals are low, though higher than in NPN and PNP electronics. It is anyhow possible to apply indifferently the Push-Pull electronics also to NPN or PNP receivers, which is also TTL compatible (5 Vdc power supply).

Push-Pull scheme

Line-driver

The Line-Driver output is employed when operating environments are particularly exposed to electrical interferences or when the encoder is quite far from the receiver system.
Data transmission and reception work on two complementary channels, so the noise caused by the cross-talk from other cables is reduced. In Line-Driver instead, signals are transmitted and received in «differential» way; in other words, the communication works based on the difference of voltage between complementary channels.
This type of transmission is used in 5 Vdc systems and is compatible also with RS422; it’s also available with power supplies up to 24 Vdc for harsh environments applications.

Line-Driver scheme

Output stage protection

A highly integrated driver is used to protect outputs from short circuits. This solution is based on an active sensor which controls instantly the temperature reached by the element to be protected. In this way, protection is very effective.
Moreover, it ensures a constant protection against repetitive and permanent short circuits, which is why it is strongly suggested for heavy duty applications.
It’s available for Line-Driver and Push-Pull electronics.

Output stage protection scheme

For further information, please check the complete PDF on-line.