High-performance photocouplers for speed-challenged applications

Toshiba Electronics Europe GmbH has released four photocouplers that address the issues induced by signals with slow signal rise and fall times as well as slow startup power supplies.

Photocouplers utilise light emitters and receivers along with a light-transmissive insulator to supply a high degree of electrical insulation in a small package. The applications are wide and varied, although one of the most popular applications is in PLC, which is essential to automating modern factories.

To operate correctly, photocouplers need input signals to conform to a minimum rise time to avoid undesirable switching at the output. The four new photocouplers (TLP2362B, TLP2368B, TLP2762B, TLP2768B) are compliant with IEC 61131-2 (Type 1) and deliver hysteresis for the input forward current threshold and for the power supply circuit, making them ideal for use in high EMC noise environments.

Providing this hysteresis within the device ensures that the output will maintain its ‘high’ or ‘low’ state without further switching. Built-in hysteresis eradicates the necessity for external circuitry (such as Schmitt triggers) and reduces complexity and cost.

Demanding applications such as PLCs require photocouplers with data transmission rates that exceed the typical levels of a few Kbps. The four new photocouplers include a high-gain, high-speed amplifier that permits the TLP2362B and TLP2762B to support 10Mbps and the TLP2368B and TLP2768B to support 20Mbps. This allows faster communication in end applications.

All devices can deliver an output current (Io) of 25mA and can tolerate input rise and fall times for as long as 60s. The operation remains unaffected, provided that the supply voltage (VCC) is established within the 60s.

The TLP2368B and TLP2768B achieve a propagation delay of less than 60ns. The TLP2362B and TLP2368B are housed in a 5-pin SO6 package measuring 3.7mm x 7mm x 2.3mm with an isolation voltage (BVs) that exceeds 3750 Vrms. The TLP2762B and TLP2768B are housed in a SO6L package (3.84mm x 10mm x 2.3mm) and are rated for BVs greater than 5000 Vrms.

All four of the new photocouplers are able to operate at ambient temperatures as high as 125C (and as low as -40C), thereby ensuring that end applications such as PLCs can operate reliably in all conditions.