Momentary Load ON at Power-Up (Transistor Output)

What does MOMENTARY-ON-POWERUP mean?

When the external power supply is turned on, a load connected to a transistor output module momentarily turns on. This occurs due to stray capacitance (C) between the photocoupler's collector and emitter, allowing current (Ic) to flow into the transistor's gate, activating the output Y0 for a brief period (e.g., 100µs). This is more pronounced with high-sensitivity loads like solid-state relays or if the external power supply's voltage rise time is too fast (less than 10ms).

• Rapid voltage rise time (t1 < 10ms) of the external power supply at power-on.
• Stray capacitance (C) between the collector and emitter of the photocoupler, allowing current (Ic) to flow into the transistor's gate.
• Use of high sensitivity loads (e.g., solid-state relays) that are easily triggered by small currents.
• Output modules like RY40PT5P, RY41PT1P, RY42PT1P (source type) are susceptible to this characteristic.

Click steps to track your progress.

1. 1

   Ensure the external power supply's voltage rise time (t1) is 10ms or more at power-on. Install a switch (SW1) on the primary side of the external power supply to control the power-on sequence.

2. 2

   If a secondary side switch is required, connect a capacitor (C1, several hundreds of µF, 50V) and a resistor (R1, several tens of Ω) in parallel across the supply lines to slow down the voltage rise time to 10ms or more.

3. 3

   For output modules RY40PT5P, RY41PT1P, RY42PT1P (source type), Action 2 is not effective due to their power supply circuit characteristics; use Action 1 instead.

4. 4

   When installing a diode (D1) for a circulation path, ensure its reverse voltage VR(VRM) is approximately 10 times the rated voltage (e.g., 200V for 24VDC), and its forward current IF(IFM) is more than twice the maximum load current (e.g., 4A or more for 2A/common).