SCR Definitions: Holding Current vs Latching Current

Understanding the difference between holding current and latching current is key to operating a Silicon Controlled Rectifier (SCR) correctly.

• Holding Current ($I_H$): This is the minimum anode current required to keep the SCR in the conducting (ON) state. If the anode current falls below $I_H$, the SCR turns OFF.
• Latching Current ($I_L$): This is the minimum anode current required to turn the SCR ON *and ensure it stays ON* after the gate pulse is removed. The SCR "latches" into the ON state.

Relationship Between Holding and Latching Current

To ensure the SCR reliably latches ON after triggering, the anode current must exceed the latching current ($I_L$) during the turn-on process. Once triggered and the gate signal is removed, the anode current can fall, but it must remain above the holding current ($I_H$) to stay conducting. Therefore, the latching current must always be greater than the holding current.

The relationship is:

$I_H < I_L$

Conclusion

Based on the definitions and operational requirements:

• Holding current is the minimum current to maintain conduction.
• Latching current is the minimum current to ensure the device stays ON after trigger removal.
• For reliable latching operation, the current needed to latch ($I_L$) must be greater than the minimum current needed to hold ($I_H$).

Thus, the correct relation is $holding current < latching current$.