The PTCM-4×5×6 type IC card holder anti-attack thermistor module represents a key application of PTC thermistors. This module plays a crucial role in enhancing the security of IC card readers and related devices by significantly improving their resistance to various external threats, such as static electricity, overvoltage, and accidental short circuits. The core principle is illustrated in the diagram below: under normal operation, the PTC thermistor functions as a current-limiting resistor connected in series, maintaining a stable resistance value. However, during abnormal conditions—such as an unexpected surge in current—the resistance of the PTC thermistor increases dramatically, typically by 4–5 orders of magnitude, effectively switching it into an open state to protect the circuit from damage.

First, the application circuit:

Note: Depending on the specific requirements, CPU cards or memory cards can choose between four, five, or six groups of PTC modules for optimal performance.

Second, recommended settings:

To further enhance the protective capabilities of your meter against electrostatic discharge (ESD), it is advisable to configure the peripheral circuit and layout of the IC card anti-attack module as follows:

• Connect a ferrite bead in parallel with the 4148 switch transistor between the GND of the card holder and the GND of the anti-attack module.
• Place a 50Ω 1W wirewound resistor between VCC and pin 1 of the attack module's VCC pin.

These adjustments help ensure better signal integrity and improved protection against electrical stress, making the system more robust and reliable in real-world applications.

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