The Impact of Reverse Voltage on MBRS360T3G Schottky Diode s

The Impact of Reverse Voltage on MBRS360T3G Schottky Diodes : Fault Analysis and Solution Guide

Schottky diodes, like the MBRS360T3G, are designed to have low forward voltage drop and fast switching times, making them ideal for high-efficiency circuits. However, when these diodes are subjected to reverse voltage beyond their specified ratings, it can lead to severe issues. This article will analyze the faults that occur due to reverse voltage, explain the root causes, and provide a clear and simple step-by-step solution to resolve these issues.

1. Understanding the Fault:

The MBRS360T3G Schottky diode is designed to handle a maximum reverse voltage (VR) of 30V. If a reverse voltage higher than the rated value is applied, the diode can be damaged. This damage is typically seen as reverse breakdown, where the diode no longer acts as a one-way current path and begins to conduct in the reverse direction.

Symptoms of Reverse Voltage Faults: Permanent Short Circuit: The diode may permanently short-circuit in the reverse direction, causing a continuous current flow that can damage the surrounding components. Increased Leakage Current: If the diode survives reverse voltage damage but is not destroyed, it might still function with increased leakage current, leading to inefficiency in the circuit. Overheating: Prolonged reverse voltage stress can cause excessive heat generation in the diode, affecting the overall reliability of the circuit.

2. Fault Analysis: Why Does This Happen?

The primary cause of failure in Schottky diodes like the MBRS360T3G is the reverse breakdown phenomenon. Schottky diodes have a lower reverse breakdown voltage compared to traditional pn-junction diodes, and they are more sensitive to reverse voltage spikes. When exposed to a reverse voltage exceeding the rated 30V, the diode’s junction can break down, leading to catastrophic failure.

3. Step-by-Step Guide to Solve the Fault:

Step 1: Verify the Reverse Voltage

Before diagnosing further, ensure that the reverse voltage applied to the diode does not exceed its rated voltage. Use a multimeter or an oscilloscope to check the voltage across the diode.

Action: If the reverse voltage exceeds 30V, this confirms that the diode has been exposed to damaging conditions. Step 2: Identify the Faulty Diode

If reverse voltage has already been applied, check whether the diode is damaged.

Action: Disconnect the diode from the circuit.

Use a Multimeter: Set the multimeter to diode testing mode.

Place the multimeter probes on the anode and cathode of the diode in both directions.

In normal condition, the diode should show a forward voltage drop of around 0.2V to 0.4V when tested in the forward direction, and should show no conduction (infinite resistance) when tested in reverse.

If the diode shows conductivity in reverse or if the forward voltage drop is unusually high or low, replace the diode.

Step 3: Replace the Damaged Diode

Once the damaged diode is identified, replace it with a new MBRS360T3G diode or a suitable replacement with similar specifications.

Action: Ensure proper orientation during installation. The cathode (marked with a stripe) should be connected to the more positive side of the circuit, and the anode to the more negative side. Step 4: Protect the New Diode from Future Reverse Voltage

To prevent future failures, it’s crucial to limit reverse voltage exposure.

Action: Implement a clamping diode or a Zener diode with a breakdown voltage slightly lower than the maximum voltage rating of the Schottky diode. This will protect the diode by clamping the reverse voltage within safe limits. Step 5: Implement a Reverse Voltage Protection Circuit

To further safeguard the diode in future designs, add a reverse voltage protection circuit such as:

Series Resistor: A small resistor (e.g., 1kΩ) placed in series with the anode to limit reverse current and help the system to absorb voltage spikes. Schottky Diode in Parallel: Another Schottky diode, connected in parallel but with its polarity reversed, can divert current away from the main diode during reverse voltage events.

4. Preventive Measures and Best Practices:

Double-check the Circuit Design: Always verify that the circuit is designed to ensure the diode is not exposed to reverse voltage higher than its rated value. Use a Voltage Clamping Device: Consider adding a TVS diode (Transient Voltage Suppressor) or a Zener diode for clamping excessive voltages. Add Protection Components: In high-voltage circuits, adding additional protection components such as varistors or fuses can help prevent overvoltage conditions that could damage the diode.

5. Conclusion:

Reverse voltage can severely impact the performance and reliability of Schottky diodes like the MBRS360T3G, leading to potential failures such as short circuits, leakage currents, and overheating. By identifying the faulty diode, replacing it, and implementing protective measures such as clamping diodes and reverse voltage protection circuits, you can prevent future damage and ensure reliable circuit operation.

By following the steps outlined above, you can quickly identify, resolve, and prevent issues caused by reverse voltage in Schottky diodes, ensuring your circuit operates smoothly and efficiently.