Overvoltage is a leading cause of thyristor failure. When the voltage across the thyristor exceeds its rated VDRM (peak off-state voltage) or VRRM (reverse repetitive peak voltage), the device’s junctions may break down, causing irreversible damage. Transient voltage spikes from lightning strikes, inductive load switching, or faulty voltage regulators are common culprits . For instance, a sudden voltage surge during motor startup can generate transient voltages that exceed the thyristor’s capacity, leading to thermal runaway and burnout.
Solution:
YFW’s MCR100-8 thyristor (Figure 1) is rated for 800V VDRM, making it suitable for high-voltage applications. To protect against transients, designers should implement snubber circuits (RC networks) across the thyristor to limit dv/dt (voltage rise rate) . Additionally, surge suppressors like metal oxide varistors (MOVs) can clamp excessive voltages, ensuring the thyristor operates within safe limits.
Excessive current flow through the thyristor can rapidly increase junction temperatures, causing thermal stress. Overcurrent may arise from short circuits, load mismatches, or inadequate current limiting. For example, a faulty motor winding can draw currents exceeding the thyristor’s IT(RMS) (rated on-state current), leading to localized heating and eventual burnout .
Solution:
YFW’s BT138-600E thyristor features a 600V VDRM and 8A ITSM (non-repetitive surge current rating), offering robust protection against transient overcurrents. To prevent thermal overload, proper heat dissipation is essential. YFW recommends using aluminum or copper heat sinks with low thermal resistance (RthJC ≤ 2.5K/W) and ensuring adequate airflow . For high-power applications, active cooling systems like fans or liquid cooling may be necessary.
High rates of voltage change (dv/dt) or current change (di/dt) can trigger unintended thyristor conduction or cause localized heating. A rapid voltage rise (dv/dt) can charge the junction capacitance, mimicking a gate trigger signal and turning on the device prematurely . Similarly, a high di/dt during turn-on can lead to uneven current distribution, creating hotspots near the gate-cathode junction .
Solution:
YFW’s thyristors are engineered to withstand high dv/dt and di/dt rates. For example, the MCR100-8 has a dv/dt rating of 50V/μs, minimizing false triggering. To further mitigate risks, designers should incorporate dv/dt protection circuits (snubbers) and di/dt limiting inductors in series with the thyristor .
Improper triggering signals can cause thyristors to fail. Insufficient gate current (IGT) may prevent full conduction, leading to high power dissipation and overheating. Conversely, excessive gate current can damage the gate-cathode junction. Additionally, noise or electromagnetic interference (EMI) in the triggering circuit can induce false triggers .
Solution:
YFW’s thyristors, such as the MCR100-8, have a gate trigger voltage (VGT) of 800mV and IGT ≤ 5mA, ensuring reliable triggering with minimal power consumption. To enhance noise immunity, shielded cables and RC filters can be added to the gate circuit. Proper grounding and decoupling capacitors also reduce EMI-related issues .
Harsh operating conditions, including high ambient temperatures, humidity, or dust, can degrade thyristor performance. For example, prolonged exposure to temperatures above the rated TJ (junction temperature) (e.g., >110°C for YFW’s MCR100-8) accelerates material aging and increases leakage current .
Solution:
YFW’s thyristors are designed for wide temperature ranges (-40°C to +110°C) and feature hermetic packaging to resist moisture and contaminants. Regular maintenance, such as cleaning heat sinks and inspecting for physical damage, is crucial. In extreme environments, enclosures with temperature-controlled cooling systems are recommended .
Manufacturing defects, such as impurities in semiconductor materials or poor junction fabrication, can weaken thyristors over time. Aging also reduces the device’s ability to handle voltage and current stresses, leading to gradual performance degradation .
Solution:
YFW employs rigorous quality control processes, including 100% automated testing, to ensure consistent performance. Our ISO 9001-certified facilities adhere to strict standards, minimizing defects. For critical applications, periodic replacement of aging thyristors is advised to prevent unexpected failures .
Thyristor burnout is often a result of electrical, thermal, or environmental stresses. By understanding these causes and implementing YFW’s high-quality thyristors (Figure 1) with robust protection circuits, designers can significantly enhance system reliability. YFW’s MCR100-8 and BT138-600E thyristors exemplify our commitment to durability and performance, offering industry-leading ratings and advanced thermal management features. For optimal results, always refer to YFW’s datasheets and consult our technical support for customized solutions.
