Issue link: https://resources.mouser.com/i/1442796
The recommended solution in Figure 2 provides protection by limiting the voltage the protected circuit is exposed to. When a fast-rising surge appears at the -48 V power supply input, the Power TVS diode reacts first and begins to clamp the voltage. A large rate of change of current through the inductor develops a voltage, allowing the voltage across the GDTs to rise to a level that results in an impulse sparkover. Together, the GDTs and Power TVS diode limit the residual voltage, and divert the surge current, protecting the downstream circuitry. The Stacked GDT offers a significant advantage over a single GDT. A single GDT, after sparking over, will pull the supply to a low voltage equal to the "arc" voltage of the GDT. If the supply continues to source current, the single GDT may not extinguish, and remain in the arc or glow state for a prolonged period of time, which can be destructive to the GDT. When a Stacked GDT sparks over, the voltage across the stack is the sum of the arc voltages of the individual GDTs. This voltage approaches or exceeds the supply voltage and allows the Stacked GDT to fully extinguish once the surge has passed. Bourns designed a small evaluation board that can be populated with different component types and values to allow testing of different surge protection solutions tailored to specific requirements. The board in Figure 3 includes test points to facilitate the attachment of voltage and current probes to support a detailed evaluation. Stacked GDTs with 800V and 1,400V DC sparkover voltages are available, as are a variety of Power TVS diodes with a range of clamping voltages and surge current ratings. An example Bill-of-Materials is provided in Table 2. | 14 | Figure 3: Bourns ® DC Power Supply Surge Protection Evaluation Board Table 2: DC Power Supply Protection Design Bill-of-Materials Example Digi ® XBee ™ Cellular LTE Cat 1 TBU ® -DF DUAL CHANNEL HIGH-SPEED PROTECTORS • Protect against faults caused by short circuits, overvoltage transients, and faults in battery cells • Feature MOSFET detection circuit triggering that provides an effective barrier • Ideal for RS-485 interfaces, general electronics, and factory automation application Figure 2: Protection Design Schematic Quantity Vendor Part Number Description 1 Bourns 2033-80-G5-LF Stacked GDT, 800V 4 AVX 1206GC101KAT1A Capacitors, 100pF 2KV 1 Bourns Custom Inductor 4.7 - 10uH air core inductor 1 Bourns PTVS6-076C-M Power TVS Diode, 76V Additional protection solution options: • Bourns ® Model 2033-140-G5-LF, Stacked GDT, 1400V • Bourns Power TVS (wide range of voltage and current ratings) • Bourns 5.0SMDJ70A, 5,000W TVS Diode, SMDJ, Vwm=70V (wide range of voltage ratings) SUMMARY A robust circuit protection scheme has been developed to provide an enhanced level of protection for the -48V DC power input on exposed communication equipment. Bourns' broad portfolio of discrete circuit protection components is available to handle the surge protection levels required for this application example and for a wide variety of protection needs in today's communication equipment. LEARN MORE 4