Surge protection devices are core components in electronic systems designed to withstand overvoltage interference such as lightning strikes and electrical fast transients; their performance directly determines the protection effect. This article focuses on four typical types of devices: P1900MEL (SIDACtor device), varistors (MOV), TVS diodes (transient voltage suppressor diodes), and GDTs (gas discharge tubes). It analyzes their performance advantages and disadvantages, individual application circuits, and combined application schemes, providing practical references for circuit design.

I. Comparison of Performance Advantages and Disadvantages of Core Devices

The four types of devices have fundamentally different working mechanisms, resulting in significant differences in key indicators such as response speed, current carrying capacity, and clamping characteristics. A detailed comparison is shown in the table below:

II. Design Considerations for Individual Application Circuits of Each Component

Based on the characteristics of each component, its individual application must match the surge level, signal frequency, and protection accuracy requirements of the scenario. The following are typical application circuits and design considerations:

1. P1900MEL Individual Application Circuit – CATV Power Port Protection

The P1900MEL's shutdown voltage (155V) is higher than the CATV power supply peak voltage (approximately 127V), making it suitable for CATV system power supply protection. It needs to be used in conjunction with a compensation inductor to address high-frequency signal interference.

Circuit Structure: Connect the P1900MEL in parallel between the CATV power input line and ground, and connect the compensation inductor in series in the signal line. The compensation inductor should be designed as a fast-saturation type. Recommended parameters: core permeability approximately 900Wb/A·m, 24 gauge wire winding, inductance value 20-30μH, must withstand 200V voltage and 1000A surge. Actual values need to be verified through laboratory testing.

Design Considerations: The compensation inductor must meet the insertion loss and reflection loss requirements of the CATV network to avoid affecting RF signal transmission; the parallel connection position of the P1900MEL should be close to the power inlet to shorten the surge discharge path.

2. Varistor (MOV) Standalone Application Circuit – Primary Protection for Single-Phase Power Supply

Variators have high energy tolerance and are suitable for primary lightning surge protection in power distribution systems, typically applied at the input of a single-phase AC220V power supply.

Circuit Structure: MOV1 is connected in parallel between the L and N lines; MOV2 and MOV3 are connected in parallel between the L and N lines and ground, respectively, forming a common-mode + differential-mode protection architecture. MOV Selection: Varistor voltage V1mA = 1.8-2.2 times the rated voltage (470V or 560V for AC220V systems); current carrying capacity is selected according to the regional lightning strike level (generally 10-20kA/8/20μs).

Design Considerations: A 10Ω/2W current-limiting resistor is connected in series with the MOV to prevent excessive leakage current and overheating during normal operation. A discharge gap is connected in parallel across the MOV to prevent short circuits and fires caused by MOV aging.

3. TVS Transistor Standalone Application Circuit – Sensitive Chip Pin Protection

TVS transistors offer extremely fast response and precise clamping, making them suitable for ESD and low-energy surge protection of sensitive chips such as MCUs and sensors. Taking 5V microcontroller I/O port protection as an example:

Circuit Structure: A unidirectional TVS transistor (bidirectional for AC signals) is connected in reverse parallel between the I/O pin and ground. The TVS breakdown voltage Vbr should be 1.2-1.5 times the operating voltage (6.8V or 7.5V for 5V systems), and the peak power should be above 500W.

Design Considerations: The TVS transistor should be placed close to the chip pin to shorten lead length and reduce parasitic inductance. For high-speed signals (such as USB 3.0), a low-capacitance TVS transistor with parasitic capacitance <1pF should be selected to avoid signal distortion.

4. GDT Standalone Application Circuit – CATV High-Frequency Signal Line Protection

GDTs have extremely low parasitic capacitance and high insulation resistance, making them suitable for surge protection of high-frequency signal lines such as CATV and Ethernet.

Circuit Structure: Two GDTs are connected in parallel between the center conductor and the shielding layer of the coaxial cable. The GDT breakdown voltage should be selected as 150-200V (compatible with the CATV signal voltage range), and the current carrying capacity should be 5kA/8/20μs.

Design Considerations: The GDT should be in an SMD package to reduce space footprint; due to the risk of follow current in the GDT, this circuit is only suitable for short-term surge scenarios. For long-term overvoltage applications, it needs to be used in conjunction with other components.

III. Combined Application Reference Circuit Design

Single components cannot fully meet the requirements of "strong surge discharge + precise residual voltage clamping." Combined applications achieve complementary performance through multi-level protection. The following are combined solutions for three typical scenarios:

1. Three-Level Power Port Protection Circuit (GDT + MOV + TVS)

Applicable Scenarios: Outdoor equipment power input (such as base stations, solar inverters), requiring protection against lightning surges exceeding 10kA while ensuring residual voltage in downstream circuits <50V.

Circuit Architecture:

• Level 1 (Coarse Protection): A GDT is connected in parallel between the L/N lines and ground to discharge lightning surges exceeding 10kA, solving the problem of strong energy impact;

• Level 2 (Medium Protection): An MOV is connected in parallel between the L/N lines to absorb the remaining surge energy, reducing the residual voltage to below 200V;

• Level 3 (Fine Protection): A bidirectional TVS is connected in parallel between the rectifier bridge output and ground to clamp the final residual voltage to below 50V, protecting the downstream DC/DC module.

Key parameter matching: GDT breakdown voltage > MOV varistor voltage > TVS breakdown voltage. A 50-100μH inductor is connected in series between each stage to achieve graded surge energy absorption.

2. Communication Interface Protection Circuit (GDT + P1900MEL + TVS)

Applicable scenarios: RS-485, Ethernet, and other communication interfaces requiring both high-frequency signal integrity and surge protection (e.g., 2kA lightning-induced surge).

Circuit Architecture:

• Stage 1: A GDT (Gas Transmitter Adapter) is connected in parallel between the signal bus and ground to dissipate most of the surge current. Parasitic capacitance <0.5pF does not affect signal transmission.

• Stage 2: A P1900MEL (Power Supply Unit) is connected in series, utilizing its negative resistance characteristics to further suppress surges. The shutdown voltage matches the bus operating voltage (e.g., a 155V P1900MEL for RS-485).

• Stage 3: A low-capacitance TVS (Transmitter Voltage Suppressor) is connected in parallel near the interface chip to clamp residual voltage to the chip's tolerance range (e.g., a 4.7V TVS for a 3.3V system).

Design Considerations: The distance between the GDT and P1900MEL should be <5cm to reduce voltage spikes caused by lead inductance.

3. High-Frequency Signal Port Protection Circuit (P1900MEL + Compensating Inductor + TVS)

Applicable Scenarios: High-frequency signal ports such as CATV and satellite receivers (operating frequency 5-1000MHz), requiring insertion loss <0.5dB and protection against 5kA surges.

Circuit Architecture: A compensating inductor (20-30μH) is connected in series at the signal input. A P1900MEL is connected in parallel to ground after the inductor, and a TVS is then connected in parallel to ground after the P1900MEL. The compensating inductor suppresses interference from the parasitic capacitance of the P1900MEL on high-frequency signals, and the P1900MEL discharges energy surges. The TVS provides final residual voltage clamping.

Verification Points: Insertion loss and reflection loss are tested using a network analyzer to ensure normal signal transmission within the operating frequency band; an 8/20μs 5kA surge test verifies that the residual voltage is <100V.

IV. Selection and Design Summary