I. Overview
In AC power supply systems, transient overvoltages—caused by lightning-induced surges, grid switching operations, or the switching of inductive loads—can damage power input circuits, rectifier bridges, and downstream power components.
Metal Oxide Varistors (MOVs) are widely used surge protection components. They leverage their non-linear voltage-current characteristics to absorb transient energy and limit overvoltage within a circuit.
The Semiware 10D621K is a 10mm leaded zinc oxide varistor with a maximum continuous AC operating voltage of 385VAC, making it well-suited for AC power protection circuits that require higher operating voltage ratings.
With a nominal varistor voltage of 620V, a maximum clamping voltage of 1025V, and a standard surge current capacity of 2500A, this device serves as an effective surge protection solution for AC switching power supplies, industrial control equipment, and various other AC-powered electronic devices.
II. Key Parameters of the 10D621K
The 10D621K is constructed from zinc oxide (ZnO) ceramic material and exhibits bidirectional, non-linear voltage-current (V-I) characteristics.
Key Electrical Parameters:
| Parameter | Specification |
| Package | 10D (10mm) |
| Maximum AC Voltage (VAC) | 385V |
| Maximum DC Voltage (VDC) | 505V |
| Varistor Voltage (1mA) | 620V |
| Varistor Voltage Tolerance | ±10% |
| Maximum Clamping Voltage | 1025V |
| Standard Surge Current (8/20μs) | 2500A |
| Maximum Energy | 102J |
| Capacitance | 160pF |
| Operating Temperature | -40°C to +125°C |
III. Typical Application Scenarios for the 10D621K
The 10D621K can be used for surge protection at the input of various AC-powered devices, helping to mitigate the impact of transient overvoltages on power circuits and sensitive electronic components.
3.1 AC-DC Switching Power Supplies
During operation, switching power supplies may be subjected to transient overvoltages resulting from grid disturbances, lightning-induced surges, or power switching operations.
The 10D621K can be connected in parallel across the AC input to suppress transient voltages, thereby reducing the voltage stress on the rectifier bridge and subsequent power conversion circuitry. Typical applications include:
- Industrial AC-DC switching power supplies
- Power supply modules for electronic equipment
- Power supplies for commercial equipment
- Power conversion units
3.2 Industrial Control Equipment
In industrial control systems, the starting, stopping, and switching of inductive loads—such as motors, relays, and contactors—can easily generate transient voltage surges.
The 10D621K can be used for surge protection in the following equipment, depending on specific circuit conditions:
- PLC power supply circuits
- Industrial controllers
- Electricity meters and smart metering devices
- Relay and solenoid valve control circuits
- Industrial electronic control modules
For inductive load protection, the voltage rating and installation location of the MOV must be determined based on the actual operating voltage, transient characteristics, and load circuit configuration.
3.3 Household Appliances
Household appliances typically incorporate AC input circuits, switching power supplies, and motor control modules, which may be subjected to transient overvoltages during fluctuations in mains voltage or load switching.
The 10D621K is a suitable component for AC input protection circuits in appliances such as:
- Washing machines
- Dishwashers
- Refrigerator control systems
- Water heaters
- Other AC-powered household electronic devices
Its primary function is to suppress transient overvoltages at the input, thereby reducing the stress on power supply and control circuits.
3.4 Communication and Security Equipment
Communication and security equipment is generally powered via external power supply modules. For devices that utilize long power supply lines or operate in electrically complex environments, surge protection at the power input is particularly critical.
Typical applications include:
- IP camera power supplies
- Access control systems
- Set-top boxes
- xDSL equipment
- Communication power supply modules
In these devices, the 10D621K is primarily used for protection at the power input, rather than for signal protection on low-voltage data interfaces.
3.5 Protection for Semiconductors and Switching Circuits
Varistors can also be used in circuits containing power semiconductors and switching components—such as transistors, diodes, ICs, thyristors, and triacs—to suppress transient overvoltages.
IV. How to Select the Appropriate MOV for AC Power Supplies?
When selecting an MOV, one should not rely solely on the nominal varistor voltage; other parameters must also be taken into account.
4.1 Maximum Continuous Operating Voltage
The maximum continuous operating voltage of an MOV must be higher than the highest normal operating voltage of the circuit being protected, while also accounting for power grid fluctuations and supply tolerances.
For example, the 10D621K has a maximum continuous AC operating voltage of 385 VAC; however, this does not mean it is suitable for all 380 V three-phase power systems. The selection must also consider the actual voltage across the MOV, the grounding configuration, and potential abnormal operating conditions.
4.2 Nominal Varistor Voltage
The nominal varistor voltage of the 10D621K is 620 V (with a tolerance of ±10%), measured at a test current of 1 mA.
While this parameter helps distinguish between MOVs of different voltage ratings, it should not be used as the sole criterion for determining circuit compatibility.
4.3 Maximum Clamping Voltage
The maximum clamping voltage refers to the voltage across the MOV under specified surge current test conditions.
The 10D621K has a maximum clamping voltage of 1025 V. During selection, this value should be compared against the voltage withstand capability of downstream components, while also accounting for additional voltage induced by PCB parasitic inductance.
4.4 Surge Current and Energy Handling Capability
The 10D621K has a standard surge current capacity of 2500 A (based on an 8/20 μs waveform) and a maximum energy rating of 102 J; specific values depend on the test conditions defined in the datasheet.
These parameters help determine whether the device can withstand expected transient surges. In cases of repetitive surges, factors such as the number of surge events, ambient temperature, and actual operating conditions must be considered regarding their impact on the device's service life.
4.5 Package Size
The 10D through-hole package is well-suited for surge protection designs where PCB space is limited.
However, the package size should not be selected based solely on the equipment's power rating; it must be determined by considering surge current, energy absorption, thermal dissipation, and the expected service life.
Summary
For engineers designing surge protection for AC power inputs, the 10D621K offers a compact component solution.
Need a datasheet or samples? Visit the Semiware 10D621K product page to download the datasheet for the MOV-10D series.
https://en.semiware.com/varistors/10d621k
Please feel free to contact Semiware for product specifications, samples, and technical support.
