| Packing | ■ | Bulk | 200pcs/bag | 800pcs/box | 1600pcs/carton |
| □ | Tape&Reel | ----pcs/reel | ------pcs/box | ------pcs/carton |
| □ | Ammopack | ----pcs/bag | -------------------- | ------pcs/carton |
Features
• Designed to facilitate compliance to UL1449 for SPD products
• High peak surge current rating up to 10kA
• Wave solderable
• Standard lead form and spacing option
• -55°C to +85°C operating temp range
• Three-lead version available for indication purposes
Select the Right Varistors for Overvoltage Circuit Protection
Varistors, also called metal-oxide varistors (MOVs), are used to protect sensitive circuits from a variety of overvoltage conditions. Essentially, these voltage-dependent, nonlinear devices have electrical characteristics similar to back-to- back Zener diodes.
Step 1: To find the voltage rating of the MOV, allow for 20% headroom to account for voltage swell and power-supply tolerances: 24 V dc × 1.2 = 28.8 V dc. Given that no varistors have a voltage rating of exactly 28.8 V, check the datasheets for specifications for 31-V dc MOVs.
Step 2: To determine which MOV disc size to use, first identify the MOV series that minimally meet the 1000-A surge requirement. Inspecting the table above suggests a 20-mm MOV with a 31-V dc maximum continuous voltage rating (part number V20E25P) as a possible solution to meet the requirements.
Step 3: Use the pulse-rating curves (Fig. 2) in the same datasheet to determine pulse capabilities relative to the 40 pulses at the 1000-A requirement.
2. The MOVâ€s datasheet will provide a pulse-rating curve; this example is for a 20-mm MOV.
Step 4: Use the V-I curve (Fig. 3) in the MOV’s datasheet to verify that leak voltage will be less than the 300-V ceiling.
3. An MOV datasheet will also feature a voltage-versus-current curve, such as this maximum clamping-voltage curve for the 20-mm device in Fig. 2.
Protecting MOVs Against Thermal Runaway
4. A thermal disconnect can open a circuit, preventing a catastrophic failure of a degraded MOV.
