How to choose varistors

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深圳市伟莱达电子有限公司 | Date：2019/6/28 | View：982

如何選用 VDR 壓敏電阻

HOW TO SELECT A VDR (Metal Oxide Varistor)

Three steps for most of applications,

選用壓敏電阻三步曲,

1) Maximum Allowable Voltage: (What is the operation / working Voltage?)

確認最大容許電壓: (產品工作電壓)

1.1 What type of the power source? AC or DC?

電源供應系統: 交流或直流?

1.2 Be careful with the Stability of Power Source: ±10%, ±20% or ±30% ?

注意供電電壓的穩定性: ±10%, ±20% or ±30% ?

1.3 From Song Long Catalog, select the Maximum Allowable Voltage that equal or higher

than the power source peak working voltage

選擇產品電壓(型錄中之Maximum Allowable Voltage)大於或等於電源峰值電壓的型號;

1.4 Refer to Maximum Allowable Voltage selection, point out the Varistor Voltage (Vb).

A simple calculation: Vac = Vb@1mA x 0.63 ; Vdc = Vb@1mA x 0.81

參考最大允許工作電壓, 對應岀VDR崩潰電壓. (也可由上述公式計算出)

2) Maximum Clamping Voltage: (What is acceptable transient to the equipment?)

最大抑制電壓(設備可接受的暫態突波電壓)

2.1 Under a certain current, what is the maximum transient voltage that the equipment or the

device to be protected can withstand?

在一定電流下,電路或設備可抵抗且被保護的最大瞬時電壓;

2.2 From 1.3 selection, choose a Maximum Clamping Voltage that the equipment can endure.

It is easy to find a VDR clamping voltage from V-I curve when the transient current is known.

從1.3節中挑選的基礎上, 選擇一個設備可容許的最大抑制電壓之壓敏電阻器.

如知道瞬時電流, 從壓敏電阻器的 V-I 曲線圖中可以很容易找出 VDR的最大抑制電壓.

2.3 It may refer to a minimum VDR size, or special design VDR with specified clamping voltage.

亦可參考VDR的最小尺寸或設計指定抑制電壓的特殊規格.

3) The MOV Size (Diameter): (The concerns of using MOV safely.)

VDR尺寸(直徑): (安全使用VDR的要點)

Find the suitable VDR in diameter that can meet the following requirements

選擇適當尺寸的壓敏電阻器需滿足以下條件:

3.1 Withstanding Transient Energy (10/1000μs)

To determine the energy absorbed by the MOV, the following equation can be applied：

Energy=K * Vclamp(V) * Ipeak(A) *Time(s)

Where K is a constant. K value is 1.0 for a rectangular waveform, 1.4 for a 8/20μs and

10/1000μs waveform. And Ip is the peak current applied, Vc is the clamping voltage

which was current applied. T is the pulse width

壓敏電阻器之能量 (Energy)計算公式如上述. 式中: K為常數,

脈衝波為方形波時K值為1, 脈衝波為 8/20 μs 及 10/1000 μs 時K值約為1.4

IP 指所使用的峰值電流;VC 為通入電流時的抑制電壓;T為脈衝時間.

The issued energy does not represent the entire quality of VDR, but can be a valuable

indication when comparing the different series of VDR which have the same varistor

voltage.

A VDR with better (less) clamping voltage will absorb less energy, but have better

performance to protect device.

型錄之值並非壓敏能量電阻的品質指標. 同一崩潰電壓但不同尺寸即有不同能量值.

抑制電壓小的壓敏電阻只可吸收較小的能量值, 但對其鄰近裝置可提供更好的安全保護.