HOW TO SELECT A VDR (Metal Oxide Varistor)
Three steps for most of applications,
选用压敏电阻三步曲,
1) Maximum Allowable Voltage: (What is the operation / working Voltage?)
确认最大容许电压: (产品工作电压)
1.1 What type of the power source? AC or DC?
电源供应系统: 交流或直流?
1.2 Be careful with the Stability of Power Source: ±10%, ±20% or ±30% ?
注意供电电压的稳定性: ±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
选择产品电压(型錄中之Maximum Allowable Voltage)大于或等于电源峰值电压的型号;
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
參考最大允许工作电压, 对应岀VDR崩溃电压. (也可由上述公式计算出)
2) Maximum Clamping Voltage: (What is acceptable transient to the equipment?)
最大抑制电压(设备可接受的暂态突波电压)
2.1 Under a certain current, what is the maximum transient voltage that the equipment or the
device to be protected can withstand?
在一定电流下,电路或设备可抵抗且被保护的最大瞬时电压;
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.
从1.3节中挑选的基础上, 选择一个设备可容许的最大抑制电压之压敏电阻器.
如知道瞬时电流, 从压敏电阻器的 V-I 曲线图中可以很容易找出 VDR的最大抑制电压.
2.3 It may refer to a minimum VDR size, or special design VDR with specified clamping voltage.
亦可參考VDR的最小尺寸或设计指定抑制电压的特殊规格.
3) The MOV Size (Diameter): (The concerns of using MOV safely.)
VDR尺寸(直径): (安全使用VDR的要点)
Find the suitable VDR in diameter that can meet the following requirements
选择适当尺寸的压敏电阻器需满足以下条件:
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
压敏电阻器之能量 (Energy)计算公式如上述. 式中: K为常數,
脉衝波为方形波时K值为1, 脉衝波为 8/20 μs 及 10/1000 μs 时K值约为1.4
IP 指所使用的峰值电流;VC 为通入电流时的抑制电压;T为脉衝时间.
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.
型錄之值并非压敏能量电阻的品质指标. 同一崩溃电压但不同尺寸即有不同能量值.
抑制电压小的压敏电阻只可吸收较小的能量值, 但对其邻近装置可提供更好的安全保护.