选用产品安全因素的考虑

一、额定电压与工作电压

（1）  在正常使用条件下，薄膜电容器的工作电压不能超出其额定电压，否则会产生击穿并损坏制成品，但对有自愈能力的金属化电容器，当施加电压超过额定电压，有时不会立即发生短路，但绝缘电阻会降低，随着通电时间的加长，漏电流逐渐增大，电容器会发热击穿，导致冒烟或起火。

（2）  如标注直流电压的电容器用在交流线路中，产品的最高工作电压会受发热和放电的限制，转换成交流的最大工作电压随型号不同而不同，具体情况可与我方详议。

二、额定电压与工作温度和频率

电容器用在高频时，由于自身发热，会使薄膜介质老化而性能恶化，产生击穿，所以在高频时必须降低电容的额定电压。另外在考虑电容器工作环境温度时又要顾及产品的自身温升，确保在允许的自身温升值内，而且当电容器工作在电流有效值大或脉冲电流大的电路中时，必须确保电容器的工作温度（即环境温度+自身温升）不超过额定上限温度。（见表1、表2）

                Factors Contributing To The Safe Usage of Capacitors

一、Rated Voltage & Working Voltage

(1)   Normally, the working voltage shall not exceed the rated voltage; otherwise there will be breakdown and damage. For self-healing metallized film capacitor, short-circuit may not happen immediately when it is applied with over-voltage, but the insulation resistance will decrease gradually, making the leak current increase gradually, and finally the capacitor will break down, even causing possible fire or smoking.

(2)   In case the capacitor used for DC circuit is adopted in AC circuit, the maximum working voltage will drop due to heat and discharge. The conversion depends on different models. Please contact us for more details.

二、Rated Voltage, Working Temperature & Working Frequency

When operating under high frequency, the film dielectric will be aged by generated heat, resulting possible breakdown. For safe purpose, the rated voltage under high frequency shall be decreased properly. The temperature rise shall be also taken into account. When used in those circuits with high effective voltage or high peak-peak voltage, make sure that the total rise in temperature (self-temperature-rise + ambient temperature rise) will not exceed the allowable temperature limit (Table1, Table2).

表格1.各种电容器的额定上限温度，可用上限温度和可用上限温度时的电压下降率。（供参考）

Table 1. Rated Temp, workable Temp and Voltage Drop under Workable Temperature (For Reference Only)                        

注：额定上限温度：在直流额定电压时，能连续使用的上限温度。

可用上限温度：降低直流额定电压时，能连续使用的上限温度。

*Note：Rated Temperature：the fault-free upper temperature limit under rated DC voltage.

Workable Temperature：the fault-free upper temperature limit by decreasing rated DC voltage.

表格2. 电容器自身温升范围表

Table 2. The Self-Temperature-Rise

表格3.  各种波形的有效值计算

Table 3. Effective Value Calculation for Different Wave Form

三、允许电流和工作电流

（1）        因为薄膜电容器内部阻抗较低。故会有较大的充放电流。当充放电流超过允许值范围时，会由于发热而恶化介质导致击穿。允许电流根据击穿方式分成脉冲电流（峰值电流）和连续电流（有效值电流）来考虑。即使用时必须确保这两个电流在允许范围内。

（2）        脉冲允许电流一般由电压的爬升速率（dv/dt值）和电容量的乘积而得。允许有效电流随产品介质类型，工作频率及容量的改变而改变。而薄膜电容器的dv/dt (v/μs)值由芯子结构决定，特别对金属化电容器来讲，其内部的镀层电极和外部引出电极是通过金属接触（喷金）来连接的，dv/dt值上限度较低，故需注意。实际使用时，可向我方咨询。

三、Allowable Current & Working Current

(1)     Compared to other capacitors, the film capacitor has a smaller internal resistance, leading to a larger charging & discharging current. When the current exceeds the allowable range, the internal dielectric may be deteriorated and broken down. The allowable current can be categorized into impulsive current (peak value) and continuous current (effective current) depending on different breakdowns. Make sure that working current does not exceed the allowable value.

(2)      Generally, the allowable pulse current is a product of change of voltage (dv/dt)and the capacitance, and varies with different dielectric, working frequency and capacitance, for film capacitor, dv/dt(v/μs)is decided by its mandrel structure, for metallized capacitor, the internal electrodes and the leading-out slabs are linked by metal contacts, so the upper limit of dv/dt is relatively low,  which shall be considered. Please contact us for more details.

典型的金属化聚酯薄膜电容器最大爬升速率（dv/dt值）（仅供参考）单位：v/μs

Typical maximum dv/dt of the metallized film capacitor(for reference oniy) unit：v/μs