SMD safety paper capacitors Y2 & X2
Kemet introduces 2 new series of safety capacitors in SMD design. The SMP253 and SMP255 series are manufactured with metallised paper, a technology that has been proven to guarantee high insulation resistance and self-healing properties.
The metallised paper technology is ideal for ensuring high robustness due to the fault mode, an open circuit and meets the most demanding reliability requirements for safety capacitors without the need for redundancy. This is coupled with a solid ability to handle voltage pulses, doubling the performance of typical film capacitors.
The SMP253 Y2 and SMP255 X2 capacitors fulfil the requirements for high reliability and high THB classes in surface mount technology. These key features offer significant advantages to designers looking for robust, surface mount safety capacitors. SMP253 and SMP255 are well suited for AC/DC converters in onboard chargers for xEVs, smart grid hardware, EMI filtering in variable frequency drives (VFDs) and high energy density applications such as capacitive power supplies.
SMP255 Class X2 Key data
- SMP255 class X2 ‘across the line capacitor’
- Cap. Range: 10 nF - 150 nF
- Nominal voltage: 310 VAC
- Max. Recommended DC voltage: 630 VDC
- Automotive Grade (AEC-Q200)
- High pulse voltage and dV/dt (1,200 V/µs)
- High vibration resistance (IEC 60068 2-6/2-27)
- THB Grade IIB (85°C, 85% RH, 500 hours)
- Long service life and power stability
SMP253 Class Y2 Key data
- SMP253 Class Y2 “line to ground capacitor”
- Cap. Range: 1.0 nF – 4.7 nF
- Rated Voltage: 300 VAC
- Max. Recommended DC Voltage: 1,500 VDC
- Safe Failure Mode
- Automotive Grade (AEC–Q200)
- High Impulse Voltage and dV/dt (2,000 V/µs)
- High Vibration Withstand (IEC 60068 2-6/2-27)
- THB Grade IIB (85°C, 85% RH, 500 hours) at 300 VAC
What are EMI suppression capacitors?
EMI suppression capacitors are a specialised subset of commercially available capacitors designed to filter electrical noise from the power supplied to the circuit by reducing the input impedance of the system.
EMC interference suppression capacitors are often used to suppress noise in AC power lines. They are sometimes connected in the “X” configuration, ‘between the lines’, as shown in the figure above: C1 and C2. And as a “Y” configuration, ‘conductor to ground’, such as C3 and C4. If a capacitor in an “X” configuration fails, there is a risk of fire. However, if a capacitor fails in a “Y” configuration, there is a risk of electric shock instead. Due to the danger of these failure modes, these capacitors are designed to fail “safely” to prevent fire or shock. For this reason, many EMI capacitors are also known as safety capacitors.
How are EMC capacitors specified?
EMC capacitors are classified according to their intended use (X or Y configuration), their rated operating voltage and the peak surge voltage they can safely withstand. The subclasses and associated ratings for these capacitors are shown in the following figures.
What are harsh environments?
In addition to miniaturisation, many designs must be operated under harsh environmental conditions throughout their entire service life. Some examples are:
- On-board chargers for electric and hybrid vehicles that can withstand higher temperatures and extreme thermal shock cycles
- Miniaturised solar micro-inverters and smart energy meters with an expected service life of up to 25 years without maintenance, in environments with potentially high humidity.
- Smart meters that are expected to operate reliably outdoors for many years or even decades
To meet the requirements of these harsh environmental conditions, the electronics industry has developed a recognised accelerated life test standard for active and passive components - the Temperature-Humidity-Bias (THB) test, an IEC standard for EMI suppression film capacitors. Capacitor manufacturers must include the THB class for their certified solutions in the specification.
The following tables show the different temperature-humidity bias (THB) test conditions according to IEC standards. The higher the class, the more robust the capacitor is in harsh environments and a longer service life can be expected.
