Many passive components can be used to make passive snubber circuits that absorb the energy of the reactance in the power switching circuit. The snubber circuit can clamp the ripple noise or reduce the power loss during turn-off. Another application is to reduce the peak switching voltage. Buffer circuits are critical to improving the efficiency of most switching semiconductor circuits.
There are several different passive components to choose from when designing the snubber circuit. As in high pulse applications, thin film polypropylene capacitors are often used as buffer circuits to control the rate of voltage rise (dV/dt). Standard high voltage MLCC capacitors (multilayer ceramic capacitors) can also be used as snubber circuits during device startup to clamp the voltage to a fixed level. MLCC capacitors can also be used to clamp harmful transient voltages. These capacitors can clamp harmful transient voltages on semiconductor switching devices such as bipolar or MOS transistors.
The disadvantage of these capacitors is the large size. Film capacitors have leads and require through-hole mounting on the board, which can take up a lot of board space. To date, 390pF, 1kV high voltage MLCC capacitors are only available in 1812 size.
The new HVArc Guard high voltage MLCC capacitors do not have these limitations. This capacitor combines high breakdown voltage, low impedance and wide operating frequency range characteristics, while the size is only 0805. Design engineers can reduce the footprint of capacitors while maintaining the same capacitance and voltage levels of various medium and high voltage snubber circuits.
Small size benefits
The HVArc Guard surface mount MLCC capacitors are small in size and are ideal for snubber circuits. The high voltage breakdown performance of such capacitors is especially useful for high voltage inverter sections where snubber capacitors or capacitors are required in the application. In fact, the breakdown voltage of HVArc Guard MLCC capacitors is more than twice that of similar standard high voltage capacitors.
Excellent surge suppression
Vishay performed a series of surge tests on HVArc Guard capacitors. The basic surge waveforms are as follows. The rise time of the pulse applied to the HVArc Guard capacitor is only 2μs.
The surge test results on the X7R and NP0 HVArc Guard capacitors are shown in the table below.
Waveform C0G(N0P)HVArc Guard X7R HVArc Guard
1.2μs × 50μs 1650V 500V
10μs × 700μs 1800V 1200V
10μs × 160μs > 1500V 1200V
Design snubber circuit with HVArc Guard
During the power circuit's turn-on and turn-off cycles, a simple passive RC snubber circuit is commonly used to consume energy and clamping voltage. For example, in applications where a high voltage MOSFET is used as a switching device, a rapid change in the drain-to-source voltage step occurs during MOSFET operation, which produces voltage transient noise at the gate of the MOSFET. A capacitor is connected between the source and drain as a buffer to bypass harmful switching noise.
In these applications, HVArc Guard MLCC capacitors require much less board space than standard high voltage capacitors. The figure below is an example of a snubber circuit for a totem pole MOSFET circuit.
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