Low-ohmic snubber shunt developed for high pulse loads

With fast switching operations in power electronics, such as in the automotive sector, voltage peaks can cause inductances, damaging or destroying sensitive downstream components in the circuit. A so-called RC snubber shunt can dampen these voltage peaks, which dissipates the excess energy outwards. Isabellenhütte has created a powerful low-ohmic snubber shunt, SMT-V, with an exceptionally high pulse power rating.

An RC member consists of a resistor and a capacitor connected in series. The resistor converts the energy discharged from the capacitor into heat. Snubbers are used in conjunction with contactors, power relays, thyristors/triacs, IGBTs, MOSFETs or bipolar transistors. Special IGBTs, triacs and MOSFETS are employed to precisely control motors. Rapid switching operations of the IGBTs and MOSFETs are required to ensure this.

The SMT-V developed by the company has a low resistance value at 17.5mOhm and a minimal compact design. It is based on the existing current measuring resistor SMT, which with a very large Cu legs allows for excellent heat dissipation from the respective component and already has a high pulse power rating and long-term stability. However, the design and material of the new SMT-V were adapted to withstand this particular pulse load better. The development arose from a customer request since no adequate standard component with this resistance value was available. The unique feature of this snubber shunt compared to other shunt series from the company is that it is not employed for current measurement but is intended to specifically absorb high pulse loads.

The high pulse power rating is achieved using the in-house resistance material NOVENTIN, with a specific resistance nearly twice as high as MANGANIN employed in current measuring resistors. The component’s basic structure was kept. Only the film design was optimised, and the resistance material was altered accordingly. This makes much higher pulse loads and power losses at the resistor possible.

The device can absorb a pulse energy of 2.5J at a pulse duration of 0.1 s at a terminal temperature of 120C and several 50 pulses over the life cycle with a corresponding gap time. This corresponds to a power loss per pulse of 25W. An application example of protective circuitry in HEV Snubber shunts can, for example, be utilised as part of a protective circuit for semiconductors in an AC/DC converter of a 48V MHEV.