A DC-link film capacitor stabilises the DC bus of an inverter or converter, so it must handle the ripple current and the fast dV/dt of the power stage while keeping the self-inductance low enough that the switches are not stressed by overvoltage. Choosing the wrong voltage, capacitance or inductance costs efficiency and reliability. This guide gives a repeatable method for selecting a TDK EPCOS DC-link film capacitor.

Step 1: Fix the Voltage Class

Choose the voltage class with margin above the worst-case bus voltage plus switching overshoot. TDK EPCOS DC-link film capacitors span 350 V to 1600 V DC and beyond, so a class fits every common bus, from a 400 V drive to an 800 V EV architecture. Because a film capacitor does not dry out, it tolerates the long life that an EV or solar design demands.

Film or Electrolytic

A film capacitor handles high ripple and fast dV/dt and does not dry out, so it suits long-life, high-frequency designs and high-reliability equipment. An aluminum electrolytic offers more capacitance per unit volume and cost at lower frequency. Many designs combine a film capacitor for the high-frequency bus with an electrolytic for the bulk energy.

Step 2: Size the Capacitance and Current

Size the capacitance for the acceptable bus ripple and the required hold-up, then check the RMS ripple current and the dV/dt against the capacitor rating. The MKP DC construction offers a high capacitance density, so a compact part can meet a demanding requirement, and the low loss keeps the heating small. Confirm the current at your switching frequency and ambient.

Step 3: Check the Self-Inductance and Layout

At high switching speed the self-inductance of the capacitor and its busbar sets the voltage overshoot across the switches, so choose a low-inductance part and plan a low-inductance busbar. TDK EPCOS offers DC-link capacitors with self-inductance in the nanohenry range, and the benefit is only realized if the layout is tight. Keep the commutation loop small and measure the overshoot on the bench.

Case and Terminal

Choose the case and terminal for your mechanical design. The B25620 series uses a cylindrical aluminum can with female M6 or male M8 terminals and an M12 mounting stud; the B32320I series is a compact PCB-mount cylinder. Both are RoHS compliant and self-healing.

Step 4: Validate on the Bench

After selection, validate the design with the real ripple and dV/dt. Measure the bus ripple, the capacitor temperature and the switch overvoltage, and confirm that the self-inductance benefit is realized. Our FAE team can review the measurements and help interpret them.

Getting Help

If you send your bus voltage, capacitance, current and switching frequency to our FAE team, we will propose a shortlist with inductance, current and stock status and support the design-in. BeiLuo holds mainstream TDK EPCOS film capacitors in regional stock and ships them with import declaration, certificate of origin and RoHS documents.