Knowles has expanded its Cornell Dubilier Flatpack™ portfolio with the Type CLS, a 105°C-rated family of prismatic aluminum electrolytic capacitors in stainless-steel cases.
The Knowles CLS series targets applications that need substantial bulk capacitance and ripple-current capability in a low-profile format, but do not require a 125°C temperature rating.
Key features and benefits
- 105°C temperature class: The CLS series is rated from -55°C to +105°C, providing a middle option between the existing 85°C MLPS and 125°C MLSG Flatpack™ ranges.
- High bulk capacitance in a thin package: Rated capacitance spans 150 µF to 83,000 µF, enabling designers to consolidate energy-storage and filtering functions that might otherwise require several parallel capacitors.
- Voltage ratings up to 300 Vdc: This range supports intermediate-voltage DC buses, bulk storage stages and power-supply filtering where low-profile mechanical integration is critical.
- 10,000-hour load-life rating: Knowles specifies 10,000 hours at 105°C and rated ripple current. For electrolytic capacitors, this type of rating is especially relevant because operating temperature and ripple-current heating strongly influence useful service life.
- Stainless-steel Flatpack™ enclosure: The manufacturer identifies the stainless-steel case as a means to improve thermal dissipation while providing a rugged, low-profile package.
- Reduced interconnect count: A single prismatic capacitor can replace a parallel bank of smaller units, reducing PCB connection points and associated assembly or reliability concerns.
- High-vibration suitability: The series brief specifies a 10 g standard vibration rating, with 30 g available using the HV design. Knowles also lists operation at altitudes up to 80,000 ft.
Technical highlights
| Parameter | Type CLS specification |
|---|---|
| Capacitor technology | Prismatic aluminum electrolytic, stainless-steel Flatpack™ case |
| Rated voltage range | 10 Vdc to 300 Vdc |
| Capacitance range | 150 µF to 83,000 µF |
| Capacitance tolerance | -20% / +20% |
| Operating temperature | -55°C to +105°C |
| Load life | 10,000 hours at 105°C and rated ripple current |
| Ripple-current capability | Up to 8.67 A at 20 kHz |
| Profile height | 12.7 mm |
| Case width options | 25.4 mm or 44.45 mm |
| Case length options | 25.4 mm to 76.2 mm |
| Vibration rating | 10 g standard; 30 g with HV design |
| Altitude capability | Up to 80,000 ft |
The available catalogue range uses a 12.7 mm height, with multiple case footprints and lead-spacing options. This makes the series relevant where a conventional cylindrical electrolytic capacitor is mechanically unsuitable because of enclosure height, board clearance or packaging constraints.
The CLS family is a polarized aluminum electrolytic capacitor. Its practical advantage is high capacitance density for bulk energy storage; designers must nevertheless respect polarity, voltage limits, ripple-current limits and temperature-dependent lifetime behaviour.
Typical applications
Knowles identifies the CLS series for demanding power-electronics and defence-related systems, including:
- Military aircraft and airborne electronics
- Military vessels
- Ground-based radar equipment
- Drones and unmanned platforms
- Missile-defence systems
- Aircraft radar systems
- Low-profile, high-density commercial power supplies
- Mission-critical power conversion and filtering equipment
Application fit
| Design requirement | Why CLS may fit |
|---|---|
| Restricted enclosure height | The 12.7 mm profile supports flat or densely stacked assemblies |
| Large bulk capacitance requirement | Values up to 83,000 µF can reduce the number of parallel capacitor positions |
| High ripple-current loading | The manufacturer specifies up to 8.67 A at 20 kHz; verify the rating for the selected part number and operating conditions |
| Harsh mechanical environment | Stainless-steel packaging and specified vibration capability support mechanically demanding platforms |
| -55°C start-up environment | The rated low-temperature limit is suited to systems exposed to severe ambient conditions |
| Long service expectation | The 10,000-hour 105°C load-life rating provides a defined baseline for lifetime assessment |
For DC-bus and bulk-storage functions, the capacitor may act as an energy buffer between a rectified source and a switching load. A DC-link capacitor must be assessed as a circuit element, not only as a capacitance value: allowable ripple current, ESR, thermal path, bus inductance and transient requirements all affect the final design.
Design-in notes for engineers
- Derive ripple current from the real waveform. The published maximum ripple-current value is a series-level headline figure. Confirm the RMS ripple current, frequency, ambient temperature and permitted temperature rise for the exact CLS part number. See how ripple current affects capacitor performance for the link between ripple current, ESR loss and self-heating.
- Treat the 10,000-hour load-life figure as a rated-condition value. Lifetime modelling should account for the actual capacitor hot-spot temperature, ripple-current heating and mission profile rather than using the headline duration as a universal system-life value.
- Check capacitance tolerance at the system minimum. With a -20% / +20% tolerance, hold-up, transient-energy and ripple-voltage calculations should be performed using the minimum specified capacitance.
- Validate voltage margin and polarity. Use the selected part’s manufacturer documentation to establish appropriate voltage derating, surge behaviour, reverse-polarity protection and fault response for the specific converter topology.
- Design the thermal interface deliberately. The flat metal enclosure can provide a useful heat-spreading surface, but only if the mechanical arrangement provides a repeatable thermal path to the chassis, airflow or other cooling structure.
- Evaluate mechanical loading at the assembly level. Verify lead or terminal arrangement, mounting scheme, PCB flexure, vibration direction and any additional restraint required for the mass of the selected capacitor.
- Qualify the specific ordering code. Catalogue options vary by capacitance, voltage, case dimensions and connection geometry. Final selection should use the current manufacturer datasheet and applicable environmental or system-level qualification plan.
Further reading
- Aluminum Electrolytic Capacitors
- DC-Link Capacitors – Design Tips
- Ripple Current and its Effects on the Performance of Capacitors
- Capacitor Ripple Current Testing: A Design Consideration
Source
This article is based on the Knowles press release and associated Cornell Dubilier Type CLS manufacturer documentation. Engineers should consult the current manufacturer datasheet and product documentation for final component qualification, application verification and design release.
