DC780-105K

FAQFrequently Asked Questions

• What are the key differences between the DC780-105K and its substitute part number 1120-102K when designing a 1 mH inductor stage? The DC780-105K is a 1 mH unshielded drum core inductor rated for 1 A continuous current with an 818 mOhm maximum DC resistance and 3.5 A saturation current. The 1120-102K substitute may differ in core material composition, DC resistance tolerance, saturation characteristics, or physical footprint despite matching the nominal 1 mH inductance. Before substituting, verify the 1120-102K's exact DCR specification, saturation current rating, and frequency response curve at your operating frequency. Differences in core loss or Q factor at your switching or signal frequency could affect filter performance, efficiency, or harmonic suppression in your circuit.
• Can the DC780-105K handle 1.5 A continuous current in a power supply filter application, or will DC resistance losses become problematic? The DC780-105K is rated for 1 A continuous current maximum. At 1.5 A, the inductor would operate beyond its rated current envelope and risk accelerated core saturation, increased winding losses, and shortened component life. With an 818 mOhm maximum DC resistance, operating at 1.5 A would dissipate approximately 1.84 W in resistive loss alone, versus 0.82 W at rated 1 A. For applications requiring higher current handling, select an inductor with a higher current rating or lower DCR specification to stay within safe thermal and magnetic operating margins.
• How should I account for the DC780-105K's 818 mOhm resistance when designing buck converter or LDO post-filter stages? The 818 mOhm DC resistance of the DC780-105K will introduce a voltage drop and resistive losses in series with your output filter network. In a buck converter operating at 1 A output, this inductor contributes 0.818 V ripple voltage drop across the DCR alone, reducing effective regulation and increasing load transient settling time. When designing the output filter, calculate total loop impedance including the DC780-105K's resistance, and adjust capacitor selection or control loop compensation accordingly. For noise-sensitive analog circuits or low-dropout applications, the DCR of the DC780-105K may limit achievable output impedance; consider pairing with a low-ESR output capacitor or selecting an inductor with lower DC resistance if ripple or noise performance is marginal.
• What is the saturation behavior of the DC780-105K, and when should I derate its 1 A rating in my design? The DC780-105K has a saturation current (Isat) of 3.5 A, meaning inductance degradation begins when current exceeds this threshold. The continuous 1 A rating provides safe margin below saturation in steady-state operation. However, in transient conditions—such as inrush current during power-on, load step events in switchers, or fault conditions—peak current can momentarily exceed 1 A. If your circuit design permits transient currents in the 1.5 to 3.5 A range, the DC780-105K will retain its inductance but at reduced value. For safety-critical applications or where inductance stability is essential across the entire operating current range, either derate the DC780-105K to operate well below 1 A continuous, or select an inductor with higher saturation current.
• Is the DC780-105K suitable for high-frequency switching applications above 100 kHz, or is it limited to lower frequency circuits? The DC780-105K is specified at 1 kHz for inductance measurement, and the self-resonant frequency (SRF) is not published. Unshielded drum core inductors typically exhibit lower SRF and higher core loss compared to shielded designs at higher frequencies. If your application operates significantly above 100 kHz, the DC780-105K's impedance will become increasingly dominated by parasitic capacitance and core losses rather than its nominal 1 mH inductance, reducing filter effectiveness. For high-frequency switch-mode power supplies or RF filter stages operating in the 500 kHz to several MHz range, verify the actual impedance curve of the DC780-105K or select an inductor specifically designed for your frequency band to avoid degraded performance and efficiency.
• Can the DC780-105K be used as a current-sensing inductor in series with a shunt resistor, or does its high DC resistance complicate the measurement circuit? The DC780-105K's 818 mOhm DC resistance is relatively high for precision current sensing. If you use the DC780-105K in series with a low-ohm shunt resistor to measure current, the inductor's resistance will be in parallel with the measurement path through the shunt amplifier input, introducing a significant offset error and reducing measurement accuracy unless high input impedance is ensured. Additionally, the DC780-105K's unshielded design may couple magnetic flux into nearby signal traces or shunt resistor leads, introducing noise into the current measurement. For precision current-sensing applications, use a separate low-DCR current-sense inductor, or design your measurement circuit to reject or compensate for the DC780-105K's series resistance contribution.
• What thermal derating should I apply to the DC780-105K when operating at 125°C in an industrial environment versus room temperature? The DC780-105K is rated for operation from -55°C to 125°C. As temperature increases, the ferrite core material's permeability decreases, reducing inductance value and Q factor. At 125°C ambient, core loss also increases, raising component temperature further under load. While inductance tolerance is ±10% at nominal conditions, the actual inductance at 125°C operating temperature may drift downward by an additional 5–10% depending on ferrite composition. For applications with tight inductance requirements or thermal headroom constraints, measure the DC780-105K's inductance at your expected operating temperature, or derate the maximum continuous current to maintain safe thermal margins and preserve inductance stability across the industrial temperature range.
• Is the unshielded design of the DC780-105K problematic in multi-layer PCB designs with sensitive analog or RF circuitry nearby? The DC780-105K is unshielded, so its magnetic field radiates into surrounding circuit space. In dense PCB layouts with analog-to-digital converters, low-noise amplifiers, or RF signal paths in close proximity, this radiated magnetic flux can couple into sensitive traces and degrade signal integrity or introduce conducted noise. If your design includes unshielded inductors near high-impedance analog signal paths, consider routing the DC780-105K's field-sensitive circuits away from the inductor, using Faraday shielding or guard traces, or selecting a shielded inductor variant to reduce crosstalk. In mixed-signal or RF applications, the unshielded characteristic of the DC780-105K may impose PCB layout constraints that increase design complexity or reduce board density.
• How does the DC780-105K compare to shielded inductor alternatives for EMI filtering in power distribution networks? The unshielded drum core design of the DC780-105K radiates magnetic energy more effectively than a shielded inductor, which can increase EMI emissions in the near field. In power distribution networks where EMI compliance is a requirement, shielded inductors confine magnetic flux and reduce emissions to external circuits, though at the cost of higher core loss and lower Q. If the DC780-105K is used in an input or output filter stage feeding regulatory agency compliance testing, radiated emissions from the unshielded design may exceed limits unless additional shielding, filtering, or board layout mitigation is applied. For EMI-sensitive applications, compare the DC780-105K's EMI signature empirically or select a shielded alternative to simplify compliance.
• What is the expected DC resistance stability of the DC780-105K over its -55°C to 125°C operating range, and how should I account for temperature drift in power loss calculations? The DC780-105K specifies a maximum DC resistance of 818 mOhm at an unspecified reference temperature (typically 20°C). Copper wire resistance increases approximately 0.4% per °C temperature rise; at 125°C, the actual DCR could increase by roughly 40–45% from the 20°C baseline, approaching 1.15–1.18 Ohms in worst case. This temperature coefficient directly affects I²R losses and thermal dissipation budget. In a 1 A continuous design operating at elevated temperature, account for DCR increases as temperature climbs, and verify that thermal design margin remains adequate. For precision power loss budgeting in industrial or automotive applications operating near 125°C, use elevated-temperature DCR specifications from the manufacturer datasheet or empirical measurement rather than room-temperature values.
• Can the DC780-105K be paralleled with another inductor to achieve lower DC resistance and higher current rating for a distributed power architecture? Paralleling inductors to reduce effective DCR and increase current capacity is possible but requires careful design. Two DC780-105K inductors in parallel theoretically halve the DCR to 409 mOhm and double the current rating to 2 A, but practical challenges arise: inductors have parasitic resistance and capacitance variations that cause unequal current sharing, leading to one inductor saturating before the other or carrying disproportionate current. Temperature drift and winding asymmetries between components worsen current imbalance. For a robust parallel inductor configuration, select matched pairs with tight tolerance specifications, verify through simulation or measurement that current shares within acceptable limits, and consider adding small series resistances or selecting matched components from the same production batch. For new designs requiring higher inductance, lower DCR, or higher saturation current, evaluate a single higher-rated inductor as a simpler alternative to paralleling multiple DC780-105K units.
• What RoHS and compliance restrictions apply to the DC780-105K in EU and regulated market applications? The DC780-105K is marked as RoHS non-compliant, indicating the presence of restricted substances (lead, cadmium, mercury, hexavalent chromium, or flame retardants) in concentrations above RoHS limits. For designs destined for the European Union, China, or other markets with strict RoHS enforcement, the DC780-105K may not be acceptable without exemption claims or design revisions using RoHS-compliant inductors. The part carries REACH Unaffected status, meaning it is not subject to REACH substance registration, and falls under ECCN EAR99 for export control purposes. Before committing the DC780-105K to production for regulated markets, verify RoHS exemption applicability with your compliance team and confirm that customer acceptance of non-compliant components is documented. If RoHS compliance is mandatory, identify an equivalent shielded or unshielded 1 mH inductor from the substitute list or alternative sources that meets RoHS and customer requirements.