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A standard noise filter was used for conducted noise suppression in a phase-controlled temperature controller. However, the margin relative to the regulatory limits was insufficient, and additional countermeasures are now being considered.
While it is possible to add phase-to-phase capacitors as an external measure, the shipment deadline is approaching, leaving no time to review component mounting methods, wiring, or mechanical modifications.
In this situation, is there an effective alternative approach?
Limitation on the number of crimp terminals 
Securing space for relay terminal blocks 
Man-hours required for processing fixed and live parts -
This may be due to normal mode noise. In such cases, the "U option" which enhances normal‑mode attenuation, is effective.
Because the U Option has the same external dimensions as the standard model, no mechanical redesign is required, allowing for an easy drop‑in replacement.
Reason
A phase-controlled temperature controller adjusts output power by switching based on the AC voltage phase. This switching operation generates normal‑mode noise.
*The switching element used is typically a TRIAC, which consists of two thyristors connected in reverse parallel.
Solution Decision
The U Option provides improved normal‑mode attenuation in the low-frequency range.
Since its external dimensions and mounting footprint are identical to the standard product, it can be replaced directly without design changes.
This eliminates issues such as:
Additional crimp terminals required for
-external capacitors
-Securing terminal block space
-Designing and mounting external capacitor fixtures
Commentary
(1) Attenuation characteristics comparison
Compared with the standard model, the U Option delivers greater low‑frequency normal‑mode attenuation. It achieves noise suppression equivalent to adding external capacitors.
(2) Internal Circuit Differences
Inside the noise filter, a phase‑to‑phase capacitor is incorporated to suppress ormal‑mode noise.
-Standard model: Y (Star) connection
-U Option: Δ (Delta) connection
This difference in connection topology significantly affects low‑frequency performance.
(3) Impedance Characteristics Comparison
Using the TAC‑50‑103 as an example, switching the capacitor connection from Y to Δ increases the inter‑phase capacitance to roughly three times (model dependent). This lowers the low‑frequency phase‑to‑phase impedance, thereby enhancing normal‑mode attenuation.
However, because Δ connection results in higher voltage across the capacitor, the rated voltage differs:
The following series support the U option.
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JAC series
Three-phase 500VAC 6-60A
Compact and low profile
High-attenuation from 150kHz to 1MHz
1-stage filter -
TAH series
Three phase 500VAC 4-150A
General purpose
Low profile
Ultra high-attenuation type from 9kHz to 1MHz
1-stage filter -
FTA series
Three-phase 500VAC 40-150A
General-purpose Book type
High-attenuation from 150kHz to 1MHz
1-stage filter -
FSB series
Three-phase 500VAC 10-150A
Book type
EMI/EMC Filter for motor drive system
2-stage filter -
TAC series
Three phase 500VAC 4-300A
General purpose
Low profile
High-attenuation type from 150kHz to 1MHz
1-stage filter
- *2For other series, please contact us.
