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IEC 62317-13: Ferrite Cores Dimensions – PQ-Cores for Power Supply Applications
💡 Standard Snapshot: IEC 62317-13 (Edition 2.0, 2015) specifies the critical dimensions for mechanical interchangeability of PQ-cores and low-profile PQI-cores made of ferrite, used primarily in power supply transformers and inductors. The standard covers 12 PQ-core sizes from PQ 20/16 to PQ 107/87 and 3 PQI-core sizes, including effective parameter values and coil former dimensions.
1. Scope and Design Philosophy
IEC 62317-13 defines the dimensions essential for mechanical interchangeability of a preferred range of PQ-cores and low-profile PQI-cores made of ferrite materials. It also specifies the locations of terminal pins on a 2.54 mm printed wiring grid relative to the core base outlines. The standard is part of the broader IEC 62317 series under the general title “Ferrite Cores – Dimensions,” prepared by IEC Technical Committee 51 (Magnetic components and ferrite materials).
The selection of core sizes is based on industrial standardization philosophy — including sizes that are either recognized in national standards or have broad-based industrial adoption. This second edition added three new large core sizes (PQ 65/54, PQ 78/39, and PQ 107/87) along with their effective parameters, coil former dimensions, and gauge dimensions, reflecting the growing demand for higher-power-density power supply designs.
⚠️ Engineering Insight: The PQ-core design philosophy centers on minimizing the design factor “q” (le/Ae — lw/Aw) with a uniform cross-section area along each magnetic path. A minimized “q” factor yields the highest possible inductance and the lowest copper losses in transformers and inductors. This is achieved through the unique PQ geometry where the center pole area is optimized relative to the winding window, giving PQ-cores a distinct advantage over traditional E-cores in high-efficiency power supply designs.
| Core Size | A (mm) | B (mm) | C (mm) | D (mm) | E (mm) | Ae (mm²) | Ve (mm³) | Amin (mm²) |
|---|---|---|---|---|---|---|---|---|
| PQ 20/16 | 20.10 – 20.90 | 8.00 – 8.20 | 13.60 – 14.40 | 5.00 – 5.30 | 17.60 – 18.40 | 64.3 | 2400 | 59.3 |
| PQ 26/20 | 26.05 – 26.95 | 9.95 – 10.20 | 18.55 – 19.45 | 5.60 – 5.90 | 22.05 – 22.95 | 123 | 5490 | 113 |
| PQ 35/35 | 34.50 – 35.70 | 17.25 – 17.50 | 25.50 – 26.50 | 12.35 – 12.65 | 31.50 – 32.50 | 171 | 13600 | 161 |
| PQ 50/50 | 49.00 – 51.00 | 24.85 – 25.10 | 31.50 – 32.50 | 17.90 – 18.20 | 43.30 – 44.70 | 332 | 37600 | 314 |
| PQ 107/87 | 105.00 – 109.00 | 43.10 – 43.90 | 68.50 – 71.50 | 27.50 – 28.50 | 93.70 – 97.30 | 1430 | 291000 | 1320 |
2. Core Geometry and Effective Parameters
2.1 Principal Dimensions and Tolerances
The standard defines nine critical dimensions (A, B, C, D, E, F, G, J, L) for PQ-cores, each with specified minimum, nominal, and maximum values. Dimension A represents the overall length, B the core height, C the width, D the center pole diameter, and E the outer leg spacing. The tight tolerances ensure consistent magnetic performance and mechanical fit across manufacturers. For low-profile PQI-cores, additional dimensions B1 and B2 replace the single B dimension to accommodate the asymmetric profile.
2.2 Effective Parameters and Core Factor
Tables 3 and 4 of the standard provide the effective parameters (C1, C2, Ae, le, Ve, Amin) calculated according to IEC 60205. These parameters are fundamental for magnetic circuit design:
- C1 (Core Factor): The sum of the magnetic path lengths divided by the corresponding cross-sectional areas, expressed in mm&supmin;¹. A lower C1 indicates a more efficient magnetic circuit.
- Ae (Effective Cross-Sectional Area): The equivalent uniform cross-section area that would produce the same magnetic behavior as the actual core geometry. Values range from 41.7 mm² (PQI 16/7.8) to 1430 mm² (PQ 107/87).
- Ve (Effective Volume): The product of Ae and le, representing the effective magnetic volume. This is a critical parameter for core loss calculations under given flux density and frequency conditions.
- Amin (Minimum Cross-Sectional Area): The smallest cross-section along the magnetic path, which determines the maximum flux density before saturation occurs.
✅ Design Application: When designing a high-frequency transformer with a PQ 50/50 core, the effective cross-sectional area of 332 mm² allows the designer to calculate the minimum number of primary turns required to avoid saturation: N = (Vin x ton) / (Ae x dB). The large Ve of 37,600 mm³ indicates substantial core loss at high frequencies, so thermal management must be carefully considered in the overall design.
3. Coil Former Specifications and Mounting Guidelines
3.1 Coil Former Dimensions
The standard specifies five critical dimensions for coil formers (D1, D2, D3, H1, H2) along with the maximum overall dimensions (a, b) and minimum wall thickness (h). These dimensions ensure that wound coil formers fit correctly within the core assembly while maximizing the available winding area. The coil former must accommodate the winding without exceeding the core’s winding window, and the pin locations must align precisely with the 2.54 mm grid pattern specified in the pin location diagram.
3.2 Mounting Recommendations
For cores larger than PQ 35/35 (including PQ 35/35), the standard recommends mechanical fixing to the printed circuit board using mounting assemblies at two opposite sides of the coil former, due to the significant weight of these larger cores. For low-profile PQI-cores, no mounting assemblies are defined; instead, fixing the two core halves with adhesive or tape is recommended. This distinction reflects the different mechanical stress profiles encountered in practical applications.
| Coil Former for | D1 Min (mm) | D1 Max (mm) | H1 Min (mm) | H1 Max (mm) | a Max (mm) | b Max (mm) | h Min (mm) |
|---|---|---|---|---|---|---|---|
| PQ 20/16 | 17.05 | 17.45 | 9.60 | 9.95 | 23.35 | 23.35 | 6.1 |
| PQ 32/30 | 26.35 | 26.85 | 20.35 | 20.95 | 32.35 | 34.35 | 6.6 |
| PQ 40/40 | 35.75 | 36.25 | 28.55 | 29.05 | 41.30 | 42.45 | 6.1 |
| PQ 50/50 | 42.65 | 43.15 | 34.75 | 35.25 | 51.00 | 51.25 | 9.6 |
3.3 Gauge Verification
Annex B of the standard provides an informative example of gauge dimensions for checking winding space compliance. The gauge must be fully insertable into the core without forcing, and when fully inserted, must meet the mating surface of the outer legs. This practical quality control method ensures that the winding window dimensions are within specification before coil former insertion.
💡 Key Design Benefits of PQ-Cores: (a) The outside legs cover the coil former more than 40%, providing excellent magnetic shielding compared to E-cores. (b) The absence of base plates on the sides of the center pole area allows the innermost wire to be taken out directly, making it easier to meet specified withstand voltage requirements. (c) PQ-cores deliver more transmission power from the same transformer footprint compared to similar-sized alternative core shapes.
4. Frequently Asked Questions
Q: What is the advantage of PQ-cores over E-cores in power supply design?
A: PQ-cores offer three key advantages: superior magnetic shielding (outer legs cover >40% of the coil former), easier high-voltage insulation design (innermost wire can exit directly without crossing other wires), and higher power density for a given footprint due to the optimized “q” design factor.
Q: How do I select the right PQ-core size for my SMPS transformer design?
A: Start by calculating the required Ae based on your switching frequency, input voltage, and maximum flux density. Then verify that the core’s Ve is sufficient to handle the expected core losses at your operating frequency. The effective parameter tables in IEC 62317-13 provide the necessary data for this calculation. Finally, ensure the winding window (related to coil former dimensions D1-D3) can accommodate your required number of turns with the selected wire gauge.
Q: What changes were introduced in the 2015 edition compared to 2008?
A: The second edition added three new larger core sizes (PQ 65/54, PQ 78/39, and PQ 107/87) to address the growing demand for higher-power applications. Corresponding updates were made to the effective parameter tables, coil former dimensions, and gauge dimensions for these new sizes.
Q: Can PQI-cores be used interchangeably with standard PQ-cores?
A: No. PQI-cores (low-profile PQ-cores) have different height and geometry characteristics optimized for space-constrained applications. Their effective parameters differ significantly from standard PQ-cores of similar footprint, and they do not have defined mounting assemblies. Designers should select PQI-cores when profile height is the primary constraint.
