# PP Series NTC Inrush Current Limiters

> Phenolic-coated radial power NTC thermistors for inrush current limiting. R25 2.5–200 Ω, max. steady-state current up to 5 A, operating temperature up to +155 °C.

- Series code: NTC-PP
- Product line: [Thermistors (NTC / PTC)](https://www.songtian-ste.com/en/products/thermistors/) › NTC inrush current limiters
- Part numbers: 508 · [part list (JSON)](https://www.songtian-ste.com/data/parts/power-pp.json)
- Page: https://www.songtian-ste.com/en/products/ntc-thermistors/power-pp/
- Chinese version: https://www.songtian-ste.com/zh/products/ntc-thermistors/power-pp/
- [Ask AI about this series](https://www.songtian-ste.com/en/products/ntc-thermistors/power-pp/?ask=Help%20me%20choose%20a%20part%20from%20the%20STE%20NTC-PP%20series.)

## Key specifications

| Parameter | Value |
| --- | --- |
| Resistance R25 | 2.5–200 Ω |
| Max. steady-state current (25 °C) | 0.2–5.0 A |
| Residual resistance at max. current | 0.088–5.007 Ω |
| B value | 2,500–3,400 K |
| Disc size | 5D–20D |
| Operating temperature | −40 °C to +155 °C |

## Engineering details

### Overview

Phenolic-coated radial power NTC thermistors (MF72 type) for inrush current limiting. Disc sizes 5D to 20D, R25 2.5–200 Ω ±20%, max. steady-state current 0.2–5.0 A at 25 °C, residual resistance 0.088–5.007 Ω. Operating temperature −40 °C to +155 °C.

#### Series features

- Seven disc sizes from 5D to 20D
- R25, max. steady-state current, residual resistance, B value, thermal time constant and dissipation constant specified per part number
- Phenolic-resin coating; bulk or taped packing and five lead forms
- CQC and VDE certified, UL/cUL recognized to UL 1434; coverage depends on model and construction

#### Typical applications

- Inrush current limiting in AC-input rectifiers and switch-mode power supplies
- Transformers, adapters, motors, projectors, ballasts and LED drivers
- Converter, appliance and industrial power inputs
- Passive soft-start stages where residual loss and cool-down time are acceptable

### Specifications

|   |   |
| --- | --- |
| Function | Self-heating radial NTC thermistor for inrush current limiting. High cold resistance limits the turn-on current; resistance falls as load current heats the ceramic. |
| Type | PP (phenolic coating), MF72 power NTC thermistor type |
| Encapsulation | Phenolic resin · code P = phenolic, RoHS; R = phenolic, halogen-free |
| Disc sizes | 5D · 7D · 9D · 11D · 13D · 15D · 20D |
| Rated zero-power resistance R25 | 2.5–200 Ω; available values depend on disc size |
| R25 tolerance | M = ±20% |
| Max. steady-state current | 0.2–5.0 A at 25 °C; depends on R25 and disc size |
| Residual resistance at max. current | 0.088–5.007 Ω |
| B value | 2,500–3,400 K ±10% (reference temperatures and R/T data on request) |
| Thermal time constant | <18 to <105 s; per part number |
| Dissipation constant | >6 to >25 mW/°C; per part number |
| Operating temperature | −40 °C to +155 °C |
| Max. voltage and capacitance | Max. operating voltage and permissible DC-bus capacitance on request. R25 and max. current alone do not qualify an inrush design. |
| Restart and recovery | Min. off-time, resistance-recovery curve and repetitive-start limits on request. A hot NTC gives little inrush limiting at restart. |
| Dimensions, 5D | D max. 6.5 mm · T max. 4.0 mm · lead pitch F 5.0 ±0.5 mm · lead Ø d 0.6 ±0.05 mm |
| Dimensions, 7D | D max. 8.0 mm · T max. 4.5 mm · lead pitch F 5.0 ±0.5 mm · lead Ø d 0.6 ±0.05 mm |
| Dimensions, 9D | D max. 9.0 mm · T max. 5.5 mm · lead pitch F 5.0 ±0.5 mm · lead Ø d 0.6 ±0.05 mm |
| Dimensions, 11D | D max. 11.5 mm · T max. 6.0 mm · lead pitch F 7.5 ±0.5 mm · lead Ø d 0.8 ±0.05 mm |
| Dimensions, 13D | D max. 14.5 mm · T max. 6.5 mm · lead pitch F 7.5 ±0.5 mm · lead Ø d 0.8 ±0.05 mm |
| Dimensions, 15D | D max. 16.5 mm · T max. 6.5 mm · lead pitch F 7.5 ±0.5 mm · lead Ø d 0.8 ±0.05 mm |
| Dimensions, 20D | D max. 21.5 mm · T max. 7.0 mm · lead pitch F 10.0 ±0.5 mm · lead Ø d 1.0 ±0.05 mm |
| Lead forms | Long straight · short straight · single outward bend · inward bend · front/rear raised |
| Lead length | Long straight ≥16 mm; short and bent forms 2.5–<6 mm ±0.5 mm or 6–10 mm ±1.0 mm. Coating-to-bend height depends on the lead form. |
| Lead pitch codes | B = 5.0 mm · E = 7.5 mm · D = 10.0 mm |
| Packing | B = bulk · T = taped; taping for 5.0 and 7.5 mm lead pitch; H0 and component pitch depend on the lead form |
| Hand soldering and rework | 350 °C max. · 3 s max. · solder point at least 2 mm from the coating |
| Storage climate | ≤35 °C · ≤70% RH |
| Storage | 12 months · first in, first out · sealed with desiccant; avoid corrosive, oxidizing, flammable or explosive gases, oil, water, solvents and direct sunlight |
| Climate category (CQC) | 40/155/42 |
| Environmental compliance | RoHS and REACH compliant; encapsulation code R is halogen-free. Material declarations on request. |
| Further data | On request: current derating and hot resistance versus ambient temperature; inrush energy rating (J or test capacitance at 110/120 VAC and 230/240 VAC); coating flammability class, abnormal-overload behavior and max. surface temperature; reliability test results. |
| System protection | A power NTC thermistor is not a fuse, relay, isolation device or hot-restart limiter. Coordinate fault current, bypass contacts, enclosure temperature, fire containment and service behavior at equipment level. |

### Variants

Ranges by dielectric, package and lead style within this series.

| Variant | Body dimensions | R25 range | Max. steady-state current / residual resistance | Lead / land pattern | Notes |
| --- | --- | --- | --- | --- | --- |
| 5D-PP | D max. 6.5 mm · T max. 4.0 mm | 5–60 Ω | 0.3–1.0 A · 0.353–2.653 Ω | F 5.0 ±0.5 mm · d 0.6 ±0.05 mm | Smallest size. |
| 7D-PP | D max. 8.0 mm · T max. 4.5 mm | 5–50 Ω | 0.2–2.0 A · 0.283–3.7059 Ω | F 5.0 ±0.5 mm · d 0.6 ±0.05 mm | Compact size for power inputs. |
| 9D-PP | D max. 9.0 mm · T max. 5.5 mm | 3–200 Ω | 0.5–3.0 A · 0.120–5.007 Ω | F 5.0 ±0.5 mm · d 0.6 ±0.05 mm | Widest R25 range, up to 200 Ω. |
| 11D-PP | D max. 11.5 mm · T max. 6.0 mm | 2.5–120 Ω | 1.1–4.0 A · 0.095–2.253 Ω | F 7.5 ±0.5 mm · d 0.8 ±0.05 mm | Mid-size disc. Validate thermal derating and life at the actual load. |
| 13D-PP | D max. 14.5 mm · T max. 6.5 mm | 2.5–120 Ω | 1.2–5.0 A · 0.088–2.124 Ω | F 7.5 ±0.5 mm · d 0.8 ±0.05 mm | Higher current, up to 5.0 A. |
| 15D-PP | D max. 16.5 mm · T max. 6.5 mm | 4–120 Ω | 1.8–5.0 A · 0.112–1.652 Ω | F 7.5 ±0.5 mm · d 0.8 ±0.05 mm | Large size. Validate energy and hot loss before design-in. |
| 20D-PP | D max. 21.5 mm · T max. 7.0 mm | 6–16 Ω | 4.0–5.0 A · 0.113–0.212 Ω | F 10.0 ±0.5 mm · d 1.0 ±0.05 mm | Largest size in the series. Availability on request. |

### Selection guide

Start from the energy and the permissible inrush current of the input stage, not from disc size. Then select R25, check continuous current and hot loss at max. ambient temperature, define the restart duty, and specify approval, drawing and packing with the part number.

1. **Calculate startup energy and duty**
   Define line or DC-bus voltage, tolerance, frequency, downstream capacitance or transformer magnetizing energy, series impedance, number of starts and min. off-time. The energy (J) or test-capacitance rating, available on request, must exceed the application stress.
2. **Select cold resistance from the permissible inrush**
   Estimate R25 from peak voltage, existing series impedance and the weakest bridge, fuse, switch or load limit. Include the ±20% R25 tolerance and the coldest start temperature.
3. **Check current, hot resistance and temperature**
   Max. current and residual resistance apply only at their stated condition (25 °C). Data on request for ambient derating, hot resistance versus current, body and lead temperature, airflow and mounting conditions, and life at the actual load.
4. **Define restart, bypass and fault behavior**
   A hot NTC has low resistance and limits little at restart. Define recovery time, repetitive starts, bypass-relay timing and contact stress, fuse coordination, abnormal overload and safe end of life.
5. **Specify the exact part number**
   Fix R25, max. current, drawing, lead form, packing, coating code and approval scope with the exact part number before production approval.

### Approvals & reliability

#### Approvals & qualifications

Approvals are issued for MF72 types. CQC approval covers climate category 40/155/42.

| Agency | Standard | Certificate | Scope |
| --- | --- | --- | --- |
| CQC CQC | GB/T 6663.1-2007 · CQC11-471552-2015 rule | CQC19001213204 | MF72 types, ±20%, disc sizes 5, 7, 9, 11, 13, 15 and 20 mm, listed per resistance value; climate category 40/155/42. Valid to 9 Apr 2029, subject to surveillance. |
| UL UL / cUL | UL 1434 | E474052 | Recognized component. The file lists individual inrush-limiting NTC models with their conditions of acceptability. |
| VDE VDE | DIN EN 60539-1:2017-01 · EN 60539-1:2016 | 40050168 | Covers listed MF72 types under factory surveillance. |

Each certificate covers the types and ratings listed on it.

### Design notes

#### Start from energy, not only R25

For a capacitor-input supply, ½CV² is a first estimate; source impedance and waveform also matter. The selected part needs an energy or test-capacitance rating, available on request, above the actual startup energy and duty.

#### Protect the weakest series element

Choose cold resistance from peak voltage, minimum source impedance, tolerance and cold temperature so that the bridge, fuse, switch, relay contacts and load stay below their turn-on limits.

#### Treat max. current as a thermal rating

Continuous current heats the NTC. Validate ambient, airflow, PCB heat sinking, enclosure temperature, residual resistance, loss, body and lead temperature and current derating. The 25 °C value does not apply at higher ambient temperature.

#### Do not connect NTC limiters in parallel

Self-heating causes current hogging between parallel parts. If one part cannot meet the current or energy requirement, select a larger size or an active precharge or bypass circuit.

#### Design for hot restart and bypass timing

A recently energized NTC stays hot and low in resistance and may not limit a fast restart. Define min. off-time, recovery detection, bypass-relay timing, contact stress and repetitive-start fault behavior.

#### Control hot surfaces, fusing and assembly

Keep spacing from heat-sensitive materials, coordinate upstream protection and fire containment, use the lead and packing drawing of the exact part number, observe the 350 °C / 3 s rework limit and store the parts dry and sealed.

### Part numbering

Example ordering code. Not every combination is available.

`MF · 05 · 100 · X8 · M · 3 · B · X7 · F · P · B · 0 · 0`

| Code | Meaning |
| --- | --- |
| MF | Power NTC thermistor prefix (MF72 type) |
| 05 | Disc diameter: 05 = 5 mm; up to 20 mm |
| 100 | R25: 100 = 10 Ω; decimal values written as 0R5 |
| X8 | Max. steady-state current: X8 = 0.8 A; other codes on request |
| M | R25 tolerance: M = ±20% |
| 3 | Lead form: 3 = short straight; 1 = long straight, 2 = single outward bend, 4 = inward bend, 8 = front/rear raised |
| B | Lead pitch: B = 5.0 mm; E = 7.5 mm, D = 10.0 mm |
| X7 | Lead length, bulk: X0–X9 cover 2.0–2.9 mm; exact length: see part drawing |
| F | Lead material: F = tin-plated copper-clad steel wire |
| P | Encapsulation: P = phenolic resin, RoHS; R = phenolic resin, halogen-free |
| B | Packing: B = bulk; T = taped |
| 0 | Factory code, assigned by STE |
| 0 | Factory code, assigned by STE |

## Datasheets & approval documents

- [Datasheet: PP series power NTC thermistors, phenolic resin coated, 18-character part numbers — short-form datasheet (2018-04)](https://www.songtian-ste.com/documents/source-cn/%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8%E7%B3%BB%E5%88%97%E4%BA%A7%E5%93%81%E8%A7%84%E6%A0%BC%E4%B9%A6/%E8%B4%9F%E6%B8%A9%E5%BA%A6%E7%B3%BB%E6%95%B0%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8-PP%E7%B3%BB%E5%88%97%28%E9%85%9A%E9%86%9B%E6%A0%91%E8%84%82%29%E7%AE%80%E7%89%88%E8%A7%84%E6%A0%BC%E4%B9%A6-201804%20%20%2018%E7%A0%81.pdf) — PDF · Chinese · 2018-04 · 371 KB
- [Datasheet: PP series power NTC thermistors, small sizes, 19-character part numbers — short-form datasheet (2024-01)](https://www.songtian-ste.com/documents/source-cn/%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8%E7%B3%BB%E5%88%97%E4%BA%A7%E5%93%81%E8%A7%84%E6%A0%BC%E4%B9%A6/%E8%B4%9F%E6%B8%A9%E5%BA%A6%E7%B3%BB%E6%95%B0%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8-PP%E7%B3%BB%E5%88%97%E7%AE%80%E7%89%88%E8%A7%84%E6%A0%BC%E4%B9%A6-202401%20%20%2019%E7%A0%81%E5%B0%8F%E5%B0%BA%E5%AF%B8.pdf) — PDF · Chinese · 2024-01 · 369 KB
- [Certificate: Thermistor safety approval certificates (2024-07)](https://www.songtian-ste.com/documents/source-cn/%E5%AE%89%E8%A7%84%E8%AE%A4%E8%AF%81%E8%AF%81%E4%B9%A6/4-%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%AE%89%E8%A7%84%E8%AE%A4%E8%AF%81%E8%AF%81%E4%B9%A6-2024%E5%B9%B47%E6%9C%88%E7%89%88%E6%9C%AC.pdf) — PDF · Chinese · 2024-07 · 2.1 MB

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