H IGHEST RATED ,

BROADEST RANGE OF

INRUSH CURRENT L IM I TERS

Protect your sensitive electronic components from damaging surge

currents that can occur when electrical circuits are switched on. Ametherm’s durable, highly-rated inrush current

limiters are designed to effectively control damaging surges in a wide

range of applications.

HIGHEST RATED, BROADEST RANGE OF INRUSH CURRENT L IMITERS

Protect your sensitive electronic components from damaging surge currents that can occur when electrical circuits are switched on. Ametherm’s durable, highly-rated inrush current limiters are designed to effectively control damaging surges in a wide range of applications.

For Power Supplies with

Outputs from 50 to 7,500 watts

and 1.0 To 50 AMPs SSI

800-808-2434 • www.ametherm.com

A transformer draws inrush current that can exceed saturation current affecting the magnetic property of the core. This happens even if the transformer is on no load with its secondary open. The magnitude of the inrush current depends on the instant on the AC wave at which the transformer is switched on. If the instant happens to be such that the AC voltage wave is going through its peak value, then there will be no inrush current drawn by the transformer. The magnitude of the current in this case will be at normal no load value. If the instant happens to be such that the AC wave is going through its zero value, then the current drawn will be very high that exceeds the saturation current (see Figure 1). In this scenario, the transformer has to be protected from inrush current.

Each transformer rating: 1000 VA, Each transformer step-down: 30 V Total transformer rating: 2000 VA Filter capacitors used: 30V, 2300 µF

T: 800-808-2434 775-884-2434

(Outside the US and Canada)F: 775-884-0670

www.ametherm.cominfo@ametherm.com

3111 N. Deer Run RoadCarson City, Nevada 89701 USA

DELIVERING HIGH-QUALITY INRUSH CURRENT LIMITING PRODUCTS & SOLUTIONS

Since 1994, Ametherm has provided the most reliable and effective inrush current limiting solutions available. We deliver on that promise through innovative design, quality manufacturing, and exceptional customer support.

• Broadest range of inrush current limiting power thermistors available• Experienced engineering team to help you find the best solutions• Durable products that are UL and CSA approved, and RoHS compliant• ISO:9001:2008 certified manufacturing processes• Free samples shipped quickly for testing and evaluation• Short lead times to meet your production demands• Competitive prices on long-lasting, reliable products

Contact us today for more informationor to order your f ree samples.

T: 800-808-2434 : 775-884-2434 (Outs ide the Uni ted States and Canada) : www.ametherm.com : info@ametherm.com

Figure 1

Figure 2

This application note provides a convenient solution (see Figure 2) to deal with the problem of inrush current exceeding saturation current in transformers. The solution uses NTC Thermistor in series with the primary. This NTC Thermistor offers high resistance at the beginning of switching and limits the inrush current. After a short time, the NTC Thermistor resistance decreases to a low value due to self heating and does not affect normal operation.

TRANSFORMER PROTECTION FROM INRUSH CURRENT – USE AN NTC THERMISTOR

PROBLEM STATEMENT

PROTECTION OF THE TRANSFORMER

Energy required for the NTC:

Inductive reactance of the transformer

Note: Peak Inrush Current occurs in one cycle = 564 A, as measured on the oscilloscope Input Voltage = 120 VAC Frequency = 60 Hz

Energy rating for the NTC =

Assume, Efficiency of transformer: 90%, Ambient Temperature: 85 =

For this transformer, is calculated as =

Normally Thermistors are rated up to 65ºC for their operating current, and then a derating factor must be taken in to account.

Decision criteria: choose an NTC Thermistor that can provide at least the steady state current as calculated above:

Using the de-rating curve (see Figure 3) at 80, use 90% of max rated steady state current

You can use any of the NTC Thermistors that are rated up to 36.0 A to meet your Steady State Current and Energy Requirements. See the charts for part numbers.

100

80

60

40

20

0

0 25 50 75 100 125 150-25-50

Ambient TemperatureDegrees Centigrade (C )

Percentof RatedImax

65-40

NTC SELECTION CRITERIA: ENERGY

Figure 3

Input Voltage

KVA of Transformer(Efficiency of Transformer)x(Minimum Input Voltage)

steady

120 V

564 AInrush Current

I =

L = 565 µH= (565 x 10

–6) (564)2 = 90 Joule

= 0.9 x 36 A = 32.40 A

XL = = 0.213Ω=

steadyI (2.0 KVA)

(0.70) x (90 V)= 31.75 A

XL = 2 π f L = 2 x 3.14 x 60 x L, Calculate Inductance L Yields

LI212

LI212

12

NTC SELECTION CRITERIA: STEADY STATE CURRENT

For a complete list of Ametherm distributors, please visit www.ametherm.com

INTERNATIONALDigi-Key www.digikey.comNewark www.newark.com

EUROPEThomatronik www.thomatronik.de

UNITED KINGDOMRhopoint Components www.rhopointcomponents.com

CHINAIBS Electronics www.ibselectronics.com

MALAYSIAIC Resource www.icresource.com.sg

ALSO AVAILABLE THROUGH:

Big Amp inrush current

limiters are high current,

high energy handling

devices capable of

absorbing up to 250Js and

suitable for large switch

mode power supplies,

UPSs, HVAC, and motor

speed controllers.

Protection.

DESIGN TIPS FOR INRUSH CURRENT L IMITERS MOUNTING INRUSH CURRENT L IMITERS

The SL22 series of inrush current limiters is CSA & UL approved, and other SL series parts are CSA approved. Refer to the following guidelines when using these designs.

1. The body should not touch other components on the PCB.2. A fuse rated at the maximum current rating of the device (allowing for any derating that may be needed for ambient temperatures in excess of 65°C) or lower than the maximum current rating of the 7.87 mm device should be used.

Inrush current limiters are power NTC

thermistors manufactured from a

specially-formulated metal oxide

ceramic material that is capable of

suppressing high inrush current surges.

Connected in series with the load at

switch-on, the thermistor’s relatively

high cold resistance limits the current.

As the current flows, the thermistor

heats, reducing its resistance value so

that once the initial surge has been

safely held off, the resistance in the

circuit is held at a low value to maxi-

mize efficiency. Applications include:

• Power Supplies

• Lighting Circuits

• Any Circuit Subject To

• Switch-On Current Surges

• Electric Motors

• Thermostat Protection

PROTECTING YOUR ELECTRONIC COMPONENTS WITH INRUSH CURRENT L IMITERS

INRUSH CURRENT L IMITERS BIG AMP INRUSH CURRENT L IMITERS MEGA SURGE CURRENT L IMITERSINRUSH CURRENT L IMITERS

SL03 10001 1 10.0 20 0.80 2.0 120 3.0 3.0 0.5SL03 22101 1 220.0 20 2.20 2.0 120 3.5 3.5 0.5SL05 5R001 1 5.0 25 0.80 5.0 120 6.0 3.5 0.5SL05 60001 1 60.0 20 0.82 3.0 120 6.0 4.5 0.5SL05 12101 1 120.0 20 1.40 1.5 120 6.0 4.5 0.5SL08 10002 2 10.0 20 0.29 9.0 240 8.8 4.5 0.5SL08 33001 2 33.0 20 0.75 8.0 240 8.5 4.5 0.5SL08 50001 1.1 50.0 20 0.90 8.0 265 8.0 4.0 0.5SL08 12101 1 120.0 20 1.60 8.0 265 8.5 5.5 0.5SL08 10101 1 100.0 20 1.40 8.0 265 8.5 5.5 0.5

Standard Inrush Current LimitersSL10 5R002 2 5.0 20 0.35 20 265 10.5 4.0 0.5SL12 5R002 2 5.0 20 0.30 25 265 12.0 6.0 0.8SL12 20002 2 20.0 20 0.45 30 265 12.5 5.1 0.8SL12 25002 2 25.0 20 0.55 30 265 12.5 5.1 0.8SL15 22102 2 220.0 25 0.90 50 265 15.0 4.5 0.8SL10 10003 3 10.0 15 0.26 17 265 10.0 4.0 0.5SL12 25003 3 25.0 20 0.35 30 265 12.5 5.1 0.8SL12 12103 3 120.0 20 0.48 25 265 12.0 5.0 0.8SL12 5R004 4 5.0 15 0.15 25 265 12.5 5.1 0.8SL15 7R004 4 7.0 20 0.10 55 265 15.5 5.0 0.8SL12 12004 4 12.0 20 0.22 40 265 12.5 6.0 0.8SL15 16004 4 16.0 20 0.25 50 265 15.0 5.2 0.8SL15 40004 4 40.0 20 0.30 30 265 15.5 5.0 0.8SL10 2R505 5 2.5 30 0.12 30 265 10.0 5.0 0.5SL15 5R005 5 5.0 20 0.15 50 265 15.5 5.1 0.8SL12 10005 5 10.0 20 0.13 40 265 12.5 5.1 0.8SL12 10006 6 10.0 20 0.12 40 265 12.0 5.1 0.8SL15 2R507 7 2.5 20 0.06 40 265 15.5 4.5 0.8SL15 5R007 7 5.0 20 0.09 50 265 15.0 5.0 0.8SL15 4R008 8 4.0 20 0.07 40 265 15.0 4.5 0.8SL15 2R509 9 2.5 20 0.04 40 265 15.0 5.5 0.8SL18 2R508 8 2.5 20 0.06 90.0 265 19.0 5.0 1.0SL18 5R006 6 5.0 20 0.14 75.0 265 19.0 5.0 1.0SL18 10005 5 10.0 20 0.18 75.0 265 19.0 6.0 1.0SL18 30006 6 30.0 25 0.17 75.0 265 19.0 6.0 1.0SL18 47003 3 47.0 25 0.13 75.0 265 19.0 6.0 1.0

SL 10 100 04

Steady state current

Resistance at 25*C

Diameter

Series

100 = 10

221 = 220

PART NUMBERING

Inrush current limiters may get hot in operation.

For best results, use the following guidelines:• Do not place on the PCB near temperature sensitive components.• Use a high temperature solder on the PCB.• If equipped, use a ceramic spacer to stand off the surge gard from the PCB or contact us for pre-formed devices.• Keep away from wiring looms.

Part Number

Imax. Max Steady State

Current (Amperes)

Resistance at 25°C (ohms)

Resistance Tolerance %

Rimax Resistance at Max Current

(ohms)

Jmax Energy Rating

(Joules) (Ws)

Vmax Voltage Rating

Dmax (mm) Max Dia.

Over Coating

Tmax (mm) Max

Thickness Over Coating

Lead Dia. (mm)

SL22 12103 3 120 25 0.9 80 265 22 6.0 1.0SL22 50004 4 50 20 0.44 80 265 22 6.0 1.0SL22 30005 5 30 20 0.4 80 265 22 6.0 1.0SL22 14007 7 14 25 0.12 75 265 22 6.0 1.0SL22 10008 8 10 20 0.095 90 265 22 6.0 1.0SL22 2R510 10 2.5 20 0.04 90 265 22 6.0 1.0SL22 7R010 10 7 20 0.08 100 265 22 6.0 1.0SL22 0R712 12 0.7 20 0.03 120 265 22 6.0 1.0SL22 5R012 12 5 20 0.05 100 265 22 6.0 1.0SL22 4R014 14 4 20 0.05 100 265 22 6.0 1.0SL22 2R515 15 2.5 20 0.03 90 265 22 6.0 1.0SL22 0R516 16 0.5 20 0.02 160 265 22 6.0 1.0SL22 2R018 18 2 20 0.037 90 265 22 6.0 1.0SL22 1R020 20 1 20 0.015 65 265 22 6.0 1.0SL32 0R230 30 0.25 25 0.010 100 265 32 6.0 1.0

Part Number

Imax. Max Steady State

Current (Amperes)

Resistance at 25°C (ohms)

Resistance Tolerance %

Rimax Resistance at Max Current

(ohms)

Jmax Energy Rating

(Joules) (Ws)

Vmax Voltage Rating

Dmax (mm) Max Dia.

Over Coating

Tmax (mm) Max

Thickness Over Coating

Lead Dia. (mm)

SL32 10015 15 10 20 150 265 0.048 0.074 0.102SL32 5R020 20 5 20 200 265 0.034 0.056 0.082SL32 2R025 25 2 20 250 265 0.025 0.031 0.049SL32 0R530 30 0.5 20 150 265 0.011 0.019 0.058SL32 1R030 30 1 20 160 265 0.014 0.018 0.048SL32 1R036 36 1 20 160 265 0.01 0.015 0.028

Part Number

Imax. Max Steady State

Current (Amperes)

Resistance at 25°C (ohms)

Resistance Tolerance %

Jmax Energy Rating

(Joules) (Ws)Vmax Voltage

Rating

Resistance at 100% SS

Current (ohms)

Resistance at 70% SS

Current (ohms)

Resistance at 50% SS

Current (ohms)

With energy ratings to 900J, Megasurge inrush current limiters are suitable for very high power applications, such as:

• AC Motors

• Compressors

• Frequency Generators

• High Power Motor Controllers

• High Power Battery Chargers

• Motor Drives

• MRI Machines

• Plasma Cutting Tools

• Power Supplies

• Toroidal Transformers up to 7.5 KVA

• Welding Machines

Features

• Up to 50A SSI

• 0.5 ohm to 220 ohms

• Limits up to 900 Joules of inrush energy

MS12 15102 2 150 25 110 440 560 1.05 1.9 2.71MS22 12103 3 120 25 220 440 1100 1.2 1.4 2.5MS22 22103 3 220 25 75 265 580 1.4 1.67 3MS15 66003 3.5 66 25 125 440 600 0.4 0.824 1.73MS15 40004 4 40 25 135 440 700 0.4 0.623 0.96MS22 50004 4 50 25 240 440 1200 0.4 0.625 1.1MS22 75004 4 75 25 240 440 1200 0.5 0.77 1.35MS22 20005 5 20 25 180 440 1000 0.32 0.5 0.72MS32 20008 8 20 25 250 440 1250 0.2 0.33 0.9MS35 20010 10 20 25 500 680 1000 0.3 0.4 0.5MS32 10015 15 10 25 250 440 1250 0.06 0.1 0.19MS35 10018 18 10 25 500 680 1000 0.1 0.32 0.48MS32 5R020 20 5 25 300 440 1250 0.035 0.06 0.1MS32 2R025 25 2 25 300 440 1500 0.02 0.032 0.06MS35 5R025 25 5 25 600 680 1000 0.05 0.1 0.15MS35 3R030 30 3 25 750 680 1250 0.03 0.052 0.08MS35 2R035 35 2 25 750 680 1600 0.02 0.027 0.04MS32 1R036 36 1 25 300 440 1500 0.012 0.015 0.03MS35 1R040 40 1 25 800 680 1700 0.012 0.02 0.03MS35 0R550 50 0.5 25 900 680 2000 0.008 0.013 0.02

Part Number

Imax. Max Steady State

Current (Amperes)

Resistance at 25°C (ohms)

Resistance Tolerance %

Jmax Energy Rating

(Joules) (Ws)

Vmax Voltage Rating

Max Cap @ Max V uF

Resistance at 100% SS

Current (ohms)

Resistance at 75% SS

Current (ohms)

Resistance at 50% SS

Current (ohms)

Part Series D mm (Nom) T mm (Nom) Lead Dia. (mm) S mm (Nom) L mm (Nom) C mm (Nom) MS12 12.0 Nom 7.0 Nom 1.0 Nom 7.80 Nom 38.0 Nom 3.42 Nom MS15 15.0 Nom 7.0 Nom 1.0 Nom 7.80 Nom 38.0 Nom 6.70 Nom MS22 22.0 Nom 8.5 Nom 1.0 Nom 7.80 Nom 38.0 Nom 3.82 Nom MS32 32.0 Nom 8.5 Nom 1.0 Nom 7.80 Nom 38.0 Nom 4.5 Nom MS35 35.0 Nom 10 Nom 2.5 Nom 19.0 Nom 39.0 Nom 7.50 Nom

T: 800-808-2434 : 775-884-2434 (Outs ide the Uni ted States and Canada) : www.ametherm.com : info@ametherm.com T: 800-808-2434 : 775-884-2434 (Outs ide the Uni ted States and Canada) : www.ametherm.com : info@ametherm.com T: 800-808-2434 : 775-884-2434 (Outs ide the Uni ted States and Canada) : www.ametherm.com : info@ametherm.com

32 6 1.0 7.9 38

Dmax (mm) Max Dia. Over Coating

Tmax (mm) Max Thickness Over Coating Lead Dia. (mm)

Lead Spacing (mm) Nominal

Length (mm) Nominal