TFSD274RFE [OHMITE]

Fixed Resistor, Metal Glaze/thick Film, 1W, 274ohm, 1% +/-Tol, 100ppm/Cel, Surface Mount, ROHS COMPLIANT;


型号：	TFSD274RFE
厂家：	OHMITE MFG. CO.
描述：	Fixed Resistor, Metal Glaze/thick Film, 1W, 274ohm, 1% +/-Tol, 100ppm/Cel, Surface Mount, ROHS COMPLIANT 电阻器
文件：	总1页 (文件大小：67K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

F E A T U R E S

S P E C I F I C A T I O N S

• Ideal for medical surge protec-

tion applications

Material

TFS Series

Resistive Element: Thick Film

Encapsulation: Screen Printed

Glass

Electrical

Resistance Value: 100Ω up to

100KΩ

• Ideal to replace standard carbon

composition resistors

• Custom dimensions, values,

tolerances and characteristics

available

Surge Capable Resistors

Thick Film Non Inductive

Temperature Coefficient:

100ppm/°C

Tolerance: 1%, 2%, 5%, 10%

Operating Temperature: -55°C to

+200°C

0.50mm

Test: VDE 0750 (Pulse Duration

10 msec)

0.25mm

S I N G L E P U L S E E N E R G Y R A T I N G

Energy* Power

Dimensions (mm)

Although Ohmite’s TFS Series resistors have been specially

designed and developed to absorb much more energy than

standard resistors, pulses and transients require special consid-

eration since they cause an instanta-

Type

TFSA

TFSB

TFSC

TFSD

TFSE

TFSF

(KV)

(J)

(W)

0.5

0.75

3.5

5.5

10.5

0.7

0.9

1.1

1.3

neous temperature rise in the resistor

film. This application note can guide

you through these considerations.

For applications with transients,

pulses or surges the following must

be considered:

1. Do not exceed the normal rated

operating voltage of the device.

2. Using the figure at right, estimate

the energy (Ea) and the pulse dura-

tion (ta) for a single pulse in your

application.

3. Calculate the energy ratio in per-

cent (Er) between the nominal

energy rating of the model you

have chosen (see table) and the

single pulse energy in your appli-

cation (Ea from step 2) using the

formula:

V²t

E = –––

1.5

*Published energy rating is for 10ms pulse. For shorter pulses energy rating has to be

derated according to Max. Individual Pulse Rating chart (below) and Single Pulse Energy

Rating considerations (left).

E = –CV²

t = RC

O R D E R I N G I N F O R M AT I O N

V²t

E = –––

RoHS Compliant

� ꢀ ꢁ ꢂ ꢃ ꢄ ꢄ ꢅ ꢆ ꢇ

Series

Type

Ohm Value

Tolerance

F = 1%

G = 2%

See chart Example:

V²t

E = –––

100R = 100�

2K40 = 2400� J = 5%

K = 10%

E = Energy

t = Time

V = Voltage

(joules)

(seconds)

(volts)

M A X I M U M I N D I V I D U A L P U L S E R A T I N G

Er = –––––––– x 100

Enominal

R = Resistance (ohms)

C = Capacitance (farads)

1000

4. Refer to the Pulse Chart. On this

chart find the point where the energy ratio (Er), found at step

3, and time (ta) coincide. Qualify that this point falls below the

maximum pulse energy curve. If the point is above the curve a

bigger model should be chosen.

100

E X A M P L E

A 1µF capacitor is charged

to 3.5kV and model TFSC,

1KOhm has been selected.

Model TFSC is rated for 4kV,

so the peak voltage of 3.5kV is

acceptable.

A bigger model should be cho-

sen, for example TFSD. Model

TFSD, 1KOhm, can be used

for this application because

we have an energy ratio Er

of 18%, which is below the

energy curve.

0.1

1 µs

10 µs 100 µs

1 ms

10 ms 100 ms

Pulse Width

N O T E S

• For pulses over 100ms, refer to the momentary overload

specification on the product data sheet. Always verify designs

with pulse and surge conditions through thorough testing of

the design at maximum operating temperature and maximum

pulse loading (or some margin above maximum pulse load-

ing).

Ea = ––CV²= 6.1J

6.1J

Er = ––– x 100 = 18%

33J

ta = R C = 1 ms

6.1J

Er = ––– x 100 = 55%

11J

• Damage to the resistor by excessive pulse loading is generally

indicated by an increasing resistance of the resistor.

According to the pulse chart,

an energy ratio of 55% for a

pulse width of 1ms falls well

above the energy curve. The

limit is actually located around

25-30%. Model TFSC cannot

be used for this application.

• Energy ratings are based on single pulses (at least 1 minute

between pulses).

• For multiple pulse applications the energy pulse rating should

be reduced and the average power should not exceed the

nominal power rating of the selected model.

Ohmite Mfg. Co. 1600 Golf Rd., Suite 850, Rolling Meadows, IL 60008 • Tel. 1-866-9-OHMITE • Fax 1-847-574-7522 • www.ohmite.com • info@ohmite.com

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