Download 21044 Determining Nominal Resistance.fm

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Switched-mode power supply wikipedia, lookup

Current mirror wikipedia, lookup

Power electronics wikipedia, lookup

Resistive opto-isolator wikipedia, lookup

Surge protector wikipedia, lookup

Current source wikipedia, lookup

Ohm's law wikipedia, lookup

Electrical ballast wikipedia, lookup

Rectiverter wikipedia, lookup

Audio power wikipedia, lookup

Power MOSFET wikipedia, lookup

CMOS wikipedia, lookup

Valve RF amplifier wikipedia, lookup

Transcript
VISHAY MILWAUKEE
www.vishay.com
Resistive Products
Application Note
Grid Resistors: Determining Nominal Resistance
By Daniel Featherstone
SCENARIO
The customer wants to dissipate 100 V at a rate of 100 A continuously.
100 V x 100 A = 10 kW
100 V / 100 A = 1 
FACT
Nearly all resistor materials change resistance as temperature increases. Depending on the material, this change can range from
a few percent to 50 % and higher at 100 % duty on the resistor (100 % duty raises the resistor temperature to ~ 375 °C over
ambient).
In the scenario above, there are two ways to handle the resistor design (assuming a material with a 33 % change in resistance
at 100 % power and that the voltage applied across the resistor is constant).
Design 1
Voltage across resistor (cold) = 100 V
Voltage across resistor (hot) = 100 V
Cold resistance (0 % power) = 1 
Hot resistance (100 % power) = 1.33 
Initial current (at 1 ) = 100 A
Hot current (100 % power) = 75.2 A
Initial power rating = 10 kW
Continuous duty power rating = 7.52 kW
120
1.4
100
1.2
1.0
Resistance (Ω)
60
40
0.8
0.6
0.4
20
0
0.2
0
20
40
60
80
100
Time (s)
Revision: 08-Jul-15
120
140
160
180
0
0
20
40
60
80
100
120
140
160
180
Time (s)
Document Number: 21044
1
For technical questions, contact: vishaymilwaukeeresistor@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
Current (A)
80
Application Note
www.vishay.com
Vishay Milwaukee
Grid Resistors: Determining Nominal Resistance
Design 2
Voltage across resistor (cold) = 100 V
Voltage across resistor (hot) = 100 V
Cold resistance (0 % power) = 0.752 
Hot resistance (100 % power) = 1.0 
Initial current (at 10 ) = 133 A
Hot current (100 % power) = 100 A
Initial power rating = 13.3 kW
Continuous duty power rating = 10 kW
160
1.2
140
1.0
Resistance (Ω)
120
Current (A)
100
80
60
0.8
0.6
0.4
40
0.2
20
0
0
20
40
60
80
100
120
140
160
180
Time (s)
0
0
20
40
60
80
100
120
140
160
180
Time (s)
Design 1 is good when there is a desire to limit the current flow.
Design 2 is good when a nominal current flow or power dissipation is desired at the steady state / continuous conditions.
The customer should decide which way they would prefer the resistor be designed based on their application. In the above
scenario, Design 2 would likely be better because at continuous duty (100 % power) the resistor will be dissipating the desired
power at the desired current rate.
www.vishay.com/doc?31833
GRE2 Application Form
www.vishay.com/doc?31875
NGR datasheet
www.vishay.com/doc?31873
Load Bank Application Form
www.vishay.com/doc?49893
Dynamic Braking Application Form
www.vishay.com/doc?49887
NGR Application Form
www.vishay.com/doc?49904
Harmonic Filter Application Form
www.vishay.com/doc?49889
Revision: 08-Jul-15
Document Number: 21044
2
For technical questions, contact: vishaymilwaukeeresistor@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
GRE1 datasheet