- #1
Calculating resistor for IGBT and choosing flyback diode
In summary, the conversation discusses how to calculate a current limiting resistor for the gate of an IGBT and how to choose a flyback diode for a motor. Suggestions are made to use application notes and a Google search to find information on choosing a suitable resistor and diode. Additionally, the importance of considering transient current surges and reverse voltage for the diode is mentioned.
- #2
berkeman
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I don't use IGBTs, but since it's a FET input, why does it need a current-limiting resistor? I've seen resistors to ground to turn them off faster, but I'm not sure I've seen current limiting resistors into their gates. Of course, I could be wrong.nothing909 said:
For the flyback diode, you need to figure out the max reverse voltage and the max forward current. The max forward current can be calculated from the parasitic capacitance (or an explicit capacitance that you add) and the winding inductance.
- #3
gneill
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There are some application notes that show how to choose a series gate resistor to limit current and improve switching. From what I can tell it has to do with the IGBT gate looking like a small capacitive load and taking advantage of the driving resistance to "tune" the response as well as curtail current spikes. Took me all of ten seconds to spot them with a google search ("IGBT gate resistor").berkeman said:
But the OP should show some effort here and do the search and some reading.
- #4
berkeman
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Thanks, I love learning new things here.gneill said:
- #5
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The IGBT will be saturated and the inductive nature of the motor load will limit transient current surges so I don't see the point of a series gate resistor to limit load surges. Maybe to protect the TLP251 driver though as the gate capacitance can be substantial.nothing909 said:
As for the flyback diode, just make sure it can handle the transient load current when the IGBT shuts off, and of course the 18V reverse voltage.
FAQ: Calculating resistor for IGBT and choosing flyback diode
What is an IGBT and why is it important in circuit design?
An IGBT (Insulated Gate Bipolar Transistor) is a type of electronic switch that is commonly used in power electronics. It combines the characteristics of both a MOSFET and a BJT, allowing for efficient control of high power loads. In circuit design, IGBTs are important because they can handle high current and voltage levels, making them suitable for use in motor control, power supplies, and other applications.
Why is it necessary to calculate the resistor for an IGBT?
The resistor in an IGBT circuit is used to limit the current flowing through the device. This is important because IGBTs have a limited current handling capability, and exceeding this limit can cause them to overheat and fail. By calculating the appropriate resistor value, the current can be kept within safe limits, ensuring the reliability and longevity of the IGBT.
What factors should be considered when choosing a flyback diode for an IGBT circuit?
Flyback diodes are used in IGBT circuits to protect the device from voltage spikes and reverse current. When choosing a flyback diode, it is important to consider its maximum forward current rating, reverse voltage rating, and switching speed. The diode should also have a low forward voltage drop to minimize power losses in the circuit.
How do I calculate the resistor value for an IGBT circuit?
The resistor value can be calculated using Ohm's Law (R=V/I), where V is the voltage across the resistor and I is the desired current. The voltage across the resistor can be determined by subtracting the IGBT's threshold voltage (typically 5-10V) from the supply voltage. To ensure the resistor can handle the power dissipation, its power rating should also be considered in the calculation.
Can I use a flyback diode with a higher voltage or current rating in an IGBT circuit?
It is recommended to use a flyback diode with at least the same voltage and current ratings as the IGBT. Using a diode with higher ratings can provide additional protection, but using one with lower ratings can lead to the diode failing and potentially damaging the IGBT. It is important to select a flyback diode with appropriate ratings for the specific application and circuit design.
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