How to calculate a Gate resistor? IGBT gate resistor Calculation | MOSFET gate resistor Calculation

hey guys I've received so many comments on my last video which I made on K travel register selection that I actually actually how to calculate the value well I did some research on it and this video is on public demand so let's start well choosing a propagate register is a critical task in order to optimize igbd or mosfet switching loss we already know how important it is to select the propagate resistor if the value of the gate resistor is too high then the switching speed of the device will decrease will be secondary turn on and its participation will increase also if the value of this gate resistance it's too small then there will be effects on a mosfet or igbt like I idea by DT gate ringing voltage overshoot and Emi so there is no thumb rule or a particular method to calculate the right value of the gate resistor in this video we'll see what is the minimum or maximum value of a gate resistor that can be used for our socket there's a method to calculate the minimum value of the gate resistor add a different method to calculate the maximum value of the gate resistor this calculation might work for both igbts and mosfets before we begin with the calculation I would like to give you an disclaimer I found these Concepts and calculation by doing some research on different application nodes research papers related to gate travel resistor I can provide the conceptual knowledge but how will the result of this resistor calculations that can be figured out only after testing it on a proper circuit setup I hope you understand I have added all the references to these calculations in the description now coming back to the video first we'll start with the method to find out the minimum gate resistor value let's imagine we are selecting a gate register for an igbt it all starts with the gate voltage we already know how to determine a gate voltage for the igbt for a particular load or collector current let's consider there is a need of positive tank bolts gate voltage to turn on the igbt and negative 10 volts to turn it off effectively we already know when there is a gate by default it has the input capacitance which needs to be charged first the sooner which are this capacitor the faster the igbt will turn on and so now we discharge this capacitor the faster it will turn off the capacitor is done you provide the voltage to it it will charge right away the capacitor charges with a fraction of second and it Demands a very high current for a small amount of time which might be in the range of several amps and this current is provided by one and only gate travel but providing a very high required current might not be possible for this poor guy there would be some limitations for this driver also right let's check the data sheet of a sample gate server IC ir2010 there are some current sourcing and syncing capabilities mentioned for this driver IC if you check this graph it can Source only one ampere current if the supply voltage is 10 volts now assuming this Supply voltage is the same that we are providing to the igbt gate also it can sink one amp per current while turning off so this is the maximum current that has to flow through the output of the driver IC a basic Ohm's law always helps us in such problems we have the current we need to calculate the gate resistance value now we need the voltage this voltage is nothing but the Delta gate voltage which is the difference between positive gate voltage and negative gate voltage which will be around 20 volts so the minimum gate resistance value would be 10 ohms there are some travel ICS which provide different gate output connections to give dedicated on Signal and off signals for better control over switching of the device such drivers also have different current source and sync ratings we can just replace this formula with it and will have a different value for both on gate resistance and off-gate resistance well we got the minimum gate resistance value but that does not mean if the minimum register value is 10 ohms we can use 100 ohms as well there is an upper limit as well if you use a very high gate resistor value even then the device might be destroyed let's understand it in a better way for igbt turn off is a bit difficult due to the tail current which we have already seen in this video during the turn of operation store charge in the base region must be swept away by the emitter current which is quite tricky and it's also known as the tail current problem but that can be minimized with high switching speed because of the high DB by DT rate this stock is nothing but the change in The Collector diameter voltage with respect to time the higher it will be the faster an igbt will switch but there is a phenomenon that occurs with the mosfets which is called secondary turn on as you already know the igbt has a mosfet on the input side and this secondary turn on occurs due to very fast DV by DT rates on the train voltage which can be in the range of thousands of volt per microsecond although igbts don't typically switch as fast as mosfets they can still experience very high DB by DQ rates due to high voltages this leads to a secondary turn on if the gate resistance is too high let's check this when the gate signal is put Low by the driver the ihbt begins to turn off and connected to emitter voltage starts Rising if this rise in voltage on The Collector is very fast then it generates a voltage on the gate due to the voltage divider of the cgc and cge as the voltage is not constant these capacitors act like short circuit and if the gate resistance is too high the current would not pass within the time and the gate voltage might rise high enough to turn on the igbt back on and this is called a secondary turn on this causes a power loss which can overheat and sometimes destroy the device to avoid that we can use this formula well this is the rate of the rising collector voltage with respect to time at the turn off it is the gate pressure voltage provided to the igbt this is total gate resistance and it is the gate to emitter capacitance and as we know the cge represents the input capacitance and this capacitor value is mentioned in the data sheet this RG is the addition of external calculated gate resistance gate travel impedance and internal gate resistance of the igbt the internal gate resistance of this igbt may be given in the datasheet the travel impedance may be found on the data sheet itself if it uses fat output if it is not then it can be calculated with this formula where VCC is the driver voltage and this is the Peak Drive current which is the source and sink current this parameter is similar to what we just saw earlier now finding DV by DT can be a daunting task it needs a full circuit setup and needs to be measured with high gate resistor let's see the example from an application node this waveform shows turn off characteristics for three different igbts for the same motor application circuit and the value of d by DT is this I have no idea how this would work until an endless we test a proper socket if you know how to do it please let me know in the comment section assuming we get this value from testing then we could use this formula to calculate the maximum value of gate resistance now the RG should be less than 47 ohms here we have to consider the internal gate resistance driver resistance and also Trace resistance including all of those resistance values our gate resistance should be in the range of 10 ohms to 47 ohms well we cannot select a perfect gate resistor but with the help of these calculations at least we got the window of acceptable gate resistance value one more important thing the wire length between driver and the switching device must be as short as possible to minimize the parasitic inductance and resistance value the passwordic inductance and resistance are formed in the travel Loop if the distance between the driver and the device is too much plus if you don't add any gate resistance then an RLC circuit forms which result in gauge ringing we can also calculate the power rating of this resistor with this formula where rgsd gate resistance and this is the peak gate current I hope this video would have been helpful if you are struggling with the gate resistor calculation if you like my video then hit the like button and subscribe to my channel it helps the YouTube algorithm to promote my videos to more electronic enthusiasts like you if you have any questions you can write them down in the comment section or email me and finally thank you so much for watching this video

Channel: Foolish Engineer

Views: 12,179

Keywords: foolish engineer, IGBT, power electronics, switching devices, industrial electronics, motor control, inverter technology, energy efficiency, IGBT applications, high voltage, IGBT module, IGBT driver, IGBT testing, power conversion, IGBT design, renewable energy, solar inverters, IGBT gate driver, electric vehicles, IGBT protection, IGBT thermal management

Id: BsAN09tsi2U

Length: 10min 23sec (623 seconds)

Published: Thu Mar 23 2023