How can I make a bipolar isolated DC-DC power supply for gate drivers? - Page 1
Forum section: electronics / beginners

author: JonasConstant
author_rank: Newbie
timestamp: March 09, 2023, 09:12:29 am
content: Hello all,I want to design a gate driver board to drive 6 SiC MOSFETs/PWR IGBT where the VBus can go up to 1200V. I need to use an isolated DC-DC power supply that can make dual bipolar rails (+15V/-8V or +15/-5V) from a 15V input, something like in the image (65.png).Q1: for this kinda application (1200V/100A), Is it necessary to use this approach, meaning all gate drivers are powered with individual isolated power supplies? or is it ok to use the approach where (lower gate drivers are powered with a common power supply and each high-side driver with its own power supply (66.png))? [ Attachment Invalid Or Does Not Exist ]I used the formula found in the document below to calculate IGBT drive power and it came out to be 1.5W, meaning that a 60-80mA for each power rail would be enough.https://www.ti.com/lit/an/slla354/slla354.pdfP(drv) = Q(gate) * f(in) * DeltaV (gate)Q2: Is this method of calculating drive power for IGBTs right?I tried looking into some reference designs for bipolar DC-DC power supplies for gate drivers but I didn't find any that matched my needs because most of them either have a custom-made transformer or a chunky and expensive one.Here are some reference designs I found:Isolated Push-Pull Power Supply Circuit:https://www.ti.com/lit/ug/tidue55b/tidue55b.pdfIsolated Bias power and Gate Driver daughter board:https://www.ti.com/lit/df/tidmaw5/tidmaw5.pdffinally, I found this design below which actually looks like a good choice but the design is a four-layer board with a high component count:Isolated IGBT Gate-Drive Push-Pull Power Supply with 4 Outputs:https://www.ti.com/lit/an/slla354/slla354.pdfIf I have to go with the (all gate drivers are powered with individual isolated power supplies) approach, I need to have a low-cost, small-footprint power supply to go with the small form factor gate driver board I am designing! hence, I would appreciate any suggestions, or tips on how to make these types of DC-DC power supplies for gate drivers?Also, I have been told that gate driver transformers can be used for this kinda application i.e. as a power transformer and not as a gate signal isolation! If this is true, this could be a good thing for me as they are usually smaller in size and cheaper.Thanks,

author: Psi
author_rank: Super Contributor
timestamp: March 09, 2023, 10:18:15 am
content: Please fix your links. atm I cant right click open any of them because the tags are messed up.One option if your BOM can handle it is isolated DCDC modules.These sort of thing. They come in many different input voltage ranges but you get 12V out at 83mA or 15V at a little less current.https://www.digikey.co.nz/en/products/detail/mornsun-america-llc/B0312S-1WR3/16348126

author: JonasConstant
author_rank: Newbie
timestamp: March 09, 2023, 11:46:44 am
content: If I use isolated DCDC modules that means I have to use 6 of them which will be very expensive.Plus, I haven't seen them being used in high-power products before so I don't know if they are that reliable.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 09, 2023, 03:29:40 pm
content: Gate drive transformers are easy to apply and they don't need any HV side support circuitry- have a look at, for examplevacuumschmelze.com/products/Inductive-Components-and-Cores/Gate-Drive-Transformers, about $6.

author: JonasConstant
author_rank: Newbie
timestamp: March 09, 2023, 04:29:17 pm
content: Quote from: Terry Bites on March 09, 2023, 03:29:40 pmI don't mean to use the GD transformer to isolate gate signals because the gate driver I am using already has a 5kv reinforced isolation barrier but rather I wanna use it as a power supply transformer to form an isolated power supply (isolate input voltage rails from gate driver rails).

author: jmelson
author_rank: Super Contributor
timestamp: March 09, 2023, 07:04:15 pm
content: Quote from: JonasConstant on March 09, 2023, 11:46:44 amGenerally, ONLY the high-side drivers need to have isolated power, all the low-side ones can use common power rails.Jon