Off-the-shelf flyback transformers for a 3-phase inverter gate drivers - Page 1
Forum section: electronics / projects

author: sbat
author_rank: Newbie
timestamp: October 07, 2024, 07:01:49 am
content: I'm in the process of developing a 3-phase inverter and I'm designing a flyback DC/DC for the gate drivers. I feel this is a common use case so I expected I'd find more flyback transformers with a single primary, an aux and 4 secondary windings (one for each phase high-side switches and one for the low-side switches). So far I've been able to find only TDK VGT series, but I'm not happy with the turn ratios and inductances.https://product.tdk.com/system/files/dam/doc/product/transformer/transformer/gate-drive/catalog/trans_gate-drive_vgt_en.pdfAm I wrong in assuming this would be a common use case and I'd expect to find more transformers, or am I just not searching for the right thing?This will not go into production, I'm just looking to make a few prototypes so I'm looking to avoid designing my own custom transformer.

author: jonpaul
author_rank: Super Contributor
timestamp: October 07, 2024, 07:28:28 am
content: coilcraft, pulse electronics off the shelfj

author: Kleinstein
author_rank: Super Contributor
timestamp: October 07, 2024, 07:29:12 am
content: This looks like an odd idea. It would need 4 well isolated secondaries, which is tricky with a small flyback, as a flyback wants tight magnetic coupling.I don't think a flyback to power the high side gate drives is already rare. The more common versions are a diode and capacitor or the transformer directly for the gate signal.So probably a bad idea and not just the wrong search term.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 07, 2024, 08:35:30 am
content: Quote from: sbat on October 07, 2024, 07:01:49 amThat would need good insulation between windings.More common is 3 x smaller, simpler transformers - maybe work backwards from simple drivers ?Likehttps://www.nexperia.com/products/analog-logic-ics/isolation/transformer-drivers

author: sbat
author_rank: Newbie
timestamp: October 07, 2024, 09:27:40 am
content: Quote from: Kleinstein on October 07, 2024, 07:29:12 amI've looked into the idea of using gate drive transformers a bit, it seems to me that they are used at higher frequencies. I'm planning on switching with 16kHz and 18V, which would make my V*t product 1125uVs and with a quick search of Wurth electronic gate drive transformers i noticed most of them are in the range ~50-100uVs. Unless my logic is wrong, that would make the gate transformers saturate way too soon.As for the bootstrap method, it's my understanding that this method is used for lower voltages and I'm planning to upscale this prototype to 600V at a later stage.One other reason why I assumed the flyback configuration would be more common is that the Tesla model 3 inverter uses it as a main power supply option for it's gate drivers.

author: Phoenix
author_rank: Frequent Contributor
timestamp: October 07, 2024, 11:56:55 am
content: At 600V bootstrapping is perfectly fine, just use a fast 1000V diode. Main drawback is no negative gate drive rail and can't operate 100% duty cycle.Otherwise it's also very common to use a small transformer on each switch to supply the rail. Either with a dedicated transformer driver ic like that from nxp or ti, or with an oscillator and power driver to run multiple transformers.I have also seen running three secondaries from the main aux flyback for gate drive supplies but custom transformer using flying leads. Isolation and pcb layout will be interesting with a transformer like the ones you linked. Also need to make sure they have appropriately rated sec-sec withstand.Finally 16 kHz is very low for an aux supply. They normally operate around 130 khz (just below the conducted emissions band).