Single non-isolated gate driver WITH MILLER CLAMP. Wanted! - Page 1
Forum section: electronics / general

author: MikeP
author_rank: Regular Contributor
timestamp: November 14, 2020, 09:15:12 am
content: Hello.I probably wasn't working hard enough... However, I didn't find what I needed: a single, non-isolated gate driver with Miller-clamp. The required current is 3-5A.All offered components with the Miller-clamp function are insulated... I'm very surprised.I will be very grateful for help.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 14, 2020, 11:00:56 am
content: Well, Miller clamp is typically used with very large IGBTs where you do want to use gate resistance to limit turn-off speed somewhat, yet at the same time, donotwant to use gate resistance to keep the IGBT reliably off while the another IGBT of the bridge switches. With the separate Miller clamp pin, the gate resistor is selectively bypassed, offering gate resistance during the initial phase of turn-off, but then bypass Rg at the end of turn-off.The question is:Seeing you don't want isolation, you are likely building a smaller converter, running lower power, likely using MOSFETs, no? Why do you think you want to have the Miller clamp feature? What are you actually doing?

author: f4eru
author_rank: Super Contributor
timestamp: November 14, 2020, 12:54:43 pm
content: doesn't the low part of the Half-brige in the driver act a a miller clamp ?I recommend the LM5110 or any similar device with both channels in paralell.

author: langwadt
author_rank: Super Contributor
timestamp: November 14, 2020, 01:14:48 pm
content: Quote from: Siwastaja on November 14, 2020, 11:00:56 amthere are also several gate drivers with separate sink and source outputs that can accomplish the same

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 14, 2020, 01:37:37 pm
content: Quote from: Siwastaja on November 14, 2020, 11:00:56 amThat is absolutely not the case, a large IGBT has big Ciss and thus higher ratio of Ciss/Crss than most power mosfets, in which the shoot-through problem is worse. Compounded with the slower dV/dt of a igbt vs mosfet, clearly although the miller-clamp can be used in both, is more interesting in high voltage high speed mosfets.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 14, 2020, 02:19:43 pm
content: Quote from: f4eru on November 14, 2020, 12:54:43 pmGoogle it for proper explanation. Like I said, the idea is to provide two different gate resistances for low output level; use higher gate resistance in the beginning of turn-off, then go to lower Rg after Vg is below about 2V. You can build this from several discrete components, but if you need it, it's handy it's done by the IC manufacturers for you.But IC manufacturers only build things that are ordered in large enough number. It seems the combination of non-isolation and miller clamp isn't on that list.

author: Weston
author_rank: Regular Contributor
timestamp: November 14, 2020, 08:22:34 pm
content: Why do you care if it's isolated?The isolated drivers typically still have pretty fast propagation delays and delay matching and are not really any more expensive than the non-isolated drivers.

author: MikeP
author_rank: Regular Contributor
timestamp: November 15, 2020, 09:00:44 am
content: Friends, thanks. The driver is already isolated, quite complex. I want to reduce the number of components. Unfortunately this is not possible. I don't use IGBT.