Rate this discrete gate driver circuit - Page 1
Forum section: electronics / projects

author: Dabbot
author_rank: Regular Contributor
timestamp: November 16, 2023, 11:33:12 am
content: A discrete gate driver circuit I came up with while working on something else. I did consider the usual suspects but there were no real constraints for this.Pros:- Rail to rail- Configurable rise and fall times via R4 and R5 gate resistors- Configurable logic level via R1 and R2- Separate logic and gate drive supplies- Inverting (pictured) and non-inverting (swap Q1 Q2 common-base and common-emitter connections)Cons:- Discrete and probably slow (<1uS from measurements on the breadboard)- Shoot-through (Mitigated by R4 and R5. Can be further mitigated with baker clamping on Q3 and Q4)- A bit partsy (Jellybean parts though)Edit: Added b-e resistors to Q3 and Q4

author: magic
author_rank: Super Contributor
timestamp: November 16, 2023, 06:56:24 pm
content: I had a similar idea, but also tie Q1 and Q2 bases together to reduce shoot-through. They could be biased to VCC/2 or driven by another GPIO. If the latter, two GPIOs should switch in anti-phase. Setting them equal makes the driver output hi-Z - not a great idea for gates, though maybe useful for other applications.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2023, 08:55:21 pm
content: Q4 & Q4 could do with base-emitter resistors.

author: MarkT
author_rank: Frequent Contributor
timestamp: November 16, 2023, 10:02:16 pm
content: Well its got stored-charge issues and Miller effect slowing it down. This is why FETs make a good choice for gate drivers being capable of snappy switching and and switch off as fast as they switch on. But why not just choose a suitable MOSFET or IGBT drive chip.100 ohms is very high output resistance to drive a big MOSFET, again slow... Checkout my fave driver chip, MIC4422 (inverting version MIC4421) for what you are competing with.

author: boz
author_rank: Regular Contributor
timestamp: November 17, 2023, 12:15:07 am
content: What voltages are we talking about ?

author: xavier60
author_rank: Super Contributor
timestamp: November 17, 2023, 01:52:30 am
content: ST has a family of Gate drivers that might be useful to know about. Ill likely never use anything else.This part has the option of separate outputs or single plus Miller clamp.https://www.st.com/resource/en/datasheet/stgap2hs.pdfSO-8WideEdit: beware of parts that are intended for driving SiC MOSFETs which can have UVLO voltage which is too high for Si MOSFETs.SO-8 versionhttps://au.mouser.com/datasheet/2/389/stgap2s-1499130.pdf

author: Dabbot
author_rank: Regular Contributor
timestamp: November 17, 2023, 07:31:08 am
content: Quote from: magic on November 16, 2023, 06:56:24 pmIn the schematic they are tied together and biased at half the logic supply.Quote from: magic on November 16, 2023, 06:56:24 pmI might give this a try. I'll just have to be careful not to reverse-bias Q1 and Q2 b-e junctions too far.Quote from: Zero999 on November 16, 2023, 08:55:21 pmOops. I missed that. Thanks!Quote from: boz on November 17, 2023, 12:15:07 am12V gate drive, 5V logic.Quote from: MarkT on November 16, 2023, 10:02:16 pmQuote from: xavier60 on November 17, 2023, 01:52:30 amI do have some gate drivers on hand. Both of those are some very nice options. Noted for my next digikey buy.This application wasn't very demanding speed-wise, so I tried a discrete approach.

author: xavier60
author_rank: Super Contributor
timestamp: November 17, 2023, 07:57:15 am
content: I have added an important edit to Reply #5.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 17, 2023, 05:04:33 pm
content: You might find this of interest:https://www.seventransistorlabs.com/Images/Diode_Recovery_Tester.pdfI later added a complementary emitter follower output anyway, which somewhat obviates the slope control due to its current gain, to get moderately-fast dI/dt out of a moderately sized (ballpark 600V 20A) transistor. A little Miller capacitance (from follower output to driver base) could be used to control gate dV/dt again, and thus drain dI/dt to an extent.Typical current rates are on the order of 500A/us:That's 5A/div and 20V/div. DSEP29-06A, If = 10A, t_rr ~ 44ns, dI/dt ~ 500 A/us (kinda has two slopes either because of uncompensated stray inductance in the shunt, source inductance, or transistor characteristics), Irr ~ 13A. Which I think was using a STP19NM50N for the switch.Tim

author: Zero999
author_rank: Super Contributor
timestamp: November 17, 2023, 06:37:28 pm
content: I posted a similar circuit here a few years ago. It doesn't have the output resistors, which are a good idea.https://www.eevblog.com/forum/beginners/op-amp-as-buffer-not-behaving-as-expected/msg1535255/#msg1535255

author: Dabbot
author_rank: Regular Contributor
timestamp: November 17, 2023, 10:20:16 pm
content: Quote from: T3sl4co1l on November 17, 2023, 05:04:33 pmI'm looking at D6 and D13 amongst the b-e resistors. Keeping the drivers out of saturation?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 17, 2023, 11:10:21 pm
content: Crude Vbe compensation: they're current sources.Tim

author: Dabbot
author_rank: Regular Contributor
timestamp: November 17, 2023, 11:55:49 pm
content: Quote from: T3sl4co1l on November 17, 2023, 11:10:21 pmI see it now.