Totem pole gate drivers on the web are poor - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: October 09, 2022, 01:27:45 am
content: Hi,All the totem pole gate drivers i find on the web dont have the "extras" that are needed to make this work well.Eg, they dont have an upper Darlington for the upper txtor of the totem pole.And thus they lack the added circuitry to sweep out minority carriers from the Darlington to make it switch faster.They also lack the cctry added to sweep out the minority carriers from the lower PNP of the totem pole.Also, the web offerings lack the diode used to reduce cross conduction.As you know, the easiest way to do totem pole driver is to actuate the totem pole with a low side common emitter BJT to pull down the centre point....and a resistor to pull up the centre point..But as discussed, the ones on the web are all pretty awful.Do you know of any with the needed "extras"?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 09, 2022, 01:38:19 am
content: Whose totem pole are you sniffing up this time?I haven't used a bipolar gate driver in......ever? Oh, there was probably a BiCMOS one I used. That was fine. Most are CMOS. Do you mean "totem pole" because the high side is a source follower? Those are out there. Hm but no, you're clearly talking bipolar. Do you mean discrete circuits? Who bothers with that?I suppose if one wanted to make a really powerful, reasonably fast, discrete stage, one could do something like this...You know, the usual, copyrights reserved, patent pending, if laid out improperly your dick will rot off, etc...But that's a lot of components and layout space for not a lot of value.Tim

author: tggzzz
author_rank: Super Contributor
timestamp: October 09, 2022, 09:35:54 am
content: Quote from: Faringdon on October 09, 2022, 01:27:45 amAh, another wonderful treez/faringdon OP.Make what work well?What's a "txtor"?Which "web offerings"?Define "awful" and by extension "not awful". I use that word in the same vein as Humpty Dumpty used "glory".Quote from: T3sl4co1l on October 09, 2022, 01:38:19 amArguably that's too polite

author: Faringdon
author_rank: Super Contributor
timestamp: October 09, 2022, 02:51:54 pm
content: Thanks,I said "totem pole"...but i now hear that these things are better termed "symetric pushpull driver"Anyway, the high switch is a NPN Darlington.The bottomn switch is a single PNP.There is a 1N4148 diode between the bases of Darlington and PNP (cath to PNP base)There is a CE BJT which pulls down the centre point to turn on the PNP...and a 4k7 pullup which turns on the upper Darlington.It makes you wonder what the diode is for between the bases.I wish i could show the schem but am restricted......ours also does have a BJT/Zener "thing" which stops it giving gate pulses when the high side gate drive rail falls too low.......there is then a 1MEG resistor from that circuit to the base of the PNP....and its this 1MEG that i cant work out what its for.......getting rid of it on the LTspice sim makes no real difference to the switching.....however, the 1MEG does keep current flowing in the diode between the base's when the Darlington is ON....so i wonder if its to make this diode turn on quicker?....ie, turn on quicker when the PNP gets turned ON?......Also, when the (upper) Darlington is ON, the base-to-base diode would have very low voltage across it if it werent for this 1MEG....so maybe this is it...ie, it keep the base of upper and lower switchs apart from each other when the upper switch (DARLINGTON) is ON?....this may lead to even less shoot-through i am wondering....or in fact, by keeping the base-to-base diode in conduction when the Darlington is ON....then maybe there is a minority carrier sweep-out path for the PNP?...thus the PNP turns ON and OFF quicker.?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 09, 2022, 10:32:44 pm
content: Oh that's not even a switch, that's a complementary emitter follower. Well, not very complementary if one isn't Darlington, but...Tim

author: Faringdon
author_rank: Super Contributor
timestamp: October 10, 2022, 05:15:46 am
content: QuoteThanks...AYK, its a "switch driver"...A "FET driver".......do you think its properties make it poor at this?