Everything is working with simple passive mosfet drive. But if we increase switching frequency or place powerful mosfet (or even several mosfets)? There is no load in gate circuit, but there is gate capacitance. And if we need fast switching we must charge and discharge gate very quickly. With passive drive there are limitations. We can use active charge-discharge circuit. Also this circuit uses inverter transistor for proper signaling:
Totem pole mosfet drive (push-pull)
Few comments about schematics. R5 is TL494 output load- anything about 1K. R1 is Q1 load, not critical- 1K. Q1 inverts signal from controller. R2 is used to prevent overload of totem pole bases. Q2 and Q3 are complementary pair. R3 are useful if are few mosfets on the output, only few ohms. Q1 and Q3- C945, Q3-A733. All transistors from old PC power supply. R4 – load simulation.
(C945- npn transistor, ~50V, 100mA, 200mW; A733- pnp, ~50V, 100mA, 200mW)
Connect pair of these totem poles and connect to transformer like in older post. You can notice small increase of the performance. Don’t overload. There are lots of parasitic oscillations in this circuit.
Pingback: Savel brain dump in English! » Blog Archive » TL494 - magic chip, Part 4
Googled in following MOSFET driver image, *finally* thought to put the …829a in your blog’s search-box.
Couldn’t find what Vcc was in *this* circuit, but I’ll re-work generic values for 12 Volts ( Lead-acid 10–15
anyway…
Hmm: I’d add a 5v6 zener Gate / Source, but I’m paranoid.
“May The Magic Smoke Remain In Your Circuits !!”
Nik
These schematic dos not work, why because R1 activate Q3 so mosfet is fully ON hotttttt. Just remove R1, R5, Q1, and R2. Connect directly to pin 9&10 and pin 9, 10 need resistor 3.9K to ground. Work nice trust me I spend to much time with this.
Schematics are working and fully tested.
I desagree with Jef because you should take into account that Q1′s base is kept low because of 494 Cx output is active low, so Q1 is normally active => R2 is connected to ground, leaving the MOSfet off