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low budget low voltage uc3842 h-bridge

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kerver

Fri Apr 27 2007, 08:09AM

Registered Member #522 Joined: Thu Feb 15 2007, 01:04AM
Location: The Netherlands
Posts: 33

Hello, Guy's (i never see a female here)
This is my first post

I read the forum for a few years now with fun en joy en think it is time start with something simple.
So here it is a low budget uc(un controlled)3842 half bridge.... from the low lands, yeah i life behind a wall next to the sea.

I ad the circuit layout later.

Dalus

Fri Apr 27 2007, 12:20PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Looks nice, but where are youre zeners and resistors on the gates. And what are you going to do with it drive a small SSTC? Here's an idea, the decoupling caps are on the back of the heat sink.

kerver

Fri Apr 27 2007, 01:58PM

Registered Member #522 Joined: Thu Feb 15 2007, 01:04AM
Location: The Netherlands
Posts: 33

Hi Dulas,
Your bridge looks very clean.
Mine is cut in 2 parts becouse it wash a clean full bridge first.
I don't have any zeners laying here, En i drive it with 16 volt.
But there are very nasty spike's on the begin en end of scoop picture

I use 30 volt 75 ampere fet's from a old ups battrey charger, Boght it in a army dump store 4 euro for 48 fets. (very robuste one's)
It is a hip4082 controller with 4 half bridge's i want to drive a coil with it ,but didn't make same time to check the layout of it.

Dalus

Fri Apr 27 2007, 03:04PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

You really need fet's with a higher voltage rating to drive a sstc, I'm using 450 volt fet's for my bridge. Maybe you can post some scope pics so i can find the cause of your voltage spikes.

kerver

Sun Apr 29 2007, 11:12AM

Registered Member #522 Joined: Thu Feb 15 2007, 01:04AM
Location: The Netherlands
Posts: 33

Here i the schematic.
I now it is not perfect but i draw it fast en it is a low budget vercie.
It works. Nothing more

Sulaiman

Sun Apr 29 2007, 11:30AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I also think that the voltage is a little low for good results,
but once it's working you could EASILY convert to dual-resonance mode
where Lp x Cp = Ls x Cs in other words,
make the primary a series resonant circuit at the same frequency as the secondary.

You could either put a 'tuning' capacitor in series with the primary inductor, or better,
change each of the 1uF capacitors for half the required capacitance, and put the two 1uF capacitors across the supply.

Add a fuse (or circuit breaker) because if the UC3844 operates at exactly the resonant frequency,
the current draw will be enormous!
(an interruptor or stochatto circuit is usually used to limit the current rise)

The result will be DRAMATICALLY different.

P.S. a DRSSTC is a good transistor killer

Dr. Shark

Mon Apr 30 2007, 10:10AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I am surprised the 3842 can source enough current to drive the gates all by itself; Is suppose once you get into Tesla Coil frequencies and voltages you will have to add gate drivers like the TC4422 you can sample here

But then, if you are really going for an SSTC, you better go the whole way with 600V devices, protective Zeners and Varistors etc.
The circuit you have now seems ideally suited to motor control or robotics, so if you want to swap some 30V FETs for 600V FETs let me know

kerver

Wed May 02 2007, 06:03AM

Registered Member #522 Joined: Thu Feb 15 2007, 01:04AM
Location: The Netherlands
Posts: 33

Hello,
So, i have found 2 tc4420, 2 irf2125, gate drive chips 6 irfp460, 2 irf840, 2 irf44 fets en 2 hip4082 en a couple of tl494 in my big used parts store.
Also 4 foil 1uf 630 volt caps, waiting in a box with a lot of big en small (ferriet) trafo's en flyback's.
Now i start to buils a function generator with a xr2206 wich i found to 2, with a bit luck it do 1 mhz.
I now going to look at some picture's here in the forum to build mi full-bridge so i get some idea's for mine.
Is it better to use thermale pads under the fets? when i use 4 seperate cooling blocks?
Futher can somebody help mi with the design with seperate board setup, like drive board > gate drive boards > main (2 half?) bridge boards.
The problem is i don't have a non inverted gate driver.

Thanks

uzzors2k

Wed May 02 2007, 10:17AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Thermal pads improve the contact to the heatsink, and provide insulation, so I would put some on. Handy incase you ever touch the heatsink!

Marko

Wed May 02 2007, 08:18PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Kerver: don't turn mad at me, but there are few critical things that none mentioned among others:

UC3842 is a current mode controller with widely variable duty cycle, and generally very troublesome to set up for a SSTC. NE555 would probably be easier than it!

Your GDT configuration splits voltage in half, and as I see you are using 1:1:1 GDT?

SG3525 would be much better solution in general, but still, for a SSTC, self resonant setup will spare you much of trouble and probably blown mosfets.

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