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No, I don't have any snubbers on the fets of the H-bridge.
Thanks for the diagrams. Okay, so I'm a little confused. The PWM outputs from the IC, do have the appropriate deadtime. They look like your "correct" diagram. In the second pic the blue line is the upper fet, so this wave is also...
Well, unfortunately it isn't the CS that is killing the H-bridge. I have tied the CS pin to VSS with the same results.
The same thing keeps happening, which is the left side MPSA42 breaks down and shorts the gate of the high side fet to ground. This happens only at higher loads, specifically...
Thanks so much for your help. The BJT overheating issue is solved! The load current was taking the wrong path. I replaced my Rs and removed the 6800pF caps.
Now, I have a new problem that I was hoping you could help me with. I went all the way up to a 75W load and the AC voltage begins to drop...
Hi Alterlinks, thanks for the analysis.
Originally, I thought it was only one side, apologies.
I guess I wasn't clear enough in my latest post. This is happening on both upper sides, both MPSA42s get cooked with a load. I know all legs of the H-bridge need to be balanced. I only increased the...
No, the fets are fine. I haven't destroyed one of those yet. It is the MPSA42s that keep burning up. I have increased the 200 Ohm resistors to 30K, and placed another resistor between the charging diodes and the collectors. I have also increased the base resistance to 820 Ohms. They still cook...
Howdy, I am trying to use a TI UCC28089 PWM controller, that has a modified square wave H-bridge inverter schematic on page 11. I have built and tested the circuit, driving it with 155V. The circuit works just fine without a load. With just a 7.5W bulb as the load the circuit starts whining a...
Right, I had to dramatically decrease the current sense resistor values, and even added one in parallel (hence R83) to deal with the large amount of current. It does exactly that, limits the switching current to 100A. Previously, I had a .2 Ohm current sense resistor but the output voltage...
Try using a NPN transistor such as the 2N3904 as the switch instead of the NMOS. The transistor is current controlled unlike the gate of the NMOS which is voltage controlled. Make sure to put a resistor on the base and a resistor in series with the LED.
I used a couple of different equations from app notes or online. The easiest one that I remember is Cin = (1uF/W)(Pin), and depending on efficiency Pin changes. If you know an equation or capacitor value that is best for my design please point me in the right direction.
Probably not, how would...
The supply is designed and intended to supply 200W.
I agree with low ESR and the value should be increased, but 10,000uF seems excessive. How do you validate this value? From calculations for Cin, I get anywhere from 80uF to 330uF.
Hi, thanks for responding. I am about 98% sure that the input capacitor blew first. Could this be caused by ripple current? After, Cin blew, I noticed U10 had a pin size hole near the VCC pin. Next I replaced U10, left off Cin, and M4 was not operating anymore. So I don't know if it happened all...
Hi all, I had posted a long time with a project for a 12V to 110VAC inverter. The front end that creates the high voltage needed by the H-bridge is a 2-switch forward converter. It takes in 12V and produces 155V, and it works up until it breaks. Looking at the schematic, C14 (Cin) blows and then...
Hi, I'm trying to design a test fixture that will test for continuity on multiple wires (traces, solder joints), but I am concerned about the current that will be applied to the powered off ICs. The test fixture also injects signals onto these wires so there has to be a disconnect from the...
Hi, I am new to using PADS layout and am currently editing a design. Every via has a "plane hatch void" surrounding it.
How are these created? When I insert a new via what do I do to get this "plane hatch void" outline?
Thanks!
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