neddie
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Best RegardsYes you can , but you need a pretty precise driver ! because if both of them don't be on at the same time , both will born ! you'll need some feedback loops to be sure about on time and off time .
Hi AlbertThanks goldsmith.
It was not my intention to advice it for series transistors but for a single N-channel high side mosfet. If I understand correctly a pulse transformer (and associate circuit) is a suitable driver for series transistors ?
Certainly . For such a application ( if we use a power element in high speed system ) we've to take feedback from current and voltage and also from driving signals . but in this application ( a power element just as a key , it can be neglected and with some simple tricks he can handle this aim )I would like to know more about the feedback circuits that you mention here:
Hi dear FvMThe discussion seems to me somehow bloodless without considering application parameters. The problem discussed in the original post would be usually solved with a single 1000 - 1200 V N-MOSFET or IGBT and isolated gate driver. It's no good example for series connected switches.
Other applications have quite different requirements. I've seen series connected MOSFET e.g. for kV/ns pulse switches. Power electronic would refer to HV IGBT (6.5 kV rating is state-of-the-art) and think about series connection above e.g. 2 or 3 kV.
I don't think capacitive voltage dividers or RC snubbers will be effective in equalizing the voltage drop if the circuit ever has to maintain the "off" state indefinitely. For DC, capacitors cannot compensate for a mismatch in open resistance. Varistors may do the job if their leakage resistance is matched. But how are you going to ensure that? They don't generally spec two-sided limits for varistor leakage resistance.Tunelabguy
Very interesting point.
Do you think that placing RC snubbers would form a capacitor voltage divider to equalize the voltages? As capacitor voltage dividers work in DC too.
Can varistors in parallel do the job?
Best Regards
Hi dear FvMI understand that he thought a PMOS switch would be a simple solution to switch a load connected
I agree ( completely ) .As soon as you need to consider series connected switches, that require some kind of floating driver, you can better go for a single NMOS or IGBT. It utilizes a floating switch too, but with less overall effort. That's my simple point related to the original post.
Arc ? why arc ? speed of switching isn't high , and there are many many contactors available for high voltages too .I wonder, if forum members suggesting contactors for switching 800 V DC have ever seen a high current DC contactor. It's a really bulky component, involving a large arc quenching chamber, or made as a rather expensive vacuum contactor.
He has mentioned in his other posts that just like a key .P.S.: It's not clear at all, if the nature of application (switching frequency, speed) allows contactors at all. Thus I didn't refer to it in my post.
Hi AlertlinksCan a IRG4PH50U driven by a pulse transformer with a snubber network can't do the trick?
I think we agree about preference for single switches if applicable.
Arcing will mostly happen when breaking a circuit of sufficient operation voltage or inductive loads. In AC switching, the arc is quenched during the next current zero crossing, for DC, special means are required., e.g. magnetic blowouts and arc quenching chambers.
A simple method for isolated MOSFET gate drive would be a photovoltaic coupler. Unfortunately it's rather slow (ms range), so it causes additional switching losses unless combined with some kind of bistable waveform shaper. Pulse transformers can be supplemented by circuits that convert pulse trains to static gate signals. Both methods (photovoltaic and transformers with signal conversion) are used in DC solid state relays.
i have study IRF840 and other mosfets. those have PULSED Current parameter. i want to use that.
You are right. It's difficult to get a clear picture about what the original poster wants. If it's pulsed switching for a limited period, a gate transformer might work.In post#4 he is talking about non repetitive pulse.
You are right. It's difficult to get a clear picture about what the original poster wants. If it's pulsed switching for a limited period, a gate transformer might work.
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