12V to 300V DC-DC Boost Converter

Its 19V to 300V where does the 19V are coming from, from a batterie?

No, a laptop charger would do the trick. The inrush current is a bit high (around 20A), but it is for less than a ms, so the charger's current limiting shouldn't engage.

А 12V battery should do the trick, with some modifications though.

A laptop charger needs mains 230VAC. From 230VAC there are easier methodes todo 300VDC

Good point

@Hurz you are correct - there are easier ways to get 300VDC from 220VAC, but they revolve around big transformers that are expensive - LC filters for smoothing - basically things that are outdated nowadays. Ideally, a circuit like this one will fit in a matchbox if designed properly.

why "big" transformers? How many watt do you expect to get from this solution here?

All in all it looks overcomplicated e.g. why this triangle generator plus a transistor. Why not a single OpAmp/comparator. I dont see a reason for an extra transistor. Also for the left part in descret form, why not with OpAmps. So many descrets where some of them are not needed. Check this, simplified triangle generator http://everycircuit.com/circuit/6590750574510080 and im sure the left part of descrets can be completely removed. BTW, a high voltage NMos with a 50mOhm Rdson is not so common. Rdson with 1.5Ohm or even higher is more resalistic. So yours here with a width of 200um and 1.5Ω instead of 4.4mm an about 50mOhm is more realistic. Vt with 4V is ok and realistic.

I'll answer you @hurz. The most left part is discrete because it needs to have a somewhat low output in respect to ground. A easy to get op amp for me is TL071, but the lowest output it can achieve in respect to ground is 2-3V. I need less than 1V. I mean, yeah, you can always adjust the offset on the second op amp you see, but that's how I designed it here - you can always modify it. The two other op amps you see are actually a LM311 comparators with a common emitter output, so I'm simulating them as close as possible to what the topology would look life in reality. As for the MOS - you are right. I was originally working on a step up transformer version, which minimises the voltage spikes on the MOS, and forgot to change the transistor afterwards. Thanks for the heads up BTW.

I'm planning to use an IRF740, so that's 600um at 4V Vt

Thats why im asking, and i had the feeling its not an opamp its an comparator. The extra external transistor does bring an inversion in logic. Thats importante to mention. If i do that, i limit the output voltage to around 817mV and connect directly the transistor default model, which emulates then a 20mA current sink output of an comparator perfectly. http://everycircuit.com/circuit/6172670572625920 BTW, 20mA which most comparators drive is not much enough to pull 310 Ohm down to zero. Lookup the spec if your comparator can drive more then 20mA. Anyway, IRF840 i looked up with Rdson 0.85 Ω while IRF740 will have 0.55 Ω, lets check if 600um is good for 550mOhm. With 600um is see 472mOhm and with 500um its closer 566mOhm

There is now an IRF740 in the library, you could try if you like.

I dont like some of the Library settings, cause i love it to code for example 740um for IRF740 the width so i do not need to remember one value. Lenght i try to set as small as possible while Kp is used to finetune. In best case i just need to remember one value Kp. Another example for IRLB3034 width 303um length 4nm Kp results is 1.24mA/V² so i just have to remember this 1.24mA/V²

Easiest the best, thanks @hurz,.

I'm thinking of an LM311 comparator, which has an output current sink of around 50mA I think.

An improvement might be if you use a step up transformer on the output instead of a regular coil. This way, you can go with a lower Vds mosfet, and lower Rdon. Most mosfets have lower rdon at lower vds voltages. The step up output transformer will create lower voltage spikes at the drain of the transistor.

Although, there are some MOSFETS out there that are very decent - for instance the SPP20N60C3 has a Vds of 650V at Rds of 0.19R which is very convenient in our case.

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