Automatic Pulse Width Modulation 40V to 20 or 30V Buck Convertor

205

03:11:45

This automatically adjusts the pulse width to attain the right output voltage. You can see it in action by flipping the switch to switch between 20V out and 30V out.

published 8 years ago

hurz

8 years ago

And whats the 555 for? http://everycircuit.com/circuit/6664770290974720

jason9

8 years ago

Pulse width modulation of course! I’ll check out that link in a moment.

hurz

8 years ago

The 555 is a horrible voltage controled PWM generator

jason9

8 years ago

I see. The 555 timer locks the frequency within a certain range.

jason9

8 years ago

A better pulse width modulator would use a triangle wave (possibly generated by a 555) and a comparator. I didn’t think about that when I made this circuit and anyway it might look messy.

jason9

8 years ago

I tried that and the simulator doesn’t cope too well with that method. Apparently there aren’t that many solutions with that method and far too often there is no solution.

hurz

8 years ago

Right, the same is problematic in your previews thread. EC stability for regulating loops is horrible. Anyway, this other thread is poisoned by a messy troll who believes he solves mankind problems by mess up mosfet settings. Sorry for that idiot.

2ctiby

8 years ago

@jason9 ... nice to see that the Mosfet alteration enabled you to continue. I notice that the suggested Pmos is in place here too.

jason9

8 years ago

Right. The NMOS would’ve worked just fine if it could’ve gone through a couple of cycles allowing the bootstrap capacitor to charge allowing the gate to be lifted well above 40V.

hurz

8 years ago

Take care about maximum Vgs its for most MOSFETS below 20V or even less. The 555 does already the right logic, inverting twice is only need if you drive the gate with full 40V swing, which will kill it. Anyway there are more elegant ways to bridge form 555 to supply level. Check this http://everycircuit.com/circuit/4598834113282048

jason9

8 years ago

Clever.

jason9

8 years ago

The only issue with that is the higher MOSFET resistance. This will reduce the efficiency significantly that it will produce a good amount of heat and the resistance is so high that even with a 100% duty cycle it can’t even reach 30V with a 1ohm load creating over 300W dissipation if it attempts to do so.

hurz

8 years ago

Its your mosfet, I just changed the way to drive it. Make Rdson as low as you wish to have, and you can buy one.

hurz

8 years ago

Note, 555 cant give you 100% duty cycle, only then this capacitor bridge can work and makes sense, it needs continues activity on/off. Anyway,

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