Re: 555 to drive mosfet/igbt
- From: "jsmith" <juddo@xxxxxxxxxxxxx>
- Date: Sat, 2 Apr 2005 16:45:28 -0500
Possibly you may not need the electrolytic capacitor since your B+ is a
battery??
"kell" <kellrobinson@xxxxxxxxxxxx> wrote in message
news:1111729615.820255.39480@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> I was experimenting driving various mosfets and igbts with a NE555 at a
> low freq around one per sec turning a small bulb on and off just to
> check how well the 555 works before I try to build the actual circuit I
> have in mind, which will have an inductor operating at a few KHz in a
> topology similar to a boost converter. (The inductor is intended to
> reach a peak current of several amps.) I used no gate resistor, just
> connected pin 3 directly to the gate.
> Anyway, when I tried the IRF740 and a IGBT designed for car ignitions
> (HGTP14N...), which both come in the TO-220 case, the bulb turned on
> and off cleanly. But when I tried a couple of devices that come in the
> big TO-247 case, the bulb didn't turn off cleanly. With the IRG4PC30F
> IGBT, the bulb dimmed before it turned off. With the STW18NB40 mosfet,
> the bulb didn't even turn off, it just flickered a little.
> I used a sealed lead acid battery and connected the Vcc pin of the 555
> through a 75 ohm resistor to B+. I had a 100uF electrolytic across the
> power pins.
> I was powering the 555 through a resistor because that is the way I
> intend to use it in the final circuit, as a way of protecting it from
> the inductive spiking.
> What is it about these big mosfets and IGBTs, that a 555 can't turn
> them off?
>
.
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