This is actually a continuation of this thread describing making a 3V--> 9V boost converter, but I'm starting a fresh thread since I can't seem to get the answers to the questions I have. Instead, the answers I get mostly go off on tangents that, while they may be interesting, are not actually useful to my project. (I do understand that sometimes it is better to just state what you're trying to accomplish and let those answering determine the best way to do it, as crutschow has pointed out several times. But in this case I have a pretty good idea of what I want to do and how I want to do it.)
So I'd like those responding to really focus on what my specific questions are here.
I've come up with the following circuit which works well in simulation (LTspice, file attached below):
**broken link removed**
Here's what I get from it:
Not too shabby for a couple of AA cells input. In addition, regarding the problems I described in that other thread about getting a decent MOSFET drive waveform, I'm happy to report that it's much cleaner now (see attached pic below). No more ringing!
The problem, and what I'm asking about here, is selecting an actual FET. I chose one that I found (the IRLML6346) available through Digi-Key, very cheap ($0.41). However, this MOSFET is surface-mount (SOT-23). I'm really looking for something more along TO-92 lines, since I'm hand-fabricating my project.
And of course, what's really more crucial are the device parameters. Of course I'd like to see the lowest Rds(on) possible, the lowest capacitance possible, and the highest current and power ratings possible. But I also want to use a small transistor, not a big old heat-sinked TO-3 or something. It's very difficult wading through lists of hundreds of devices trying to find one that's suitable. I actually find Digi-Key's parametric search the most useful here, as you can narrow down your search based on one or more parameters (Rds, power, etc.), but even that is time-consuming and frustrating; for instance, their Rds parameters not only specify the resistance, but also the DS voltage, so you end up going through the parameters one at a time, often returning zero results (since I'm looking for devices I can buy as onesies-twosies, not having to buy a lot of 2,000). So I need help!
Another problem is finding Spice models for them. This one was conveniently included with LTspice. However, there's another one that looks intriguing (the IRFD110, available from Digi-Key). This FET is owned by Vishay, who apparently bought it from IR (hence the "IRF" designation). Vishay has this page that has Spice models for many of their MOSFETs, but unfortunately not for this device. This is very frustrating. One would think that the manufacturer would make the simulation model available as a matter of course (and this is a somewhat mature device), but it seems to actually be much more random or ad hoc than that. In addition, I found nothing through a Google search (the closest you'll get is a link to a 400-megabyte PDF from one of those datasheet archive sites, which only has a list of available Spice models, not an actual model).
And please don't direct me to the Yahoo! Spice user's group. I joined, and searched their file list: they simply don't have a model for this device, so far as I can tell.
Aaaaaargh.
So I'd like those responding to really focus on what my specific questions are here.
I've come up with the following circuit which works well in simulation (LTspice, file attached below):
**broken link removed**
Here's what I get from it:
- Vo (into 10Ω): 7.2V
- Io: 720mA
- Fo: 20kHz
Not too shabby for a couple of AA cells input. In addition, regarding the problems I described in that other thread about getting a decent MOSFET drive waveform, I'm happy to report that it's much cleaner now (see attached pic below). No more ringing!
The problem, and what I'm asking about here, is selecting an actual FET. I chose one that I found (the IRLML6346) available through Digi-Key, very cheap ($0.41). However, this MOSFET is surface-mount (SOT-23). I'm really looking for something more along TO-92 lines, since I'm hand-fabricating my project.
And of course, what's really more crucial are the device parameters. Of course I'd like to see the lowest Rds(on) possible, the lowest capacitance possible, and the highest current and power ratings possible. But I also want to use a small transistor, not a big old heat-sinked TO-3 or something. It's very difficult wading through lists of hundreds of devices trying to find one that's suitable. I actually find Digi-Key's parametric search the most useful here, as you can narrow down your search based on one or more parameters (Rds, power, etc.), but even that is time-consuming and frustrating; for instance, their Rds parameters not only specify the resistance, but also the DS voltage, so you end up going through the parameters one at a time, often returning zero results (since I'm looking for devices I can buy as onesies-twosies, not having to buy a lot of 2,000). So I need help!
Another problem is finding Spice models for them. This one was conveniently included with LTspice. However, there's another one that looks intriguing (the IRFD110, available from Digi-Key). This FET is owned by Vishay, who apparently bought it from IR (hence the "IRF" designation). Vishay has this page that has Spice models for many of their MOSFETs, but unfortunately not for this device. This is very frustrating. One would think that the manufacturer would make the simulation model available as a matter of course (and this is a somewhat mature device), but it seems to actually be much more random or ad hoc than that. In addition, I found nothing through a Google search (the closest you'll get is a link to a 400-megabyte PDF from one of those datasheet archive sites, which only has a list of available Spice models, not an actual model).
And please don't direct me to the Yahoo! Spice user's group. I joined, and searched their file list: they simply don't have a model for this device, so far as I can tell.
Aaaaaargh.
