apply that to pin 5 of a 555 and you get a pwm output on pin 3. the 2-comparator design is essentially a 555.Here is the control:
whether you need a mosfet driver will depend on the factors I outlined earlier.
apply that to pin 5 of a 555 and you get a pwm output on pin 3. the 2-comparator design is essentially a 555.Here is the control:
Either the MCP1407 or the slightly more expensive TC4420 that dannyf recommended would do fine. Digi-Key stocks both.What kind of MOSFET drivers should I be looking for that I can use with that comparator PWM design, or even for a 555 PWM design?
I like that FAN7311 has both a low and high side driver (forward/reverse?) but it is harder to come by.And there are so many 'half bridge drivers' that come in 8pin dip IC's that is what I buy. They have a high and low side driver in them. But either one can be used on it's own, so you only need one chip. And it only takes the same board space as a 555. Then when you "need" a H-bridge you can use two of the drivers. I like the FAN73xx(Fairchild) series of drivers, because of their higher amperage capability.
I'm fairly new to the world of electronics so take this with a grain of salt. From my research on this the IR(international rectifier) drivers are among the lowest amp output drivers. There are Ebay sellers that carry the FAB73xx series drivers that are US based sellers, don't know where your from though. And for forward/reverse it takes two drivers and four mosfets.EDIT~
Only looks good for 1/3 of an Amp, dang!
1) I want to try something different, maybe switch large, parallel bank of MOSFETS for a winch or something big.What are you doing differently from the working circuit that you need a driver?
A 555 output should be able to switch pretty much any but the highest current MOSFETs at 20 KHz without a driver.
Now, if you want to switch at 200KHz or higher, that is another story.
Bob
Great. What kind of MOSFET drivers should I be looking for that I can use with that comparator PWM design,
or even for a 555 PWM design?
I don't think I would worry to much about the input voltage. You can always use a divider as the inputs take almost no current.I like that FAN7311 has both a low and high side driver (forward/reverse?) but it is harder to come by.
This one looks good to me, IR2101, with up to 15v input signal, or logic level at 3v & 5v... but what do I know?
Floating channel designed for bootstrap operation
Fully operational to +600V
Tolerant to negative transient voltage
dV/dt immune
• Gate drive supply range from 10 to 20V
• Undervoltage lockout
• 3.3V, 5V, and 15V logic input compatible
• Matched propagation delay for both channels
• Outputs in phase with inputs (IR2101) or out of
phase with inputs (IR2102
====
EDIT~
Only looks good for 1/3 of an Amp, dang!
From the datasheet:
IO- Output low short circuit pulsed current 270 360 — VO = 15V
if it did exist, the TC44xx would be the closest to it.the most
popular MOSFET drivers,
A 555 output should be able to switch pretty much any but the highest current MOSFETs at 20 KHz without a driver.
So you guys are saying the 200mA 555 output has no problems with driving a mosfet?before you invest in drivers, you should work out the math to see if switching losses are indeed an issue for your application. otherwise, you may be wasting time / money on a non-existent problem.
switching losses can be a huge factor for some applications. here is what I typically do to estimate it.you should work out the math
Usually ok. It depends on how fast you want it to switch.So you guys are saying the 200mA 555 output has no problems with driving a mosfet?
My eyes are bloodshot from reading every datasheet linked over here:if it did exist, the TC44xx would be the closest to it.
before you invest in drivers, you should work out the math to see if switching losses are indeed an issue for your application. otherwise, you may be wasting time / money on a non-existent problem.
Danny,switching losses can be a huge factor for some applications. here is what I typically do to estimate it.
the gate looks like a capacitor to the drivers. most of them are in the 3000pf - 4000pf range (higher for logic level mosfets). the key is to estimate how long it takes the mosfet to cross that region and at what power dissipation levels.
assume that the driver's output resistance is 100R (typical for a 555-class driver and much lower for a dedicated driver). with 430R external resistance that brings total resistance to 500R. and rc constant of 500R * 4000pf = 2us.
I usually to 2x rc time constant (slightly less than 10/90%) and that makes it 4us. and I need to cross that twice (off->on and on-> off) each cycle so 8us.
at 20Khz switching frequency, the device spends 8us * 20K = 0.16s/s doing that.
assume that your load is rated 12v@10amp -> 120w. I usually assume half of that will be dissipated by the mosfet -> 60w during switching. that number is conservative.
60w * 0.16s/s -> 10w -> that requires a to220 device + reasonably large heatsink.
that number far exceeds the typical conduction losses -> 10mohm * 10amp * 10amp = 1w.
in comparison, if you were to use a 1amp driver to bring total resistance to 50ohm, you would have reduced switching loss to 1w and that is potentially a to220 device + copper traces or stand alone.
most mosfet OEMs have calculators, online or spreadsheet, that help you work out more comprehensively but the math above shows you the gist of the calculation that you need to do before sizing up the mosfet / driver required for a given job.
The totem pole discrete driver?in your case, it is much easier to just use an emitter / follower to expand the 555's current capabilities.
only because it has been out for a long time -> multi-sourced and dirt cheap.the TC4420 et al. drivers look to be the "rodeo, two world's fairs, & a picnic" of MOSFET driver tech.
that will work too. at 12Vcc, you should be able to deliver 10v onto the gate. that's enough to turn fully on even the most stubborn of the mosfets.The totem pole discrete driver?
Ron, I think you and I are on danny's ignore list.Danny,
You should review your assumptions. There are some problems there.
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