How to use MOSFETs ?
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Posted by Jan Nielsen on June 20, 2007, 9:20 pm
Please log in for more thread options Hi, I was told on another forum, that the way to switch "large" currents is a MOSFET since a regular transistor cant, atleast not from a mcu output. Now I have a few of these IRF530 MOSFETs, and are trying to get them working. I connect ground/common to one of the outer legs, a led (cathode) to the other outer leg. The anode of the led to VDC+ (4V) Then I connect the base to a 1K resistor and then to common/ground. So in my understanding, when I apply power the led should be off, well its not, no matter where I connect the base with 1K resistor, the led is always on. I tried searching google for some guides, and found some, but I cant get their exsamples to work, the led is either always on or off, no matter what the gate/middle led is. /Jan | |||||||||||||||||||||||||
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Posted by Lord Garth on June 20, 2007, 10:09 pm
Please log in for more thread options You don't connect ground to "one of the outer legs". Insure you connect the Vss leg ground. That is the 'S' lead or source. Connect the LED cathode to the Vdd leg. That is the 'D' or drain pin. You then need a current limiting resistor in series with the LED anode. The value of the resistor depends upon the power supply voltage and the current specified for the LED. 10mA is a good round number. Connect the other end of the resistor to the positive power source. The 'G' or gate of the IRF-530 doesn't require a limiting resistor as the device is a MOSFET. It is an N channel MOSFET so applying a positive voltage to this pin will activate the LED. Grounding the pin will deactivate the LED. The device is sensitive to static electricity so you can damage it by touching the pins or by not observing ESD precautions. | |||||||||||||||||||||||||
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Posted by John Popelish on June 20, 2007, 10:30 pm
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Jan Nielsen wrote: > Hi,
> > I was told on another forum, that the way to switch "large" currents is > a MOSFET since a regular transistor cant, atleast not from a mcu output. > > Now I have a few of these IRF530 MOSFETs, and are trying to get them > working. > > I connect ground/common to one of the outer legs, a led (cathode) to the > other outer leg. > The anode of the led to VDC+ (4V) > Then I connect the base to a 1K resistor and then to common/ground. > > So in my understanding, when I apply power the led should be off, well > its not, no matter where I connect the base with 1K resistor, the led is > always on. > > I tried searching google for some guides, and found some, but I cant get > their exsamples to work, the led is either always on or off, no matter > what the gate/middle led is. The first hit is the data sheet: http://kitsrus.com/pdf/irf530.pdf Terminal 3 is the source, which goes to ground. Jumper that to terminal 1 to turn the gate off, and connect your led and current limiting resistor between the positive supply and terminal 2 (also the tab), which is the drain. This should result in a very dim or off led (just the leakage current). Turning the mosfet on is accomplished by bringing the gate up to a positive voltage with respect to the source. Unfortunately, from the Electrical Characteristics section, you will find that 10 volts is needed to get the thing essentially all the way on. The gate threshold voltage (where the channel just begins to turn on) may be anywhere between 2 and 4 volts. If you want to switch a large current from a logic level signal, you need a logic level (low gate threshold) device. For instance: http://www.fairchildsemi.com/ds/RF/RFP3055LE.pdf | |||||||||||||||||||||||||
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Posted by ehsjr on June 21, 2007, 2:08 am
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Jan Nielsen wrote: > Hi,
> > I was told on another forum, that the way to switch "large" currents is > a MOSFET since a regular transistor cant, atleast not from a mcu output. > > Now I have a few of these IRF530 MOSFETs, and are trying to get them > working. > > I connect ground/common to one of the outer legs, a led (cathode) to the > other outer leg. > The anode of the led to VDC+ (4V) > Then I connect the base to a 1K resistor and then to common/ground. > > So in my understanding, when I apply power the led should be off, well > its not, no matter where I connect the base with 1K resistor, the led is > always on. > > I tried searching google for some guides, and found some, but I cant get > their exsamples to work, the led is either always on or off, no matter > what the gate/middle led is. > > /Jan _____ | o | |_____| /_____/| | IRF || | 530 || |_____|/ | | | | | +----Source | +------Drain Gate Source to ground, drain to LED, LED to resistor, resistor to + Ed | |||||||||||||||||||||||||
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Posted by Jan Nielsen on June 21, 2007, 5:42 am
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ehsjr skrev: > _____
Oh, I thought gate was the middle, since the datasheet didnt show a
> | o | > |_____| > /_____/| > | IRF || > | 530 || > |_____|/ > | | | > | | +----Source > | +------Drain > Gate > > Source to ground, drain to LED, LED to resistor, > resistor to + > > Ed clean pinout, atleast not the one I found. Thanks, it works. /Jan | |||||||||||||||||||||||||
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>
> I was told on another forum, that the way to switch "large" currents is
> a MOSFET since a regular transistor cant, atleast not from a mcu output.
>
> Now I have a few of these IRF530 MOSFETs, and are trying to get them
> working.
>
> I connect ground/common to one of the outer legs, a led (cathode) to the
> other outer leg.
> The anode of the led to VDC+ (4V)
> Then I connect the base to a 1K resistor and then to common/ground.
>
> So in my understanding, when I apply power the led should be off, well
> its not, no matter where I connect the base with 1K resistor, the led is
> always on.
>
> I tried searching google for some guides, and found some, but I cant get
> their exsamples to work, the led is either always on or off, no matter
> what the gate/middle led is.
>
> /Jan