Mosfet as switch (irf510)

Thread Starter

mikezoubi

Joined Nov 4, 2016
11
I have a PIR sensor that outputs 3.7v when active. it is powered by a 6v battery. I am trying to run flashing LED's (built in resistors) off 6v battery as well when the PIR sensor is high at 3.7v. is the IRF510 gate capable of being switched at 3.7v from the PIR sensor? also what else do I need to hook this up and how? The reason want the lights triggered with 6v rather than 3.7v is because they are too dim under 3.7v

Thanks in advance
 

ronv

Joined Nov 12, 2008
3,770
I have a PIR sensor that outputs 3.7v when active. it is powered by a 6v battery. I am trying to run flashing LED's (built in resistors) off 6v battery as well when the PIR sensor is high at 3.7v. is the IRF510 gate capable of being switched at 3.7v from the PIR sensor? also what else do I need to hook this up and how? The reason want the lights triggered with 6v rather than 3.7v is because they are too dim under 3.7v

Thanks in advance
Are your LEDs made to run on 6 volts?
 

johndeaton

Joined Sep 23, 2015
63
Hi Mike,

When you evaluate a MOSFET, look in the datasheet for the graph Vgs vs. Ids. This will tell you how much drain to source current can flow given a certain amount of gate voltage. In the datasheet that crutschow posted, this graph is in figure 8 (see attached). This shows that if you energize the gate with 3.7 volts, the MOSFET can sink ~15 Amps. So this one will work for you.

John
 

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crutschow

Joined Mar 14, 2008
26,426
................
When you evaluate a MOSFET, look in the datasheet for the graph Vgs vs. Ids. This will tell you how much drain to source current can flow given a certain amount of gate voltage. In the datasheet that crutschow posted, this graph is in figure 8 (see attached). This shows that if you energize the gate with 3.7 volts, the MOSFET can sink ~15 Amps. So this one will work for you.
That graph shows the current for a Vds of 15V which is of marginal usefulness for characterizing the MOSFET as a switch.
Attached is a more pertinent graph.
It shows that at a Vgs of 3.7V and a drain current of 14A the nominal ON resistance is <100mΩ.
But note these are typical and not worst-case values.

upload_2016-11-7_21-57-4.png
 

John P

Joined Oct 14, 2008
1,872
Crutschow, what was the origin of that Figure 9 that you showed? The IRF510 data sheet from Vishay is quite different, and shows what Dannyf said--in fact the "Typical transfer characteristics" graph doesn't even go below Vgs = 4V, and the curve is pretty close to zero at that point. The data sheet also lists a maximum continuous current of 5.6A.

See Figure 3 here: http://www.mouser.com/ds/2/427/sihf510-105610.pdf

Oh, now I see in the Saturday 12:04 post, that's not the IRF510. That explains it!
 

Thread Starter

mikezoubi

Joined Nov 4, 2016
11
So I set this up with the mosfet listed above, however the mosfet appears to be latching. the negative drain and source stay connected after the gate voltage drops to zero.
 

crutschow

Joined Mar 14, 2008
26,426
So I set this up with the mosfet listed above, however the mosfet appears to be latching. the negative drain and source stay connected after the gate voltage drops to zero.
What do you mean "negative drain"?
The drain voltage must be positive with respect to the source.
Post a schematic of your circuit.
Try connecting a 10kΩ resistor from the gate to source of the MOSFET.
 
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