555 driving N mosfet

Tony Stewart

Well-Known Member

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• Jun 10, 2023

• #41

You need to link datasheets, part numbers and why no heatsink? That schematic is not helpful.
To switch 2A and only dissipate 0.2 W (not too hot) you need a 0.1V drop (2A*0.1V=0.2W) which means Ron = 1V/2A = 0.5 ohm

The IRF520 is 0.27 ohm max at Vgs=10 but more than 2x this at 150'C so a heatsink is needed.

Use 12V for gate voltage.

 

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MrDEB

Well-Known Member

• Jun 10, 2023

• #42

I think I located desired component

https://www.mouser.com/datasheet/2/308/1/RFP12N10L_D-2319858.pdf

this is a logic-level mosfet that will handle 5A

 

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Tony Stewart

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• Jun 10, 2023

• #43

Here's an update to follow if you like the 30:1 frequency range You can make the IRF520 work if you follow my advice. Use 12V for gate voltage add small heatsink. There are about 1,000 logic level FETs to choose from.

https://tinyurl.com/279a9d4m

 

Last edited: Jun 10, 2023

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audioguru

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• Jun 10, 2023

• #44

The Vgs(th) is the gate voltage that turns it OFF, you need the gate voltage that turns it ON which is usually 10V for a common old Mosfet. A moderm "logic level" Mosfet fully turns on with a 5V gate voltage.

 

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Tony Stewart

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• Jun 10, 2023

• #45

Technically Vt or Vgs(th) or gate threshold voltage is defined by the range of voltages due to mfg tolerances that result in current of 250µA with Vgs=Vds. So iif Vt was say 2.5V then RdsOn= 2.5V/0.25 mA = 10 kohm. . not quite off or on.

 

Last edited: Jun 10, 2023

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audioguru

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• Jun 10, 2023

• #46

I can't remember how many Amps his LED strips will draw, way more than 0.25mA.

 

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MrDEB

Well-Known Member

• Jun 10, 2023

• #47

the 16.4 ft. strip draws 5A
don't plan to run a strip 16' long all at one time

 

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MrDEB

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• Jun 10, 2023

• #48

the Vgs(th) states 1-2v

 

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Tony Stewart

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• Jun 10, 2023

• #49

audioguru said:

I can't remember how many Amps his LED strips will draw, way more than 0.25mA.

Click to expand...

Yes we know very dim in the dark, probably off, but not recommended to prevent acceleration of matalization and LM70 wear times.

 

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Tony Stewart

Well-Known Member

Most Helpful Member

• Jun 10, 2023

• #50

MrDEB said:

the Vgs(th) states 1-2v

Click to expand...

1. OK with 1 to 2V actually with 12V gate drive you can use 2 to 4V too. ok?
2. I gave 0.2 ohm as a limit for the example using the IRF FET getting hot (TO220 without a heatsink and not an ideal target for a FET resistance. ok?

3. But there are tons of different FETs in catalogs, so why not get one to handle 5A easily. or RdsOn of <= 25 mohms. 5^2 * 0.025 = 63 mW , cool ')

I suggest for you, https://www.mouser.com/ProductDetail/onsemi-Fairchild/NDP6060?qs=7qg/USZkK87eR6XCHfQYeA== in future.

 

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S

shokjok

Member

• Jun 17, 2023

• #51

lito.beth.09 said:

Should you say 16 ohms?

Click to expand...

0.25mA = 250 microamps ( uA). The result should be 16K, not 16 ohms.

 

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