Switching MOSFET - Page 1
Forum section: electronics / beginners

author: Thepunydiode
author_rank: Newbie
timestamp: May 17, 2020, 11:42:39 am
content: Hey there, I am new here. I am working with MOSFETs IRFZ44N to be more specific. I am trying to switch it at 50 Hz. But Its output Waveform looks weird. There is no gate resistor. Vds is 12v . R_load is 750 ohm. I am giving Vgs 5v with arduino. There is no Inductos/Capacitor attached. I have connectrd 10 kohm resistor across gate and source.

author: Zero999
author_rank: Super Contributor
timestamp: May 17, 2020, 09:50:51 pm
content: Please post a plot of the gate voltage.

author: Thepunydiode
author_rank: Newbie
timestamp: May 18, 2020, 05:33:24 am
content: Here it is bro. Just to remind you that there is no gate resistor. I tried to change MOSFET too, but still getting same result.

author: WattsThat
author_rank: Frequent Contributor
timestamp: May 18, 2020, 06:09:49 am
content: You’re trying to control a device that requires a 10v gate signal but you’re only providing a 5 volt level. Perhaps that discrepancy might be the source of you difficulties.

author: xavier60
author_rank: Super Contributor
timestamp: May 18, 2020, 06:22:21 am
content: It looks like the Gate is being driven via a very high resistance. Maybe there is something wrong inside of the MOSFET.Check the Source waveform also.

author: stafil
author_rank: Regular Contributor
timestamp: May 18, 2020, 06:54:08 am
content: Try reducing the the RLoad

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 18, 2020, 06:56:49 am
content: Quote from: WattsThat on May 18, 2020, 06:09:49 amPerhaps you are looking at a different datasheet? The one I'm looking on will has a threshold of max 4.0V...

author: stafil
author_rank: Regular Contributor
timestamp: May 18, 2020, 07:02:52 am
content: Quote from: stafil on May 18, 2020, 06:54:08 amYou see the triangular wave because of the high R-load and the capacitance at the drain.

author: Wytnucls
author_rank: Super Contributor
timestamp: May 18, 2020, 08:55:25 am
content: I replicated your circuit with a similar MOSFET IRFZ46N and load. I get a square wave output with a 5mA draw current.Recheck all your GDS connections.

author: Manul
author_rank: Super Contributor
timestamp: May 18, 2020, 08:59:14 am
content: It looks like capacitor charging and discharging throughprecisely sameresistance. Also knowing that it is 50Hz, it should involve huge capacitor or huge resistor. I can not see how it is possible to get such waveform with the components which were mentioned in any configuration possible. And it is not about gate drive.Please post information about your power supply, how you are probing the output and everything else.

author: Thepunydiode
author_rank: Newbie
timestamp: May 18, 2020, 08:59:35 am
content: What is the highest frequency at which I can toggle this mosfet with load of 10K ?What MOSFET should I use to switch it at 10 MHz with same load?

author: xavier60
author_rank: Super Contributor
timestamp: May 18, 2020, 09:41:14 am
content: I often use IRF44Zs with 5V drive for light loads. I have just bench tested one. It passed 3A with a 250mV D-S drop.With 5V on the Gate and the 750Ω load, D-S must be only a few millivolts.Maybe the MOSFET is faulty in some way.Time to show us some photos.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 18, 2020, 11:25:34 am
content: Quote from: Thepunydiode on May 17, 2020, 11:42:39 ameven a cheap crap knock off in my stock wont produce such a weird Vd plot (even in BJT lines). i think what you got is a sheet crap knock off stock from an "immitator" who dont believe they will be judged in the afterlife. IRFZ44N should be doing fine up to more than 10A at 5V Vgshttps://www.vishay.com/docs/91291/91291.pdflet alone your 750ohm load.

author: Raj
author_rank: Frequent Contributor
timestamp: May 23, 2020, 07:54:13 am
content: Quote from: Thepunydiode on May 17, 2020, 11:42:39 amCould it be your power supply impedance and too much capacitance on the load?the load is 750 ohms?...16mA? that's not huge btw...Also...if you're using an SMPS/ chink bench power supply try some other method.Also, do know that, Indian shops don't handle mosfets properly enough to not damage them with static electricity.

author: exe
author_rank: Unknown
timestamp: May 23, 2020, 08:38:37 am
content: I also think the power supply may have troubles driving the circuit. I'd put a capacitor between Vdd and ground to see if it makes a difference. Say, 100uF or more.

author: mikerj
author_rank: Super Contributor
timestamp: May 23, 2020, 10:57:45 am
content: Do you actually have a ground connection between the Arduino and the MOSFET source?

author: Raj
author_rank: Frequent Contributor
timestamp: May 23, 2020, 11:22:00 am
content: Quote from: mikerj on May 23, 2020, 10:57:45 ammaybe in that case...it's switching because of mains background noise