how can i choose MOSFET fit to me??

Thread Starter

Kim-JiHoon

Joined May 3, 2020
31
hello, I have a question about MOSFET

I want 24v 3A motor control.

In detail, there was 24v 3A MOTOR for FAN and this MOTOR have a select switch for controlling motor speed

I want change this 'SELECT SWITCH' to 'IC SWITCH' (SELECT SWITCH too big for my PCB CASE)

I tried controlling maximum amp 5A mosfet, but mosfet temp too high.

I searched kind of "using high current mosfet for low current motor, less heat?"

and i found mosfet easy too buy and cheap enough for me.

IRFZ44N
fet1.png
fet2.png

and here is my cal
℃ ²
T + (amp, i need (3A) x Rds x juction)
25℃ +(3² x 0.0175 x 62)
= 25℃ + 9.765
= 34.765℃

it means if motor use 3A mosfet temp is 34.765℃ right?

So...

1. (For Not using heatsink)
5v MCU controlling that MOTOR with IRFZ44N + N chanel TR(like 2N3904)
is this possible?

2. If 5V control is not possible, is there any method? just using small VR like this (not using MCU)

vr.png
 

Audioguru again

Joined Oct 21, 2019
1,776
The datasheet guaranteed "Electrical characteristics" says that with a gate-source voltage of 4V then only some of them turn on a tiny current. It says that all of them turn on well when the gate-source voltage is 10V.
Your input is a logic 5V so you need a logic level Mosfet like an IRL540 (see the L?) that will have a max on-resistance of 0.077 ohms with your 5V input. An IRF540 needs a gate-source voltage of 10V.
 

Audioguru again

Joined Oct 21, 2019
1,776
What is the potentiometer going to do? If if controls the voltage of the gate of the Mosfet then the Mosfet will get very hot at some settings and the motor will have poor torque. A modern motor speed controller has a pot controlling a Pulse-Width-Modulation (PWM) motor speed controller circuit that keeps the Mosfet cool and keeps plenty of torque for the motor but it controls the motor speed properly.
Your MCU can do the PWM.
 

Audioguru again

Joined Oct 21, 2019
1,776
I stopped downloading datasheets when Datasheet Archive started giving ads instead of datasheets.
Just now I downloaded the IRLZ44 datasheet directly from IR.
 

Thread Starter

Kim-JiHoon

Joined May 3, 2020
31
Thank you all
I'm sorry i'm not native
So i translated with google

I think i know what PWM is, and VR doing motor voltage control for motor speed

But I miss understood with PWM

I want 24v 3a motor speed control

That is all

And i thought "there is two way"

One is not using mcu

And the other one is using mcu

But i coludn't find "which IC is low temp"

So i searched "high voltage motor control" and i found that IC, calculation

I calculated, and i thought use high current IC to use low current, is there any solution?
(10A IC to use only 30%)

Because, i don't want to use select switch (big one)

And i want to make PCB in small case

So i worried about HEAT issue

It's why i wrote this thread

I have to googling IRL540 and circuit right?
 

peterdeco

Joined Oct 8, 2019
205
We use a variation of the IRFZ44N. It is IRLZ44N. We never had a problem switching it on with as low as 3V. We run them at 2 amps without a heatsink all the time.
 

Thread Starter

Kim-JiHoon

Joined May 3, 2020
31
my mcu is atmega328p and it have pwm

PWM is kind of loop on/off and set long or short that frequency right?

Than 24v -> lm7805 -> pwm

I think lm7805 will very hot

Than what should I search about low heat PWM?
 

bertus

Joined Apr 5, 2008
20,664
Hello,

Do you mean that the 7805 is powering the MCU that is generating the PWM signal?
The 7805 can get hot when no decoupling capacitors are used.

3-pin_low_power_regulators_with_capacitors.png

Bertus
 

bertus

Joined Apr 5, 2008
20,664
Hello,

Where does the PWM come from, as you say it is not from the MCU?
You can not put the PWM at the input of the 7805.

Bertus
 

Thread Starter

Kim-JiHoon

Joined May 3, 2020
31
Hello,

Where does the PWM come from, as you say it is not from the MCU?
You can not put the PWM at the input of the 7805.

Bertus
There will be one input 24v

And

1. this will run mcu(using lm7805)

mcu will run some led or fnd

2. this will run motor(24v 3a)

So now, i want motor speed control

Motor have selector switch already
(Big one)

I want make motor speed controller
(with small plastic case)

I don't know how..

I can that big selector switch seperate with mcu, but that will be awful

So i decided "make motor coltroller"

Sorry my english is bad

But thank you guys

And now i know lm7805 is not a good one for PWM i have to use such as lm2570

But i don't want change regulator

So,

"Not through mcu, just want to motor speed controller. Than is there any way?"( + low temp)

So far this is my conclusion
 

Audioguru again

Joined Oct 21, 2019
1,776
PWM uses the width of high frequency pulses for DC motor speed control. Wide pulses= high speed and narrow pulses= low speed.
The Mosfet switching the pulses on and off stays cool.
There is no selector switch, instead a little potentiometer controls the PWM pulse widths.
The datasheet of a 555 shows a PWM circuit and a dual opamp can make a triangle waveform that is compared to a variable DC voltage like this:
 

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Audioguru again

Joined Oct 21, 2019
1,776
The datasheet for the 555 shows that it will not do anything with its trigger pin2 and its threshold pin 6 grounded.
Pin 5 of the 555 should never be grounded like yours is.

The second circuit has the transistor always turned on.
Why is the output of the Atmega shorted to 5V?
What is the function of D1?
The datasheet for the IRFZ44 shows that its gate is destroyed if its voltage is higher than 20V, your circuit gives it 24V.
 

Thread Starter

Kim-JiHoon

Joined May 3, 2020
31
Thank you for your reply!

first schematic i totally wrong.

second schematic, I read datasheet again i missed gate voltage

IRFZ44, IRF540N, IRF640N i bought this but none of them can accept 24v....OMG

could you recommand mosfet?..

and i found some schematic.

second schematic, IRFZ44 ->STS5NF60L

driverIC.png

but i can't get this IC...
 

Audioguru again

Joined Oct 21, 2019
1,776
D1 is not needed.
Simply replace D1 with a 10k resistor then the maximum gate voltage will be +12V.
PWM usually has a frequency higher than our hearing (>20kHz) but your D2 is a very slow one.
Also, the resistors turn the Mofset on and off slowly because the gate has a high capacitance.
I corrected your schematic but it will not work at a high PWM frequency.
 

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