Voltage Divider To "ON" and "OFF" IRF610

[JackJTR]

Greetings everyone, I have a question here regarding the voltage divider and the IRF610. Soo basically what happen is when i apply 5V to the voltage divider, the IRF610 does't turn on although the output from the voltage divider is approximately 5V. May i ask why the IRF610 didn't turn on although the Vgs is approximately 5V? And according to datasheet the Vgs(threshold) of IRF610 min is 2V and max is 4V?

Here is the connection for the IRF610, why wont the IRF610 turn on ?

Thanks in advance!

 

[Les Jones]

The threshold voltage is the gate to source voltage when it JUST starts to conduct, (It is specified as 250 uA on the data sheet. The IRF610 is a poor choice for your application. You either need to drive it with a higher voltage or ose a logic level mosfet.

Les.

 

[shortbus=]

The value of R1 is not helping you at all either. But mainly it's what Les said wrong type of mosfet for the voltage.

 

[JackJTR]

Ahhh i see, may i also ask what is the 250uA the datasheet was talking about ? Sorry if the question is dumb but I am quite new to this field . And also for shortbus, may i also ask wht does the R1 didnt helping either ?

Thank you for replying and thanks for the help! Much appreciated!

 

[Les Jones]

If you look at the 4th row down and the right hand column (Conditions.) you will see the drain current that is specified for the threshold voltage.

If you motor only required 250 uA then your circuit would work. (I have never seen a motor that would work with that current.)

Edit.I have just noticed that I have copied the table from the wrong data sheet. The threshold values are different to your IRF610. A more significant difference is the value of Rds(on) for your IRF610 is specified with with Vgs of 10 volts and it has a value of 1.5 ohms which is much higher than for the IRLZ44 in the above data sheet. (You have not specified the current the motor requires so I can't say how significant a Rds (on) value of 1.5 ohms would be for your circuit.) The IRLZ44 would be a much better choice for your circuit.

Les.

 

[shortbus=]

The normal R1 value would be between 10 and 50 Ohms. Using a high value like shown will slow down the charging of the gate. A mosfet gate is a form of capacitance, so the faster you can charge it the faster the mosfet turns on. Putting a high value resistor in the cicuit like your R1, slows down the time to charge the gate. The problem with that is the slower the mosfet turns on the longer it stays in a region of operation the cause the mosfet to heat up, called the "ohmic region", where the mosfet is more resistive. When the mosfet is fully on this region of operation is much less.

 

[ronsimpson]

may i also ask what is the 250uA the datasheet was talking about

This is for when the part just starts to turn on. It is not on. Just on the edge of on.

 

[kubeek]

in this graph you can see that the mosfet with Vgs=4.5V can barely allow 60mA, and a bit less than 300mA with Vgs=5V. You have to either increase the gate voltage, or use another, usually called logic level mosfet, with much lower threshold voltage - Vgsth.
Also, using an almost ancient 200V mosfet with 1.5 ohms Rdson is very much sub optimal at 12V. I suggest you choose a modern 30-40V-ish mosfet instead.
So the main question here is, how much current does the motor draw when you stall the shaft? Use that number to choose appropriate current rating of the mosfet with some healthy margin.

 

[JackJTR]

Ahhhhh i see where is the problem, the 12V fan require 0.16A to operate. I think that the reason why it fail... Thanks for all the help i get! Much appriciated!