How to use TLP250 with a P-channel Mosfet with source of 180V

Hi everybody!

I am having problems to use a P-Channel mosfet. I've made a circuit using a N-Channel Mosfet(IRF640) and another CI to switching(Til113 with the signal coming from a PIC). The circuit works fine but I noticed that it wasn't so efficient. Now I am trying to use the IRF9640 with TLP250.




I have a source of 180(15~180 using capacitors) and I need to keep a brush motor DC with constant voltage of 24v(after I am going to work this voltage that will vary from 0 to 24V).

I already written the code and built the hardware to read the Vin(15~180) so I can work with the PWM signal.

My problem is: P-Channel mosfet doesn't work with a 15V input gate and Source of 180V. After searching a lot, I read that the solution of my problem is using a 'Totem-pole Switching Circuit'(http://www.irf.com/technical-info/appnotes/an-940.pdf).
Sadly I didn't understand exactly how it works, and I don't even know from where should I start.


Could someone help me?

I am having problems to use a P-Channel mosfet. I've made a circuit using a N-Channel Mosfet(IRF640) and another CI to switching(Til113 with the signal coming from a PIC). The circuit works fine but I noticed that it wasn't so efficient. Now I am trying to use the IRF9640 with TLP250.

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Hi Jester
You mentioned it was not so efficient , reasons behind power loss in a mosfet are different . i can note some of them here :
1- there was very high rise time and fall time in your signals thus your mosfet will work in linear region ( in a short time ) so it will deliver bad efficiency .
2- you didn't drove it as well and in a proper condition . i mean you should refer to the datasheet of the threshold voltage of your mosfet and for maximum VGS . and be sure that your mosfet is operating in on / off region as well ( for usual mosfets it would be around 15 volts although there are many of the mosfets with lower VGS .
3- your load ! it is very important .
4- Large value of Rdson . you should use mosfets with low Rdson for high currents .
5- Low value of IG ! or as a matter of fact you should use mosfets with low Ciss . so it your frequency is higher than the rating of Ciss of your mosfet you'll need to inject more current and if you don't then it will go through the linear region .

So check those parameters out .
Before involving with your main question , may i ask you why you are interested in P mosfets for your design ? i use them too but most of the times i prefer use N mosfets . because of many of the reasons .

Sadly I didn't understand exactly how it works, and I don't even know from where should I start.

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Well , a totem pole circuit will be provided usually with two transistors . one of them will conduct while you are about to turn your mosfet on and it will prepare the required surge current of GS capacitor . and the other one is supposed to be turn on while you are about to turn your mosfet off . thus it will discharge the GS intrinsic capacitor . that's all .
But i think if you can go through N mosfets it would be so easier and most better .
Best Wishes
Goldsmith

goldsmith said:

5- Low value of IG ! or as a matter of fact you should use mosfets with low Ciss . so it your frequency is higher than the rating of Ciss of your mosfet you'll need to inject more current and if you don't then it will go through the linear region .

Goldsmith

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How can I know the value of frequency that should I use? What is 'value of IG'(IG?)?

goldsmith said:

Before involving with your main question , may i ask you why you are interested in P mosfets for your design ? i use them too but most of the times i prefer use N mosfets . because of many of the reasons .
Goldsmith

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If I use a P mosfet, I will can have the GND of the motor in common with the whole circuit. And I will can read the value of Vload directly from the motor, then will be easier say if I need increase duty cicle(PWM) or not.
And if I use a N mosfet, when I brake the motor I guess that I will need to use the P mosfet.


I was reading, and find out DC-DC converter, class C. Would I try this ways?

\/

How can I know the value of frequency that should I use? What is 'value of IG'(IG?)?

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Hi Jester
It is easy . refer to the datasheet which is produced by manufacturer and then you'll see these times :
td(on) : Turn-On Delay Time
tr : Rise Time
td(off) :Turn-Off Delay Time
tf : Fall Time

The maximum frequency which a mosfet will be operated on , is harvested by : tf+tr+td(both td) (1+20/100 ) . it will be achieved if you can guarantee that the required fate instantaneous current is prepared as well .
Regarding the gate current , as you probably know a mosfet has a DC input impedance through gate which is pretty high . but as you probably know too , each semiconductor ( each PN junction ) has an intrinsic capacitance too . so in higher frequencies then you can not say impedance is nearby infinite . an as you perhaps know a capacitor is short circuit in first steps of transient time . so it will require very high value of surge current to be charged as well . this capacitor will apply an exponential function through the GS command signal . so if you want guarantee that your mosfet has been drove in a proper condition of on / off ( just like a key with very low value of turn on resistance ( rdson ) ) you'll need to inject high value of surge current through the GS which it's optimum value depends of frequency of operation / value of Ciss / value of input inductance and many of the other things . that's all !

If I use a P mosfet, I will can have the GND of the motor in common with the whole circuit. And I will can read the value of Vload directly from the motor, then will be easier say if I need increase duty cicle(PWM) or not.

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Who told if you use N mosfet you can't have direct access to the GND of your motor ? did you heard about float drivers and boot strap drivers like IR2117 ? or perhaps preparing a floated ground supply ?
It can be easily done with N mosfet .

And if I use a N mosfet, when I brake the motor I guess that I will need to use the P mosfet.

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Again i've to ask who told you have to use P mosfet at breaking time ?

I was reading, and find out DC-DC converter, class C. Would I try this ways?

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Why such a circuit ? i think if you tell me about characteristics of your required circuit i can guide you in the best way . would you like this way ?

Best Wishes
Goldsmith

goldsmith said:

Who told if you use N mosfet you can't have direct access to the GND of your motor ? did you heard about float drivers and boot strap drivers like IR2117 ? or perhaps preparing a floated ground supply ?
It can be easily done with N mosfet .

Again i've to ask who told you have to use P mosfet at breaking time ?


Goldsmith

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Well, thanks for explain about the time of switching of mosfet.
If I use a float ground, I couldn't read the value of Volts with a PIC.

how can I break the DC brush motor?

Well, thanks for explain about the time of switching of mosfet.
If I use a float ground, I couldn't read the value of Volts with a PIC.

how can I break the DC brush motor?

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Hi Jester
Let me draw something for you , thus i think you'll get the idea as well .
Here you can see what drew :





Any Question ?
Best Wishes + Good Luck
Goldsmith

Those are my drews.

Goldsmith iam studying your drews.


Well, am planning to use the IRF540.

arquivo.jpg
arquivo01.jpg

Those are my drews.

Goldsmith iam studying your drews.


Well, am planning to use the IRF540.

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Hi Jester
I hardly could read what you wrote( your handwriting ) ( sorry english is not my native language and i can not read all kind of hand writings easily ) ;-)
Anyway
In your first attachment :you've used a P Mosfet , thus you have direct acess tot he main ground , but i understood your aim before .
Regarding your 2nd attachment , it is not what i've suggested you ! when i told you use your load in drain of the N mosfet ? if you precisely see what i drew , you'll get that i've used the motor in source of your N mosfet and i've used two popular ways to turn the N mosfet on and off . so thus you have fully access to the ground of your motor . isn't it ?
By the way , when you want drive an N mosfet you should not use such an arrangement ( as you have showed ! ) each mosfet needs a totem pole network to do it's best and be drove as well ! ( are you familiar with totem pole and it's duty ? )

Well, am planning to use the IRF540.

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IRF450 is good but IRF740 and IRFP450 can be good too .
Best Wishes + Good Luck
Goldsmith

goldsmith said:

Regarding your 2nd attachment , it is not what i've suggested you ! when i told you use your load in drain of the N mosfet ? if you precisely see what i drew , you'll get that i've used the motor in source of your N mosfet and i've used two popular ways to turn the N mosfet on and off . so thus you have fully access to the ground of your motor . isn't it ?
By the way , when you want drive an N mosfet you should not use such an arrangement ( as you have showed ! ) each mosfet needs a totem pole network to do it's best and be drove as well ! ( are you familiar with totem pole and it's duty ? )

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Don't worry, english isn't my native language too.



But, where I did an outline, it should be a short circuit, shouldn't ?

i read something about totem pole, but it wasn't enougth to I understand. I have no ideia of what to do.

Don't worry, english isn't my native language too.

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Hi jester

Now i feel better , ha ha :-D

But, where I did an outline, it should be a short circuit, shouldn't ?

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No of course it is not a short circuit . because as i've mentioned before , and as you can see in my drawing , nv is your main power supply ( e.g 180 volt ) with it's own ground . but the ground which has been connected to the source of mosfet is not ground of nv supply ! itis coming from the different source which is a transformer so the ground is completely isolated from your main ground , because it is incoming from transformer .

i read something about totem pole, but it wasn't enougth to I understand. I have no ideia of what to do.

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Well , no problem , i can describe it for you .
another drawings ! take a look here please :







Best Wishes + Good Luck
Goldsmith

goldsmith said:

Well , no problem , i can describe it for you .
another drawings ! take a look here please :

Goldsmith

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Hii Goldsmith, it really help me. I finally understand!!

I am going to try this way, then I post to you what happen!

tx!

Totem pole works when I use the same VCC that is connect do the transistors.

But doesn't work with another power supply(i tested with 24v).

Totem pole works when I use the same VCC that is connect do the transistors.

But doesn't work with another power supply(i tested with 24v).

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Hi Jester
What do you mean by that ? can you show me what you have did , with a schematic ? totem pole with what kind of situation ?

Best Wishes
Goldsmith