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

[JesterBR]

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?

 

[goldsmith]

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.

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.

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

 

[JesterBR]

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

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

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

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?

\/

 

[goldsmith]

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

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.

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.

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?

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

 

[JesterBR]

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

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?

 

[goldsmith]

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?

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

 

[JesterBR]

Those are my drews.

Goldsmith iam studying your drews.


Well, am planning to use the IRF540.

 

[goldsmith]

arquivo.jpg
arquivo01.jpg

Those are my drews.

Goldsmith iam studying your drews.


Well, am planning to use the IRF540.

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.

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

 

[JesterBR]

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 ? )

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.

 

[goldsmith]

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

Hi jester

Now i feel better , ha ha :-D

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

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.

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







Best Wishes + Good Luck
Goldsmith

 

[JesterBR]

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

Goldsmith

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

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

tx!

 

[JesterBR]

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).

 

[goldsmith]

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).

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