N-Channel MOSFET based H-Bridge

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An emitter follower is called like that because the emitter has always 0.6-0.7v difference from the voltage of the base.
If you give 10v to the base you get 9.3v to the emitter, if you give 4.5v you get 3.8v.
The totem pole are are two emitter follower tied together, they give to the output the voltage you give to the base -0.7 (NPN) and +0.7 (PNP), if it gets 3.8 the output will be 3.1v ..... not 24v
 
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    Ashkar

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oh now I under stud the logic.Very well explained
and should I couple a not gate ic to turn the logic low if noting is connected to the bridge??:|
 

If you mean the input A and B then a simple resistor from the input to the positive supply (pull up) would work fine.
If you want to invert the inputs A and B to be active with positive signal then you can use one more transistor in each input to invert the incoming signal, in that case use pull down at the new inputs.
The pump frequency should probably be close to the PWM frequency, if you intend to use 20KHz PWM then use higher pump frequency too.
Your pump generated voltage will be close to 20-21v, the pump totem pole output is about 11.5v and 0.5v and you also have a couple of diodes that will drop another 0.5v each.
I don't know if you 'll have a problem with the gate during normal operation (Vgs>20v), also when the mosfet 12v supply shuts down before the pump capacitor discharges you can have a problem with the Vgs.
This is the difference with the bootstrap method because there you had a capacitor with a charge of 12v that was added to the source voltage so whatever the source voltage the gate was always +12v higher, no more than that.

Alex

EDIT: I have changed the pull down in the above text to pullup because you need to have positive voltage at the inputs to turn the bridge off.
 
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That's good one alex you must be a good teacher, you are absolutely right about your transistor analysis.
 
I'm afraid it doesn't work this way, the totem pole will be able to give more than an Ampere, your zener will burn almost immediately when the voltage rises above 15v.
The zener diode is usually used with a resistor, when the voltage across the zener rises above the specified voltage so does the current and this creates a voltage drop on the resistor so that output voltage reduces.
The problem is that even if you put the zener after the gate resistor the value of the resistor is too low to allow the zener to operate properly, on the other hand if you increase the resistance then you slow down the mosfet.

Alex
 

So how Should I tackle this Problem.Should I use an Resistance after the totem pole (around 100ohm) and place a zener after that.
 

There is also no point to limit the gate voltage with respect to the gnd, what you want it to limit the gate voltage with respect to the source.
If you want to limit the gate voltage with reference to the gnd then you can simply use two resistors instead of one in the collector of the BC547, for example 500+1500 ohm to get 3/4 of the voltage , you get the point.
The problem using that way is that you will get a lower Vgs , if you provide 15v then when the mosfet turns on it will just remain 15v(G)-12v(S)=3v.
I'm afraid I can't think of a solution for this, this is one problem that the bootstrapping method (connected to the source) didn't have.
EDIT: that resistor divider in the collector can only limit the lower part of the voltage not the high, so with 3/4 you will get 5-20v not 0-15.

Alex

---------- Post added at 17:54 ---------- Previous post was at 17:51 ----------

You want the gate resistor to be low (10 ohm or lower) so increasing it is not the solution, you went to all this trouble to create a proper driver that can provide the needed current just to use a high value gate resistor, no way.
If you use 100 ohm you will limit the gate current of the switching will slow down, you don't want that because the mosfet losses will increase.

Alex
 
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How would will the circuit work Of i use Simple 1n4007 Diode(1v per diode) to limit the charge current on 24v rail on high side.
 
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how can a diode limit the charge current?
I think you can protect the Vgs from going above 20v using a zener and a diode back to back from the source of the upper mosfet to the input of the totem pole.
Cathode of the diode to the source, anode of the zener to the anode of the diode and the cathode of the zener to the totem pole input.
It seems to be working in simulation, with a zener of about 16v.
 

You can't use 1N4001 in the pump because the frequency is very high, you need fast diodes.
The capacitors you have used have a high value, I have tried with 10uf and I got a ripple of 0.5v with a 100ohm resistor load.
I would suggest a current of about 50mA for the BC547 to drive the totem pole stronger (220 ohm for 12v and about 390 for 21v).
Also you have used am emitter resistor at the pump transistor, I don't see the purpose for that.

Alex
 

What is the purpose of that resistor?
You will not be able to drive the totem pole with 0v with that emitter resistor, you will have a swing between about 4v and 21v instead of 0v and 21v.
 

so what should I do,How do I limit the voltages on the gate.
 

I told you in post #31, didn't you read it?

---------- Post added at 19:49 ---------- Previous post was at 19:29 ----------

No that is not what I have described, cathode is the side with the triangle tip and the line.
Cathode of the diode to the source, anode of the zener to the anode of the diode and the cathode of the zener to the totem pole input.
Click to expand...
You should reverse the diodes and connect the totem pole side to the two transistor input, where the collector of BC547 is.
the other side goes to the source not the gate.
Also one is diode and the other is 16v ZENER

Alex
 

Sorry I just Forget to read it,Now this thing would help me a lot,Thank You.Could you please explain the zener back to back network ,how would it limit Vgs.
 

When the voltage at the totem pole input is more than 16v+0.7 compared to the source then the diode will conduct and draw current through the resistor connected to the collector and you will get a voltage drop and a lower voltage driving the totem pole.
 
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I am little confused, could you please edit my circuit high side driver parameter to show how this is Implemented.
 

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