N-Channel MOSFET based H-Bridge

from http://obrazki.elektroda.pl/77_1307291856.jpg
reverse both diodes , then zener cathode (the triangle tip) goes to the BC547 collector and the diode cathode goes to the source pin of the mosfet.
**broken link removed**

Thank you For your wonderful Support.now please check this up.

Correct placement wrong diodes, you have to use a fast diode in place of 1n4007 and a 16v zener in place of 1n4148.
I would also suggest to use lower capacitors in the pump, I have tried with 10uf and I got a ripple of 0.5v with a 100ohm resistor load, your load is 390 (1/4 of the current) so you will have less ripple.
You can also use a higher resistor in the collector of the BC547 in the pump circuit, the output current doesn't need to be high so a 1k is fine.
A final suggestion can you please put my name too on the schematic :lol::lol::lol::lol::lol::lol::lol:... just joking.

Alex

Changed diodes to schottky( 1N5818 ) and zener 16v and update the values of pump to 1k and put pull down resistors on the input side to 1k each.
Hates off to you,without you patience and help I wouldn't able to built this circuit Thank you,
Any further suggestions and criticisms are welcome,Would I now start building it.
this is my final schematic(I guess so) .:roll:

make the second capacitor in the pump 10uf too (from 47uf).
You have connected pull down resistors in the inputs, if you turn power on this way you will activate all four mosfets and you will burn them, A and B are active with gnd and off with positive, you have inverted operation.
The pull down resistors should be changed to pull up (connect them to positive voltage) because a pull down keeps the mosfets always on.
Use a higher value like 47k, the first reason is to use less current, the second is the divider it creates with the input resistor 1K, if you use 1K resistor then when you apply 0v then the transistor base will get Vpullup * (1k/2k).
You have three options:
A) connect a 47k resistor from each input A,B to the +12v, any mcu connected to A shouldn't have a problem with the 12v because of the high resistor value.
B) use a voltage divider, connect one 27k resistor from A to +12 and a 10K resistor from A to gnd (the same for B), this will keep the input to about 3.3v (1/4 divider) when A or B are floating
C) use one additional transistor in eack input A and B to invert the input signal, in this case the new input will be off with gnd so you can use a pull down with a value of about 22k-47k

P.S. you can use one voltage pump for both sides, it is up to you.

Alex

I have opted to go with the First suggestion ,Can you please tell me that how much current this charge pump would provide(with formulas)
and please tell me that how to calculate the capacitance required by the load (assuming I got an Inductive load of 80 Ampere Peak),I.e if I want to use it place near the Input of h-bridge mosfets Input supply.

I don't have the formulas to calculate the pump current but because you are using a high frequency of 20K the current can be high and the ripple low with just a small capacitor because the capacitor gets charges 20000 times/sec not 100 like in a simple mains psu.
there are many websites that provide the formulas to calculate the output ripple for a specified current, a google search will give many more
Power Supplies
Website of Wayne Stegall - Power Supply Ripple Calculations and Capacitor Size

I suppose the psu capacitor size depends on the type of psu, for transformer designs the rule of thumb is about 1000uf for every Ampere of output, in a pulse psu the capacitor is much lower because the frequency is higher.
Will you make your own power supply for that much current?
A commercial pulse psu would probably be more practical.

Alex

It seems suboptimal, that the 390 ohm resistors of the predriver are consuming most of the charge pump output power. The resistors have to be rated for > 1W. You can go for a totem-pole predriver (requires an additional transistor and a diode) and a factor >10 increased load resistor.

A rough estimation suggests, that the dimensioning of the charge pump will be O.K. with 10 uF ceramic caps or good low ESR electrolytic. But switching times have to be considered, so I suggest a simulation.

P.S.: I also think, that a standard boostrap driver chip, supplemented with a small charge pump for 100% duty cycle operation will result in a lower overall part count and less power consumption. If the output current of these drivers is insufficient, you still can add complementary followers to increase it.

I can't exactly picture what you mean, I can understand a totem pole driving the second totem pole but the resistor I would place in this case would be between the totem poles (between emitter of first stage and base of the second) to limit the base current.
I don't understand how I can use a higher resistor (3k9) to drive the second totem pole, this would give just 5mA to the base.
I can't picture the diode functionality and how to make the first totem pole provide 20v in the output when the input is from an mcu at about 3v.
Can you please explain the topology of your suggestion.
Another way I can think of to limit the current consumption would be with a PNP that has the 390 ohm resistor as load, in that case the 50mA would flow only when the PNP is on but a NPN is also needed to drive it from a 3v mcu control signal.

Alex

So ,Finally Should i start building my circuit or not???

I'm not sure, this circuit works as it is but FvM suggested a change using a totem-pole predriver with a higher value resistor and a diode but I'm not sure how to implement it.

Alex

In my understanding, "totem-pole" is exclusively referring to the structure comprised of R1,
Q1 and D1. It's copied from good old TTL technology.



Unfortunately, it's substracting another diode voltage drop from the available gate voltage. I mainly wanted to "grumble" about high driver current consumption and at least provide a solution. Using a darlington for the upper NPN is another option, of course. But as said, I would prefer integrated drivers.

If you can tolerate the power dissipation, you should start with the 390 ohm load. I didn't intend to confuse the discussion.

I like "grumble", it motivates me to do things better

I have seen the NPN/PNP pair called a totem pole in application manuals for mosfet drivers etc. so I don't know if it has two meanings.

**broken link removed**

I have seen a similar circuit before, it was driving the mosfet directly


Yes it limits the consumption and it can actually provide higher currents to the base of the totem pole pair (as long as it is needed) so the current provided to the mosfets gate will be higher too.
After the mosfets charge the consumption drops to about 7mA (I have used a 5k resistor) when q4 is on or almost 0 when it is off.

Ashkar, it is up to you, you can use either way.

Alex

I also remembered the meaning of "totem-pole" incorrectly. I see, that's originally designating the classical all-NPN TTL output stage. So there's a certain similarity to a complementary push-pull stage, but I think we shouldn't overstress the historical term.
TTL

Thank you Guys these wonderful posts, and now I would Resume to build my circuit ,May be Starting the prototype from tomorrow .Any further suggestions .................

Any further suggestions ................

Click to expand...

Use an integrated driver.....:lol::lol::lol::lol::lol::lol:

Alex

Why? We came all the way up to just Implement the Dedicated driver!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Doing a discrete mosfet driver is very useful to learn how things work, it can work fine but you will probably get better performance from a dedicated driver chip and it will take less space too.

Alex

I have started building this circuit on my breadboard,I have successfully drives the bootstrap circuit ,but there is a problem,ie the voltage level is around 19.3vdc at the output.and when hocked up with the single mosfet driver stage the o/p becomes 15.88vdc.

When I used 30uf/50v caps the voltage level was too lo around 15.7v (without load)
and now I am using 470uf/35v caps I am getting an o/p of 19.3v.

Also I wanted to use An Totem -pole pre-drive that would give a more efficiency.

Have you used this schematic https://obrazki.elektroda.pl/34_1307328587.jpg with a separate pump?
What is the frequency of the pump and how fast are you switching the mosfet?
How fast are you switching the mosfet?
Have you tried to turn the mosfet on (steady, no switching) and measure the voltage?
for a pre-driver you can use the one shown by FvM in post #52

Alex