Mosfet driver IR2112 help needed

[TKS]

I'm now realising that the only reason for me to use this chip is that its for purposes of positive feed to the N channel Fet..

Is it possible to fit a bootcap to a normal driver for example the 9amps TI one i earlier posted??

Tks

some pics to!

 

[TKS]

James,

i was studing the datasheet and i saw that COM = low side return, the above pic its just ground..(page 1)
watching at VCC its Low side supply is it true that bove are for me ground?? how the hell that cap can then charge it self??

wich sense has the diode?? or is it that the back EMF (negative vols charge that cap??

Tks

 

[hjames]

okay, where to start...

The diodes should be more than sufficient.

Can i eliminate the resistance of 10R?? i don't have a 10R with significant wattage...

Mosfets have capacitve gates - there is only current going through that resistor when the mosfet turns on and off, otherwise there is no current going through them, and I'd expect acual power dissipation in them to be in the milli - microwatt range.

anyways 6fets of my size should give me 600amps continous and 2400ams pulses sow i gues it should be quit bullet proof also i hope that the amd cpu cooler will let the lot stay cool.

Considering "0000" copper wire (i.e. 1/2 inch or 13mm copper rod) is rated for 400amps, and I don't see any of that, I'd expect the realistic rating is a bit lower...

sow in fact i though of charging the cap with the back emf of the motor?????
maybe a diode to prevent to blow the chip? before the pin?

? the back emf from the motor won't cause the voltage on the capacitor to increase (by much). If the motor is being forced to turn externally, then you'll need to worry about over-voltage.

I'm now realising that the only reason for me to use this chip is that its for purposes of positive feed to the N channel Fet..

If you mean: "The only reason to use this chip is to drive a high-side FET", then yes, that would be it (and a good reason as well). You can find less capable chips, and might be able to save ~20% of the cost of the chip or something.

i was studing the datasheet and i saw that COM = low side return, the above pic its just ground..(page 1)
watching at VCC its Low side supply is it true that bove are for me ground?? how the hell that cap can then charge it self??

This chip has two *different* sections. One side is built to drive a low-side mosfet, the other side can drive a high-side mosfet. The low-side mosfet is easy to drive and doesn't need the bootstrap capacitor or diode. The high-side on the other hand -

The idea is that when the high-side mosfet is off, the motor terminal will be at ground. At this time, the capacitor will have 11.4V across it (because of the bootstrap diode). When the high-side mosfet turns on, the motor terminal will be at 12V, the capacitor will *still* have 11.4V across it, and the upper capacitor terminal will be at 12+11.4=23.4V, which is enough to turn the mosfet fully on.

James

 

[TKS]

Don't untherstand, the gate resistor can be anything?? where are the high amps needed for the fast charging???

also i now use no lower side mosfet...its just the upper one and the diodes...

Problem to use one lower is that the pwm signal should then be splitted or tapped and i will need an inventor to make from my low pulse a high pulse and feed that signal into the chip, problem is that its scaries me because overlapping is then serious a problem altough it would be in the nanosecond...

anyway i guess it should work atleast it does if the gate charge is wat you say!

 

[TKS]

am i correct in saying that the Bootstrap cap has to be the impedance charge of all the fets + a margin for sure + a load to be at the same load as them sow in fact 6x charge per fet * 2 ??

just a logical thinking really...

Have soldered a bit more Pb on the strips to the fets... to make sure they are better balanced... my old soldermachine couldn't cope with the heat (think because of the heatsink)

but i'm sute uts quite balanced now..

is the lower one cruisucial??

Tks

 

[hjames]

Each mosfet has a gate charge of ~100nC. Current is defined as I = dq/dt, so if you want to turn on a mosfet in 100nsec, you need 1A of current. The peak power on a 10 ohm resistor is going to be I^2*R = ~10W, but this is over a very, very short period. Since I don't want to remember how to integrate this properly - average power per transition is <~1 microwatt. So if you have a 1KHz PWM signal, dissipated power would be < 1mW.

I made a bit of a mistake though - I didn't realize this chip was only capable of driving a small amount of gate current - 200mA sourcing, 400mA sinking. The amount of gate current is important because you want to drive the mosfet on and off as fast as you can in order to reduce the amount of power wasted in the mosfet.

As I've said before, only using a high-side mosfet should mostly work, but you'll need to try it out and see if it has any issues - if the high-side mosfets get too hot or something else happens, then we'll know it wasn't good enough.

 

[TKS]

James, is it a option of cutting out a couple of fets..

for example try it out with 4 of them...(400amps continous in theory) then the capacitance will go lower and the mili amps per gate higher right? I have in the post mail some 7/9 amps drivers but then i need the bootstrap solution externally??

isn´t their a way of using one mosfet just for turning on the rest of them???

Then we have 200mili amps for 1 mosfet and the rest of them are switched on by that mosfet???? For example: the source of 1 fet is connected to the gates of the rest of the 5 exept his own gate. Sow in fact the first 12volts go very fast then the last boost to 24volts is done by the cap.

also i tought of a 27volt zener (have them in stock) to protect the gates from overcharging i know that a silly bit over the limit ruins them... maybe a good mod to-be-sure if something happens we then know that the gate voltage wasn´t to high..

TKs

p.d. anyways i will lower the Frequency to 1Khz the less switches per second the cooler it will run..

 

[TKS]

I have 5 of this chips each:

https://www.electro-tech-online.com/custompdfs/2006/08/21420d.pdf

Item: TC4421EPA inverted
Item: TC4422EPA non inverted


https://www.electro-tech-online.com/custompdfs/2006/08/21418C.pdf

Item: TC4404EPA
Item: TC4405EPA

If i take just a normal driver chip would i be able with a zener or something to make a bootstrap sow that the gate will be charged up??

also in the last link we see a sheme where the gate is just hooked up to VDD
page 7 fig 3-4 in a full bridige config...

 

[TKS]

mhh studing the fact for the zener i just noticed that there is a absolute max rating of 20volts gate source voltage!

sow i source is 12volts then gate can be max 32volts right??

but when device is of i have to ensure the cap is empty not?

Tks

decided that i first try with this chip, else after this chip i will fit some 9A drivers.. maybe 2 of them in parrallel will be enough!

perhaps with an extra bootstrap??!

in fact to protect it right i need a 19volts zener and put it to source right?

 

[hjames]

James, is it a option of cutting out a couple of fets..

for example try it out with 4 of them...(400amps continous in theory) then the capacitance will go lower and the mili amps per gate higher right? I have in the post mail some 7/9 amps drivers but then i need the bootstrap solution externally??

isn´t their a way of using one mosfet just for turning on the rest of them???
...
also i tought of a 27volt zener (have them in stock) to protect the gates from overcharging i know that a silly bit over the limit ruins them... maybe a good mod to-be-sure if something happens we then know that the gate voltage wasn´t to high..

TKs

p.d. anyways i will lower the Frequency to 1Khz the less switches per second the cooler it will run..

Don't worry about changing the number of mosfets. When you test it out, you can figure out if you need to improve the switching speed. Although I would suggest that you just use 1 fet while you are initially testing just so you don't blow out an entire bank of mosfets at the same time.

If you want to protect the mosfet gates, put a 15V - 19V zener between the gate and source connections, after the 10R resistor. This is usually only needed in extreme circumstances - If you look at the capacitor, it is relative to the mosfet source. The capacitor voltage will never be greater than 11.4V + V(mosfet source) and there is no way of desroying the mosfet with this capacitor unless something gets shorted/disconnected.

I have 5 of this chips each:
...
Item: TC4421EPA inverted
Item: TC4422EPA non inverted
...
Item: TC4404EPA
Item: TC4405EPA

If i take just a normal driver chip would i be able with a zener or something to make a bootstrap sow that the gate will be charged up??

You could use any of these chips to generate a high voltage if you want. The idea behind the bootstrap capacitor is that on every PWM pulse, the capacitor will charge up a little bit, and it is always safe. If you use an external high voltage supply, you will need to add a zener to protect the mosfets. (With the bootstrap approach, the gate zener is *not* required).

James

 

[TKS]

Ok, sow in fact the best thing what i can do perhaps is to just drop this chip and place a 9Amps in his position. And use an external bootstrap configuration???

Should i use 10R for all the gates or per gate???

If you think that with the 9amps driver i will get better results tell me, i have atleast two 9 amp driver (TI model)

problem i see is that in the datasheet they don't mention bootstrap configs??
could i blow out a pin??

Tks

 

[TKS]

Ok,

i'm gonna test the setup..

I have placed 6 resistor 1/4watts in parrallel of each 126ohms it gives us thus 21ohms...

to sink the maximum chip current 420ma i need 30ohms sow we are well unther it...

Hopes it will work..

Tks

 

[hjames]

Ok, sow in fact the best thing what i can do perhaps is to just drop this chip and place a 9Amps in his position. And use an external bootstrap configuration???

Should i use 10R for all the gates or per gate???

If you think that with the 9amps driver i will get better results tell me, i have atleast two 9 amp driver (TI model)

problem i see is that in the datasheet they don't mention bootstrap configs??
could i blow out a pin??

Tks

The best thing to do is to finish building the circuit, then decide what you need to improve, and go on from there. There are literally a couple dozen different parts with different tradeoffs that you could use in this circuit. There may also be mosfets which are better suited for this application. The number of combinations is infinite...

I'd suggest that you build any circuit, test it (possibly to failure) and figure out what you need to improve, if anything at all. It's all about experience - build the circuit, learn something and go on further. You can spend an endless amount of time twiddling with the details, but the only thing that counts is whether the car moves or ends up in a big puff of blue smoke, and there's only one way of telling...

In any case, you should have one gate resistor per mosfet (total of 6 in your circuit). When the mosfet transitions between on-off, source of the mosfet is going to see a very rapid transition. This ends up capacitivly coupling into the gate (along with some other effects) and might cause some oscillations. The gate resistors keep these from interacting with the other mosfets. Personally I just like having a resistor between the gate and the driver chip so that it's easier to diagnose a blown mosfet.

All the 9amp TI mosfet drivers I see are low side drivers. Bootstrap stuff is only used on high-side drivers. Those chips won't work in this app.

James

 

[hjames]

Ok,

i'm gonna test the setup..

I have placed 6 resistor 1/4watts in parrallel of each 126ohms it gives us thus 21ohms...

to sink the maximum chip current 420ma i need 30ohms sow we are well unther it...

Hopes it will work..

Tks

The resistor value is fine - chip internally limits it's current and won't be damaged.

James

 

[TKS]

Ok, James, i now hat ite in parrallel if it isn't dangerous i let it be sow and test the setup...

first with a bulb just looking if it reaches full brightness then i will connect a motor up and start with low pwm and look what it does...

i only have 6ohms and 14ohms..

Tks

p.d. atleast i now have 6x 1/4 watts of resistor power sow in fact an 1,5Watt 21ohm resistor

 

[TKS]

Ok, i have hooked up everything cables where prepared terminals where put on. Have brought some 4mm dia cable..

Ok, first i connected it all up to the battery a small spark occured the 10.000uF cap charged.

Then i prepared the gearbox program to work with the reverse controller.
I made a small test program wich puts some pins high and wich outputs a PWM signal to the board.

First thing i noticed was that the relais didn't switch sow i guessed that the transistor was wrong, changed the transistor and it worked.

Sow at least when i select reverse the universal relais is activated, the fan will start blowing, the reverse light on the car will light up, the starter solenoid will be meshed up with the gear ring.

Anyway that point i reached... then i tested the mosfets...

i hooked up a bulb as load and applied with my multimeter in amp mode i made the connection between VDD (12volts) and the gate the bulb lighted up, the see the difference i touched also directly the bulb and offcourse it lit up a fairly bit more my amp meter showed 1,75amps... (21watts bulb)..

when i touched the gate it shows 0,08amps.. when i touch the gate before the resistors it shows 0,04 but the bulb lights up the same amount.

Sow i started to investigate where wy the chip didn't responded i touched the HIN pin with the 12volts but it did nothing to the bulb..

i checked the pwm signal with a led (keeped iluminating, while the multimeter said 0,01volts) sow i guessed it wasn't that.. comeing home i remembered a Enable pin, watching the datasheet this morning is saw a input SD pin.. INPUT shutdown pin.

If you read the description you would think if high then it shutsdown.. but when i look at the symbols i see it going to AND symbols and to SET symbols sow i guess i just have to wire a 2K Resistor to VDD to that pin not????

Tks

- Didn't tried yet this solution..

 

[TKS]

Ok, its not the SD pin because of the timing sheme explaning it all...

Think i have got the VCC pin connected to 0volts/ground.. and i think it needs to be to VDD Huge fault because i have no clue on how the cap should charge sow a bit of NEWBIE error, hope i didn't broke the chip..

We shall see..

Fase 2 is untherway

Tks

 

[TKS]

Well Fase 2 Succesfully ended!! BUT one small side is that the chip needs 8,5 / 9 volts minimum input voltage!! on the HIN pin!!! thought it was TLL compatible but it isn't sow! there is a solution needed to convert 5volts in 10 volts..

The good news is that when i manualy tick the HIN pin to VDD (12volts) the bulb iluminates!! on full brightness altough i have to say that it automaticly shutsdown but when i tick fast its clearly to see that it iluminates more then when only applying 12volts to the gates sow almost don would i say and then we can try the motor!!!

can i convert this with a NPN transistor?? or do i need a PNP one?? or just an opamp (more hassle??)

Tks

 

[TKS]

-

Well wich of the 2 cant choose wont make a huge different i guess

Don't want to use a opamp because i have limited room...

I made the 2nd one because i think i don't have a PNP in my toolbox sow basicly i just made 2 invert setups but feeded the resistors with 12volts..

TKs

 

[hjames]

Well Fase 2 Succesfully ended!! BUT one small side is that the chip needs 8,5 / 9 volts minimum input voltage!! on the HIN pin!!! thought it was TLL compatible but it isn't sow! there is a solution needed to convert 5volts in 10 volts..

Tks

It *does* support different threshold voltages. Connect Vdd to the logic power supply(5V) and leave Vcc connected to 12V