Is anyone familiar with the IR2304 MOSFET driver?

[Tom.G]

P.S. What did you think of the ON/OFF switch methodology I thought of (previous post) for measuring di/dt of the inductors? I assume there is a better method though?

Yes, that could be a practical way of measuring the inductance.
Other methods:

• Borrow or purchase an Inductance meter. An LCR meter that measures Inductance, Capacitance, Resistance is in the $150USD range. Depending on what type of circuitry you tend to work on they may not be used much, but when needed are a huge time saver. You can even measure the characteristic impedance of a transmission line with them!
  
• If you have a variable frequency Audio signal generator available.
  • Connect the inductor the the Audio generator thru a series resistor (100 to a few 1000 Ohms)
  • Connect a known value capacitor across the inductor. NOT an electrolytic, their tolerance is often -50% to +100% and are not stable.
  • Connect your 'scope across the inductor/capacitor pair to measure voltage
  • Vary the Audio generator frequency to find the peak reading on the 'scope
  • This is the resonant frequency of the LC tuned circuit, from which you can calculate the inductance using L= (1/(2⋅π⋅f))²/C
    Where L is in Henries, F in Hertz, C in Farads (oh, and π of course, 3.14...)

The core you specified is being sold for power transformer usage, meaning it is a low frequency core. At the switching frequencies you are considering, that core will likely have high losses and poor magnetic performance. Don't expect it to do much more than waste energy.

Cheers,
Tom

 

[Baluncore]

Tom.G is correct.
But there is no point measuring the inductance of a low frequency inductor at low frequencies, if you are going to operate it at higher frequencies where it will have significantly lower inductance, with a much higher loss. Iron powder cores will get too hot when PWM, driven by an H-bridge.

To uneducated sellers of cores, the word “ferrite” is closely associated with the term toroid. The inclusion of the word “ferrite” on those web sites get a greater hit rate and increase sales. It does not mean the material really is a high frequency ferrite.

The frequency characteristics of a core is determined by composition. Different composition materials have different standard colour codes. Green is not ferrite, it identifies the composition as iron powder. It has electrically conductive iron particles with a low frequency response in a non-conductive ceramic or resin binder. For higher frequency applications you need to specify a more appropriate electrically non-conductive ferrite based material.

It is not for us to recommend or guess what material you should use. It is for you to work out why you need an inductor in that circuit in the first place. If you need an inductor, a design engineer must select a material and core dimension based on design specifications.
I would throw out the inductors and drive the inductance of the motor directly with the H-bridge.

 

[Tom.G]

I would throw out the inductors and drive the inductance of the motor directly with the H-bridge.

If throwing out the inductors, watch out for those 3uF caps across the motor windings. At 20kHz they have 2.6Ω impedance, 14Amps from a 36Volt supply. At 250kHz, 0.21Ω, 170Amps. Ouch! Better turn off your smoke alarms.

Cheers,
Tom

 

[tim9000]

Yes, that could be a practical way of measuring the inductance.
Other methods:

• Borrow or purchase an Inductance meter. An LCR meter that measures Inductance, Capacitance, Resistance is in the $150USD range. Depending on what type of circuitry you tend to work on they may not be used much, but when needed are a huge time saver. You can even measure the characteristic impedance of a transmission line with them!
  
• If you have a variable frequency Audio signal generator available.
  • Connect the inductor the the Audio generator thru a series resistor (100 to a few 1000 Ohms)
  • Connect a known value capacitor across the inductor. NOT an electrolytic, their tolerance is often -50% to +100% and are not stable.
  • Connect your 'scope across the inductor/capacitor pair to measure voltage
  • Vary the Audio generator frequency to find the peak reading on the 'scope
  • This is the resonant frequency of the LC tuned circuit, from which you can calculate the inductance using L= (1/(2⋅π⋅f))²/C
    Where L is in Henries, F in Hertz, C in Farads (oh, and π of course, 3.14...)

The core you specified is being sold for power transformer usage, meaning it is a low frequency core. At the switching frequencies you are considering, that core will likely have high losses and poor magnetic performance. Don't expect it to do much more than waste energy.

Cheers,
Tom

I didn't expect the seller to fully understand the specific application of the toroid, but I shouldn't have taken "ferrite" for granted. And I didn't realize there was such a colour code. However, what confuses me, is that I bought 5, and out of the 5, two of them I wound as isolation transformers. Then I wired it up in such a way that there was one diode on the secondary of each core, and I used this to make a full wave DC rectifier. So one core would rectify one half of the wave, and the other core would rectify the other half of the wave. Now, I had 80 turns on each of the cores, yet they still seemed to saturate at about 1.5A, and would audibly hum. That is why I concluded they must be used for high frequency applications (not the 50hz I was rectifying).

 

[Tom.G]

two of them I wound as isolation transformers. Then I wired it up in such a way that there was one diode on the secondary of each core, and I used this to make a full wave DC rectifier. So one core would rectify one half of the wave, and the other core would rectify the other half of the wave.

AIEE! (look it up).
You would do better by using one transformer and a bridge rectifier.

 

[tim9000]

AIEE! (look it up).
You would do better by using one transformer and a bridge rectifier.

I know, I have a ton of bridge rectifiers, I am going to make a proper DC supply using darlington transistors. But the point of this was I wanted to see if it would work (I wanted to just use two diodes for a rectifier). And my point now is that I have no idea how these bloody cores are behaving.

 

[Baluncore]

And my point now is that I have no idea how these bloody cores are behaving.

You can get an introduction to the uses of magnetic saturation from the first chapter of “Magnetic Amplifiers” By Paul Mali, 1960. http://mirror.thelifeofkenneth.com/lib/electronics_archive/Magnetic_Amplifiers_Paul_Mali_1960_text.pdf
Those green cores might make a good magnetic amplifier if you put two next to each other sharing a common winding.

 

[tim9000]

You can get an introduction to the uses of magnetic saturation from the first chapter of “Magnetic Amplifiers” By Paul Mali, 1960. http://mirror.thelifeofkenneth.com/lib/electronics_archive/Magnetic_Amplifiers_Paul_Mali_1960_text.pdf
Those green cores might make a good magnetic amplifier if you put two next to each other sharing a common winding.

I know magnetic amplifiers quite well, but I'm not sure there is much practical modern application for them?

Realistically, it looks like I might have to sideline the existing green toroids until I get some time to do some testing on them and figure out what the go is, with them.

Okay I've done some very cure research, and it seems:
Gray 175 50 Khz to 500 Khz
Blue 100 500 Khz to 5 Mhz
Red 57 2 Mhz to 30 Mhz
Yellow 47 10 to 50 Mhz
Black 32 30 to 100 Mhz

as a rule of thumb?

Ideally I think:
https://www.ebay.com.au/itm/Magneti...283326415854?_trksid=p2385738.m4383.l4275.c10

would suit me best for 250khz. However, when factoring in the shipping, that is way too expensive for me. But what about:
https://www.ebay.com/itm/NEW-1PC-T300-2-imported-magnetic-ring-iron-core-magnetic-ring/112550397278?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20131003132420%26meid%3D4e15f26d6f044a0c91fba72d2c7de169%26pid%3D100005%26rk%3D1%26rkt%3D5%26sd%3D283326415854%26itm%3D112550397278&_trksid=p2047675.c100005.m1851

I assume they mean 35 relative permeability between 250khz-10Mhz, but they say it can handle half a kW. Is 'Carbonyl E' a suitable material for such an application?

Thanks

P.S. Is there a simple setup for measuring the permeability of a core? Or you need to make a BH curve and figure it out.

 

[Baluncore]

P.S. Is there a simple setup for measuring the permeability of a core? Or you need to make a BH curve and figure it out.

You will be able to answer that yourself when you have read sufficient technical literature on magnetic circuits and materials.

 

[tim9000]

You will be able to answer that yourself when you have read sufficient technical literature on magnetic circuits and materials.

Okay, and did you have any thoughts on:

https://www.ebay.com/itm/NEW-1PC-T300-2-imported-magnetic-ring-iron-core-magnetic-ring/112550397278?_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=20131003132420&meid=4e15f26d6f044a0c91fba72d2c7de169&pid=100005&rk=1&rkt=5&sd=283326415854&itm=112550397278&_trksid=p2047675.c100005.m1851

 

[Baluncore]

Okay, and did you have any thoughts on:

Electronic engineering is not like playing with children's construction blocks.
You appear to be quite unaware that engineering involved calculations.
I cannot give my approval for specific components in an unspecified circuit.

 

[tim9000]

Electronic engineering is not like playing with children's construction blocks.
You appear to be quite unaware that engineering involved calculations.
I cannot give my approval for specific components in an unspecified circuit.

Okay, I'll try some quick maths, so taking: https://www.ebay.com.au/itm/Magneti...283326415854?_trksid=p2385738.m4383.l4275.c10

for example, because they give better data: "Toroid Core Size: OD = 61mm (2.4 inch) x ID = 36 mm (1.4 inch) x HT=12.7 mm (0.5 inch)Material Grade: Permeability of 10,000, Max Permeability 20,000
Saturation Flux density 4300 gauss at 10 oersted, 25 deg C
Residual Flux Density 800 gauss, Volume resistivity 15 ohms-cm, Curie temp 125 deg C.
Le = Effective Magnetic Path Length: 14.5 cm
Ae = Effective Cross Section Area: 1.57 cm2
Ve = Volume : 22.7cm3
Al = Inductance Factor : 13,690 nH/t or mH/1000turns
RoHS Compliant
Application / Uses :
W material with permeability of 10,000 is used as Common Mode chokes for 100 Khz to 1 Mhz.
It is also used in resonant circuit in 1 Khz to 250 Khz. "

Note, I don't understand if they're saying it can work for frequency range 100 k to 1 Mhz, but I'll assume so.
I believe 4300 gauss is equal to 0.43 T, which is my maximum flux density.

for my application I'll be using maybe 15A rated current, I can specify the number of turns I want, they give the relative permeability (I think it's relative) and effective length of the magnetic path 0.145m. If I take the permeability to be 10,000*4Pi*10^-7 = 0.0126 (H/m) and the number of turns is 80, therefore: B = μ*N*I/L = 104 T. So yeah, clearly something isn't right. I noticed this yesterday, but I put it down to hasty calculation.

P.S. I just did the T300-2 core too:

outside diameter - diameter = 28.2 cm

L = 2*Pi*(28.2/2) = 88.6 cm

u = 35*4*Pi*10^-7 = 4.4*10^-5 (H/m)

N = 80

I = 15 A

B = 4.4*10^-5*80*15/0.886 = 0.0596 T

Which looks okay, but they don't give a maximum gauss, so I don't know.

 

[Baluncore]

for my application I'll be using maybe 15A rated current

Maybe they will work, maybe they won't.

 

[tim9000]

Maybe they will work, maybe they won't.

Well it's only the T300 I would expect to work without saturating, but good to get another opinion anyway (especially as I am so inexperienced).

 

[jim hardy]

Then I wired it up in such a way that there was one diode on the secondary of each core, and I used this to make a full wave DC rectifier. So one core would rectify one half of the wave, and the other core would rectify the other half of the wave. Now, I had 80 turns on each of the cores, yet they still seemed to saturate at about 1.5A, and would audibly hum. That is why I concluded they must be used for high frequency applications (not the 50hz I was rectifying).

And my point now is that I have no idea how these bloody cores are behaving.

A transformer supplying a nontrivial half wave rectified load will saturate.
That's because during the half cycles that the load conducts, primary current is higher than the opposite half cycle..
That means - during those half cycles the primary IR drop is more, leaving less voltage across the transformer's inductance.
So the voltage across the inductance has a DC component.
and that drives flux up the BH curve and the core saturates .

see
http://support.fluke.com/find-sales/download/asset/2103547_a_w.pdf

Theory and analysis
Some older electrical devices use half wave rectifiers to reduce power consumption. An example would be an early hair dryer with a “high/low” switch. At low speed, a series diode allows the circuit to draw current on only half of the voltage cycle. At high speed, the switch shorts out the diode — to allow current to flow during the full cycle. These devices wreak havoc on ac power distribution systems, because they generate dc current in the half wave configuration. The dc current will unbalance the magnetic flux in the transformer and push the transformer core into saturation on one half of the current cycle. The process of going in and out of saturation will produce strange noises from the transformer core.

 

[tim9000]

A transformer supplying a nontrivial half wave rectified load will saturate.
That's because during the half cycles that the load conducts, primary current is higher than the opposite half cycle..
That means - during those half cycles the primary IR drop is more, leaving less voltage across the transformer's inductance.
So the voltage across the inductance has a DC component.
and that drives flux up the BH curve and the core saturates .

See http://support.fluke.com/find-sales/download/asset/2103573_a_w.pdf

Hey Jim,
Thanks for the reply, hope you're well (it's 45 degrees Celsius today where I am).
The toroids for the rectifier were 64 turns each for primary and secondary (wound twisted bifilar) for each of the two toroid cores. The issue is that the load was literally kΩs (pretty sure even when open circuit secondary). So I've put this on the back-burner for the time being.
But I don't really understand when you say 'opposite half cycle' because even though there is probably a DC component in the Fourier sense, as far as I can see, each core is seeing a current 'hump' on the half of the cycle when it is forward conducting. Maybe this is what you mean. But if this is the case, any transformer that supplies a rectifier would experience the same thing, if not with a bigger DC component.
I had to sketch it out from memory to think about it:

I have not had a chance to supply the primary sides in parallel. This might help.

 

[tim9000]

I think I found some better data on the T300-2:
https://www.aliexpress.com/store/pr...l?spm=2114.12010612.8148356.14.c0652f262mrFin

 

[jim hardy]

I have not had a chance to supply the primary sides in parallel. This might help.

yeah, you're trying again to make two transformers have equal primary but unequal secondary currents,
so something's got to give.

reason it out
at any instant what's Ipri on both transformers? What's Isec ?

Math and reasoning got to agree.
If they don't , either the reasoning is wrong or you picked the wrong math to go with it.

 

[jim hardy]

lessee 45 X 2 = 90, - 10% is 81 , +32 is 113F? I'm from Florida - Can air really get that hot ?

45 F was our high today, Daffodils are trying to sprout.. Had snow a couple days ago but it melted yesterday.

 

[tim9000]

yeah, you're trying again to make two transformers have equal primary but unequal secondary currents,
so something's got to give.

reason it out
at any instant what's Ipri on both transformers? What's Isec ?

Math and reasoning got to agree.
If they don't , either the reasoning is wrong or you picked the wrong math to go with it.

Woops, I think I did the dot convention depiction wrong!
SORRY
From memory the dots should be both UP or both DOWN at the same time!

 

[tim9000]

lessee 45 X 2 = 90, - 10% is 81 , +32 is 113F? I'm from Florida - Can air really get that hot ?

45 F was our high today, Daffodils are trying to sprout.. Had snow a couple days ago but it melted yesterday.

I stand corrected, it got up to 46.8 dec C peak today :-|

 

[essenmein]

Couple of things I'll throw in here, some may have been mentioned already.

1) Put a small series resistor with the boot strap diode, makes life bit easier for it since limits the charge current to the caps.
2) You should not need such large boot caps, it only needs to provide hold up for one cycle and your gate charge is not that much, then you need to have a boot charge initial pulse (ie turn all low sides on before starting drive).
3) I'd leave the 1M ohm in there, its standard practice for us to have several 100kOhm in there to keep gates from building charge in case of a disconnect or failure (there is usually a lot of energy on the DC bus that an erroneous turn on would cause some erm "problems").
4) Its not a bad idea to put a 16V zener gate to source to protect the gate from transients (depending on how you are building this when you start to switch currents they will become a problem if your loop inductances are too high).
5) A motor designed for inverter/PWM use should NOT have any capacitance added between windings. Cut them out if you can.
6) Do NOT use external freewheeling diodes unless you are using IGBT, FETs have them for free, and they are typically rated with the same current as the FET. Plus that diode should only be conducting during the dead time if you are being good and switching both HS and LS actively.
7) Do not bother with filtering on the output of the inverter, motors have large inductances (that is after you get rid of the caps).
8) Distinct lack of motor phase current sense, which is needed to do any meaningful motor control.

 

[tim9000]

Couple of things I'll throw in here, some may have been mentioned already.

1) Put a small series resistor with the boot strap diode, makes life bit easier for it since limits the charge current to the caps.
2) You should not need such large boot caps, it only needs to provide hold up for one cycle and your gate charge is not that much, then you need to have a boot charge initial pulse (ie turn all low sides on before starting drive).
3) I'd leave the 1M ohm in there, its standard practice for us to have several 100kOhm in there to keep gates from building charge in case of a disconnect or failure (there is usually a lot of energy on the DC bus that an erroneous turn on would cause some erm "problems").
4) Its not a bad idea to put a 16V zener gate to source to protect the gate from transients (depending on how you are building this when you start to switch currents they will become a problem if your loop inductances are too high).
5) A motor designed for inverter/PWM use should NOT have any capacitance added between windings. Cut them out if you can.
6) Do NOT use external freewheeling diodes unless you are using IGBT, FETs have them for free, and they are typically rated with the same current as the FET. Plus that diode should only be conducting during the dead time if you are being good and switching both HS and LS actively.
7) Do not bother with filtering on the output of the inverter, motors have large inductances (that is after you get rid of the caps).
8) Distinct lack of motor phase current sense, which is needed to do any meaningful motor control.

Hi Essenmein,
Thanks very much for the reply.
1) I can put a series resistance with the boot strap diode, but why would we want/need to limit the charge current to the caps? Do you mean something like 0.01Ω resistance? for example
2) what size ceramic boot cap do you think I should use across VB and VS?
3) Okay, if you think I should leave the 1MΩ resistors in there, I'll do so.
4) I'll keep the loop inductances in mind, if I get any issues, I will put some 16V zeners into protect the gates. In future designs I will do it anyway.
5) Alright, I will remove the capacitance and inductors from the BLDC inverter and implement this in future non-BLDC inverter designs, when I hopefully have a more clear idea about how the inverter is operating.
6) So you're saying that with FET (i.e. MOSFET) the internal body diode should already be able to handle the current?
7) Okay, refer to my point #5.
8) I'm not sure what you are saying here. I have tested the output of my hall sensors and it triggers my code to output the three phase sequence as per a binary table I got online. So I am hopeful about the control code for the BLDC.

Thanks!

 

[Baluncore]

1) Put a small series resistor with the boot strap diode, makes life bit easier for it since limits the charge current to the caps.

Initial current is limited sufficiently by the circuit inductance, foil and diode resistance, and supply rise-time.

2) You should not need such large boot caps, it only needs to provide hold up for one cycle and your gate charge is not that much, then you need to have a boot charge initial pulse (ie turn all low sides on before starting drive).

The proposed mosfets have huge gate capacitance, so will require significant drive charge through the 60mA driver. For the very low PWM rate expected from such weak drivers with such high cap loads, I would increase the capacitance to maintain sufficient gate drive.

3) I'd leave the 1M ohm in there, its standard practice for us to have several 100kOhm in there to keep gates from building charge in case of a disconnect or failure (there is usually a lot of energy on the DC bus that an erroneous turn on would cause some erm "problems").

Those idiot resistors are always across the bridge drivers and bootstrap caps. Those structures should maintain gate off conditions during power up and down. If there is no gate control because the circuit is broken the fuse will blow.

4) Its not a bad idea to put a 16V zener gate to source to protect the gate from transients (depending on how you are building this when you start to switch currents they will become a problem if your loop inductances are too high).

The mosfet gates are sufficiently protected by internal zener diodes and by external gate stopper resistors.

5) A motor designed for inverter/PWM use should NOT have any capacitance added between windings. Cut them out if you can.

Those capacitors are not for the motor, they are part of the inverter output low-pass filter. This inverter is not designed to be an efficient motor controller.

6) Do NOT use external freewheeling diodes unless you are using IGBT, FETs have them for free, and they are typically rated with the same current as the FET. Plus that diode should only be conducting during the dead time if you are being good and switching both HS and LS actively.

This inverter is designed to have both Hi and Lo sides in continuous PWM. The flyback diode is not being used for soft commutation as would be done in an energy efficient motor controller.

7) Do not bother with filtering on the output of the inverter, motors have large inductances (that is after you get rid of the caps).
8) Distinct lack of motor phase current sense, which is needed to do any meaningful motor control.

But tim9000 is generating a variable frequency three phase voltage output, then running the motor as a synchronous motor. That is why low-pass output inductors and capacitors are needed for this 3PH inverter voltage source. Vector current control is NOT being used for torque management as it would be in a motor controller.

 

[tim9000]

The proposed mosfets have huge gate capacitance, so will require significant drive charge through the 60mA driver. For the very low PWM rate expected from such weak drivers with such high cap loads, I would increase the capacitance to maintain sufficient gate drive.

I was actually thinking about putting something like 0.1uF, 1uF, and 10uF ceramic caps in parallel so it would charge up fast and hold significant charge. Just a thought. What do people think?

Those capacitors are not for the motor, they are part of the inverter output low-pass filter. This inverter is not designed to be an efficient motor controller.

As I just said (post #58), I'll remove the capacitors & inductors for the BLDC specific application, since LC filtering isn't necessary.

Those structures should maintain gate off conditions during power up and down. If there is no gate control because the circuit is broken the fuse will blow.

?? So the 1MOhm resistors aren't just unnecessary, but they are a BAD idea?

But tim9000 is generating a variable frequency three phase voltage output, then running the motor as a synchronous motor. That is why low-pass output inductors and capacitors are needed for this 3PH inverter voltage source. Vector current control is NOT being used for torque management as it would be in a motor controller.

The motor is trapazoidally wound, not sinusoidally distributed windings. This is not a sine wave output inverter. As I said previously, I am using a standard step binary table controlled by the position of the hall sensors, e.g.:

And another opposite table output for reverse rotation direction.

The mosfet gates are sufficiently protected by internal zener diodes and by external gate stopper resistors.

Okay, I won't bother with the 16V zeners here or in future projects then.

Thanks!

 

[essenmein]

Initial current is limited sufficiently by the circuit inductance, foil and diode resistance, and supply rise-time.

Diode resistance I will agree, and certainly you can size the diode so that the current spike is no issue, this is just not a luxury you have if product cost is an concern. You do not want inductance to limit the current unless your favorite thing is EMI. However, if you don't want it to ring like a bell, and you want to put the smallest practical diode in there, then a small resistor (~1Ohm or so) gets you there, and it damps the boot circuit nicely.

The proposed mosfets have huge gate capacitance, so will require significant drive charge through the 60mA driver. For the very low PWM rate expected from such weak drivers with such high cap loads, I would increase the capacitance to maintain sufficient gate drive.

Huge is relative, its an adorable little guy from my perspective, on the power modules we build gate charges have exceeded 1200nC.

Then, there is only one "depletion" at turn ON before it gets recharged, so you charge a what 10-15nF cap from a 1uF, once the fet is on there is no more depletion, do the charge exchange math you loose a few volt off the boot cap, no problem. To put into perspective, 470nF happily run ~400nC bridge @ 20kHz, now, 1uF won't hurt it, its just unnecessary money if you are making lots of units.

But I agree that a 60mA driver won't do the job, generally that 60mA is more of an indication of its internal resistance, most likely thing to happen will be v slow switching times and maybe burn up the fets if they spend too much time in linear region. I'd use either the IR2301 or UCC27201, both basically the same thing with more drive current.

Those idiot resistors are always across the bridge drivers and bootstrap caps. Those structures should maintain gate off conditions during power up and down. If there is no gate control because the circuit is broken the fuse will blow.

Those idiot resistors quite nicely deal with a few lines in a DFMEA, 0.08c is a small price to pay, IMO, for that alone. They are not there for power up down, they are there when a solder joint breaks, or a gate lead comes off the DBC due to power temp cycle or what ever other fatigue failure the world throws at us (we put them on the module DBC not on control board).

Fuses? lol.

The mosfet gates are sufficiently protected by internal zener diodes and by external gate stopper resistors.

I'm sure you can find specialty fets with protection, however any "normal" discrete power fet I've seen does not have any zener diodes in the silicon. If you exceed Vgs by generally +/-20V your device is dead. Then there is loop inductance kick on turn off on your source, but that's probably not an issue with a 20A inverter unless the layout is super poor.

Those capacitors are not for the motor, they are part of the inverter output low-pass filter. This inverter is not designed to be an efficient motor controller.

Then they should be easy to remove.

This inverter is designed to have both Hi and Lo sides in continuous PWM. The flyback diode is not being used for soft commutation as would be done in an energy efficient motor controller.

Using the fly back diode, at all, does not make an energy efficient inverter, you synch rect or go home. Unless its IGBT which can only conduct in one direction.

Soft commutation is not a motor drive thing, the inverter defines the voltage states, if you let the machine somehow do this you are no longer applying the voltage you thought you were.

But tim9000 is generating a variable frequency three phase voltage output, then running the motor as a synchronous motor. That is why low-pass output inductors and capacitors are needed for this 3PH inverter voltage source. Vector current control is NOT being used for torque management as it would be in a motor controller.

Says BLDC several times, even if not closed loop current control (FOC etc) ie just comutating the voltage at the right time, you still don't need a filter on the inverter, the machine is a comparatively large inductance. (obviously as long as the switching frequency is high enough).

 

[Baluncore]

As I just said (post #58), I'll remove the capacitors & inductors for the BLDC specific application, since LC filtering isn't necessary.

So throw out the LPF transformer cores, move from voltage output to control of motor current.
That changes the game completely, and makes most of this thread redundant.

But I agree that a 60mA driver won't do the job, generally that 60mA is more of an indication of its internal resistance, most likely thing to happen will be v slow switching times and maybe burn up the fets if they spend too much time in linear region.

So, avoid the old IR2304, specify a higher current driver. Next consider more efficient, faster switching mosfets with lower gate capacitance.

Those idiot resistors quite nicely deal with a few lines in a DFMEA, 0.08c is a small price to pay, IMO, for that alone.

Is that $0.08 = 8 cents or 0.08 cents?
Engineering and manufacturing a product line involves a quite different design attitude than does building one experimental circuit. Removing the LPF cores from the circuit was an essential move, but it took three pages of topic.

 

[tim9000]

So throw out the LPF transformer cores, move from voltage output to control of motor current.
That changes the game completely, and makes most of this thread redundant.

I was thinking that the PWM control would still work without the inductors, because I was expecting the inductance of the motor windings to limit the rise of the current, similar to the LPF inductors.
So PWM voltage control won't work at all without the inductors?

Also, could you please address:

I was actually thinking about putting something like 0.1uF, 1uF, and 10uF ceramic caps in parallel so it would charge up fast and hold significant charge. Just a thought. What do people think?

?? So the 1MOhm resistors aren't just unnecessary, but they are a BAD idea?

 

[Baluncore]

Also, could you please address:
...I was actually thinking about putting something like 0.1uF, 1uF, and 10uF ceramic caps in parallel...

Everything that is important is addressed in the manufacturers data sheets and application notes.
You will have your answer when you read those notes.

 

[tim9000]

Everything that is important is addressed in the manufacturers data sheets and application notes.
You will have your answer when you read those notes.

Well, regarding "the idiot resistors" since they didn't depict it in the datasheet, I'll steer clear.

I may be mistaken, but I didn't see the bootstrap capacitance specified for the IR2304, but I'll look again.

Okay, so the higher the output short circuit current i.e. 60mA, the quicker the gate capacitance can charge up and turn ON, very interesting!

IR2301 or UCC27201

P.S. I'm looking at the IR2301, but I don't see it for that either.
For the UCC27201, I see an example circuit of 0.1uF. But would there be any harm in including a larger one in parallel for good measure?

Neither of these seem to have the internal shoot-through protection though. Doesn't this mean I have to be more careful triggering the Hin and Lin timing??

Stupid question, but if IR3201 and IR2304 are the same price, then what application would IR2304 be more suitable for than '01?

Taa.

 

[Baluncore]

Get a copy of the IR Application Handbook from irf.com
http://www.irf.com/technical-info/apphandbook.pdf
It is a descriptive index into their technical library.

Start by looking at things like design tip DT98-2 Bootstrap Component Selection
Study every sentence and every equation. Notice what it says about tantalum and ceramic capacitors.

Read everything relevant that they publish. Then read it again until it makes sense.
Keep doing that till next spring in Australia.
Don't ask questions that demonstrate you have not read the literature.

P.S. The bootstrap capacitor is not part of the chip. You must look in the application notes.

 

[essenmein]

Is that $0.08 = 8 cents or 0.08 cents?

Its 0.08 dollar cents, it almost costs more in SMT machine time to place the damn things.

 

[essenmein]

Well, regarding "the idiot resistors" since they didn't depict it in the datasheet, I'll steer clear.

I may be mistaken, but I didn't see the bootstrap capacitance specified for the IR2304, but I'll look again.

Okay, so the higher the output short circuit current i.e. 60mA, the quicker the gate capacitance can charge up and turn ON, very interesting!

P.S. I'm looking at the IR2301, but I don't see it for that either.
For the UCC27201, I see an example circuit of 0.1uF. But would there be any harm in including a larger one in parallel for good measure?

Neither of these seem to have the internal shoot-through protection though. Doesn't this mean I have to be more careful triggering the Hin and Lin timing??

Stupid question, but if IR3201 and IR2304 are the same price, then what application would IR2304 be more suitable for than '01?

Taa.

The required boot strap capacitance is a calculation you have to do based on the power devices you are using and other circuitry in the gate drive. Basically the boot cap has to provide enough charge to get the gate up to the right voltage (>10V), and have enough hold up time based on any charge bleed resistors you have. So its a simple charge exchange, and then RC discharge, then the goal would be to keep the gate above some minimum (8-10V) for your longest ON time and minimum supply voltage on the driver. One problem with boot strap type gate drivers is they cannot do 100% duty cycle, you always have to refresh the cap. There is no one "right" value.

The IR2301 and IR2304 are not the same price. They might be priced similarly on digikey or what ever, but make no mistake if you buy significant volume, the smaller driver will be cheaper, other wise there is zero point in making them. The smaller driver will have smaller output FETs, and the output FETs are what drives die size (the logic portion is quite small), and die size is what drives cost (parts per wafer).

Regarding shoot through, this is something you will have to manage in your software with these "dumb" gate drivers.

 

[tim9000]

Still reading through all the App notes...

 

[tim9000]

Update, I have finished soldiering the MOSFET driver. Can people please have a look at the attached pictures and offer thoughts. The circuit shown is the part of the circuit which interfaces between the micro-controller and the MOSFETS. So basically it houses the ICs and the digital outputs from the raspberry PI are wired into HIN and LIN. (There is a separate module for the Hall sensors to interface with the PI).

HO, VS and LO are connected to the mosfets as per the attached circuit diagram.

Much appreciated and sorry for the long delay.

P.S. in case you can't make the diode out in the circuit diagram, they are 1N4148 small signal diodes which have a forward conduction in the nano-second range from memory. I think they were rated for about 500mA or something.
The MOSFETS are NMOS IRF3205. I am willing to change these components if necessary, same goes for the IR2304. Happy to go with IR2301 if necessary, but will need to implement some anti-shoot through in the code to accommodate that IC. (Also would consider IR2104 if anyone thought it was preferable).