Is anyone familiar with the IR2304 MOSFET driver?

[tim9000]

Yes, the magnetic energy E = ½⋅L⋅I² becomes current, so it can get back to the supply capacitor, where it will be stored as energy E = ½⋅C⋅V².You have the Engineering all back to front. What value of inductance is required by the circuit to function correctly. What maximum current will flow in that circuit. What component is available that will meet those specifications.

Ah, so that's the significance of the supply capacitor. I didn't realize that. So I suppose once I calculate the Energy stored on the Inductor, that defines the minimum size of my supply capacitor. I have heard that electrolytic capacitors have a higher ESR, do you think this makes them inappropriate for this application? (Since they need to charge fast?)

With respect, I appreciate that I have the construction method back-to-front, but I did say that I'd refine the necessary design, such as inductance, as I go, and that I do expect to have some teething issues (like blown MOSFETS) along the way.

Thanks again

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?

 

[Baluncore]

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?

I do not see the point. The inductance is specified in the data sheet, and you know the voltage. That only requires arithmetic.

 

[tim9000]

I do not see the point. The inductance is specified in the data sheet, and you know the voltage. That only requires arithmetic.

As I said, I purchased the large ferrite torroids and I wound them myself from silicone insulated wire. They do not have a datasheet.

 

[Baluncore]

They do not have a datasheet.

The torroid core will have a data sheet with an A_L value.
If you counted the turns, you can calculate the inductance. L = A_L ⋅ n²

 

[tim9000]

The torroid core will have a data sheet with an A_L value.
If you counted the turns, you can calculate the inductance. L = A_L ⋅ n²

One would like to think so, however I did ask multiple sellers, none of whom could provide the datasheet.
This may not be the exact one (as I just typed it in the search) but it will give you an idea:
https://www.ebay.com.au/itm/Power-T...bF8TqAALjW0K2FFuLU4y5MV7BstRA=&frcectupt=true

 

[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!