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IR2110 gate driver issues.

P

Pooh Bear

Jan 1, 1970
0
Hi all,

I'm using an IR2110 high and low side gate driver in a smps that I
mentioned some time back in the group under the thread 'should I use a
SG3525'.

I've had some 'odd' power device failures that I didn't expect in
entirely benign situations, such as the half bridge output simply
driving the primary of my transformer.

I realised that it happened a couple of times when I wound down the
input volts ( I'm supplying the board via a variac and isolating
transfomer for development ).

The IR2110 has undervoltage lockout. Fine ! I checked it carefully today
and the UVLO for the low side and high side aren't linked. Indeed a
careful look at the data sheet does indeed show that there's no
connection. The low side drive activates at about 8V and the high side
about a volt higher.

Needless to say this creates 'issues' !

Anyone here used this part and care to comment ?


Regds, Graham
 
H

Harry Dellamano

Jan 1, 1970
0
Pooh Bear said:
Hi all,

I'm using an IR2110 high and low side gate driver in a smps that I
mentioned some time back in the group under the thread 'should I use a
SG3525'.

I've had some 'odd' power device failures that I didn't expect in
entirely benign situations, such as the half bridge output simply
driving the primary of my transformer.

I realised that it happened a couple of times when I wound down the
input volts ( I'm supplying the board via a variac and isolating
transfomer for development ).

The IR2110 has undervoltage lockout. Fine ! I checked it carefully today
and the UVLO for the low side and high side aren't linked. Indeed a
careful look at the data sheet does indeed show that there's no
connection. The low side drive activates at about 8V and the high side
about a volt higher.

Needless to say this creates 'issues' !

Anyone here used this part and care to comment ?


Regds, Graham

Hey Poop,
What is this, Electronics 101! Sure these parts are old enought. You should
worry about electromigration.
The SG3525A has UVLO at about 7VDC and locks it's outputs low. Make sure it
goes down before the IR2110. YMMV with the SG3525.

Harry
 
W

Winfield Hill

Jan 1, 1970
0
Pooh Bear wrote...
I'm using an IR2110 high and low side gate driver in a smps that
I mentioned some time back in the group under the thread 'should
I use a SG3525'.

I've had some 'odd' power device failures that I didn't expect in
entirely benign situations, such as the half bridge output simply
driving the primary of my transformer.

Device failure meaning damaged components, or meaning, a FET that
didn't do what you expected under a certain circumstance, but yet
wasn't actually damaged.
I realised that it happened a couple of times when I wound down the
input volts ( I'm supplying the board via a variac and isolating
transfomer for development ).

The IR2110 has undervoltage lockout. Fine! I checked it carefully
today and the UVLO for the low side and high side aren't linked.
Indeed a careful look at the data sheet does indeed show that
there's no connection. The low side drive activates at about 8V
and the high side about a volt higher.

IR has to separately detect the low-side and high-side voltages,
because the latter is the voltage across the flying capacitor.

The mismatch you observed sounds good: the high side should stop
working well before the low side, thereby preventing any shoothro
current, which could be disasterous.
Needless to say this creates 'issues'!
Anyone here used this part and care to comment?

Let's hear about your issues.

BTW, recognizing the need for low-voltage protection, and the need
for a benign response to low-voltage conditions, you could easily
add a comparator operating at lower voltages, plus shutoff gates
managing the IR2110's three logic inputs, per your special needs.
 
P

Pooh Bear

Jan 1, 1970
0
Harry said:
Hey Poop,
What is this, Electronics 101! Sure these parts are old enought. You should
worry about electromigration.

LOL !
The SG3525A has UVLO at about 7VDC and locks it's outputs low. Make sure it
goes down before the IR2110. YMMV with the SG3525.

The 3525 isn't the prob - it does indeed UVLO around 7V and has 300mV of
hysteresis.

The 2110 low side UVLO appears to be @ 8V and the high side @ around 8.9V. So as
the power rails sag the high side device stops conducting but the low side
doesn't. Interesting. Doesn't appear to be any hysteresis on the 2110 either.

I reckon I'm going to have to implement my own undervoltage lock out to stop the
3525 @ about 10V.

Just curious if anyone else had noticed this.

Choice of devices was partly determined / influenced by their use by the major
US manufacturer of pro-audio amplifiers in a similar application.

Graham
 
J

Joerg

Jan 1, 1970
0
Hello Winfield,
BTW, recognizing the need for low-voltage protection, and the need
for a benign response to low-voltage conditions, you could easily
add a comparator operating at lower voltages, plus shutoff gates
managing the IR2110's three logic inputs, per your special needs.

Or use a TLV431 for UVLO purposes. They are pretty accurate and cheap.

Regards, Joerg
 
P

Pooh Bear

Jan 1, 1970
0
Winfield said:
Pooh Bear wrote...

Device failure meaning damaged components, or meaning, a FET that
didn't do what you expected under a certain circumstance, but yet
wasn't actually damaged.

Device going short. Either just the high side device or both. I've
established to my satisfaction that there are 2 failure scenarios.

1. Ramping the voltage down on the variac ( quickly ) . E.g. after
I've been testing @ line voltage. There's a bzzt and the high side device
goes short. I suspect a mixture of the UVLO mismatches and possible
'mis-track' of the main bus and supervisory rail. Doesn't happen if I
ramp the volts down slowly ( or so it seems ). Hence my thoughts about
the droop of the rails.

2. Both devices fail - this first happened after I'd been running the
transformer primary only for about 1/2 hour just to establish likely
practical core temp rise. It ran fine for ages - I turned my back to do
some calcs and the thing bzzt'ed at me. It was still working so I thought
I was hearing things ! Did it terminally 3 mins later. Looking closely
I'm seeing the high side drive terminate prematurely under circumstances
I have yet to exactly determine the cause of. Maybe insufficient
bootstrap C ? Was looking at this last thing today. Will investigate
further tomorrow wrt all the drive waveforms.

IR has to separately detect the low-side and high-side voltages,
because the latter is the voltage across the flying capacitor.

True. I wish they'd OR the UVLOs though.
The mismatch you observed sounds good: the high side should stop
working well before the low side, thereby preventing any shoothro
current, which could be disasterous.

I'd prefer it if both terminated together !

Let's hear about your issues.

Well, the devices failing for one !

The 2110 UVLO is sensitive to line ripple. It appears to result in a
effect that's like weird duty cycles when it's hovering around the UVLO
threshold(s).
BTW, recognizing the need for low-voltage protection, and the need
for a benign response to low-voltage conditions, you could easily
add a comparator operating at lower voltages, plus shutoff gates
managing the IR2110's three logic inputs, per your special needs.

That's what I imagine I may indeed have to do. Or I can shutdown the
3525.

Was curious if anyone had experienced similar when using the 2110.

Cheers, Graham

p.s. I now understand why smps design has always had a reputation for
being 'tricky'. Also why when quizzed about them - some vendors go all
shy when talking about the reliability of smps versions of their audio
amps ! I have no plans to put anything into production that's marginal.
 
P

Pooh Bear

Jan 1, 1970
0
Joerg said:
Hello Winfield,


Or use a TLV431 for UVLO purposes. They are pretty accurate and cheap.

Regards, Joerg

Guess what I sketched late this afternoon ! With an LM393. It may be wise
to OR my own UVLO on both supervisory and main bus rails.

Graham
 
W

Winfield Hill

Jan 1, 1970
0
Pooh Bear wrote...
Guess what I sketched late this afternoon ! With an LM393. It may be
wise to OR my own UVLO on both supervisory and main bus rails.

Graham, you're way ahead of us. But the real issue is what the actual
operating modes are and their etiologies. We'll discuss that pursuant
to your other response.
 
T

Terry Given

Jan 1, 1970
0
Pooh said:
Winfield Hill wrote:




Device going short. Either just the high side device or both. I've
established to my satisfaction that there are 2 failure scenarios.

1. Ramping the voltage down on the variac ( quickly ) . E.g. after
I've been testing @ line voltage. There's a bzzt and the high side device
goes short. I suspect a mixture of the UVLO mismatches and possible
'mis-track' of the main bus and supervisory rail. Doesn't happen if I
ramp the volts down slowly ( or so it seems ). Hence my thoughts about
the droop of the rails.

2. Both devices fail - this first happened after I'd been running the
transformer primary only for about 1/2 hour just to establish likely
practical core temp rise. It ran fine for ages - I turned my back to do
some calcs and the thing bzzt'ed at me. It was still working so I thought
I was hearing things ! Did it terminally 3 mins later. Looking closely
I'm seeing the high side drive terminate prematurely under circumstances
I have yet to exactly determine the cause of. Maybe insufficient
bootstrap C ? Was looking at this last thing today. Will investigate
further tomorrow wrt all the drive waveforms.





True. I wish they'd OR the UVLOs though.




I'd prefer it if both terminated together !





Well, the devices failing for one !

The 2110 UVLO is sensitive to line ripple. It appears to result in a
effect that's like weird duty cycles when it's hovering around the UVLO
threshold(s).




That's what I imagine I may indeed have to do. Or I can shutdown the
3525.

Was curious if anyone had experienced similar when using the 2110.

Cheers, Graham

p.s. I now understand why smps design has always had a reputation for
being 'tricky'. Also why when quizzed about them - some vendors go all
shy when talking about the reliability of smps versions of their audio
amps ! I have no plans to put anything into production that's marginal.

what caps are you using for your bootstrap supplies?

Cheers
Terry
 
P

Pooh Bear

Jan 1, 1970
0
Winfield said:
Pooh Bear wrote...

Graham, you're way ahead of us. But the real issue is what the actual
operating modes are and their etiologies. We'll discuss that pursuant
to your other response.

Thank you for kind response.

I'm especially interested in what's causing the premature termination ( under
certain circumstances ) of the high side drive. At one point just poking the
probe of a Fluke 77 on the Vboot pin caused the effect ! At times like this 4
channel scopes ( and diff amps ) are a really attractive proposition.

The UVLO issue seems like a trivial one in comparison. Just surprised that I
haven't seen similar measures in other commercial designs I've looked at.

Graham
 
P

Pooh Bear

Jan 1, 1970
0
Terry said:
what caps are you using for your bootstrap supplies?

Box polyester film. You gonna say I should be using ceramic ?

Graham
 
P

Pooh Bear

Jan 1, 1970
0
Harry said:
Hey Poop,
What is this, Electronics 101!

For you maybe !

Have I seen your name on any ABs I may have read btw ? I'm thinking maybe
Unitrode ?


Graham
 
H

Harry Dellamano

Jan 1, 1970
0
Pooh Bear said:
For you maybe !

Have I seen your name on any ABs I may have read btw ? I'm thinking maybe
Unitrode ?


Graham
Your thinking of my brother, Robert Mammano, the original designer of the
SG3525 at Silicon General. Now I believe semi retired with TI-Unitrode.
I'm still in El-101.
cheers,
Harry
 
P

Pooh Bear

Jan 1, 1970
0
Joerg said:
Hello Graham,


Great. Although I tend to turn that extra dime for the comparator around
and around, then usually end up with "poor man's" ORing with transistors.

Hah - I used some diode ORing on the separate plug-in pcb that has supervisory
stuff. It works fine !

Graham
 
P

Pooh Bear

Jan 1, 1970
0
I'm going to investigate a higher value and probably polypropylene dielectric too.
and there is **** all inductance in the gatedrive loops.

This one that bothers me. How distant would you suggest the IR211 should be from the
power devices max ?

I do the layouts myself. far easier.

Well, I supervise but sometimes the layout guy gets carried away when I'm not around.

They have a cruddy CAD ( Vutrax ) system and I'm blowed if I'm learning it when we're
looking at junking it.

or Vds drop.

yep. dont forget to check your diode forward recovery time as well. that
can bite a chunk off your supply.

In the bootstrap supply it's a UF4004.

I had to solve a non-regulating flyback supply once (with TL431 + opto
feedback) that in large part was due to the use of a seriously shit
diode for a rectifier (I forget which diode, almost 1N400x type, Trr was
a us or two). I had worked on some of the designers other stuff, didnt
recognise the part number so just assumed he would use a suitable part.
there were other serious problems too, but the diode made me waste a few
days. both forward and reverse recovery were problematic.

I had a sub-contractor supply my first 'proper' flyback supply with a 1N4004 fitted
where there should have been a UF4004. Luckily on an aux rail so the thing was stable.
The 1N4004 fried in due course naturally.

It became a production problem because the output voltage just happened
to be right (ish, calibrate on test) when fed from 115Vac. problem was
it was a universal ac input ups battery charger, and batteries started
dying.....
I'm erring towards local bootstrap supply now.




MUR 460 in parallel with the switch. ~50ns

que? bootstrap diode (havent read IR2110 data sheet, it may include
them) from -Vdc bias supply to flating supply, cap to E, current
flows when lower switch turns on.


I got at cross purposes there. UF4004 as mentioned above.

I've been using both FETs and IGBTs as the power switches. Some of the IGBTs don't
have internal reverse diodes. So there's an external c-e MUR460 there too. 4A - 50ns -
600V

Cheers, Graham
 
P

Pooh Bear

Jan 1, 1970
0
R said:
Add a electrolytic of some sort for long term hold up if the high sides
are going to be on for a while.

Ton is 4.5us typ.
I don't see whyhaving the FETs turn off when the power goes low is an
issue though. Hmm, unless they are oscillating on/off at high frequency
as the power is sagging. I didn't think the 2110s were prone to that
but...

As the supply sags I see some very odd duty cycles coming out of the driver
stage. I'll definitely add my own UVLO to stop this dead.

Graham
 
J

Joerg

Jan 1, 1970
0
Hello Graham,
Hah - I used some diode ORing on the separate plug-in pcb that has supervisory
stuff. It works fine !

Done it, too, with ye olde BAV70.

Regards, Joerg
 
P

Pooh Bear

Jan 1, 1970
0
Winfield said:
I think you're going down the wrong track. If a FET fails to turn
on because of an activated UV lockout, this should not be the cause
of a MOSFET short. What would be the mechanism for that? Yes, the
desired switching function is interrupted, but benignly so.

OK - it is a bit of a puzzle.

I suspect you have a different common and deadly problem, namely
fast MOSFET source-voltage spikes from reverse-recovery-time
snapoff. This occurs if the FET's intrinsic body diode conducts,
and the ns spikes can damage the FET's delicate gate insulation.
V = L di/dt where L is your FET's source-lead inductance, and the
di/dt is high because dt can be under 1ns during t_rr snapoff.

I should point out that I've been using both FETs and IGBTs and seen the
same effect.

In all failure cases the gate has shorted to the rest of the device though.

Don't know enough about " reverse-recovery-time snapoff ". Could you
elaborate ?

The FET diode's will clamp the flyback from your transformer's
leakage inductance if during the delay after the other FET turns
off the flyback voltage swing is high enough. This clamping with
the resultant spike will happen if you have an inadequate snubbing
network across the FETs to prevent the flyback from swinging across
your entire raw dc voltage supply.

It doesn't. It's quite benign. Really slow in fact. In another test with a
resitive load made of wirewound Rs it gets to maybe 70 - 80 % of supply
before ringing.
The snubber network can simply
be a drain-source capacitor, to absorb the leakage-inductance energy
or it can be more complex. But whatever your choice, don't ever let
the FET's body diodes conduct!!!

You mean don't let the body diode of the FET / IGBT that's just about to
turn on conduct ? I can see that might be bad.

I've been careful to look at the dV/dt at switch off and make sure it's
under control. IGBTs make this easy on account of tail current.
Note, the transformer's leakage-inductance energy is proportional
to current, which means it's flyback effect is minimal under no
load, and worst under full load. Carefully examine your switching
waveforms to see how they change as you increase the load on the
transformer output.

No load yet ! I'm taking this very much bit by bit. In this application
there are instances where there will be no effective load to talk of - so
I'm simply driving the magnetising inductance at present ( or a resistor ).

BTW, did you tell us what FETs you're using? And tell us more
about your transformer and the operating voltages and currents.
Did you measure the transformer's leakage inductance?

I've tried several. One IGBT I've been using is the Infineon SGW30N60. One
of the FETs was also Infineon - one of their CoolMos range a SPW20N60C3
IIRC.

Vbus is 320V @ normal line.

Transformer used is an ETD49 core in N87 (oh no 3C90 - similar - couldn't
get the Epcos core from Farnell ). Pri turns are 16. I.e. 10V / turn - this
works out similar to my observations on a well known design by a major audio
mfr.


Cheers, Graham
 
T

Terry Given

Jan 1, 1970
0
Pooh said:
R Adsett wrote:




Ton is 4.5us typ.




As the supply sags I see some very odd duty cycles coming out of the driver
stage. I'll definitely add my own UVLO to stop this dead.

Graham

Excellent, start-up and shut-down behaviour really requires close
attention. slowly ramping supply rails can uncover a variety of nasties.


Cheers
Terry
 
T

Terry Given

Jan 1, 1970
0
Pooh said:
I'm going to investigate a higher value and probably polypropylene dielectric too.


This one that bothers me. How distant would you suggest the IR211 should be from the
power devices max ?

its not the distance, its the inductance, so minimise the total loop
area the current flows in. My gate drives have a solid return plane
under the entire circuit, connected to the emitter(source) [usually to
the gate drive kelvin connection]. I use a wide conductor for the gate,
and place the final emitter follower + bypass caps + gate resistor
network as close as possible to the gate connection.

Lg serves to increase Rg whenever miller capacitance pumps current into
the gate. this makes the gatedrive less stiff, so Vg will have a wider
flat spot, switching times increase and, if Lg is too large, Vg may rise
high enough to poke a hole in the gate oxide.

look at the Lg-Rg-Cg resonant circuit too, and keep Q low - a bit of
resonant peaking is another good way to poke a hole in the gate oxide.

say 5R and 1nF. for Z=5R L = 25nH. 100nH will have Q=2
Well, I supervise but sometimes the layout guy gets carried away when I'm not around.

They have a cruddy CAD ( Vutrax ) system and I'm blowed if I'm learning it when we're
looking at junking it.

fair enough. I have done the same thing. as long as the
engineer-draughtsman feedback occurs.

if you want to email me a pdf of the layers I can give you my opinion
offline.
In the bootstrap supply it's a UF4004.
fine.



I had a sub-contractor supply my first 'proper' flyback supply with a 1N4004 fitted
where there should have been a UF4004. Luckily on an aux rail so the thing was stable.
The 1N4004 fried in due course naturally.

ayup. I made a lot of money out of that as a tech once, I contracted to
repair some psu's for $50 each. about 100 of them (3 years worth) had
been "repaired" by another tech a month or two earlier, and they all
crapped out. 1N540x in this case.

[snip]
I got at cross purposes there. UF4004 as mentioned above.

I figured
I've been using both FETs and IGBTs as the power switches. Some of the IGBTs don't
have internal reverse diodes. So there's an external c-e MUR460 there too. 4A - 50ns -
600V

Cheers, Graham

Cheers
Terry
 
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