I always include gate resistors so I can trade efficiency against EMI.
33 ohms is sort of the default value, but I've used much bigger ones.I tend to pick resistors that used to be my favorite color codes. Even in Spice.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
33ohms would cause spectacular fireworks in most of my designs. Sometimes I provide the "angst pads" for a gate resistor but generally end up with 0R in there. Could also be used for a bead or a peaker inductor so it's a good excuse to have.
I always wondered why switcher IC mfgs proudly proclaim "1 ohm gate drive!" or "10 amps gate drive!" and then people waste all that with series resistance. When it comes to efficiency in a non-zero switcher there is nothing that can replace gate drive, except more gate drive.
Though there is no color code to exactly match your Audi. My favorite color is blue but 666 would be a bad omen.
-- Regards, Joerg http://www.analogconsultants.com/
I think you are generally doing bigger stuff than I am. I am cosidering some gnarly (like 6KV, 100 KHz) Pockels cell drivers, where
33 ohm gate resistors might not be best. 2.2K 10%.My favorite
Too many ohms.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 22 Mar 2016 13:15:07 -0500, Tim Wescott wrote:
How are you measuring efficiency - is this a real measurement or a simulated measurement?
Try getting a real SRF on the real secondary winding, then go back to make the model do something similar. If there's a working unit, simply look at the secondary winding voltage after secondary rectifier stops conducting and tune the simulation to do likewise.
Subharmonic operation can occur when the primary switch terminates prematurely on the noise of this cap discharge.
At the same time, a conduction cycle that synchronises with resonant self-discharge gets ZVS assistance.
When you're subharmonic, but still regulating, leakage inductance energy in the clamp can multiply x 5 ; peak current can triple at the halved frequency - energy is Llk x Ip^2. This doesn't including further loss generated during the ineffective, prematurely terminated cycles, in between. RC snubbing can tame this a bit, but is lossy again in a low power circuit.
Raising the clamp voltage won't reduce the energy it dissipates.
The secondary resonance can be used if the switching frequency is somewhat higher to get regular ZVS assistance.
If the switch current is too ringy at turn-on of the switching cycle, due to leakage inductance, the peak sensor will mis-detect on the ringing, again with irregular subharmonic effect.
Leading edge blanking and RC sense filtering can deal only with the leading edge, where, among other things, gate drive current will be present in simple source resistot sensing.
Regardless of the source of subharmonic oscillation, some slope compensation summed into the current sensing signal can act as noise suppression. It's generally recommended for flybacks operating above
50% duty cycle, anyways.No comment re regulation feedback. If it works, it works.
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112 WIRE 64 144 64 112 WIRE 2352 144 2352 64 WIRE 2352 144 2304 144 WIRE 2512 144 2512 112 WIRE 2512 144 2352 144 WIRE 336 160 288 160 WIRE 512 160 400 160 WIRE 928 160 832 160 WIRE 1008 160 1008 64 WIRE 1008 160 928 160 WIRE 1680 160 1008 160 WIRE 1744 160 1744 64 WIRE 1744 160 1680 160 WIRE 288 192 288 160 WIRE 1872 192 1872 112 WIRE 3072 192 3072 160 WIRE 2496 208 2400 208 WIRE 1520 240 1520 80 WIRE 2144 240 2144 80 WIRE 2144 240 1520 240 WIRE 2400 240 2400 208 WIRE 512 256 64 256 WIRE 960 256 832 256 WIRE 1088 256 960 256 WIRE 1152 256 1088 256 WIRE 1184 256 1152 256 WIRE 1408 256 1264 256 WIRE 1520 256 1520 240 WIRE 1520 256 1408 256 WIRE 3488 272 3440 272 WIRE 3488 288 3488 272 WIRE 64 304 64 256 WIRE 2944 304 2944 -352 WIRE 240 352 224 352 WIRE 352 352 320 352 WIRE 480 352 352 352 WIRE 512 352 480 352 WIRE 960 352 832 352 WIRE 1792 352 960 352 WIRE 1904 352 1792 352 WIRE 1952 352 1904 352 WIRE 2096 352 2032 352 WIRE 2400 352 2400 320 WIRE 1408 384 1408 256 WIRE 352 400 352 352 WIRE 3488 400 3488 368 WIRE 896 416 896 64 WIRE 1088 416 1088 256 WIRE 1520 416 1520 256 WIRE 1792 416 1792 352 WIRE 1904 432 1904 352 WIRE 2048 432 1904 432 WIRE 2192 432 2128 432 WIRE 2240 432 2192 432 WIRE 2288 432 2240 432 WIRE 2400 432 2368 432 WIRE 2544 432 2464 432 WIRE 64 464 64 384 WIRE 416 464 416 64 WIRE 672 464 672 416 WIRE 2496 464 2496 208 WIRE 2544 480 2544 432 WIRE 2544 480 2528 480 WIRE 3264 480 2544 480 WIRE 3376 480 3344 480 WIRE 3392 480 3376 480 WIRE 352 496 352 464 WIRE 1408 496 1408 464 WIRE 1408 496 1296 496 WIRE 2240 496 2240 432 WIRE 2464 496 2240 496 WIRE 1408 512 1408 496 WIRE 2800 512 2528 512 WIRE 2944 512 2944 384 WIRE 2944 512 2800 512 WIRE 3392 512 3392 480 WIRE 896 528 896 480 WIRE 1088 528 1088 480 WIRE 1520 528 1520 496 WIRE 2944 528 2944 512 WIRE 2800 544 2800 512 WIRE 1792 560 1792 496 WIRE 2496 560 2496 528 WIRE 416 592 416 544 WIRE 1408 608 1408 576 WIRE 1680 640 1680 160 WIRE 1680 640 1648 640 WIRE 1744 640 1680 640 WIRE 2800 640 2800 608 WIRE 2944 640 2944 608 WIRE 3392 640 3392 592 WIRE 1648 656 1648 640 WIRE 1744 672 1744 640 WIRE 1152 768 1152 256 WIRE 1488 768 1152 768 WIRE 1648 768 1648 736 WIRE 1648 768 1568 768 WIRE 1680 768 1648 768 WIRE 1744 768 1744 736 WIRE 1744 768 1680 768 WIRE 1680 784 1680 768 WIRE 1680 880 1680 848 FLAG -240 144 0 FLAG 672 464 0 FLAG 1520 528 0 FLAG 896 528 0 FLAG 64 464 0 FLAG 928 160 Vg1 FLAG 2560 -160 0 FLAG 3168 96 0 FLAG 3072 192 0 FLAG 48 -160 0 FLAG 256 64 0 FLAG 2512 -352 Vout FLAG 1728 -64 Vsnub FLAG 176 -304 Vin FLAG 480 352 Vc FLAG 960 352 Vfbx FLAG 1136 128 0 FLAG 1872 192 0 FLAG 192 -48 Vgs FLAG 416 592 0 FLAG 3392 640 0 FLAG 2496 560 0 FLAG 3440 272 Vvg FLAG 3488 400 0 FLAG 2944 640 0 FLAG 2192 432 Vvcmd FLAG 2096 352 Vvg FLAG 224 352 Vvg FLAG 2400 352 0 FLAG 1792 560 0 FLAG 352 496 0 FLAG 64 144 0 FLAG 3376 480 Vcmd FLAG 1296 496 VHV_Curr FLAG 2336 -160 0 FLAG 1712 -160 0 FLAG 1408 608 0 FLAG 1088 528 0 FLAG 960 256 Vsense FLAG 288 192 0 FLAG 2800 640 0 FLAG 1696 -352 P1 FLAG 2336 -304 P2 FLAG 1520 -96 DS1 FLAG 2144 -96 DS2 FLAG 1760 -176 0 FLAG 2384 -128 0 FLAG 1680 880 0 FLAG 2304 144 Vin SYMBOL voltage -240 16 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=10m SYMATTR InstName V1 SYMATTR Value PWL(0 0 1m 3.2) SYMBOL PowerProducts\\LT3757A 672 208 R0 SYMATTR InstName U1 SYMBOL cap 880 416 R0 SYMATTR InstName C1
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SYMATTR SpiceLine Rser=12.5m Rpar=20 SYMATTR Type ind SYMBOL res 2144 416 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL res 48 288 R0 SYMATTR InstName R4 SYMATTR Value 140k SYMBOL cap 2544 -256 R0 SYMATTR InstName C4
SYMBOL res 3152 -240 R0 SYMATTR InstName R11 SYMATTR Value 2.80k SYMBOL nmos 3120 -48 R0 SYMATTR InstName M3 SYMATTR Value FDS2734 SYMBOL voltage 3072 64 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 12 4m 1u 1u 500u 1m 5) SYMBOL cap 32 -256 R0 SYMATTR InstName C7
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SYMBOL ind2 1712 -288 M0 SYMATTR InstName L2
SYMATTR Type ind SYMATTR SpiceLine Rser=3 Cpar=470E-12 SYMBOL diode 1808 -336 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value RFN2L6S SYMBOL cap 2336 0 R0 SYMATTR InstName C3
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When you have almost no resistance between the driver and the gate, have you ever had problems with latch-up/destruction of the driver, since now any surges/bursts can travel into the driver output port via the drain source capacitance?
Cheers
Klaus
Of course we linguists know that 'omen' is the German plural of "ohm".
;)
Cheers
Phil Hobbs
Resistance iss futile.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Then conductivity is inevitable?
But the Audi isn't truly red unless the photos I saw were spectrally distorted.
In Southern Germany that would be gondugdividy.
-- Regards, Joerg http://www.analogconsultants.com/
I never did. If it ever were to happen I'd want a meeting with the engineers of the IC manufacturer.
Datasheets usually also do not show any gate resistors:
-- Regards, Joerg http://www.analogconsultants.com/
In person, it looks pretty red to me. It was custom-built in Germany by a car nut. He had six sporty cars on lease and then lost his job. Honda does the best true red.
A digital camera and a computer monitor won't reproduce colors very well. It could be that cameras and monitors and eyes all have different definitions of R and G and B.
Not to change the subject (what, me???) but I've got interested in playing with monitor color settings as related to circadian rhythm sleep behavior. I got some blue-filtering glasses from Amazon but they are not impressive; most blue still gets through. I might install f.lux and see what happens. No big deal, but sometimes I wake up at
3AM and think, and I'd rather sleep.-- John Larkin Highland Technology, Inc lunatic fringe electronics
Surprising that it had the required emissions ratings for California. I could not take my Audi to the US because of that issue. Now 29 years old and our former neighbors still drive it between Germany and Sweden. They said it is almost as good as new.
That's a problem I almost never had. I sleep like a log. Except last night where I woke up at 5:45am and started the lab equipment. Got a board with an assortment of OPA695 and LT6233 that produce a weird latch-up or whatever, collapsing the positive supply and actually pulling it slightly negative. All tiny SMT stuff, power planes, can't cut traces for testing, grrrr.
-- Regards, Joerg http://www.analogconsultants.com/
I normally sleep hard, 8 to 10 hours, but lately I sometimes wake up around 3AM for a while. No big deal; I think for a while and go back to sleep. I was wondering if it was related to my new PC, with its giant bright ASUS monitor. Or maybe it's too much chocolate.
I sometimes do good thinking at 3AM, so it's OK. I must think in my sleep too, because problems get solved overnight, answers delivered in the shower. I catch a lot of design bugs that way, usually before a board is done.
Latchup is a chronic historical industry problem. I don't know anything about semiconductor fab, but it must be really tricky to avoid latchup... otherwise everybody would always review their designs and fix them. Mixed-signal things are especially bad.
Both TI and LTC are usually pretty good about latchup. What's the board do? Could the problem be systemic?
A thermal imager is great to have around. After it latches, snoop the board and find the hot part.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Similar with me. Sometimes I wake up at 4 or 5 ... Aha! This is why there is always a notepad and pencil in my nightstand.
I sure wish I had a FLIR camera now but I don't. Nothing other than the regulator gets hot. I'll now remove all ICs one by one to (hopefully) find out which one causes it. Might be a bad batch, who knows.
-- Regards, Joerg http://www.analogconsultants.com/
I wish I could image current! A tiny magnetometer probe would be fun.
A good DVM can measure microvolt drops in power traces and even power planes, to close in on the guy hogging the current. I've even calibrated things like that.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I tell the kids: measure, think, don't solder.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
This can be an indication of internal impedance of driver mosfet structures.
As a result, the actual drive may be dominated by driver output resistance, especially at turn-off, where the difference between ground and the gate plateau is small. A bipolar output structure that doesn't reduce in current capability under this condition is preferable - often the reason that emitter followers are seen tacked on despite drive capability claims.
You'll see gate resistor bridged by schottkys, for faster turn-off, working with the same issue.
None of these considerations can effect internal gate resistance in the mosfet switch itself, which has been seen (in some older parts) to exceed 10R and is seldom specified. Seldom seen it specified below 3R. It can be roughly estimated by looking at the difference between visible turn-on and turn-off gate plateau levels at estimable drive current levels - the actual internal plateau being invariable.
Not so much latch-up, but irregular behaviour and even logic inversion in both singles and duals that was MFR specific: frequently related to local drive supply and input logic decoupling sensitivity. Without impedance buffering, the potential also exists for aggravation of ground bounce effects in the area.
RL
Hmm, so do you use transconductance amps to tell time?
(Gnomen? Gnomon, the thingy standing up on a sun dial. G from conductance. Although, G * R == mu, the amplification factor, so maybe you'd use a triode? Anyway......nevermind...)
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
I just got a Flir One at work. For $250, you can't beat it. Of course you need a smart phone to use it, so Luddites like you two guys needn't bother. ;-)
I had an HP magnetometer circuit tracer at one time. It worked, sorta.
This worked much better than the magnetometer. Neither work well in really noisy environments or on noisy signals, though.
Most parents would tell them something entirely different: Don't do any of that. Instead, become a laywer, dentist, doctor. Or better yet, prison guard or something like that with fat cradle to grave health care and pension.
-- Regards, Joerg http://www.analogconsultants.com/
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