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LM2917 F/V Tachometer simulation problem
A few days ago, 'hitec92407' uploaded the file "LM2917Test.zip" to the group's Temp area. ?Through my mistake, the discussion ended up on the [LTspiceFiles] group rather than this one.
hitec92407's questions included these: He created a dual-collector transistor model. ?He was unsure about it. My response: It looks good to me. ?I think you did it right and I don't think it is why the simulation doesn't work. He noticed the output of the tach circuit always stays the same and doesn't do what it should. My responses follow.
The circuit, taken right out of Figure 14 in National Semi's Applications Note AN-162, is peculiar because the on-chip "ground" (VSS?) pin is not grounded. ?It is connected to a point that is nominally half-way between power and actual ground. ?That means some of the signal pins are well below on-chip VSS. ?Usually the on-chip VSS is the substrate, and nothing should ever be more negative than that. ?It just doesn't seem right.
I have a strong suspicion that Figure 14 might not actually work.
In addition, there might be problems with the IC model too, in spite of the fact that it looks like a faithful replica of their Figure 2. ?The on-chip regulator is a few volts off. ?The input pin has a 10K series resistor, which seems to prevent the input from noticing zero-crossings (i.e., it's impossible to bring pin 1 low enough to ever toggle the Schmitt trigger ... so it never sees any AC input!). ?There may be issues with mismatch between diodes and transistors, which prevents some transistors from ever turning on. ?Those are the problems I saw so far.
I can see nothing happening in the Charge Pump. ?Its input seems to be forever stuck high. ?The problem starts in the input hysteresis amplifier.
It might be possible to "patch up" your LM2917 schematic and make it work, but there may be a better approach. ?There already is an LM2917 LTspice model in this group's Files section. ?It is not in schematic form, and I can give no guarantee about how accurate it is, but apparently someone found it useful enough to upload it here. ?Try it out.
Regards,
Andy |
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Re: SMPS switching losses in LTspice?
potstuvich,
I don't think it's a question of how accurate is LTspice, but instead, how good is the transistor model?? If I really wanted to know the answer to this, I would build a switching time test circuit that matches that used in the data sheet and see how the results compare to the data sheet.? I realize there is not much information on the data sheet, but it's better than nothing.? I would also compare the data sheet capacitancs to the model. Rick |
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Re: SMPS switching losses in LTspice?
I would expect it to be modestly accurate, then.
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Jim Wagner On May 23, 2014, at 1:19 PM, potstuvich@... [LTspice] wrote:
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Re: SMPS switching losses in LTspice?
Should have written, instead of "losses will be mostly resistive" it ought to be "inductor losses will be mostly resistive" since gate charge losses CAN be significant.
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Jim Wagner Oregon Research Electronics On May 23, 2014, at 12:54 PM, Jim Wagner wagnejam99@... [LTspice] wrote:
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Re: SMPS switching losses in LTspice?
Those voltage dependent FET capacitances are modeled well, if a good model is supplied, For an external FET switcher, that is up to you.
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The switching loss estimate is as good as your model. For example, if the inductor stays well away from saturation, then the losses there will be mostly resistive. If you have a reasonable series resistance in that model, then its good. But, if it is driven into saturation and you do not have a model that includes saturation, then the loss number will be overly optimistic, maybe by a lot. Jim Wagner Oregon Research Electronics On May 23, 2014, at 12:43 PM, potstuvich@... [LTspice] wrote:
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SMPS switching losses in LTspice?
Hello, LTspice calculates a switching loss of 1.07W in the FET of the buckboost smps that I have uploaded to the Temp Files area. "Buckboost SMPS _switching loss.asc". How accurate is this to the real circuit? I mean, the switching Mosfet capacitances, especially Cgd, are voltage dependent, and this would need modelling to make the switching losses accurate. How accurate is it in LTspice? |
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Re: Pull-Push transformer for valve amp in LTspice
¿ªÔÆÌåÓýTip:Ferrite cores are identified by an Al number, which allows quick determination of the number of turns, using the formula L=Al.N? Le 23/05/2014 15:15,
pha0001@... [LTspice] a ¨¦crit?:
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Re: Pull-Push transformer for valve amp in LTspice
pha0001?asked: ? ?"why did you take a quarter of the total primary inductance? Why not just half it?"
Adding to what Vlad already wrote (which should lead you to your answer), it does depend on the amount of coupling between inductors. ?You used a coupling coefficient of 1.
If the inductors had been uncoupled (K=0), then it would have been correct to use half.
Regards,
Andy |
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Re: Pull-Push transformer for valve amp in LTspice
What's the equality between the ratios of the inductances and the number of turns? Vlad ______________________ -- holding, among others: a universal analog/digital filter, block-level models for power electronics (and not only), math blocks with a more stream-lined approach, some digital ADC, DAC, (synchronous-)counter, JKflop, etc. On Fri, May 23, 2014 at 4:15 PM, pha0001@... [LTspice] <LTspice@...> wrote:
> > ? > > Thank you so much!!! Things are starting to become much clearer now. > > > If you don't mind, may I ask, why did you take a quarter of the total primary inductance? Why not just half it? |
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Re: Lock horizontal axis
Hi Helmut
It's really the X-axis I'm having problems with - see "X-Axis different scales" in Temp. ?? Top: Initial plot ?? Middle: Set precise manual limits on time range ?? Lower: Only one plot pane is "time-zoomed". Whilst this can be useful, I'd also like to be able to zoom all plots simultaneusly - all plots get same time range. Regards Stephen. |
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Simulating a TI DRV103 with LTspice?
Walking Through
I was looking for an electronic "dash pot" for a solenoid and found the TI DRV10{2, 3} series of delayed-start PWM devices.? Downloaded TI's DRV103 spice file, looked, did a few sort-of educated guesses, and tried to simulate it with Cd=10 nF, R(osc) = 523K, and R(duty_cycle) = 40.2K.
Thought something was "not quite right" when LTspice kept flipping in and out of DefCon. Anyone worked with this device before?? Is there something in Linear Tech's collection that might be usable as a delayed-start PWM solenoid driver? Thanks. Mark |
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(No subject)
Sam Jesse
I also tried .meas ampx MAX V(Out_1) I(V1) thinking I can plot the max of V(Out_1) vs. I(V1).meas ampx MIN I(V1) On Fri, May 23, 2014 at 7:35 AM, Sam Jesse <revrvr@...> wrote:
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(No subject)
Sam Jesse
Helmut Is there a way to optimize on 2 or 3 variables and plot results like you did? i.e. Ton Tperiod R of the inductor for example?? On Fri, May 23, 2014 at 7:07 AM, helmutsennewald@... [LTspice] <LTspice@...> wrote:
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