[info] Power supply - kb1gtt

[kb1gtt]

It appears this Chinese switcher chip is likely a LM2576 marked LM2596. You can see on the a primary switch frequency of about 50kHz as noted in the picture I posted here http://rusefi.com/forum/viewtopic.php?f=4&t=569&start=168 Notice that's 150kHz/div, with the first spike about 1/3 of the first block. I found this claim in comments of the below web page.

http://www.kerrywong.com/2015/07/24/lm2596-dc-dc-converter-module-testing/

I'm tempted to add an inductor location to the power supply input, such that we have a physical place to put such a choke if it's needed. As it stands now I don't have solid indication that it's needed, and I don't know what values to put there if it's needed. Hmmm, how to resolve this concern..... For now I guess I'm reading EMC PDFs about switch mode supplies. I'm currently absorbing this one http://www.ti.com/lit/an/snva489c/snva489c.pdf

[kb1gtt]

From this link, http://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/15/ it looks like the LISN is a 5uH device wired as noted in this schematic.

CISPR 16-1-2 5uH Schematic.png

Here's a picture of my conducted emissions probe. However I have no idea if that's 5uH as noted above or not.

probe.JPG

This web page is the closest thing I have to a datasheet.
http://www.solar-emc.com/MIL-STD-461F.html
I guess I can connect that probe and sniff it even if it's not the correct impedance.

[Rhinoman]

I came across this today, I haven't looked at it in any detail:

http://www.diodes.com/downloads/9551

[kb1gtt]

Nice to see they make these specifically for automotive applications. The one I'm using now is 30V 4.0A and Rds = 50mohm. The one mentioned in that PDF is physically much larger, 40V and Rds = 11mohms. Seems the ones that diodes inc. list for automotive and SOT23 are only in the 1A range. I wonder if an automotive 4A or more SOT23 can be found.

[Rhinoman]

P FETs have higher RDSon, in the past I've used an N FET and bootstrapped it from a switching regulator. You won't get a very big die in a SOT23 and the thermal performance isn't that good which limits the current it can handle.

[kb1gtt]

Looks like this is an option http://www.mouser.com/ds/2/427/sq2301es-534673.pdf it allows 3.9A. The upstream voltage clamp was 20V, I just changed that to 19V.

[Rhinoman]

Looks like this is an option http://www.mouser.com/ds/2/427/sq2301es-534673.pdf it allows 3.9A. The upstream voltage clamp was 20V, I just changed that to 19V.

3.9A at 120mR is 1.83W, Tja is quoted as 166C/W with Tj max 175C.

[kb1gtt]

The gate is being driven by a 7.5V zener, the 125mohm is when driven to 4.5v. I expect that when driven to 7.5V it will have an Rds closer to .075 ohms. See attached picture that shows my eyeball of the graph that indicates the Rds. So that's 0.31V/4A = 0.075ohms instead of 0.125ohms. The design is for 3A as noted on the power supply schematic. So watts would be 0.675W. At hotter temperatures it could have a 1.5 multiplier on the resistance. So at a hotter temperature it could be 1.01W.

Rds.png

The chip has 50C/W to the pads on the chip, the additional thermal resistance is dependent on your PCB layout. The 166C/W assumes reasonably small traces connected to the pads, with a certain distance to your heat sink. My layout has fat traces, with thermal via's, so I expect a more thermally conductive path to the heat sink. Unfortunately I don't know the exact thermal resistance. See "figure 8" and "table 4" on this PDF for how they measured the thermal resistance and got about 200C/W instead of the MFG's datasheet which notes 166C/W.

http://www.njr.com/semicon/PDF/package/ae02220.pdf

I'm expecting ambient to be up to 85C as noted here http://rusefi.com/wiki/index.php?title=Manual:Hardware#General_suggested_environment, the chip can handle 175C, so we have 90C to work with. That would be a need of between 90C/1.01W to 90C/.657W which means we would need to be 90C/W to 133C/W or less. We know we have 50C from the die to the lead, but will the PCB layout be less than 40C to 83C to ambient. I don't really know. I suspect it's reasonably close. As well I suspect we won't be running a continuous 3A at a continuous 85C ambient.

Perhaps the 3A should be derated a bit for thermal purposes. Or perhaps I can find a chip with a lower Rds, or perhaps I can put in a larger chip. For now we don't have any applications that come close to the 3A limit, so the real word applications shouldn't have any problems. Thermal issues are hard to predict until you build it and test it while looking at it with a thermal camera.

[Rhinoman]

I found another interesting app note regarding high frequency switching noise here:

http://www.linear.com/docs/11877

[AndreyB]

It has been some time, where have we left it? Should I populate current version 0.4 for a validation?

[Rhinoman]

I haven't had time to look at this in detail, I will be producing a different board for my Vitara because I need a peak-hold injector driver. Currently I'm working some distance from home and I spend 3 1/2 to 4 hours a day commuting.

[kb1gtt]

I know it's a bit OT for the power supply thread, but for lowz you may find this interesting http://puma.freeems.org/ I was one of the people working on that and it worked reasonably well at least from the very few data points we had to work with the lowz worked well.

I've been busy busy busy. Perhaps at the holidays wind down I can find some time to jump back into this. I still have the spectrum analyzer almost ready to run, and I have the frankenso sitting here almost ready to connect and test. But I haven't found the time to actually run it.

[AndreyB]

Just placed an oshpark order for rev 0.4 board.

[AndreyB]

It does produce 5 volts - now it probably needs some deeper testing.

[kb1gtt]

Very nice, very nice.

[AndreyB]

I remember you ran some tests of the power supply but I cannot find these scope traces, do you remember where were these?

[Abricos]

this device for sale ???
or is still under development ???
and what is its value or Price ???

[kb1gtt]

Hmmm, I agree I should have some scope shots, which show the ripple and such. But I can't find them either.

[AndreyB]

On the previous power supply design (the one users on Frankenso 0.4) the two through-hole diodes were 1N4747, were they? Why do we not mention 1N4747 anywhere?

On the newer design we now have two different through-hole diodes, do these have an 1Nxxxx code?

[kb1gtt]

The power supply on Frankenso R0.4 calls for fairchild,BZX79C20 which looks to be about the same as the 1N4747. I forget if the 1N4747 was used at some point. A quick look seems to show it's the same as the BZX79C20. I may recall that was how it was listed at sky-macau, but it's not listed that way right now.

In Frankenso R0.5 D1002 and D1003 both have 1NXXXX designations. D1001 is BZT52C7V5-7-F which could probably have a 1NXXXX designation. Something like 1N5343BRLG would probably be good enough.

[AndreyB]

In Frankenso R0.5 D1002 and D1003 both have 1NXXXX designations. D1001 is BZT52C7V5-7-F which could probably have a 1NXXXX designation. Something like 1N5343BRLG would probably be good enough.

What is the difference between 1N5343BRLG and 1N5343? eBay likes 1N5343 much more.

Please confirm 1N5343 is the one we want and please give me the other ones when you have time, I will order some from eBay.

Now I see 1N5244B and 1N5359B as part of the BOM

[kb1gtt]

It looks like the base number is 1N5343B, then the RL means it was produced on a real / tape of 4000, instead of a box of 1000. Then the G seems to just hang out. I don't see any real differences in the diodes. I think they difference is simply packaging in how they are stored.

[kb1gtt]

So I finally got around to testing this board. It looks like something wrong with the Q2 MOSFET. It's simply acting like a wire, and not clamping the voltage.

Ooops, I see the tab of the Q2 MOSFET should be drain, and it was the source. Oops. It worked for @russian, as the diode was conducting. I cut the trace, lifted the MOSFET leg and added some wires to re-wire it. Then it worked as expected.

My bench top power supply goes up to 65V, and it works fine for that range. Q2 keep the voltage at about 16.5V and didn't kick in until about 14V. Also some good news the axial inductors worked just fine. i was a bit concerned about the magnetic fields, but it doesn't seem to matter that those fields are vertical.

So I'll be doing R0.5.

[AndreyB]

ordered rev 0.1 of https://svn.code.sf.net/p/rusefi/code/trunk/hardware/frankenso-PWR-Supply/

[kb1gtt]

This board is cut from the Frankenso R0.5, it's just the power supply and it's on a 2 layer board.

[AndreyB]

How about we replace IXTA6N50D2 with IRF640S / RF640SPBF? Is it the same package / size / pinout? $4 cheaper.


[video][/video]

[mobyfab]

Seems like those are not depletion mosfets.

If you want to go cheap, go LDO. It's not like it's using a lot of power anyway right?

[AndreyB]

for fuses do we like F0603C2R50FWTR and F0603C3R00FWTR? 16 VDC 2.5A and 3A Current Rating.

[AndreyB]

Seems like those are not depletion mosfets.

http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyDN2625K4-G ?

[kb1gtt]

Sweet, I only changed to the IXT chip, because I could not find the DN2625. The DN2625 is specifically called out of by the app note I was using when I designed this circuit. See page 4 of the below. So yes that DN2625 is perfect. I see Vgs is -1.5 to -2.1 vs the IXT at -2.5 to -4.5. So I will probably need to change D1002 for a slightly higher voltage. But that should not be a big deal.
http://ww1.microchip.com/downloads/en/AppNotes/AN-D66.pdf

Hmmm, I see Rds of 3.5 ohms. That's quite high and will create heat. It's the regulator is producing 5A at 5V and 80% effeciency, the regulator will draw about 2.5A at 12V. Then 3.5 * 2.5^2 = 22 watts. That's allot of heat. However if we can use the IRF chip with an internal resistance of 0.18W, that drops the watts from 22W to 1W, and if it's the 0.55 ohms of the IXT, the watts drops from 22W to 3.5W. However as pointed out, we don't run full power. So is it reasonably to expect that if someone uses the 5A output, they also either add a heat sink, or they use the different chip which would generate less heat? I say use the low cost chip, then add an alternative note to the schematic. Also for now I say get all three chips, and I can check them all out. However for starters lets populate the DN2625.

A note about the IRF640. The graphic of the MOSFET symbol shows a depletion, but the spec for Vgs is positive, while the IXTA6N50D2 shows the depletion graphic, and specifically notes depletion mode, then it also specifies Vgs with a negative number. I'm not sure if IRF640 is depletion or not, so it may or may not work.

@motofab, feel free to compare this switching regulator against this linear http://rusefi.com/forum/viewtopic.php?f=4&t=893&p=16027&hilit=PWR_5V_linear#p16027 It's basically the same thing, but linear vs switching. Both regulators have max voltage limits, which are being extended by this depletion MOSFET. Also please keep in mind that many older dash boards drive the gauges off a 5V supply, which consumes allot more amps than we are consuming. This circuit only costs like $2 for the regulator, the high voltage suppression is what's currently expensive. Both linear and switching need this suppression.