Cuk Buck/Boost based on J. Larkin idea

Hi,

Based n Sepic DC/DC converter from Larkin, i investigate to make a Cuk from it and it works finally.

Version 4 SHEET 1 2996 1968 WIRE 0 880 -80 880 WIRE 160 880 80 880 WIRE 688 880 160 880 WIRE 944 880 832 880 WIRE 1024 880 944 880 WIRE 1664 880 1088 880 WIRE 1792 880 1664 880 WIRE 1936 880 1792 880 WIRE 2048 880 1936 880 WIRE 2160 880 2048 880 WIRE 832 896 832 880 WIRE 1664 912 1664 880 WIRE 2160 912 2160 880 WIRE 688 928 688 880 WIRE 944 928 944 880 WIRE 1088 928 1088 880 WIRE -80 944 -80 880 WIRE 160 944 160 880 WIRE 1792 960 1792 880 WIRE 2048 992 2048 880 WIRE 2160 1040 2160 992 WIRE -80 1056 -80 1024 WIRE 0 1056 -80 1056 WIRE 160 1056 160 1024 WIRE 160 1056 64 1056 WIRE 688 1056 688 1008 WIRE 832 1056 832 1040 WIRE 832 1056 688 1056 WIRE 944 1056 944 992 WIRE 944 1056 832 1056 WIRE 2496 1056 2208 1056 WIRE 2496 1072 2496 1056 WIRE -80 1104 -80 1056 WIRE 688 1104 688 1056 WIRE 2272 1104 2208 1104 WIRE 1024 1120 1024 880 WIRE 1024 1120 944 1120 WIRE 1088 1120 1088 1008 WIRE 1088 1120 1024 1120 WIRE 1664 1120 1664 976 WIRE 1792 1120 1792 1024 WIRE 160 1136 160 1056 WIRE 1936 1152 1936 880 WIRE 2048 1152 2048 1072 WIRE 2160 1152 2160 1120 WIRE 2160 1152 2048 1152 WIRE 2272 1152 2272 1104 WIRE 2272 1152 2160 1152 WIRE 432 1184 288 1184 WIRE 640 1184 512 1184 WIRE 944 1216 944 1120 WIRE 1088 1216 1088 1120 WIRE 2160 1216 2160 1152 WIRE 2496 1216 2496 1152 WIRE 32 1248 -80 1248 WIRE 352 1248 288 1248 WIRE 480 1248 432 1248 WIRE 528 1248 480 1248 WIRE 688 1248 688 1200 WIRE 688 1248 608 1248 WIRE 480 1280 480 1248 WIRE 688 1280 688 1248 WIRE -80 1296 -80 1248 WIRE 320 1312 288 1312 WIRE 1536 1328 1536 1280 WIRE 1600 1328 1536 1328 WIRE 944 1344 944 1280 WIRE 1008 1344 944 1344 WIRE 1088 1344 1088 1280 WIRE 1088 1344 1008 1344 WIRE 1536 1344 1536 1328 WIRE 1008 1360 1008 1344 WIRE 1600 1360 1600 1328 WIRE 1600 1360 1568 1360 WIRE 1376 1376 1312 1376 WIRE 1504 1376 1376 1376 WIRE 480 1392 480 1344 WIRE 688 1392 688 1360 WIRE 688 1392 480 1392 WIRE 1696 1392 1568 1392 WIRE 1760 1392 1696 1392 WIRE 1936 1392 1936 1232 WIRE 1936 1392 1840 1392 WIRE -80 1408 -80 1360 WIRE 0 1408 -80 1408 WIRE 160 1408 160 1360 WIRE 160 1408 80 1408 WIRE 320 1440 320 1312 WIRE 496 1440 320 1440 WIRE 688 1440 688 1392 WIRE 1312 1440 1312 1376 WIRE 1536 1440 1536 1408 WIRE 160 1456 160 1408 WIRE 1696 1504 1696 1392 WIRE 1728 1504 1696 1504 WIRE 1824 1504 1792 1504 WIRE 1936 1504 1936 1392 WIRE 1936 1504 1904 1504 WIRE 1536 1552 1536 1520 WIRE 1312 1584 1312 1520 WIRE 1312 1584 1072 1584 WIRE 1312 1632 1312 1584 WIRE 1376 1648 1376 1376 WIRE 1552 1648 1376 1648 WIRE 1696 1648 1696 1504 WIRE 1696 1648 1632 1648 WIRE 1312 1760 1312 1712 WIRE 1072 1840 1072 1584 FLAG 160 1456 0 FLAG 688 1440 0 FLAG 1664 1120 0 FLAG -80 1104 0 FLAG 496 1440 FB_N FLAG 1008 1360 0 FLAG 1312 1760 0 FLAG 1792 1120 0 FLAG 2160 1216 0 FLAG 1072 1840 FB_N FLAG 1536 1280 0 FLAG 1536 1552 0 FLAG 2496 1216 0 SYMBOL PowerProducts\\LTC3803 160 1248 R0 SYMATTR InstName U2 SYMBOL ind2 672 912 R0 WINDOW 0 -27 38 Right 2 WINDOW 3 -15 71 Right 2 SYMATTR InstName L3

SYMATTR Type ind SYMATTR SpiceLine Ipk=3.0 Rser=0.32 Cpar=1pF SYMBOL ind2 1072 912 R0 SYMATTR InstName L4

SYMATTR Type ind SYMATTR SpiceLine Ipk=20 Rser=0.32 Cpar=2pF SYMBOL nmos 640 1104 R0 WINDOW 0 110 45 Left 2 WINDOW 3 81 83 Left 2 SYMATTR InstName Q2 SYMATTR Value CSD17506Q5A SYMBOL res 672 1264 R0 WINDOW 0 89 24 Left 2 WINDOW 3 78 58 Left 2 SYMATTR InstName R9 SYMATTR Value 20m SYMBOL res 144 928 R0 WINDOW 0 69 18 Left 2 WINDOW 3 51 56 Left 2 SYMATTR InstName R10 SYMATTR Value 250 SYMBOL res 1296 1536 M180 WINDOW 0 -71 69 Left 2 WINDOW 3 -99 32 Left 2 SYMATTR InstName R11 SYMATTR Value 1.25k SYMBOL cap 1648 912 R0 WINDOW 0 -61 25 Left 2 WINDOW 3 -64 58 Left 2 SYMATTR InstName C4

SYMATTR SpiceLine Rser=10m SYMBOL voltage -80 928 R0 WINDOW 123 -220 84 Left 2 WINDOW 0 49 44 Left 2 WINDOW 3 49 79 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName Vin1 SYMATTR Value 12 SYMBOL res -16 896 R270 WINDOW 0 -39 62 VTop 2 WINDOW 3 -46 61 VBottom 2 SYMATTR InstName Rin1 SYMATTR Value 1m SYMBOL cap 64 1040 R90 WINDOW 0 60 70 VBottom 2 WINDOW 3 69 74 VTop 2 SYMATTR InstName C8

SYMBOL schottky 928 1216 R0 SYMATTR InstName D3 SYMATTR Value 30BQ060 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 928 928 R0 WINDOW 0 45 16 Left 2 WINDOW 3 45 50 Left 2 SYMATTR InstName C9

SYMATTR SpiceLine V=25 Irms=9.89 Rser=0.0110995 Lser=0 SYMBOL res 1296 1616 R0 WINDOW 0 -67 34 Left 2 WINDOW 3 -64 72 Left 2 SYMATTR InstName R15 SYMATTR Value 5K SYMBOL cap 1776 960 R0 WINDOW 0 55 17 Left 2 WINDOW 3 55 52 Left 2 SYMATTR InstName C10

SYMATTR SpiceLine Rser=1m SYMBOL res 624 1232 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R16 SYMATTR Value 100 SYMBOL cap 464 1280 R0 SYMATTR InstName C12 SYMATTR Value 100p SYMBOL schottky 1072 1216 R0 SYMATTR InstName D4 SYMATTR Value 30BQ060 SYMATTR Description Diode SYMATTR Type diode SYMBOL voltage 1536 1424 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 3.3 SYMBOL res 1920 1136 R0 SYMATTR InstName R17 SYMATTR Value 10 SYMBOL res 1856 1376 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R18 SYMATTR Value 100K SYMBOL res 1648 1632 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R19 SYMATTR Value 20k SYMBOL Opamps\\AD8605 1536 1440 R180 SYMATTR InstName U1 SYMBOL res 448 1232 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 3k SYMBOL res 96 1392 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 150K SYMBOL cap -96 1296 R0 SYMATTR InstName C1 SYMATTR Value 5n SYMBOL res 528 1168 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 17 SYMBOL cap 816 896 R0 WINDOW 0 45 16 Left 2 WINDOW 3 45 50 Left 2 SYMATTR InstName C2

SYMATTR SpiceLine V=25 Irms=9.89 Rser=0.0110995 Lser=0 SYMBOL res 816 944 R0 SYMATTR InstName R4 SYMATTR Value 1 SYMBOL cap 1792 1488 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1n SYMBOL res 1920 1488 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 150K SYMBOL res 2144 896 R0 SYMATTR InstName R6 SYMATTR Value 100 SYMBOL sw 2160 1136 R180 SYMATTR InstName S1 SYMATTR Value Load_ON SYMBOL voltage 2496 1056 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(00 1 10m 100n 100n 50m 100m 10) TEXT 744 856 Bottom 2 !K2 L3 L4 0.99 TEXT 672 800 Left 2 ;DRQ127 1:1 TEXT 344 1416 Left 2 ;0.8V TEXT 464 1496 Left 2 ;T770 VH SUPPLY\nJ LARKIN July 23, 2019 TEXT -114 1950 Left 2 !.tran 200m TEXT 2184 1024 Left 2 !.model Load_ON SW(Ron=10m Roff=100K Vt=0.5 Vh=0.1)

Reply to
habib
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Cute diode configuration.

It does ring a lot. You could move the snubber across the diodes, and scale the impedance up pretty hard.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

It rings because of non continuous conduction mode, nothing less than a normal behaviour, you're right nevertheless, 25 Ohm is not a light load so i need to re-compute the coupled inductor i think i made a mistake ; please John see after 10ms it does not rings so much with nominal load (coupled coeff K has is part in this)

I think there are some actual tricky things around the mosfet and the voltage at Sense, one should minimize the parasitic inductance in the current path.

Hab

Reply to
habib

What are the input / output / operating specs?

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 Thanks, 
    - Win
Reply to
Winfield Hill

Of course i forgot to mention.

Vin 12VDC, Vout 5W max @-5VDC (Vsense reach 70mV @5W output)

Reply to
habib

The DRQ127 has tiny leakage inductance, probably better than 0.99. But it still rings.

I'd move the RC snubber across the diodes. Rough values like 50 ohms+50 nF to start maybe.

I see that you lowpass filtered the shunt signal. I thought that was a good idea but seems to be unnecessary. Maybe the LTC chip ignores inductive spikes from the shunt.

I sometimes use a voltage divider after the shunt, so I don't have to use silly low shunt resistor values. That allows the effective shunt value to be trimmed easily, too. The shunt divider and slope compensation resistor merge into two resistors.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

I'm an unredeemable sinner in my old age, but I mostly buy surface-mount potted DC/DC converters these days.

5 watts can be an expensive brick, so it might make sense to build that one from parts. The 1 and 2 watt blobs are cheap.
--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

Dunno at the moment ... i'll see. Another surprise of this chip when overload occurs at the output ... it simply stop switching ! Strange for a so called "Current Mode Control"

Good, or a transformer.

Hab

Reply to
habib

Yeap that is exactly the purpose of this small DC/DC design, a decent output -5V/5W from 11V...14VDC input with short-circuit protection.

I'll see later the LTC3803 promises are real ... i'll see.

Hab

Reply to
habib

Not switching limits the current!

Another gotcha is that, at not-so-light loads, it goes into economy burp mode, which increases output ripple.

What can you expect for six pins?

That's scary.

Given a fixed supply voltage, at some given shunt resistor value the output is almost constant-power limited. That can be very useful.

I wonder what it would do with no shunt resistor. Might still work.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

They seem to behave like they simulate.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

Ok John but some other chips perform a real current limit even in short circuit condition (e.g. LM5155)

mhh ... yes right, No SoftSart pin, No UVLO pin, No Ext SYNC ... ok six pins, low cost but the chip do the job.

Reply to
habib

And it does :-)

Reply to
habib

TPS54302 does have an enable pin with a well defined threshold, which can be used for UVLO. You can even program the hysteresis. It does have internal soft-start.

I don't like to sync switchers. The 54302 is spread-spectrum, so you couldn't sync it anyhow.

--
John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Sync switchers are about all we use (we do use some 6MHz switchers). It's easier to deal with EMI when you know where it it's going to be and if that's not enough, the frequency can be changed to dodge radios.

Reply to
krw

Spread-spectrum is cool. It avoids having either a bunch of spectral lines from separate switchers, or one giant one if you synchronize them. If you want regulatory compliance, dodging radios isn't good enough.

That TI chip looks radical

formatting link

but the spreading doesn't seem to create any visible noise on the DC output. Must be shaped cleverly.

I've made ordinary switchers spread by injecting a small triangle into their frequency-set pin.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

Our customer's standards are much tighter than regulatory standards. With radios in the same box, particularly AM radios, EMI mitigation gets important.

That's what the output capacitors are for.

Sure, that was the original technique.

Reply to
krw

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