Is a balancing diode really necessary for the Balanced Boost converter?

Question

Please pardon all of the information that precedes the question -- I didn't want you to actually have to go read the paper itself. This question is in two parts, but they are really equivalent, so it's really just one question.

This question refers to this 2003 paper, "Balanced Switching Converter to Reduce Common-Mode Conducted Noise" by Masahito Shoyama, Member, IEEE, Ge Li, and Tamotsu Ninomiya, Fellow, IEEE

https://ieeexplore.ieee.org/iel5/41/28070/01254613.pdf and also an earlier version of the paper that can be found here, for those who don't have IEEE membership.

Here is the abstract:

Because conventional switching converters have usually used unbalanced circuit topologies, parasitic capacitance between the drain/collector of an active switch and the frame ground through its heat sink may generate the common-mode conducted noise. This paper proposes a balanced switching converter circuit, which is an effective way to reduce the common-mode conducted noise. As an example, a boost converter version of the balanced switching converter is presented, and the mechanism of the common-mode noise reduction is explained using an equivalent circuit. This good feature is confirmed by experimental results. The concept of the balanced switching converter is applied to some other types of switching converters.

and here is figure 1A and 1B:

Fig. 1. Concept of the balanced switching converter circuit applied to boost converter. (a) Conventional unbalanced boost converter. (b) Proposed balanced boost converter.

Also, here is how they are measuring the improvement:

In the article, diodes aren't really mentioned, and this is one reason why I question whether balanced diodes are really called for.

I understand that the coupled inductor is beneficial when trying to reduce EMI, but I question whether adding the balancing diode is really beneficial enough to justify the reduction in efficiency due to the accompanying, and in my mind, unnecessary, voltage drop of D2, the diode added to "balance".

Question Part 1 of 2: Is diode D2 of Figure 1B really necessary?

Here is a simplified representation of my current boost application (consider L1, L2, and L3 95% coupled):

Question Part 2 of 2: Is diode D2 of this circuit really necessary?

Thanks, because unfortunately, I really don't have the capability to measure this.

It shouldn't matter, but L3 is feedback winding for this Joule-Thief like self-oscillating boost, and the coupling is currently "K1 L1 L2 L3 0.95"

To get this simulating in LTspice, add a voltage pulse source from QN1 emitter, through a resistor, to base. Give all components values. Then you can try without D2. Remember to add "K1 L1 L2 0.95" as an instruction to mutually link the inductors. — rdtsc, Commented Jan 24, 2022 at 20:34
It makes sense to me and the 20 dB improvement in conducted noise is significant to balance the diode surge currents and their CM coupling to FG. I especially like that they avoided the need to add a coupling cap on diagonal into to output to reduce feed-thru noise which degrades DC grounded lightning immunity, — Tony Stewart EE75, Commented Jan 24, 2022 at 21:57
Ok. Sorry for the deleted comment. In my young years, I used another means to reduce EMI, by adding an isolated shield between the transistor and the radiator. But I don't know if this was very "effective". Did not own at this time a network analyzer. — Antonio51, Commented Jan 24, 2022 at 22:14
@TonyStewartEE75 - Yes, but how much of that 20dB is the set of balanced inductors, and how much of that 20dB is the set of balanced diodes? I'm trying not to lose efficiency by having to add an additional Schottky. — MicroservicesOnDDD, Commented Jan 24, 2022 at 22:17
Unless one has made one and verified performance , we can only speculate from similar experiences but Verbal Kint ought to know — Tony Stewart EE75, Commented Jan 25, 2022 at 21:42

rdtsc · Accepted Answer · 2022-01-28 17:21:01Z

Here is a (fixed) testbench for comparing the traditional model, against a "balanced" model, with and without the extra diode. It's a beast to simulate. "Real" components were chosen to more closely replicate real results. The gates are pulsed at 20kHz, 20% duty, after 50ms delay and for a duration of 40ms. The output caps, input and load resistances were changed just to allow it to "boost" more in the short time shown.

Comparing the three input voltages (POS terminals):

Here we can see that the Traditional Boost (red trace) is feeding much more noise back into the supply, even with typical LISN and Noise Filter. And so is the Balanced without Diode (blue) - they behave very similarly in this aspect. The Balanced with Two Diodes (green) excels here, with very little noise coupled.

As for output, we measure the current into the load resistors:

Without the second diode (blue trace), it performs slightly worse than the traditional boost (red) in terms of conducted output noise. But with the 2nd diode (green), output noise is greatly reduced. Checking the inductor currents:

The balanced version inductor current (green) is similar to the Traditional version (red.) But the No Diode version (blue) has much greater peaks. Zooming in:

The "Balanced with No Diode" does have much higher peaks, and oscillates near 3.3MHz at the switching transition - just from removing the diode.

As for the Cs currents:

These are different but average out to be similar. Specifically, over the 40ms of operation:

Traditional RMS into Cs was 6.1374A.
Balanced RMS (Cs1) was 5.4478A.
Balanced No-Diode (Cs1) was 4.1483A.

Question Part 1 of 2: Is diode D2 of Figure 1B really necessary?

Necessary, no. But it seems to reduce noise significantly, both into the supply and the load.

Both balanced versions stress the Cs capacitors less. If the diode is included, the Cs capacitor stress is higher, but conducted noise is greatly reduced.

Question Part 2 of 2: Is diode D2 of this circuit really necessary?

Ditto. Without it, the combined inductance at the switching nodes seem to want to oscillate briefly at transitions. Given the gate is driven from a coupled winding, the whole thing would likely start oscillating at 3MHz.

Here is the (fixed) .asc file, it is quite big:

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SYMATTR Value 100µ
SYMATTR Type ind
SYMATTR SpiceLine Ipk=5 Rser=0.028 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX100-5-52"
SYMBOL cap 1248 800 R0
SYMATTR InstName C27
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL diode 1456 736 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D3
SYMATTR Value RFN5TF8S
SYMBOL voltage -32 1120 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 124 Left 2
SYMATTR SpiceLine Rser=1
SYMATTR InstName V5
SYMATTR Value 320
SYMBOL ind 240 1104 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L12
SYMATTR Value 50µ
SYMATTR SpiceLine Ipk=5 Rser=0.021 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX50-5-52"
SYMBOL ind 240 1296 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L13
SYMATTR Value 50µ
SYMATTR SpiceLine Ipk=5 Rser=0.021 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX50-5-52"
SYMBOL cap 112 1312 R0
SYMATTR InstName C28
SYMATTR Value 1µ
SYMATTR SpiceLine V=400 Irms=0 Rser=0.0252581 Lser=10.4595n mfg="Würth Elektronik" pn="890283326009CS WCAP-FTBP 22.5 x 26 x 17 x 8.5" type="Box"
SYMBOL cap 192 1312 R0
SYMATTR InstName C29
SYMATTR Value 1µ
SYMATTR SpiceLine V=400 Irms=0 Rser=0.0252581 Lser=10.4595n mfg="Würth Elektronik" pn="890283326009CS WCAP-FTBP 22.5 x 26 x 17 x 8.5" type="Box"
SYMBOL cap 352 1312 R0
SYMATTR InstName C30
SYMATTR Value 0.1µ
SYMATTR SpiceLine V=630 Irms=556m Rser=0.01433 Lser=0 mfg="KEMET" pn="C1812C104KBRAC" type="X7R"
SYMBOL cap 432 1312 R0
SYMATTR InstName C31
SYMATTR Value 0.1µ
SYMATTR SpiceLine V=630 Irms=556m Rser=0.01433 Lser=0 mfg="KEMET" pn="C1812C104KBRAC" type="X7R"
SYMBOL res 352 1376 R0
SYMATTR InstName R5
SYMATTR Value 50
SYMBOL res 432 1376 R0
SYMATTR InstName R6
SYMATTR Value 50
SYMBOL cap 560 1152 R0
SYMATTR InstName C32
SYMATTR Value 0.22µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.0466984 Lser=14.381n mfg="Würth Elektronik" pn="890493426011CS WCAP-FTBE 22.5 x 26 x 18 x 9" type="Box"
SYMBOL ind2 736 1072 R90
WINDOW 0 5 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName L14
SYMATTR Value 6m
SYMATTR Type ind
SYMATTR SpiceLine Ipk=2 Rser=0.5 Rpar=527520 Cpar=0
SYMBOL ind2 624 1296 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 4 56 VBottom 2
SYMATTR InstName L15
SYMATTR Value 6m
SYMATTR Type ind
SYMATTR SpiceLine Ipk=2 Rser=0.5 Rpar=527520 Cpar=0
SYMBOL cap 720 1152 R0
SYMATTR InstName C33
SYMATTR Value 0.22µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.0466984 Lser=14.381n mfg="Würth Elektronik" pn="890493426011CS WCAP-FTBE 22.5 x 26 x 18 x 9" type="Box"
SYMBOL cap 800 1104 R0
SYMATTR InstName C34
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL cap 800 1200 R0
SYMATTR InstName C35
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL polcap 960 1152 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 470µ
SYMATTR InstName C36
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=450 Irms=2.89 Rser=0.076 Lser=9.10993n mfg="Würth Elektronik" pn="861011486024 WCAP-AIG8 35x47" type="Al electrolytic"
SYMBOL ind2 1008 1104 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L16
SYMATTR Value 100µ
SYMATTR Type ind
SYMATTR SpiceLine Ipk=5 Rser=0.028 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX100-5-52"
SYMBOL sym\\nmos 1152 1136 R0
SYMATTR InstName M3
SYMATTR Value R6020PNJ
SYMBOL cap 1328 1168 R0
SYMATTR InstName C37
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL diode 1376 1104 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value RFN5TF8S
SYMBOL polcap 1504 1152 R0
WINDOW 3 24 56 Left 2
SYMATTR Value 220µ
SYMATTR InstName C38
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=450 Irms=2.89 Rser=0.076 Lser=9.10993n mfg="Würth Elektronik" pn="861011486024 WCAP-AIG8 35x47" type="Al electrolytic"
SYMBOL cap 1584 1104 R0
SYMATTR InstName C39
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL cap 1584 1200 R0
SYMATTR InstName C40
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
SYMBOL voltage 1200 1408 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V6
SYMATTR Value PULSE(0 15 50m 1n 1n 10u 50u 800)
SYMBOL res 1712 1120 R0
SYMATTR InstName RL3
SYMATTR Value 4.7k
SYMBOL ind2 1120 1264 R90
WINDOW 0 4 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName L17
SYMATTR Value 100µ
SYMATTR Type ind
SYMATTR SpiceLine Ipk=5 Rser=0.028 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX100-5-52"
SYMBOL cap 1248 1328 R0
SYMATTR InstName C41
SYMATTR Value 0.022µ
SYMATTR SpiceLine V=1K Irms=0 Rser=0.117514 Lser=12.0417n mfg="Würth Elektronik" pn="890493425001CS WCAP-FTBE 15 x 18 x 11 x 5" type="Box"
TEXT 272 -48 Left 2 ;LISN
TEXT 656 -48 Left 2 ;Noise Filter
TEXT 672 416 Left 2 ;Ground
TEXT 136 208 Left 2 ;NEG
TEXT 1240 -48 Left 2 ;Traditional Boost
TEXT 760 0 Left 2 !K1 L3 L4 1.0
TEXT 1120 336 Left 2 ;20kHz, 20% duty
TEXT 672 944 Left 2 ;Ground
TEXT 136 736 Left 2 ;NEG
TEXT 1152 1024 Left 2 ;"Balanced" Boost Without Diode
TEXT 760 528 Left 2 !K2 L8 L9 1.0
TEXT 1000 896 Left 2 ;20kHz, 20% duty
TEXT 1136 528 Left 2 !K3 L10 L11 1.0
TEXT 672 1472 Left 2 ;Ground
TEXT 136 1264 Left 2 ;NEG
TEXT 760 1056 Left 2 !K4 L14 L15 1.0
TEXT 1000 1424 Left 2 ;20kHz, 20% duty
TEXT 1400 1472 Left 2 !.tran 100m startup uic
TEXT 1136 1056 Left 2 !K5 L16 L17 1.0
TEXT 1232 496 Left 2 ;"Balanced" Boost
LINE Normal 640 176 720 176
LINE Normal 720 80 640 176
LINE Normal 640 80 720 80
LINE Normal 640 704 720 704
LINE Normal 720 608 640 704
LINE Normal 640 608 720 608
LINE Normal 1104 608 1024 608
LINE Normal 1024 704 1104 608
LINE Normal 1104 704 1024 704
LINE Normal 640 1232 720 1232
LINE Normal 720 1136 640 1232
LINE Normal 640 1136 720 1136
LINE Normal 1104 1136 1024 1136
LINE Normal 1024 1232 1104 1136
LINE Normal 1104 1232 1024 1232
RECTANGLE Normal 512 464 96 -32 2
RECTANGLE Normal 928 272 544 -32 2
RECTANGLE Normal 512 992 96 496 2
RECTANGLE Normal 928 800 544 496 2
RECTANGLE Normal 512 1520 96 1024 2
RECTANGLE Normal 928 1328 544 1024 2

Have tried "harmonic" analysis. For D2, It is "pertinent" and clearly very "useful". — Antonio51, Commented Jan 26, 2022 at 20:46
I entered your testbench before you added the file source code to your very nice answer. I was wondering why my output was different from yours, and then I found that the three models are cross-connected via V2, V4, V6, and the gates of all 3 MOSFETs on Label G1, which I have as Labels V2, V4, and V6 on my testbench. — MicroservicesOnDDD, Commented Jan 26, 2022 at 21:22
I also added a capacitor just like C27 and C41 on the Traditional Boost (but I'm not sure it belongs). And finally, I changed 470u to 480u on Traditional, all 100u to 120u, and 120u couplings to 0.99 on both Balanced, to try to more evenly match the inductances. And my inductors are not real ones. — MicroservicesOnDDD, Commented Jan 26, 2022 at 21:25

Antonio51 · Accepted Answer · 2022-01-26 22:07:53Z

1

Tried analysis of schematic in a particular case, did not include capacitor between Drain and ground, nor between source and ground.

Results are voltages inputs and currents main inputs (spectrum) for comparison.

So, clearly showing that the "D2" added diode is "useful".

answered Jan 26, 2022 at 22:07

Antonio51

14.3k1 gold badge8 silver badges23 bronze badges

\$\begingroup\$ Is this quasi-peak such that the alternating peaks cancel? or is the BW high enough to show true peak conduction noise. \$\endgroup\$
– Tony Stewart EE75
Commented Jan 27, 2022 at 22:15
\$\begingroup\$ What simulator is that? \$\endgroup\$
– MicroservicesOnDDD
Commented Jan 28, 2022 at 1:49
1

\$\begingroup\$ @MicroservicesOnDDD - Free simulator microcap 12 spectrum-soft.com/download/download.shtm \$\endgroup\$
– Antonio51
Commented Jan 28, 2022 at 5:42
1

\$\begingroup\$ @TonyStewartEE75 sorry, don't understand (BW ?) what you mean. The first picture shows that the second circuit (short-circuited diode D4) is noisier on current inputs. In particular, at the harmonics frequencies of the switching (20 kHz- 50% duty). (EE&O) \$\endgroup\$
– Antonio51
Commented Jan 28, 2022 at 5:53
1

\$\begingroup\$ NB: voltages are referenced to ground, and are noisy in the unbalanced case. But, If (Vg1-Vg2) and (Vg3-Vg4) are drawn (rectified sinusoidal wave), these voltages are obviously "clean". I did not show all current inputs which are obviously noisy in the unbalanced case ... \$\endgroup\$
– Antonio51
Commented Jan 28, 2022 at 6:05

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Is a balancing diode really necessary for the Balanced Boost converter?

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Is a balancing diode really necessary for the Balanced Boost converter?

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