Forums

Switching current limiter for safe charging of large capacitors, and short circuit protection

Started by P E Schoen June 17, 2012
In a previous post about minimizing spikes on a square wave push-pull=20
transformer drive, my simulations discovered a very large and probably=20
destructive current surge due to the large capacitor load on the output =
of=20
the step-up transformer and FWB. I proposed using a brute force linear=20
current regulator, but the SOA of the transistors would be exceeded. I =
need=20
an output of at least 1500 watts, and the energy storage in the =
capacitors=20
(6600uF at 300V, or 990 watt-seconds) was such that I would need to use=20
multiple power transistors and also a controlled charge current with a =
long=20
time constant to be reasonable.

But I realized that a switching regulator would be much more efficient =
and=20
better for many reasons, so I endeavored to make one using LTSpice. The=20
basic premise was to apply the battery voltage to an inductor and read =
the=20
current, and then switch off the drive when it became a certain maximum=20
value, such as 100A, and then turn on again when it dropped to about =
80A. I=20
found that a reasonable value was 4.7 uH and I found a commercially=20
available model good for 60A for about $13.
http://www.newark.com/vishay-dale/ihth1125mzeb4r7m5a/inductor-4-7uh-20-55=
a/dp/51R6660?Ntt=3D51R6660

At first I tried using a PMOS but the standard models did not have one =
that=20
was suitable. I also had difficulty finding a good gate driver, and the =
ones=20
I tried to concoct from op-amps were too slow and caused peak power=20
dissipation of many kW in the MOSFET, for a significant period of time. =
So I=20
changed the design to use an NMOS and a high-side driver:
http://www.newark.com/linear-technology/ltc4440ems8e-pbf/ic-mosfet-gate-d=
river-high-side/dp/56M9553

So my simulation shows a peak current of about 90A and the voltage at =
the=20
transformer stabilizes within about 1.5 mSec with a 2200 uF capacitor. =
Then=20
I turn on the gate drives to the MOSFETs for the transformer, and the=20
current limit goes into effect again, with a maximum current of 150A, =
while=20
the series MOSFET dissipates about 35 watts. The circuit oscillates at =
about=20
220 kHz. It stabilizes by 90 mSec at which point the battery is =
supplying=20
1.15 kW and the output resistor load is 1.06 kW, for an efficiency of =
92%.=20
This includes the current limiter which is about 10W, the switching=20
transistors which are 20W each, 6W in the inductor, and 15W in the two=20
output capacitors which are still charging.

Following is the ASC file. I'll have to give this a try before I do any =
more=20
testing with the DC-DC converter. And I can probably do the same thing,=20
essentially, by modulating the gate drives of the transformer driver=20
MOSFETs. In that case, I will probably need to leave the inductor in the =

center tap of the transformer to the battery. But for now, the current=20
limiter seems to work well, and it may be a good device to make as a=20
stand-alone current limiter for working with batteries.

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D

Version 4
SHEET 1 880 680
WIRE 0 -32 -352 -32
WIRE -352 0 -352 -32
WIRE -160 0 -272 0
WIRE -352 80 -352 64
WIRE -272 80 -272 64
WIRE -272 80 -352 80
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WIRE -320 240 -448 240
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WIRE -96 560 -160 560
WIRE 0 560 0 480
WIRE 0 560 -96 560
WIRE -544 608 -544 528
FLAG -1136 560 0
FLAG 592 384 0
FLAG 560 128 Vout
FLAG -448 240 in
FLAG 96 144 m1
FLAG 112 336 m2
FLAG -960 160 batt
FLAG -240 464 g1
FLAG -80 416 g2
FLAG -96 560 src
SYMBOL ind2 112 128 R0
SYMATTR InstName L1
SYMATTR Value 180=B5
SYMATTR Type ind
SYMATTR SpiceLine Rser=3D100u
SYMBOL ind2 112 240 R0
WINDOW 0 45 35 Left 2
WINDOW 3 41 61 Left 2
SYMATTR InstName L2
SYMATTR Value 180=B5
SYMATTR Type ind
SYMATTR SpiceLine Rser=3D100u
SYMBOL ind2 240 176 M0
WINDOW 0 21 -5 Left 2
WINDOW 3 -9 113 Left 2
SYMATTR InstName L3
SYMATTR Value 32m
SYMATTR Type ind
SYMATTR SpiceLine Rser=3D10m
SYMBOL nmos -208 384 R0
SYMATTR InstName M1
SYMATTR Value IRFZ44N
SYMBOL nmos -48 384 R0
SYMATTR InstName M2
SYMATTR Value IRFZ44N
SYMBOL voltage -1088 192 R0
WINDOW 123 0 0 Left 2
WINDOW 39 -32 107 Left 2
WINDOW 3 -16 55 Left 2
SYMATTR SpiceLine Rser=3D8m
SYMATTR InstName V1
SYMATTR Value 24
SYMBOL diode 384 288 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value MUR460
SYMBOL diode 320 224 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D3
SYMATTR Value MUR460
SYMBOL polcap 480 288 R0
WINDOW 3 24 64 Left 2
SYMATTR Value 220=B5
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.016 Lser=3D0
SYMBOL res 576 192 R0
SYMATTR InstName R1
SYMATTR Value 75
SYMBOL voltage -384 320 R0
WINDOW 123 0 0 Left 2
WINDOW 39 -43 57 Left 2
WINDOW 3 228 271 Left 2
SYMATTR SpiceLine Rser=3D100
SYMATTR Value PULSE(0 10 0.5u 10n 10n 499u 1000u 350)
SYMATTR InstName V2
SYMBOL voltage -256 320 R0
WINDOW 123 0 0 Left 2
WINDOW 39 -43 57 Left 2
WINDOW 3 100 298 Left 2
SYMATTR SpiceLine Rser=3D100
SYMATTR Value PULSE(0 10 500.5u 10n 10n 499u 1000u 350)
SYMATTR InstName V3
SYMBOL diode 320 144 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value MUR460
SYMBOL diode 384 384 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value MUR460
SYMBOL polcap -480 368 R0
WINDOW 3 24 64 Left 2
SYMATTR Value 2200=B5
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=3D25 Irms=3D20 Rser=3D100m Lser=3D0
SYMBOL polcap 512 128 R0
WINDOW 3 24 64 Left 2
SYMATTR Value 220=B5
SYMATTR InstName C3
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.016 Lser=3D0
SYMBOL cap -528 304 R0
SYMATTR InstName C5
SYMATTR Value .47=B5
SYMATTR SpiceLine V=3D250 Rser=3D100u
SYMBOL schottky -576 416 R180
WINDOW 0 24 64 Left 2
WINDOW 3 -17 -52 VRight 2
SYMATTR InstName D5
SYMATTR Value MBRB2545CT
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -144 544 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value .001
SYMBOL cap -336 464 R0
SYMATTR InstName C6
SYMATTR Value .047=B5
SYMATTR SpiceLine V=3D250 Rser=3D100u
SYMBOL cap -96 464 R0
SYMATTR InstName C7
SYMATTR Value .047=B5
SYMATTR SpiceLine V=3D250 Rser=3D100u
SYMBOL diode -288 0 R0
SYMATTR InstName D6
SYMATTR Value MUR460
SYMBOL diode -336 0 M0
SYMATTR InstName D7
SYMATTR Value MUR460
SYMBOL cap -368 96 R0
SYMATTR InstName C10
SYMATTR Value 2.7=B5
SYMBOL res -288 80 R0
SYMATTR InstName R6
SYMATTR Value 1K
SYMBOL res -784 512 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 0.002
SYMBOL res -912 144 R0
SYMATTR InstName R4
SYMATTR Value 100
SYMBOL res -768 432 R0
SYMATTR InstName R5
SYMATTR Value 220
SYMBOL pmos -608 208 M270
SYMATTR InstName M3
SYMATTR Value Si4401DY
SYMBOL Opamps\\LT1630 -912 304 R0
SYMATTR InstName U1
SYMBOL res -672 208 R0
SYMATTR InstName R7
SYMATTR Value 100
SYMBOL npn -720 320 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL res -752 304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 1K
SYMBOL res -1024 384 R0
SYMATTR InstName R9
SYMATTR Value 10
SYMBOL res -992 272 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R10
SYMATTR Value 2.4k
SYMBOL res -944 304 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R11
SYMATTR Value 20k
SYMBOL ind -608 256 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L5
SYMATTR Value 4.7=B5
SYMATTR SpiceLine Ipk=3D62 Rser=3D0.00094 Rpar=3D350 Cpar=3D6.13p
SYMBOL res -784 336 R0
WINDOW 0 -34 54 Left 2
SYMATTR InstName R12
SYMATTR Value 220
SYMBOL cap -976 464 R0
SYMATTR InstName C4
SYMATTR Value 0.47=B5
SYMATTR SpiceLine V=3D250 Rser=3D100u
SYMBOL voltage -1216 336 R0
WINDOW 123 0 0 Left 2
WINDOW 39 -32 107 Left 2
WINDOW 3 -14 53 Left 2
SYMATTR SpiceLine Rser=3D8m
SYMATTR InstName V4
SYMATTR Value 10
TEXT 32 88 Left 2 !K1 L1 L2 L3 0.998
TEXT -536 576 Left 2 !.tran 0 400m 0 2u startup
TEXT 216 -24 Left 2 ;Primary 2x8 turns 2V/turn at 600 Hz=20

On a sunny day (Sun, 17 Jun 2012 04:05:13 -0400) it happened "P E Schoen"
<paul@peschoen.com> wrote in <jrk33q$18u$1@dont-email.me>:


Since you are a PIC user, a current and voltage regulated supply:
 http://panteltje.com/panteltje/pic/pwr_pic/index.html

For more current use bigger inductors (physicaly),
and bigger MOSFETS, and a real MOSFET driver.

I have used this as lab supply now for more than year,
and it is absolutely the greatest,

On Sun, 17 Jun 2012 04:05:13 -0400, P E Schoen wrote:

> Following is the ASC file. I'll have to give this a try before I do any more > testing with the DC-DC converter. And I can probably do the same thing, > essentially, by modulating the gate drives of the transformer driver > MOSFETs. In that case, I will probably need to leave the inductor in the > center tap of the transformer to the battery. But for now, the current > limiter seems to work well, and it may be a good device to make as a > stand-alone current limiter for working with batteries.
I see about 24V of HF hash at M3 drain. Apparently due to L5 resonating with various capacitances. BTW, what was the thinking behind specifying both series *and* parallel parasitic resistances for L5? They're each just a different way of specifying the same quantity. If the 350 ohms is a physical damping resistor, it should ideally show on the circuit. Any reason why you restricted the number of cycles of drive to M1 and M2, rather than letting it run for the full simulation time? Why not just use a simple precharge resistor, switched out with a contactor, or maybe a triac? That's the way the VFD guys do it. Otherwise, your suggestion of PWM-ing the gate drives would work. There are driver ICs available that current limit in just that way. Please, pretty please, get rid of that Greek "mu" (Control Panel - Netlist Options). -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
On Sunday, June 17, 2012 4:05:13 AM UTC-4, P E Schoen wrote:
> In a previous post about minimizing spikes on a square wave push-pull=20 > transformer drive, my simulations discovered a very large and probably=20 > destructive current surge due to the large capacitor load on the output o=
f=20
> the step-up transformer and FWB. I proposed using a brute force linear=20 > current regulator, but the SOA of the transistors would be exceeded. I ne=
ed=20
> an output of at least 1500 watts, and the energy storage in the capacitor=
s=20
> (6600uF at 300V, or 990 watt-seconds) was such that I would need to use=
=20
> multiple power transistors and also a controlled charge current with a lo=
ng=20
> time constant to be reasonable. >=20 > But I realized that a switching regulator would be much more efficient an=
d=20
> better for many reasons, so I endeavored to make one using LTSpice. The=
=20
> basic premise was to apply the battery voltage to an inductor and read th=
e=20
> current, and then switch off the drive when it became a certain maximum=
=20
> value, such as 100A, and then turn on again when it dropped to about 80A.=
I=20
> found that a reasonable value was 4.7 uH and I found a commercially=20 > available model good for 60A for about $13. > http://www.newark.com/vishay-dale/ihth1125mzeb4r7m5a/inductor-4-7uh-20-55=
a/dp/51R6660?Ntt=3D51R6660
>=20 > At first I tried using a PMOS but the standard models did not have one th=
at=20
> was suitable. I also had difficulty finding a good gate driver, and the o=
nes=20
> I tried to concoct from op-amps were too slow and caused peak power=20 > dissipation of many kW in the MOSFET, for a significant period of time. S=
o I=20
> changed the design to use an NMOS and a high-side driver: > http://www.newark.com/linear-technology/ltc4440ems8e-pbf/ic-mosfet-gate-d=
river-high-side/dp/56M9553
>=20 > So my simulation shows a peak current of about 90A and the voltage at the=
=20
> transformer stabilizes within about 1.5 mSec with a 2200 uF capacitor. Th=
en=20
> I turn on the gate drives to the MOSFETs for the transformer, and the=20 > current limit goes into effect again, with a maximum current of 150A, whi=
le=20
> the series MOSFET dissipates about 35 watts. The circuit oscillates at ab=
out=20
> 220 kHz. It stabilizes by 90 mSec at which point the battery is supplying=
=20
> 1.15 kW and the output resistor load is 1.06 kW, for an efficiency of 92%=
.=20
> This includes the current limiter which is about 10W, the switching=20 > transistors which are 20W each, 6W in the inductor, and 15W in the two=20 > output capacitors which are still charging. >=20 > Following is the ASC file. I'll have to give this a try before I do any m=
ore=20
> testing with the DC-DC converter. And I can probably do the same thing,=
=20
> essentially, by modulating the gate drives of the transformer driver=20 > MOSFETs. In that case, I will probably need to leave the inductor in the=
=20
> center tap of the transformer to the battery. But for now, the current=20 > limiter seems to work well, and it may be a good device to make as a=20 > stand-alone current limiter for working with batteries. >=20 > Paul >=20 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D
>=20 > Version 4 > SHEET 1 880 680 > WIRE 0 -32 -352 -32 > WIRE -352 0 -352 -32 > WIRE -160 0 -272 0 > WIRE -352 80 -352 64 > WIRE -272 80 -272 64 > WIRE -272 80 -352 80 > WIRE -352 96 -352 80 > WIRE -272 96 -272 80 > WIRE 256 96 224 96 > WIRE 256 128 256 96 > WIRE 320 128 256 128 > WIRE 432 128 384 128 > WIRE 528 128 432 128 > WIRE 544 128 528 128 > WIRE 560 128 544 128 > WIRE 592 128 560 128 > WIRE -160 144 -160 0 > WIRE 96 144 -160 144 > WIRE 128 144 96 144 > WIRE -1008 160 -1088 160 > WIRE -960 160 -1008 160 > WIRE -896 160 -960 160 > WIRE -704 160 -896 160 > WIRE -592 160 -608 160 > WIRE -1008 176 -1008 160 > WIRE -352 176 -352 160 > WIRE -320 176 -352 176 > WIRE -272 176 -320 176 > WIRE 224 192 224 96 > WIRE -1088 208 -1088 160 > WIRE 320 208 288 208 > WIRE 432 208 432 128 > WIRE 432 208 384 208 > WIRE 528 208 528 192 > WIRE 528 208 464 208 > WIRE 592 208 592 128 > WIRE -688 224 -688 208 > WIRE -688 224 -752 224 > WIRE -656 224 -688 224 > WIRE -752 240 -752 224 > WIRE -752 240 -896 240 > WIRE -592 240 -592 160 > WIRE -464 240 -512 240 > WIRE -448 240 -464 240 > WIRE -320 240 -320 176 > WIRE -320 240 -448 240 > WIRE 128 240 128 224 > WIRE 128 240 -320 240 > WIRE 128 256 128 240 > WIRE 544 256 544 128 > WIRE 544 256 496 256 > WIRE 288 272 288 208 > WIRE 288 272 224 272 > WIRE 320 272 288 272 > WIRE 416 272 384 272 > WIRE -1008 288 -1008 256 > WIRE -928 288 -1008 288 > WIRE -320 288 -384 288 > WIRE -80 288 -256 288 > WIRE 496 288 496 256 > WIRE -512 304 -512 240 > WIRE -912 320 -1216 320 > WIRE -848 320 -848 288 > WIRE -656 320 -656 304 > WIRE -912 336 -912 320 > WIRE -384 336 -384 288 > WIRE -256 336 -256 288 > WIRE 0 336 0 -32 > WIRE 112 336 0 336 > WIRE 128 336 112 336 > WIRE -1216 352 -1216 320 > WIRE -944 352 -960 352 > WIRE -768 352 -768 320 > WIRE -720 352 -768 352 > WIRE -592 352 -592 240 > WIRE -848 368 -848 320 > WIRE -848 368 -880 368 > WIRE -720 368 -720 352 > WIRE -464 368 -464 240 > WIRE 256 368 256 128 > WIRE 320 368 256 368 > WIRE 416 368 416 272 > WIRE 416 368 384 368 > WIRE 464 368 464 208 > WIRE 464 368 416 368 > WIRE 496 368 496 352 > WIRE 496 368 464 368 > WIRE 592 368 592 288 > WIRE 592 368 496 368 > WIRE -1008 384 -1008 288 > WIRE -944 384 -1008 384 > WIRE -160 384 -160 144 > WIRE 0 384 0 336 > WIRE 592 384 592 368 > WIRE -1008 400 -1008 384 > WIRE -80 416 -80 288 > WIRE -1088 432 -1088 288 > WIRE -912 432 -912 400 > WIRE -912 432 -1088 432 > WIRE -768 432 -912 432 > WIRE -656 432 -656 416 > WIRE -656 432 -768 432 > WIRE -960 448 -960 352 > WIRE -752 448 -960 448 > WIRE -960 464 -960 448 > WIRE -320 464 -320 288 > WIRE -240 464 -320 464 > WIRE -208 464 -240 464 > WIRE -80 464 -80 416 > WIRE -48 464 -80 464 > WIRE -1216 528 -1216 432 > WIRE -1136 528 -1216 528 > WIRE -1088 528 -1088 432 > WIRE -1088 528 -1136 528 > WIRE -1008 528 -1008 480 > WIRE -1008 528 -1088 528 > WIRE -960 528 -1008 528 > WIRE -880 528 -960 528 > WIRE -752 528 -800 528 > WIRE -592 528 -592 416 > WIRE -592 528 -752 528 > WIRE -544 528 -592 528 > WIRE -512 528 -512 368 > WIRE -512 528 -544 528 > WIRE -464 528 -464 432 > WIRE -464 528 -512 528 > WIRE -384 528 -384 416 > WIRE -384 528 -464 528 > WIRE -320 528 -384 528 > WIRE -256 528 -256 416 > WIRE -256 528 -320 528 > WIRE -240 528 -256 528 > WIRE -80 528 -240 528 > WIRE -1136 560 -1136 528 > WIRE -240 560 -240 528 > WIRE -160 560 -160 480 > WIRE -96 560 -160 560 > WIRE 0 560 0 480 > WIRE 0 560 -96 560 > WIRE -544 608 -544 528 > FLAG -1136 560 0 > FLAG 592 384 0 > FLAG 560 128 Vout > FLAG -448 240 in > FLAG 96 144 m1 > FLAG 112 336 m2 > FLAG -960 160 batt > FLAG -240 464 g1 > FLAG -80 416 g2 > FLAG -96 560 src > SYMBOL ind2 112 128 R0 > SYMATTR InstName L1 > SYMATTR Value 180=B5 > SYMATTR Type ind > SYMATTR SpiceLine Rser=3D100u > SYMBOL ind2 112 240 R0 > WINDOW 0 45 35 Left 2 > WINDOW 3 41 61 Left 2 > SYMATTR InstName L2 > SYMATTR Value 180=B5 > SYMATTR Type ind > SYMATTR SpiceLine Rser=3D100u > SYMBOL ind2 240 176 M0 > WINDOW 0 21 -5 Left 2 > WINDOW 3 -9 113 Left 2 > SYMATTR InstName L3 > SYMATTR Value 32m > SYMATTR Type ind > SYMATTR SpiceLine Rser=3D10m > SYMBOL nmos -208 384 R0 > SYMATTR InstName M1 > SYMATTR Value IRFZ44N > SYMBOL nmos -48 384 R0 > SYMATTR InstName M2 > SYMATTR Value IRFZ44N > SYMBOL voltage -1088 192 R0 > WINDOW 123 0 0 Left 2 > WINDOW 39 -32 107 Left 2 > WINDOW 3 -16 55 Left 2 > SYMATTR SpiceLine Rser=3D8m > SYMATTR InstName V1 > SYMATTR Value 24 > SYMBOL diode 384 288 M270 > WINDOW 0 32 32 VTop 2 > WINDOW 3 0 32 VBottom 2 > SYMATTR InstName D2 > SYMATTR Value MUR460 > SYMBOL diode 320 224 R270 > WINDOW 0 32 32 VTop 2 > WINDOW 3 0 32 VBottom 2 > SYMATTR InstName D3 > SYMATTR Value MUR460 > SYMBOL polcap 480 288 R0 > WINDOW 3 24 64 Left 2 > SYMATTR Value 220=B5 > SYMATTR InstName C1 > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.016 Lser=3D0 > SYMBOL res 576 192 R0 > SYMATTR InstName R1 > SYMATTR Value 75 > SYMBOL voltage -384 320 R0 > WINDOW 123 0 0 Left 2 > WINDOW 39 -43 57 Left 2 > WINDOW 3 228 271 Left 2 > SYMATTR SpiceLine Rser=3D100 > SYMATTR Value PULSE(0 10 0.5u 10n 10n 499u 1000u 350) > SYMATTR InstName V2 > SYMBOL voltage -256 320 R0 > WINDOW 123 0 0 Left 2 > WINDOW 39 -43 57 Left 2 > WINDOW 3 100 298 Left 2 > SYMATTR SpiceLine Rser=3D100 > SYMATTR Value PULSE(0 10 500.5u 10n 10n 499u 1000u 350) > SYMATTR InstName V3 > SYMBOL diode 320 144 R270 > WINDOW 0 32 32 VTop 2 > WINDOW 3 0 32 VBottom 2 > SYMATTR InstName D1 > SYMATTR Value MUR460 > SYMBOL diode 384 384 M270 > WINDOW 0 32 32 VTop 2 > WINDOW 3 0 32 VBottom 2 > SYMATTR InstName D4 > SYMATTR Value MUR460 > SYMBOL polcap -480 368 R0 > WINDOW 3 24 64 Left 2 > SYMATTR Value 2200=B5 > SYMATTR InstName C2 > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=3D25 Irms=3D20 Rser=3D100m Lser=3D0 > SYMBOL polcap 512 128 R0 > WINDOW 3 24 64 Left 2 > SYMATTR Value 220=B5 > SYMATTR InstName C3 > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.016 Lser=3D0 > SYMBOL cap -528 304 R0 > SYMATTR InstName C5 > SYMATTR Value .47=B5 > SYMATTR SpiceLine V=3D250 Rser=3D100u > SYMBOL schottky -576 416 R180 > WINDOW 0 24 64 Left 2 > WINDOW 3 -17 -52 VRight 2 > SYMATTR InstName D5 > SYMATTR Value MBRB2545CT > SYMATTR Description Diode > SYMATTR Type diode > SYMBOL res -144 544 R90 > WINDOW 0 0 56 VBottom 2 > WINDOW 3 32 56 VTop 2 > SYMATTR InstName R3 > SYMATTR Value .001 > SYMBOL cap -336 464 R0 > SYMATTR InstName C6 > SYMATTR Value .047=B5 > SYMATTR SpiceLine V=3D250 Rser=3D100u > SYMBOL cap -96 464 R0 > SYMATTR InstName C7 > SYMATTR Value .047=B5 > SYMATTR SpiceLine V=3D250 Rser=3D100u > SYMBOL diode -288 0 R0 > SYMATTR InstName D6 > SYMATTR Value MUR460 > SYMBOL diode -336 0 M0 > SYMATTR InstName D7 > SYMATTR Value MUR460 > SYMBOL cap -368 96 R0 > SYMATTR InstName C10 > SYMATTR Value 2.7=B5 > SYMBOL res -288 80 R0 > SYMATTR InstName R6 > SYMATTR Value 1K > SYMBOL res -784 512 R90 > WINDOW 0 0 56 VBottom 2 > WINDOW 3 32 56 VTop 2 > SYMATTR InstName R2 > SYMATTR Value 0.002 > SYMBOL res -912 144 R0 > SYMATTR InstName R4 > SYMATTR Value 100 > SYMBOL res -768 432 R0 > SYMATTR InstName R5 > SYMATTR Value 220 > SYMBOL pmos -608 208 M270 > SYMATTR InstName M3 > SYMATTR Value Si4401DY > SYMBOL Opamps\\LT1630 -912 304 R0 > SYMATTR InstName U1 > SYMBOL res -672 208 R0 > SYMATTR InstName R7 > SYMATTR Value 100 > SYMBOL npn -720 320 R0 > SYMATTR InstName Q1 > SYMATTR Value 2N2222 > SYMBOL res -752 304 R90 > WINDOW 0 0 56 VBottom 2 > WINDOW 3 32 56 VTop 2 > SYMATTR InstName R8 > SYMATTR Value 1K > SYMBOL res -1024 384 R0 > SYMATTR InstName R9 > SYMATTR Value 10 > SYMBOL res -992 272 R180 > WINDOW 0 36 76 Left 2 > WINDOW 3 36 40 Left 2 > SYMATTR InstName R10 > SYMATTR Value 2.4k > SYMBOL res -944 304 R270 > WINDOW 0 32 56 VTop 2 > WINDOW 3 0 56 VBottom 2 > SYMATTR InstName R11 > SYMATTR Value 20k > SYMBOL ind -608 256 R270 > WINDOW 0 32 56 VTop 2 > WINDOW 3 5 56 VBottom 2 > SYMATTR InstName L5 > SYMATTR Value 4.7=B5 > SYMATTR SpiceLine Ipk=3D62 Rser=3D0.00094 Rpar=3D350 Cpar=3D6.13p > SYMBOL res -784 336 R0 > WINDOW 0 -34 54 Left 2 > SYMATTR InstName R12 > SYMATTR Value 220 > SYMBOL cap -976 464 R0 > SYMATTR InstName C4 > SYMATTR Value 0.47=B5 > SYMATTR SpiceLine V=3D250 Rser=3D100u > SYMBOL voltage -1216 336 R0 > WINDOW 123 0 0 Left 2 > WINDOW 39 -32 107 Left 2 > WINDOW 3 -14 53 Left 2 > SYMATTR SpiceLine Rser=3D8m > SYMATTR InstName V4 > SYMATTR Value 10 > TEXT 32 88 Left 2 !K1 L1 L2 L3 0.998 > TEXT -536 576 Left 2 !.tran 0 400m 0 2u startup > TEXT 216 -24 Left 2 ;Primary 2x8 turns 2V/turn at 600 Hz
Haven't looked at the sim yet but I know right off that I wouldn't even con= sider this approach. Since the actual current limit is not that critical, I= would monitor the VDS drop across the RDS of the on MOSFET and ground the = gate drive at IDS of approximately 60A. All you need is some HCT logic work= ing in conjunction with your PIC, UCC27321(?) drivers, and a dual comparato= r. Then hang a slo-blow fuse off the BATT(+) to kill everything in the even= t of a hard failure.
On Sun, 17 Jun 2012 04:05:13 -0400, "P E Schoen" <paul@peschoen.com>
wrote:

>In a previous post about minimizing spikes on a square wave push-pull >transformer drive, my simulations discovered a very large and probably >destructive current surge due to the large capacitor load on the output of >the step-up transformer and FWB. I proposed using a brute force linear >current regulator, but the SOA of the transistors would be exceeded. I need >an output of at least 1500 watts, and the energy storage in the capacitors >(6600uF at 300V, or 990 watt-seconds) was such that I would need to use >multiple power transistors and also a controlled charge current with a long >time constant to be reasonable.
Why not just soft-start the inverter that you already have? Why not use smaller caps?
On 17 Jun., 10:05, "P E Schoen" <p...@peschoen.com> wrote:
>
snip
>
looked at something like a IR2086 ? -Lasse
On Sun, 17 Jun 2012 04:05:13 -0400, "P E Schoen" <paul@peschoen.com>
wrote:

>In a previous post about minimizing spikes on a square wave push-pull >transformer drive, my simulations discovered a very large and probably >destructive current surge due to the large capacitor load on the output of >the step-up transformer and FWB. I proposed using a brute force linear >current regulator, but the SOA of the transistors would be exceeded. I need >an output of at least 1500 watts, and the energy storage in the capacitors >(6600uF at 300V, or 990 watt-seconds) was such that I would need to use >multiple power transistors and also a controlled charge current with a long >time constant to be reasonable. > >But I realized that a switching regulator would be much more efficient and >better for many reasons, so I endeavored to make one using LTSpice. The >basic premise was to apply the battery voltage to an inductor and read the >current, and then switch off the drive when it became a certain maximum >value, such as 100A, and then turn on again when it dropped to about 80A. I >found that a reasonable value was 4.7 uH and I found a commercially >available model good for 60A for about $13. >http://www.newark.com/vishay-dale/ihth1125mzeb4r7m5a/inductor-4-7uh-20-55a/dp/51R6660?Ntt=51R6660 > >At first I tried using a PMOS but the standard models did not have one that >was suitable. I also had difficulty finding a good gate driver, and the ones >I tried to concoct from op-amps were too slow and caused peak power >dissipation of many kW in the MOSFET, for a significant period of time. So I >changed the design to use an NMOS and a high-side driver: >http://www.newark.com/linear-technology/ltc4440ems8e-pbf/ic-mosfet-gate-driver-high-side/dp/56M9553 > >So my simulation shows a peak current of about 90A and the voltage at the >transformer stabilizes within about 1.5 mSec with a 2200 uF capacitor. Then >I turn on the gate drives to the MOSFETs for the transformer, and the >current limit goes into effect again, with a maximum current of 150A, while >the series MOSFET dissipates about 35 watts. The circuit oscillates at about >220 kHz. It stabilizes by 90 mSec at which point the battery is supplying >1.15 kW and the output resistor load is 1.06 kW, for an efficiency of 92%. >This includes the current limiter which is about 10W, the switching >transistors which are 20W each, 6W in the inductor, and 15W in the two >output capacitors which are still charging. > >Following is the ASC file. I'll have to give this a try before I do any more >testing with the DC-DC converter. And I can probably do the same thing, > >essentially, by modulating the gate drives of the transformer driver >MOSFETs. In that case, I will probably need to leave the inductor in the >center tap of the transformer to the battery. But for now, the current >limiter seems to work well, and it may be a good device to make as a >stand-alone current limiter for working with batteries. > >Paul
As the asc file doesn't include the modifications mentioned, specifically in the inrush limiting section, you shouldn't expect this proposed schematic to be much use to others. As the load doesn't look like a battery and is fixed resistive - the simulation does not illustrate the the battery charging condition or loading effects. Supposedly you intend to controll these things at some point, reflecting the mfr's charge and float recommendations for the batteries used. It's probably not a good idea to let the RC values of the current sensor set the switching frequency. This is actually the source of the first single cycle surge at turn-on, in the posted asc file, as the C in this sensor's filter charges to an initial value that is not related to actual switch current. How you handle this as the driver changes (removing a known fixed hysterisis and altering the threshold to larger logic levels) is not indicated. The integrated driver mentioned will not respond nicely to load values less than the peak limit, as it's gate drive bootstrap source requires periodic refreshing. The choice of unsynchronized frequencies can be an issue, as may be the audible frequency intended for the DC-DC transformer section. The former introduces a periodic flux imbalance in the downstream transformer. The latter will just be annoying. To get a better idea of snubbing energy losses in switching the DC-DC section, you might apply more realistic coupling coefficients, as the high power coupler is unlikely to aproach 0.998 . It's not a wise idea to have two voltage sources (ie capacitive storage or batteries) on both sides of a DC-DC transformer. At some time this will look like a short circuit, resulting in incontrollable current peaks in the switches at both switching and control frequencies. RL
wrote in message=20
news:e4e3cc77-e5e4-4d2f-9628-410d5309425c@m10g2000vbn.googlegroups.com...=


> looked at something like a IR2086 ?
That may be a good candidate, but it's not recommended for new designs.=20 However, there are similar parts. I found a reference design for a 300W=20 DC-DC converter: http://www.irf.com/technical-info/userguide/ug-0601.pdf This is mostly a conceptual design. Actually an SG3526 would probably = work=20 well enough. But I'd like to use a PIC so I can combine other features. = I'm=20 using a PIC16F684 for the PWM drive now (with gate drivers), but its PWM = is=20 not suited for push-pull except at 50% duty cycle. Also its internal=20 comparator conflicts with the PWM module. The PIC16F616 has a different=20 comparator module so it might be suited to use as a hardware-based=20 current-limited start-up. But I may also consider using something like = the=20 PIC18F2331 which has the three-phase motor control module. Another candidate might be http://www.linear.com/product/LT1683. It is a = low=20 noise push-pull device with integrated MOSFET drivers, programmable slew = rate, overcurrent protection, and other goodies. I'm not fond of the = tiny=20 package with 0.65mm pitch, but I have worked with them in prototypes. No = problem for automated production assembly, however. Thanks, Paul=20
"Jan Panteltje"  wrote in message news:jrk9ab$vko$1@news.albasani.net...

> Since you are a PIC user, a current and voltage regulated supply: > http://panteltje.com/panteltje/pic/pwr_pic/index.html
> For more current use bigger inductors (physicaly), > and bigger MOSFETS, and a real MOSFET driver.
> I have used this as lab supply now for more than year, > and it is absolutely the greatest,
That looks like a nice unit. But I'm not sure about using a SEPIC to = boost=20 the voltage from 12, 24, 36 or 48VDC to 320 or 640VDC. That's a really = hefty=20 inductor, and I think it would be bigger and heavier and more difficult = to=20 design than a transformer. And I really don't need output adjustment or=20 regulation. All I want is basically a DC transformer about 15/1 ratio. Thanks, Paul=20
"Fred Abse"  wrote in message=20
news:pan.2012.06.17.12.32.55.121045@invalid.invalid...

> On Sun, 17 Jun 2012 04:05:13 -0400, P E Schoen wrote:
>> Following is the ASC file. I'll have to give this a try before I do =
any=20
>> more >> testing with the DC-DC converter. And I can probably do the same =
thing,
>> essentially, by modulating the gate drives of the transformer driver >> MOSFETs. In that case, I will probably need to leave the inductor in =
the
>> center tap of the transformer to the battery. But for now, the =
current
>> limiter seems to work well, and it may be a good device to make as a >> stand-alone current limiter for working with batteries.
>I see about 24V of HF hash at M3 drain. Apparently due to L5 resonating > with various capacitances.
> BTW, what was the thinking behind specifying both series *and* =
parallel
> parasitic resistances for L5? They're each just a different way of > specifying the same quantity. If the 350 ohms is a physical damping > resistor, it should ideally show on the circuit.
Those were just from a model that I chose from the inductor menu. Then I = changed the resistance and inductance to match a larger one that I = found. It=20 would probably simulate more quickly by removing those parasitic values.
> Any reason why you restricted the number of cycles of drive to M1 and =
M2,
> rather than letting it run for the full simulation time?
It was taking like 1/2 hour to run 100 mSec, so I usually stopped it = once it=20 seemed to settle.
> Why not just use a simple precharge resistor, switched out with a > contactor, or maybe a triac? That's the way the VFD guys do it.
That may be a viable option. I figure I would need about 0.5 ohms for 50 = amps at 24V. About 1200 watts to start. Or I could put it on the output, = which is about 300V and 4A, so a 75 ohm will work. With the original = 6600 uF=20 the TC would be 0.5 seconds, so about 2.5 seconds until it reaches full = voltage. I could use an SPDT relay which would first just charge the=20 capacitors and then remove the resistance and apply the voltage to the = VF=20 drive. But if I don't use the doubler I can just use the VFD's internal=20 capacitors, which are probably about 200 uF. I could still monitor its = bus=20 voltage and keep the resistor in the circuit until it reaches about = 250V,=20 and then kick it out. The VFD draws only about 200 mA or less without a=20 motor load. That's probably the easiest thing to do now, just to get something = working.=20 Since I already have the PIC, I can monitor the output voltage and just = keep=20 the current limit resistor on until it comes up. Maybe I can use a = MOSFET or=20 my original choice of a power darlington on the input side, and use like = a 5=20 ohm resistor to charge the 2200 uF capacitor to 24V. Then I could use a=20 fairly small relay for the output capacitor charging. I'll have to work = out=20 the details, and see how it responds to a short circuit failure. = Hopefully I=20 can switch it to current limit mode before it reaches extreme levels, = but=20 high enough to trip the breaker quickly enough. And of course a fuse for = apocalyptic situations :)
> Otherwise, your suggestion of PWM-ing the gate drives would work. > There are driver ICs available that current limit in just that way.
I will look into those before I make a final design. My purposes now are = more to get something working so I can determine just how much power I = need=20 for my tractor under various conditions.
> Please, pretty please, get rid of that Greek "mu" (Control Panel - =
Netlist
> Options).
I thought I had done that. But maybe I updated LTSpice since then. And I = also found that, to take effect, I had to change something in the = schematic=20 and then save again. Sorry... Thanks, Paul=20