1
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I got the possibly hare-brained idea to cause a single TRIAC gate pulse to go positive and negative, and thus fire in (maybe not all four but) more quadrants:

Forcing Multiple-quadrant TRIAC operation?

ThecLTspice simulation seems to show this Q8025K6 TRIAC (model here) working as expected in multiple quadrants.

The intent is to control the speed of a universal AC motor, 1.75 HP on 120 VAC, as a "spindle" motor "controller" of sorts. I am only considering the AC phase control here.

Blue is the gate voltage/current, red is the output current, and grey is the mains voltage. The output phase goes from 0% to 100% twice in the time shown, due to the opto pulse source having a period of 8 ms on a mains period of 16.667 ms.

However, SPICE models are never all-encompassing; do you think this would even work in reality? Am I overlooking anything that would be problematic?

Gate pulses are about 15 µs wide positive (150 mA peak drive) and 20 µs when negative (100 mA peak drive, from LC components.)

Gate pulse with Negative Traversal

Here is the LTspice project (LTspic3.asc) if you want to try it:

SHEET 1 880 680
WIRE 144 -80 -96 -80
WIRE 336 -80 224 -80
WIRE 608 -80 336 -80
WIRE 624 -80 608 -80
WIRE -96 -64 -96 -80
WIRE 336 -48 336 -80
WIRE -592 32 -640 32
WIRE -496 32 -512 32
WIRE -96 32 -96 0
WIRE -96 32 -304 32
WIRE -640 48 -640 32
WIRE 336 64 336 32
WIRE 480 64 336 64
WIRE -96 80 -96 32
WIRE -96 80 -192 80
WIRE -80 80 -96 80
WIRE 336 112 336 64
WIRE 608 112 608 -80
WIRE -592 128 -640 128
WIRE -496 128 -592 128
WIRE -272 128 -304 128
WIRE -256 128 -272 128
WIRE 480 144 480 128
WIRE -592 160 -592 128
WIRE 32 176 32 160
WIRE 32 176 -192 176
WIRE 80 176 32 176
WIRE 160 176 144 176
WIRE 288 176 240 176
WIRE -272 192 -272 128
WIRE -96 192 -96 80
WIRE -48 192 -96 192
WIRE 32 192 32 176
WIRE 288 192 288 176
WIRE -96 208 -96 192
WIRE -48 208 -48 192
WIRE 336 240 336 176
WIRE 480 240 480 224
WIRE 480 240 336 240
WIRE -272 288 -272 272
WIRE -96 288 -96 272
WIRE -96 288 -272 288
WIRE -48 288 -48 272
WIRE -48 288 -96 288
WIRE 32 288 32 272
WIRE 32 288 -48 288
WIRE 288 288 288 272
WIRE 288 288 32 288
WIRE 336 288 336 240
WIRE 336 288 288 288
WIRE 608 288 608 192
WIRE 608 288 336 288
WIRE 624 288 608 288
WIRE -96 320 -96 288
FLAG -592 160 0
FLAG -96 320 0
FLAG -80 80 10Vcc
FLAG 32 160 Vsw
FLAG 624 -80 Hot
FLAG 624 288 N
SYMBOL Misc\\TRIAC 304 112 R0
SYMATTR InstName U1
SYMATTR Value Q8025K6
SYMBOL voltage 608 96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 124 Left 2
SYMATTR SpiceLine Rser=0.1
SYMATTR InstName V1
SYMATTR Value SINE(0 170 60)
SYMBOL cap 464 64 R0
SYMATTR InstName C3
SYMATTR Value 0.1µ
SYMBOL res 464 128 R0
SYMATTR InstName R6
SYMATTR Value 100
SYMBOL res 320 -64 R0
SYMATTR InstName RLOAD
SYMATTR Value 11
SYMBOL res 240 -96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 6.8k
SYMBOL zener -80 272 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value BZX84B10VL
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL diode -112 -64 R0
WINDOW 0 42 13 Left 2
WINDOW 3 39 41 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4004
SYMBOL polcap -64 208 R0
SYMATTR InstName C1
SYMATTR Value 100µ
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=105m Rser=0.7499 Lser=4.17n mfg="Würth Elektronik" pn="860020272005 WCAP-ATG5 5x11" type="Al electrolytic"
SYMBOL sym\\npn -256 80 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res -256 288 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 256 160 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 33
SYMBOL sym\\ZZZ\\OPTO\\4n35 -400 80 R0
SYMATTR InstName U2
SYMBOL voltage -640 32 R0
WINDOW 3 -26 175 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 5 0 0 0 10u 8m)
SYMATTR InstName V2
SYMBOL res -496 16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 270
SYMBOL res 304 176 M0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL ind 16 176 R0
SYMATTR InstName L1
SYMATTR Value 120µ
SYMATTR SpiceLine Ipk=2.55 Rser=0.0817 Rpar=11304 Cpar=0 mfg="Coilcraft" pn="PCH-45X-124"
SYMBOL cap 144 160 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 0.1µ
SYMATTR SpiceLine V=630 Irms=0 Rser=0.0138 Lser=813p mfg="Würth Elektronik" pn="885342211006 WCAP-CSMH 1812" type="X7R"
TEXT 240 320 Left 2 !.lib Q8025K6.txt
TEXT -664 296 Left 2 !.tran 0 0.6 0.2 startup uic
TEXT -640 -96 Left 2 ;Forcing 4-quadrant operation via gate ringing?
TEXT 160 -24 Left 2 ;3W

And the TRIAC SPICE excerpt with attrib (Q8025K6.txt):

**********************************
**
** Littelfuse, LP
** TRIAC SPICE Models
** Qxx25xx-Qxx25xHx
**
** T. Chenoski
** Irving Technical Center
**
** A 06/08/08
**
**********************************
**********************************

.SUBCKT Q8025K6    1    2         3
*       TERMINALS: MT2  G         MT1
Qnpn1   5          4    3         NoutF   OFF
Qpnp1   4          5    7         PoutF   OFF
Qnpn2   11         6    7         NoutR   OFF
Qpnp2   6          11   3         PoutR   OFF
Dfor    4          5    DZ        OFF
Drev    6          11   DZ        OFF
Rfor    4          6    12MEG
Ron     1          7    10m
Rhold   7          6    50
RGP     8          3    12
RG      2          8    5.8
RS      8          4    100
DN      9          2    DIN       OFF
RN      9          3    4
GNN     6          7    9         3       0.1
GNP     4          5    9         3       0.1
DP      2          10   DIP       OFF
RP      10         3    3.56
.MODEL  DIN        D    (IS=382F)
.MODEL  DIP        D    (IS=382F  N=1.19)
.MODEL  DZ         D    (IS=382F  N=1.5   IBV=50U  BV=800)
.MODEL  PoutF      PNP  (IS=382F  BF=0.5  CJE=380p TF=0.3U)
.MODEL  NoutF      NPN  (IS=382F  BF=3    CJE=380p CJC=76p  TF=0.3U)
.MODEL  PoutR      PNP  (IS=382F  BF=3    CJE=380p TF=0.3U)
.MODEL  NoutR      NPN  (IS=382F  BF=0.5  CJE=380p CJC=76p  TF=0.3U)
.ENDS
\$\endgroup\$
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  • \$\begingroup\$ Neat idea, but.... why? And if you just want to know whether multi-quadrant firing works, the answer is too short to accept ("yes") :) \$\endgroup\$ Nov 8, 2022 at 17:11
  • \$\begingroup\$ Why, because the original (typical) circuit will not fire on the negative-going mains without a negative gate pulse, or vice-versa. Remove L1/C2 and it's a fancy half-wave phase-controlled rectifier. \$\endgroup\$
    – rdtsc
    Nov 8, 2022 at 17:30
  • \$\begingroup\$ What typical circuit? If you mean like an MOCxxx driver, it's simply negative gate with negative mains because...that's how it's wired. Positive gate and negative mains works too, it's just less often you have a common ground with a control circuit (implied: DC supply) and a TRIAC where that would apply. Or if you needed half wave operation, just use an SCR? Or are you saying the SPICE model isn't meeting datasheet quadrant behavior? \$\endgroup\$ Nov 8, 2022 at 17:47

1 Answer 1

1
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Yep, totally hair-brained.

This is simpler, and works in quadrants I and III specifically:

Opto-TRIAC in Quadrants I / III

Seems in the original question I was trying to force operation in quadrants II / IV because the pulse reference was MT1; swapping the reference to MT2 makes the device much easier to fire, and doesn't require any negative input pulses at all.

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