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Fix SCR convergence failure with series resistor #297

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Fix SCR convergence failure with series resistor #297

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1b0ea53
Fix SCR convergence failure with series resistor (#851)
esaruoho Mar 3, 2026
e9b7c75
Fix SCR oscillation: use latching trigger/hold logic like TriacElm
esaruoho Mar 12, 2026
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25 changes: 20 additions & 5 deletions src/com/lushprojects/circuitjs1/client/SCRElm.java
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Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,7 @@ void reset() {
volts[anode] = volts[cnode] = volts[gnode] = 0;
diode.reset();
lastvag = lastvac = curcount_a = curcount_c = curcount_g = 0;
state = false;
}
int getDumpType() { return 177; }

Expand All @@ -97,6 +98,7 @@ void undumpXml(XMLDeserializer xml) {
double ia, ic, ig, curcount_a, curcount_c, curcount_g;
double lastvac, lastvag;
double gresistance, triggerI, holdingI;
boolean state;

final int hs = 8;
Polygon poly;
Expand Down Expand Up @@ -217,6 +219,24 @@ void stamp() {
diode.stamp(nodes[inode], nodes[cnode]);
}

// Evaluate the on/off state once per timestep, not during Newton-Raphson
// iterations. Previously the state switching was inside doStep(), causing
// the anode resistance to flip-flop between on (0.0105) and off (10e5) on
// every sub-iteration when an external series resistance was present,
// preventing convergence (issue #851).
//
// Use separate trigger/hold conditions with latching, matching the pattern
// used by TriacElm. Once the gate current exceeds triggerI the SCR latches
// on, and stays on until the anode current drops below holdingI. The gate
// only triggers; it does not need to remain driven to keep the SCR on.
void startIteration() {
if (ia < holdingI)
state = false;
if (ig > triggerI)
state = true;
aresistance = state ? .0105 : 10e5;
}

void doStep() {
double vac = volts[anode]-volts[cnode]; // typically negative
double vag = volts[anode]-volts[gnode]; // typically positive
Expand All @@ -226,11 +246,6 @@ void doStep() {
lastvac = vac;
lastvag = vag;
diode.doStep(volts[inode]-volts[cnode]);
double icmult = 1/triggerI;
double iamult = 1/holdingI - icmult;
//System.out.println(icmult + " " + iamult);
aresistance = (-icmult*ic + ia*iamult > 1) ? .0105 : 10e5;
//System.out.println(vac + " " + vag + " " + sim.converged + " " + ic + " " + ia + " " + aresistance + " " + volts[inode] + " " + volts[gnode] + " " + volts[anode]);
sim.stampResistor(nodes[anode], nodes[inode], aresistance);
}
void getInfo(String arr[]) {
Expand Down
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