DRSSTC phase lead
Published tools do the forward pass only: give them an L and they return a time. This one works in either direction, because inductance, angle and time are the same thing once the frequency and the burden are known. It also handles the part that causes trouble. The circuit holds a constant angle, but the switch needs a time. The frequency falls across the ramp, so the lead in nanoseconds drifts with it. The time the switch needs is not constant either: about two thirds of it is the electronics, which is fixed, and a third is the ZVS floor, which rises as the frequency falls and takes up about half of the drift.
The delay chain, in nanoseconds. The defaults are a datasheet estimate for an IPW65R080CFD, not a measurement. The CT line is subtracted, because a current transformer contributes lead rather than delay.
TL3116 7 ns, 74HC 17, UCC27324 25, output stage 15, GDT 5, and 37 ns of dead time. The first three come from their datasheets. The output stage, the GDT and the dead time are on no datasheet; for a driver of your own, get them with a scope, or measure the whole chain below.
Or measure the chain instead of adding it up. Put one probe on the burden, which is what the comparator sees, and one on the switch. Trigger on the burden crossing and read the gap to the actual turn-off. That gives the whole chain, your own layout included. Filling this in overrides every field above.
The bridge, for the ZVS floor. These fields feed the charge criterion: the node has to finish recharging inside the dead time, and whether it does depends on your devices. It is solved at every frequency in the table. Snubber capacitance belongs in the node figure, so count it there. The last field matters most. A warm switch is slower, turns off later and so breaks less current, which means a lead set on a cold bridge can lose ZVS under load. The working point is computed hot.
Ramp end puts the node exactly on the criterion where the arc is longest and the current highest, and accepts a small shortfall at the top of the ramp, where a transition carries little energy. Whole ramp covers every point of it and pays for that at the far end, breaking the current early where it is largest. The table below prints what each choice costs at the other end.
Two allowances that are rarely measured: 200 pF of extra capacitance on each bridge node, ±15 % on the delay sum. Change them only if you know better.
The node carries capacitance beyond the switches: the pads under them, the wiring, any snubber across a switch. The delay chain is a sum of datasheet figures, each typical. Because of these two, the page reads the bridge three ways: the optimist takes no extra capacitance and the short end of the delays, the expected case takes them as given, and the pessimist takes twice the capacitance and the long end.
wind this1.39 µHexpected case, 1.69 µH total less 0.30 of leads
zone1.11 … 2.20 µHoptimistic to pessimistic reading of the inputs
works on every readingno such bandthe pessimistic case needs the 60° ceiling of 2.03 µH
must break at turn-off50 Awarm, at 490 kHz
T_lead(f) = ΣT_delay - T_CT + T_ZVS(f) T_ZVS(f) = smallest Δt with I_pk/ω · [cos(ω(Δt - t_dead)) - cos(ω·Δt)] ≥ C_node·V_bus ω = 2πf, C_node = n_dev · C_o(tr) + extra node C leads: twisted pair ≈ 0.63 µH/m, loose wires ≈ 1.29, coax ≈ 0.25 at the design frequency f_d (the worst point of the ramp, or its end) φ = 360° · f_d · T_lead(f_d) L = R · tan(φ) / (2πf_d) then across the ramp, L and R fixed φ(f) = arctan(2πfL / R) t(f) = φ(f) / (360°·f) margin(f) = t(f) - T_lead(f) swing = |Z| / R = 1/cos φ, |Z| = √(R² + (2πfL)²) in-phase fraction = R / |Z| = cos φ
Why calculate when you have a scope. They answer different questions. A scope tells you what is, that T_d is 210 ns. It does not tell you what to fit; that conversion is what this page does. And you cannot measure until the bridge runs, which needs the lead to be roughly right already. So wind the value this page gives, power up, then trim on the screen.
Two more things a waveform will not give you. A scope shows one frequency while a ramp crosses hundreds, and the drift table turns a single measurement into the whole sweep. When the lead is wrong the screen shows a symptom; the numbers here show the trade-offs: |Z|, the swing, the in-phase share, and the point past 60° where more inductance adds little angle. They tell you what to change, not just that something is off. The measurement still decides: set the final L1 on the scope, never by its nominal value.
The three inputs are one quantity. Give any of the inductance, the angle or the time and the other two follow from the frequency and the burden. The page converts to a lead time first and works from there, so every mode reaches the same arithmetic.
The signal is taken across L + R, not across the burden alone. It has to be: with the CT behaving as a current source, the voltage across a burden on its own is I·R whatever the inductor does, and there would be no lead at all. So the swing at the sense point grows as 1/cos φ rather than shrinking. What falls is R/|Z|, the in-phase share: how much of the signal is still about the current rather than about dI/dt.
Past 60° the returns diminish. Amplitude is not the limit. Going 45→60° costs 1.73× the inductance, 60→75° another 2.15×, and 70→85° costs 4.16× (the inductance goes as tan φ); 90° would need an infinite coil. In davekni's words, further inductance increases generate diminishing increases in phase lead.
Finding your own T_d. These defaults are added up from datasheets, and the largest term is not read off one directly. The IPW65R080CFD is quoted at 85 ns for t_d(off) with a 1.8 Ω gate resistor on a 13 V unipolar drive, and at 10.75 Ω on ±15 V the plateau current falls, which scales it to about 110 ns. The default here is 115, a little on the slow side of that. Every link has a caveat like this, and this term also grows as the die heats, which is what the hot column is for.
So measure the chain rather than trusting the sum, and put the result in the field above. Probe the burden, not the comparator output: the burden is what the comparator sees, and triggering on its output would leave the comparator's own 7 ns outside the measurement. The CT stays outside it either way, which is why it is still subtracted separately. Measure after the current transformer is final, because the CT supplies part of the lead and rewinding it moves the number.
The CT enters with a minus. Magnetising current shunts the burden, so the burden signal leads the primary current; the transformer gives lead, not delay. At the 51 Ω stock burden getting that sign wrong would be 12 ns out of 270, or 4 %; at 3.9 Ω the term is 0.45 ns and the sign no longer matters.
The model treats the chain as a pure series L + R. The 150 pF sitting across the burden is 2165 Ω at 490 kHz against 3.9 Ω of burden, which moves the angle by about 0.1°. It is left out on purpose.
T_ZVS has a floor, not an optimum. It is the residual current the bridge needs to recharge its own node during the dead time, and the criterion is simply that the node finishes. Turning off exactly at the zero crossing is the failure case: nothing is left to recharge with, and the opposite switch turns on into the full bus. ZCS and ZVS trade against each other, and this sets which side you get. Below the floor a transition costs about 77 µJ per device at 440 V (half of C_o(tr)·V²), about 600 W across the bridge at 490 kHz; above it the switch breaks the current early and the overshoot grows.
What sets the floor is the node capacitance, so it moves with your snubbers, and it does not move with the ramp amplitude: charge wanted scales with V_bus and charge available with I_pk, so raising both together leaves it where it was. Checked at 30, 60 and 100 % of the working point, 91.3 ns each time, so one operating point is enough and only frequency is swept. On the IPW65R080CFD's datasheet 794 pF the floor is 91.3 ns with no snubber, 100.7 at 100 pF, 113.4 at 235 and 136.0 at 470 (snubber capacitance per device, on all four). The notes' hand sheet read 80, 90, 105 and 125, and this page matched it at 80.3, 89.5, 102.2 and 124.5, because both used 675 pF, a figure on no Infineon sheet for the part. The page switched to the datasheet's figure on 02.11.2026.
Where the ramp is tightest is a property of the bridge. Two curves race down it, the floor rising and what an arctan gives back also rising, and either can win. On this coil the top of the ramp is the tight point; on a fast bridge with a short dead time it moves to the bottom, and in between the curve can dip and come back. So the page scans the ramp and prints the frequency it fitted, rather than assuming an end. An earlier version read the start instead of the extremum, an error worth 1.4 % on a bridge whose two ends agree to four digits.
Earlier mistakes on this page. It said the swing at the sense point shrinks with the angle; it grows, as 1/cos φ, and what shrinks is the in-phase share. It printed the growth in lead down the ramp as though all of it were spare margin, overstating it twice over on the defaults and more on a longer ramp. It sized L1 at the ramp start rather than at the worst point of the ramp. And it told a reader with a starved bridge to fit a faster driver when the floor, not the chain, was spending the angle. They are listed because a reader who acted on any of them would have trimmed something that had nothing to give.
Trimming it on the bridge output. Set right, there is a small bump at the end of the edge and a clean trace after it. That bump is the optimum, not a defect. Too little L1 and the switch opens after the current zero, so the edge rings and every transition overshoots. That side of the problem is the inductor, and the fix is more of it. The sharper form of the same test is that Vce on the lower switch should fall almost to zero before its Vge crosses about 5 V.
A long triple transition is not too much L1. It means the dead time is longer than the lead, so the opposite device turns on after the current has already reversed. The fix is at the gate and the gate transformer, not here. Winding L1 down on seeing a bigger bump makes it worse: the triple transition appears once the lead falls below the dead time, so backing off walks towards it, and it pushes turn-off towards the current zero, which is the side that kills. Adding lead only masks it, paying turn-off current for a fault that is somewhere else. No triple transition at any L1 is the opposite reading, a dead time that is too short. Genuine excess lead shows as neither: a clean edge carrying a high turn-off current, which is loss rather than damage, and worth taking back only once the dead time is right.
Trim from small to large, because falling short is the more dangerous side, and repeat it warm: a hot bridge needs more lead, so the setting moves. Set it by the screen, not by the nominal value. The zone above only says where to start and when to stop.