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Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
Hey guys,
I finally plunked down the cash for a good digital scope (Agilent MSO6104A), and I've got some captures from my DRSSTC.
These were taken on the coil shown in this thread, with no secondary in place and a 70VDC bus voltage.
Channels: 1: Bridge O/P 1 2: Interrupter output 3: Bridge O/P 2 4: Primary current, 200A/div (1024:1 feedback CT + current probe) Math(thin purplish trace): ∫(Ch3 * Ch4)dt, Energy delivered to primary (200mJ/div, one side of bridge only, double result for total energy)
Note that the asymmetry between the two bridge outputs when they're near ground is due to current circulating through the scope probe ground leads. They're grounded at each end of the inverter board, and the trace resistance causes some voltage between the two probe grounds.
The large variations on the bridge O/P look bad because of the low bus voltage along with high current. Also note the lack of significant voltage spikes, at least at this bus voltage.
Overview:
Ramp-up:
Ramp-down:
One transition:
Other transition, note the extra 100ns delay compared to the other transition:
Ringing at end of ramp-down:
The bridge seems to switch about 300ns after current zero crossing. The edges seem fast and have ringing, would slowing the gate drive help?
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
Sorry, O/P means output, so "Bridge O/P" means one of the H bridge output terminals.
I believe the ringing at the end is due to the primary coil inductance and the IGBT collector to emitter capacitance forming a resonant circuit. The main tank capacitor is so much bigger than the IGBT capacitance that the tank cap is essentially a short circuit.
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Detailed DRSSTC Waveforms
