Hi,
The attached LTspice sim and PDF schem, is a 300W Full Bridge with Current Doubler output.
Vout = 32V, Pout = 300W, Vin = 10-36Vdc, F(sw) = 125kHz (ie, each full bridge diagonal FET pair switches at 125kHz).
The transformer turns ratio needs to be Ns/Np = 9:1.
As such, when Vin is at 36V, the V(reflected) to the secondary is 324V, and on top of that, AYK, the output diodes suffer the leakage inductance voltage spike.
The Vds ringing due to the leakage inductance, and high voltage on the sec diodes, means that this SMPS dissipates too much in the secondary diode snubbers, and indeed overvoltages the 600V secondary diodes….however, with an Active Capacitor Snubber (as shown), its possible to damp the Vds ringing (to less than 400V) and indeed , allow paralleled 600V SiC diodes to be used. SiC’s share current so no trouble there either.
The trouble is the amount of auxiliary circuitry that’s necessitated (as shown)….And, the Active Capacitor Snubber means that huge 200A spike currents are seen in the primary FETs at start up…therefore, the Active Capacitor has to be pre-charged with a dual cascaded boost converter (as shown). Also, the Active Capacitor Snubber needs the shown flyback converter to constantly switch the energy building up in the Active Capacitor to the output of the Full Bridge.
The problem is the Dual cascaded boost, …..ie, we really need a controller with two overcurrent sense inputs for it, but a long search shows there are none.
Do you know of any?
The attached LTspice sim and PDF schem, is a 300W Full Bridge with Current Doubler output.
Vout = 32V, Pout = 300W, Vin = 10-36Vdc, F(sw) = 125kHz (ie, each full bridge diagonal FET pair switches at 125kHz).
The transformer turns ratio needs to be Ns/Np = 9:1.
As such, when Vin is at 36V, the V(reflected) to the secondary is 324V, and on top of that, AYK, the output diodes suffer the leakage inductance voltage spike.
The Vds ringing due to the leakage inductance, and high voltage on the sec diodes, means that this SMPS dissipates too much in the secondary diode snubbers, and indeed overvoltages the 600V secondary diodes….however, with an Active Capacitor Snubber (as shown), its possible to damp the Vds ringing (to less than 400V) and indeed , allow paralleled 600V SiC diodes to be used. SiC’s share current so no trouble there either.
The trouble is the amount of auxiliary circuitry that’s necessitated (as shown)….And, the Active Capacitor Snubber means that huge 200A spike currents are seen in the primary FETs at start up…therefore, the Active Capacitor has to be pre-charged with a dual cascaded boost converter (as shown). Also, the Active Capacitor Snubber needs the shown flyback converter to constantly switch the energy building up in the Active Capacitor to the output of the Full Bridge.
The problem is the Dual cascaded boost, …..ie, we really need a controller with two overcurrent sense inputs for it, but a long search shows there are none.
Do you know of any?
