hide side mosfet driving

[jegandren]

Actually the 300V that im trying to switch is isolated via a isolation transformer, sorry it was not stated clearly in the picture.

This method is to improve transient response . From the attached diagram, an additional parallel circuit denoted as VISI is connected to the conventional VMC control based SMPS. The parallel circuit consists of an isolation transformer, a bridge rectifier, a MOSFET switch, a filter inductor and a feedback control circuit. The isolation transformer with winding ratio of 1:1 is used to isolate the ac voltage to the output. The bridge rectifier rectifies the secondary voltage of the isolation transformer to obtain a high dc voltage. The dc voltage is switched in a similar manner as a buck converter. As usual the ripple of the output current is filtered using an inductor. The feedback control circuit receives output voltage as an input and produces gate pulse to the switch. This method is operated only during the transient operation of the SMPS.

Here in this method a high dc voltage from the input is injected to the lower inductance of the output filter inductor during step increase of load. Therefore, when a high dc voltage passes through a smaller effective inductance, the rate of change of current that is supplied to the load would be faster. during steady state condition the auxiliary converter does not come in.

[jegandren]

Dear All,

I have attached some changes, because as earlier the bootstrap capacitor is not charged..


At the beginning of the initial cycle during startup, the bottom-side MOSFET switch is turned on. This pulls the Vs pin to ground, which charges up the bootstrap capacitor to through bootstrap diode .

When the high-side driver is enabled during the next half cycle, the driver can turn on the high-side mosfet, and the Vs pin will rise up to VIN (0-300 V) .

Then the cycle repeats itself—high mosfet is switched off, bottom mosfet turned back on, the Vs pin is pulled down to ground, and bootstrap capacitor is recharged.

[guitar_joe]

Whatever you are trying to do is madness.
Please don't build it.
These circuits are not safe.

[star882]

If you're trying to perform sag correction, wouldn't a better approach be to use an additional winding to charge a large capacitor a few volts above the rail and use a MOSFET operating as a linear regulator to limit sag when the load increases?

[Eva]

The idea is pointless because the auxiliary control loop will not be able to react faster than the main control loop, particularly if it's controlled by a PIC with ADC latencies and calculation delays.

The own main control loop (frequency compensation and output filter) may be designed for optimum transient response without requiring additional loops.