Parallel switch current control

1. A method of controlling a power converter having a plurality of parallel-connected switching devices, the method comprising:

measuring a threshold voltage of each of the parallel-connected switching devices at start up of the power converter in an initial self-calibration process;

measuring a gate current of each of the parallel-connected switching devices at start up of the power converter in the initial self-calibration process;

extracting the threshold voltage of each switching device as its gate-to-source voltage at a time when a spike of the gate current occurs, indicating a discontinuity in an input capacitance of the respective switching device; and

determining synchronization of the times when the spikes of gate current of the respective switching devices occurred.

2. The method of claim 1 , wherein the initial self-calibration process comprises, on start up of the power converter:

i) turning on all parallel-connected switching devices except one of said switching devices;

ii) thereafter, gradually turning said one switching device on; and

iii) extracting the threshold voltage of said one switching device; and

iv) repeating steps i) to iii) for each of the parallel-connected switching devices as said one switching device; and wherein the synchronization is determined from differences in the extracted threshold voltages.

3. The method of claim 2 , wherein the synchronization is determined from the following equation:

t

Vgs

=

Vth

=

-

R

*

C

*

ln

⁢

{

1

-

V

th

⁢

V

gs

,

max

}

R—Gate resistance

C—input capacitance of the one switching device

V th —Threshold voltage of the one switching device

V gs,max —Maximum input gate source voltage.

4. The method of claim 3 , wherein the synchronized turn-on time is determined by varying C by adding external voltage controlled capacitance at the input of the respective switching device and applying a control-bias voltage on the one switching device to effectively change the value of C in real-time to synchronize the turn-on time of the switching device.

5. A system for controlling a power converter having a plurality of parallel-connected switching devices, the system comprising:

means for measuring a threshold voltage of each of the parallel connected switching devices at start up of the power converter in an initial self-calibration process;

means for measuring a gate current of each of the parallel connected switching devices at start up of the power converter in the initial self-calibration process;

means for extracting a threshold voltage of each switching device as its gate-to-source voltage at a time when a spike of the gate current occurs, indicating a discontinuity in an input capacitance of the respective switching device; and

means for synchronizing the times at which the threshold voltages of the respective switching devices are extracted.

6. A method of controlling a power converter having a plurality of parallel-connected switching devices, the method comprising:

measuring a threshold voltage of each of the parallel-connected switching devices at start up of the power converter in an initial self-calibration process; and

determining synchronization of the times when spikes of gate current of the respective switching devices occurred;

wherein the initial self-calibration process comprises, on start up of the power converter:

i) turning on all parallel-connected switching devices except one of said switching devices;

ii) thereafter, gradually turning said one switching device on; and

iii) extracting the threshold voltage of said one switching device; and

iv) repeating steps i) to iii) for each of the parallel-connected switching devices as said one switching device; and wherein the synchronization is determined from differences in the extracted threshold voltages.

7. The method of claim 6 , wherein the synchronization is determined from the following equation:

t

Vgs

=

Vth

=

-

R

*

C

*

ln

⁢

{

1

-

V

th

⁢

V

gs

,

max

}

R—Gate resistance

C—input capacitance of the one switching device

V th —Threshold voltage of the one switching device

V gs,max —Maximum input gate source voltage.

8. The method of claim 7 , wherein the synchronization is determined by varying C by adding external voltage controlled capacitance at the input of the respective switching device and applying a control-bias voltage on the respective switching.