Description

AN4390

4/14

DocID025494 Rev 1

flows from Q1 source to Q2 drain. Vice versa, when Q3 and Q4 are turned on, the voltage

becomes negative. Typical switching frequencies are in the range of 50-100 kHz. In

Figure 3, relevant gate signals for a H-bridge topology are showed.

Figure 3. MOSFET gate signals in H-bridge DC-AC converter

As per previous picture, when Q1 is turned off, the load current freewheels through Q4. In

this way, FETs of the same leg cannot be in ON state simultaneously avoiding any shoot-

through risk. Same considerations are valid during Q2 and Q3 switching. Together with

MOSFET power losses and efficiency analysis, evaluation tests on UPS systems include

two important tests:

•

Short-circuit test: the output of DC-AC section is shorted for few seconds to test both

semiconductor cross-conduction robustness and system protection intervention.

•

Back-feed test: back-feed protection prevents the electric shock from any electric

current feeding when a main supply fails.

GIPD120920131422FSR