drive%20mosfet

As can be seen in fig 15 gate drive transformers

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Unformatted text preview: to implement overload/short circuit protection for the upper MOSFET/IGBT. As can be seen in Fig. (15), gate drive transformer’s primary is fed from the output of a Driver IC. For 1:1 transformer, the peak output current and voltage on the secondary is the same as the Driver IC’s output values. As explained in section 5.0 before, knowing the switching frequency, rise and fall times desired, gate resistor used, total gate charge for the MOSFET/IGBT and the voltage swing, one can calculate the peak currents in the transformer primary and secondary. Calculating the average values for these currents will enable one to either design the gate drive transformer or to enable one to select the appropriate commercially available gate drive transformers. These bi-directional switches form nodes for matrix converters or for A.C. to D.C. convert ers. Driving IGBTs in these bi-directional switches can be easily implemented using the gate drive transformers, as shown in Fig. (15). As can be appreciated, R , R2, 1 R3 and R4 help wave shaping by facilitating core resetting. Z1, Z2, Z3 and Z4 protect the gate of IGBT from voltage spikes above 18.7 volts. Another method uses opto-couplers, as illustrated in Fig. (16). As can be seen, opto-couplers need isolated power supply. However, they facilitate D.C. to several Mbits/sec of pulse rate and do provide kilovolts of isolation. Keeping the same chain of opto-coupler and Driver IC in each complementary signal path will nullify the effect of slight propagation delay through these opto-couplers and Driver ICs. It is assumed here that difference in propagation delays between two same type opto-couplers is negligible. Opto-couplers have the following features: IXAN0009 1.Adequate galvanic isolation is possible. Many opto-couplers are U/L listed. 2.Most opto-couplers are compatible with TTL/CMOS/HCMOS inputs. Their outputs depend on Vcc of isolated power supply. They do need isolated power supply. 3.They are not immune to severe dv/dt transients. 4.Signals experience propagation delays...
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