IGBT has become the preferred power device for power electronic devices such as high-power switching power supply due to its advantages of low saturation voltage and high working frequency. However, like thyristor, IGBT has low anti-overload capability.Therefore, how to design IGBT drive overcurrent protection circuit, so that it has perfect drive overcurrent protection function, is a problem that designers must consider.
1. The principle of driving overcurrent protection for overcurrent protection circuit
The technical data of IGBT indicate that IGBT is at 10&mu.S can withstand 2 times the rated current of the largest, but often sustain life flows here a premature aging, therefore the design principle of IGBT driver over-current protection circuit for: one, when a current value is less than 2 times the rated current value, can adopt the method of instantaneous blockade grid voltage to realize protection;Second, when a current value is greater than 2 times the rated current value, because the instantaneous blockade grid voltage can make the di/dt is very big, in the primary loop induction of high peak voltage, so the soft turn-off method should be adopted to make grid voltage in 2 & mu;S—5 & mu;The time of S drops to zero voltage to the final minus 5 volts of reverse voltage;Appropriate grid drive voltage is adopted.Based on the above ideas, the driving overcurrent protection circuit is divided into two parts: the separating element drives over current protection circuit and the module drives over current protection circuit.
2.Drive over current protection circuit design
Taking the multi-power driven overcurrent protection circuit as an example, the separation element drives the overcurrent protection circuit as shown in figure 1.
In FIG. 1, T1, T4 and T5 constitute IGBT's driving circuit, while DZ1, T3, D2 and C4 constitute time-lapse voltage reduction circuit.T6 and 555 integrated circuits and optocoupler LP2 constitute delay circuits.In normal opening, the T1 and T4 conduction, because of the D1 and R6, point B can't more than DZ1 circuit breakdown voltage, T3 as of right now, D point potential will not fall, don't delay time delay circuit, T2 cutoff.When IGBT flows through the short-circuit current, the emitter pressure drop of IGBT increases, and the C point potential increases.
2.1 the separation element drives the overcurrent protection circuit
In addition, the principle of a single-power over-current protection circuit is similar to that of the above multi-power over-current protection circuit.
Attention should also be paid to :(1) select the appropriate grid drive voltage;The positive voltage value is generally 12V&mdash.15V is suitable, 12V is the best, and the reverse voltage is generally 5V&mdash.10 v;
(2) select the appropriate grid series resistance value, generally several ohms to ten ohms;
(3) select the appropriate grid emitter and interconnect resistance or voltage stabilizer diode.
It can be seen from the above analysis that the separation element drives the overcurrent protection circuit complex, but the design is flexible.
Several IGBT - driven overcurrent protection circuits are introduced.Separation of components drive over-current protection circuit is complex, but the design flexible, protection work surface, drive over-current protection circuit module simplifies the design of the circuit and have a certain protective function, but the protection function is limited, unavailable, consider to expand its function.As to which method is used in practical application, it should depend on the actual situation.