Extended application of IR2110

1. Bootstrap principle of high-voltage side suspension drive

In the circuit diagram of IR2110 shown in Figure 2 for driving a half-bridge, C1 and VD1 are bootstrap capacitors and diodes, respectively, and C2 is the filter capacitor of VCC. Assume that during S1 is off, C1 has been charged to a sufficient voltage (Vc1≈Vcc). Then, when HIN is high, VM1 is turned on, VM2 is turned off, VC1 is added between the gate and emitter of S1, and C1 is discharged through VM1, Rg1 and the gate capacitance Cgc1 of S1, so that Cgc1 is charged.

At this time, VC1 can be equivalent to a voltage source. When HIN is low level, VM2 is turned on, VM1 is turned off, and the gate charge of S1 is quickly released through Rg1 and VM2, so that S1 is turned off. Then after a short dead time (td), LIN is high, S2 is turned on, VCC charges C1 through VD1, S2, and quickly replenishes energy for C1, and the cycle repeats.

It can be seen that the bootstrap circuit must be in the constant high and low level changes of the IR2110 input signal, and the bootstrap capacitor can be charged and discharged repeatedly to play a normal bootstrap function, and when the input signal of the IR2110 is DC level During the signal, the bootstrap capacitor will not be able to complete the charge storage, that is, it will not be able to be charged normally, so it will not be able to provide a driving signal for the high-side diode. If the lack of this function of IR2110 is not solved, when the motor load is actually working at a duty cycle of 1, and the voltage across the load is zero, the motor will stop working; at the same time, it will also bring a large current rate of change to the power switch tube. , Thereby affecting the service life and long-term reliability of the power tube. Therefore, the following two technical measures should be taken in the work.

(1) Application of input amplitude discrimination circuit

In order to overcome the above-mentioned shortcomings, can design the input amplitude discriminating circuit in the work, its circuit is shown as in Fig. 3. This circuit can not only ensure that the widened square wave signal is output in the linear region of the input signal, but also, when the input signal is outside the linear region, the circuit can also output a fixed duty cycle signal, thus ensuring that the motor is linear It can also rotate normally outside the area, and it also ensures that the output load current will not produce a big sudden change.

(2) Charge pump circuit

When the circuit inputs a 100% duty cycle signal, its core oscillator circuit CD4093 will generate a square wave signal with a certain frequency. When the square wave signal is low, the power supply +Vs charges the energy storage capacitor C3 through D5; and when the square wave signal is high, C3 charges the bootstrap capacitor C2 through D4 to maintain the bootstrap capacitor The energy of the circuit finally makes the H-bridge output a 100% duty cycle signal when the circuit is inputting a signal with a 100% duty cycle, while also ensuring the continuity of the output current. Figure 4 shows the circuit diagram of the charge pump.

2. Anti-through conduction delay circuit

After adding complementary signals to the upper and lower arm power transistors of the H-bridge drive circuit, the turn-off time of the transistor is usually longer than the turn-on time under load. In this way, when the lower-arm transistor is not turned off in time and the upper-arm is turned on first, There will be a so-called "bridge arm through" failure. This will cause the current to increase rapidly when the bridge arm is through, which will cause damage to the power switch. Therefore, it is necessary to set the on-delay and dead time.

IR2110 has a certain dead time, its size is 10 ns and cannot be externally adjusted. In actual use, the turn-off time of the MOSEFT tube is sometimes greater than 10 ns than the turn-on time. At this time, an external delay circuit is needed to increase the dead time. Zone time to prevent the circuit from being through. Figure 5 shows a turn-on delay circuit and its waveform.

The turn-on delay can also be set by the RC time constant. For GTR, it can be set according to 0.2μs/A; for MOSFET, it can be designed according to 0.1～0.2μs, and has nothing to do with current; IGBT can be designed according to 2～5μs. If the f of GTR is 5 kHz once bipolar work, the widening area is T/2=1/10=0.1 ms, at this time if I is 100 A, then △t=0.2×100=20μs. In this way, the maximum possibility of PWM modulation resolution is: 

This shows that the dead time occupies 1/5 of the modulation cycle, which is obviously not feasible. Therefore, for a 100 A motor system, the switching frequency of the GTR must be lower than 5 kHz. For example, below 2 kHz, the resolution can reach about 12.5.

In conclusion

IR2110 is a kind of drive integrated circuit with relatively good performance. Its bootstrap levitation drive power can drive the upper and lower switching devices of the same bridge arm at the same time. The drive voltage is up to 500 V, the working frequency is 500 kHz, and it has a power shortage Voltage protection shutdown logic. The output of IR2110 uses totem pole structure, driving peak current is 2 A, and two channels are also equipped with low voltage delay block (50ns).

In addition, the chip also has a protection terminal SD that blocks two outputs. When SD inputs a high level, both outputs are blocked. These advantages of IR2110 bring great convenience to the actual system design, especially the bootstrap floating drive power supply greatly simplifies the drive power supply design, because only one power supply can be used to drive the two power switching devices of the upper and lower bridge arms. However, compared with other driver integrated circuits, the protection function of IR2110 is slightly insufficient, and the dead time cannot be externally adjusted; when the circuit works at 100% duty cycle signal input, an external charge pump circuit is also required to maintain sufficient energy of the bootstrap capacitor. However, these deficiencies can be improved and supplemented in practical applications through the expanded application circuit described in this article.