Mosfet driver waveform

In fact, if you look in the datasheet at Figure 7, you will see just this type of waveform. If you wanted to just see the gate waveform, you would need to use 2 probes, 1 for the gate and 1 for the switching node and take the difference your scope should be able to do that.

Then you would see a more square, or really rectangular, waveform. However , assuming that scope trace you've attached is what's on the battery, that's still very concerning - I don't think your bq is operating stably.

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Learn more. Asked 6 years, 8 months ago. Active 6 years, 8 months ago. Viewed times. However, the Miller effect still takes place when the device is turned off.

Several device manufacturers also provide literature covering this subject in some detail. Back to home page. Bad gate drive waveform with excessive low-frequency ringing. This cannot be corrected by increasing the damping resistance. It would need too much resistance, and the rising and falling edges would be too slow.

We must reduce the excessive leakage inductance by redesigning the gate drive transformer. Poor gate drive waveform with excessive high-frequency ringing. Add some damping resistance! Also try to reduce leakage inductance if you can. Good gate drive waveform except for overshoots. Increase series damping resistor slightly and the overshoot should diminish. The perfect gate drive waveform! Slightly overdamped gate drive waveform.

Decrease the damping resistor, to make the rising and falling edges faster. Massively overdamped gate drive waveform. Decrease the damping resistor, or use a more powerful gate drive IC. Slightly sloping tops and bottoms to waveform. Too few turns on the drive transformer, - This is not a problem as long as the amount of droop is less than a couple of volts, Add a few more turns to the primary and secondary windings to reduce the droop. Excessively drooping tops and bottoms to waveform.

Notice in Fig. This is due to the relatively slow switch on time compared with the operating frequency of the opto-isolator. However, looking at the drain waveforms in Figs. Note that the 4N25 opto-isolator is not rated as particularly fast; there are a number of faster devices, which use opto diodes instead of opto transistors as the output component, however they do tend to cost more and are more likely to be used in higher frequency systems.

On testing the temperature rise for the whole circuit used in Figs. Higher than the calculations suggest but still well within safe limits when using a 3A motor as the load. With the circuit connected to the 36Watt lamp however, as shown in Fig. The switch therefore worked well with both resistive 12V lamp and inductive brushed DC motor loads upto 3A when driven from a 12V supply with an input from a 5V logic source.

The input signal was provided by either a simple pulse width modulator circuit or the Arduino. The extra expense in using an opto-isolator compared with a wrecked Arduino is therefore justified. However there are some applications where this may not be suitable, as when the load requires a ground connection in common with other load devices. Whilst this may not be a problem at low voltages, MOSFETs can be used to switch high voltage circuits where having a high voltage present on an apparently inactive circuit can be a safety problem by creating a shock hazard.

To eliminate either of these problems, High Side Switching can be used, as shown in Fig. As the supply voltage and now also the source voltage is likely to be the highest voltage in the circuit, the Gate voltage cannot be made higher than the Source voltage and control is lost. To make High Side Switching possible there are a number of methods that can be used. The circuit symbols for each are shown in Fig. The only difference in these symbols is the direction of the arrow indicating the channel; in the P channel MOSFET the arrow now points away from the P type channel.

The drain is now connected to the more positive side of the load, and the load's negative terminal is connected to ground. Notice the similarities and differences between Figs. Firsly in Fig.