Study of MOS and IGBT transistors at switching with variable duty cycle

In this paper, the functionality of MOS and IGBT transistors is examined under identical working conditions, both in terms of command frequency and load circuit. A variable duty cycle and variable frequency signal generator is used to control transistors. Various electronic components and Arduino-UNO modules, as well as the 16×2 LCD screen, were used to create the signal generator. The control signal is amplified by a current amplifier to adapt the output voltage to the value required to control the transistors. The operation of MOS and IGBT transistors at various operating frequencies with resistive or inductive loads is compared. Thus, the communication times of the transistor capsules were determined at various operating temperatures. The temperature was determined indirectly by connecting a thermistor to the transistor capsule.


Introduction
The signal generator is made on the basis of an Arduino board, one that allows obtaining the output of a rectangular signal of variable frequency and duty cycle.
Arduino is a family of microcontroller and affordable development boards that can be programmed using a programming language similar to C/C++ with the help of the Arduino IDE development environment.The power devices used in static converters operate in switching mode to give the equipment high energy yields.The MOS transistor is a fully controlled device requiring voltage signals in the grid (G) control circuit (S).For this reason, the power required in the control is practically zero, which significantly simplifies the related circuits [1], [2].The IGBT transistor is the most widely used transistor on an industrial scale for electrical equipment and is fully command-in.It possesses both the qualities of the MOS transistor in terms of control signal and switching times, as well as the quality of the bipolar transistor in the force circuit, the saturation voltage being reduced and the voltage/current capacities being higher [3][4][5].The switching times of the MOS transistor are the shortest, which is why it is mainly used in applications where high switching frequency is required at medium and low power [6], [7].

Making and operating the signal generator
AVR ATmega developed by Atmel is the "brain" of the Arduino board, it is based on the modified Harvard RISK eight-bit architecture.
Arduino UNO and Arduino Nano use the ATMEGA328P microcontroller (it has 28 DIP pins) that is part of the mega AVR series (Figure 1).

Figure 1. AVR ATmega 328P processor
For the use of the Arduino board, it is necessary to load into its flash memory an executable program written in machine code, that is, a sequence of bytes that are interpreted as instructions and executed.
The Arduino board has two outputs with a maximum current of 50 mA and differing voltages of 5 V and 3.3 V.
Arduino UNO requires a supply voltage between 7 V and 12 V to operate.The voltage is automatically adjusted on the board by a module called a voltage regulator, which converts the supply voltage to a voltage of 5 V, necessary for the operation of the board.
Often projects with Arduino are autonomous, that is, they are independent of the computer therefore it is necessary for the user to visualize the characteristics of the input signal on a display device.For this purpose, display screens called LCDs are used (Figure 2).

Figure 2. LCD screen
An LCD communicates with Arduino via a parallel interface, which makes it necessary for the microcontroller to simultaneously manipulate multiple pins in order to transfer the information to be displayed.
A rectangular signal generator has been implemented for the study of the operation of the switching transistors.The generator is made with Arduino UNO.
The circuit allows to change the duty cycle and the frequency of the generated rectangular signal.The change of these parameters is made by means of 4 buttons, 2 for increasing/decreasing the duty cycle and 2 for increasing/decreasing the frequency.Connecting the buttons to the corresponding pins on the Arduino UNO board was achieved by means of resistors of 10 kΩ value.
The LCD screen displays the following control signal information: Signal period, duty cycle, signal frequency and frequency change step.
A potentiometer has been used to adjust the screen resolution.
The duty cycle can be changed by actuating two buttons in the ascending and descending direction, from 1% to 99%, but also vice versa.The signal obtained at the signal generator output was viewed on the oscilloscope screen.The frequency of the signal from the output of the control circuit can also be modified increasing or decreasing in the range (1 Hz ÷ 1 MHz) by means of two buttons.Changing the frequency can be done in different steps.Setting the desired step see it does by means of a button and allows the choice of value steps 1 Hz, 10Hz, 100Hz and 1 kHz.

Programming the Arduino board
The Arduino board programming was carried out in the Arduino IDE application using the C++ programming language.
Two libraries were required for the application: -TimerOne.h,a library that is not found in the standard libraries of the Arduino IDE application and which has been added later, which controls and/or runs a periodic pause function.
-LiquidCrystal.h, a library that is also not found in the standard libraries of the Arduino IDE application and which was later added, a library that communicates with the LCD screen.
The next step was to program the Arduino board to change the frequency according to its step.If the button connected to pin 10 of the Arduino board that has the variable reference kn4 in the algorithm is pressed once, the step increases from 1 Hz to 10 Hz, if pressed twice increases from 1Hz to 100Hz, and if pressed three times it will increase from 1Hz to 1 kHz.
The next step was to calculate the duty cycle according to the pulse duration and the pulse repetition period, k being the pulse duration that equals 512 the initial value, and the signal period is 1024 µs.
The last step in programming was to program the LCD screen using the "lcd.print"function to display the necessary information.

Analysis of switching operation of MOS and IGBT transistors
The circuit for the study of the operation of MOS and IGBT transistors in switching mode was experimentally developed.The circuit contains both transistors, which can be connected in the circuit depending on the study done.
Experiments were made with the two types of transistors for both resistive and inductive resistive load [8], [9].
Rectangular signal was applied to different frequencies and with different duty cycle, waveforms were viewed on a two-channel digital oscilloscope.
The current in the transistor drain for different signal frequencies applied and for different duty cycle values was determined using a measuring instrument.

Switch control circuit with resistive load of MOS transistors
In the experimental circuit (Figure 4) the connections were made so that the MOS transistor (RFP50N06) was connected and works with resistive load (Figure 5).The influence on the signal from the output of the generator is observed with the increase of the command frequency.atthe frequency of 1 kHz the rectangular shape is preserved in the collector of the transistor MOS, but with its increase there are small delays in the switching of the transistor [6].They also propagate on the control signal, not having galvanic separation between the ordered transistor and the signal generator.A series of determinations were made at the aforementioned frequencies and at the command signal duty cycle of 25%, 50% and 75%.From the data obtained there is a reduction of the drain current proportional to the increase of the working frequency for all three values of the duty cycle.

Switch control circuit with inductive resistive load of MOS transistors
In the experimental circuit (Figure 4) the connections were made so that the MOS transistor (RFP50N06) is connected and operates with inductive resistive load (Figure 7).
The behavior of a n-channel MOSFET-type transistor of type RFP50N06 in switching mode has been studied.
The load circuit is of type R-L.The values of the elements in the load circuit are: R = 7 Ω, L=2.786 mH, RL = 3.9 Ω.There may be a lower delay in the transistor locking as the temperature of the junction increases [1], [7].The temperature is measured indirectly by determining the resistance of the thermistor that changes with the temperature capsules of the transistor on which it is mounted.The calculation relationship is: Where: B-the material constant of the thermistor T1 -ambient temperature, 25 0 C R1 -resistance of thermistor to 25 degrees R-resistance of thermistor at determined temperature The results obtained for 50% duty cycle at 30 kHz frequency are shown in Table 1.The measurements were recorded at a time interval of 30 seconds over 10 minutes.The temperature of the CEE ACE capsules has been doubled, and the latency of the transistor has been reduced.At the entrance to the conduction, there was no change from the initial situation when the ambient temperature was.
Determinations were made for different frequencies, namely 1 kHz, 10 kHz, 30 kHz, 50 kHz, 100 kHz, or 200 kHz, and at duty cycles of 25%, 50%, and 75%.The results do not differ significantly from those presented, which is why they are not explicitly mentioned in the paper.They will remember where the differences are.
It is also noted that the drain current is reduced when the command signal frequency is increased for the same duty cycle.
At the 130 kHz frequency of the control signal, measurements were made to study the influence of temperature on the switching regime of the power transistor by forcing external heating of the transistor [6]. Figure 9 a) shows the waveforms for the control signal and the output signal for the resistance of the RT = 470 Ω thermistor.
Figure 9 b) shows the waveforms for the control signal and the output signal for the resistance of RT = 10 Ω thermistor.
When the temperature of the transistor capsule rises, there is a delay in the entry into conduction that remains constant as the frequency rises.The temperature has no effect on the lock switch.

Switch control circuit with resistive load of IGBT transistors
In the experimental circuit (Figure 4) the connections were made so that the IGBT transistor (IRG4BC20U) is connected and operates with resistive load (Figure 10). Figure 11 shows the waveforms obtained for frequencies of 30 kHz, 50 kHz with a duty cycle of 50%.
It is a small delay at the entrance to the conduction and a switching front with a slightly smaller slope than at MOS transistors.The collector current variation is similar to the variation found at the previously analyzed transistor [10], [11].

Switch control circuit with inductive resistive load of IGBT transistors
The circuit diagram for transistor control is shown in Figure 12.

Figure 12. Switching control circuit with resistive inductive load of IGBT transistors
The behavior of an IGBT transistor, IGB4BC20U, has been studied.The load circuit is of type R-L.The values of the elements in the load circuit are: R = 7Ω, L = 2.78 mH, RL = 3.9 Ω.
Figure 13 a) shows the waveforms of the control and output signals at the time of starting measurements when the resistance of the thermistor is 460 Ω (t = 0).In Figure 13 b) shows the waveforms of the control and output signals after 9.5 minutes, when the resistance of the thermistor is 136 Ω.At relatively low frequency, the waveforms do not differ from the situation of the resistive load, keeping the delay at the entrance to the line.The results obtained are presented in table 2, from which a 3-fold increase in the temperature of the capsule can be seen after 10 minutes of operation.The results are similar for the other values of the duty cycle [12][13][14].A similar behavior is observed at 100 kHz as at 50 kHz, with the observation that the conduction time of the transistor is significantly reduced due to the delay in the entry into the conduction.
At the 100 kHz frequency of the control signal measurements were made to study the influence of temperature on the switching regime of the power transistor by forced external heating.
Figure 15 shows the waveforms for the control signal and the output signal for the resistance of RT = 10Ω thermistor (387.4716C°).At 100 kHz there is no significant change in the forced temperature rise of the transistor capsule.In the further increase of the frequency of the command signal, the IGBT transistor works worse and worse when it no longer enters the conduction, the delay at the entry into the conduction is longer than the conduction time of the transistor.

Conclusions
The measurements for the resistive load MOS RFP50N06 obtained the data given in Table 1 from which the following are to be found: When increasing the control frequency, the drain current decreases to all the values of the studied duty cycle.
With the increase of the duty cycle, the ratio of the current corresponding to the frequency of 1 kHz to that corresponding to a higher frequency with major differences at frequencies above 100 kHz is reduced.
Reducing the lead time of the transistor with increasing the transistor control frequency above 50 kHz.At the same time, above this value it is found that the delay time at the switch is approaching the command time.
Delay at switching causes drastic reduction of the output current above the 50 kHz frequency.Measurements made for the MOS RFP50N06 resistive -inductive load have led to results that highlight the reduction of the drain current with the increase of the working frequency at all the analyzed duty cycle values.
More significant reduction is achieved at frequencies above 100 kHz when switching times are comparable to lead time.
In all the presented situations, a small accentuation of the results obtained with the increase in the temperature of the transistor capsule is observed.
The operation of the MOS transistor at external heating was analyzed, obtaining waveforms close to those in normal operation.There is a reduction in the amplitude of the switching oscillations but increases the stabilization time with the increase in the control frequency.
The operation of the IGBT transistor was also analyzed under the same conditions as the MOS transistor.The results of the measurements show optimal operation at lower frequencies, but with the increase of the control frequency there is a worsening of the characteristics of the transistor.In the case of this transistor there is no oscillation at the lock, with only a voltage peak of slightly higher amplitude than in the MOS transistor.

Figure 3 Figure 3 .
Figure 3. a) LCD display of signal period, duty cycle, signal frequency and step change the frequency b) the waveform of the signal with the displayed characteristics

Figure 5 .Figure 6 .
Figure 5. Switching control circuit with resistive load on MOS transistors

Figure 7 .Figure 8 .
Figure 7. Switching control circuit with resistive inductive load on MOS transistors

Figure 8 a
) shows the waveforms of the control and output signals at the time of starting measurements when the resistance of the thermistor is 488 Ω. (t = 0) Figure8b) shows the results obtained after 9.5 minutes, when the resistance of the thermistor is 296 Ω.

11thFigure 9 .
Figure 9. Waveforms for control signal and output signal at 130 kHz frequency and 50% duty cycle when heating the MOS transistor

Figure 10 .
Figure 10.Switching control circuit with resistive load of IGBT transistors

Figure 11 .
Figure 11.Waveforms for the control signal with a 50% duty cycle and the signal in the IGBT transistor collector

11thFigure 13 .
Figure 13.Waveforms for control voltage with 50% duty cycle and voltage in transistor collector at 50 kHz frequency

Figure 14 a
Figure 14 a)  shows the waveforms of the control and output signals at the time of starting measurements when the resistance of the thermistor is 465 Ω (t = 0).Figure14 b) shows the waveforms of the control and output signals after 9.5 minutes, when the resistance of the thermistor is 158 Ω.

Figure 14 b
Figure 14 a)  shows the waveforms of the control and output signals at the time of starting measurements when the resistance of the thermistor is 465 Ω (t = 0).Figure14 b) shows the waveforms of the control and output signals after 9.5 minutes, when the resistance of the thermistor is 158 Ω.

11thFigure 14 .
Figure 14.Waveforms for control voltage with 50% duty cycle and voltage in transistor collector at 100 kHz frequency

Figure 15 .
Figure 15.Waveforms for control signal and output signal at 100 kHz frequency and 50% duty cycle for resistance of RT thermistor = 10 Ω (387.4716°C)

Table 1 .
Experimental results for 30 kHz and 50% duty cycle

Table 2 .
Results obtained for 50% duty cycle and 50 kHz

Table 3 .
Results obtained for 50% duty cycle and 100 kHz