CN115549444A

CN115549444A - SiC MOS drive circuit that transformer was kept apart

Info

Publication number: CN115549444A
Application number: CN202211033151.8A
Authority: CN
Inventors: 尚新磊; 赵岩; 王美婷; 徐琳琳
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2022-08-26
Filing date: 2022-08-26
Publication date: 2022-12-30

Abstract

The invention belongs to the technical field of MOS (metal oxide semiconductor) tube driving, and particularly relates to a SiC MOS (metal oxide semiconductor) driving circuit for transformer isolation, which comprises an isolation transformer, wherein a primary winding of the isolation transformer is a control waveform input end, a secondary winding of the isolation transformer is provided with a middle tap, and the middle tap is connected with an output terminal S; one tap of the other two taps of the secondary winding of the isolation transformer is connected with an output terminal G through a first rectifier diode; the last tap of the secondary winding of the isolation transformer is connected with the grid of the low-power discharge SiCMOS tube through a second rectifier diode; the drain electrode of the low-power discharge MOS tube is connected with an output terminal G; a resistor is connected in parallel between the source electrode and the grid electrode of the low-power discharge MOS tube; the output terminal G and the output terminal S are connected in parallel with a capacitor. The problem that an existing transformer-isolated MOS driving circuit is large in size, high in cost and not suitable for being used under the condition of relatively low frequency and relatively large duty ratio range change can be solved.

Description

SiC MOS drive circuit that transformer was kept apart

Technical Field

The invention belongs to the technical field of MOS (metal oxide semiconductor) tube driving, and particularly relates to a SiC MOS driving circuit for transformer isolation, which can realize the isolation of a transformer under the conditions of lower frequency and larger duty ratio range.

Background

A MOS (Metal Oxide Semiconductor) Transistor is a fully-controlled switching device, belongs to one of FET (Field Effect Transistor), has the advantages of fast switching speed, small volume, easy parallel connection, easy control, etc., and has been widely applied to various fields such as power supplies, power amplifiers, motor drives, etc. SiC (silicon carbide) is a new type of semiconductor material, and SiC MOS is a new type of semiconductor switching device based on SiC materials. Compared with the traditional MOS switch device, the SiC MOS has the advantages of high temperature resistance, high pressure resistance, small volume, low on-resistance, high switching speed, no need of negative pressure shutoff and the like, and is widely applied to the advanced fields of aviation power supplies, electric automobiles, petroleum logging instruments and the like.

The driving modes of the MOS tube are divided into an isolation type and a non-isolation type, wherein the MOS drive isolated by the transformer in the isolation drive has the advantages of simple structure, stability, reliability and the like, and the application is very wide. However, the existing transformer-isolated MOS drive technology also has its limitations.

The structure of a conventional transformer-isolated MOS drive circuit is shown in fig. 1. The device comprises a damping resistor R1, a blocking capacitor C1, an isolation transformer T1, secondary voltage stabilizing diodes D1 and D2 and a secondary resistor Rgs. The Vin1 and Vin2 end is connected with the pulse output circuit, and the G end and the S end are respectively connected with the G pole (grid) and the S pole (source) of the driven MOS tube. Driving pulses input from a Vin1 end and a Vin2 end enter a primary side of the transformer through R1 and C1 to provide driving energy for the transformer, the output of the transformer is connected with a series circuit formed by secondary side voltage stabilizing diodes D1 and D2, the series voltage stabilizing diodes D1 and D2 play a role in voltage clamping, and meanwhile, the output of the transformer forms induced current in a secondary side loop generated by Rgs and generates driving voltage Vgs to drive the MOS to be switched on or switched off. The working waveform is shown in fig. 2, wherein Vin is a pulse voltage waveform input by a Vin1 terminal and a Vin2 terminal, and Vin = Vin1-Vin2; vgs is the output waveform of the transformer-isolated MOS drive circuit; iy is the primary current waveform of the transformer; if is the secondary current waveform of the transformer. As can be seen from the waveforms at each position in fig. 2, the isolation transformer of the conventional MOS driving circuit with transformer isolation is always in an excited or demagnetized state during the driving process. If the input pulse frequency is low and the duty ratio variation range is large, a series of design measures are required to be taken to realize that the magnetic core of the isolation transformer is always in an excitation or demagnetization state without magnetic saturation in the whole driving process: for example, a high-permeability and high-saturation magnetic conductive material is required, the sectional area of the transformer needs to be designed to be large enough, the voltage of the input pulse Vin is designed to be high, the number of turns of the transformer coil is designed to be as large as possible, the value of the blocking capacitor C1 is large, and the values of the resistors R1 and Rgs are as large as possible. It can be seen that applying the existing transformer-isolated MOS driving circuit to the conditions of low frequency and large duty ratio variation range can cause the problems of complicated pulse generation circuit, overlarge pulse transformer volume, high cost, and the like, so that the lower limit of the frequency of the existing transformer-isolated MOS driving circuit is only thousands of Hz generally and the duty ratio variation range cannot be too large.

To ensure sufficient transmission power while ensuring that the primary side current slope of the transformer is small, the following considerations are taken into account: (1) In order to ensure that the magnetic core of the transformer is not saturated, a high-saturation magnetic conduction material is required to be adopted, and the sectional area of the transformer needs to be designed to be large enough; (2) In order to realize normal operation under low frequency, the slope of the primary side current of the transformer needs to be small, but the inductance needs to be large under the condition of meeting the requirement of enough transmission power.

To achieve this goal, the saturation flux of the isolation transformer needs to be designed large enough, and the drawback of meeting this requirement is the need to increase the isolation transformer design. In addition, if the input pulse frequency is low or the duty ratio variation range is large, the magnetic core of the isolation transformer needs to be unsaturated in the whole driving process, so that the isolation transformer with a very large volume needs to be designed. Therefore, the existing transformer-isolated MOS drive circuit is not suitable for applications with low frequency and large duty cycle variation.

Disclosure of Invention

The invention aims to provide a transformer-isolated SiC MOS drive circuit, which can solve the problems that the existing transformer-isolated MOS drive circuit has large volume and high cost and is not suitable for being used under the conditions of lower frequency and larger duty ratio range change.

The present invention has been accomplished in such a manner that,

a transformer isolated SiC MOS driver circuit, the driver circuit comprising:

the primary winding of the isolation transformer is a control waveform input end, the secondary winding of the isolation transformer is provided with a middle tap, and the middle tap is connected with an output terminal S; one of the other two taps of the secondary winding of the isolation transformer is connected with an output terminal G through a first rectifier diode; the last tap of the secondary winding of the isolation transformer is connected with the grid electrode of the low-power discharge SiC MOS tube through a second rectifier diode; the drain electrode of the low-power discharge MOS tube is connected with an output terminal G; a resistor is connected in parallel between the source electrode and the grid electrode of the low-power discharge MOS tube; the output terminal G and the output terminal S are connected in parallel with a capacitor.

Furthermore, an input terminal Vin1 of the primary winding of the isolation transformer is connected in series with the input resistor and then connected in series with the input capacitor, and then connected to a tap of the primary winding of the isolation transformer, and the other tap of the primary winding of the isolation transformer is connected with another input terminal Vin2 to form an input loop.

Further, the resistance value of the input resistor is 1 ohm to 90 ohms, and the range of the input capacitor is 0.1 microfarad to 90 microfarad.

Further, the secondary winding of the isolation transformer T31 has the same polarity as the source winding.

Further, the waveform is a square wave.

Compared with the prior art, the invention has the beneficial effects that:

the edge response speed is fast and can be used in the case of lower frequency and large duty cycle range variation: the driving circuit provided by the invention adopts a larger blocking capacitor C1 on the primary side of the isolation transformer and greatly reduces a current-limiting resistor R1; an energy storage capacitor is used on the secondary side of the isolation transformer to replace an energy consumption resistor Rgs, and meanwhile, a winding and a circuit for discharging the energy storage capacitor are added. The drive circuit provided by the invention has faster response to rising edges and falling edges by adjusting the parameters and changing the structure, and the isolation transformer does not transmit energy when in high level or low level, namely, does not need to be in the magnetizing and demagnetizing processes in the whole high level or low level interval, so that the drive circuit is very suitable for driving the SiC MOS which does not need negative pressure turn-off and is suitable for being used under the condition of larger change of lower frequency and duty ratio range.

Miniaturization of the isolation transformer: because the isolation transformer in working and pulse states only transmits energy at the rising edge and the falling edge of the driving pulse, the isolation transformer does not need to transmit energy at the high level or low level stage of the input pulse, and the isolation transformer does not need to be in the magnetizing and demagnetizing processes all the time at the high level or low level stage of the whole pulse. In addition, in the process of transmitting the rising edge and the falling edge of the driving pulse, because the AC impedance of the primary side and the secondary side of the isolation transformer is very low, the magnetic flux generated by the primary side driving current and the reverse magnetic flux generated by the secondary side induced current can be mutually cancelled, and the requirements of the driving circuit on the saturation magnetic flux and the magnetic permeability of the isolation transformer are greatly reduced. Specifically, the isolation transformer does not need to adopt a high-permeability and high-saturation magnetic material as the magnetic core of the transformer, the sectional area of the isolation transformer can be made very small, and the number of turns of the transformer coil can be very small. That is to say, the isolation transformer in the invention has the advantages of small volume, light weight, less turns, low cost and the like.

Drawings

FIG. 1 is a diagram of a typical structure of a conventional transformer-isolated MOS driving circuit;

FIG. 2 is a waveform diagram of a conventional transformer isolated MOS driver circuit;

FIG. 3 is a schematic diagram of a transformer isolated SiC MOS driver circuit according to the present invention;

fig. 4 is a waveform schematic diagram of a transformer isolated SiC MOS driver circuit provided in the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.

The structure diagram of the transformer-isolated SiC MOS driver circuit provided in the embodiment of the present invention is shown in fig. 3, and includes: the device comprises a primary damping resistor 31, a primary blocking capacitor 32, an isolation transformer 33, a secondary first rectifier diode 34, a secondary second rectifier diode 35, a secondary energy storage capacitor 38, a low-power discharge MOS tube 37 and a gate-source resistor 36 of the low-power discharge MOS tube. The input resistor 31 of the circuit has a low resistance, typically in the range of a few ohms to a few tens of ohms, for example: 1 ohm to 90 ohm range; the capacitance value of the input capacitor 32 of the circuit is large, generally from a few tenths of a microfarad to a few tens of microfarad, for example: 0.1 microfarads to 90 microfarads; the input terminal Vin1 is connected in series with the input resistor 31 and then connected in series with the input capacitor 32, and then connected to one tap of the primary side of the isolation transformer 33, and the other tap of the primary side of the isolation transformer 33 is connected to the input terminal Vin2, so as to form an input loop. The secondary winding and the source winding of the isolation transformer 33 have the same polarity, and the secondary winding is provided with a middle tap which is connected with an output terminal S; one of the other two taps of the isolation transformer T31 is connected to the output terminal G through the first rectifier diode 34; the last tap of the secondary side of the isolation transformer T31 is connected to the gate of the low-power discharge SiC MOS transistor 37 through the second rectifier diode 35; the drain of the low-power discharge MOS transistor 37 is connected to the output terminal G; a resistor 36 is connected in parallel between the source and the grid of the low-power discharge MOS tube 37; a capacitor 38 is connected in parallel between the output terminal G and the output terminal S.

The schematic diagram of the input and output waveforms of the transformer isolated SiC MOS driver circuit provided in this embodiment is shown in fig. 4, and includes: the input waveform 41 of the transformer driving signal applied to the two input ends of Vin1 and Vin2, the output waveform 42 for connecting the G end and the S end of the driven SiC MOS, the current waveform 43 of the primary side of the transformer, the current waveform 44 flowing through the first rectifier diode of the secondary side, and the current waveform 45 flowing through the first rectifier diode of the secondary side.

The operation principle of the transformer isolated SiC MOS driver circuit according to this embodiment will be described with reference to fig. 3 and 4. The energy for driving the SiC MOS is firstly connected to the input terminals Vin1 and Vin2 of the transformer isolated SiC MOS driving circuit provided in this embodiment in the form of a square wave, as shown by the waveform 41 in fig. 4, in which the low level in the waveform corresponds to the driving state of the SiC MOS drive being off, and the high level in the waveform corresponds to the driving state of the SiC MOS drive being on. The transition from low level to high level is a rising edge, and the transition from high level to low level is a falling edge. Assuming that the input in the initial state is low, the voltage between the two electrodes of the primary blocking capacitor 32 is zero, and the voltage between the two electrodes of the secondary energy-storage capacitor 38 is zero. The primary side of the isolation transformer can generate forward pulse current on the rising edge of the input waveform, the pulse current is gradually reduced from small to large to the maximum value along with the rise of the voltage of the primary side blocking capacitor 32, and the pulse current is reduced to zero after damped oscillation. Meanwhile, the secondary side generates a sensing current 44, the sensing current 44 generated by the secondary side flows through the secondary side first rectifying diode 34 to charge the secondary side energy storage capacitor 38, and the secondary side energy storage capacitor 38 outputs a high level through the output terminals G and S as shown by an output waveform 42 in fig. 4. Since the isolation transformer is not transferring energy during the high level after the rising edge, and since there is leakage current between the gate and source of the driven SiC MOS, the output voltage of the output waveform 42 will slowly drop during the high level after the rising edge. The primary side of the isolation transformer can generate reverse pulse current at the falling edge of the input waveform, the process corresponds to the discharging process of the primary side blocking capacitor 32, the reverse pulse current is gradually reduced after reaching the maximum value from small to large, and is reduced to zero after damped oscillation. Meanwhile, the secondary side generates an induced current 45, the induced current 45 generated by the secondary side flows through a loop formed by the secondary side second rectifying diode 35 and the resistor 36 connected in parallel between the source and the gate of the low-power discharge MOS transistor 37, a control voltage for controlling the low-power discharge MOS transistor 37 is generated on the resistor 36, and the low-power discharge MOS transistor 37 is controlled to enter a conducting state to release the charge of the secondary side energy storage capacitor 38, so that the output terminals G and S output low levels as shown in an output waveform 42 in fig. 4. Since the isolation transformer is not transferring energy during the low level after the falling edge, and since there is no charge in the secondary storage capacitor 38, the output waveform 42 remains low for a long period of time after the falling edge.

The driving transformer is designed to be in a pulse working state, namely the driving transformer transmits energy only at the rising edge and the falling edge of the driving pulse, and the transformer does not need to transmit energy at the high level or the low level of the input pulse. That is, the driving transformer of the invention does not need to be in the magnetizing and demagnetizing process all the time in the high level or low level stage, thus the requirements on the inductance and saturation magnetic flux of the transformer can be reduced.

The driving circuit adopts a larger blocking capacitor C1 on the primary side of the driving transformer and greatly reduces a current limiting resistor R1. The driving circuit uses an energy storage capacitor on the secondary side of the driving transformer instead of the dissipative resistor Rgs. The drive circuit adds windings and circuitry for effecting discharge of the storage capacitor.

The primary side alternating current impedance and the secondary side alternating current impedance of the driving circuit provided by the invention are small through the parameter adjustment and the structural change.

The magnetic flux generated by the primary side driving current and the reverse magnetic flux generated by the secondary side induced current can cancel each other, that is, the transformer can not generate higher magnetic flux change in the process of transmitting the rising edge and the falling edge of the driving pulse, and the requirement on the saturation magnetic flux of the transformer is further reduced.

Lower ac impedance results in faster edge response speed and better edge pulse energy transfer capability.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A transformer isolated SiC MOS driver circuit, the driver circuit comprising:

2. The transformer-isolated SiC MOS driver circuit of claim 1, wherein an input terminal Vin1 of the primary winding of the isolation transformer is connected in series with the input resistor, the input capacitor, and then connected to a tap of the primary winding of the isolation transformer, and another tap of the primary winding of the isolation transformer is connected to another input terminal Vin2 to form an input loop.

3. The transformer isolated SiC MOS driver circuit of claim 2,

the resistance value of the input resistor is 1 ohm to 90 ohm, and the range of the input capacitor is 0.1 microfarad to 90 microfarad.

4. The transformer isolated SiC MOS driver circuit of claim 1,

the secondary winding and the source winding of the isolation transformer T31 have the same polarity.

5. The transformer isolated SiC MOS driver circuit of claim 1, wherein the waveform is a square wave.