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   Abstract: Along with the Semiconductor Technology and the large scale integrated circuit technology’s development, the digital signal processor is getting more and more broad in the exchange velocity modulation and the motion control domain application. Digital signal processor and power component interface circuit design reasonable consummation direct relation system long lasting work reliability. At the same time, the low pressure power supply digital signal processor also to actuated the interface circuit design to set the request. Through analyzes IGBT to actuate the reliable request and to apply in frequency changer’s several kind of digital signal processor’s PWM mouth driving force, has designed one kind of reliable driving circuit plan.

    Key word: IGBT; Digital signal processor; PWM mouth; Actuation; Reliability

Introduction

In the redundant reliable rank’s equipment, must guarantee semiconductor device’s failure rate nominal value in 10 to 100 between FIT(1FIT=10-9/h). Must realize such reliability, according to assigns the characteristic use module great importance. IGBT most has one of application prospect power semiconductor devices as the electric power electron system, its durable intensity and service life direct relation overall system’s reliability. Speaking of the IGBT component itself, reliable driving circuit design direct relation its service life. At the same time, along with the microelectronic technology and the semiconductor integration technology’s swift development, the digital signal processor is becoming the electric power electronic technology and the motion control domain application more and more broad micro controller gradually. Designs the reliable actuation plan to become take the digital signal processor one of as core motion control system long-term reliability service key links. This article through analyzes IGBT to the reliable actuation request, and in several kind of frequency conversion velocity modulation commonly used digital signal processor’s driving force, has given one kind of reliable driving circuit plan, this plan has the good application prospect in reality.

1 IGBT characteristic and driving circuit reliability design request

1.1 IGBT characteristics

IGBT is the voltage actuation youngest son electric conduction component, is high speed easy to actuate MOSFET, clear working place wide same bipolarity component low saturated pressure drop union product. Figure 1 has given the IGBT equivalent circuit, it has the following characteristic:

- - the high input impedance, causes it to be possible to use the general low cost the actuation line;

- - high-speed switch characteristic;

- - conducting state’s loss is low.

1.1.1 IGBT rated values

IGBT can withstand the electric current, the voltage, the power and so on biggest permissible value is defined generally as the most large quantity definite value. When the line designs, whether correctly the understanding and is the recognition most large quantity definite value, as well as the service life specially finally important to the IGBT reliable work.

    1.1.2 short-circuit current characteristic

The IGBT short-circuit current may reach above nominal current 10 times, short-circuits the magnitude of current decided by the IGBT grid bias and the transconductance. Controls IGBT the short-circuit current is the IGBT reliable work essential safeguard correctly.

1.1.3 perceptual load shutdown characteristics

In the motion control system, the perceptual load is the common load, when IGBT shutdown, adds from several V rises in the above voltage the instant to the supply voltage (passes condition electric current maintains invariable), produces very big dv/dt, this will threaten the IGBT long lasting work seriously the reliability. In the circuit design, through increases the resistance value may limit and reduce the shutdown dv/dt when the electronics grid driving circuit.

1.1.4 biggest grid emission pole tension (VGE)

The grid bias is decided by electronics grid oxide layer thickness and the characteristic. The electronics grid to emitter electrode’s breakdown voltage is 80V generally, to assure the security, the grid bias usually limits below 20V.

1.1.5 electronics grid input capacity

IGBT input capacity characteristic immediate influence to electronics grid driving circuit’s reliable design. IGBT takes one kind of youngest son electric conduction component, the switch characteristic actuates youngest son injection with compound as well as the electronics grid the condition the influence to be big. In reality, considered the miller effect, electronics grid driving circuit’s driving force should be bigger than in the handbook 2~3 times.

1.1.6 clear working place characteristics

Youngest son component when big electric current high voltage on-off state work, as a result of electric current non-uniform distribution, when surpasses the trouble-free service limit, causes the component damage frequently. Current distribution way and di/dt related, thus the clear working place is divided into frequently the forward clear working place and the reverse clear working place.

1.2 IGBT driving circuit reliability design request

The IGBT grid bias may from the different driving circuit production, the electronics grid driving circuit design fit and unfit quality direct relation system long-term movement reliability. May carry on the design based on the following several requests.

    1.2.1 component bias request

When the IGBT electronics grid replenishes suffices to make it to produce the completely saturated forward grid-voltage (for example 15V~20V), may cause to pass condition the loss to reduce to is smallest, simultaneously may limit the power stress which the short-circuit current and it brings. When the grid bias is a zero hour, IGBT is in the off-state. But, to guarantee presents the dv/dt noise when IGBT C-E still maintained the shutdown, must add the reverse bias in the electronics grid (for example - 5V~-15V); At the same time, uses the reverse bias to be possible to reduce the shutdown to lose, enhances the IGBT work the reliability.

1.2.2 electronics grid electric charge request

The IGBT clear and the shutdown realize through grid circuit’s charging and discharging, therefore, the grid resistor chooses whether suitable direct relation IGBT dynamic characteristic.

1.2.3 bear soundness request

IGBT is in shutdown period, exerts may cause on IGBT collecting electrode - grid capacity’s dv/dt to have the electric current to wind through the grid circuit. The false electric current is so big enough, produces the voltage in the grid resistor, has the possibility to cause IGBT to clear by mistake, therefore, the small grid resistor may increase the IGBT actuation to bear soundness (i.e. to prevent dv/dt to bring harms clear). But, the small grid resistor causes IGBT the clear di/dt fill-out, will cause high dv/dt, increased the after flow diode will restore when the surge voltage.

Therefore, when designs the grid resistor must give dual attention to these two aspect question.

1.2.4 electronics grid driver power request

The IGBT switch must consume from the electronics grid power source’s power. Its power loss is actuated the electronics grid, the negative bias differential value δvge, electronics grid total electric charge QG and the operating switch frequency f influence, the type (1) has given the power source average power.

PAV=ΔVGE×QG×f    (1)

2 digital signal processor PWM mouth driving force

The IGBT driving signal’s production may through the simulation and the digit two

Plants the way to realize. Along with the micro processing technology’s development (including processor, system structure and memory component), the digital signal processor by its superior performance in the exchange velocity modulation, the motion control domain obtained the widespread application. Uses velocity modulation system which the digital signal processor constitutes, integrates PWM by the processor the module power production unit (IGBT) driving signal. But PWM connection driving force and with IGBT interface circuit’s design immediate influence to system work reliability.

2.1 TMS320LF2407A and TMS320F240PWM mouth driving force compares

At present, the digital signal processor chip supply manufacturer mainly had TI Corporation, AD Corporation, Motorolar Corporation and so on, this article to exchanges in the velocity modulation system widespread application TI Corporation’s TMS320LF2407A to carry on the comparison with TMS320F240LIANG product PWM mouth driving force, thus has provided the powerful data for the design reliable driving circuit. According to the data book may know, in the most large quantity will decide under the condition to move absolutely for a long time will affect component’s reliability. Table 1 gives the F240 working voltage absolute rated value as well as under the recommendation working condition PWM mouth actuation output current ability. Table 2 give the LF2407A working voltage absolute rated value as well as under the recommendation working condition PWM mouth actuation output current ability.

Table 1 F240 actuation output current ability

Table 2 LF2407A actuation output current ability

May see by Table 2, LF2407A in two event supervisor’s PWM mouth driving force is different. At the same time, the comparison table 1 and Table 2 may see F240 and LF2407A, although uses the CMOS technology, but, F240 uses the 5VCMOS level but LF2407A uses the 3.3VCMOS level low pressure to supply power the way, therefore, PWM mouth driving force is different. For guarantee system reliability, when design driving circuit should consider the above characteristic fully.

2.2F240 and LF2407APWM connection actuation design

The microprocessor uses the different integrated technology, when designs the interface circuit should consider its driving force and the level match fully. Regarding F240, uses the 5VCMOS technology, directly with the TTL level compatible, does not need to consider some special interface circuit. But from reliability design angle embarking, may increases between the processor and the actuation chip isolates the actuation chip, as shown in Figure 2.

LF2407A uses the 3.3VCMOS technology, this technology causes

The electric circuit has realized the low power loss work, simultaneously has also brought some questions,

Namely connection level match and driving force question. Figure 3 has given 3.3V

CMOS outputs MOSFET the input interface circuit. Many MOSFET must achieve the saturated breakover electronics grid level under certain load current to be bigger than 3.3V, therefore designs uses standard 5VCMOS buffer 74HC240 to transform 3.3VCMOS to the 5VCMOS level.

3 based on digital signal processor’s actuation project design

May know through the above analysis, based on digital signal processor (DSP) the IGBT driving circuit’s reliability design, the request understands and grasps IGBT and the DSP related electrical specification and the reliability design principle fully. Here used HP Corporation’s HCPL-316J gate to actuate the optical coupler to unify TMS320F240 extremely to give one kind of reliable IGBT actuation plan.

3.1 HCPL-316J characteristics

HCPL-316J is one kind of 2AIGBT gate which produces by HP Corporation actuates the optical coupler extremely, its internal integrated collecting electrode launch pole tension undersaturation examination electric circuit and malfunction feedback circuit. Mainly has the following some characteristics:

- - compatible CMOS/TTL level;

- - light isolation, malfunction feedback;

- pneumatic switch speed biggest 500ns;

- - “soft” IGBT shutdown;

- - The VCE undersaturation examination and the belt stagnate the link undervoltage locking protection;

- - wide working voltage scope (15~30V);

- - the user may dispose the automatic reset, the automatic shut-off.

DSP realizes the IGBT actuation with this coupler union, causes the IGBTVCE undersaturation examination structure to be compact, and the low cost easy to realize, simultaneously has satisfied the wide scope security and the adjustment need.

Figure 4

    3.2 actuation project design

At present, various companies promote use in the IGBT actuation the electric circuit being unique. HP Corporation’s HCPL-316J integrated the VCE undersaturation examination and the malfunction feedback circuit, has provided the safeguard for driving circuit’s reliable work, meanwhile has the characteristic which simple easy to realize. Figure 4 has given based on the DSPF240 IGBT actuation plan schematic diagram.

4 conclusions

This article through analyzes the IGBT power component’s characteristic, as well as applies to the reliable actuation request in frequency changer’s several kind of digital signal processor’s PWM mouth driving force, has designed one kind of reliable IGBT actuation plan. This plan obtained the application in the spring day frequency changer driving circuit, and has made the very good progress. Along with the IGBT widespread use, this plan will have good profits from the significance and the application prospect.