Insulation grid double pole transistor IGBT is one kind of
component which bonds by MOSFET and the double pole transistor
becomes, its input extremely MOSFET, output extremely PNP transistor,
therefore, may regard as it is MOS the input Darington tube. It
fused these two kind of components merit, both has the MOSFET
component to actuate simple and the fast merit, and has the double
pole component capacity big merit, thus, obtained the more and more
widespread application in the modern electric power electronic
technology.
In in center high efficiency switching power supply installment,
IGBT because its control actuation electric circuit simple, the
operating frequency is higher, a capacity more major characteristic,
has gradually substituted for the crystal thyratron or GTO. But
in switching power supply installment, because it works high frequency
in with the high voltage, under the big electric current condition,
makes it to be easy to damage, moreover, the power source takes the
system the front level, because the electrical network undulation, is
struck by lightning the stress which and so on the reason influence
enables it to withstand to be bigger, therefore the IGBT reliability
directly relates the power source the reliability. Thus, when
chooses IGBT besides must do falls the volume consideration, the
protection design also is the power source designs when needs the key
consideration to IGBT a link.
1IGBT principle of work
The IGBT equivalent circuit like chart 1 shows.
May know by chart 1, if adds on the actuation positive voltage
in between the IGBT electronics grid and the emitter electrode, then
MOSFET leads passes, such PNP transistor collecting electrode and the
base extremely between become the low resistivity condition to cause
the transistor to lead passes; If between the IGBT electronics
grid and the emitter electrode the voltage is 0V, then the MOSFET
closure, shuts off the PNP transistor base current the supplies,
causes the transistor closure.
Thus it may be known, the IGBT security is reliable or not
mainly decided by the below factor that,
- Between IGBT electronics grid and emitter electrode voltage;
- Between IGBT collecting electrode and emitter electrode
voltage;
- Has flowed the IGBT collecting electrode - emitter electrode
electric current;
- The IGBT knot heats.
If between the IGBT electronics grid and the emitter electrode
voltage, namely the slaving voltage excessively is low, then IGBT
cannot stabilize normally works, if between excellent electronics grid
- emitter electrode pressure resistance then IGBT possible
irremediable defect; Similarly, if adds the voltage which
permits in the IGBT collecting electrode and the emitter electrode to
surpass between the collecting electrode - emitter electrode the
pressure resistance, flows the IGBT collecting electrode - emitter
electrode electric current warm to surpass the maximum current which
the collecting electrode - emitter electrode permits, the IGBT knot
surpasses it to tie the warm permissible value, the IGBT all possible
meeting irremediable defect.
2 protective measures
When carries on the circuit design, should aim at
affects the IGBT reliable factor, takes the corresponding protective
measures with a clear goal.
2. 1IGBT electronics grid protection
IGBT electronics grid - emitter electrode slaving
voltage VGE guarantee value for ±20V, if adds on in between its
electronics grid and the emitter electrode surpasses the guarantee
value the voltage, then possibly can damage IGBT, therefore, must
establish 栅压 the limiter circuit in the IGBT actuation electric
circuit. Moreover, if the IGBT electronics grid and the launch
interelectrode lead the way, but adds on the voltage between its
collecting electrode and the emitter electrode, then along with
collecting electrode electric potential change, because between the
electronics grid and the collecting electrode and the emitter
electrode the parasitic capacity existence, causes the grid potential
to elevate, the collecting electrode - emitter electrode has the
electric current to flow. By now if the collecting electrode and
the launch interelectrode were at time the high-pressured condition,
possibly could cause IGBT to give off heat even damages. If the
equipment causes the grid return separation in the transportation or
the vibration process, in the situation which realized to the main
circuit is not added on the voltage, then IGBT possibly can damage.
In order to prevent this kind of situation occurrence, should
connects in parallel fashion a several dozens k Omega resistance in
the IGBT electronics grid and the launch interelectrode, this
resistance should approach the electronics grid and the emitter
electrode as far as possible. Like chart 2 shows.
Because IGBT is power MOSFET and the PNP bipolar transistor
complex, specially its electronics grid is the MOS structure,
therefore besides above should have the protection, likes other MOS
structure component to be same, IGBT regarding the static voltage also
is extremely sensitive below, when carries on the assembly welding
work to IGBT also must pay attention to the item:
- In needs to use the hand to contact in front of IGBT, after
should first again carry on the human body on static discharge the
operation, and do not have to contact the module as far as possible
the actuation 端子 to be partial, must contact when must guarantee
on this time human body brings the static electricity has completely
bled off;
- When welding work, in order to prevent the static electricity
possibly damages IGBT, the welding machine certainly must reliably
earth.
2.2 collecting electrodes with launch the interelectrode
过压保护
过电?the production mainly has two kind of
situations, one kind is exerts the IGBT collecting electrode - to
launch the interelectrode direct current 电压过高, another kind
for collecting electrode - emitter electrode on surge 电压过高.
2.2.1 direct current 过电?
The direct current pressure has produced the reason is
because the input alternating current supply or the IGBT preceding
level of inputs occurs exceptionally is the result of. Solution
is when selects IGBT, carries on falls the volume design;
Moreover, but is examining this has pressed the time-sharing to
break IGBT the input, guarantees IGBT the security.
2.2.2 surges voltages protection
Because in the electric circuit the distributed
inductance existence, adds the IGBT shutter speed to be higher, when
IGBT shuts off and connects in parallel fashion with it reverse
restores when the diode reversion restores, can produce very big surge
voltage Ldi/dt, threatens IGBT the security.
The usual IGBT surge voltage waveform like chart 3 shows.
In chart: VCE is IGBT? The electrode - launches the
interelectrode the voltage waveform;
Ic is the IGBT collecting electrode electric current;
Ud is inputs IGBT the DC voltage;
VCESP=Ud + Ldic/dt, is the surge voltage peak value.
If VCESP surpasses IGBT collecting electrode - launch
interelectrode pressure resistance value VCES, the possibility damages
IGBT. Solution mainly has:
- When selects IGBT considers the design 裕量;
- When circuit design adjusts IGBT to actuate the electric
circuit Rg, causes di/dt to be as far as possible small;
- Approaches as far as possible the electrolysis electric
capacity the IGBT installment, reduces the distributed inductance;
- Installs the cushion protection circuit according to the
situation, the bypass high frequency surge voltage.
As a result of the cushion protection circuit to the IGBT
trouble-free service very vital role, makes in this the cushion
protection circuit type and the characteristic an introduction.
- C cushion electric circuit like chart 4 (a) shows, uses the
thin film electric capacity, approaches the IGBT installment, its
characteristic is the electric circuit simple, its shortcoming is
constitutes the LC acceptor by the distributed inductance and the
cushion electric capacity, is easy to have the voltage vibration, when
IGBT clears the collecting electrode electric current is bigger.
- RC cushion electric circuit like chart 4 (b) shows, its
characteristic is suits to cuts the wave electric circuit, but when
uses large capacity IGBT, must cause the cushion resistance value to
increase, when, clears collecting electrode electric current
oversized, causes the IGBT function to receive the certain limit.
- RCD cushion electric circuit like chart 4 (c) shows, compares
its characteristic with the RC cushion electric circuit is, the
question which increased the cushion diode when to cause the cushion
resistance to increase, avoids has cleared the IGBT function is
blocked.
In this cushion electric circuit the cushion resistance produces
the loss is
P=LI2f + CUd2f in the formula: In L primarily
electric circuit distributed inductance;
I is IGBT shuts off when the collecting electrode electric
current;
F is the IGBT turn-on frequency;
C is the cushion electric capacity;
Ud is the DC voltage value.
- Electric discharge preventing cushion electric circuit like
chart 4 (d) shows, compares its characteristic with the RCD cushion
electric circuit is, produces the loss is small, suits to the high
frequency switch.
The loss in the cushion resistance produces which in this
cushion electric circuit is
P=1/2LI2f+1/2CUf
According to the actual situation selection suitable
cushion protection circuit, the suppression shuts off the surge
voltage. Is carrying on installs 配时, must reduce the main
circuit and the cushion electric circuit distributed inductance as far
as possible, the wiring shorter thicker is better.
2.3 collecting electrodes electric currents have flowed the
protection
Has flowed the protection to IGBT, mainly has 3 methods.
2.3.1 uses the resistance or the current transformer examines
has flowed in a line of protection
Like chart 5 (a) and chart 5 (b) shows, may use the
resistance or the current transformer and the IGBT series, the
examination has flowed the IGBT collecting electrode electric current.
When has has flowed the situation occurs, the control
implementing agency separates IGBT the input, achieved protects IGBT
the goal.
2.3.2 (sat) examines by IGBT VCE has flowed in a line of
protection
Like chart 5 (c) shows, because of VCE (sat) =IcRCE
(sat), when Ic increases, VCE (sat) also increases along with it, if
the grid bias is the high level, but VCE is high, then this time has
has flowed the situation occurrence, this time the AND gate outputs
the high level, will cross flows the signal output, the control
implementing agency separates IGBT the input, will protect IGBT.
2.3.3 examinations load current carries on the protection
This method and chart 5 (a) the center examination
method basic is same, but chart 5 (a) is the direct method, this is
间接? like chart 5 (d) shows. Front when the load
short-circuits or the load current enlarges, also possibly causes the
level IGBT collecting electrode electric current to increase, causes
IGBT to damage. (Or the IGBT latter level of electric circuits)
examine after the load place exceptionally, the control implementing
agency shuts off IGBT the input, achieves the protection the goal.
2.4 hot protections
Ordinary circumstances obscene IGBT electric current
bigger, turn-on frequency higher, therefore component loss also quite
big, if the quantity of heat cannot promptly disperse, causes the
component knot warm Tj to surpass Tjmax, then IGBT is possible to
damage.
The IGBT power loss and dynamic moves including the stable state
power loss consumes, its dynamic power loss includes clears the power
loss and shuts off the power loss. When carries on the hot
design, not only must guarantee it when normal work can fully radiate,
moreover also must guarantee it when has the momentary overload, the
IGBT knot warm does not surpass Tjmax.
Certainly, equipment volume and weight and so on limit as well
as natural price compared to the consideration, the cooling system
unlimitedly is impossible to expand. But is approaching IGBT
place to install a temperature relay and so on, examines IGBT the
operating temperature. The control implementing agency when
occurs exceptionally shuts off IGBT the input, protects its security.
Below in addition, installs fixedly toward the radiator on when
should pay attention IGBT the item:
- Because the thermal resistance installs the position along
with IGBT the difference and the difference, therefore, if only
installs time IGBT on the radiator, should install it in center, in
order to causes the thermal resistance to be smallest; When
must install several IGBT, should act according to each IGBT to give
off heat the situation to keep the corresponding space;
When - use belt trace radiator, should be suitable the radiator
trace a IGBT wider direction, reduces the radiator the distortion;
- Radiator installment 表面?fineness should <= 10 mu m, if
the radiator surface is uneven, greatly will increase the radiator and
the component contact thermal resistance, even will have the very big
tensity in between the IGBT tube core and on the shell substrate, will
damage IGBT the insulating layer;
- In order to reduce the contact thermal resistance, should
better spreads in the radiator and the IGBT module wipes the heat
conduction silicon fat.
3 conclusions
When applies IGBT should act according to the actual
situation, takes the corresponding protective measures. So long
as after has pressed, has flowed, the heat and so on several aspects
all has taken the effective protective measures, can obtain the good
effect in the practical application, guaranteed IGBT safely reliably
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