JPH08126300A - Driving circuit with protective circuit for power device - Google Patents

Abstract

PURPOSE: To prevent the damage of a power device by varying the overcurrent protective trip of the device according to the drive current or voltage value of the device. CONSTITUTION: When a power source voltage Vcc (gate voltage Vge ) drops below a certain value, the overcurrent protective threshold voltage Vsin of the compared voltage of a comparator 10 is lowered at a certain gradient. In this case, generating means 14 of the voltage sin controls the threshold voltage changeover switch 16 by the output voltage of the monitor 15 of the power source voltage Vcc of the driver 2, the fixed threshold voltage Vs1 and the power sources voltage Vcc are switched with the variable threshold voltage Bs2 divided by resistors R1 , R2 , and the saturated current Isa1 always becomes larger than the overcurrent protective trip value, and protecting function is operated. Thus, the damage of the power device can be prevented.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a power transistor,
The present invention relates to a drive circuit with protection circuit for power devices such as power MOSFETs and IGBTs.

[0002]

2. Description of the Related Art A conventional drive circuit with a protection circuit for an IGBT which is one of power devices will be described with reference to the drawings.

FIG. 4 is a block diagram of a conventional drive circuit with protection circuit for an IGBT, in which an input terminal 1 is connected to a gate terminal 4 of an IGBT 3 with a sense terminal via a drive circuit 2. Reference numerals 5 and 6 are a collector terminal and an emitter terminal of the IGBT 3 with a sense terminal, and an FRD (Firs
t Recovery Diode) 7 is connected. Reference numeral 8 denotes a current detection terminal which is a sense terminal of the IGBT 3 with a sense terminal, and a current of a few thousandths of the current flowing through the collector terminal 5 flows therethrough. Sense voltage V appearing at the end
sen is applied to the comparator 10 together with the overcurrent protection threshold voltage Vsth, and its comparison output terminal 11 is connected to the control input terminal 12 of the drive circuit 2. Thirteen
Is a Vcc power source of the drive circuit 2. Sense voltage Vs
When en exceeds the overcurrent protection threshold voltage Vsth, the IGBT
Since an overcurrent has flown into the collector terminal 5 of the comparator 3, the signal of the comparison output terminal 11 of the comparator 10 turns off the output of the drive circuit 2 and interrupts the current of the IGBT 3. In this case, the relationship between the collector-emitter voltage Vce and the collector current Ic when the gate drive voltage Vge of the IGBT 3 is changed is shown in the voltage-current characteristic diagram of FIG. In FIG. 5, it can be seen that when the gate drive voltage Vge of the IGBT 3 changes, the saturation current value Ic of the IGBT 3 changes, and when the gate drive voltage Vge decreases, the saturation current also decreases.

When the IGBT 3 is used in such a state, as shown in the time-current waveform diagram of FIG. 6, even when the collector current Ic becomes large due to load fluctuation, it is normal, that is, the gate drive voltage Vge. When the level is equal to or higher than the level, the collector current Ic increases without being saturated as shown by the dotted line. Therefore, the overcurrent protection trip value Itc is exceeded and the comparator 10 outputs a control signal to turn off the output of the drive circuit 2 for protection. Call. However, at this time, when the gate drive voltage Vge drops significantly, the collector current Ic enters the saturation current region, and the overcurrent protection trip value It
c cannot be exceeded, the comparator 10 cannot output a control signal for turning off the output of the drive circuit 2,
The protection is not applied, the collector-emitter voltage Vce of the IGBT 3 rises, and the loss of the IGBT 3 increases, leading to thermal breakdown.

[0005]

As described above, in the prior art, there is a problem that the overcurrent protection does not operate when the gate drive voltage of the IGBT drops and the device is destroyed in the saturation current region of the collector current Ic. there were.

[0006]

In order to solve the above-mentioned problems, the present invention provides a power device having a current detection function, in which an overcurrent protection trip value of the power device is set according to a driving current value or a driving voltage value of the power device. The above problem is solved by changing

[0007]

By the above means, it is possible to obtain a highly reliable drive circuit with a protection circuit for a power device that does not cause device breakdown.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a drive circuit with a protection circuit for a power device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a drive circuit with a protection circuit for an IGBT which is an embodiment of the present invention, except for a means 14 for generating an overcurrent protection threshold voltage Vsth to be applied to a comparator 10 as one of comparison voltages. Since the operation and operation are the same as those of the conventional example shown in FIG. 4, the same reference numerals as those in FIG. 4 are used and the description thereof is omitted.

Overcurrent protection threshold voltage Vsth generating means 1
4 is a monitoring circuit 15 for the power supply voltage Vcc of the drive circuit 2.
Is configured to switch the fixed threshold voltage Vs1 and a variable threshold voltage Vs2 obtained by dividing the power supply voltage Vcc by the resistors R1 and R2. ing.

The overcurrent protection threshold voltage V thus configured
The overcurrent protection threshold voltage Vsth, which is the output of the sth generating means 14, is compared with the sense voltage Vs, which is another comparison voltage.
It is applied to the comparator 10 together with en.

Here, the gate drive voltage Vge of the IGBT 3 is
= 13 to 17V, the fixed threshold voltage Vs1 is selected by the threshold voltage changeover switch 16, and when the gate drive voltage decreases to Vge ≦ 13V, the monitoring circuit 15 sets the power supply voltage Vcc (gate drive voltage Vge). A proportional and variable threshold voltage Vs2 is selected. This state is the power supply voltage V
FIG. 2 shows the relationship between cc and the overcurrent protection threshold voltage Vsth. As can be seen from FIG. 2, the power supply voltage Vcc
When the (gate drive voltage Vge) becomes a certain value or less, the overcurrent protection threshold voltage Vs which is the comparison voltage of the comparator 10
th decreases with a certain slope d. Further, the relationship between the overcurrent protection trip value and the power supply voltage Vcc (gate drive voltage Vge) is as shown in the relationship diagram of FIG. 3, and in the past, the overcurrent protection trip value was fixed as shown by the dotted line.
In the part where the saturation current Isat of T3 is lower than the overcurrent protection trip value, the protection function does not work and the breakdown region B is
In the circuit of this embodiment, as shown by the solid line, the saturation current Isat of the IGBT 3 is always higher than the overcurrent protection trip value, and the protection function is activated.

[0013]

As is apparent from the description of the embodiments of the present invention, when the drive current or drive voltage of the power device falls below a certain value, the overcurrent protection trip value of the power device is lowered. % Destruction in the saturation current region of the power device that had occurred is no longer occurring. Further, there is a trade-off relationship between the saturation current value and the short-circuit withstand voltage / Vce (STA) value. When this drive circuit is adopted, there are less restrictions on the saturation current value, and the short-circuit withstand voltage / Vce (S)
TA) value can be improved. As described above, according to the present invention, a power device having high reliability and improved characteristics can be supplied.

[Brief description of drawings]

FIG. 1 is a block diagram of a drive circuit with a protection circuit for a power device according to an embodiment of the present invention.

FIG. 2 is a relationship diagram showing a relationship between a power supply voltage Vcc and an overcurrent protection threshold voltage Vsth in one embodiment of the present invention.

FIG. 3 is a relationship diagram showing a relationship between an overcurrent protection trip value and a power supply voltage Vcc.

FIG. 4 is a block diagram of a conventional drive circuit with a protection circuit for a power device.

FIG. 5 is a collector-emitter voltage V of the power device.
voltage-current characteristic diagram showing the relationship between ce and collector current Ic

FIG. 6 is a time-collector current Ic waveform diagram of the power device.

[Explanation of symbols]

 1 Input Terminal 2 Drive Circuit 3 IGBT with Sense Terminal 4 Gate Terminal 5 Collector Terminal 6 Emitter Terminal 7 FRD 8 Current Detection Terminal 9 Sense Resistance 10 Comparator 11 Comparison Output Terminal 12 Control Input Terminal 13 Vcc Power Supply 14 Overcurrent Protection Threshold Voltage Vsth Generating means 15 Vcc power supply voltage monitoring circuit 16 Threshold voltage changeover switch Vge Gate drive voltage Vs1 Fixed threshold voltage Vs2 Variable threshold voltage Vsen Sense voltage Vsth Overcurrent protection threshold voltage

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // H02M 3/00 C

Claims (3)

[Claims] In a power device having a current detection function, a drive circuit with a protection circuit for a power device that changes an overcurrent protection trip value of the power device according to a drive current value or a drive voltage value of the power device. 2. The drive circuit with a protection circuit for a power device according to claim 1, wherein the power device is a power module. 3. A drive circuit with a protection circuit for a power transistor, which has a function of decreasing the overcurrent protection trip value in proportion to the gate drive voltage when the gate drive voltage of the power transistor drops below a certain level and drops below a certain voltage value. circuit.