JP3108917B2 - Semiconductor protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for lowering a gate voltage, cutting off a power MOS and protecting the power MOS when an overcurrent flows through the power MOS.

[0002]

2. Description of the Related Art In a conventional protection device, an enhancement MOS is connected between a gate and a source of a power MOS, and the gate of the enhancement MOS is connected to a power MOS.
When an overcurrent flows, the enhancement type MOS is turned on to lower the gate voltage of the power MOS.

[0003]

In a power MOS to which a conventional protection device is connected, an enhancement type MOS connected between a gate and a source when a gate voltage of the power MOS rises and falls by a gate drive circuit. Since the large gate current temporarily flows through the source through the gate, the gate having a current capacity many times larger than that of the normal gate drive circuit of the power MOS in which the enhancement type MOS is not connected between the gate and the source. Unless the driving circuit is used, there is a problem that the gate voltage of the power MOS cannot be raised and lowered.

According to the present invention, when the gate voltage of a power MOS rises and falls, it temporarily passes through an enhancement type MOS connected between the gate and the source.
It is an object of the present invention to provide a protection device capable of raising and lowering a gate voltage of a power MOS by a normal gate drive circuit without a large gate current flowing to a source.

[0005]

In order to achieve the above object, in a protection device according to the present invention, a depletion type MOS is connected in series with an enhancement type MOS between a gate and a source of a power MOS, and an enhancement type MOS is connected. The MOS gate is connected to a power M by a resistor and a diode.
Connected to the drain of OS, and power M
Connect to the source of the OS and press the depletion type M
The gate of the OS is connected to the gate of the power MOS by a resistor and connected to the source of the power MOS by a capacitor.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a conventional protection device will be described with reference to FIG. The gate of an N-type power MOS 1 (hereinafter, referred to as MOS 1) is connected to an N-type enhancement type MOS 2 (hereinafter, MOS 1).
2), the resistor 3 is connected to the source of the MOS2, the gate of the MOS2 is connected to the drain of the MOS1, and the anode of the diode 4 is connected to the other end of the resistor 3 not connected to the MOS2. Then, the cathode of the diode 4 is connected to the source of the MOS1, and the gate drive circuit is connected to the gate of the MOS1. (A P-type MOS can also be used.)

Now, a positive voltage is applied to the drain of the MOS1 and a negative voltage is applied to the source, the gate voltage is negative with respect to the source, and the MOS1 is in a non-conductive state. Since the power supply voltage is applied to both ends of the MOS1, the gate voltage of the enhancement type MOS2 is
The voltage is equal to or higher than the threshold voltage of S2, and MOS2 is conductive. Although the gate voltage of MOS1 is negative with respect to the source, the diode 4 causes no current to flow from the source of MOS1 to the gate (between the source and drain of MOS2).

Next, in order to make the gate voltage of the MOS 1 higher than the threshold voltage and to make the MOS 1 conductive, the MOS 1
When a positive voltage is applied to the gate of 1 and the source, the gate current flows through the MOS 2, the resistor 3, and the diode 4 to the source of the MOS 1 because the MOS 2 is initially conductive. . Due to the gate current, a voltage drop generated in the resistor 3 becomes equal to or higher than the threshold voltage of the MOS1, and when the gate voltage becomes equal to or higher than the threshold voltage, the MOS1 is turned on.

When a normal current flows through the MOS 1 in the conductive state, the drain-source voltage of the MOS 1 becomes several volts (volts). Thereby, when the gate voltage of the MOS2 connected to the gate of the MOS1 becomes lower than the threshold voltage of the MOS2, the MOS2 is turned off and the MOS1 is turned off.
Stops the gate current from flowing to the source.

Accordingly, when a positive voltage is applied to the gate of the MOS1 with respect to the source to make the MOS1 conductive, the gate current of the MOS1 is changed until the MOS2 changes from the conductive state to the nonconductive state. Through the gate to the source, a gate current that is many times larger than the current that only charges the gate of MOS1 flows.

When a negative voltage is applied to the gate of the MOS1 in the conductive state with respect to the source to make the MOS1 nonconductive, if the gate voltage of the MOS1 drops, the gate voltage is still higher than the source. Although positive, the voltage between the drain and the source increases, the gate voltage of the MOS2 becomes higher than the threshold voltage, and the MOS2 changes from the non-conductive state to the conductive state. At that time, the gate current of the MOS1 becomes M
Since the current flows through OS2 to the source, a gate current that is many times larger than the discharge current of the gate of MOS1 flows.

For this reason, there is a problem that a driving circuit having a current capacity several times larger than that of a normal gate driving circuit of a power MOS is required.

Next, a semiconductor protection device according to the present invention will be described with reference to FIG. The gate of the N-type MOS 1 is connected to the drain of the N-type enhancement type MOS 2, the source of the MOS 2 is connected to the resistor 3, the other end of the resistor 3 not connected to the MOS 2 is connected to the anode of the diode 4, Is connected to the drain of an N-type depletion type MOS5 (hereinafter, referred to as MOS5), the source of MOS5 is connected to the source of MOS1, the gate of MOS2 is connected to the resistor 8, and the gate of MOS2 is connected to the resistor 8. The other end is connected to the drain of MOS1, the gate of MOS2 is connected to the anode of diode 9, the cathode of diode 9 is connected to the drain of MOS1, and the gate of MOS2 is simultaneously connected to the capacitor. The other end of the capacitor 10 that is not connected to the gate of MOS2 is connected to the source of MOS1. Connected to MOS5
Is connected to the resistor 6, the other end of the resistor 6 not connected to the gate of the MOS5 is connected to the gate of the MOS1, and at the same time, the gate of the MOS5 is connected to the capacitor 7, The other end that is not connected to the gate is connected to the source of MOS1, and the gate drive circuit is connected to the gate of MOS1.

Now, a positive voltage is applied to the drain of the MOS1 and a negative voltage is applied to the source, the gate voltage is negative with respect to the source, and the MOS1 is in a non-conductive state. Since the power supply voltage is applied to both ends of the MOS1, the gate voltage of the MOS2 is equal to or higher than the threshold voltage of the MOS2, and the MOS2 is in a conductive state. Although the gate voltage of the MOS 1 is negative with respect to the source, the diode 4 causes no current to flow from the source of the MOS 1 to the gate.

Since the gate voltage of MOS1 is negative with respect to the source, the gate voltage of MOS5 is also
The voltage is negative with respect to the source of the MOS 5, and the capacitor 7 is also charged with the voltage.

Therefore, the gate voltage of MOS1 is
When a positive voltage is applied to the gate of MOS1 with respect to the source in order to make the MOS1 conductive by setting the threshold voltage of 1 or higher, MOS2 is conductive at first, but the gate voltage of MOS5 is , MOS5 is in a non-conductive state with respect to the current from the drain to the source of MOS5.
Then, through the resistor 6, the capacitor 7 and the gate of the MOS 5 are charged, and the MOS 5 is in a non-conductive state until the gate voltage of the MOS 5 becomes equal to or higher than the threshold voltage.

While the MOS 5 is not conducting, the MOS 5
1 can be charged above the threshold voltage, and at the same time, the charging voltage of the gate of MOS2 and the capacitor 10 is rapidly discharged through the diode 9, so that MOS2 is brought out of conduction. Since the gate is turned off, the gate can be started up and the MOS1 can be turned on with a gate current sufficient to charge the gate of the MOS1. Thus, the resistance 3
Can use a resistor having a smaller resistance value than the resistor 3 in FIG. 4 (conventional example).

Next, when a negative voltage is applied to the gate of the MOS1 in the conductive state with respect to the source to make the MOS1 nonconductive, when the gate voltage of the MOS1 falls, the gate voltage becomes higher than the source. While the voltage is still positive, the voltage between the drain and the source increases, but until the capacitor 10 connected to the gate of the MOS 2 is charged by the charging current through the resistor 8 to a voltage higher than the threshold voltage of the MOS 2, Is in a non-conductive state. While the MOS2 is in the non-conductive state, the gate voltage of the MOS1 can be discharged to be equal to or lower than the threshold voltage. Can be turned off.

Also, when an overcurrent flows through the conductive MOS1 and the drain-source voltage of the MOS1 increases, the gate voltage of the MOS2 becomes higher than the threshold voltage of the MOS2. Becomes MOS
The gate voltage of No. 1 falls below the threshold voltage of MOS1, and MOS1 is turned off. And MOS1
Cuts off the overcurrent.

The MOS1 is required to have a delay property that does not cut off a short-time overcurrent within a range allowable for the load circuit protected by the MOS1,
Even if an overcurrent flows to the MOS 1 and the drain-source voltage of the MOS 1 increases, the capacitor 10 connected to the gate of the MOS 2
It is in a non-conductive state until it is charged above the threshold voltage of OS2, and MOS1 is not cut off. Therefore, by changing the time constant of the resistor 8 and the capacitor 10, the delay of the cutoff of the MOS 1 can be adjusted according to the load circuit to be protected.

Next, another embodiment of the present invention will be described with reference to FIG. Parts that are the same as in the embodiment of FIG. 1 are given the same numbers. N-type depletion type M at the gate of N-type MOS1
Connect the drain of OS11 and connect a resistor 3 to the source of MOS11.
And the drain of the P-type depletion-type MOS 12 is connected to the other end of the resistor 3 not connected to the MOS 11,
The source of the MOS12 is connected to the source of the P-type depletion type MOS13, the drain of the MOS13 is connected to the drain of the MOS5, the source of the MOS5 is connected to the source of the N-type depletion type MOS14, and the drain of the MOS14 is connected to the source of the MOS1. The gate of the MOS11 is connected to the resistor 8, and the other end of the resistor 8 not connected to the gate of the MOS11 is connected to the drain of the MOS1.
The gate of S11 is connected to the anode of diode 9, the cathode of diode 9 is connected to the drain of MOS1,
At the same time, the gate of MOS11 is connected to the capacitor 10,
The other end of the capacitor 10 not connected to the gate of the MOS 11 is connected to the source of the MOS 1, the gate of the MOS 5 is connected to the resistor 6, and the other end of the resistor 6 not connected to the gate of the MOS 5 is At the same time, the gate of the MOS5 is connected to the capacitor 7, and the other end of the capacitor 7, which is not connected to the gate of the MOS5, is connected to the source of the MOS1 .
The gate is connected to the gate of MOS1, and the gate drive circuit is connected to the gate of MOS1.

In this embodiment, the enhancement type MOS 2 of the embodiment of FIG. 1 is replaced with a depletion type N-type MOS.
The diode 4 is replaced by a depletion-type P-type MOS 12 and an N-type MOS 14 in 11 and a P-type MOS 13.

First, the function of the N-type MOS 14 and the P-type MOS 12 will be described. With the above connection, N-type MOS
In the P-type MOS 14 and the P-type MOS 12, the voltage drop in the P-type MOS 12 becomes the gate voltage of the N-type MOS 14, and the voltage drop in the N-type MOS 14 becomes the gate voltage of the P-type MOS 12. MOS
When the gate voltage of 1 is negative with respect to the source,
The gate voltage is between the drain (plus) of the N-type MOS 14 and P
This is applied between the drain (minus) of the type MOS 12. When a gate voltage greater than the sum of the threshold voltages (absolute values) of the N-type MOS 14 and the P-type MOS 12 is applied, the voltage drop in the P-type MOS 12 becomes larger (as an absolute value) than the threshold voltage of the N-type MOS 14, Since the voltage drop in the p-type MOS 14 becomes larger than the threshold voltage of the p-type MOS 12,
The N-type MOS 14 and the P-type MOS 12 are turned off. As a result, the N-type MOS 14 and the P-type MOS 12
Since the current flowing from the source 1 to the gate can be stopped, the diode 4 functions.

Next, the function of the N-type MOS 11 and the P-type MOS 13 will be described. When the gate voltage of MOS1 is positive with respect to the source, the gate voltage is
It is applied between the drain 11 (plus) and the drain (minus) of the P-type MOS 13. When a gate voltage greater than the sum of the threshold voltage (absolute value) of the N-type MOS 11 and the P-type MOS 13 is applied to the potential difference of the MOS 1 in the conductive state, and the MOS 1 is turned on, the N-type MOS
Since the voltage drop at 11 becomes the gate voltage of the P-type MOS 13 and the voltage drop obtained by subtracting the potential difference at the MOS 1 in the conductive state from the voltage drop at the P-type MOS 13 becomes the gate voltage of the N-type MOS 11, MOS11 and P
The gate voltage of the type MOS 13 becomes larger than the respective threshold voltages (absolute values), and the N-type MOS 11 and the P-type MOS 13
Becomes non-conductive. As a result, the N-type MOS 11
The P-type MOS 13 can stop the current flowing from the gate of the MOS 1 to the source, so that the enhancement type MOS 2 works.

Therefore, when a positive voltage is applied to the drain and a negative voltage is applied to the source of the MOS 1 and the gate voltage is negative with respect to the source and the MOS 1 is in a non-conductive state, the N-type MOS 14 and the P-type MOS 12 are in a non-conductive state. become,
No current flows from the source of MOS1 to the gate.

Then, the gate voltage of the MOS 1 is
When a positive voltage is applied to the gate of the MOS1 with respect to the source in order to make the MOS1 conductive by setting the threshold voltage of 1 or more, while the MOS5 is in the nonconductive state,
The gate voltage of the MOS 1 can be charged to be higher than the threshold voltage, and at the same time, the charging voltage of the gate of the N-type MOS 11 and the capacitor 10 is rapidly discharged through the diode 9, so that the N-type MOS 11 From the conducting state to the non-conducting state, and the P-type MOS 13 also becomes non-conducting state. Therefore, as in the embodiment of FIG.
S1 can be made conductive.

When a negative voltage is applied to the source of the MOS1 to apply a negative voltage to the source to make the MOS1 nonconductive, if the gate voltage of the MOS1 drops, the gate voltage is still higher than the source. While the voltage is positive, the drain-source voltage increases, but the capacitor 10 connected to the gate of the N-type MOS 11 is charged by the charging current passing through the resistor 8 to a voltage higher than the threshold voltage of the N-type MOS 11. Until then, the N-type MOS 11 and the P-type MOS 13 are in a non-conductive state. While the N-type MOS 11 and the P-type MOS 13 are in a non-conductive state, the gate voltage of the MOS 1 can be discharged to be equal to or lower than the threshold voltage.
Substantially, the gate is lowered by the gate current of only the discharge current of the gate of the MOS1, and the MOS1 can be turned off.

Also, when an overcurrent flows through the conductive MOS 1 and the drain-source voltage of the MOS 1 increases, the gate voltage of the MOS 11 becomes higher than the threshold voltage of the MOS 11. become. MOS
When the MOS transistor 11 is turned on, the MOS 13 is also turned on, and M
The gate voltage of OS1 falls below the threshold voltage of MOS1, and MOS1 is turned off. And MOS
1 shuts off the overcurrent.

Then, an overcurrent flows through the MOS 1 and the MO 1
Even if the drain-source voltage of S1 increases, the MOS
The MOS transistor 1 is not turned off until the capacitor 10 connected to the gate of the MOS transistor 11 is charged by the current flowing through the resistor 8 to a voltage higher than the threshold voltage of the MOS 11. Therefore, by changing the time constant of the resistor 8 and the capacitor 10, the delay of the cutoff of the MOS 1 can be adjusted according to the load circuit to be protected.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment is different from the embodiment of FIG. 2 in that when an overcurrent flows through the MOS1 between the gate of the MOS1 and the gate drive circuit and the MOS1 is cut off,
It has a circuit for interrupting the gate and the gate current flowing to the source. In this embodiment, the same parts as those in the embodiment of FIG. 2 will not be described, and the connection and function of the added circuits will be described.

The drain of the depletion type N-type MOS 16 is connected to the gate drive circuit, the source of the N-type MOS 16 is connected to the source of the depletion type P-type MOS 15,
The drain of the P-type MOS 15 is connected to the gate of the MOS 1, the resistor 17 is connected to the gate of the N-type MOS 16, the other end of the resistor 17 not connected to the gate of the MOS 16 is connected to the drain of the MOS 15, The capacitor 18 is connected to the gate of the MOS 16, and the other end of the capacitor 18 that is not connected to the gate of the MOS 16 is connected to the drain of the MOS 16,
The resistor 19 is connected to the gate of the MOS15, and the MOS15 of the resistor 19 is connected.
Is connected to the drain of the MOS16.

Now, an overcurrent flows through the conductive MOS1 and the MOS11 and the MOS13 become conductive.
The gate voltage of the MOS transistor falls below the threshold voltage of the MOS1,
When MOS1 cuts off the overcurrent, the gate drive circuit
Since the gate drive circuit is still operating, a gate current tends to flow from the gate drive circuit to the gate of the MOS 1 and to the source. However, the gate voltage of the gate drive circuit is reduced by the drain (plus) of the N-type MOS 16 and the P-type MOS 15. When the voltage is applied between the drain (negative), the gate voltage becomes N-type MOS 16 and P-type.
Since it is larger than the sum of the threshold voltages (absolute values) of the type MOS 15, the N-type MOS 16 and the P-type MOS 15 are turned off. As a result, the gate current when the MOS 1 interrupts the overcurrent can be stopped.

Resistance connected to the gate of N-type MOS 16
N-type MOS by the time constant of 17 and capacitor 18
By adjusting the time constant, the N-type MOS 16 and the P-type MOS 15 remain conductive when the normal current flows, since the time from when the conductive 16 changes to the non-conductive state can be changed. Only when the current flows and the MOS1 is cut off, it can be turned off.

[0034]

The present invention is configured as described above, and has the following effects.

Even if the protection circuit of the present invention is connected to a power MOS, an ordinary gate drive circuit can be used as it is.

Since the portion where the gate current flows can be constituted by a depletion type N-type MOS or a P-type MOS, a protective device having stable temperature characteristics can be provided.

The delay of the cutoff of the MOS1 can be adjusted in accordance with the load circuit protected by the MOS1.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor protection device according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the semiconductor protection device of the present invention.

FIG. 3 is a circuit diagram showing an embodiment of the semiconductor protection device of the present invention.

FIG. 4 is a circuit diagram showing a conventional semiconductor protection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Power MOS 2 Enhancement type MOS 3, 6, 8, 17, 19 Resistor 4, 9 Diode 5, 11, 12, 13, 14, 15, 16 Depletion type M
OS 7, 10, 18 Condenser

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/04 H01L 27/06-27/06 101 H01L 27/08-27/08 101 H02H 3/08- 3/253 H02H 7/20 H02H 9/00-9/08 H03K 17/00-17/70

Claims (3)

(57) [Claims] 1. The drain of an N-type enhancement type MOS (2) is connected to the gate of the N-type enhancement type MOS (1), the resistor (3) is connected to the source of the MOS (2), and the resistance of the resistor (3) is The anode of the diode (4) is connected to the other end not connected to the MOS (2), and the cathode of the diode (4) is connected to an N-type depletion type MOS.
Connected to the drain of (5) and the source of MOS (5) is M
The gate of the MOS (2) is connected to the resistor (8), and the other end of the resistor (8) that is not connected to the gate of the MOS (2) is connected to the source of the OS (1). The gate of the MOS (2) is connected to the anode of the diode (9), and the cathode of the diode (9) is connected to the drain of the MOS (1).
The gate of (2) is connected to the capacitor (10), and the other end of the capacitor (10) that is not connected to the gate of the MOS (2) is connected to the source of the MOS (1).
Is connected to the resistor (6), and the MOS of the resistor (6) is connected.
The other end not connected to the gate of (5) is MOS (1)
At the same time, the gate of the MOS (5) is connected to the capacitor (7), and the MO of the capacitor (7) is
The other end not connected to the gate of S (5) is MOS
(1) Connect to the source, connect the gate drive circuit to the gate of the MOS (1), keep the non-conductive state when normal current flows from the drain to the source of the MOS (1), Without flowing the gate drive current to the source of the MOS (1), the transistor becomes conductive when an overcurrent flows, and the gate drive current from the gate drive circuit flows to the source of the MOS (1) to
Reduce the gate voltage of S (1) below the threshold voltage
A semiconductor protection device that protects MOS (1) by setting (1) in a non-conductive state. 2. The drain of an N-type depletion type MOS (11) is connected to the gate of an N-type MOS (1).
A resistor (3) is connected to the source of (11), and M of the resistor (3) is connected.
The drain of the P-type depletion type MOS (12) is connected to the other end not connected to the OS (11), and the MOS (12)
The source of the P-type depletion type MOS (13) is connected to the source of the MOS (13), the drain of the MOS (5) is connected to the drain of the MOS (13), and the source of the N-type depletion type MOS (14) is connected to the source of the MOS (5). Connect source and MOS
The drain of (14) is connected to the source of MOS (1),
The gate of the OS (11) is connected to the resistor (8), and the resistor (8)
Of the MOS (11) that is not connected to the gate is M
The drain of the OS (1) is connected, the gate of the MOS (11) is connected to the anode of the diode (9), and the cathode of the diode (9) is connected to the drain of the MOS (1). The gate of (11) is connected to the capacitor (10), the other end of the capacitor (10) not connected to the gate of the MOS (11) is connected to the source of the MOS (1), and the gate of the MOS (5) is connected. Is connected to the resistor (6), and the other end of the resistor (6) that is not connected to the gate of the MOS (5) is connected to the gate of the MOS (1).
The gate of the OS (5) is connected to the capacitor (7), and the other end of the capacitor (7) that is not connected to the gate of the MOS (5) is connected to the source of the MOS (1).
A gate drive circuit is connected to the gate of (1). When a normal current flows from the drain to the source of the MOS (1), the gate drive circuit is kept in a non-conductive state, and the gate drive current from the gate drive circuit is supplied to the MOS (1). When an overcurrent flows without flowing to the source, the state becomes conductive, and the gate drive current from the gate drive circuit flows to the source of the MOS (1) to cause
Reduce the gate voltage of S (1) below the threshold voltage
A semiconductor protection device that protects MOS (1) by setting (1) in a non-conductive state. 3. The depletion type N-type MOS (16) has a drain connected to a gate drive circuit and an N-type MOS (16).
Is connected to the source of the depletion type P-type MOS (15), and the drain of the P-type MOS (15) is
The resistor (17) is connected to the gate of the N-type MOS (16), and the other end of the resistor (17) that is not connected to the gate of the MOS (16) is connected to the MOS (15). The capacitor (18) is connected to the gate of the MOS (16), and the other end of the capacitor (18) that is not connected to the gate of the MOS (16) is connected to the drain of the MOS (16). The resistor (19) is connected to the gate of the MOS (15), and the other end of the resistor (19) that is not connected to the gate of the MOS (15) is connected to the drain of the MOS (16). When a normal current flows from the drain to the source in (1), the conduction state is maintained, and the gate drive current from the gate drive circuit flows to the gate of the MOS (1), and an overcurrent flows to cause the MOS (1) to flow. When shut off, it becomes non-conductive,
3. The semiconductor protection device according to claim 2, wherein a circuit for stopping a gate drive current from the gate drive circuit from flowing to the gate of the MOS (1) is connected between the gate of the MOS (1) and the gate drive circuit.