JP3113931B2 - Overcurrent 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 overcurrent protection device for protecting a load circuit from overcurrent.

[0002]

2. Description of the Related Art Fuses, breakers, and the like are used as devices connected in series to a load to protect the load from overcurrent.

[0003]

A fuse or a breaker causes a rush current when power is turned on to flow to a load as it is. Also, when an overcurrent flows, even for a short time,
Overcurrent flows through the load circuit. Whenever a rush current or an overcurrent flows, there is a problem that a stress is applied to a normal circuit component, the component is deteriorated, and this causes a failure of a new load circuit.

When the rush current is about to flow, the inventor suppresses the rush current to about 1.5 to 2 times the steady current until the rush current state at the time of turning on the power is completed. , And also, if an overcurrent is about to flow, for a period of time, 1.
An overcurrent protection device that suppresses overcurrent by about 5 to 2 times, and when the overcurrent state ends in a short time, then supplies a steady current, and when the overcurrent state continues, shuts off the circuit. Flat 4
-98351.

The inventor's earlier invention is a two-terminal overcurrent protection device in which an overcurrent cutoff circuit is connected between the gate and the drain of an enhancement type MOS. 2 of structure that becomes voltage
When a voltage is gradually applied between the source and the drain of the enhancement type MOS because it is a terminal, the drain current does not flow at first, and the voltage drop (gate voltage) between the source and the drain becomes higher than the threshold voltage. Become,
Start flowing. Therefore, when a steady current (rated current) flows, the voltage drop between the source and the drain becomes about 1.5 V.

The present invention relates to an overcurrent protection device in which an overcurrent cutoff circuit is connected between the gate and the drain of an enhancement type MOS. The device has a three-terminal structure for supplying a gate voltage from another place. It is an object of the present invention to provide an overcurrent protection device in which a gate voltage is set to a threshold voltage or more and a voltage drop between a source and a drain when a steady current flows is about 0.8 V.

[0007]

Means for Solving the Problems The overcurrent protection device of the present invention is configured as follows. An N-type and P-type depletion-type MOS is formed. When a voltage is applied, a current starts flowing, and one end of an overcurrent cut-off circuit that cuts off when a current of a predetermined magnitude or more flows is connected to an enhancement-type MO.
The gate of the enhancement type MOS is connected to the gate of S through the other end of the overcurrent cutoff circuit through a constant current circuit.
The voltage can be higher than the threshold voltage.
And at the same time connected to a feed point of kill the gate voltage, connected to the drain of the enhancement type MOS through the diode, and is obtained by connecting a resistor and zener diode in parallel between the source and the gate of the enhancement type MOS. The other end of the constant current circuit connected to the gate of the enhancement type MOS and the enhancement type M
The source and drain of the OS are three terminals.

[0008]

The overcurrent protection device constructed as described above is connected to a portion of the load circuit to be protected, and when a current flows through the load circuit, the constant current connected to the gate of the enhancement type MOS of the overcurrent protection device. A constant current from the circuit flows through the resistance and the Zener diode between the source and the gate of the enhancement MOS. When the Zener voltage of the Zener diode is set to be equal to or higher than the threshold voltage of the enhancement type MOS, the gate voltage becomes equal to or higher than the threshold voltage. A steady current of the circuit can flow.

When an overcurrent flows through the load circuit, the voltage drop between the source and the drain of the enhancement type MOS increases. When the voltage drop between the source and the drain exceeds the gate voltage, the overcurrent cutoff circuit supplies a diode through the diode. Current starts to flow to the drain of the enhancement type MOS. When the current flowing to the drain through the diode increases, the current flowing in the overcurrent cutoff circuit increases, and the overcurrent cutoff circuit is cut off.

When the overcurrent cutoff circuit is cut off, the resistance between the source and the gate of the enhancement type MOS and the current flowing through the Zener diode are cut off, so that the gate voltage becomes 0 V and the enhancement type MOS is cut off.

Therefore, when an overcurrent of a certain magnitude or more flows through the load circuit, the enhancement-type MOS is cut off, so that this device functions as an overcurrent protection.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the overcurrent protection device of the present invention will be described.
This will be described with reference to FIG. P-type enhancement type MOS
A Zener diode 2 and a resistor 3 are connected in parallel between a source and a gate of the PES 1 (hereinafter abbreviated as P-type EMOS).
The anode of the Zener diode 2 is connected to the gate and the cathode is connected to the source. A resistor 4 and a P-type depletion type MOS (hereinafter referred to as P-type DMO) are connected to the gate of the P-type EMOS 1.
S is abbreviated as S). P-type DMO
The source of S5 is connected to the gate of the P-type EMOS1 through the resistor 4, and the gate of the P-type DMOS5 is connected to the P-type EMOS1.
Connect to the gate of This constant current circuit will be referred to as a second constant current circuit for the sake of simplicity.

An overcurrent cutoff circuit is connected to the drain of the P-type DMOS 5. The overcurrent cutoff circuit connects the source of the N-type DMOS 9 to the source of the P-type DMOS 10 and
9 is connected to the N-type DMOS 9 through the capacitor 7.
Connected to the drain of a P-type DMOS 10 through a resistor 8, and the gate of the P-type DMOS 10
Is connected to the drain of the N-type DMOS 9 through the gate. The drain of the P-type DMOS 5 and the drain of the N-type DMOS 9 are connected.

A constant current circuit is connected to the drain of the P-type DMOS 10 of the overcurrent cutoff circuit. The source of the P-type DMOS 13 is connected to the drain of the P-type DMOS 10 through the resistor 12, and the gate of the P-type DMOS 13 is connected to the drain of the P-type DMOS 10. This constant current circuit is referred to as a first constant current circuit. The drain of the P-type DMOS 10 is a diode
11 to the drain of the P-type EMOS1. The anode of the diode 11 is connected to the drain of the P-type DMOS 10, and the cathode is connected to the drain of the P-type EMOS 1.

The source of the P-type EMOS 1 is a terminal S,
This is a three-terminal overcurrent protection device in which the drain of the type EMOS1 is the terminal D and the drain of the P-type DMOS13 of the first constant current circuit is the terminal G.

The constant current capacity of the second constant current circuit is about 1.3 to 5 times the constant current capacity of the first constant current circuit, and the breaking current capacity of the overcurrent breaking circuit is the first constant current circuit. It is larger than the constant current capacity of the current circuit and smaller than the constant current capacity of the second constant current circuit.

As shown in FIG. 1, the terminal S of this overcurrent protection device is connected to a positive (+) power supply, the terminal D is connected to a load circuit to be protected, and the terminal G is connected to ground (gate voltage supply point). Connecting. The other end of the load circuit is connected to the ground.

Assuming that the plus power supply is turned on, first, a current flows through the gate circuit of the P-type EMOS1. The current from the positive power supply is a Zener diode 2, a resistor 3, a second constant current circuit, an overcurrent cutoff circuit, and a first
Flows to the ground through the constant current circuit. With the constant current of the first constant current circuit, a P-type EMOS 1
If the constant current capacity of the first constant current circuit and the capacity of the Zener diode 2 and the resistor 3 are set so that a constant potential difference equal to or greater than the threshold voltage of the P-type EMOS 1 is obtained, this potential difference Become a P-type EMOS
1 conducts and causes a current (drain current) to flow through the load circuit.

First, a description will be given of the static characteristic of the current cutoff of the overcurrent protection device. P-type EMO in a conductive state in which the gate voltage has become a constant voltage equal to or higher than the threshold voltage
When a positive voltage is applied to the source of S1 and a negative voltage is applied to the drain and the voltage is gradually increased, the drain current of the P-type EMOS1 gradually increases in the linear region. However, when the voltage is further increased, the drain current increases in the saturation region. It becomes constant. When the voltage is continuously increased, the drain current is constant. However, when the voltage drop (source / drain voltage) in the P-type EMOS 1 increases, and when the source / drain voltage becomes higher than the gate voltage, the diode 11 becomes conductive. As a result, a large current flows through the gate circuit.

When the current of the gate circuit is N-type DMOS 9 and P-type
When the current exceeds the breaking current value of the overcurrent breaking circuit of the type DMOS 10, the N-type DMOS 9 and the P-type DMOS 10
The current of the gate circuit is cut off, the gate voltage becomes 0 V, and the P-type EMOS 1 is cut off.

FIGS. 2 and 3 show the static characteristics of the current interruption.
Shown in The P-type EMOS 1 has a source / drain voltage of about 0.8 V, a drain current of 2 A, a source / drain voltage of about 1.6 V, and a drain current of 4 A. Then, the source / drain voltage is increased from about 1.6V to about 4.3V.
At V, the drain current saturates at 4A, and when the source-drain voltage rises above about 4.3V and exceeds the gate voltage, diode 11 conducts and the drain current shuts off.

The overcurrent cutoff circuit will be described. N type D
Connect the source of MOS9 and the source of P-type DMOS10,
The gate of the N-type DMOS 9 is
Connected to the drain of a P-type DMOS 9 and simultaneously connected to the drain of a P-type
Since the gate of 10 is connected to the drain of the N-type DMOS 9 through the resistor 6, the potential difference in the P-type DMOS 10 becomes the gate voltage of the N-type DMOS 9 and the N-type DMOS 9
The potential difference at 9 becomes the gate voltage of the P-type DMOS 10.

Therefore, when a positive voltage is applied to the drain of the N-type DMOS 9 and a negative voltage is applied to the drain of the P-type DMOS 10 and the voltage is gradually increased, the current gradually increases, but when the current increases, the N-type DMOS 9 and the P-type DMO
The potential difference at S10 increases, and thereby the respective gate voltages of P-type DMOS 10 and N-type DMOS 9 increase. Therefore, the current increases linearly up to a certain value, but when the current exceeds a certain value, the gate voltage increases and the N-type DMOS 9 and the P-type DMOS 10
Comes to suppress the current, and the potential difference becomes larger. When the individual potential difference becomes larger, the respective gate voltages are repeatedly increased, whereby the N-type DMOS 9 and the P-type DMOS 10 cut off the current.

Although this overcurrent cutoff circuit requires a certain degree of delay, since the capacitor 7 and the resistor 8 are connected in series to the gate of the N-type DMOS 9, the time constant of the capacitor 7 and the resistor 8 is reduced. The blocking can be delayed for a proportional amount of time. By changing the size of the capacitor 7 and the resistance 8, the cutoff time (delay) can be adjusted. The current value cut off by the overcurrent cutoff circuit is set to be larger than the steady current capacity of the first constant current circuit and smaller than the steady current capacity of the second constant current circuit.

A case where a rush current flows will be described. When the power is turned on and a rush current is about to flow in the load circuit, the source / drain voltage of the P-type EMOS1 is still large at first, so that the current flows to the gate circuit of the P-type EMOS1 through the first constant current circuit. At the same time as the steady current, a large current tends to flow through the diode 11, and the second constant current circuit suppresses the current to the magnitude of the constant current.

Therefore, since a current larger than the constant current by the second constant current circuit does not flow through the Zener diode 2 and the resistor 3 connected in parallel, the gate voltage is changed to the Zener voltage of the Zener diode 2 by a rush current. It can be kept almost constant even at the time of current.
Flows the drain current 4A in the saturation region as a rush current. When the rush current state of the load circuit ends and a steady current is reached, the source of the P-type EMOS 1
The drain voltage becomes about 0.8 V, the diode 11 also becomes non-conductive, and the current of the gate circuit of the P-type EMOS 1 becomes
It becomes the constant current of the first constant current circuit.

FIG. 4 shows the state of the rush current.
The solid line is the rush current of this overcurrent protection device. When the power is turned on, the rush current rises to 4 A, flows for about 0.3 mS at 4 A, and then gradually decreases to about 2 mS, a steady current of 2 A. The dashed line is the rush current of the load circuit not using this overcurrent protection device. When the power is turned on, it rises to about 10 A, drops to 4 A at about 0.2 mS, and reaches a steady current of 2 A at about 1 mS.

A case where an overcurrent flows will be described.
Now, if a steady current is flowing and an overcurrent suddenly flows,
The drain current of the P-type EMOS 1 changes from 2A in the linear region to 4A in the saturation region, and returns to 2A of the steady current when the overcurrent ends within the allowable delay time.
If overcurrent continues for longer than the allowable delay time, P-type EMO
S1 cuts off the overcurrent after an allowable delay time.

FIG. 5 shows the state of the overcurrent. The solid line is
This is the case where the overcurrent protection device cuts off the overcurrent. When an overcurrent flows, it rises from 2A of the steady current to 4A, flows 4A for an allowable delay time, and
Later, the overcurrent is shut off. The broken line indicates a case where the overcurrent of the load circuit is cut off by a fuse or a breaker without using the overcurrent protection device. From 2A of steady current,
After rising to 8A, 8A flows as it is, and after 1 mS, a fuse or a breaker or the like is cut off to cut off an overcurrent.

In this embodiment, a P-type EMOS is used, but an N-type EMOS is used. The first constant current circuit, the overcurrent cutoff circuit, the second constant current circuit, etc. S
The overcurrent protection device may be configured to connect a negative voltage to the terminal and a positive voltage to the terminals D and G.

[0031]

Since the present invention is configured as described above, it exhibits the following effects.

When a steady-state drain current flows, the voltage drop in this overcurrent protection device is about 0.8 V or less, so even if it is connected in series to a load circuit requiring protection, It can be easily used in various places without affecting the voltage of the circuit.

When this overcurrent protection device is connected in series to a load circuit through which a rush current of 5 times and 10 times the steady current flows, the rush current can be suppressed to about twice the steady current. In addition, the steady-state current of 4
When the overcurrent flows twice or more times, if this overcurrent protection device is connected in series with the load circuit, the overcurrent can be suppressed to about twice as much as the steady-state current and cut off. Therefore, this overcurrent protection device can prevent a rush current or an overcurrent from stressing normal circuit components and deteriorating the components. Reliability can be greatly improved.

Capacitor 7 and resistor 8 of overcurrent cutoff circuit
By changing the size of the overcurrent protection device, the cutoff time (delay) of the overcurrent protection device can be adjusted according to the characteristics of the load circuit.

By changing the Zener voltage of the Zener diode of the gate circuit of the P-type EMOS 1 and the constant current capacity of the first and second constant current circuits, the magnitude of the rush current or overcurrent can be changed to the load circuit. In addition, it can be adjusted to 1.5 times, 2 times, or 3 times the steady state current.

By changing the voltage / current capacity (characteristic) of the P-type EMOS 1 and changing the voltage / current capacity of each part of the gate circuit in accordance with the change, the rated voltage can be changed from several tens of volts to several thousand volts.
Overcurrent protection devices of various capacities having a rated current of several mA to several tens A can be formed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overcurrent protection device.

FIG. 2 is a diagram showing a drain current of static characteristics of a current interruption of the overcurrent protection device.

FIG. 3 is a diagram showing a drain voltage of a static characteristic of a current interruption of the overcurrent protection device.

FIG. 4 is a diagram showing a rush current characteristic of the overcurrent protection device.

FIG. 5 is a diagram showing interruption of overcurrent by the overcurrent protection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 P-type EMOS 5, 10, 13 P-type DMOS 9 N-type DMOS 2 Zener diode 3, 4, 6, 8, 12 Resistance 7 Capacitor 11 Diode

Continued on the front page (58) Fields 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 (6)

(57) [Claims] 1. A zener diode (2) and a resistor (3) having opposite directions connected in parallel between a source and a gate of a P-type enhancement type MOS (1). -One end of a second constant current circuit for keeping the gate current of the P-type enhancement MOS (1) flowing through the diode (2) and the resistor (3) constant.
The other end of the second constant current circuit is connected to the gate of the P-type enhancement type MOS (1), and the other end of the overcurrent cutoff circuit that cuts off when a current of a predetermined magnitude or more flows. A forward diode (11) connected to conduct when the overcurrent flows through the other end of the overcurrent cutoff circuit (11)
Through the gate, and at the same time, when a normal current flows, a constant current for making the gate voltage of the P-type enhancement type (1) a constant voltage equal to or higher than the threshold voltage is applied. 1, the other end (terminal G) of the first constant current circuit is connected to the ground (-), and the source (terminal S) of the P-type enhancement type (1) is connected. Is connected to a plus (+) power supply, the drain (terminal D) is connected to one end of the load circuit, the other end of the load circuit is connected to ground (-), and a P-type enhancement MOS (1) When an overcurrent flows from the source to the load circuit, the gate current of the P-type enhancement MOS (1) becomes constant by the second constant current circuit, and the gate voltage becomes the Zener current of the Zener diode (11). It is held in the P-type enhancement type MO
When S (1) suppresses the overcurrent and the overcurrent continues for a long time, the overcurrent cutoff circuit cuts off the gate current of the P-type enhancement type MOS (1) which is increased by the conduction of the diode (11) and the P-type. An overcurrent protection device in which the enhancement type MOS (1) blocks overcurrent. 2. The source of a P-type depletion type MOS (5) is connected to the gate of a P-type enhancement type MOS (1) via a resistor (4), and the gate of the P-type depletion type MOS (5) is connected to the P-type enhancement type. MO
2. The overcurrent protection device according to claim 1, wherein a circuit connected to the gate of S (1) is a second constant current circuit. 3. The source of an N-type depletion type MOS (9) is connected to the source of a P-type depletion type MOS (10), and the gate of the N-type depletion type MOS (9) is connected to the N-type depletion type MOS through a capacitor (7). It is connected to the drain of a MOS (9), connected to the drain of a P-type depletion MOS (10) through a resistor (8), and the gate of the P-depletion MOS (10) is connected to the N-depletion through a resistor (6). MOS
N-type depletion type M connected to the drain of (9)
2. The overcurrent protection device according to claim 1, wherein the drain of the OS (9) is connected to the drain of the P-type depletion type MOS (5) of the second constant current circuit to form an overcurrent cutoff circuit. 4. A source of a P-type depletion type MOS (13) is connected to a drain of a P-type depletion type MOS (10) of an overcurrent cutoff circuit through a resistor (12).
The gate of the depletion type MOS (13) is connected to the drain of the P type depletion type MOS (10) of the overcurrent cutoff circuit, and the drain (terminal G) of the P type depletion type MOS (13) is connected to the ground (-). The overcurrent protection device according to claim 1, wherein the connected one is a first constant current circuit. 5. An anode of a diode (11) is a drain of a P-type depletion type MOS (10) of an overcurrent cutoff circuit, and a cathode is a P-type enhancement type MOS (10).
Connected to the drain of (1), the anode of the Zener diode (2) is a P-type enhancement type MOS
(1) P-type enhancement type M for gate and cathode
2. The overcurrent protection circuit according to claim 1, wherein the overcurrent protection circuit is connected to a source of the OS (1). 6. The constant current capacity of the second constant current circuit is equal to the first constant current circuit.
1.3 to 5 times the constant current capacity of the constant current circuit of
The overcurrent protection device according to claim 1, wherein a breaking current capacity of the overcurrent cutoff circuit is larger than a constant current capacity of the first constant current circuit and smaller than a second constant current capacity.