JP2000193692A - Over-current detection circuit and over-current detection/protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an overcurrent detection without using a sense resistance. SOLUTION: A standard circuit connected, in parallel with a series circuit of load L and a power MOSFETQA, is constituted by a series circuit of a standard resistance Rr and a standard MOSFETQB equivalent to the load L and the power MOSFETQA. The standard circuit detects an overcurrent flowing in the standard MOSFETQA, based on a difference of voltage between a drain/source of the standard MOSFETQB in which a standard current flows and the voltage between the drain/source of the power MOSFETQA in which magnitude of the current is varied by the overcurrent. The number of the standard MOSFETQBs is made less than that of the power MOSFETQAs, and a resistance value of the standard resistance Rr is determined so that it becomes the expression: (Resistance value of load L)×(the number of power MOSFETQAs/the number of standard MOSFETQBs).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent detection circuit and an overcurrent detection / protection circuit, and more particularly, to power semiconductor switching for controlling on / off of power supply from a power supply to a load such as an electric component for a vehicle. Power MOS as an element
The present invention relates to an overcurrent detection circuit for detecting overcurrent of an FET and an overcurrent detection / protection circuit for shutting off a power MOSFET by detecting overcurrent.

[0002]

2. Description of the Related Art Power MOSFETs (Metal Oxide Semiconductors) are used for controlling high voltages and large currents such as solenoids, lamps and switches of DC motors as automotive electrical components.
r Field Effect Transistor) and other power semiconductor switching elements are used. The power semiconductor switching element has a safe operation area determined in accordance with the magnitude of the output current and the conduction time. Excessive accidents can occur if a current exceeding this area flows for a long time or if the load is short-circuited. When a current flows, the power semiconductor switching element and the wiring are overheated and thermally destroyed. Therefore, in order to prevent such a situation from occurring, the output current and the temperature of the power semiconductor switching element are monitored, and when an overcurrent or overheating is detected, the current is limited or cut off to prevent the power semiconductor switching element from flowing. 2. Description of the Related Art There is known a device provided with a protection device for preventing overheating or destruction of a switching element or wiring.

Conventionally, as an overcurrent detection circuit for detecting that an excessive current has flown, a sense resistor is connected between the power semiconductor switching element and the load, and all of the current flowing to the load through the power semiconductor switching element is connected. To the sense resistor, a voltage corresponding to the current is generated at both ends of the sense resistor to perform current-to-voltage conversion, and when this voltage exceeds a predetermined reference voltage, an overcurrent flows. The thing which was made to detect that was generally used.

[0004]

As described above, in the case of detecting an overcurrent using a sense resistor, a large current flows through the sense resistor. In order to reduce the resistance as much as possible and to reduce heat generation in the resistor, it is necessary to use a large-capacity resistor having a small resistance value. This type of resistor is very large and is not suitable for integrating into a power semiconductor switching element to integrate it into an integrated circuit.Therefore, the size of the overcurrent detection circuit is increased, and variation between lots is large, and high accuracy detection is possible. When it is attempted to do so, it is necessary to provide a troublesome adjusting means, and this has led to an increase in cost coupled with the expensive sense resistor.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and has been made in view of the above-mentioned problems. And an overcurrent detection / protection circuit.

[0006]

According to a first aspect of the present invention, there is provided a power supply apparatus comprising a power supply M connected in series with a load, for turning on and off the connection of the load to a power supply.
An OSFET, and a reference circuit connected in parallel with the series circuit of the load and the power MOSFET, wherein the reference circuit is connected to the load and the power MOS of the series circuit.
An overcurrent flowing through the power MOSFET is detected based on a difference between a drain-source voltage of the power MOSFET and a drain-source voltage of the reference MOSFET. In the overcurrent detection circuit.

According to the configuration of the first aspect, the reference circuit connected in parallel with the series circuit of the load and the power MOSFET is constituted by a series circuit of a reference resistor and a reference MOSFET equivalent to the load and the power MOSFET. ,
The overcurrent flowing through the power MOSFET is detected based on the difference between the drain-source voltage of the reference MOSFET through which the reference current flows and the drain-source voltage of the power MOSFET whose current changes due to the overcurrent. Therefore, it is not necessary to insert a sense resistor in series with the power MOSFET, and the detection operation is performed differentially.

According to a second aspect of the present invention, in the overcurrent detection circuit according to the first aspect, the number of the reference MOSFETs is made smaller than the number of the power MOSFETs, and the resistance of the reference resistor is multiplied by the resistance of the load. (The power MOSF
(The number of ETs / the number of the reference MOSFETs).

According to the above configuration, the number of reference MOSFETs is made smaller than the number of power MOSFETs, and the resistance value of the reference resistor is changed to the resistance value of the load by the MOSFET.
T is multiplied by the number ratio of T, so that the reference MOSFE
The number of T can be reduced as compared with the power MOSFET.

According to a third aspect of the present invention, there is provided an overcurrent detection circuit according to the first or second aspect, wherein the reference circuit is formed in the same chip as the power MOSFET.

According to the third aspect of the present invention, since the reference circuit is formed in the same chip as the power MOSFET, it can be formed by the same process.

According to a fourth aspect of the present invention, in the overcurrent detection circuit according to any one of the first to third aspects, the reference MOS
The power supply side terminal and the gate terminal of the FET are connected to the power MOS.
A power supply side terminal and a gate terminal of the FET are interconnected, and a reference resistance connection terminal of the reference MOSFET is provided independently of a load connection terminal of the power MOSFET, and a potential of the reference resistance connection terminal and a potential of the load connection terminal are determined. To detect an overcurrent flowing through the power MOSFET.

According to the above configuration, the power supply side terminal and the gate terminal of the reference MOSFET are connected to the power M.
Interconnected with the power supply side terminal and the gate terminal of the OSFET,
Connect the reference resistance connection terminal of the reference MOSFET to power MOSF
The terminals are provided independently of the load connection terminals of the ET, and the terminals are shared except for those used independently.

According to a fifth aspect of the present invention, in the overcurrent detection circuit according to any one of the first to fourth aspects, a current having a value equivalent to a maximum current flowing through the power MOSFET in a normal state flows through the reference circuit. Set to the power MOS
The drain-source voltage of the FET is equal to the reference MOSFET.
An overcurrent detection circuit is characterized by detecting that an overcurrent is flowing when the voltage between the drain and the source of T is exceeded.

According to the above-described configuration, the power MOSFET is set so that a current having a value equivalent to the maximum current flowing through the power MOSFET in a normal state flows through the reference circuit.
Since the overcurrent is detected when the drain-source voltage of the FET exceeds the drain-source voltage of the reference MOSFET, the error factor can be minimized.

According to a sixth aspect of the present invention, in the overcurrent detection circuit according to any one of the first to fifth aspects, the reference resistance is selected from a plurality of resistances prepared in advance. The overcurrent detection circuit has a feature.

According to the above configuration, since the reference resistor is selected from a plurality of resistors prepared in advance, one circuit can correspond to a plurality of specifications.

According to a seventh aspect of the present invention, there is provided the overcurrent detecting circuit according to the third aspect, further comprising a terminal for connecting an adjusting resistor in parallel with the reference resistor. .

According to the above configuration, since the terminal for connecting the adjustment resistor in parallel with the reference resistor is provided, the specification can be easily set using this terminal.

The invention according to claim 8 is a power MOSFET with a temperature sensor connected in series with a load for turning on / off the connection of the load to a power supply, and a series circuit of the load and the power MOSFET with the temperature sensor in parallel. A reference circuit having a series circuit of a reference resistor and a reference MOSFET connected thereto, and
The drain-source voltage of the SFET and the reference MOSF
An overcurrent detecting means for detecting an overcurrent flowing through the power MOSFET with the temperature sensor based on a difference between a drain-source voltage of the ET, and an overcurrent detecting means for detecting the overcurrent by the overcurrent detecting means. Power MOSFET with temperature sensor and reference MOSFET until
Overcurrent detection, comprising: drive means for turning on and off the power MOSFET; and overheat cutoff means for detecting overheating by the temperature sensor of the power MOSFET with the temperature sensor and overheating the power MOSFET with the temperature sensor.・ It exists in the protection circuit.

According to the above configuration, the reference circuit connected in parallel with the series circuit of the load and the power MOSFET is constituted by a series circuit of a reference resistor and a MOSFET equivalent to the load and the power MOSFET. The drain-source voltage of the reference MOSFET through which the reference current flows, and the power M whose magnitude changes due to the overcurrent
Since the overcurrent flowing in the power MOSFET is detected based on the difference between the drain-source voltage of the OSFET, it is not necessary to insert a sense resistor in series with the power MOSFET, and the detection operation is performed differentially. Is being done. Also, according to the detection of the overcurrent by the overcurrent detection means,
The driving means turns on and off the power MOSFET with the temperature sensor and the reference MOSFET until the overcurrent detection is eliminated.
Since the power MOSFET with the temperature sensor is detected by the temperature sensor included in the power MOSFET and overheated, the current can be interrupted without external control.

According to a ninth aspect of the present invention, in the overcurrent detection / protection circuit of the eighth aspect, an on / off cycle of the driving means is used as a clock for control. Exists in the protection circuit.

According to the above configuration, since the ON / OFF cycle of the driving means is stable, it is not necessary to provide a separate clock for control.

According to a tenth aspect of the present invention, there is provided a power MOSFET connected in series with a load for turning on / off the connection of the load to a power supply, and the load and the power MOSFET.
Reference resistance and reference M connected in parallel with the series circuit of ET
An overcurrent for detecting an overcurrent flowing through the power MOSFET based on a difference between a drain-source voltage of the power MOSFET and a drain-source voltage of the reference MOSFET. Detecting means, driving means for turning on and off the power MOSFET and the reference MOSFET in response to detection of overcurrent by the overcurrent detecting means until the overcurrent detection is eliminated, and on / off times by the driving means And when the result of the integration exceeds a certain value, the power M
An overcurrent detection / protection circuit according to the above description, further comprising: an interruption means for interrupting the OSFET.

[0025] According to the above configuration,
The on / off times by the driving means are integrated, and when the result of the integration exceeds a certain value, the power MOSFET is cut off by the cutoff means. It can be cut off by the number of times, and the time until the cutoff can be set arbitrarily.

[0027] According to an eleventh aspect of the present invention, there is provided a power MOSFET with a temperature sensor connected in series with a load for turning on / off the connection of the load to a power supply, and a series circuit of the load and the power MOSFET with the temperature sensor in parallel. A reference circuit having a series circuit of a reference resistance and a reference MOSFET connected thereto, and
OSFET drain-source voltage and said reference MOSF
An overcurrent detecting means for detecting an overcurrent flowing through the power MOSFET with the temperature sensor based on a difference between a drain-source voltage of the ET, and an overcurrent detecting means for detecting the overcurrent by the overcurrent detecting means. Power MOSFET with temperature sensor and reference MOSFET until
Drive means for driving the power MOSFET with the temperature sensor on and off, and overheat cutoff means for detecting overheating by the temperature sensor of the power MOSFET with the temperature sensor to cut off the heat of the power MOSFET with the temperature sensor. Is integrated, and when the result of the integration exceeds a certain value, the overheat cutoff means cuts off the power MOSFET.

[0027] According to the above configuration,
In addition to detecting overheating, the power MOSFET with the temperature sensor is not only overheated and shut off, but also the number of ON / OFF operations by the driving means is integrated, and the power MOSFET is shut off when the result of the integration exceeds a certain value. , Power MOSF in response to detection of overcurrent from small current to large current
ET can be properly blocked.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of an overcurrent detection circuit according to the present invention. In FIG. 1, a portion surrounded by a dotted line is an overcurrent detection circuit 1 formed as an IC. The overcurrent detection circuit 1 has an N-channel MOSFET QA having a DMOS (Dbule MOS) structure as a power MOSFET. Both FETs QA and QB are
They are formed on the same chip by the same process, and are both composed of a plurality of transistors. The transistor ratio is QA> QB, and the current ratio is in accordance with the transistor ratio. As an example, QA: QB = 1000: 1 will be described. In order to reduce the chip occupation area of the FET QB, it is desirable to reduce the number of transistors to reduce the size. The drain terminal D of the FET QA is connected to a power supply connection terminal T1 to which a DC power supply VB (= 12 V) including a vehicle-mounted battery is connected, and the source terminal SA is connected to a load L such as a lamp load.
Are respectively connected to the load connection terminals T2 to be connected.

The overcurrent detection circuit 1 also has a reference MOSFE
It has an N-channel MOSFET QB as T.
The drain terminal D of the FET QB is connected to the drain terminal D of the FET QA, the gate terminal TG is connected to the gate terminal of the FET QA,
The source terminal SB is connected to the other end of the reference resistor Rr whose one end is grounded. MOSFE
The TQB and the reference resistor Rr are connected in series, and form a reference circuit connected in parallel with a series circuit of the power MOSFET QA and the load L. The reference resistance Rr is 5A
The same drain-source voltage V as when a load current flows
DS is set to a value that causes MOSFET QB to generate DS.

The overcurrent detection circuit 1 also supplies a charge pump output voltage VP (= VB + 10 V) to the gates TG of the MOSFETs QA and QB to drive them ON.
One. The drive circuit 11 has a pair of NPN transistors Tr1 and Tr2, and turns on and off the transistors Tr1 and Tr2 in response to the input of an ON instruction signal generated when the external input switch C1 is turned ON, and inputs an OFF instruction signal. , The transistors Tr1 and Tr2 are turned off and on. The transistor Tr1 of the drive circuit 11
Turns on, the charge pump output voltage is supplied to the gates TG of the MOSFETs QA and QB through the resistors R8 and R7.

The drain D of the MOSFET QB of the reference circuit
The voltage VDSB between the input and the source SB is input to the negative terminal of the comparator CP. Further, the voltage VDSA between the drain D and the source SA of the MOSFET QA is divided by the parallel resistance of the resistors R3 and R1 and the resistor R2 and input to the + terminal of the comparator CP. When the MOSFETs QA and QB operate in the pinch-off region, they constitute a current mirror, and the drain current IDQA = 1000 × IDQB. Therefore IDQA
= 5A, IDQB = 5mA
VDS and VTGS of SFETs QA and QB match. That is, VDSA = VDSB and VTGSA = VTGSB (VDSA: Q
A drain-source voltage). When the MOSFET QB is completely turned on, the reference resistance Rr which is the load thereof
, The power supply voltage VB is almost applied to both ends of Rr = 1
2V / 5mA = 1.4KΩ. This is MOSFET
This is the load of MOSFET QB equivalent to the 5A load of QA.

The VDS value (curve) when a 5 A load current flows through the MOSFET QA is used as a reference.
MO with smaller transistor ratio (current ratio) than QA
By configuring a reference circuit using SFETQB,
The required functions can be realized with a small circuit area and a small chip occupied area. In addition, MOSFET QB
By configuring on the same chip in the same chip process as QA, it is possible to eliminate the effects of lot-to-lot variation and temperature drift, thereby greatly improving detection accuracy.

The diode D1 and the resistor R5 form a hysteresis circuit, and the resistor R3, the MOSFET Q2 and the resistor R
4. A circuit including the MOSFET Q1, the Zener diode ZD2, and the resistors R6 and R9 is for changing the overcurrent determination value between the pinch-off region and the ohmic region.

(A) Operation in the pinch-off region The region where the MOSFET QA operates in the pinch-off state from the time when the MOSFET QA is turned on to the time when the drain-source voltage VDS is saturated.
When the SFET QA is turned on, its drain current IDQA rises toward the final load current value determined by the circuit resistance. The gate-source voltage VTGSA is equal to the drain current I.
Takes the value determined by DQA, the drain-source voltage VDSA
While the brake is applied by the Miller effect of the gate-drain capacitance CGD due to the decrease in the voltage.

The gate-source voltage VTGSB of the MOSFET QB is the drain current IDQB = 5 mA (IDQA = 5 A
) Until VTGDB = VTGSA, but thereafter becomes constant at IDQB = 5 mA in the pinch-off region, so that the gate-source voltage VTG of MOSFET QB
SB is also constant. For example, in the case of Hitachi, the constant value is about 2.7 V in HAF2001. Gate of MOSFET QA
Since the source-to-source voltage VTGSA increases as the drain current IDQA increases, VTGSB <VTGSA.
Since VDSA = VTGSA + VTGB and VDSB = VTGSB + VTGD, VDSA-VDSB = VTGSA-VTGSB. VTGSA-
Since VTGSB represents IDQA-5A, IDQA-5A can be obtained by detecting VDSA-VDSB.

VDSB is directly input to the comparator, and VDSA is a value obtained by dividing (R1 // R3) and R2, that is, VDSA × (R1 // R3) / ((R1 // R3) + R2) ( B) is input to the comparator.

Immediately after the MOSFET QA turns on, the MOS
Although the drain-source voltage VDSB of the FET QB is larger than the value of the above equation (a), as the drain current IDQA increases, the value of the above equation increases, and the output from the comparator changes from L to H, and this is driven. By applying the voltage to the circuit 11 to turn on the transistor Tr2, the MOSFET QA
Turn off the gate.

The diode D1 and the resistor R5 form a hysteresis circuit. When the MOSFET QA is turned off, the gate circuit is grounded by the transistor Tr2 of the drive circuit 11, and the cathode side potential of the diode D1 becomes (VDSA-
0.7 (forward voltage of Zener diode ZD1)), current flows in the order of (R1 // R3) → R5 → D1, and the drive circuit 11 turns on the potential of the + input terminal of the comparator. Lower than when. Smaller than when turned off (V
DSA-VDSB), the MOSFET QA keeps off, and then turns on. Note that the hysteresis circuit may have other configurations.

VDSA when MOSFET QA turns off
Is VDSATH, VDSATH−VDSB = R2 / (R1 // R3) × VDSB (at 5 mA) (b) The overcurrent determination value is determined by the above equation (b). To change this determination value from outside the IC, a variable resistor R is connected in parallel with R2.
V may be added to shift the determination value downward. For this purpose, a terminal T3 for connecting an adjustment resistor is provided in advance.

(B) Operation in the Ohmic Region When the MOSFET QA is turned on while the wiring is in a normal state, the MOSFET QA is turned on continuously, so that the gate-source voltages VTGSA and VTGSB of both MOSFETs QA and QB reach nearly 10 V, and the MOSFET QA Both QBs operate in the ohmic region. In this region, there is no one-to-one relationship between the drain-source voltage VDS and the drain current ID.

When the MOSFET is the above-mentioned HAF2001, the on-resistance RDS (ON) = 30 mΩ (VDS = 10V
VDSA = 5A × 30 mΩ = 0.15 V, VDSA = IDQA × 30 mΩ VDSA−VDSB = 30 mΩ (IDQA−5A) (C)

When IDQA increases due to a short circuit in the wiring, the value of the above equation (c) increases, and when the value exceeds the overcurrent determination value, the MO
Turn off SFET QA. Thereafter, the state shifts to a pinch-off region, and the MOSFET QA performs on / off operations, leading to overheating interruption. If the wiring returns to normal before the heat interruption (for example, due to an intermittent short circuit), M
The OSFET QA returns to the continuous ON state, and returns to the operation in the ohmic region.

As the overcurrent determination value, the same value is used for both the pinch-off region and the ohmic region. When Δ (VDSA−VDSB) / ΔID in the pinch-off region is obtained,
In the case of HAF2001, from the characteristic curve, ΔVTGSA / ΔIDQA = 80 mV / A..., And ΔVTGSA = Δ (VDSA−VDSB) × 1200 pf / (1
800pf + 1200pf) = Δ (VDSA−VDSB) ×
Therefore, Δ (VDSA−VDSB) / ΔID = 200 mV / A (d). Δ (VDSA-VDSB) in ohmic region
From the above equation (c), / ΔID is Δ (VDSA−VDSB) / ΔID = 30 mV / A (E). Comparing the above equations (d) and (e), the current sensitivity is more sensitive in the pinch-off region than in the ohmic region,
Even if the overcurrent determination value is appropriate in the ohmic region, it may be too low in the pinch-off region and may be determined as overcurrent.

A circuit for changing the overcurrent judgment value between the pinch-off region and the ohmic region is represented by a resistor R3 and a MOS transistor shown in FIG.
It comprises an FET Q2, a resistor R4, a MOSFET Q1, a Zener diode ZD2, and resistors R6 and R9.
Determination of pinch-off area or ohmic area is MOSFE
The operation is performed with the magnitude of the gate-source voltage VTGSA of TQA.
As the drain current ID increases, the gate-source voltage VTGSA in the pinch-off region increases, but does not exceed 5 V even in the case of a dead short. Therefore VTGSA
If it is> 5V, it can be determined that it is in the ohmic region.

Immediately after the MOSFET QA is turned on, MOSFE
TQ1 is off and MOSFET Q2 is on. M
To turn on the OSFET Q2, a power supply voltage higher than the power supply VB, for example, VB + 5V is required. If the Zener voltage of the Zener diode ZD2 is set to 5V-1.6V (threshold voltage of Q1), when VTGSA> 5V, the MOSFET Q1 is turned on and the MOSFET Q2 is turned off. Removed. Since the compression ratio of the gate-source voltage VDSA becomes smaller, the difference (VDSA-VDSB) between the drain-source voltage determined as an overcurrent becomes smaller. Due to the presence of this circuit, an overcurrent is determined with a smaller current value in the ohmic region than in a non-existent one.

However, there are cases where the above circuit need not be used. When the final load current value is small in the pinch-off region, the voltage completely rises in the pinch-off region. That is, when the final load current value reaches the final load current value in the pinch-off region, when the final load current value is large, the current is still rising in the pinch-off region, and the current value in the pinch-off region is limited to about MAX40A even in the case of the dead short. . That is, as the final load current value increases, the current rise curve converges with a certain gradient, and the difference in VDSA becomes smaller as the difference in final load current value increases. Because of this phenomenon, even if the current sensitivity in the pinch-off region is large, (VDSA-VDSB) does not increase, and practical use is possible without using the above circuit depending on the selection of the reference current value.

In short, when the wiring is normal, the MO
When the SFET QA is turned on, the SFET QA enters the ohmic region and stays in the ohmic region as long as the wiring is normal. An abnormality occurs in the wiring and the current increases (VDS
When A-VDSB exceeds the overcurrent determination value, the circuit turns off and enters a pinch-off region. MOSFET QA as long as wiring abnormality continues
Keeps on and off, stays in the pinch-off region, and leads to overheat interruption.

To realize the basic concept and optimize the control, the overcurrent judgment value must satisfy the following conditions. The MOSFET QA is never turned off in the normal current range. After the overcurrent is determined in the ohmic region, the MOSFET QA keeps on and off in the pinch-off region unless the wiring abnormality is improved. This is on,
Necessary for stabilizing the off cycle. Stabilizing the ON / OFF cycle leads to the stability of the control, and since the timer described later is set using the ON / OFF cycle,
Therefore, stabilization of the period is necessary. Is satisfied, the overcurrent determination value in the ohmic region is set to “normal current MAX value + α” (corresponding to VDSA−VDSB).
And set the overcurrent judgment value in the pinch-off area to the "normal value MA".
X + β ”. At this time, α> β. α-β is an offset amount necessary for staying in the pinch-off region.

In the above embodiment, the MOSFET QA
And the gates of QB are interconnected, but may be modified as shown in FIG. In FIG.
The gate of the ETQB is disconnected from the gate of the MOSFET QA, and the resistance R41 is used as the gate resistance of the MOSFET QB.
Has been added. According to this configuration, the drain current ID of the MOSFET QB can be set by the resistance ratio between the resistor R41 and the resistor R7, and the transistor number ratio does not need to be increased as in the above-described example. Can also. However, in such a case, the size of the resistor R41 becomes very large. Therefore, in consideration of cost and productivity, the transistor number ratio may be about 1: 100.

It may be necessary to set a mask for prohibiting the overcurrent detection control for a certain period of time after the MOSFET QA is turned on for the following reason. When the load L is a lamp load, when the lamp load is turned on, an inrush current several times to several tens times the current in a stable state flows. The period varies depending on the magnitude of the lamp load, and is 3 to 20 ms. If the overcurrent control is performed during this period, the period is extended, and a delay in lamp lighting may become a problem. Therefore, as shown in FIG. 3, an inrush current mask circuit 12 for inhibiting the overcurrent detection control for a certain period after the MOSFET QA is turned on is provided.

When the MOSFET QA is turned on, the gate-source voltage rises through the D11 and R11 to the MOSFET Q1.
MOSFETQ through D11 and R12 to the gate of 1
Twelve gates are added to each. MOSFET Q1
The gate of 2 is connected to MOS by an external capacitor C11.
Because it is connected to the source of FET QA, MOSFET
Immediately after QA is turned on, since the capacitor C11 has not been charged yet, the voltage is not sufficiently applied to the gate of the MOSFET Q12, and the MOSFET Q12 cannot be turned on. M
OSFET Q11 is on while MOSFET Q12 is off, coupling the-input terminal of the comparator to the MOSFET QA source. Therefore, the output of the comparator CP is kept in the H state, and even if a large inrush current flows, the MOSFET QA
Does not turn off.

As time passes, the capacitor C1
1 is charged through the resistor R12 and finally MOSFE
TQ12 turns on. As a result, the MOSFET Q11 is turned off, the mask period ends, and the overcurrent detection control operates. The mask time is determined by a time constant R12 × C11. C11 can be added outside the IC, and the mask time can be adjusted by changing the size of the capacitor C11. The resistor R13 is a discharge resistor for resetting the capacitor C11 after the MOSFET QA is turned off. R12 <R13 is set so as not to affect the mask time. R14 is MOSFE
When TQ11 is turned on, it is inserted so as not to affect the source of MOSFET QB.

After the overcurrent is detected, the MOSFET Q
As means for shutting off A, an overheat shutoff is used. When the drain current ID is large, the overheat cutoff works immediately. However, when the drain current ID is small, it takes time until the overheat is cut off. Therefore, as shown in FIG.

In the overcurrent control, the capacitor C21 is charged through the resistor 22 and the diode 21 every time the gate is periodically turned on (H). The MOSFET Q21 is turned off at first when the gate voltage is lower than the threshold, but when the voltage of C21 rises, the gate voltage exceeds the threshold and the MOSFET Q21 is turned on.

When the MOSFET Q21 is turned on, the resistance R
A current flows from the gate TG to GND through 21, and the charge stored in the gate TG decreases. Therefore, even for the same drain current ID, the voltage VDSA between the drain and the source is increased, the power consumption of the MOSFET QA is increased, and the overheating is cut off earlier. The smaller the resistance R21, the earlier the overheat cutoff. The resistance R23 is a discharge resistance of the capacitor C21,
Select so that 22 << R23.

In the overheat interruption, when the drain current ID is small, the time until the interruption is long. Therefore, as an alternative method, as shown in FIG. 4, the number of ON / OFF times of the overcurrent control is integrated and added to the set value. When it reaches, an on / off frequency integrating circuit 14 for shutting off the MOSFET QA is provided in parallel with the overheat shutoff circuit 15.

Each time the gate is turned on, the capacitor C31 is charged through the resistor R32 and the diode 31. While the gate is off, the diode D31 prevents backflow to the drive circuit side. When the voltage of the capacitor C31 rises and exceeds the gate threshold of the MOSFET Q31, the MOSFET Q31 turns on. The anode side of the temperature sensor consisting of four series diodes is diode D3.
2, the condition becomes the same as the high temperature condition, the MOSFET QS is turned on, the VTSA-VDSA is short-circuited, and the MOSFET QA is cut off. The cutoff time based on the number of times is set to about 1 second.

In order to operate the integrating circuit stably, the MO
It is necessary to stabilize the ON / OFF cycle of the SFET QA.

When the temperature rises, the four diodes have a greater negative temperature dependency than the resistance R41, so that the divided voltage of the gate of the MOSFET Q41 as the temperature detecting element decreases as the temperature rises. When the temperature rises above a predetermined temperature, the voltages of the four diodes become MOSFET Q
Since it drops below the threshold of 41, the MOSFE
TQ41 is turned off. Therefore, when a positive input voltage is supplied to the external gate, the drain voltage of the MOSFET Q41 becomes H level. The latch circuit is composed of a pair of MOSFETs Q42 each having a gate and a drain cross-coupled as a set element.
43, Q44 and resistors R42, R4, which are load resistance elements.
3 basically. Since the load resistor R43 has a higher resistance than the load resistor R42, this latch circuit is an asymmetric flip-flop.

Therefore, the temperature is low, and M
When the OSFET Q42 is off, the MOSFET Q43 is off and Q44 is on due to the asymmetry of the latch circuit, the drain of the MOSFET Q44, which is the output of the latch circuit, is at the L level, and the MOSFET QS is kept off. Therefore, it is driven by the input signal applied to the gate of MOSFET QA. When the temperature rises, Q41 is turned off and Q42 is turned on. In the flip-flop of the latch circuit, Q43 is turned on and Q44 is turned off, so that MOSFET QS is turned on and MOSFET QA is controlled to be cut off. , The temperature drops.

In the above-described example, the reference circuit is fixed so as to correspond to the 5 A load, and the load is changed by changing the overcurrent determination value. That is, an IC is created by setting the resistors R1, R2, and R3 in accordance with the maximum load to be used. When the load is small, a variable resistor RV is added in parallel outside the IC to reduce the overcurrent determination value. I was

However, in this method, the control accuracy decreases as the overcurrent determination value increases, and when the overcurrent determination value needs to be changed between the pinch-off region and the ohmic region, the overcurrent determination value in the pinch-off region is strictly determined. Must be adjusted to the ID rising gradient, but there is a problem that it is difficult to exactly match the ID rising gradient because the ID rising gradient changes when the wiring inductance and the wiring resistance change.

Therefore, the reference circuit is set according to the load. A reference circuit corresponding to the maximum current value of the load is set, and the VDS of the reference circuit (VDSB of MOSFET QB)
Is slightly over the VDS of the load drive MOSFET QA (VDSA of QA), it is determined that an overcurrent has occurred.

In this method, it is not necessary to change the overcurrent determination value between the pinch-off region and the ohmic region. Since it is sufficient to determine whether or not VDS of the reference circuit has been exceeded, the detection accuracy is determined by the resolution of the comparator.

Further, the effects of temperature drift, variation between IC lots, and wiring inductance / resistance can be eliminated, and power supply voltage variation is not affected as long as the comparator operates normally. Therefore, a device with few (no) adjustment elements can be realized. Therefore, as shown in FIG. 5, the reference circuit is changed by changing Rr. That is, R
By arranging several types of r in parallel and selecting them from among them, the setting can be changed without increasing the types of ICs. Note that an external resistor may be added in parallel with Rr.

Although the overheat cutoff circuit 15 is not shown in the embodiments of FIGS. 1 to 3, a power MOSFET having a temperature sensor is used as the power MOSFET QA as shown in the embodiment of FIG. Making it possible to shut off the overheating can be easily performed as necessary.

[0067]

As described above, according to the first aspect of the present invention, since the overcurrent is detected without using the sense resistor, the problem associated with the use of the sense resistor can be solved. Since the detection operation is performed differentially, an in-phase error factor can be removed, and an overcurrent detection circuit with improved detection accuracy can be provided.

According to the configuration of the second aspect, the number of MOSFETs in the reference circuit can be reduced as compared with the power MOSFET, so that an overcurrent detection circuit in which the reference circuit is downsized can be provided. .

According to the above configuration, the reference circuit is formed in the same chip as the power MOSFET,
Since they can be formed by the same process, it is possible to provide an overcurrent detection circuit that can reduce or eliminate the effects of temperature drift and lot-to-lot variation.

According to the configuration of the fourth aspect, terminals other than those used independently are shared with each other.
An overcurrent detection circuit that facilitates chip formation can be provided.

According to the above configuration, the voltage between the drain and the source of the power MOSFET is equal to the reference MO.
Since it is possible to detect that an overcurrent is flowing when the voltage between the drain and the source of the SFET is exceeded, and to minimize the error factor, it is possible to provide an overcurrent detection circuit capable of performing accurate detection.

According to the above configuration, the reference resistor is selected from a plurality of resistors prepared in advance, and a single circuit can correspond to a plurality of specifications. An overcurrent detection circuit that can be shared by a load can be provided.

According to the seventh aspect of the present invention, there is provided a terminal for connecting an adjusting resistor in parallel with the reference resistor, and using this terminal to adjust the connected adjusting resistor to adjust the reference resistor. Since the value can be changed, it is possible to provide an overcurrent detection circuit that can easily perform specification setting.

According to the configuration of the eighth aspect, it is not necessary to insert a sense resistor in series with the power MOSFET, and the detection operation is performed differentially.
In addition to eliminating the error factors, the temperature sensor detects overheating that rises due to ON / OFF drive until overcurrent detection is eliminated, and shuts off the overheating.Therefore, current interruption is performed without external control. An overcurrent detection / protection circuit capable of protecting MOSFETs and wiring can be provided.

According to the configuration of the ninth aspect, since a clock for control is generated by a stable ON / OFF cycle of the driving means, it is not necessary to separately provide an overcurrent detection / protection. A circuit can be provided.

According to the above-described structure of the tenth aspect,
It shuts off when the integrated number of on and off times exceeds a certain value, so even if the current value is small and it takes time to shut off overheating, it can be shut off by the number of times and the time to shut off can be set arbitrarily An overcurrent detection / protection circuit can be provided.

According to the above-described structure of the eleventh aspect,
In addition to detecting overheating and shutting off the overheating, it also shuts off when the integrated number of on and off times exceeds a certain value, so the power MOSFET can be turned on in response to the detection of overcurrent from small current to large current. An overcurrent detection / protection circuit that can be appropriately cut off can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overcurrent detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the overcurrent detection circuit according to the present invention.

FIG. 3 is a circuit diagram showing still another embodiment of the overcurrent detection circuit according to the present invention.

FIG. 4 is a circuit diagram showing an embodiment of an overcurrent detection / protection circuit according to the present invention.

FIG. 5 is a diagram showing a modification of a part of FIGS. 1 to 4;

[Explanation of symbols]

 L load VB power supply QA power MOSFET QB reference MOSFET Rr reference resistance 1 overcurrent detection means 11 drive means 15 overheat cutoff means (cutoff means)

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2G035 AA03 AA06 AA16 AA26 AB02 AC02 AC13 AC16 AD02 AD03 AD04 AD08 AD10 AD13 AD17 AD23 AD54 5J055 AX31 AX44 BX16 CX28 DX13 DX22 DX53 DX54 EX04 EX06 EY01 EY02 EY10 EY10 EY10 EY12 EY10 EZ31 EZ55 FX05 FX06 FX32 FX33 FX38 GX01

Claims (11)

[Claims] 1. A reference circuit comprising: a power MOSFET connected in series with a load to turn on / off connection of the load to a power supply; and a reference circuit connected in parallel to a series circuit of the load and the power MOSFET. Is constituted by a series circuit of a reference resistor and a reference MOSFET equivalent to the load and the power MOSFET of the series circuit, and based on a difference between a drain-source voltage of the power MOSFET and a drain-source voltage of the reference MOSFET. And the power MOSF
An overcurrent detection circuit for detecting an overcurrent flowing through the ET. 2. The number of the reference MOSFETs is set to be smaller than the number of the power MOSFETs, and the resistance of the reference resistor is determined by the resistance of the load × (the number of the power MOSFETs / the number of the reference MOSFETs). The overcurrent detection circuit according to claim 1, wherein the overcurrent detection circuit is set. 3. The power MOSFET according to claim 1, wherein the reference circuit is a power MOSFET.
3. The overcurrent detection circuit according to claim 1, wherein the overcurrent detection circuit is formed in the same chip as the circuit. 4. A power supply side terminal and a gate terminal of the reference MOSFET are interconnected with a power supply side terminal and a gate terminal of the power MOSFET.
A reference resistance connection terminal of T is provided independently of a load connection terminal of the power MOSFET, and a potential of the reference resistance connection terminal is compared with a potential of the load connection terminal to compare the power MOSFET.
4. The overcurrent detection circuit according to claim 1, wherein an overcurrent flowing through the FET is detected. 5. A normal current having a value equivalent to a maximum current flowing through the power MOSFET is set to flow through the reference circuit, and a drain-source voltage of the power MOSFET is set to a drain-source voltage of the reference MOSFET. The overcurrent detection circuit according to any one of claims 1 to 4, wherein it is detected that an overcurrent is flowing when the current exceeds the threshold. 6. The overcurrent detection circuit according to claim 1, wherein said reference resistor is selected from a plurality of resistors prepared in advance. 7. The overcurrent detection circuit according to claim 3, further comprising a terminal for connecting an adjustment resistor in parallel with said reference resistor. 8. A power MO with a temperature sensor connected in series with a load to turn on and off the connection of the load to a power supply.
An SFET and the power M with the load and the temperature sensor
A reference circuit having a series circuit of a reference resistor and a reference MOSFET connected in parallel with a series circuit of an OSFET, and a drain-source voltage of the power MOSFET with the temperature sensor and a drain-source voltage of the reference MOSFET. An overcurrent detecting means for detecting an overcurrent flowing in the power MOSFET with the temperature sensor based on the difference; and an overcurrent detecting means for detecting the overcurrent by the overcurrent detecting means until the overcurrent detection is eliminated. Power MOS
A drive unit that turns on and off the FET and the reference MOSFET, and an overheat shutoff unit that detects overheating by a temperature sensor of the power MOSFET with the temperature sensor and shuts off the power MOSFET with the temperature sensor. Overcurrent detection and protection circuit. 9. The overcurrent detection and protection circuit according to claim 8, wherein an on / off cycle of said driving means is used as a clock for control. 10. A power MOSFET connected in series with a load for turning on and off the connection of the load to a power supply;
A reference circuit having a series circuit of a reference resistor and a reference MOSFET connected in parallel with the series circuit of the load and the power MOSFET, wherein a drain-source voltage of the power MOSFET and a drain-source voltage of the reference MOSFET are provided. And the power MO
Overcurrent detection means for detecting an overcurrent flowing in the SFET, and drive means for turning on and off the power MOSFET and the reference MOSFET in response to the detection of the overcurrent by the overcurrent detection means until the overcurrent detection is eliminated. An overcurrent detection / protection circuit according to claim 1, further comprising: an interruption means for accumulating the number of on / off times by said driving means, and interrupting said power MOSFET when a result of the accumulation exceeds a predetermined value. 11. A power M with a temperature sensor connected in series with a load to turn on and off the connection of the load to a power supply.
An OSFET, a reference circuit having a series circuit of a reference resistor and a reference MOSFET connected in parallel with the series circuit of the load and the power MOSFET with the temperature sensor, and a drain-source voltage of the power MOSFET with the temperature sensor and the reference circuit. An overcurrent detecting means for detecting an overcurrent flowing through the power MOSFET with the temperature sensor based on a difference between a drain-source voltage of the reference MOSFET, and an overcurrent detecting means for detecting the overcurrent by the overcurrent detecting means. Power MOS with temperature sensor until detection is canceled
A drive unit that turns on and off the FET and the reference MOSFET; and an overheat cutoff unit that detects overheating by a temperature sensor of the power MOSFET with the temperature sensor and shuts off the power MOSFET with the temperature sensor. The overcurrent detection / protection circuit according to claim 2, wherein the number of times of on / off is integrated, and when the result of the integration exceeds a certain value, the overheat interrupting means shuts off the power MOSFET.