JPH0685632A - Mos transistor with overcurrent protecting function - Google Patents

Abstract

PURPOSE:To provide a MOS transistor TR containing an overcurrent protecting function which eliminates the effect of the overcurrent protecting function to quickly start the load in a load start state and also can protect the overcurrent in a load steady state. CONSTITUTION:When the voltage is applied to the other end of an input resistance 105, the 1st and 2nd MOS TR 101 and 103 conduct and the load 111 is started to supply a large current (flush current). When a large current flows to the TR 101, a large current also flows to the TR 103 in proportion to the TR101. Thus a protection means 107 is actuated. However, a capacitor 109 having no stored charge is apparently short-circuited and the voltage is never dropped by the resistance 105. As a result, both TR 101 and 103 are not turned off despite the actuation of the means 107.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an M with overcurrent protection function.
The present invention relates to an OS type transistor.

[0002]

2. Description of the Related Art As a conventional MOS transistor with an overcurrent protection function, there is, for example, the one shown in FIG. 8, which will be described below with reference to FIG.

First, the configuration will be described.

MOSFET 801 and MOSFET 803
The drains of and are both connected to one end of the load 111, and the other end of the load 111 is connected to the power supply. See also MOSFE
The gates of T801 and MOSFET 803 are both connected to one end b of the input resistor 805. MOSFET801
Is grounded, and the source of the MOSFET 803 is grounded via the resistor 809.

Here, the MOSFET 801 has a large number of MOs.
It is a power MOSFET in which SFETs are connected in parallel. The MOSFET 803 is a MOSFET having a smaller number of cells than the MOSFET 801.
A MOSFET 801 is provided between the drain and source of 803.
A small current that is proportional to the current that flows between the drain and source of the. That is, MOSFET 803 is MOSFET
It is the current mirror of T801.

The drain of the MOSFET 807 is MOSF.
Connected to the gates of ET801 and 803, MOSFE
The gate of T807 is connected to the source of MOSFET 803, and the source of MOSFET 807 is grounded.

Next, the operation will be described.

The other end of the input resistor 805 (terminal a in FIG. 8)
When a predetermined voltage is applied to the gate, the predetermined voltage is applied to the gates of the MOSFET 801 and 803, and M
The OSFETs 801 and 803 are both in a conductive state (hereinafter, changing from a non-conductive state to a conductive state is called a turn-on, and the opposite is called a turn-off), and a current flows through the load 111.

Due to the abnormality of the load 111, the MOSFET 80
When the current flowing between the drain and the source of No. 1 increases and the current flowing between the drain and the source of the MOSFET 803 increases, the voltage generated by the resistor 809, that is, the gate voltage of the MOSFET 807 increases. This voltage is M from the gate voltage of the MOSFETs 801, 803, that is, the drain voltage of the MOSFET 807.
When the voltage becomes higher than the voltage at which the OSFET 807 turns on, the MOSFET 807 turns on. As a result, a current flows from the terminal a through the resistor 805 and the MOSFET 807 to the ground. At this time, since there is a voltage drop due to the resistor 805, one end b of the input resistor, that is, the MOS
The gate voltage of the FETs 801 and 803 decreases.

Therefore, an overcurrent does not flow between the drain and source of the MOSFET 801, and the MOSFET
It is possible to prevent the destruction of T801.

[0011]

However, in such a conventional MOS transistor with an overcurrent protection function, a load 111 having a low resistance at start-up, for example, in the case of a lamp, the moment when the MOSFET 801 is turned on is still present. Since the filament in the lamp is cold and the electric resistance of the filament is low, an overcurrent (rush current) flows between the filament and the drain / source of the MOSFET 801. Since a current having a magnitude proportional to this overcurrent also flows between the drain and source of the MOSFET 803, the MOSFET that constitutes the overcurrent protection circuit.
807 turns on, lowering the gate voltage of the MOSFET 801 and reducing the current flowing through the filament. For this reason, there is a problem that the temperature rise of the filament in the lamp is delayed, and it takes time for the lamp to emit light.

The present invention has been made to solve the above-mentioned problems. When the load is started, the effect of the overcurrent protection function is canceled to quickly start the load, and when the load is in a steady state, the overcurrent protection is performed. It is an object of the present invention to provide a MOS type transistor with an overcurrent protection function capable of performing the above.

[0013]

In order to achieve such an object, the invention described in claim 1 is the first M for driving a load 111 as shown in the claim correspondence diagram of FIG.
An OS-type transistor 101, a second MOS-type transistor 103 for a current mirror having a smaller number of cells than the first MOS-type transistor 101, the drain and gate of which are commonly connected to the first MOS-type transistor 101. , One end of which is connected to the gates of the first and second MOS type transistors, and the other end of which is connected to an input resistor 105 to which a voltage is applied, and at least the source of the second MOS type transistor 103, MO
A protection means 107 for lowering the voltage applied to the gates of the first and second MOS transistors via the input resistor when the potential of the source of the S-type transistor 103 exceeds a predetermined value; A MOS transistor with an overcurrent protection function was constructed from a capacitor 109 electrically connected in parallel to the resistor 105.

[0014]

In the invention described in claim 1, the load 111
When a voltage is input to the other end of the input resistor 105 to drive the, the voltage is applied to the gates of the first and second MOS type transistors to activate the load. Since the rush current flows through the load when the load starts, the first MOS
A current (rush current) larger than the steady current also flows between the drain and source of the type transistor 101.

Since a large current flows between the drain and the source of the first MOS type transistor 101, the first M-type transistor 101
Second that is a current mirror of the OS-type transistor 101
A current having a magnitude proportional to the large current also flows between the drain and the source of the MOS transistor 103. Then, when the potential of the source of the second MOS transistor 103 becomes equal to or higher than a predetermined value, the protection means operates. But,
When a voltage is input to the other end of the input resistor 105, the capacitor 109 is virtually equivalent to a short-circuited state, so that no current flows through the input resistor 105 and there is no voltage drop due to this input resistor 105. Therefore, even if the protection means operates, the voltage input to the other end of the input resistor 105 is applied to one end of the input resistor 105, that is, the gates of the first and second MOS transistors, via the capacitor 109. First MOS transistor 101
It is possible to supply to the gate a voltage sufficient to cause a rush current to flow between the drain and source of the. Therefore, the load 11
Since the rush current flows at the time of starting No. 1, load 111
Can be started quickly.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the circuit diagram of FIG.

First, the structure will be described.

Reference numeral 111 is a load, for example, a room lamp of a vehicle. Reference numeral 201 denotes a MOSFET as a first MOS transistor in which a large number of MOSFETs are connected in parallel to drive the load 111. 203 is M
Second MOS with a smaller number of cells than OSFET201
MOSFET as a MOS transistor, and MOSF
Used for current mirror of ET201. 20
7 is a bipolar transistor, and 209 is a resistor. (This bipolar transistor 207 and resistor 2
09 together constitute the protection means described in claim 1. ) 205 is an input resistance. This input resistance 205
Is when the bipolar transistor 207 becomes conductive (hereinafter, turning from a non-conductive state to a conductive state is called turn-on, and the opposite is called turn-off).
It is for dropping the potential generated at one end of the input resistor 205 (hereinafter referred to as the connection point b), and is sufficiently larger than the internal resistance of the bipolar transistor 207, and has a resistance value of 2 MΩ, for example. 211 is the input resistance 2
05 connected in parallel with the capacitor having a capacity of 0.022 μF. This is for continuing to turn on the MOSFETs 201 and 203 even when the bipolar transistor 207 is turned on for a time determined by the capacity of this capacitor and the voltage applied to this capacitor. The MOSFETs 201 and 203
The time to keep turning on is set to the same as or slightly longer than the time from the start of the load to the steady state.

Drain of MOSFET 201 and MOSF
The drains of the ET 203 are both connected to the load 111.

Gate of MOSFET 201 and MOSFE
The gates of T203 are both connected to the connection point b, and from the other end of the input resistor 205 (hereinafter referred to as the voltage input point a), M
A voltage for turning on the OSFET 201 and the MOSFET 203 is input. The source of MOSFET 201 is grounded and the source of MOSFET 203 is resistor 2
It is grounded through 09.

The base of the bipolar transistor is MO
It is connected to the source of the SFET 203, the collector is connected to the connection point b, and the emitter is grounded.

Next, the operation will be described.

First, the operation when the load 111 is activated will be described.

At the moment when a voltage is input to the voltage input point a to drive the load 111, the MOSFET 201 and the MO
The voltage input to the voltage input point a is applied to the gate of the SFET 203, and a current flows between the drain and source of the MOSFET 201 and the load 111.

The initial state in which current flows through the load 111 is
When the load 111 is, for example, a lamp, the resistance is small and a large current (rush current) occurs while the filament is cold.
Flows into the filament.

A current larger than the steady-state current is MOSFET
By flowing between the drain and source of 201, MOSF
MOSFET 203 which is the current mirror of ET201
A current of a magnitude proportional to the above-mentioned large current flows between the drain and source of the.

As a result, the source potential of the MOSFET 203 is changed by the voltage generated by the resistor 209 to cause the MOSF
When the potential of the gate of the ET 203 becomes higher than the turn-on voltage of the bipolar transistor 207 by a predetermined value or more (the predetermined value or more), the bipolar transistor 207 operates.
However, at this time, the capacitor 211 is not yet fully charged, so that the voltage input to the voltage input point a is applied to the connection point b. Then, a current flows through the capacitor 211 and the collector-emitter of the bipolar transistor 207. However, since the bipolar transistor 207 has an internal resistance, the potential of the connection point b does not drop to the ground potential (0V) and the voltage input to the voltage input point a is directly applied to the gates of the MOSFETs 201 and 203. 203 keeps turning on. Therefore, the MOSFETs 201 and 20
3 can keep the rush current flowing through the lamp.

As current flows through the lamp and the filament warms up, the resistance also increases,
Settles down in a certain state (a certain amount of current) (becomes a regular state). When the rush current flowing in the load 111 becomes small and the load 111 enters a fixed state, the MOSFET
Since the current flowing between the drain and source of 201 decreases, the current mirror of MOSFET 201, MO
The current flowing between the drain and source of the SFET 203 also decreases. This causes the bipolar transistor 207 to turn off and then when the capacitor 211 is full of charge, no current can flow through the capacitor 211.

As described above, the load 111 can be quickly started because a sufficient rush current can flow through the MOSFET 201 without turning off the MOSFET 201 even when the load 111 is started.

If the time constant related to the capacity of the capacitor 211 is determined so that the time until the electric charge is full in the capacitor 211 is about several mmsec, even if the load starts, an abnormality occurs in this load. In case of MOSF
MO due to heat generated by large current flowing through ET201
Before SFET201 is broken, MOSFET201
Can be turned off.

Next, the operation when the load 111 is abnormal will be described.

After the load 111 has settled in a steady state,
When an abnormality occurs in the load 111 and a current larger than the steady-state current flows, the current flowing between the drain and the source of the MOSFET 201 increases, and at the same time, the MOSFET 203.
Since the current flowing between the drain and source of is also large,
The voltage generated by the resistor 209, that is, the base voltage of the bipolar transistor 207 becomes high. When this voltage becomes higher than the gate voltage of the MOSFETs 201 and 203, that is, the collector voltage of the bipolar transistor 207 by a voltage equal to or more than the voltage at which the bipolar transistor 207 is turned on, the bipolar transistor 207 is turned on and a current is supplied from the voltage input point a to the ground. Flowing. At this time, the capacitor 211 is fully charged, so
A current flows from the voltage input point a to the ground via the input resistor 205 and the bipolar transistor 207. Since the resistance value of the input resistance 205 is sufficiently smaller than the resistance value of the internal resistance of the bipolar transistor 207, the voltage drop across the input resistance 205 lowers the voltage applied to the gates of the MOSFETs 201 and 203, and thus the MOSFE
T201 and 203 turn off. Therefore, MOS
Overcurrent does not flow between the drain and the source of the FET 201 for a long time, and the MOSFET 201 can be prevented from being destroyed. Further, when the voltage input to the voltage input point a becomes 0 V (switch OFF), the capacitor 21
The charge accumulated in 1 disappears through the input resistor 205 and returns to the initial state.

As described above, in the first embodiment, when the load 111 is activated, a sufficient rush current can be passed through the load 111, so that the load 111 can be activated quickly.

Next, according to the circuit diagram of FIG.
An example will be described. 2 described as the first embodiment.
The same parts as those of the configuration 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the second embodiment, the capacitor 211 of the first embodiment is electrically connected in parallel to the input resistor 205, and the resistor 213 is connected in series between the capacitor 211 and the voltage input point a. .

Next, the operation of this embodiment will be described. The operation when the load 111 is abnormal is the same as that in the first embodiment described above, and therefore omitted, and only the operation when the load 111 is started will be described.

Similar to the first embodiment, the voltage input point a
The moment the voltage is applied to the MOSFETs 201 and 203
The voltage input to the voltage input point a is applied to the gate of
The MOSFETs 201 and 203 are turned on (hereinafter, turning from a non-conducting state to a conducting state is called turn-on, and the opposite is called turn-off). Since a large current flows through the load 111 at the time of startup, a proportional current also flows through the MOSFET 203, which is the current mirror of the MOSFET 201. Then, when the bipolar transistor 207 is turned on, the capacitor 211 is not full of electric charge at this time, so that a current flows through the resistor 213, the capacitor 211, and the bipolar transistor 207.

At this time, since the time until the electric charge is full in the capacitor 211 depends on the capacity of the capacitor 211 and the voltage applied to the capacitor 211, the resistance value of the resistor 213 should be set to an arbitrary value. Capacitor 2 depending on the voltage applied to capacitor 211 by
The time until the electric charge is full in 11 can be set arbitrarily.

Therefore, by setting the resistance value of the resistor 213 to a predetermined value, the time during which the rush current flows between the drain and the source of the MOSFET 201, that is, the time during which the rush current flows through the load 111 can be adjusted. .

From the above description, in this embodiment, in addition to the effect of the first embodiment described above, the input resistance 205 is further added.
In this embodiment, a rush current can be made to flow to the load 111 for a required time only by appropriately setting the resistance value of the resistor 213 via a resistor 213 in series with a capacitor 211 electrically connected in parallel to. It has a unique effect.

Next, the third embodiment of the present invention will be described with reference to the circuit diagram of FIG.
An example will be described. 2 described as the first embodiment.
The same parts as those of the configuration 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the third embodiment, the above-mentioned first
A comparator 227 is connected instead of the bipolar transistor 207 of the embodiment. Comparator 227
Is connected to the source of the (-terminal) MOSFET 203, and the reference voltage is input to the VREF terminal 229 which is the other (+ terminal) of the input terminals of the comparator 227. The output terminal of the comparator 227 is MOSF
It is connected to the gates of the ET 201 and the MOSFET 203. One of the terminals of the operating power supply of the comparator 227 is connected to the voltage input point a, and the other of the terminals of the operating power supply is grounded. When the potential of one (−terminal) of the input terminals of the comparator 227 is equal to or lower than the potential of the other (+ terminal), the same voltage as the voltage input to the voltage input point a is output from the output terminal as the Hi output, and the comparator 227 When the potential of one (-terminal) of the input terminals becomes higher than the potential of the other (+ terminal), the same potential (0 V) as the ground potential is output from the output terminal as Lo output.

Next, the operation of the third embodiment will be described.

First, the operation when the load 111 is activated will be described.

Similar to the first embodiment described above, the voltage input point a
When a voltage is applied to the MOSFET 201 and the MOS
The FET 203 is in a conductive state (hereinafter, changing from a non-conductive state to a conductive state is called turn-on, and the opposite is called turn-off). When the load 111 is, for example, a lamp, the electric resistance is low when the filament of the lamp is cold, so a current larger than the current flowing through the load 111 in the steady state flows between the drain and source of the MOSFET 201. Then, since a potential difference is generated between the ground potential (0 V) and the source of the MOSFET 203 by the resistor 209, the potential of the source of the MOSFET 203 rises, and the VREF terminal 229 of the comparator 227.
When the voltage becomes higher than the reference potential applied to, the comparator 227 outputs a Lo output of 0 V to the connection point b. The output of 0V to the connection point b means that the connection point b is grounded via the comparator 227. At this time, the capacitor 211 and the comparator 22 are not yet fully charged.
A current will flow through 7. However, since the comparator 227 has an output resistance (the internal resistance of the comparator 227 existing in the stage before the output terminal), a voltage is generated at the connection point b. The voltage input to the voltage input point a is applied to the connection point b until the capacitor 211 is fully charged, and the potential of the connection point b is equal to the potential of the voltage input point a due to the output resistance. Will be the same. Therefore, M
The OSFETs 201 and 203 continue to flow the rush current to the load 111 without being turned off. Eventually load 1
When the resistance value of 11 rises and the rush current subsides, M
When the potential of the source of the OSFET 203 drops and becomes lower than the reference potential applied to the VREF terminal 229 of the comparator 227, the voltage applied to the connection point b becomes the same as the voltage input to the voltage input point a. , MOSFE
T201 and 203 continue to turn on, and the load 1111 enters the steady state.

Next, the operation when the load 111 is abnormal will be described.

After the load 111 has settled in a steady state,
When an abnormality occurs in the load 111 and a current larger than the steady-state current flows, the current flowing between the drain and the source of the MOSFET 201 increases, and at the same time, the MOSFET 203.
Since the current flowing between the drain and source of is also large,
The voltage generated by the resistor 209, that is, the comparator 2
The voltage of the-terminal of 27 becomes high. When this voltage becomes higher than the reference voltage applied to the VREF terminal 229 of the comparator 227, Lo output of 0 V is output from the output terminal of the comparator 227, that is, the connection point b is grounded via the comparator 227. It But,
At this time, the capacitor 211 is full of electric charge and no current can flow, and a current flows from the voltage input point a to the ground via the input resistor 205 and the comparator 227.
The voltage drop across the input resistor 205 causes the MOS
The voltage applied to the gates of the FETs 201 and 203 becomes low and the MOSFETs 201 and 203 are turned off. Therefore, an overcurrent does not flow between the drain and the source of the MOSFET 201 for a long time, and the MOSFET 20
It is possible to prevent the destruction of 1. In addition, the voltage input point a
When the voltage input to is 0V (switch OFF), the charge accumulated in the capacitor 211 is input to the input resistor 205.
It disappears through and returns to the initial state.

As described above, in the third embodiment, as in the first embodiment, when the load 111 is started, a sufficient rush current can be passed through the load 111, so that the load 111 can be started quickly. Can be made.

Next, according to the circuit diagram of FIG.
An example will be described. 2 described as the first embodiment.
The same parts as those of the configuration 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the first embodiment described above, the MOSFE
The source of T203 was grounded via the resistor 209, whereas in the fourth embodiment, MO
The source of SFET 203 is connected to the base of bipolar transistor 207 via resistor 231.

Next, the operation of this embodiment will be described.

First, the operation when the load 111 is activated will be described.

Similar to the operation of the first embodiment described above, a voltage is applied to the voltage input point a, and the MOSFETs 201 and M are connected.
The OSFET 203 is in a conductive state (hereinafter, changing from a non-conductive state to a conductive state is called turn-on, and the opposite is called turn-off). When the load 111 is, for example, a lamp, the electric resistance is low when the filament of the lamp is cold, so that a current (rush current) larger than the current flowing through the load 111 in the steady state is MOSFET.
It flows between the drain and source of 201. MOSFET 2
Rush current flows between the drain and source of 01, and MO
The potential of the source of the SFET 203, that is, the base voltage of the bipolar transistor 207 rises, and this voltage becomes M
When the voltage applied to the gates of the OSFETs 201 and 203, that is, higher than the collector voltage of the bipolar transistor 207 by the turn-on voltage of the bipolar transistor 207 or more, the bipolar transistor 207 turns on. However, since the bipolar transistor 207 has an internal resistance, a potential higher than the ground potential is generated at the connection point b. Also, the capacitor 2
Since the capacitor 211 is apparently short-circuited until the charge is full in 11, the voltage input point a
Is input to the connection point b via the capacitor 211. Therefore, even if the bipolar transistor 207 turns on, the MOSFETs 201 and 203 continue to be turned on. Eventually, the filament of the lamp itself heats up, the resistance of the filament increases, the rush current subsides, and the bipolar transistor 207 turns off. After that, the capacitor 211 becomes full of electric charge and enters a steady state.

Next, the operation when the load 111 is abnormal will be described.

After the load 111 enters the steady state, the load 1
When abnormality occurs in 11 and a current larger than the steady current flows, the large current also flows in the MOSFETs 201 and 203, and the source voltage of the MOSFET 203, that is, the base voltage of the bipolar transistor 231 rises. When the base voltage becomes higher than the collector voltage of the bipolar transistor 231 by the turn-on voltage of the bipolar transistor 231, the bipolar transistor 231 is turned on. Capacitor 2 at this time
Since 11 is full of electric charge, the input resistance 2 from the voltage input point a.
Current flows to the ground through the transistor 05 and the bipolar transistor 207. At this time, the voltage drop due to the input resistor 205 depends on the connection point b, that is, the MOSFET 201.
And the voltage input to 203 drops and MOSFET2
01 and 203 turn off.

In the fourth embodiment, the MOSFET
Since the collector of 203 is not grounded, there is no current flowing through the drain-source of MOSFET 203 to ground when the load 111 is in a steady state (bipolar transistor 207 is turned off).

From the above description, in this embodiment, in addition to the effects of the first embodiment described above, the MOSFET 2
Since there is no current flowing through 03 to the ground, there is an effect peculiar to this embodiment that power consumption is smaller than that in the first embodiment.

The load is not limited to such a lamp, and a motor such as a blower motor of an air conditioner or a cell motor of an engine may be used as the load. Even when the load is the motor, the rush current can be kept flowing at the time of starting, so that the motor can be started surely and quickly.

Two circuit examples for achieving the purpose of supplying a rush current at the time of starting the load are shown below.

First, this circuit example 1 according to the circuit diagram of FIG.
Will be explained. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this circuit example 1, instead of the capacitor 211 of the first embodiment described above, a capacitor 217 is used.
Are connected in parallel to the resistor 209.

Next, the operation when the load 111 is activated will be described.

The voltage applied to the voltage input point a is MOSF.
Applied to the gates of ETs 201 and 203. And M
The OSFET 201 and the MOSFET 203 are turned on. When the load 111 is activated, if the load 111 is, for example, a lamp, the resistance is small.
The rush current flows between the drain and the source of the capacitor 217 until the capacitor 217 is fully charged.
Since the current flows through 17 to the ground,
No current flows through the base of transistor 207 and this bipolar transistor 207 does not turn on.

The rush current of the load 111 subsides, the charge in the capacitor 217 becomes full thereafter, and the current flowing through the load 111 becomes a steady state.

The time constant of the capacitor 217, that is, the time until the charge is full in the capacitor 217 depends on the capacity of the capacitor 217 and the voltage applied across the capacitor 217.

When the load 111 is in a steady state, the capacitor 217 is fully charged, so the load 1
Since the operation of 11 at the time of abnormality is the same as that of the first embodiment described above, the description thereof will be omitted.

Next, Circuit Example 2 will be described with reference to the circuit diagram of FIG. The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this circuit example 2, the capacitor 217 of the third embodiment is electrically connected in parallel to the resistor 209, and the resistor 219 is connected in series between the capacitor 217 and the base of the bipolar transistor 207. There is.

Next, the operation when the load 111 is activated will be described.

The voltage applied to the voltage input point a is MOSF.
Applied to the gates of ETs 201 and 203. And M
The OSFET 201 and the MOSFET 203 are turned on. When the load 111 is activated, if the load 111 is, for example, a lamp, the resistance is small.
Current flows between the drain and source of the
When the potential of the source of the ET203 rises, the voltage applied to the capacitor 217 depends on the resistance value of the resistor 219.
By changing the resistance value of the resistor 219, the time (time constant) until the capacitor 217 is fully charged can be changed, and the time for flowing the rush current to the load 111 can be changed.

When the load 111 is in the steady state, the capacitor 217 is full of electric charge, so the load 111
Since the action at the time of abnormality is the same as that of the first embodiment described above, its explanation is omitted.

[0072]

As described above, according to the present invention, a current larger than a steady-state current flows between the drain and the source of the first MOS transistor for driving the load when the load is activated, and the protection means operates. Even if the first M is connected by a capacitor electrically connected in parallel with the input resistance,
Since a sufficient starting current can be passed to the load to prevent the gate voltage drop of the OS transistor, the effect of the overcurrent protection function is erased when the load starts, and the load starts quickly.
Furthermore, when the load is in a steady state, overcurrent protection can be performed.

[Brief description of drawings]

FIG. 1 is a diagram for responding to a claim for claim 1.

FIG. 2 is a circuit diagram showing the configuration of the first embodiment.

FIG. 3 is a circuit diagram showing a configuration of a second embodiment.

FIG. 4 is a circuit diagram showing a configuration of a third embodiment.

FIG. 5 is a circuit diagram showing a configuration of a fourth embodiment.

FIG. 6 is a circuit diagram showing a configuration of Circuit Example 1.

FIG. 7 is a circuit diagram showing a configuration of a circuit example 2.

FIG. 8 is a circuit diagram showing a configuration of a conventional example.

[Explanation of symbols]

101 ... First MOS type transistor 103 ... Second
MOS transistor 105 ... Input resistance 107 ... Protecting means 109 ... Capacitor 111 ... Load 201 ... MOSFET 203 ... MO
SFET 205 ... Input resistance 207 ... Bipolar transistor 209 ... Resistor 211 ... Capacitor 213 ... Resistor 217 ... Capacitor 219 ... Resistor 227 ... Comparator 229 ... Comparator VREF terminal 231 ... Resistor 801 ... MOSFET 803 ... MO
SFET 805 ... Input resistance 807 ... MO
SFET 809 ... Resistance

Claims (1)

[Claims] 1. A first MOS type transistor for driving a load, and a drain and a gate which are commonly connected to the first MOS type transistor, and a current mirror having a smaller number of cells than the first MOS type transistor. Second MO
An S-type transistor, an input resistor whose one end is connected to the gates of the first and second MOS type transistors, and a voltage is applied to the other end, and an input resistor which is connected to at least the source of the second MOS type transistor Protection means for lowering the voltage applied to the gates of the first and second MOS transistors via the input resistor when the potential of the source of the second MOS transistor becomes equal to or higher than a predetermined value; A MOS transistor with an overcurrent protection function consisting of a capacitor electrically connected in parallel with a resistor.