JP2002368594A - Load drive - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To provide a power switch element in two stages by adding a little element
Lower the gate voltage of the
Protect without compromising reliability. SOLUTION: A load current I flowing to a load 17 is provided._LDetect
And the load current I_LLoad current voltage V corresponding to_COutput
Load current detection circuit 50 and load current I_LAs steady
Load current detection when an abnormal current exceeding the current value flows
The voltage V corresponding to the load current output from the circuit 50_CThe two
Selective operation of the protection switch according to the level
Gate voltage V of the word switch element 2_GReduced to two stages
And a protection circuit 51 for performing the operation. The above protection circuit 51
Are load current detection circuits with different gate threshold voltages
The same load current corresponding voltage V output from_CIs a game
The two MOSFETs 33 and 40 added to the
-Gate voltage V of switch element 2 _GIn two steps
Used as a protection switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lamp, an LED,
The present invention relates to a load driving device configured by, for example, a one-chip integrated circuit that drives a load such as an inductor, and particularly, when an overcurrent or a short-circuit current occurs, prevents thermal destruction of a power switch element included in the load driving device. It is about technology.

[0002]

2. Description of the Related Art Conventionally, in order to drive a load such as a lamp or a coil, a power supply 9 is connected to a high potential side of a load 17 and a one-chip integrated circuit is connected to a low potential side of the load 17 as shown in FIG. The output terminal 21 of the load driving device 1B is connected. The load driving voltage supplied from the outside to the input terminal 22 is connected to the power switch element 2 via the resistor 10,
For example, the power switch element 2 in the load driving device 1B is turned on / off by giving the signal to the gate of an N-channel MOSFET. Thus, the load 17 is driven by the load current I _L that flows from the power source 9 to the load 17 is turned-off.

Such a load driving device 1B generally has various protection functions. Among these protection functions, in order to realize an overcurrent protection function, a load short-circuit protection function, and the like, the voltage on the low potential side of the load 17, that is, the potential of the output terminal (drain terminal) 21 of the load driving device 1B is changed to the power The power switch element 2 is detected by a series circuit of the current detection resistors 13 and 14 connected in parallel with the switch element 2 and the power switch element 2 is cut off based on the detected potential. Is protected from.

[0004] Here, a current detection resistor 13 detects the load current I _L flowing through the load 17, the load current load current detecting circuit 60 for outputting a load current corresponding voltage V _C which corresponds to the I _L is constituted ing.

An N-channel MOSFET 15, a gate protection resistor 34, a gate protection Zener diode 37, resistors 18, 19 and an N-channel MOSFET
20, the load current I _L when the abnormal current exceeding the steady-state current value flows as the load current of the power switching element 2 according to the level of the load current corresponding voltage V _C output from the detection circuit 60 the gate voltage V _G the load current I _L is varied in the direction of decreasing the (decreasing) the protection circuit 61 flowing in the power switching element 2 is constructed.

The load driving device 1B includes a power switch element 2 for driving a load 17 and an external load driving voltage V _IN.
And a switch control circuit 62 for controlling the power switch element 2 in accordance with The switch control circuit 62 includes the load current detection circuit 60, the protection circuit 61, and the resistor 10 described above.

Next, a specific example of this load driving device will be described.
Fig. 4 shows various overcurrent protection functions and load short-circuit protection functions.
It will be described with reference to FIG. Fig. 4 shows the case of overcurrent occurrence and load short circuit.
Waveform indicating voltage / current of each part in load driving device 1B
FIG. FIG. 4 shows a load drive applied to the input terminal 22.
Dynamic voltage V_INAnd the gate voltage V of the power switch element 2 _G
And the drain voltage V of the power switch element 2_DAnd the load
Current I_LAre shown.

[0008] First, joined by the load drive voltage V _IN to the input terminal 22 from the outside is applied as the gate voltage V _G to the power switching element 2 this voltage through a resistor 10. As a result, the power switch element 2 conducts. When the load drive voltage V _IN is at a high level, an N-channel MOSFET
20 is turned on and N-channel type MOSF for current detection
ET15 is operable.

In this state, when an abnormality occurs in the load 17 and a large current flows, the load current-corresponding voltage V _C divided by the current detection resistors 13 and 14 according to the load current I _L increases, When the load current-corresponding voltage V _C exceeds the gate threshold voltage V _TH of the N-channel MOSFET 15 for current detection, the N-channel MOSFET 15 conducts, and the gate voltage V _G of the power switch element 2 via the ground terminal 23.
Is lowered to the ground level, and the power switch element 2 is turned off.

When the power switch element 2 is turned off,
−Drain voltage V of switch element 2 _DIs a steep off
Due to the flow, the voltage rises up to the withstand voltage of the power switch element 2.
You.

When the load driving voltage V _IN is at a low level, the N-channel MOSFET 20 is turned off, the N-channel MOSFET 15 for current detection is disabled, and the protection mode is not entered. Therefore, when the load drive voltage V _IN subsequently changes from the low level to the high level, the power switch element 2 can be made conductive.

Since the above operation is not preferable in view of the reliability of the power switch element 2, actually, as shown in FIG. 5, two N-channel MOSFETs 1 for current detection are used.
A load driving device 1C composed of a one-chip integrated circuit using 5, 33 is used.

[0013] The load driving device 1C includes, first worked an overcurrent protection function, in order to exert a load short-circuit protection for second stage, the gate voltage V _G of the power switch element 2 2
The configuration is such that the power switch element 2 is protected without lowering its reliability by lowering it to the stage.

In the load driving device 1C shown in FIG. 5, a series circuit of a resistor 13 and an N-channel MOSFET 33 is added in parallel with the N-channel MOSFET 15, and a Zener diode for gate protection is provided between the gate and the source of the N-channel MOSFET 33. 36, a current detection resistor 32 is added between the current detection resistors 13 and 14, and a connection point between the current detection resistors 32 and 14 is connected to the N-channel type MOSFE.
A gate protection resistor 35 is added to the gate of T33. Other configurations are the same as those shown in FIG. Further, the above-mentioned N-channel MOSFETs 15, 33
Of the gate threshold voltages V _TH and V _TH1 of the one-chip integrated circuit have substantially the same value.

Here, the current detection resistors 13, 14, 32
In, detects the load current I _L flowing through the load 17, the load current I _L in the load current corresponding voltage V _C which _{corresponds, V S (V C> V} S)
Is output.

Further, N-channel type MOSFETs 15, 3
3, the resistor 31, the gate protection resistors 34 and 35, and the gate protection Zener diodes 36 and 37, the load current I
When an abnormal current exceeding the steady current value flows as _L ,
A plurality of stages in the direction of decreasing the load current I _L flowing in the gate voltage V _G of the power switching element 2 to the power switching element 2 in response to two levels of load current the corresponding voltage V _C output from the load current detection circuit 70 A changing (decreasing) protection circuit 71 is configured.

The load driving device 1C includes a power switch element 2 for driving a load 17, and an external load driving voltage V _IN.
And a switch control circuit 72 for controlling the power switch element 2 in accordance with The switch control circuit 72 includes the load current detection circuit 70, the protection circuit 71, and the resistor 10 described above.

Specific overcurrent protection function and load short-circuit protection device
The function will be described with reference to FIG. Figure 6 shows the overcurrent
Of each part of the load driving device 1C when the load is generated or the load is short-circuited.
FIG. 3 is a waveform diagram showing pressure and current. FIG.
Drive voltage V applied to _INAnd power switch element
2 gate voltage V_GAnd the drain of the power switch element 2
Voltage V_DAnd the load current I_LAre shown.

Firstly, joined by the load drive voltage V _IN to the input terminal 22 from the outside is applied as the gate voltage V _G to the power switching element 2 this voltage through a resistor 10.

In this state, when an abnormality occurs in the load 17 and a large current flows, the load current-corresponding voltage V divided by the current detection resistors 13, 32 and 14 according to the load current I.
_{When S} rises and the load current corresponding voltage V _S exceeds the threshold V _TH of the N-channel MOSFET 33 for current detection, N
Channel type MOSFET33 is conductive, the gate voltage V _G of the power switching element 2 through the ground terminal 23 becomes the voltage reduced by dividing by the load drive voltage V _IN resistors 10 and 31, the power switching element 2 load current I _L decreases, the drain voltage V _D of the power switch element 2 flowing
Rises. Therefore, when the load current-corresponding voltage V _C rises and the load current-corresponding voltage V _C exceeds the threshold value V _TH1 of the N-channel MOSFET 15 for current detection, the N-channel MOSFET 15 conducts and passes through the ground terminal 23. gate voltage V _G of the power switching element 2 is decreased to the ground Reberuhe, the power switching element 2 is turned off Te.

[0021] Thus, in two steps by reducing the gate voltage V _G of the power switching element 2, the power switching element 2 reliability, can be protected without reducing.

As described above, in the case where an abnormality occurs in the load 17 and a large current flows, in order to prevent thermal destruction of the load driving device 1C and to prevent a voltage exceeding the withstand voltage from being applied to the power switch element 2, The overcurrent protection function and the load short-circuit protection function described above are provided.

[0023]

[0007] As shown in FIG. 5, if the fault in the load 17 is large current flows generated, two steps to the power switching element load driving device 1C to lower the gate voltage V _G of 2 Is used, the number of elements constituting the protection circuit increases. N-channel type MO for current detection
The Zener diodes 37 and 36 for protecting the gates of the SFETs 15 and 33 are necessary to prevent the N-channel MOSFETs 14 and 33 from being destroyed. That is, when the power switch element 2 is not turned on, the resistors 13, 32,
The voltage determined by 14, 34, 35 is an N-channel MOSF
In addition to ET15 and ET33, the gate will be broken beyond the breakdown voltage if it is left as it is. It voltage V _D is, for example 60V in voltage V _C, V _S is because, for example, 10V and gate breakdown voltage of the N-channel type MOSFET. Gate protection Zener diodes 37 and 36 to prevent breakdown
is necessary.

The necessity for the resistors 13, 34 and 14 to have high resistance is as follows. That is, when these resistance values are low, when the load 17 is, for example, a light emitting diode, the current passing through the resistors 13, 34, and 14 becomes a leak current, and the power switch element 2 is turned off and should be turned off. This causes a malfunction such that the light emitting diode is turned on, and a wasteful current flows.
Therefore, it is necessary to increase the resistance values to solve the above problems. In the case of a high-brightness light emitting diode, it is sufficiently lit at 10 μA. The resistance at this time is R = 60 V / (10 × 10 ⁻⁶ ) = ⁶ MΩ. In a semiconductor device, when a high resistance is formed, a chip area increases due to a resistance value ratio.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power switch element in a plurality of stages by adding a small number of elements when an abnormality occurs in a load and a large current flows. An object of the present invention is to provide a load driving device that can protect a power switch element without reducing reliability by changing a gate voltage of the power switch element in a direction to reduce a current.

[0026]

A load driving device according to the present invention comprises a power switch element for driving a load, and a switch control circuit for controlling the power switch element in response to an external load drive signal.

The power switch element and the switch control circuit are formed, for example, as a one-chip integrated circuit.

The above-described switch control circuit detects a load current flowing through the load, and outputs a load current corresponding voltage corresponding to the load current, and an abnormal current exceeding the steady current value flows as the load current. When the plurality of protection switches are selectively operated in accordance with the plurality of levels of the load current corresponding voltage output from the load current detection circuit, the control voltage of the power switch element is supplied to the current flowing through the power switch element. And a protection circuit that changes in a stepwise manner in a decreasing direction.

The above protection circuit comprises a plurality of MOSFETs each having a different gate threshold voltage and the same load current corresponding voltage output from the load current detection circuit being applied to the gate.
Is used as a protection switch.

As the above-mentioned power switch element, for example, an N-channel MOSFET or an insulated gate bipolar transistor of a voltage drive type, or a normal bipolar transistor of a current drive type is used.

According to this configuration, when an overcurrent or a load short circuit occurs, the power switch element can be protected by changing the gate voltage of the power switch element in a plurality of stages with a small addition of the element. Without reducing the reliability. Further, since MOSFETs having different gate threshold voltages are used, the configuration for current detection can be simplified, and an inexpensive load driving device can be provided.

The plurality of MOSFETs are, for example, N-channel MOSFETs, and at least one is
A P-type diffusion layer is provided in a P-type well in which an N-type diffusion layer serving as a drain is formed so as to surround the N-type diffusion layer serving as a drain, and a gate threshold voltage is offset with respect to another MOSFET. It is preferred to use

With such a configuration, the N serving as the drain
The P-type diffusion layer surrounding the P-type diffusion layer can be formed simultaneously with the P-type diffusion layer for forming the ground electrode of the P-well, and a plurality of MOSFETs having different threshold values are not particularly increased in steps. Can be created.

[0034]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a load driving device according to a first embodiment of the present invention, and FIG. 2 is a sectional view showing the structure of two N-channel MOSFETs for detecting current. It is. The voltage and current of each part are the same as those shown in FIG.

The load driving device 1A includes an N-channel MOSFET 33 connected in parallel with a series circuit of a resistor 31 and an N-channel MOSFET 33.
N-channel type MO instead of channel type MOSFET 15
The SFET 40 is connected. This N-channel type MO
The gate threshold voltage of the SFET 40 is set slightly higher than that of the N-channel MOSFET 33.

Then, the N-channel type MOSFET 33,
Forty gates are commonly connected and connected to a connection point of the current detection resistors 13 and 14 via a gate protection resistor 34. The load driving device 1A shown in FIG.
As compared with C, the gate peripheral circuits of the N-channel MOSFETs 33 and 40 are simplified. That is, the current detection resistor 32, the gate protection resistor 35, and the gate protection zener diode 35 are omitted.

The above points are different from the conventional example shown in FIG. The other points are the same as those in FIG. 5. Here, the current detection resistors 13 and 14 detect the load current I _L flowing through the load 17 and output the load current corresponding voltage V _C corresponding to the load current I _L. A load current detection circuit 50 is configured.

The N-channel MOSFETs 33, 4
0 and the resistor 31, a gate protection resistor 34, by the gate protection zener diode 37, when an abnormal current exceeding the steady-state current value as the load current I _L flows, load output from the load current detection circuit 50 by selectively operating the two protective switch in accordance with the two levels of current-dependent voltage V _C, changing in two steps the gate voltage V _G of the power switching element 2 in the direction of decreasing the load current I _L A (reducing) protection circuit 51 is configured. The protective circuit 51, a plurality of the same load current corresponding voltage V _C of the gate threshold voltage is output from each different load current detection circuit 50 is applied to gate N-channel type MO
The SFET33,40, uses a gate voltage V _G of the power switching element 2 as a protective switch for changing in two steps.

The load driving device 1A is, for example, a one-chip
A power switch configured to drive the load 17 is configured as an integrated circuit.
Switch element 2 and an external load drive voltage (load drive signal).
No.) V _INSwitch that controls the power switch element 2 according to the
Switch control circuit 52. Switch control circuit 52
Is connected to the load current detection circuit 50 and the protection circuit 51 described above.
Anti-10.

The power switch element 2 is an N-channel MOSFET of the voltage drive type described above.
Alternatively, a voltage-driven insulated gate bipolar transistor or a current-driven normal bipolar transistor can be used.

FIG. 2 is a circuit diagram of a one-chip integrated circuit.
N-channel MOSFETs with different gate threshold voltages
FIG. 3 is a cross-sectional view of a portion where 33 and 40 are formed. FIG.
In the figure, 101 is an N-type semiconductor substrate, and 102 is a P-well formed on the N-type semiconductor substrate 101. 103 is P
The N-type diffusion region formed in the well 102 serves as the drain of the N-channel MOSFET 33. Reference numeral 104 denotes an N-type diffusion layer formed in the P well 102, and serves as a common source of the N-channel MOSFETs 33 and 40. 105
Is an N-type diffusion layer formed in the P-well 102 and serves as a drain of the N-channel MOSFET 40. The N-type diffusion layers 103 to 105 are formed simultaneously.

Reference numeral 106 denotes a P surrounding the N-type diffusion layer 105.
The P ⁺ -type diffusion layer formed in the well 102 has a function of giving a predetermined offset to the gate threshold voltage of the N-channel MOSFET 40. 107 is P well 10
A P ⁺ type diffusion layer for forming a ground electrode of
The P ⁺ type diffusion layers 106 and 107 are formed simultaneously. 10
8 is the gate electrode of the N-channel MOSFET 33, 10
Reference numeral 9 denotes a gate electrode of the N-channel MOSFET transistor 40, which is formed simultaneously. The illustration of the gate insulating film is omitted.

The N-channel MOSFETs 33 and 40
In the structure of P, the offset of the drain of the N-channel MOSFET
By inserting the ⁺ -type diffusion layer 106, the gate threshold voltage of the N-channel MOSFET 40 is made higher than that of the N-channel MOSFET 33 in which the P ⁺ -type diffusion layer is not inserted as an offset below the drain N-type diffusion layer 103. Can be. This can be formed without adding a diffusion step, and can be realized without increasing the price of a semiconductor.

FIG. 6 is a waveform diagram showing the voltage or current of each part in the load driving device 1A when a load short circuit or overcurrent occurs.

Next, a load short-circuit protection function and an overcurrent protection function of the load driving device 1A according to the present embodiment will be described with reference to FIGS.

Firstly, joined by the load drive voltage V _IN to the input terminal 22 from the outside, the voltage is applied as the gate voltage V _G to the gate of the power switching element 2 through a resistor 10.

In this state, when an abnormality occurs in the load 17,
When a current flows, the load current I According to the current detection resistor
Load current corresponding voltage V divided by 13 and 14_CIs on
Rise, the load current corresponding voltage V_CIs N channel for current detection
Voltage V of MOSFET 33_TH(About 1.2V)
Exceeds N-channel MOSFET 3 for current detection
3 is turned on, and the power switch element is
2 gate voltage V_GIs the load drive voltage V_INTo the resistance 10,
31, the voltage is reduced by the voltage division, and the power switch
Current I flowing through the switch element 2_LPower switch
Voltage V of the switching element 2_DRises. for that reason,
Voltage V corresponding to load current_CRises and the load current corresponding voltage V_CBut
Slightly higher than N-channel MOSFET 33 for current detection
N-channel for current detection with high gate threshold voltage
Voltage V of MOSFET 40_TH1 (About 2.0V)
Exceeds N-channel MOSFET 4 for current detection
0 conducts and the power switch element via the ground terminal 23
2 gate voltage V_GDrops to ground level,
The switch element 2 is turned off.

[0049] Thus, in two steps by reducing the gate voltage V _G of the power switching element 2, it can be protected without the power switching element 2 less reliable.

As described above, an overcurrent protection circuit and a load short-circuit protection circuit are provided in order to prevent the thermal destruction of the load driving device 1A when a large current flows due to the occurrence of an abnormality in the load 17.

According to the embodiment of the present invention, the N-channel MOSFET 33 for current detection, and the gate and the gate of the N-channel MOSFET 33 are connected in common and have a slightly higher gate threshold voltage than the N-channel MOSFET 33. MOSFETs having different gate threshold voltages like an N-channel MOSFET 40 for detecting current
T constitutes the protection circuit 51. Therefore, the current detection resistor 32, the gate protection Zener diode 36, and the gate protection resistor 35 of the N-channel MOSFET 33
It is not needed, while simplifying the circuit configuration, when the overcurrent or load short circuit occurs, in two steps to lower the gate voltage V _G of the power switching element 2, it is possible to protect the power switching element 2, inexpensive load It becomes possible to provide a driving device.

In the above embodiment, the gate voltage of the power switch element is changed (lowered) in two steps. However, the gate voltage may be lowered in three or more steps. In this case, three or more N-channel MOSFETs having different threshold voltages may be provided, and the resistance voltage dividing circuit may be configured to change the gate voltage stepwise in three or more steps.

[0053]

As described above, according to the present invention,
When an overcurrent or load short circuit occurs, the gate voltage can be changed in a direction that reduces the current of the power switch element in multiple steps with a small addition of elements, and the power switch element can be protected while maintaining its reliability. This provides a special effect that an inexpensive load driving device can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a load driving device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of an N-channel MOSFET of the load driving device according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional first load driving device.

FIG. 4 is a waveform diagram of a voltage and a current of each unit when an overcurrent occurs and a load is short-circuited in the first load driving device of the related art.

FIG. 5 is a circuit diagram showing a configuration of a second conventional load driving device.

FIG. 6 is a waveform diagram of a voltage and a current of each section when an overcurrent occurs and a load is short-circuited in the second conventional load driving device and the load driving device according to the embodiment.

[Explanation of symbols]

 1A, 1B, 1C Load drive device 2 Power switch element 9 Power supply 10, 31, Resistance 13, 32, 14 Current detection resistance 15, 16, 33, 40 N-channel MOSFET 17 Load 21 Drain terminal 22 Input terminal 23 Ground terminal 36, 37 Zener diode for gate protection 34, 35 Resistance for gate protection 50 Load current detection circuit 51 Protection circuit 52 Switch control circuit 60 Load current detection circuit 61 Protection circuit 62 Switch control circuit 70 Load current detection circuit 71 Protection circuit 72 Switch control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 5G004 AA04 AB02 BA03 BA04 DA04 DC04 DC10 DC13 EA01 FA01 5G053 AA01 AA02 BA01 CA01 DA01 EC03 FA07 5H740 AA08 BA12 BB07 GG04 KK01 MM11 5J055 AX32 AX64 BX16 DX13 EY23 DX55 FX08 FX09 FX13 FX18 FX32 GX01 GX07

Claims (6)

[Claims] A power switch element for driving a load;
A switch control circuit that controls the power switch element in response to an external load drive signal, wherein the switch control circuit detects a load current flowing through the load and responds to the load current. A load current detection circuit that outputs a load current-corresponding voltage according to a plurality of levels of the load current-corresponding voltage output from the load current detection circuit when an abnormal current that exceeds a steady-state current value flows as the load current. A protection circuit for changing a control voltage of the power switch element in a plurality of steps in a direction to reduce a current flowing through the power switch element by selectively operating a plurality of protection switches respectively. Are different in the gate threshold voltage, and the same load current corresponding voltage output from the load current detection circuit is applied to the gate. A plurality of MOSFET to be, the load driving device characterized by using as the protective switch. 2. The semiconductor device according to claim 1, wherein the plurality of MOSFETs are of an N-channel type, and at least one of the plurality of MOSFETs surrounds the N-type diffusion layer serving as a drain in a P-type well in which an N-type diffusion layer serving as a drain is formed. 2. The load driving device according to claim 1, wherein the P-type diffusion layer is provided to offset the gate threshold voltage with respect to other MOSFETs. 3. The load driving device according to claim 1, wherein the power switch element is formed of an N-channel MOSFET. 4. The load driving device according to claim 1, wherein the power switch element is formed of an insulated gate bipolar transistor. 5. The load driving device according to claim 1, wherein the power switch element is formed of a bipolar transistor. 6. The load driving device according to claim 1, wherein the power switch element and the switch control circuit are formed by a one-chip integrated circuit.