JP4386532B2 - Voltage regulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage regulator having an overcurrent protection function.
[0002]
[Prior art]
FIG. 5 shows a circuit diagram of a conventional voltage regulator. MP11, MP12, and MP13 are pMOS transistors, and MN11 is an nMOS transistor. R11, R12, R13, and R14 are resistors, and OP2 is an error amplifier.
[0003]
In this circuit, the output voltage Vout is divided by resistors R11 and R12, taken into the error amplifier OP2, compared with the target voltage, and the transistor MP11 is controlled according to the difference, thereby holding the output voltage Vout at the target voltage. Control.
[0004]
The transistors MP11 and MP12 have a size ratio of, for example, MP11: MP12 = 10: 1, and 1/10 of the output current flowing through the transistor MP11 flows from the transistor MP12 to the resistor R13, and the voltage generated at the resistor R13. Is used to detect overcurrent. When the overcurrent flows and the voltage generated in the resistor R13 increases and the transistor MN11 is turned on, the transistor MP13 is turned on by the voltage generated by the current flowing in the resistor R14, the transistors MP11 and MP12 are cut off, and the load side is turned on. An overcurrent protection operation is performed to cut off the current supply. This overcurrent protection operation differs as follows depending on the magnitude of the power supply voltage VDD.
[0005]
Condition 1: VDD-Vout> Vth (MN11)
Vth (MN11) is a threshold voltage of the transistor MN11. This is when VDD is sufficiently high, for example, immediately after battery replacement in battery operation. At this time, the gate voltage of the transistor MN11 is obtained by the product of the resistance value of the resistor R13 and the drain current Id (MP12) of the transistor MP12. Assuming that the overcurrent to be overcurrent protected is Ia, the resistance value of the resistor R13 is
R13 = Vth (MN11) / Ia
It can be set with.
[0006]
Condition 2: VDD−Vout ≦ Vth (MN11)
This is when the power supply voltage VDD is lowered to such an extent that the battery needs to be replaced in the battery operation, for example, when the VDD drops greatly. At this time, even if the drain current Id (MP12) increases, the gate voltage of the transistor MN11 rises only to VDD, so that the transistor MN11 is not turned on. However, when the output current further increases and the output voltage Vout decreases and the potential difference between the gate and source of the transistor MN11 becomes sufficiently large, the transistor MN11 conducts and an overcurrent protection operation is performed. At this time, the drain current Id (MP12) that performs the overcurrent protection operation is Ib.
[0007]
FIG. 6 shows the current / voltage characteristics under conditions 1 and 2. When A is condition 1 and B is condition 2, Ia <Ib.
[0008]
FIG. 7 is a circuit diagram of another voltage regulator. The circuit in FIG. 7 is basically the same as the circuit in FIG. 5 except that the back gate of the transistor MN11 is connected to VSS. Here, the threshold value of the transistor MN11 is increased by ΔVth (MN11) due to the back gate effect.
[0009]
Condition 1: VDD−Vout> Vth (MN11) + ΔVth (MN11)
The gate voltage of the transistor MN11 is determined by the drain current Id (MP12) flowing through the transistor MP12 and the resistance value of the resistor R13. When the overcurrent to be detected is Ia ′, the resistance value of the resistor R13 is
R13 = {Vth (MN11) + ΔVth (MN11)} / Ia ′
Set with. Also, the overcurrent that flows when Vout = VSS is Ia, and when this is detected, the back gate effect is lost, so the resistor R13 to be set is
R13 = Vth (MN11) / Ia
It becomes.
[0010]
Condition 2: VDD−Vout ≦ Vth (MN11)
While the output voltage Vout is kept constant, the gate voltage of the transistor MN11 only rises to VDD at the maximum, so that the transistor MN11 does not conduct. When the current Id (MP12) flowing through the transistor MP12 increases from the current Ia ′ in the condition 1, the output voltage of the OP2 decreases to near the VSS level due to the regulation operation, and between the gate and source of the transistors MP11 and MP12. Is fixed, the output current is limited, and the output voltage Vout rapidly decreases.
[0011]
In this way, when the potential difference between the gate and the source of the transistor MN11 becomes sufficiently large due to the voltage drop of the output voltage Vout, the transistor MN11 is turned on, the transistor MP13 is turned on, and the transistors MP11 and MP12 are turned off to perform the overcurrent protection operation. Is done. Because of this operation, if the overcurrent during operation is Ic, this Ic is larger than the current Ib in the circuit of FIG.
[0012]
FIG. 6 shows the current / voltage characteristics under conditions 1 and 2. This is when A is condition 1 and C is condition 2.
[0013]
[Problems to be solved by the invention]
In the voltage regulator as shown in FIGS. 5 and 7, when the output current becomes large and the overcurrent protection function is activated, the output current is shown in A and B in FIG. 6 and A and C in FIG. As shown in FIG. 6 and FIG. 8, the drain current of MP12 is similar to the drain current of MP12, but the drain current of MP12 is similar to this. It is in.).
[0014]
Therefore, a large current flows before the output voltage Vout at the time of overcurrent completely becomes 0V, and heat exceeding the allowable loss may occur in the package enclosing the voltage regulator IC, which may destroy the IC of the voltage regulator. In particular, when a large overcurrent flows as shown in FIG. 6B and FIG. 8C, the problem becomes significant.
[0015]
If the package is enlarged to prevent this, the cost increases. Further, in order not to exceed this allowable loss, the output current for the overcurrent protection operation may be reduced. However, the overcurrent operation frequently occurs and the load side operation may be hindered.
[0016]
The present invention has been made in view of the points mentioned above, the purpose is to provide a voltage regulator having an overcurrent protection function to be able to effectively suppress the heat generated within the package.
[0017]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an error amplifier that converts an output voltage of an output terminal into a predetermined voltage and compares it with a target voltage, and an output that controls the output voltage according to a comparison result of the error amplifier. in the voltage regulator and a control transistor, the error and the overcurrent condition detection transistor for the output current to output voltage directly input to detect whether it is a condition that an overcurrent of the amplifier, the output voltage an output voltage detection transistor for detecting a drop in the return current supply transistor for supplying a return current to the output terminal, the output of the overcurrent condition detection result and the output voltage detecting transistor of the overcurrent condition detection transistor and a gate circuit for controlling said output control transistor and said return current supply transistor depending on the voltage detection result And Bei, the gate circuit, the overcurrent condition detection transistor is turned off the output control transistor and to detect an overcurrent condition, followed by the return current and the output voltage detection transistor detects an output voltage drop the supply transistor is turned on, followed by even longer the output voltage detection transistor detects an output voltage drop, to continue the on-off and the return current supply transistor of the output control transistor, subsequently, wherein the overcurrent condition detection transistor does not detect an overcurrent condition, and to perform control to turn off the return current supply transistor with turning on the output control transistor.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram of a voltage regulator according to one embodiment of the present invention. OP1 is an error amplifier that outputs the voltage Vout divided by resistors R1 and R2 and outputs a voltage corresponding to the difference, MP1 is a pMOS transistor for output control, MP2 is a pMOS transistor for supplying a return current, and MP3 is excessive Current condition detection pMOS transistor, MP4 is a current source pMOS transistor, MP5 is an overcurrent operation control pMOS transistor, MP6 is a return current supply control pMOS transistor, MP7 is an output cutoff pMOS transistor, and MN1 is An nMOS transistor for output voltage detection, MN2 is an nMOS transistor for overcurrent operation control, MN3 is an nMOS transistor for current source, and MN4 is an nMOS transistor for control of return current supply.
[0019]
R3 is a resistor for overcurrent detection, G is a gate circuit that determines the logic of MAIN and BUB as shown in the truth value shown in FIG. 2 by the logic of input nodes REV and OVER2, and SW is the logic of node MAIN of the gate circuit G. An analog switch to be controlled. The logic of this node MAIN simultaneously controls the transistor MP7. The logic of the node SUB complementarily controls the transistors MN4 and MP6. INV1, INV2, and INV3 are inverters. C1 is an oscillation prevention capacitor. VDD is a high-potential power supply voltage, VSS is a low-potential power supply voltage, B1 and B2 are bias voltages having a fixed relationship with VDD, and B3 is a bias voltage having a fixed relationship with VSS.
[0020]
In the present embodiment, the size of the transistor MP2 is determined so that the current (restoration current) that flows when the transistor MP2 is conductive is 100 mA. Further, the size ratio of the transistors MP1 and MP3 is set to MP1: MP3 = 100: 1. Further, the size of the transistor MP4 is a size through which 1 μA flows. Further, when the current flowing through the resistor R3 is 5 mA, the resistance value of the resistor R3 is set so that the voltage at the node OVER1 becomes a voltage that causes the transistor MP5 to conduct and the transistor MN2 to shut off. At this time, the operation of the present embodiment is as follows.
[0021]
Condition 1: Normal operation (when output current is less than 500 mA)
Since the current flowing through the transistor MP1 is smaller than 500 mA, the current flowing through the transistor MP3 whose size is 1/100 of that of the transistor MP1 is 5 mA or less, the voltage at the node OVER1 is increased, the transistor MP5 is cut off, and the transistor MN2 is turned on. . Therefore, the common drain voltage of the transistors MP5 and MN2 is “L”, and the OVER2 of the gate circuit G is “H”. Further, since the output voltage Vout is held at a predetermined value, the transistor MN1 is conductive and its drain voltage is “L”. Therefore, the REV of the gate circuit G is also “H”. Therefore, from the truth value of FIG. 2, MAIN is “H” and SUB is “L”.
[0022]
As a result, the analog switch SW is turned on and the transistor MP7 is cut off. The voltage obtained by dividing the output voltage Vout by the resistors R1 and R2 is input to the error amplifier OP1, and the regulation operation by the transistor MP1 is performed. (Area up to (1) in FIG. 3). The transistor MN4 is cut off, and the MP6 is turned on to cut off the transistor MP2.
[0023]
Condition 2: When overcurrent is detected (when the output current exceeds 500 mA)
At this time, since the current flowing through the resistor R3 exceeds 5 mA, the voltage at the node OVER1 is lowered, the transistor MP5 is turned on, and the transistor MN2 is turned off, so that the common drain voltage of the transistors MP5 and MN2 becomes “H”. OVER2 of the circuit G becomes “L”. Further, when the output voltage Vout is kept at a normal value, the transistor MN1 is conductive, so that REV of the gate circuit G becomes “H”. Therefore, from the truth value of FIG. 2, both MAIN and SUB are “L”.
[0024]
For this reason, the analog switch SW is cut off and the transistor MP7 is turned on, whereby the transistor MP1 is cut off and the regulation operation is stopped. At this time, the output current changes from (1) to (2) in FIG. 3, and the current becomes a very small current (about 5 mA) flowing through the transistor MP3 all at once.
[0025]
Condition 3: Overcurrent protection operation When the transistor MP1 is cut off due to the overcurrent detection, the output voltage Vout drops, and when the voltage Vout drops below the threshold voltage of the transistor MN1, the transistor MN1 is cut off. G REV changes to “L”. OVER2 of the gate circuit G does not change from “L”. Therefore, as in the truth value of FIG. 3, MAIN does not change from “L”, but SUB changes to “H”. For this reason, the transistor MN4 is turned on, the transistor MP6 is cut off, the bias voltage B2 is applied to the transistor MP2 and the transistor MP2 is turned on, and the set return current of 100 mA flows from the transistor MP2 to the output side. This state is indicated by (3) in FIG.
[0026]
Condition 4: When the load on the output side decreases during the overcurrent protection operation of the condition 3 at the time of return, the output voltage Vout increases, and when it exceeds the threshold voltage of the transistor MN1, the transistor MN1 becomes conductive. The REV of the circuit G changes from “L” to “H”. However, as is clear from the truth value of FIG. 2, the logic of MAIN and SUB does not change from the state of condition 3 at this time.
[0027]
During this time, the output voltage Vout continues to increase due to the return current supplied from the conducting transistor MP2, and when the voltage reaches a voltage close to normal operation ((4) in FIG. 3), the voltage at the node OVER1 increases. Then, the transistor MP5 is shut off and the transistor MN2 is turned on, so that OVER2 of the gate circuit G changes to “H”. Thus, the condition 1 is restored and normal regulation operation is resumed.
[0028]
As described above, in this embodiment, when overcurrent detection is performed, the transistor MP1 is completely cut off by the analog switch SW and the transistor MP7, and the output current and the output voltage are limited to very small values. As a result, a small return current of about 100 mA is supplied to raise the output voltage Vout to near the normal voltage, so that the internal heat generation ([VDD−Vout] × Iout) generated at that time can be prevented from greatly exceeding the allowable loss of the package. Iout is the output current.
[0029]
FIG. 4 is an explanatory diagram thereof, and the hatched area is an allowable loss area of the package. In the conventional voltage regulator shown in FIGS. 5 and 7, the current and voltage change along the curve X at the time of overcurrent protection operation and recovery, but in this embodiment, the current and voltage change along the curve Y. There is an advantage that destruction does not easily occur.
[0030]
【The invention's effect】
As described above, according to the present invention, heat generation of the package can be suppressed, and the package itself can be reduced even if the overcurrent to be operated is increased.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a voltage regulator according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a truth value of the gate circuit G of FIG.
FIG. 3 is a characteristic diagram of an overcurrent protection operation of the voltage regulator of FIG. 1;
FIG. 4 is a characteristic diagram of an allowable loss of a package.
FIG. 5 is a circuit diagram of a conventional voltage regulator.
6 is a characteristic diagram of an overcurrent protection operation of the voltage regulator of FIG.
FIG. 7 is a circuit diagram of another conventional voltage regulator.
8 is a characteristic diagram of an overcurrent protection operation of the voltage regulator of FIG.

Claims (1)

In the voltage regulator includes an error amplifier which compares the target voltage uptake by converting the output voltage of the output terminal to a predetermined voltage, and an output control transistor that controls the output voltage according to the comparison result of the error amplifier,
An overcurrent condition detection transistor for directly detecting the output voltage of the error amplifier and detecting whether the output current is in an overcurrent condition; an output voltage detection transistor for detecting a decrease in the output voltage; , a return current supply transistor for supplying a return current to the output terminal, the output control transistor in accordance with the output voltage detection result of the overcurrent condition detection result and the output voltage detecting transistor of the overcurrent condition detection transistor and comprising a gate circuit for controlling the return current supplying transistors,
The gate circuit, the overcurrent condition detection transistor is turned off the output control transistor and to detect an overcurrent condition, followed by the return current supply transistor and the output voltage detection transistor detects an output voltage drop was turned on, followed by even longer the output voltage detection transistor detects an output voltage drop, to continue the on-off and the return current supply transistor of the output control transistor, followed by the overcurrent If the condition detecting transistor does not detect an overcurrent condition, and to perform control to turn off the return current supply transistor with turning on the output control transistor,
A voltage regulator characterized by that.

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