JP4927420B2 - Switching regulator - Google Patents

Description

  The present invention relates to a switching regulator suitable for using a high efficiency amplifier, and more particularly to an overcurrent protection circuit in a switching regulator.

  In the conventional switching regulator, the output transistor is switched with a control signal having a constant frequency, and the duty of the control signal is adjusted based on the output voltage output from the output terminal, thereby maintaining the output voltage at a constant voltage. A short-circuit protection circuit that cuts off the output transistor is provided when the output voltage falls below a predetermined voltage, and is turned on when the output transistor is operated based on a control signal between the coil and the output terminal. A switching element that operates as a diode and cuts off the connection between the coil and the output terminal based on the output signal of the short circuit protection circuit is provided.

For example, the “switching regulator” described in Japanese Patent Application Laid-Open No. 2002-171749 (see Patent Document 1) distinguishes between an overcurrent that leads to a short circuit and an overcurrent that does not lead to a short circuit, and is optimal for each. An overcurrent protection circuit is provided to provide proper protection.
That is, as shown in FIG. 2, the switching regulator includes a comparator 100 that compares the oscillation output Lx and the constant voltage LMTREE1, an SR latch circuit 200 that holds the output of the comparator 100, a voltage LMTREE2 that is lower than the constant voltage LMTREE1, and an oscillation. The comparator 300 for comparing with the output Lx, the SR latch circuit 400 for holding the output of the comparator 300, the PWM controller 500, and the output for suppressing the passage of the output 800 of the PWM controller 500 by the set output of the SR latch circuit 200 or 400 The control circuit 600 includes a P-channel driver transistor 700 whose on / off is controlled by the output of the output control circuit 600.

  When an overcurrent flows instantaneously or continuously in the output voltage Vout, the H level during the ON period of the oscillation output Lx becomes lower than the power supply voltage. When the comparator 100 or 300 compares the H level during the ON period of the oscillation output Lx and the constant voltage LMTREE1 or the lower LMTREE2 with the comparator 100 or 300, The SR latch circuit 200 or 400 is set. The output control circuit 600 does not pass the output 800 from the PWM controller 500 by the set output of the SR latch circuit 200 or 400, turns off the P-channel driver transistor 700, and forcibly sets the oscillation output Lx to 0 level. As a result, when an overcurrent flows in the output voltage Vout, the P-channel driver transistor 700 can be protected without being destroyed.

JP 2002-171749 A

In the conventional overcurrent protection circuit, by comparing the oscillation output Lx depending on the on-resistance of the P-channel driver transistor and the reference voltage, when the reference voltage is lower, the P-channel driver transistor is turned off. The oscillation output Lx was forced to zero.
However, since the oscillation output Lx depending on the ON resistance greatly depends on the fluctuation of the power supply voltage or the temperature change, the accuracy of the conventional overcurrent protection circuit with respect to the power supply voltage fluctuation or the temperature change is poor.

(the purpose)
An object of the present invention is to solve such a conventional problem and to provide a switching regulator having a built-in overcurrent protection circuit with high accuracy against fluctuations in power supply voltage or temperature changes.

This onset Ming, the source power supply (Vdd), the drain is by switching each connected P-channel driver transistor in the oscillation output (Lx) (TR1), the oscillation output (Lx) to a power supply switching regulator The amplifier circuit (amplifier 10) mirrors the current flowing between the drain and source of the P-channel driver transistor (TR1) based on the potential between the oscillation output (Lx) and the drain of the P-channel driver transistor (TR1). ) And a plurality of transistors (TR2, TR3), a resistor (R7) for converting the mirrored current into a voltage, a first signal (11) converted into the voltage, and a second in which the reference current is converted into a voltage and the signal (12) comparator circuit (9) for comparing the, overcurrent, said first signal ( 1) when the second signal (12) less than a first latch circuit for holding the output of the previous SL comparator circuit (9) (10), said P based on the first latch circuit (10) It is characterized by an output control circuit (7) to turn off the channel driver transistor (TR1).

The above circuit is also characterized in that the temperature dependence of the level for determining overcurrent is reduced by using a resistor having the same temperature dependence and the reference current (8) having a small temperature dependence.
Further, the above circuit is characterized in that the dependency on the power supply voltage at a level determined to be an overcurrent is reduced by using a reference current that is less dependent on the power supply voltage.

  According to the present invention, the signal 12 obtained by voltage-converting the H level current of the oscillation output Lx is compared with the signal 11 obtained by voltage-converting the reference current. When the signal 12 becomes lower than the signal 11, the P-channel transistor is turned off. Thus, when an overcurrent flows in the output voltage, the P-channel transistor can be protected without being destroyed. Further, the temperature dependence and power supply voltage dependence of the overcurrent protection circuit can be reduced. Further, the signal 12 obtained by converting the voltage of the H level current of the oscillation output Lx and the signal 10 of the second reference current having a current value lower than the reference current are compared by the second comparator, and if the signal 12 becomes lower than the signal 10, This state is held in the second SR latch circuit, and the P-channel transistor is turned off, so that the P-channel transistor can be protected from being overdamaged when the output voltage is short-circuited. As a result, an overcurrent protection function can be provided for both an overcurrent that leads to a short circuit and an instantaneous overcurrent that does not lead to a short circuit, such as noise.

Embodiments of the present invention will be described below in detail with reference to the drawings.
(Example)
1 is a configuration diagram of a switching regulator according to a first embodiment of the present invention.
As shown in FIG. 1, the switching regulator of the present embodiment includes an amplifier circuit 10 that mirrors the current flowing between the drain and source of the P-channel transistor TR1, transistors TR2, 3, 4, and 5 that constitute the mirror circuit, A resistor R7 that converts a mirrored current into a voltage, a resistor R8 that converts a reference current into a voltage, a comparator circuit 9 that compares the signal 11 and the signal 12, and when the signal 12 is smaller than the signal 11 due to overcurrent. The SR latch circuit 10 holds the output of the comparator circuit 9 for a certain period, and the output control circuit 7 turns off the P-channel transistor TR1.

In FIG. 1, when a current flows through the terminal of the output voltage Vout, a mirror current is output by the amplifier circuit 10 and the transistors TR2, 3, 4, and 5. The output mirror current is voltage-converted by the resistor R7, thereby outputting the signal 12. The reference current 8 is converted into a voltage by a resistor R8 and a reference signal 11 is output. When the signal 12 becomes smaller than the signal 11, the SR latch circuit 10 is set, the output control circuit 7 turns off the P-channel transistor TR1, and the output voltage becomes 0V.
Reference numeral 4 is a reference voltage for comparison with a voltage proportional to the output voltage, 5 is a comparator for comparing the voltage proportional to the output voltage and the reference voltage, and 6 is a PWM controller.

At this time, if the resistors R7 and R8 having the same temperature dependence are used, the dependence of the resistances of the signals 11 and 12 due to the temperature change is reduced. Further, if the temperature dependence of the reference current is reduced, the influence of the reference signal 11 due to a change in the reference current temperature is reduced.
As a result, the temperature dependence of the overcurrent protection circuit is reduced.
Further, if the power supply voltage fluctuation of the reference current is small, the influence of the power supply voltage fluctuation of the reference signal 11 becomes small.

Thus, according to the first embodiment, the signal 12 obtained by current conversion of the H level voltage of the oscillation output Lx is compared with the reference current signal 11 , and when the signal 12 becomes lower than the signal 11, the P-channel transistor is turned off. When an overcurrent flows in the output voltage, the P-channel transistor can be protected without being destroyed. Further, according to the present invention, the temperature dependence and power supply voltage dependence of the overcurrent protection circuit can be reduced.

(Application examples)
Hereinafter, application examples of the present invention will be described.
In addition to the circuit that compares the signal 12 obtained by voltage-converting the current during the ON period of the oscillation output Lx and the signal 11 of the reference current 8 in FIG. A circuit for comparing the second reference current signal 10 with the second comparator is added. As a result of the comparison by the second comparator, when the signal 12 in the ON period of the oscillation output Lx becomes lower than the signal current of the second reference current, the second SR latch circuit is set. The output control circuit 7 turns off the P-channel driver transistor TR1 and forcibly sets the oscillation output Lx to 0 level by the set output of the SR latch circuit 7 or the second SR latch circuit.
As a result, when an overcurrent flows in the output voltage Vout, the P-channel driver transistor TR1 can be protected without being destroyed.

  In order to apply the present invention to the above circuit, the amplifier circuit 10 that mirrors the current flowing between the drain and source of the P-channel driver transistor TR1 and the plurality of transistors TR2, TR3, TR4, TR5, as in the above embodiment. And provide. As a result, it is necessary to provide the circuit with functions of power supply voltage dependency and temperature characteristic improvement.

  As described above, the signal 12 obtained by converting the H level current of the oscillation output Lx into the voltage and the signal 10 based on the second reference current whose current value is lower than the reference current are compared by the second comparator, and the signal 12 can be lower than the signal 10. For example, the state is held in the second SR latch circuit, and the P-channel transistor is turned off, so that the P-channel transistor can be protected without being destroyed against an overcurrent when the output voltage is short-circuited. .

It is a circuit block diagram of the switching regulator which concerns on Example 1 of this invention. It is a figure which shows the circuit example of the switching regulator in the past.

Explanation of symbols

Amplifier 10: Amplifier circuit that mirrors the current flowing between the drain and source of TR1 4: Reference voltage 5: Comparator 6: PWM controller 7: Output control circuit 8: Reference current 9: Comparator 10: SR latch circuit TR1, TR2, TR3 , TR4, TR5: Transistor Lx: Oscillation output Vout: Output voltage L: Coil C: Capacitance R7, R8: Resistance

Claims (3)

In a switching regulator that supplies power to the oscillation output by switching a P-channel driver transistor having a source connected to the power supply and a drain connected to the oscillation output,
An amplifier circuit that mirrors the current flowing between the drain and source of the P-channel driver transistor based on the potential between the oscillation output and the drain of the P-channel driver transistor, and a plurality of transistors;
A resistor that converts the mirrored current into a voltage;
A comparator circuit for comparing the first signal converted into the voltage and the second signal in which the reference current is converted into a voltage;
Overcurrent, when said first signal is less than said second signal, a first latch circuit for holding the output of the previous SL comparator circuit,
Switching regulator and having an output control circuit for turning off the P-channel driver transistor based on the first latch circuit. The switching regulator according to claim 1, wherein
A second comparator for comparing the first signal with a third signal with a second reference current having a value lower than the reference current;
When the first signal is lower than the signal current of the second reference current as a result of the comparison by the second comparator, the second latch circuit is set,
The output control circuit turns off the P-channel driver transistor based on one of the first latch circuit and the second latch circuit. In a switching regulator that supplies power to the oscillation output by switching a P-channel driver transistor having a source connected to the power supply and a drain connected to the oscillation output Lx,
An amplifier circuit that mirrors the current flowing between the drain and source of the P-channel driver transistor and a plurality of transistors;
A first resistor that converts the mirrored current to a voltage;
A comparator circuit for comparing the first signal converted into the voltage and the second signal converted into a voltage by a reference current and a second resistor;
A latch circuit that holds the output of the comparator circuit for a period of time when the first signal is smaller than the second signal due to overcurrent;
An output control circuit for turning off the P-channel driver transistor,
A switching regulator characterized in that the first resistor and the second resistor have the same temperature dependence .

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