JPH0662564A - Chopper mode switching regulator - Google Patents

Abstract

PURPOSE:To make it possible to effect backup when a current limiting circuit comes to failure by providing a comparator for detecting that the voltage of a voltage detecting circuit across both ends of a current detecting resistor becomes 0V. CONSTITUTION:An integrated circuit 21 is provided with a comparator 23 for detecting that an output from a voltage detecting circuit 22 which detects a voltage across both ends of a current detecting resistor 2 becomes 0V, and an AND circuit 24 for producing a logical product between an output from the comparator 23 and an output from a flip-flop circuit 15. If the current detecting resistor 2 is short-circuited by any reasons, the voltage detecting circuit 22 detects a voltage across both ends of the current detecting resistor 2. When this voltage is 0V, an output from the comparator 23 attains a 'H' logic level, and is inputted into the AND circuit 24. When both inputs to the AND circuit 24 have the 'H' logic level, a transistor 25 on the following stage is turned on, and the reference voltage becomes 0V. Thereby, the operation of a regulator circuit is suspended, and backup is effected in the case of a broken current limiting circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chopper type switching regulator, and more particularly to an improved overcurrent protection circuit for backing up the current limiting circuit in case of failure.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a configuration of a conventional chopper type switching regulator. In the figure,
A switching regulator integrated circuit 1 includes an oscillator 11, a reference voltage generation circuit 12, a comparator 13, and an AN.
It is composed of a D circuit 14, an RS flip-flop 15, output switching transistors 16 and 18, and a resistor 17.

Reference numeral 2 is a current detection resistance, and reference numerals 3 and 4 are division resistances for detecting the output voltage of the switching regulator integrated circuit 1. Further, 5 is a resistor, 6 is an input capacitance, 7 is a capacitance for setting an oscillation time constant, 8 is an output capacitance, 9 is a choke, and 10 is a diode. The above circuit elements 2 to 10 are externally attached to the integrated circuit 1.

Next, the operation will be described. In FIG. 2, resistors 3 and 4 for dividing the output V _OUT (resistance values R1 and R
Set the voltage value you want to boost in step 2). The divided output voltage divided by the resistors 3 and 4 by the comparator 13 is compared with the reference voltage V _REF generated by the reference voltage generation circuit 12, and if the divided output voltage set voltage is higher than the reference voltage, the comparator 13 L "is output.
As a result, in the AND circuit 14, the output of the oscillator 11 is masked, so that the S input of the RS flip-flop 13 becomes "L" and the Q output also becomes "L", and the output switching transistor 18 stops current switching. As a result, the energy stored in the external choke 9 is released, and the output voltage drops so as to approach the set value.

On the contrary, if the divided output voltage is lower than the reference voltage, the comparator 13 outputs "H". This causes the AND circuit 14 to pass the output of the oscillator 11,
The flip-flop 15 outputs a signal synchronized with the oscillation of the oscillator 11. As a result, the output transistors 16 and 18
Turns on and off in synchronization with the oscillator 11 charging and discharging the time constant setting capacity 7. Energy is accumulated in the choke 9 by the on / off operation of the output transistor,
The output voltage rises as it approaches the set value.

The current detection resistor 2 is for limiting the current by setting its value, and the voltage across the current detection resistor 2 is applied to the oscillator 11. The oscillator 11 makes the rising edge of the charging voltage for charging the capacitor 7 steep when this voltage exceeds a predetermined value. As a result, the ON period of the output transistor is shortened, and the output voltage of the switching regulator integrated circuit 1 is drooped to protect against overcurrent.

[0007]

Since the conventional chopper type switching regulator is configured as described above, when the current detection resistor is short-circuited for some reason, the current limiting circuit does not function and overcurrent flows. There was a problem that it would end up.

The present invention has been made to solve the above-mentioned problems, and even when the current limiting circuit fails to function due to a failure, the failure is detected and the operation of the regulator circuit is stopped. Therefore, it is an object of the present invention to obtain a chopper type switching regulator capable of backing up when a current limit circuit fails.

[0009]

SUMMARY OF THE INVENTION A chopper type switching regulator according to the present invention is a voltage detection circuit for monitoring the voltage across a current detection resistor, a comparison circuit for detecting that the voltage has reached 0V, and its output. And an AND circuit for taking a logical product of the output of the existing flip-flop circuit and the transistor driven by the output of the AND circuit.

[0010]

According to the present invention, by constructing the overcurrent protection circuit as described above, the existing reference voltage is applied when the voltage across the current detection resistor is 0V, even though the output switching transistor is on. The circuit operation is stopped by setting it to 0V.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a chopper type switching regulator according to an embodiment of the present invention. In the figure, the same symbols as those in FIG. 2 indicate the same components. A switching regulator integrated circuit 21 includes an oscillator 11, a reference voltage generation circuit 12, a comparator 13, an AND circuit 14, an RS flip-flop 15, output switching transistors 16 and 18, and resistors as in the conventional integrated circuit 1. 17 is already included. Further, in the present integrated circuit 21, 22 which is newly included is a voltage detection circuit for detecting the voltage across the current detection resistor 2, and 23 is the voltage detection circuit 2 described above.
Reference numeral 24 is a comparison circuit for detecting that the output of 2 has become 0V, and 24 is an AND circuit for taking the logical product of the output of the comparison circuit 23 and the output of the flip-flop circuit 15.
Reference numeral 5 is a transistor driven by the output of the AND circuit 24.

Next, the operation will be described. If the current detection resistor 2 is short-circuited for some reason, the voltage detection circuit 2
2 detects the voltage across the current detecting resistor 2, and when the voltage across the current detecting resistor 2 is 0 V, the output of the comparison circuit 23 becomes "H",
It is input to the AND circuit 24. Now, only when the output switching transistor 3 is on, that is, the AND circuit 2
When both of the two inputs to 4 are "H", the transistor 25 in the next stage is turned on and the reference voltage becomes 0V. This stops the operation of the regulator circuit, and backs up when the current limiting circuit fails.

As the above embodiment, the one applied to the step-up type chopper type switching regulator is shown, but the step-down type and voltage inversion type chopper type obtained by changing the external configuration of the integrated circuit 21. The present invention can be similarly applied to a switching regulator.

3 to 7 show examples of circuit configurations of various switching regulators to which the present invention can be applied.

FIG. 3 shows a step-up converter with a current buffer transistor, 31 is a current buffer transistor, and 32 is a resistor. A configuration example is shown.

FIG. 4 is a step-down converter, FIG. 33 is a diode, and 34 is a choke.

FIG. 5 shows a step-up converter with a current buffer transistor, 35 and 36 are resistors and 37
Is a current buffer transistor, 38 is a diode, 39
Is chalk.

FIG. 6 shows a polarity inverting converter, 41 is a choke, 42 is a capacitor, and 43 is a diode.

Further, FIG. 7 shows a polarity inverting converter with a current buffer transistor, 44 is a capacitor, 45 and 46 are resistors, 47 is a current buffer transistor, 48 is a choke, and 49 is a diode.

[0020]

As described above, according to the chopper type switching regulator of the present invention, even when the output switching transistor is on, the reference voltage is 0V when the voltage across the current detection resistor is 0V. Since the circuit is configured as described above, there is an effect that overcurrent protection can be performed by stopping the operation of the regulator even when the current limiting circuit fails.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a chopper type switching regulator according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional chopper type switching regulator, and is a diagram showing an example applied to a step-up converter.

FIG. 3 is a diagram showing a step-up converter with a current buffer transistor, which is an example of a switching regulator to which the present invention can be applied.

FIG. 4 is a diagram showing a step-down converter, which is an example of a switching regulator to which the present invention can be applied.

FIG. 5 is a diagram showing a step-down converter with a current buffer transistor, which is an example of a switching regulator to which the present invention can be applied.

FIG. 6 is a diagram showing a polarity inverting converter, which is an example of a switching regulator to which the present invention can be applied.

FIG. 7 is a diagram showing a polarity inverting converter with a current buffer transistor, which is an example of a switching regulator to which the present invention can be applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 switching regulator integrated circuit 2 current detection resistor 11 oscillator 12 reference voltage generation circuit 13 comparator 14 AND circuit 15 RS flip-flop 16, 18 output switching transistor 21 switching regulator integrated circuit 22 voltage detection circuit 23 comparison circuit according to one embodiment of the present invention 24 AND circuit 25 transistor

Claims (1)

[Claims] 1. A means for comparing a reference voltage with a voltage corresponding to a set voltage to be output, a flip-flop circuit to which an output of an oscillator is gated and input according to the comparison result, and a flip-flop circuit via the flip-flop circuit. In a chopper type switching regulator equipped with an output transistor that turns on and off according to the oscillation frequency of the above-mentioned oscillator input, a voltage detection circuit that monitors the voltage across the current detection resistor, and detects that the voltage has reached 0V And an AND circuit for taking a logical product of the output of the comparator circuit and the output of the flip-flop circuit, and a transistor driven by the output of the AND circuit to stop the operation of the regulator when the current limiting circuit fails. A chopper type switching regulator characterized in that