JP4676211B2 - Switching regulator control circuit and switching regulator - Google Patents

Description

  The present invention relates to a control circuit for a switching regulator, and more particularly to switching control when an input voltage value and an output voltage value are close.

  FIG. 3 is a block diagram of a conventional step-up switching regulator. A coil 102 and a rectifying element 104 are connected between the input power supply 101 and the output capacitor 105. The switching regulator control circuit 107 monitors the voltage at the output terminal A of the switching regulator and controls ON / OFF of the switch element 103 of the switching regulator.

  The switching regulator control circuit 107 includes a reference voltage circuit 111, a bleeder resistor 112 and a bleeder resistor 113 that divide the output voltage Vout of the output terminal A, an error amplifier 110, a PWM comparator 108, and a triangular wave generation circuit 109. Yes.

  Assuming that the output voltage Ver of the error amplifier 110, the reference voltage Vref1, and the voltage Vb at the voltage dividing point B of the bleeder resistor 112 and the bleeder resistor 113, Ver is high if Vref1 <Vb, and Ver is low if Vref1> Vb. The PWM comparator 108 compares the triangular wave output of the triangular wave generation circuit 109 with the output of the error amplifier 110 and outputs a switching signal (see, for example, Patent Document 1).

  However, in the conventional step-up switching regulator control circuit, when the input voltage Vin and the output voltage Vout of the switching regulator are close, the output voltage Ver of the error amplifier 110 input to the PWM comparator 108 and the output voltage Vtri of the triangular wave generation circuit 109. Is a close value. Therefore, there is a problem that the output waveform of the PWM comparator 108 becomes thin, and the operation that the pulse goes out due to instantaneous load fluctuation and the pulse width increases due to the reaction is continued.

  Hereinafter, a description will be given using a timing chart of the conventional step-up switching regulator of FIG.

  In the section a, the output voltage rises due to instantaneous load fluctuation, the output voltage Ver of the error amplifier 110 exceeds the output voltage Vtri of the triangular wave generation circuit 109, and the pulse for controlling the switch element 103 is not output from the PWM comparator 108. . Since the switch element 103 remains OFF for one cycle, no energy is supplied to the coil 102.

  Therefore, the output voltage greatly decreases in the interval b, and the output voltage of the error amplifier 110 also decreases greatly. As a result, the output of the error amplifier 110 greatly intersects with the triangular wave, and the pulse width of the pulse for controlling the switch element 103 becomes excessively large.

  As a result, in the section c, the output voltage increases greatly, the output voltage of the error amplifier 110 also increases greatly, the output voltage Ver of the error amplifier 110 exceeds the output voltage Vtri of the triangular wave generation circuit 109, and the switching element 103 is switched from the PWM comparator 108. The control pulse is not output.

  As described above, unstable operations are repeated. Therefore, in order to obtain a desired voltage, current, and ripple voltage within a desired range, it is necessary to increase the size of external components.

The present invention has been made in view of the above-described problems of the prior art. When the input voltage Vin and the output voltage Vout are close, that is, the control signal width for controlling the switch element 103 is small even when the input / output voltage difference is small. An object of the present invention is to provide a switching regulator that operates stably without increasing.
JP-A-6-311741

  The switching regulator control circuit of the present invention includes a circuit for detecting that a switching pulse for controlling a switching element has not been output, detects that a switching pulse has not been output, and determines the pulse width of the next switching pulse. A circuit for forcibly reducing the size was provided.

  As described above, according to the switching regulator control circuit of the present invention, since the switching pulse width of the switching regulator operates stably without excessively increasing, the output ripple voltage can be kept low without requiring a large external component. Therefore, a switching regulator with high output voltage accuracy and stable operation can be provided.

  FIG. 1 shows a block circuit of a switching regulator of the present invention. A coil 102 and a rectifying element 104 are connected between the input power supply 101 and the output capacitor 105. The switching regulator control circuit 207 monitors the voltage at the output terminal A of the switching regulator and controls ON / OFF of the switch element 103 of the switching regulator.

  The switching regulator control circuit 207 includes a reference voltage circuit 111, a bleeder resistor 112 and a bleeder resistor 113 that divide the output voltage Vout of the output terminal A, an error amplifier 110, a PWM comparator 108, and a triangular wave generation circuit 109. ing.

  Further, a delay circuit 209 that delays the output signal of the PWM comparator 108, a selector 208, and a select signal generation circuit 216 are provided. The select signal generation circuit 216 includes a comparator 217, a reference voltage circuit 218, a constant current circuit 219, a capacitor 220, and a switch element 221.

  The constant current circuit 219 charges the capacitor 220 with a constant current. The comparator 217 compares the voltage of the reference voltage circuit 218 and the capacitor 220. When the charging voltage of the capacitor 220 is Vchg and the voltage of the reference voltage circuit 218 is Vref2, the output of the comparator 217 is Hi when Vchg <Vref2, and the output signal of the PWM comparator 108 is output from the selector 208. When Vchg> Vref2, the output of the comparator 217 is Low and the selector 208 outputs the output signal of the delay circuit 209. The switch element 221 is connected in parallel to the capacitor 220, and discharges the charging voltage of the capacitor 220 when the output of the selector 208 is Hi.

  FIG. 2 shows a timing chart of the step-up switching regulator of the present invention.

  When the control pulse is output from the selector at a regular cycle as in the sections (1) to (3) in FIG. 2, the capacitor 220 is periodically discharged by the switch element 221. The voltage does not exceed the reference voltage Vref2 of the reference voltage circuit 218. Therefore, the output signal of the PWM comparator 108 is output from the selector 208 as it is.

  When a section where the output voltage of the error amplifier 110 and the output voltage of the triangular wave generation circuit 109 cannot cross each other as shown in (4) of FIG. 2 due to instantaneous load fluctuations, a Hi pulse is output from the selector in this section. Therefore, the capacitor 220 continues to be charged, and the voltage of the capacitor 220 exceeds the reference voltage Vref2.

  Therefore, in the section (5) in FIG. 2, the output signal of the select signal generation circuit 216 is Low, and the selector 208 outputs the output signal of the PWM comparator 108 delayed by the delay time Td through the delay circuit 209. The That is, the switch element 103 is turned ON with a delay time Td. Further, at this timing, the switch element 221 is turned ON, and the voltage of the capacitor 220 is discharged. When the capacitor 220 voltage becomes Vchg <Vref, the output signal of the select signal generation circuit 216 becomes Hi, and the output signal of the selector 208 selects the output signal of the PWM comparator 108. That is, the output signal of the selector 208 is a pulse in which the output signal of the PWM comparator 108 is shortened by the delay time Td.

  As described above, since the ON width of the switch element 103 is prevented from becoming excessively large in the section (5), the output voltage is excessively increased by eliminating the output signal omission in the next section (6). Therefore, the switching regulator can be stably controlled.

It is a block diagram of the step-up switching regulator of the present invention. 3 is a timing chart of the step-up switching regulator according to the present invention. It is a block diagram of a conventional step-up switching regulator. It is a timing chart of the conventional step-up switching regulator.

Explanation of symbols

101 Input Power Supply 102 Inductor 103, 221 Switch Element 104 Rectifier Element 105 Output Capacitance 106 Load 107, 207 Switching Regulator Control Circuit 109 Triangular Wave Generation Circuit 110 Error Amplifier 111, 218 Reference Voltage Circuit 108, 217 Comparison Circuit 208 Selector 209 Delay Circuit 216 Select Signal generation circuit 219 Constant current circuit 220 Capacity

Claims (5)

An error amplification circuit that compares the output voltage with a reference voltage and outputs a voltage corresponding to the voltage difference;
A triangular wave generating circuit for generating a triangular wave;
In a switching regulator control circuit comprising a comparison circuit for outputting a switching pulse for comparing the output of the error amplification circuit and the triangular wave and controlling a switch element,
A delay circuit for delaying the switching pulse;
A detection circuit for detecting that the switching pulse has not been output;
With
It said detection circuit detects that the switching pulse is not output Then, the switching regulator control circuit for reducing the pulse width of the subsequent switching pulse by the delay time of the delay circuit. Input the switching pulse, the switching pulse delayed by the delay circuit, and the output signal of the detection circuit,
The switching regulator according to claim 1 , further comprising: a select circuit that outputs a switching pulse delayed by the delay circuit when an output signal that detects that the switching pulse is not output is input from the detection circuit. Control circuit. The detection circuit includes:
A switch element to which a switching pulse output from the select circuit is input;
A capacitor connected in parallel with the switch element;
The switching regulator control circuit according to claim 2 , further comprising: a constant current circuit that charges the capacitor . An error amplification circuit that compares the output voltage with a reference voltage and outputs a voltage corresponding to the voltage difference;
A triangular wave generating circuit for generating a triangular wave;
In a switching regulator control circuit comprising a comparison circuit for outputting a switching pulse for comparing the output of the error amplification circuit and the triangular wave and controlling a switch element,
A detection circuit comprising: a switching element to which the switching pulse is input; a capacitor connected in parallel with the switching element; and a constant current circuit that charges the capacitor;
A delay circuit for delaying the switching pulse;
And a selection circuit for selecting the switching pulse the delay circuit is delayed by an output signal detected by the detection circuit that the switching pulse is not output,
A switching regulator control circuit that detects that the switching pulse has not been output and reduces the pulse width of the next switching pulse by the delay time of the delay circuit.   A switching regulator controlled by the switching regulator control circuit according to claim 1.

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