JPH0424952B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention compares a sawtooth wave voltage serving as a reference for the switching frequency with a voltage corresponding to load fluctuation (a fluctuation voltage with respect to the rated voltage of the output voltage), This invention relates to improvements in switching regulators that stabilize output voltage by controlling transistors on and off using pulse width modulation control.

(b) Background of the technology Switching regulators that perform pulse width control have recently been widely used as DC power sources for electronic devices because the switching frequency can be set to a high frequency, making it possible to miniaturize transformers and simplifying smoothing circuits. ing.

(c) Prior Art and Problems A conventional switching regulator and problems will be explained using the accompanying drawings.

Fig. 1 is a circuit diagram of a conventional switching regulator, Fig. 2 and Fig. 3 are time charts of waveforms at various parts in Fig. 1, Fig. 2 shows normal operation, and Fig. 3 shows double pulse generation. In this case, B to C correspond to points b to c in FIG.

To explain the operation of FIG. 1, when the difference between the voltage of the load 7 and the reference voltage Vref is determined by the operational amplifier 1,
In a normal case, the voltage will be as shown at 2 in FIG. 2A.

This voltage and the second voltage from the sawtooth voltage generator 3
When the comparator 2 compares the voltage shown at 1 in FIG. A, the sawtooth voltage generates a pulse with a larger width. When this pulse is separated by a flip-flop (hereinafter referred to as FF) 4 and AND circuits 5 and 6, a pulse as shown in FIG.
The output pulse will be .

These pulses are transmitted through transistors Tr ₁ , Tr ₂ ,
It becomes a pulse voltage that switches the main transistors Tr ₃ and Tr ₄ via the transformer T ₁ , and the main transistors Tr ₃ and Tr ₄ switch the DC power supply E,
The current flowing through the transformer T ₂ is made into an alternating current, and the voltage induced in the transformer T ₂ by this is changed to a diode.
Power is supplied to the load 7 after smoothing by D ₁ , D ₂ yoke L and capacitor C ₃ .

However, if the output of the operational amplifier 1 fluctuates due to noise as shown in 2 A, B, and C of Figure 3A, the 3rd
The sawtooth wave voltage shown at 1 in Figure A exceeds the voltage 2 at A at point A, becomes less than at point B, and exceeds it again at point C.

In this case, the outputs of the AND circuits 5 and 6 become pulses as shown in FIG. output for each sawtooth wave voltage.

On the other hand, the output pulse from the AND circuit 6 is also output every two consecutive sawtooth wave voltages, but in this case, the pulses generated due to noise have a narrow width as shown in D, so the transformer T ₂ is polarized. This may cause damage to the main transistor Tr ₃ or Tr ₄ .

The phenomenon of emitting a pulse every two consecutive sawtooth wave voltages in this way is called double pulse generation, and if this phenomenon occurs, it will cause damage to the main transistor as described above, so it is necessary to prevent double pulse generation. However, there is a problem in which no countermeasures have been taken in the past. Note that R ₁ and R ₂ in FIG. 1 are resistances.

(d) Object of the Invention In view of the above problems, an object of the present invention is to provide a pulse width control circuit that does not generate double pulses.

(e) Structure of the Invention The present invention has been made to achieve the above-mentioned object, and includes an operation for operationally amplifying the error between the output voltage and a reference voltage, which is the standard for the rated output voltage, as a voltage corresponding to load fluctuations. An amplifier, a comparator that compares the voltage corresponding to the load fluctuation with a sawtooth wave voltage that serves as a reference for the switching operating frequency, and receives the output pulse of the comparator as input and outputs a pair of inverted pulses with mutually opposite phases. a flip-flop circuit that inverts the logical product of the output pulse of the comparator and each of the pair of inverted pulses;
a pair of differentiating circuits that differentiate the output pulses of the pair of NAND circuits and feed back a voltage corresponding to the load fluctuation of the comparator; and a pair of drive pulses that invert the output pulses of the pair of NAND circuits, respectively. By configuring a pulse width control circuit consisting of a pair of output inverter circuits, when the sawtooth wave voltage exceeds the voltage corresponding to the load fluctuation, the sawtooth wave voltage will be adjusted to the load fluctuation at the longest from that point onwards. The voltage corresponding to the load change is forcibly lowered until the voltage becomes lower than the corresponding voltage.

In other words, when the difference between the sawtooth wave voltage and the voltage corresponding to the load fluctuation is small and noise is added, double pulses are generated because the sawtooth voltage exceeds the voltage corresponding to the load fluctuation. Since it was a time when
At this point, the voltage corresponding to the load fluctuation is forcibly lowered, and even if noise is added to the voltage corresponding to the load fluctuation, the voltage due to this noise does not exceed the sawtooth voltage, thereby preventing the generation of double pulses. It is designed to prevent this.

(f) Embodiment of the invention An embodiment of the invention will be described below with reference to the drawings.

Fig. 4 is a circuit diagram of a switching regulator according to an embodiment of the present invention, and Fig. 5 is a time chart of waveforms at various parts in Fig. 4. B and C correspond to points b and c in Fig. 4. There is.

Components in Figure 4 that have the same functions as those in Figure 1 are indicated by the same symbols. 5' and 6' are NAND circuits, 8 and 9 are inverter circuits, C ₄ and C ₅ are capacitors, and R ₃ and R ₄ are resistors. show.

The difference between FIG. 4 and FIG. 1 is that NAND circuits 5' and 6' are used instead of AND circuits 5 and 6 in FIG. . In between, capacitor C ₄ , resistor R ₃ and capacitor C ₅ , resistor R ₄
The point is that a series circuit consisting of the following is provided.

In this way, the output pulses of the NAND circuits 5' and 6' become inverted from the conventional ones as shown in FIG. From the input side of device 2,
A current is drawn into the output side of the NAND circuit 5' or 6' via the resistor R ₃ capacitor C ₄ or the resistor R ₄ capacitor C ₅ , and the voltage corresponding to the load 7 on the input side of the comparator 2 is The item 2 in Figure 3 A is the 5th item.
As shown at 2' in Figure D, at the point where the sawtooth wave voltage exceeds the voltage corresponding to the load fluctuation, the voltage immediately drops and recovers.

Therefore, as shown in FIG. 5D, when the sawtooth wave voltage 1 exceeds the voltage 2' corresponding to the load fluctuation, the difference, which was previously small, becomes large, and the noise is multiplied as shown in E. This eliminates the possibility of generating double pulses even when Furthermore, this voltage drop is caused by the capacitor
The values of the C ₄ resistor R ₃ and the capacitor C ₅ resistor R ₄ may be selected so that the sawtooth wave voltage is restored before it falls below the voltage corresponding to the load fluctuation.

(g) Effects of the Invention As explained in detail above, the present invention has the effect of preventing the generation of double pulses.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional switching regulator, FIG. 2, FIG. 3 is a time chart of waveforms at various parts in FIG. 1, and FIG. 4 is a circuit diagram of a switching regulator according to an embodiment of the present invention. The circuit diagram and FIG. 5 are time charts of waveforms at various parts in FIG. 4. In the figure, 1 is an operational amplifier, 2 is a comparator, 3 is a sawtooth voltage generator, 4 is a flip-flop, 5 and 6 are AND circuits, 5' and 6' are NAND circuits, 7 is a load,
8 and 9 are inverter paths, Tr ₁ to Tr ₄ are transistors, E is a DC power supply, T ₁ and T ₂ are transformers, and Vref is a reference voltage.

Claims (1)

[Claims] 1. In a switching regulator that stabilizes the output voltage by alternately controlling a pair of main switching elements on and off, the error between the output voltage and the reference voltage, which is the standard for the rated output voltage, is adjusted to correspond to load fluctuations. An operational amplifier that performs operational amplification as a voltage, a comparator that compares the voltage corresponding to the load fluctuation with a sawtooth wave voltage that serves as a reference for the switching operating frequency, and a a flip-flop circuit that outputs a pair of inverted pulses; a pair of NAND circuits that inverts the AND of the output pulse of the comparator and each of the pair of inverted pulses; and a pair of NAND circuits that respectively differentiate the output pulses of the pair of NAND circuits. and a pair of inverter circuits that respectively invert the output pulses of the pair of NAND circuits and output a pair of drive pulses. A switching regulator pulse width control circuit featuring: