JPS63244927A - Triangular wave generating circuit - Google Patents

Abstract

PURPOSE:To align a rising time with a falling time and to suppress high frequency ripple, by charging and discharging a capacitor with a constant current corresponding to third circuit output which compares differentially outputs in which the voltage of the capacitor is compared differentially with first and second threshold values respectively. CONSTITUTION:When potential at a point A exceeds potential V1, a transistor (Tr) Q32 is turned OFF, and the discharge of the capacitor CT is started. Next, when the potential at the point A drops below potential V2, Trs Q31, Q34, and Q35 are turned OFF, then, the charge of the capacitor CT is started. By repeating the above stated operation, a triangular wave can be obtained between both ends 21 and 22 of the capacitor CT. Thus, the Trs Q21 and Q22, and the Trs Q23 and Q24, and the Trs Q21 and Q26 perform differential comparison operations respectively, and the TRs Q27 and Q29 and the Trs Q28 and Q30 perform differential comparison. Therefore, since the charge/discharge of the capacitor CT are aligned perfectly, and also, inflow currents from a terminal 20 at the time of charging/discharging the capacitor CT are aligned perfectly, it is possible to prevent the high frequency ripple from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a triangular wave generating circuit, and more particularly to a triangular wave generating circuit used in a switching regulator.

BACKGROUND OF THE INVENTION FIG. 3 shows a block diagram of an example of a switching regulator.

In the figure, the switching circuit 10 is supplied with direct it pressure V
The current flowing through the primary winding of the transformer 11 is interrupted by switching IN. The voltage induced in the secondary winding of the transformer 11 is rectified by a diode 12 and a capacitor 13 to obtain a DC voltage VOLJT. This DC voltage VOUT is compared with a reference voltage VRE r- in a comparator circuit 14, and an error voltage is supplied to a pulse width converter 15. The pulse width modulator 15 compares the triangular wave supplied from the triangular wave generating circuit 16 with the error voltage to vary the pulse width of the generated switching pulse. For example, during the H level of this switching pulse, the switching circuit 10
applies the DC voltage VIN to the primary winding of the transformer 11.

The oscillation frequency of the above triangular wave, that is, the switching frequency is
The greater the number of turns of the transformer 11, the smaller the number of turns of the transformer 11, and the smaller the number of smoothing capacitors 13.

FIG. 4 shows a circuit diagram of an example of a conventional triangular wave generating circuit.

In the figure, resistors R+, R2, and R3 determine the threshold of the triangular wave, and resistors R+, R2, R3, transistor QO,
A hysteresis loop is formed in Q3. Also, transistor Q1 performs switching operation for charging and discharging capacitor "jCT".Here, when the power is turned on, transistor Q1
Assuming that the base of transistor Q6 is at H level and the base of transistor Q7 is at L level, transistor Q2 is turned on,
Both collectors are at H level. This turns off transistor Q3 and turns on transistor 01.
Transistors Qu and QI2 are turned off and transistor Q8
The collector current charges the capacitor CT.

When the base potential of the transistor Q7 is higher than the base potential of the transistor Q6, the transistors Qs and Qy are inverted and the transistor Q2 is turned off.
Transistor Q3 is turned on, transistor Q1 is turned off, and transistors On and Q+z are turned on. The collector current of the transistor Qn is approximately twice that of the transistor Q8, and the capacitor CT is discharged by the transistor Qn, and when the base potential of the transistor Q7 becomes lower than the base potential of the transistor Q6, the transistors Qs and Qy is reversed. As a result, a triangular wave is obtained at both ends of the capacitor CT.

Problems to be Solved by the Invention Each of the transistors Qo, Q+, and Q4 conducts when the capacitor CT is charged, but since they operate in the saturation region, the discharging time of the capacitor CT is affected by the storage time of these transistors. It will be longer than the charging time. In other words, there was a problem in that the rise time of the triangular wave was longer than the fall time. The ratio between the charging time and the discharging time becomes larger as the oscillation frequency becomes higher.

In addition, although transistor Q4 is required to perform high-speed switching operation, transistor Q4 is of PNP type;
High-speed switching operation is difficult compared to the conventional type.

Furthermore, transistors Q+ and Qs are alternately turned on and off, and both transistors Q1 . Since the collector current of Q3 is not the same, there is a problem in that ff1R flowing from the power supply fluctuates depending on the switching of transistors Q+ and Qs, causing high frequency ripples.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a triangular wave generation circuit in which the rise time and fall time of a triangular wave are coincident and the generation of high frequency ripples is prevented.

Means for Solving the Problems In the present invention, first and second comparison circuits differentially compare the voltage of the capacitor with first and second thresholds, respectively.

The third comparison circuit differentially compares the outputs of the first and second comparison circuits.

The charging/discharging circuit charges or discharges the capacitor with a constant current depending on the output of the third comparison circuit.

This outputs the capacitor voltage as a triangular wave.

In the present invention, the first to third comparison circuits perform differential comparison, and the charging/discharging circuit charges and discharges the capacitor with a constant current, so that the rise time and fall time of the triangular wave match. Furthermore, since the current flowing through the entire circuit during charging and discharging is the same, high frequency ripples can be prevented from occurring.

Example FIG. 1 shows an embodiment of the circuit of the present invention.

In the figure, the power supply voltage Vcc is applied to the terminal 20, and the terminal 2
1 is grounded at the common terminal.

Resistor R11°RI2 connected in series to terminal 20.21@
．． R+3 determines the triangular wave threshold, and resistor R
The potential v1 at the connection point between RI2 and RI2 becomes the maximum value of the triangular wave, and the resistance RI2. The potential V2 at the connection point of R13 becomes the minimum value of the triangular wave.

Transistor Q21. Q22 constitutes a first differential comparison circuit whose threshold value is potential V+, and each transistor is driven in a non-saturation region by constant current source I+. Transistor Q23. Q24 constitutes a second differential comparison circuit with voltage v2 as a threshold, and each transistor is driven in a non-saturation region by low current source I2.

Resistors RI4, R+s*R+s, R+7 and transistors Q25 and 02B constitute a bistable multivibrator, and each transistor is driven by a constant current source 13 in a non-saturation region.

Transistor Q27. Q28. Q29. Q3) constitutes a third differential comparison circuit, and each transistor is connected to a constant current source 14.
．． I5. It is driven in a non-saturated region by I6.

Transistor Q31. Q32. Q33. Q34. Q35
and resistor R+s, R+s is transistor 027. Q2+1
The charging and discharging circuit is comprised of the following. The above transistor Q31. Each of Q32 constitutes a current mirror circuit together with transistor Q33, and transistors Q34゜Q35
constitutes a current mirror circuit. transistor 0
33 is driven by a constant current source I7 or a resistor R21.

Note that the switch 22 selects the resistor R21 when the electric voltage Vcc is stable, and selects the constant current source I7 when it is unstable.
Select.

Here, at time t1, if the potential at point A, which is the collector of transistor Q32, is less than potential V1 as shown in FIG. Q
31, Q34, and Qys are turned off, and when the collector of transistor Q28 is at the 1'' level, transistor Q32 is turned on. This charges the capacitor CT.

At this time, the 8 points, which are the bases of transistors 026 and 025, the 0 point, and the transistor Q29. Q3) The waveforms at points D and E, which are the respective bases, and points E and G, which are the emitters of transistor Q31゜032, are shown in Figure 2 (
Shown in B) to (G).

After this, when the potential at point A exceeds potential v1 at time t2,
Transistor Q22 is turned on, the collector of transistor 027 is at H level, and transistors Q31, Q34, . QZ
turns on, and the collector of transistor 02B goes low.
At this level, transistor Q32 is turned off. This starts discharging the capacitor CT.

Next, at time t3, when the potential at point A becomes less than potential 72, transistor Q24 is turned on and the collector of transistor Q28 becomes H level, turning on transistor Q32.

At the same time, 8 points are at H level and the collector of transistor Q27 is at L level, transistors Q31, 03+1
, Q35 turns off and charging of the capacitor CT starts.

By repeating the above operation, a triangular wave is obtained between both ends of the capacitor CT, that is, between the terminals 21 and 22.

In this way, transistors Q21 and QZ2. QZ3 and Q
24. Q25 and Q26 each perform a differential comparison operation,
Transistors Q27 and 02B and 028 and Q3) perform a differential comparison operation, and transistors Q31. Q32
Either one of them performs a current mirror operation together with the transistor Q33, and the transistors Qy+ and Qya perform a current mirror operation. Therefore, the charging time and discharging time of the capacitor CT, that is, the rise time and fall time of the triangular wave, completely match, and the current flowing from the terminal 20 when charging and discharging the capacitor CT completely match. It is possible to prevent the occurrence of high frequency ripples.

In addition, the transistors Q21 to Qys are connected to the constant current sources 11 to
6 in the non-saturation region. Among the transistors Qrr to Q3G, for example, the transistor Q27. Q
When 29 is turned on, a current flows through the resistor R+s, so the collector potential of the transistor Q27 decreases, but since the transistor Q29 is provided, the base potential of the transistor 027 decreases by the base-emitter voltage drop (0.7 V). This prevents the base potential of the transistor 027 from being lower than the collector potential, and the transistor 027
27 is saturated 7 never happens. Therefore, the influence of the storage time of the transistor can be avoided, and the oscillation frequency of the triangular wave can be increased.

Effects of the Invention As described above, the triangular wave generation circuit of the present invention can generate a distortion-free triangular wave whose rise time and fall time completely match, and can prevent the occurrence of high frequency ripples, making it extremely useful in practice. be.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the circuit of the present invention, and Fig. 2 is a circuit diagram of an embodiment of the circuit of the present invention.
FIG. 3 is a block system diagram of an example of a switching regulator, and FIG. 4 is a circuit diagram of an example of a conventional circuit. CT...Capacitor, ■1~I7...Constant current source, Q
21~Qr3...Transistor, RuゝR2+-Resistance 0 Patent applicant Mitsumi Electric Co., Ltd. Figure 2

Claims (1)

[Claims] First and second comparison circuits that differentially compare the voltage of the capacitor with the first and second threshold values, and the outputs of the first and second comparison circuits are differentially compared. It is characterized by having a third comparison circuit for comparison, and a charging/discharging circuit for charging or discharging the capacitor with a constant current according to the output of the third comparison circuit, and outputting the voltage of the capacitor as a triangular wave. A triangular wave generation circuit.