JPH06216722A - Triangular wave oscillating circuit - Google Patents

Abstract

PURPOSE:To reduce a variance in an oscillation frequency due to the variance in a resistance value of each resistor for constituting the circuit, in the triangular wave oscillating circuit, especially, the triangular wave oscillating circuit formed as a semiconductor integrated circuit. CONSTITUTION:Charging and discharging currents of a capacitor 13 are set to a current value being proportional to a current I0 of a reference current circuit consisting of a transistor 2 and a resistance 5 of a current mirror circuit provided in a control circuit 12. Also, an oscillation voltage setting circuit 20 for executing control so that a difference voltage of the upper limit voltage and the lower limit voltage of an oscillation voltage is varied in accordance with a variation in the current value of the current I0 of this reference current circuit is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triangular wave oscillator circuit used for controlling an electronic device such as a switching power supply device.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a conventional triangular wave oscillator circuit. In FIG. 2, a triangular wave oscillator circuit has a transistor 2 whose emitter is connected to a power supply terminal 1 and whose collector is connected to a ground terminal through a resistor 5 and whose base and collector are short-circuited, and to the emitter and base of this transistor 2, respectively. Transistors 3 and 4 having their emitters and bases connected, transistors 6 and 7 having their collectors connected to the collector of transistor 3, their emitters connected to the ground terminal, and their bases connected to each other, and their collectors being transistors 4, the emitter of which is connected to the ground terminal, the base of which is connected to the base of the transistor 7, and the base of which is shorted to the collector of the transistor 8 and the resistor which is connected in series between the power supply terminal 1 and the ground terminal. 14, 15 and 16
An operational amplifier 9 having its output terminal connected to the collector of the transistor 4, its + input terminal connected to the collector of the transistor 3, and its-input terminal connected to the connection point between the resistors 14 and 15, and its collector connected to the resistor 15. At the connection point of 16, a transistor 11 having its emitter connected to the ground terminal and its base connected to the output terminal of the operational amplifier 9, and a capacitor 13 connected between the collector of the transistor 3 and the ground terminal are provided. 11 to control circuit 12 14-16
Constitutes the oscillation voltage setting circuit 17.

The operation of this triangular wave oscillator circuit is as follows. Transistors 2, 3 and 4 constitute a current mirror circuit, equal currents I ₀ to the current I ₀ of the reference current circuit constituted by the transistors 2 and resistor 5 flows through the collectors of the transistors 3 and 4 (transistors 2, 3 and 4 as the same capacity). Further, the transistors 8, 7 and 6 form a current mirror circuit, and a current I is supplied to the transistor 8.
_{When 0} flows (this current is supplied from the collector of transistor 4), current I ₀ flows through transistors 6 and 7, respectively. Here, when the voltage V is applied to the power supply terminal 1, the negative voltage V ₁ of the power supply voltage V divided by the resistors 14, 15 and 16 of the oscillation voltage setting circuit 17 is input to the negative input terminal of the operational amplifier 9. To be done. Equation 1 shows the voltage value of the divided voltage V _1.

[0004]

[Formula 1] V₁= (R₁₅+ R₁₆/ R₁₄+ R₁₅+ R₁₆) ・ V────
─── (1) However, R₁₄, R₁₅And R₁₆Are resistors 14 and 15 respectively
And 16 resistance values are shown. In addition, the operational amplifier 9 + input
The output terminal is capacitor 13 (at this time it is still charged)
Therefore, the voltage between both terminals is connected to the ground terminal via 0).
Since the input voltage is 0, the operational amplifier 9
The output terminal outputs a signal of "L". Output of this "L"
Signals turn off transistors 8, 7, 6 and 12
Becomes On the other hand, the current composed of transistors 2, 3 and 4
It is composed of the transistor 2 and the resistor 5 of the mirror circuit.
Current I in the reference current circuit₀Flows, this current I₀be equivalent to
Current I ₀From the collector of transistor 3 to capacitor 1
3 to charge the capacitor 13. This capacitor 1
The voltage between both terminals of 3 is input to the + input terminal of operational amplifier 9.
As a result of charging, the voltage between both terminals is shown in equation (1).
Voltage V input to the minus input terminal of the operational amplifier 9
₁When it exceeds, from the output signal “L” of the operational amplifier 9,
Switch to "H". Output signal of operational amplifier 9 is "H"
Switching to transistors 8, 7, 6 and 11
Turn on. The operational amplifier is turned on by turning on the transistor 11.
The voltage at the-input terminal of 9 is
Power source voltage V divided by 15 V₂Switch to.

[0005]

[Formula 2] V ₂ = (R ₁₅ / R ₁₄ + R ₁₅ ) ・ V ───────
(2) At the same time, when the transistors 8, 7 and 6 are turned on, the current I ₀ supplied from the collector of the transistor 8 is supplied to the transistor 8 and this current I ₀ is supplied to the collectors of the transistors 7 and 6. A current I ₀ equal to the current flows. Therefore, the capacitor 13 is discharged with this current I ₀ (capacitor 13
The inflow current into the transistor 3 is the collector current I ₀ of the transistor 3, the outflow current from the capacitor 13 is the sum of the currents of the transistors 6 and 7 2I ₀ , and the current of the subtraction I ₀ discharges the capacitor 13). Then, when the voltage between both terminals of the capacitor 13 decreases to the voltage V _{2 corresponding} to the expression (2), the output signal of the operational amplifier 9 switches from “H” to “L”. This operation is repeated and oscillation continues. Further, the divided voltages V ₁ and V ₂ define the upper limit voltage and the lower limit voltage of oscillation, respectively.

Here, the capacitance of the capacitor 13 is C, the charging time until the voltage between both terminals thereof rises to the upper limit voltage V ₁ of the oscillation voltage is t ₁ , and until the upper limit voltage V ₁ drops to the lower limit voltage V _2. When the discharge time of is t ₂ , the oscillation frequency f
Is calculated by the equation (3).

[0007]

I ₀ · t ₁ = C (V ₁ −V ₂ ) I ₀ · t ₂ = C (V ₁ −V ₂ ) ∴f = 1 / t ₁ + t ₂ = I ₀ / 2C (V ₁ − V ₂ ) ──
──── (3) In order to stabilize the oscillation operation, the transistor 11
The transistors 8, 7 and 6 are turned on after turning on, and the transistors 8, 7 and 6 are turned off after turning off the transistor 11, so that the operating times of these transistors have a slight difference.

[0008]

Since the above-mentioned triangular wave oscillator circuit is usually formed as a semiconductor integrated circuit, there is a relatively large variation in the resistance values of the resistors forming the circuit (however, the resistance between these resistors is large). The relative variation of the values is almost 0 because they are in the same integrated circuit). As described above, when the resistance value varies, the oscillation frequency relatively varies. That is, as shown in equation (3), the oscillation frequency is the current I of the reference current circuit.
_It is proportional to ₀ and inversely proportional to the difference between the upper limit voltage V ₁ and the lower limit voltage V ₂ of the oscillation voltage. When the resistance value varies, the current I ₀ of the reference current circuit varies in accordance with the variation in the resistance value of the resistor 5 in FIG. 2, but the upper limit voltage V of the oscillation voltage V
₁ and the lower limit voltage V ₂ are constant because the relative variations of the resistance values of the resistors 14, 15 and 16 are 0, and the oscillation frequency varies due to the variation of the resistance value of the resistor 5 and thus the variation of the current I ₀ of the reference current circuit. Produce equal variations.

An object of the present invention is to reduce the variation in the oscillation frequency due to the variation in the resistors constituting the circuit (however, the relative variation between these resistors is almost zero).

[0010]

In order to achieve the above object, the present invention provides an oscillation voltage setting circuit for determining an upper limit voltage and a lower limit voltage of an oscillation voltage, a capacitor, and a charging current of a predetermined current value for the capacitor. In the triangular wave oscillating circuit consisting of a control circuit for charging from the lower limit voltage to the upper limit voltage of the oscillating voltage, discharging from the upper limit voltage to the lower limit voltage with a discharge current of a predetermined current value after charging, and repeating the hereafter. The charging and discharging currents of the above are set to current values proportional to the current of the reference current circuit including the transistor and the resistor (hereinafter referred to as the first resistor) connected between the power supply and the ground of the current mirror circuit provided in the control circuit. However, the difference voltage between the upper limit voltage and the lower limit voltage of the oscillation voltage determined by the oscillation voltage setting circuit is changed according to the change of the current value of the current of the reference current circuit. To control to. The oscillation voltage setting circuit includes a second resistor, a diode and a third resistor through which a current proportional to the current value of the reference current circuit of the current mirror circuit of the control circuit is passed, and the voltage drop of the second resistor is caused. Determines the lower limit voltage of the oscillation voltage, and the sum of the voltage drops of the second resistor, the diode and the third resistor determines the upper limit voltage. The triangular wave oscillator circuit is formed as a semiconductor integrated circuit.

[0011]

The triangular wave oscillating circuit of the present invention is a reference current circuit comprising a transistor and a first resistor connected between the power supply and the ground of a current mirror circuit provided with a charging and discharging current of a capacitor in a control circuit. Since the current value proportional to the current is set and the difference voltage between the upper limit voltage and the lower limit voltage of the oscillation voltage is controlled to change in accordance with the change in the current value of the reference current circuit, the reference value of the current mirror circuit is set. First of current circuit
When the resistance value of the resistor is varied, for example, when it increases, the current value of the current of the reference current circuit decreases, which decreases the charging and discharging currents of the capacitor and reduces the difference voltage between the upper limit voltage and the lower limit voltage of the oscillation voltage. Therefore, it operates so as to suppress changes in the charging and discharging times of the capacitor. In this way, variations in oscillation frequency due to variations in resistance value are reduced. The oscillation voltage setting circuit is provided with a second resistor, a diode and a third resistor through which a current proportional to the current value of the reference current circuit of the current mirror circuit of the control circuit is passed, and the voltage drop of this second resistor is Since the lower limit voltage of the oscillation voltage is determined and the sum of the voltage drops of the second resistor, the diode and the third resistor determines the upper limit voltage, the resistance values of the second resistor and the third resistor are set to the current mirror. Since the reference current of the circuit varies in proportion to the resistance value of the first resistor of the circuit (since the resistance value of each resistor is almost zero when the circuit is formed as a semiconductor integrated circuit), The second and third resistors have a constant voltage drop because, for example, the amount of current flowing through them decreases as the resistance value increases. On the other hand, the voltage drop of the diode decreases as the conduction current decreases. Therefore, the second
The lower limit voltage of oscillation determined by the voltage drop of the resistor is constant, and the upper limit voltage determined by the diode and the third resistor decreases, so that the difference voltage between the upper limit voltage and the lower limit voltage of the oscillation voltage decreases. In this way, the difference voltage between the upper limit voltage and the lower limit voltage of the oscillation voltage can be changed according to the current value of the reference current circuit of the current mirror circuit.

[0012]

1 is a circuit diagram showing an embodiment of a triangular wave oscillator circuit of the present invention. The triangular wave oscillator circuit of the present invention shown in FIG. 1 corresponds to the conventional triangular wave oscillator circuit shown in FIG.
An oscillation voltage setting circuit 20 is provided instead of the oscillation voltage setting circuit 17 composed of 4, 15 and 16. In this oscillation voltage setting circuit 20, the emitter and the base of the transistor 2 of the control circuit 12 are connected to the emitter and the base, and the collector is connected in series to the resistor 2.
2, the transistor 21 connected to the ground terminal via the diode 23 and the resistor 24, its + input terminal is the collector of the transistor 21, and its − input terminal is the resistor 26
And the ground terminal via the reference power source 24,
The output terminal of the operational amplifier 25 is connected to the-input terminal of the operational amplifier 9, and the connecting point of the resistor 22 and the diode 23 is connected to the transistor 12. It is connected to the collector of.

The operation of this triangular wave oscillator circuit is as follows.
It Transistor 2 and transistor 21 are current mirrors
The circuit is configured and the collector of the transistor 21 is
Current of reference current circuit composed of resistor 2 and resistor 5
I₀Current equal to₀Flows (transistors 2 and 21
As the same capacity). Here the resistors 5, 22 and 24 are
Even if there are variations in the resistance value,
Because they are made, their relative variation is 0
, The voltage drop across resistors 22 and 24 is constant (eg
For example, if the resistance value of the resistor 5 increases by x%, the current I₀
Is reduced by x%. However, the resistance value of the resistor 22 or 24
Also increases by x%, the current I₀Resistance by 22
Or the voltage drop of 24 is canceled and becomes constant). one
The voltage drop of the rectangular diode 23 is,
The current magnitude so that the voltage drop will increase by 18mV
Increase depending on. Therefore, the + input terminal of the operational amplifier 25
When the transistor 12 is off, the child has a resistor 22 and a diode.
Sum E of the voltage drops of the resistor 23 and the resistor 24₁Is entered,
When the transistor 12 is on, the voltage drop E of the resistor 22 ₂But
Is entered. Operational amplifier 25, resistors 26 and 26, a group
Since the quasi-voltage 24 constitutes a linear amplifier circuit,
This input voltage E is applied to the output terminal of the amplifier 25.₁Or E
₂Output voltage V proportional to₁Or V₂Is output. This
Output voltage V ₁Or V₂Is the-input terminal of the operational amplifier 9.
Input to child. This output voltage V₁And V₂In Figure 2
Voltage V₁And V₂Same as the upper limit voltage of oscillation and
And lower limit voltage. Here, the output voltage of the operational amplifier 25
V₂Is a constant value determined by the voltage drop of the resistor 22, and the output
Voltage V₁Is the constant voltage drop across the resistor 22 and the magnitude of the current
Depending on the level, for example, when the energizing current drops, the voltage drop
It is determined by the sum of the voltage drops of the diode 23
Therefore, for example, the resistance of the reference current circuit may vary due to variations in resistance.
The resistance value of the anti-5 increases and this current I₀Low when drops
Down. Therefore, the difference between the upper limit voltage and the lower limit voltage of the oscillation voltage
Changes so as to decrease, and the oscillation frequency changes as shown in equation (3).
It operates so as to suppress the change in the wave number f. In this way
It is possible to reduce variations in oscillation frequency due to variations in resistance value.
Wear. The other operations are the same as in FIG.

[0014]

The triangular wave oscillating circuit of the present invention is stable because the variation of the oscillation frequency due to the variation of the resistance value of each resistor forming the circuit (however, the relative variation of each resistor is almost 0) is reduced. This is effective for controlling electronic devices such as switching power supply devices that require the above oscillation frequency. In particular, it is particularly effective in the case of a semiconductor integrated circuit in which the resistance values of the resistors forming the circuit have a relatively large variation and the resistors have almost no relative variation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a triangular wave oscillator circuit of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional triangular wave oscillator circuit.

[Explanation of symbols]

 2 Transistor 5 1st resistance 12 Control circuit 13 Capacitor 20 Oscillation voltage setting circuit 22 2nd resistance 23 Diode 24 3rd resistance

Claims (3)

[Claims] 1. An oscillation voltage setting circuit that determines an upper limit voltage and a lower limit voltage of an oscillation voltage, a capacitor, and a capacitor, the capacitor is charged with a charging current having a predetermined current value from the lower limit voltage to the upper limit voltage of the oscillation voltage, and after charging. Is a triangular wave oscillating circuit consisting of a control circuit that discharges from an upper limit voltage to a lower limit voltage with a discharge current of a predetermined current value, and then repeats this. And an upper limit voltage of the oscillation voltage determined by the oscillation voltage setting circuit, which is set to a current value proportional to the current of a reference current circuit including a transistor and a resistor (hereinafter referred to as a first resistor) connected between the ground and the ground. A triangular wave oscillating circuit characterized in that the difference voltage of the lower limit voltage is controlled so as to change in accordance with the change of the current value of the current of the reference current circuit. 2. The triangular wave oscillator circuit according to claim 1,
The oscillation voltage setting circuit includes a second resistor, a diode and a third resistor through which a current proportional to the current value of the reference current circuit of the current mirror circuit of the control circuit is passed, and the voltage drop of the second resistor oscillates. A triangular wave oscillating circuit characterized in that a lower limit voltage is determined, and a sum of voltage drops of the second resistor, the diode and the third resistor determines an upper limit voltage. 3. The triangular wave oscillator circuit according to claim 1, wherein the triangular wave oscillator circuit is formed as a semiconductor integrated circuit.