JPH0739148A - Switching regulator - Google Patents

Abstract

PURPOSE:To provide a switching regulator which can reduce a power loss with good controllability and whose circuit constitution is simple. CONSTITUTION:An error amplifier 41 operates an error between an output voltage Vout and a reference voltage Vr, and it sets a duty ratio duty for a transistor 44. The output VEA (which is proportional to the duty) of the error amplifier 41 is compared, by a PWM comparator 42, with triangular waves which are output from a triangular-wave oscillator 11, and it is converted into a PWM waveform. A base driver 43 is controlled so as to be turned on and off according to the PWM waveform. At this time, a multiplier 12 performs an operation so as to multiply the duty ratio duty by an input voltage Vin, and it generates an optimum base current IB. A collector current IC (a primary current i1 at a transformer 47) is changed according to the base current IB, and a secondary current i2 at the transformer 47 is changed according to its change. Then, the secondary current i2 is rectified with a rectifier circuit 48, and an output voltage VOUT is output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator.

[0002]

2. Description of the Related Art FIG. 7 shows a block circuit diagram of a conventional switching regulator. This switching regulator includes an error amplifier 41, a PWM comparator 42, a base driver (current switch) 43, and a transistor 4
4, a base driver current source 45, and a triangular wave oscillator 46
And a switching transformer (hereinafter abbreviated as transformer) 47
And a rectifier circuit 48. The rectifier circuit 4
Reference numeral 8 is a half-wave rectifying circuit including a rectifying diode 49 and a smoothing capacitor 50. The base driver current source 45 may be replaced with the resistor R.

Here, the DC input power supply voltage (hereinafter referred to as input voltage) of the switching regulator is Vin, the DC output power supply voltage (hereinafter referred to as output voltage) is Vout, the base current of the transistor 44 is IB, and the collector current (transformer 47). Primary current), the emitter-base voltage is VBE, the emitter-collector voltage is VCE, the collector-emitter saturation voltage is VCEsat, and the current (secondary current of the transformer 47) flowing through the rectifying diode 49 is Id, The voltage across the rectifying diode 49 is Vd, the reference voltage of the error amplifier 41 is Vr, and the output of the error amplifier 44 is VEA.

In this switching regulator, the error amplifier 41 calculates the error between the output voltage Vout and the reference voltage Vr, and the switching duty of the transistor 44 is calculated.
Set the duty ratio (hereinafter abbreviated as duty ratio) duty.
The duty ratio duty (actually, the output VEA of the error amplifier 44 proportional to the duty ratio duty) and the triangular wave oscillator 4
The triangular wave output from 6 is compared by the PWM comparator 42 and converted into a PWM waveform. The base driver 43 is on / off controlled according to the PWM waveform, and accordingly, the base driver current source 45 supplies the base current IB to the transistor 44. The duty of the collector current IC (the primary current of the transformer 47) changes according to the duty of the base current IB, and the duty of the current Id (the secondary current of the transformer 47) flowing through the rectifying diode 49 changes according to the change of the duty. The output voltage Vout is determined by the pulse width of the output.

The power loss of this switching regulator can be roughly classified into the following items. On-voltage loss = VCEsat-IC-duty-Equation (1) Base loss = VBE-IB-duty-Equation (2) Switching loss Base drive loss = (Vin-VBE) IB-duty-Equation (3) Transformer Loss Rectification loss = Id · Vd Other

[0006]

The base current IB is determined by the base driver current source 45, and its value is always constant. Therefore, the base current IB needs to be obtained by dividing the maximum value of the collector current IC by the current amplification factor hfe, and when the input voltage Vin is high, the base drive loss of the formula (3) becomes large.

Therefore, as disclosed in Japanese Patent Laid-Open No. 61-157265, there has been proposed a method of controlling the base current so as to be inversely proportional to the input voltage to reduce the power loss. However, in this method, since the inverse proportional relationship between the base current and the input voltage is calculated, the circuit configuration becomes complicated and the controllability is poor.

Further, as disclosed in Japanese Patent Laid-Open No. 62-23369, a method has been proposed in which large and small base current setting circuits are provided and switching is performed according to an input voltage. However, according to this method, since only two large and small base current setting circuits are provided, the base current can be switched only in two steps, and the power loss cannot be sufficiently reduced. Further, if a plurality of base current setting circuits are provided, the switching method becomes complicated and the controllability deteriorates, which is not practical.

The present invention has been made to solve the above problems, and an object thereof is to provide a switching regulator capable of reducing power loss with good controllability by a simple circuit configuration. To do.

[0010]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a first aspect of the invention by controlling a transistor connected to the primary side of a switching transformer. In the switching regulator that makes the DC output power supply voltage output from the secondary side of the switching transformer constant with respect to the DC input power supply voltage, the switching duty of the transistor is based on the DC output power supply voltage. It is provided with an error amplifier for setting a duty ratio, and base current setting means for setting an optimum base current of the transistor based on a multiplication calculation of the output of the error amplifier and the DC input power supply voltage. And

According to a second aspect of the present invention, in the switching regulator according to the first aspect, a predetermined offset current is added to the primary side current of the switching transformer by adding a predetermined current to the base current setting means. The gist of the present invention is to provide a current adding means for causing

[0012]

Therefore, according to the first aspect of the present invention, the base current setting means sets the transistor's switching duty ratio, which is the output of the error amplifier, based on the multiplication operation of the DC input power supply voltage. The optimum base current is set. Therefore, even if the DC input power supply voltage changes, the base current of the transistor is controlled to an optimum value corresponding to the change, and power loss can be minimized.

According to the second aspect of the invention, the current adding means causes a predetermined offset current to be generated in the primary side current of the switching transformer. Therefore, the switching regulator can be smoothly started by adjusting the offset current.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the present invention is embodied in a discontinuous mode switching regulator will be described below with reference to FIGS.

In the present embodiment, the same components as those of the conventional example shown in FIG. 7 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 1 shows a block circuit diagram of the switching regulator of this embodiment.

This switching regulator includes an error amplifier 41, a PWM comparator 42, a base driver 43, a transistor 44, a transformer 47, and a rectifying circuit 48.
And a triangular wave oscillator 11 and a multiplier 12. The rectifying circuit 48 is a half-wave rectifying circuit including a rectifying diode 49 and a smoothing capacitor 50.

Here, the input voltage of the switching regulator is Vin, the output voltage is Vout, the base current of the transistor 44 is IB, the collector current is IC, the emitter-base voltage is VBE, the emitter-collector voltage is VCE, and the collector-voltage is VCE. Saturation voltage between emitters is VCEsat, transformer 47
The primary current is i1, the secondary current is I2, the reference voltage of the error amplifier 41 is Vr, the peak voltage of the triangular wave output from the triangular wave oscillator 11 is VREFH, the bottom voltage is VREFL, and the output of the error amplifier 44 is VEA. The collector current IC and the primary current i1 are equal.

By the way, the discontinuous mode means the transformer 4
The induced power accumulated on the primary side of
This is the operation mode of the switching regulator in which the switching regulator is completely discharged to the secondary side every cycle.

That is, in this switching regulator, the error amplifier 41 calculates the error between the output voltage Vout and the reference voltage Vr to set the duty ratio duty of the transistor 44. The duty ratio duty (actually, the output VEA of the error amplifier 44 proportional to the duty ratio duty) and the triangular wave output from the triangular wave oscillator 11 are set to P
The WM comparator 42 compares and converts to a PWM waveform. The base driver 43 according to the PWM waveform
Is controlled on and off. Where the base driver 43
Base current IB supplied to the transistor 44 via
Is multiplied by the error amplifier 41 as described later by the multiplier 12.
Output VEA (proportional to the duty ratio duty) and the input voltage Vin. According to the base current IB, the collector current IC (the primary current i1 of the transformer 47)
Changes, and the secondary current i of the transformer 47 changes in accordance with the change.
2 changes. Then, the rectifier circuit 48 rectifies the secondary current i2 and outputs the output voltage Vout.

That is, in the conventional example shown in FIG. 7, the base driver current source 45 always supplies the constant base current IB. On the other hand, in this embodiment,
The multiplier 12 multiplies the duty ratio duty by the input voltage Vin to calculate and supply the optimum base current IB.

That is, the steady loss of the transistor 44 is
It is the sum of the on-voltage loss, the base loss, and the base drive loss, and is represented by the equation (4) which is the sum of the equations (1) to (3).

Steady loss = (VCEsat · IC + Vin · IB) duty (4) By the way, the base current IB and the collector-emitter saturation voltage VCEsat have a relationship that VCEsat decreases as IB increases. Therefore, one item and two items of formula (4) are
There is a trade-off relationship as shown in FIG. Therefore, there is an optimum ratio of the base current IB to the collector current IC, that is, the current amplification factor hfe. By keeping this current amplification factor hfe constant, the multiplier 12 realizes the operation of obtaining the optimum base current IB regardless of the input voltage Vin.

As a result, the input voltage Vin and the output voltage V
In the entire range of out, the steady loss shown in Expression (4) can be minimized and the voltage conversion efficiency of the switching regulator can be improved.

FIG. 3 shows an internal circuit of an example of the multiplier 12. The multiplier 12 is a differential two-stage amplifier including a differential circuit 22 having a current mirror load 21, a differential circuit 24 having a current mirror load 23, and current mirror circuits 25 and 26. . In addition, this multiplier 1
Since 2 is a general multiplication circuit that is widely used, the detailed description of the configuration and the operating principle is omitted.

Next, the operation of generating the base current IB by the multiplier 12 will be described. In the discontinuous mode, since the primary current i1 at the moment the transistor 44 is turned on is 0 A, the peak value i1P of the primary current i1 is as follows: the primary inductor of the transformer 47 is LP, the switching period of the transistor 44 is T, and the switching period of the transistor 44 is T. When the on-time is ton, the equation (5) is obtained.

I1P = ton.Vin / LP = (T / LP) (ton / T) Vin = (T / LP) duty.Vin (Equation (5)) Here, the primary inductor LP and the switching period T are Since it is a constant, as shown in FIG. 4, the peak value i1P
Is the duty ratio duty, the input voltage Vin and the constant (T / LP
) Will be represented by the product. Therefore, as shown in equation (6), this peak value i1P is set to the optimum current amplification factor hfe.
The optimum base IB which is the value divided by is the transistor 4
4, the steady loss shown in equation (4) is minimized.

IB = i1P / hfe = (T / LP.hfe) duty.Vin (Equation (6)) If the current amplification factor hfe is also treated as a constant value, that is, a constant, the optimum value of the base IB is It is represented by the product of the duty ratio duty, the input voltage Vin and a constant (T / LP · hfe).

The optimum base current IB is generated by the multiplier 12 performing the multiplication operation shown in the equation (6). By the way, the duty ratio duty is proportional to the output of the error amplifier 41, and is represented by the equation (7).

Duty = (VREFH-VEA) / (VREFH-VREFL) (7) The current IA supplied to the multiplier 12 is obtained by dividing the differential voltage of the differential input of the differential circuit 22 by the emitter resistance RE. Therefore, the equation (8) is established.

IA ≧ (VREFH−VEA) / RE = duty (VREFH−VREFL) / RE (Equation (8)) From this equation (8), it is understood that the current IA is proportional to the duty ratio duty. .

On the other hand, a current obtained by dividing the input voltage Vin by the resistor RB is supplied to the current mirror circuit 25. Therefore, the base current IB output from the multiplier 12 is given by the equation (9) when the gain of the multiplier 12 is A.

IB = {duty (VREFH−VREFL) / RE} Vin · A / RB (Equation 9) Therefore, from Expression (6) and Expression (9), the gain A shown in Expression (10) is obtained. If the multiplier 12 is designed, the base current IB is optimized, and the steady loss shown in the equation (4) is kept to the minimum.

A = (T / LP.multidot.hfe) (RE.multidot.RB) / (VREFH-VREFL) (Equation (10)) As described above, in the present embodiment, a simple configuration in which only the multiplier 12 is provided is used. Power loss can be minimized. Further, the control of the base current IB by the multiplier 12 is easy and reliable, so that the power loss can be reduced by the good controllability.

(Second Embodiment) A second embodiment in which the present invention is embodied in a continuous mode switching regulator will be described below with reference to FIGS.

In this embodiment, the same components as those in the first embodiment shown in FIGS. 1 to 4 are designated by the same reference numerals and detailed description thereof will be omitted. FIG. 5 shows a block circuit diagram of the switching regulator of this embodiment.

5 is different from FIG. 1 only in that a constant current circuit 31 for supplying (adding) a constant current Ir to the output of the multiplier 12 is connected. The constant current circuit 31 is connected to the input voltage Vin and generates a constant current Ir.

By the way, the continuous mode means the transformer 47.
The operating mode of the switching regulator is such that the induced power accumulated on the primary side of the switching regulator is not completely discharged to the secondary side in each switching cycle of the transistor 44. That is, in the discontinuous mode, since the primary current i1 at the moment when the transistor 44 is turned on is not 0A,
It can be considered that the primary current i1 has an offset current IO as shown in FIG.

Therefore, in order to embody the continuous mode switching regulator, a constant current Ir is supplied to the output of the multiplier 12 by the constant current circuit 31 as shown in FIG. 5 for the first embodiment. Therefore, the primary current i1 should have an offset current IO.

The rest of the operation is the same as that of the present embodiment and the first embodiment, and the effects are also the same, so the description thereof is omitted here. By the way, in the first embodiment, if the base current IB becomes 0 A when the collector current IC is 0 A, the collector current IC may not start. Therefore, also in the first embodiment, the operation is more stable when a slight offset current I0 is applied, and the switching regulator can be started smoothly.

Incidentally, the present invention is not limited to the above embodiment, and for example, the multiplier 12 does not have to have the circuit configuration shown in FIG. In addition, the rectifier circuit 4
8 is not limited to a half-wave rectifier circuit, but may be a full-wave rectifier circuit or a bridge rectifier circuit.

[0041]

As described above in detail, according to the present invention, it is possible to provide a switching regulator capable of reducing power loss with good controllability with a simple circuit configuration. There is.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a first embodiment embodying the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the first embodiment.

FIG. 3 is a circuit diagram of a multiplier 12.

FIG. 4 is a characteristic diagram for explaining the operation of the first embodiment.

FIG. 5 is a block circuit diagram of a second embodiment embodying the present invention.

FIG. 6 is a characteristic diagram for explaining the operation of the second embodiment.

FIG. 7 is a block circuit diagram of a conventional example.

[Explanation of symbols]

12 ... Multiplier as base current setting means, 31 ... Constant current circuit as current adding means, 41 ... Error amplifier, 44
… Transistors, 47… Switching transformers, Vin
... DC input power supply voltage, Vout ... DC output power supply voltage, IB
... base current, i1 ... primary side current, iO ... offset current,

Front page continuation (72) Inventor Tetsuo Tateishi 2-chome Toyota-cho, Kariya city, Aichi Prefecture Toyota Industries Corporation (72) Inventor Koji Koga 1-cho, Toyota city, Aichi prefecture Toyota Motor Corporation

Claims (2)

[Claims] 1. A DC output output from the secondary side of the switching transformer with respect to a DC input power supply voltage supplied to the primary side by controlling a transistor connected to the primary side of the switching transformer. In a switching regulator that keeps the power supply voltage constant, an error amplifier that sets the switching duty ratio of the transistor based on the DC output power supply voltage, and the output of the error amplifier multiplied by the DC input power supply voltage. A switching regulator comprising: a base current setting means for setting an optimum base current of the transistor based on a calculation. 2. The switching regulator according to claim 1, wherein a predetermined offset current is generated in a primary side current of the switching transformer by adding a predetermined current to the base current setting means. A switching regulator characterized by having.