JPH06225519A - Power-supply circuit - Google Patents

Abstract

PURPOSE:To eliminate the need of setting a DC output voltage irrespective of the type of a regulator at a posterior stage. CONSTITUTION:A power-supply circuit is provided with a bridge rectifying circuit 1 which rectifies a supplied alternating current, with a boosting chopper circuit 2 which boosts a rectified output, with a DC output detection circuit 4 which detects an output voltage and with an output control circuit 5 by which the switching frequency of a field-effect transistor Q1 in the boosting chopper circuit 2 is made variable so as to make the detection output definite. In the power-supply circuit, an AC input detection circuit 3 which detects the level of the supplied alternating current is installed, and the detection level of the DC output detection circuit 4 is made variable according to the detection level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit that rectifies an AC input and boosts the rectified output to obtain a constant voltage output having a large value.

[0002]

2. Description of the Related Art Most power supply circuits mounted on electric products have not been improved in power factor due to cost and space problems. Under such circumstances, the regulation of power supply harmonics has finally begun, and this regulation will be applied not only to new models but also to current models. Therefore, the current model will be dealt with by replacing the power supply circuit and the like.

Meanwhile, the conventional power supply circuit, as shown in FIG. 4, a bridge rectifier circuit 1 of the diode D ₁ is connected to the input terminal t _1, capacitor C for smoothing between the output terminals of the bridge rectifier circuit 1 A series circuit of choke coil L and switching element 12 is connected together with ₁ . A backflow preventing diode D ₂ is interposed between the common connection point of the choke coil L and the switching element 2 and the output terminal t _2, and a smoothing capacitor C ₂ is provided between the two output terminals t _2. Intervened. The voltage of one output terminal t ₂ is guided to the drive circuit 14 via the differential amplifier 13, and the drive circuit 14 changes the frequency of the switching pulse according to the input voltage.

In the power supply circuit having the above structure, the switching element 1 is arranged so that the AC line voltage and the load current are proportional to each other.
When switching control of 2 is performed, the filter circuit (the choke coil L, the switching element 12, and the smoothing capacitor C ₂ ) viewed from the AC line operates as a constant resistance, thereby improving the power factor. Then, as shown in FIG. 5, the power supply circuit described above receives an input AC level (AC1
The output voltage is controlled to be substantially constant (for example, about 380V) regardless of the output voltage (00V, AC240V).

[0005]

However, a regulator (in most cases, a switching regulator) arranged in the subsequent stage of the power supply circuit has an inputtable voltage range of 100V to 120V (100V) as shown in Table 1 below.
System) and for 200V to 240V (200V system). The full-wide type such as 100V to 240V is hardly mounted because of problems of cost and space.

[0006]

[Table 1]

Therefore, when exchanging the power supply circuit for the current model, the regulator sets the DC output voltage to about 200V for the 100V system and the DC output voltage to about 400V for the 200V system. It had to be set individually.

Therefore, it is an object of the present invention to provide a power supply circuit which does not require setting of the DC output voltage depending on the type of regulator in the subsequent stage.

[0009]

A power supply circuit according to the present invention for achieving the above object includes a bridge rectifier circuit for rectifying an alternating current supplied to an input terminal, and a choke coil on an output side of the bridge rectifier circuit. A step-up chopper circuit in which switching elements are connected in series, and a diode for preventing backflow is interposed between a common connection point of the choke coil and the switching element and an output terminal, and a direct current for detecting the output voltage of the output terminal In a power supply circuit including an output detection circuit and an output control circuit that changes the switching frequency of the switching element so that the detection output of the DC output detection circuit becomes constant, the level of the alternating current supplied to the input terminal is detected. An AC input detection circuit is provided, and the detection level of the DC output detection circuit is varied according to the detection level. .

[0010]

Since the detection level of the voltage at the output terminal is changed according to the input AC level and the output control circuit operates so as to keep this detection level constant, the output voltage value is changed according to the input AC level. It

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show an embodiment of the present invention. FIG. 1 shows a circuit diagram of the power supply circuit. In FIG. 1, a bridge rectifier circuit 1 composed of a diode D ₁ is connected to an input terminal t ₁ , and a boosting chopper circuit 2 is provided between output terminals of the bridge rectifier circuit ₁ together with a smoothing capacitor C _1.
Are connected.

The step-up chopper circuit 2 includes a choke coil L connected between the output terminals of the bridge rectifier circuit 1 and a series circuit of a MOS type field effect transistor Q ₁ which is a switching element, a choke coil L and a field effect transistor. It comprises a backflow blocking diode D ₂ connected between the common connection point of Q ₁ and the output terminal t ₂ . The field effect transistor Q ₁ is turned on / off by a control signal of the output control circuit 5 described below, and the output of the bridge rectifier circuit 1 is boosted by the choke coil L.
Further, between the output terminal t ₂ is connected a capacitor C ₂ for smoothing, a stable DC output is obtained thereby to the output terminal t _2. A regulator (not shown) is connected after the output terminal t ₂ .

The AC input detecting circuit 3 has a series circuit of a resistor R, a diode D ₃ and a capacitor C ₃ connected between the output terminals of the bridge rectifying circuit 1, and the diode D ₃ and the capacitor C ₃ are common. A Zener diode D ₄ of reverse connection is provided at the connection point. When the input AC voltage is 100 V, the voltage across the terminals of the capacitor C ₃ becomes less than the Zener voltage, and the input AC voltage is 200 V
When the voltage is V, the voltage across the terminals of the capacitor C ₃ is set to be equal to or higher than the Zener voltage. When the AC voltage is 100 V, the Zener diode D ₄ is at the LOW level and the AC voltage is 2
In the case of 00V, a HIGH level AC input detection signal is output to the DC output detection circuit 4.

The DC output detection circuit 4 has a series circuit of three resistors R ₁ , R ₂ and R ₄ connected between the output terminals t ₂ and is connected in parallel to the resistors R ₂ and R ₄ . And a series circuit of a resistor R ₃ and a transistor Q ₂ . Then, the voltage at the common connection point of the resistors R ₂ and R ₄ is output to the output control circuit 5 as a DC output detection signal. Wherein the base of the transistor Q ₂ is the AC input detection signal of the AC input detecting circuit 3 is guided, the transistor Q ₂ is turned on and off by an AC input detection signal. That is, the AC input is 1
In the case of 00V, the transistor Q ₂ is turned off at the LOW level and the detection level is determined by the three resistors R ₁ , R ₂ and R ₄ , and when the AC input is 200V, it is HIGH.
At the level, the transistor Q ₂ turns on and the four resistors R ₁ and R
_The detection level is determined by ₂ , R ₃ and R ₄ .

The output control circuit 5 has a differential amplifier 6, and one input terminal of the differential amplifier 6 has a reference voltage circuit (R).
The reference voltage V _ref of the EF) 7 is supplied to the other input terminal of the DC output detection signal. Comparator (CO
The output of the differential amplifier 6 and the sawtooth wave signal are input to the MP) 8, and the comparator 8 compares the both input signals and outputs a pulse signal to the drive circuit 9. The pulse width of the pulse signal is changed by the output level of the differential amplifier 6, and the drive circuit 9 is PWM-controlled. The drive circuit 9 obtains power from the starting power supply circuit (KICK) 10 and outputs a drive signal based on the pulse signal to the field effect transistor Q.
Output to ₁ . The reference voltage circuit 7 and the start-up power supply circuit 10 are configured so that power is supplied from the output of the bridge rectifier circuit 1 when the power is on and thereafter from a regulator (not shown).

The operation of the above structure will be described below. When the electronic device is a 100V system (using a regulator 100V system), 100V AC power is supplied from the input terminal t ₁ . This AC input is full-wave rectified by the bridge rectifier circuit 1 (a solid line waveform in part a of FIG. 2), and the terminal voltage E _{1 of the} capacitor C ₃
Since the (b portion solid line waveform in FIG. 2) is lower than the Zener voltage, the AC input detection circuit 3 outputs the LOW signal (c portion waveform in FIG. 2). Then, the transistor Q of the DC output detection circuit 4
₂ is turned off, the DC output detection circuit 4 has three resistors R ₁ ,
A DC output detection signal having a detection level determined by R ₂ and R ₄ is output, and the output control circuit 5 outputs based on this detection signal.
Switch-drives the field effect transistor Q ₁ .
Then, the DC output of the output terminal t ₂ (d-line solid line waveform in FIG. 2) is controlled so that the level of the DC output detection signal becomes the reference voltage V _ref . That is, the DC output V _O is

[0017]

[Equation 1]

[0018]

If the electronic device is a 200 V system (using a regulator 200 V system), 200 from the input terminal t _1.
An AC power source of V is supplied. This AC input is full-wave rectified by the bridge rectifier circuit 1 (phantom line waveform of portion a in FIG. 2), and the terminal voltage E ₂ of the capacitor C ₃ (phantom line waveform of portion b in FIG. 2) is higher than the Zener voltage. The input detection circuit 3 is HIG
The H signal (waveform c in FIG. 2) is output. Then, the transistor Q ₂ of the DC output detection circuit 4 is turned on, and the DC output detection circuit 4 outputs the DC output signal of the detection level determined by the _four resistors R ₁ , R ₂ , R ₃ and R ₄ , Based on the detection signal, the output control circuit 5 causes the field effect transistor Q to
₁ is switching driven. Then, the DC output V _O of the output terminal t ₂ (d-line virtual line waveform in FIG. 2) is controlled so that the level of the DC output detection signal becomes the reference voltage V _ref, and the DC output V _O is the V _{CE of the} transistor Q _{2 .} = 0,

[0020]

[Equation 2]

[0021] Considering the transistor Q ₂ as a constant current circuit, and letting the current flowing through the resistor R ₃ be I ₃ ,

[0022]

[Equation 3]

The DC output V _{O in} the case of 100 V system
Compared with the above, the voltage of R ₁ · I ₃ is superimposed.

That is, the value of the DC output in the above equation (1) is 10
To be within the input voltage range of 0V regulator,
Further, if the values of the resistors R _{1 to} R ₄ are set so that the value of the DC output of the above equation (2) is within the inputtable voltage range of the 200V system regulator, the desired DC output will be obtained regardless of the type of the regulator at the subsequent stage. Is automatically obtained.

FIG. 3 shows a circuit diagram of a modification of the DC output detection circuit. In FIG. 3, this modified example is different from the above-described embodiment in that a shunt regulator 11 is used, and the shunt regulator 11 has R _X · I _X = 2.5V.
The transistor Q ₂ is driven so that Although the base current of the transistor Q ₂ is superimposed, if h _fe >> 100, the value is 1% or less, which can be ignored for the DC output setting, and very accurate detection is possible.

[0026]

As described above, the first to third aspects are provided.
According to the invention, a bridge rectifier circuit for rectifying an alternating current, a step-up chopper circuit for boosting the rectified output, a DC output detection circuit for detecting an output voltage of an output terminal, and an output control circuit for controlling the detection output to be constant. In the power supply circuit equipped with, the level of the alternating current supplied is detected, and the detection level of the direct current output detection circuit is varied according to this detection level, so the direct current output is automatically varied according to the type of alternating current. Therefore, it is not necessary to set the DC output depending on the type of the regulator in the subsequent stage. or,
According to the invention of claim 3, since the shunt regulator is used in the DC output detection circuit, there is an effect that very accurate detection can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply circuit (embodiment).

FIG. 2 is an output waveform diagram of each unit (Example).

FIG. 3 is a circuit diagram of a DC output detection circuit (modification).

FIG. 4 is a circuit diagram of a power supply circuit (conventional example).

FIG. 5 is a characteristic diagram of a DC output with respect to an AC input (conventional example).

[Explanation of symbols]

1 ... bridge rectifier circuit 2 ... boosting chopper circuit 3 ... AC input detection circuit 4 ... DC output detecting circuit 5 ... output control circuit t ₁ ... input terminal t ₂ ... output terminal L ... choke coil Q ₁ ... field effect transistor (switching element ) D _{1 to} D ₄ ... Diodes C _{1 to} C ₃ ... Capacitor 11 ... Shunt regulator

Claims (3)

[Claims] 1. A bridge rectifier circuit for rectifying an alternating current supplied to an input terminal, a choke coil and a switching element connected in series on an output side of the bridge rectifier circuit, and a common connection of the choke coil and the switching element. A step-up chopper circuit in which a diode for blocking backflow is interposed between the point and the output terminal, a DC output detection circuit for detecting the output voltage of the output terminal, and a detection output of the DC output detection circuit to be constant. In a power supply circuit including an output control circuit that varies a switching frequency of a switching element, an AC input detection circuit that detects a level of an AC supplied to the input terminal is provided, and the DC output detection circuit according to the detection level. The power supply circuit is characterized in that the detection level of is changed. 2. The alternating current input detection circuit is characterized in that a series circuit of a diode and a capacitor is inserted on an output side of the bridge rectification circuit and a voltage at a common connection point of the diode and the capacitor is detected. The power supply circuit according to 1. 3. The DC output detection circuit, wherein a shunt regulator is connected in parallel to a resistor for dividing the output voltage, and the detection level is varied by turning on / off the shunt regulator. Alternatively, the power supply circuit according to claim 2.