JPH0516875Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a switching regulator, and an object of the present invention is to provide a switching regulator that can switch the output voltage by switching the voltage division ratio of the output voltage.

Generally, a portable video tape recorder uses a rechargeable battery pack as its power source when it is used as a mobile phone, and uses an AC adapter as its power source when used at home. Here, the switching regulator can be configured to have the same shape as the battery pack, but when using a portable video tape recorder at home, the switching regulator can be configured to have the same shape as the battery pack. In order to use it as a built-in AC adapter, the output voltage of the switching regulator must be set to 12V to match the portable video tape recorder. When this switching regulator was used as a charger for the battery pack, the output voltage was 12V, which is low for a charger, so it could not be used to charge the battery pack. Therefore, in order to charge the battery pack, a switching regulator with a large output voltage is used as the battery pack charger, in addition to the switching regulator that serves as the AC adapter. The drawback was that two types of power supply components were required to use the recorder: an AC adapter and a charger.

The present invention eliminates the above drawbacks and will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of a switching regulator according to the present invention. This circuit is of a pulse width modulation type, and in FIG. The input rectifier 2 rectifies the AC voltage, converts it into a DC voltage, and supplies the DC/DC converter 3 to the next stage, and high frequency noise generated in the DC/DC converter 3 is switched from the terminals 1a and 1b. It has a built-in filter that prevents it from coming out of the regulator. The DC/DC converter section 3 converts the DC voltage from the input rectifier section 2 into an AC voltage (pulse train) by turning on and off the switching transistor T _r1 according to control pulses from the output stabilization control section, which will be described later. For example, the transistor _T1 lowers the voltage, rectifies it, smoothes it, and outputs it again as a DC voltage from the output terminals 4a, 4b, while forming an output stabilization control unit 6 via an output voltage switching unit 5, which will be described later. 7 terminal.

The integrated circuit 7 has a configuration as shown in FIG. 2, and the DC voltage from the input rectifying unit 2 is supplied to its terminals by an auxiliary power supply unit 8 in the form of a DC voltage of an appropriate voltage. The DC voltage from this terminal is converted to a reference voltage of, for example, 5V by the reference voltage generator 9, and the terminal
It is supplied as a reference voltage to the error amplifier 10 via the resistor RR ₁ and the terminal. The DC voltage supplied to the terminal is compared with the reference voltage in the error amplifier 10, and an error voltage corresponding to the level difference between the two voltages is taken out and supplied to the pulse width modulator ₁₁ via the diode D1. The pulse width modulator 11 is supplied with a sawtooth wave of a predetermined frequency from the oscillator 12 and an error voltage from the error amplifier 10, and generates pulses whose repetition frequency is the same as that of the sawtooth wave and is inversely proportional to the error voltage value. Generates a pulse of width.
After this pulse is amplified by the drive circuit 13, it is taken out from the terminal ~, and is transferred to the transformer _T2 shown in the first diagram.
is supplied to the base of the switching transistor T _r1 of the DC/DC converter section 3 through the switching transistor T r1 to control the switching, thereby controlling the terminals 4a and 4b.
The output DC voltage is maintained at a predetermined value.

Next, in the output voltage switching section 5, a series circuit consisting of a resistor R ₂ , a variable resistor R ₃ , a resistor R ₄ , and a resistor R ₅ is connected.
One end of _R2 is connected to the output terminal 4a, one end of the resistor _R5 is connected to the output terminal 4b and set to the ground level, and the slider of the variable resistor _R3 is connected to the terminal of the integrated circuit 7 via the resistor _R6 . It is connected to the. Resistance R ₄ ,
The collector of a transistor T _r2 as a first switch for voltage switching is connected to the connection point of _R5 .
The emitter of the transistor T _r2 is grounded, and the base is grounded via a resistor R ₇ and connected to the input terminal 14 via a resistor R ₈ . This resistance
Let the resistance values of R ₂ , R ₄ , and R ₅ be R ₂ , R ₄ , and R ₅ , and let the resistance values of the resistor _{R 2 side} and R ₃ side from the slider of variable resistor R 3 be r ₁ , r _{2 ,} respectively. Assuming that the voltage at the output terminal 4a is V _O , when no voltage is applied to the input terminal 14 and the transistor T _r2 is in the off state, the voltage V _S of the slider of the variable resistor R ₃ is V _S = r ₂ +R ₄ +R ₅ /R ₂ +r ₁ +r ₂ +R ₄ +R ₅・V _O ...(1). In addition, for example, 12V to input terminal 14
When a voltage of 14V is applied and the transistor T _r2 is in the on state, V _S ′=r ₂ +R ₄ /R ₂ +r ₁ +r ₂ +R ₄ ·V _O ′ (2). Here, if the reference voltage supplied to the error amplifier 10 is V _REF (for example, 5V), then V _O = V _O /V _S · V _REF (3), and R ₂ + r ₁ = R _A , If r ₂ + R ₄ = R _B , (1),
From equations (2) and (3), V _O = R _A + R _B + R ₅ / R _B + R ₅・V _REF … (4) V _O ′= R _A + R _B / R _B・V _REF … (5) By turning on and off the voltage switching transistor T _r2 , the output voltages from the output terminals 4a and 4b can be switched between, for example, 12V and 14V.

Here, the output power P of the switching regulator is determined by the cross-sectional area S of the transformer core of the transformer _T1 , the maximum magnetic flux density _Bn of the transformer _T1 , the switching frequency, that is, the oscillation frequency of the oscillator 12, and the proportionality constant K. P=S・B _n・・K ...(6) It is expressed as. Therefore, the output voltage of the switching regulator can be varied by changing the oscillation frequency of the oscillator 12.

An oscillation frequency switching section 15 is provided to switch the oscillation frequency of the oscillator 12 described above. Second
The illustrated oscillator 12 has one end connected to a grounded capacitor C 1 through a terminal, and the other end of the capacitor C ₁ .
It is connected to one end of resistor _R9 through the terminal.
The other end of the resistor _R9 is connected to the other end of the resistor _R10 whose one end is grounded, and is also connected to the collector of a transistor T _r3 serving as a second switch for frequency switching. The emitter of the transistor T _r3 is grounded, and the base is grounded via a resistor R ₁₁ and connected to the input terminal 16 via a resistor R ₁₂ . Therefore, when no voltage is applied to the input terminal 16 and the transistor T _r3 is off, the oscillation circuit 12 operates at a frequency determined by the resistance values of the resistors R ₉ and R ₁₀ (R ₉ + R ₁₀ ) and the capacitor C ₁ , for example, 40 kHz. When oscillation occurs and a voltage of 12V to 14V is applied to the input terminal 16 and the transistor T _r3 is in the on state, the resistor R ₉
It oscillates at a frequency determined by the resistance value (R ₉ ) and capacitor C ₁ , for example 120kHz.

When the above switching regulator is attached to the battery pack attachment part of a portable video tape recorder and used as an AC adapter, input terminals 14 and 16 are opened, the switching frequency is 40kHz, noise is small, and the output voltage is 12V. Use as.

Next, when removing the above switching regulator from the portable video tape recorder and using it as a battery pack charger, the third
As shown in the figure, a conductive material is provided on the adapter 18 to each of the output terminals 4a, 17, 4b (the output terminal 17 is connected to the output terminals 14, 16 shown in the first figure) of the switching regulator. Terminals 19a, 19b, 20a of connectors 19, 20 of
Connect terminals 19c and 2 of connectors 19 and 20.
0b to the power terminal 2 of the battery pack 21.
Used by connecting to 1a and 21b. At this time, the input terminals 14 and 16 of the switching regulator are connected to the output terminal 4a from 12V to 12V by the connector 19.
Since 14V is applied, the switching regulator can increase the output power at a switching frequency of 120kHz, and can charge the battery pack 21 in a short time by setting the output voltage to 14V.

Note that it is connected to both ends of the resistor _R5 in place of the transistor T _r2 , and is normally left open and connected to the connector 1.
A mechanical switch may be provided that closes when the terminal 19c of No. 9 is inserted.

Note that the voltage switching section 5 may be manually switched by providing a mechanical switch _S1 as shown in FIG. 4A.
Alternatively, switching may be performed using a PNP transistor T _r4 as shown in FIG. 4B _, and as shown in FIG. 4a
The voltage is divided by resistors R _c and R _b and supplied to the terminal, and the reference voltage supplied to the error amplifier 10 is set to 12V.
However, the present invention is not limited to the above embodiments.

As described above, the switching regulator of the present invention includes a first switch that switches between an output voltage and a voltage obtained by dividing the output voltage, or a voltage division ratio that divides the output voltage to obtain a comparison voltage; 1
Since the switching regulator is provided with a second switch that changes the frequency of the switching pulse in conjunction with the switch, the output voltage and output power can be changed. When used as an AC adapter, the voltage division ratio is increased to lower the output voltage and the frequency of the switching pulse is lowered to provide low output power.When taken out from a portable video tape recorder and used as a battery pack charger, it is divided It has the advantage that it can be used as high output power by reducing the pressure ratio and increasing the frequency of the switching pulse and the high output voltage, and requires only one power supply component for the portable video tape recorder.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the switching regulator according to the present invention, FIG. 2 is a circuit diagram of the integrated circuit shown in FIG. 1, and FIG. 3 is a circuit diagram of the switching regulator shown in FIG. FIGS. 4A, 4B and 4C, which are diagrams for explaining the connection of the adapter and the battery pack, are circuit diagrams of modifications of the voltage switching section shown in the first diagram. 1a, 1b, 14, 16...input terminal, 2...
Input rectifier section, 3...DC/DC converter section, 4
a, 4b...output terminal, 5...voltage switching section, 6...
... Output stabilization control section, 7 ... Integrated circuit, 9 ... Reference voltage generator, 10 ... Error amplifier, 11 ... Pulse width modulator, 12 ... Oscillator, 13 ... Drive circuit, T _r1 - T _r5 ...Transistor, _R1 to _R12 ...
…Resistor, C ₁ …Capacitor, S ₁ …Switch.

Claims (1)

[Scope of utility model registration request] The input voltage is converted into DC by extracting the output voltage or a voltage obtained by dividing the output voltage as a comparison voltage, and obtaining a switching pulse with a pulse width determined by the error voltage obtained by comparing the comparison voltage and the reference voltage. In a switching regulator using a pulse width modulation control method, which generates the output voltage by switching the output voltage according to the pulse width of the switching pulse and then rectifying and smoothing the output voltage, the output voltage and the voltage obtained by dividing the output voltage are A first switch for switching or switching a voltage division ratio for dividing the output voltage to take out the comparison voltage, and a second switch for switching the frequency of the switching pulse in conjunction with the first switch. Switching regulator.