JP3255467B2 - Power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM (Pulse Width Modulator) for supplying a DC voltage supplied to a primary winding of an oscillation transformer.
The present invention relates to a power supply circuit for controlling and outputting a required constant current from the secondary side.

[0002]

2. Description of the Related Art For example, rechargeable electric appliances having different drive voltages depending on their outputs, such as rechargeable electric tools, include a plurality of units having different output voltages, for example, 2.4V, 7.2V, 9.6V, 12V, 24V. Are prepared. Each of the battery packs includes, for example, two batteries having a unit voltage of 1.2 V (hereinafter, referred to as unit batteries) and 6 batteries, respectively.
, 8, 10, and 20 are connected in series.

The above-mentioned battery packs have different output voltages but the same battery capacity, and are therefore charged by a common charging device that outputs a constant charging current. In such a charging apparatus, a switching element such as an FET (Field Effect Transistor) is connected in series to a primary winding of an oscillation transformer to which a DC voltage is applied, and the secondary side output current is fed back to perform PWM control to perform the above-described PWM control. The on-duty ratio of the switching element is changed to make the secondary-side output current constant.

[0004]

In the battery pack charging device for a rechargeable power tool, the battery voltage of the battery pack to be mounted is wide ranging from 2.4 V to 24 V, so that it is stable regardless of the battery voltage. It is difficult to output a constant output current.

That is, for example, in order to be able to charge the above-mentioned battery pack of 2.4V to 24V, the power supply circuit of the charging device needs at least an output voltage of 2.0V to 40V. When the on-duty ratio of the switching element at the time of the maximum output (40V) is set to 45% in consideration of the magnetic saturation prevention, the minimum output (2.4V)
On-duty ratio of the switching element is 2.25%
Next, at the time of minimum output pulse width of the switching pulse which controls the on-off driving of the switching elements becomes very narrow, it may become intermittent oscillation by some switching pulse escapes. Therefore, the output voltage of the power supply circuit becomes unstable, and the power supply to the PWM control circuit, the feedback circuit, and the like driven by using the output voltage is not stable, and the constant current control of the output current is more difficult. Becomes

[0006] The present invention has been made in view of the above problems, and has as its object to provide a power supply circuit capable of reliably performing PWM control at a suitable frequency according to an output voltage.

[0007]

According to the present invention, there is provided an oscillation transformer, and switching means connected in series to a primary winding of the oscillation transformer for interrupting a DC voltage applied to the primary winding; Pulse generating means for generating a switching pulse for turning on / off the switching means, current detecting means for detecting a secondary output current of the oscillation transformer, and holding the secondary output current at a desired current value And a PWM control means for changing the on-duty ratio of the switching pulse in accordance with the secondary output current detected by the current detection means, to detect a secondary output voltage of the oscillation transformer. Detecting means;
Frequency control means for changing the frequency of the switching pulse according to the detection result of the voltage detection means, and on-duty ratio detection means for detecting that the on-duty ratio of the switching pulse has become equal to or less than a preset reference value And control means for lowering the frequency of the switching pulse according to the secondary output voltage when the on-duty ratio of the switching pulse becomes equal to or less than the reference value.

[0008]

According to the present invention, the secondary output current of the oscillation transformer is detected, and the on-duty ratio of the switching pulse for controlling the on / off driving of the switching means is adjusted in accordance with the detected secondary output current. The secondary output current is maintained at a desired current value.

Also, the on-duty of the switching pulse
When the power ratio falls below the preset reference value, it is detected.
When the secondary output voltage of the oscillation transformer is detected,
In addition, the frequency of the switching pulse is changed according to the detected voltage . For example, the frequency of the switching pulse decreases as the secondary output voltage decreases.

As a result, even when the secondary output voltage is low and the on-duty ratio of the switching pulse is small in order to control the secondary output current at a constant current, the frequency is reduced in accordance with the decrease in the secondary output voltage. Therefore, the pulse width of the switching pulse does not become smaller than the required pulse width.

[0011]

FIG. 1 is a circuit diagram of a first embodiment of a power supply circuit according to the present invention.

This power supply circuit is applied to a charging device for charging a battery pack, and includes a drive circuit 1, a control circuit 2, a conversion circuit 3, and a rectifying / smoothing circuit 4.

The rectifying and smoothing circuit section 4 rectifies and smoothes a commercial AC power supply to generate a DC power supply. The rectifying and smoothing circuit unit 4 includes a rectifying bridge BD for rectifying an AC power input from an input terminal aa ′ into a DC power and a capacitor C41 for smoothing an output from the rectifying bridge BD. A fuse F is interposed in the line.

The conversion circuit unit 3 inputs the DC power generated by the rectification and smoothing circuit unit 4 to the primary winding L11 of the transformer T1, and drives a switching element such as an FET (Field Effect Transistor) on and off. By doing so, switching is performed at a high frequency, a voltage is induced in the secondary winding L12, converted into a DC output of a predetermined level, and output.

The above FET is composed of a primary winding L of a transformer T1.
The DC voltage output from the rectifying and smoothing circuit unit 4 is applied to a series circuit of the primary winding L11 and the FET. A bias voltage is applied to the gate of the FET by dividing the DC voltage by bias resistors R31 and R32, and a switching pulse is input from a PWM control circuit 11, which will be described later, via a resistor R33. .

The secondary circuit connected to the secondary winding L12 of the transformer T1 includes a diode D31 for rectifying the AC voltage induced by the switching operation of the switching element FET, a smoothing choke coil L31 and a capacitor C31. The circuit is composed of a freewheel diode D32 for smoothing and improving output efficiency. A resistor R34 for detecting an output current is inserted in the line of the output terminal b '(negative electrode side), and the output terminal b-b'
A resistor RB1, for dividing and detecting the battery voltage,
The series circuit of RB2 is connected.

The control circuit section 2 includes a transformer T2, which is magnetically coupled to a transformer T1 for supplying power to each control circuit, which will be described later, provided on the secondary side.
A constant current control circuit 2 that feeds back a secondary output current to a PWM control circuit 11 described later and controls the output current with a constant current
2. The battery pack detection circuit 23 for detecting that a battery pack (not shown) is mounted between the output terminals bb 'and the battery voltage are fed back to a PWM control circuit 11 described later to drive the switching element FET. And a secondary side control circuit 24 for stabilization.

The secondary power supply circuit 21 includes a transformer T
The DC power generated by the rectifying / smoothing circuit unit 4 is converted into AC and supplied through the rectifier / smoothing circuit 4. That is, the primary winding L21 of the transformer T2 is
The first primary winding L11 is magnetically coupled, and an AC voltage is induced by the on / off driving of the switching element FET. The secondary power supply circuit 21 generates a required DC power supply from the AC voltage input from the transformer T2, and
4 and photocouplers PC1 to PC5, PC to be described later
Supply to _SFT .

The constant current control circuit 22 includes the conversion circuit unit 3
And outputs a current proportional to the magnitude of the output current to the PWM control circuit 11 via the photocoupler PC _FB.
To the F / B terminal. Also, the secondary side control circuit 24
When the battery pack detection circuit 23 detects that the voltage pack has been mounted, the battery pack detection circuit 23 identifies the type of the battery pack (the type classified by the battery voltage) from the battery voltage, and switches the corresponding photocouplers PC1 to PC5. The information of the type of the battery pack mounted via the
Feedback to the F terminal.

In the case of a battery pack for a rechargeable power tool, for example, there are five types of battery packs of 2.4 V, 7.2 V, 9.6 V, 12 V, and 24 V, and each battery pack has a unit battery of 1.2 V. A predetermined number is connected in series.
Each of the photocouplers PC1 to PC5 is 2.4.
V, 7.2 V, 9.6 V, 12 V, and 24 V corresponding to the detection of each battery pack, and the secondary-side control circuit 24 outputs, for example, when the voltage of the attached battery pack is 2.4 V,
This information is fed back to the TOFF terminal of the PWM control circuit 11 via the photo coupler PC1.

The drive circuit section 1 performs PWM control on / off driving of the switching element FET of the conversion circuit section 3, and is mainly composed of a PWM control circuit 11 composed of an IC (Integrated Circuit). It has the following functions.

Vcc: drive power supply terminal GND: ground terminal VOUT: output terminal A switching pulse for PWM control is output.

TOFF: a control terminal for controlling the off time of the switching pulse. A resistor R _OFF connected to the TOFF terminal and a capacitor CF connected to a CF terminal described later.
, The off-time is determined. If the capacitor CF is constant, the off-time becomes longer as the resistance R _OFF is increased. That is, as the resistance R _OFF increases, the frequency of the switching pulse decreases.

CF: a control terminal for controlling the off time and the on time of the switching pulse.

TON: a control terminal for controlling the ON time of the switching pulse. Resistance R connected to TON terminal
_{The ON} time is determined by _ON and the capacitor CF connected to the CF terminal.
_{The ON} time becomes longer as _ON is increased.

SOFT: A terminal for adjusting the on-time of the switching pulse and adjusting the off-time. SOFT
The off time of the switching pulse becomes longer as the voltage input to the terminal decreases. That is, when the input voltage of the SOFT terminal is reduced, the frequency of the switching pulse is reduced.

REG: Output terminal of the stabilized power supply. A constant voltage having a predetermined voltage value is output from the REG terminal.

F / B: Terminal for inputting feedback current. F / B
The duty ratio of the switching pulse is changed according to the current flowing into the terminal.

COL: A drive voltage supply terminal for outputting a switching pulse from the VOUT terminal.

A DC voltage applied to the primary winding L11 of the transformer T1 is connected to the power supply terminal Vcc by the resistors R31 and R31.
32. Note that the supply voltage is
The voltage is made constant by the Zener diode Z11.
The COL terminal is connected to the primary winding L of the transformer T2.
The voltage induced at 21 is rectified by a diode 32 and a capacitor C31 to supply a predetermined voltage.

A drive circuit for turning on / off the switching FET is provided at the VOUT terminal. The drive circuit comprises a series circuit of an npn-type transistor TR1 and a pnp-type transistor TR2 and a resistor R11 connected to the bases of the two transistors TR1 and TR2. Connected to
The collector of the pnp transistor TR2 is connected between the negative electrode on the primary side of the transformer T1. The bases of the transistors TR1 and TR2 are connected to the VOUT terminal via a resistor R11, and the transistors TR1 and TR2
2 is connected to the switching element F via a resistor R33.
It is connected to the gate of ET.

When the VOUT terminal goes high, the transistor TR1 turns on while the transistor TR2 turns on.
Is turned off, and the gate of the switching element FET goes high, turning on. When the VOUT terminal goes low, the transistor TR1 turns off while the transistor TR2 turns on, and the gate of the switching element FET goes low to turn off. Therefore, the switching element FET is driven on and off in synchronization with the switching pulse output from the VOUT terminal.

The TOFF terminal has a series circuit of the output circuit of the photocoupler PC1 and R _OFF1 , a series circuit of the output circuit of the _photocoupler PC2 and R _OFF2,.
.., An output circuit of the _{photocoupler PC5} and a series circuit of R _OFF5 are connected in parallel, and the resistor R
_{OFF1 to ROFF5} can be switched and connected. Resistance R
_{OFF1 ~R OFF5} is _{R OFF1> R OFF2> R OFF3} > R OFF4> R
_It has a predetermined resistance value related to _OFF5 .

[0034] The SOFT terminal is connected to the REG terminal via a resistor R _SFT1, the said SOFT terminal, is connected to the series circuit and the capacitor C _SFT of an output circuit of the resistor R _SFT2 and photo coupler PC _SFT Have been.

The secondary side control circuit 24 turns off the photocoupler PC _SFT when the detection signal indicating that the battery pack is mounted is not input from the battery pack detection circuit 23, and when the detection signal is input, _Turn on the photo coupler PC _SFT . Therefore, when the battery pack is not mounted, the output voltage from the REG terminal is directly input to the SOFT terminal via the resistor R _SFT1 , and when the battery pack is mounted, the REG is connected to the SOFT terminal.
A divided voltage obtained by dividing the output voltage from the terminal by the resistor R _SFT1 and the resistor R _SFT2 is input.

In the above configuration, when an AC power supply is connected to the terminals aa ', the PWM control circuit 11 is activated and the VO
A switching pulse is output from the UT terminal, and the switching element FET is turned on and off. As a result, the DC voltage output from the rectifying / smoothing circuit section 4 intermittently flows into the primary winding L11 of the transformer T1 in a predetermined cycle, and correspondingly, intermittently flows in the secondary winding L12 of the transformer T1 in a predetermined cycle. Voltage is induced. This voltage is applied to the diode D
31, rectified and smoothed by the coil 341 and the capacitor C31.

When the battery pack is mounted on the terminals bb ', this mounting is detected by the battery pack detection circuit 23. When detecting the attachment of the battery pack, the secondary side control circuit 24 turns on the photocoupler PC _SFT . As a result, a predetermined voltage obtained by dividing the output voltage from the REG terminal is input to the SOFT terminal of the PWM control circuit 11.
The frequency of the switching pulse output from the OUT terminal is controlled so that the output current of the conversion circuit unit 3 becomes a predetermined constant current.

On the other hand, the output current of the converter circuit 3 is detected by the constant current control circuit 22, the constant current control circuit 22 supplies a current proportional to the output current to the photo coupler PC _FB. As a result, PW is transmitted through the photocoupler PC _FB.
A predetermined current proportional to the output current flows into the F / B terminal of the M control circuit 11, and the on-duty ratio of the switching pulse output from the VOUT terminal is controlled in accordance with the current, and the output current becomes a predetermined constant. It is held by the current.

Further, the secondary side control circuit 24 identifies the type of the attached battery pack from the battery voltage, and turns on the corresponding photocouplers PC1 to PC5. For example, when the attached battery pack is 2.4 V, the photocoupler PC1 is turned on, and the TO of the PWM control circuit 11 is
The resistance value connected to the FF terminal is referred to as a resistance R _OFF1 . Thus, the on-duty ratio of the switching pulse is set to a predetermined constant current with respect to the battery voltage of 2.4 V.

That is, the frequency of the switching pulse is set to a suitable frequency based on the output current and the battery voltage, and the output current is preferably subjected to constant current control. Especially when the battery voltage is low, if only the output current information is fed back to control the frequency of the switching pulse, the pulse width becomes very narrow, and the switching element FET is reliably turned on in synchronization with the switching pulse. -It may be intermittent oscillation without turning off, but the information of the battery voltage is fed back as described above, and the frequency of the switching pulse is switched to a lower frequency as the battery voltage becomes lower. Since the pulse width is reduced, the pulse width of both the ON and OFF of the switching pulse is widened, so that intermittent oscillation does not occur.

In the first embodiment, the battery voltage is detected,
Although the resistance value connected to the TOFF terminal of the PWM control circuit 11 is automatically set, it may be set manually.

Next, a second embodiment in which the resistors R _{OFF1 to} R _OFF5 are manually set will be described.

FIG. 2 is an external view of a charging apparatus to which a second embodiment of the power supply circuit according to the present invention is applied. FIG.
FIG. 9 is a main part circuit diagram of a second embodiment.

In FIG. 2, reference numeral 5 denotes a main body of the charging device.
Reference numeral 1 denotes a battery pack mounting unit, 52 denotes a display unit, and 53 denotes a group of changeover switches. 6. For the 2.4 V of the changeover switch group 53,
The switches for 2V,..., And 24V correspond to SW1 to SW5 in FIG. SW1-SW
Reference numerals 5 are interlocked with each other so that when one of the switches is turned on, the other switches are turned off. When all the switches SW1 to SW5 are off, the resistance R _OFF0 (> R _OFF1 ) is set to the TOFF terminal of the PWM control circuit 11.

Next, a description will be given of a third embodiment of the power supply circuit according to the present invention.

In the third embodiment, the type of the attached battery pack is detected by using the battery voltage of the temperature sensor attached to the battery pack.

FIG. 4 is a circuit diagram for detecting the type of the battery pack based on the output voltage of the temperature sensor built in the battery pack, wherein (a) to (e) are for 2.4 V, respectively.
It is a circuit diagram for 7.2V, 9.6V, 12V and 24V.

In FIG. 4, E is a battery, SW6 is a switch, 6 is a temperature sensor, RT1 to RT5 are resistors, c-
The terminal c 'is a terminal for detecting the output voltage of the temperature sensor 6.

To detect the temperature of the battery pack, the switch SW6 is turned off, and the temperature sensor 6 and the resistors RT1 to RT5 are connected to the battery E in series. For example, in the case of a 2.4 V battery pack, when the switch SW6 is turned off, a current flows through a series circuit of the temperature sensor 6 and the resistor RT1, and c
The -c 'terminal has a resistor RT connected to the output voltage of the temperature sensor 6.
1 is added and output. That is, from the cc 'terminal, the output voltage of the temperature sensor 6 is added to the voltage drop at the resistor RT1 as an offset voltage and output. Similarly, for other types of battery packs, the offset voltage corresponding to the voltage drop at the resistors RT2 to RT5 is added to the output voltage of the temperature sensor 6 from the cc 'terminal and output.

In the third embodiment, the temperature characteristics of the temperature sensors 6 built in the respective battery packs are substantially the same, but the offset voltage increases as the number of cells of the unit battery increases, and the cc 'of each battery pack is increased. The variation range of the output voltage of the temperature sensor 6 output from the terminal is prevented from overlapping.
That is, for the resistors RT1 to RT5, for example, a reference resistor Rr is set, and the resistance value increases as the number of unit cells increases, that is, RT1 <RT2 <R.
A plurality of resistors Rr are connected in series such that T3 <RT4 <RT5.

FIG. 5 is a diagram showing the temperature characteristics of the output voltage of the temperature sensor 6 output from the cc 'terminal of each battery pack. As shown in the drawing, the output voltages of the battery packs do not overlap with each other due to the offset voltages of the resistors RT1 to RT5. Is identified. For example, the output voltage of the temperature sensor 6 of each battery pack is input to the secondary side control circuit 24 instead of the output voltage of the conversion circuit 3 in FIG. 1, and the type of the battery pack is identified from the fluctuation range of the output voltage. Good to do.

Next, a description will be given of a fourth embodiment of the power supply circuit according to the present invention.

FIG. 6 is a circuit diagram of a power supply circuit according to a fourth embodiment of the present invention. In the figure, the conversion circuit unit 3 and the rectification / smoothing circuit unit 4 are the same as the conversion circuit unit 3 and the rectification / smoothing circuit unit 4 shown in FIG. The control circuit unit 2 'is different from the control circuit unit 2 shown in FIG.
The secondary side control circuit 24 and the photocouplers PC1 to PC5 are eliminated, and the drive control of the photocoupler PC _SFT is performed by the non-inverting amplifier circuit 7 including the operational amplifier OP1.

That is, the output voltages from the resistors RB1 and RB2 are output from the operational amplifier OP1, the resistors R21, R22, and R2.
The signal is amplified by the non-inverting amplifier circuit 23, input to the input side of the photocoupler PC _SFT via the output resistor R24, and fed back to the SOFT terminal of the PWM control circuit 11 via the photocoupler PC _SFT . The collector of the output circuit of the photocoupler PC _SFT is
The output circuit is connected to the Vcc terminal via a resistor R25, and the emitter of the output circuit is connected to the SOFT terminal of the PWM control circuit 11 via a diode D22.

The drive circuit section 1 'is different from the drive circuit section 1 shown in FIG. 1 in that resistors R _{OFF1 to} R _OFF5 are replaced with resistors R _{OFF1 to} R _OFF5.
OFF is connected to the TOFF terminal, and the SOFT terminal is connected to 1
A resistor R12 and a Zener diode Z12 are connected between the negative electrode on the next side.
And the resistor R _SFT2 is removed.

In the above configuration, when the battery voltage is input to the photocoupler PC _SFT via the non-inverting amplifier circuit 7,
Corresponding to the input voltage current flows into the resistor R12,
Voltage V input to SOFT terminal of PWM control circuit 11
_SOFT changes. The higher the battery voltage, the higher the voltage V _SOFT , thereby increasing the frequency of the switching pulse output from the VOUT terminal. On the other hand, when the battery voltage is low, the frequency of the switching pulse is reduced and the off period is relatively widened. Note that the voltage V _SOFT is RE
When the output voltage value from the G terminal matches, the frequency of the switching pulse becomes maximum.

As described above, since the battery voltage is detected and the frequency of the switching pulse is suitably set in accordance with the result of the detection, the same effect as in the first embodiment can be obtained. .

Next, a fifth embodiment of the power supply circuit according to the present invention will be described.

In the fifth embodiment, the feedback current flowing through the output circuit of the photocoupler PC _FB is detected, and the frequency of the switching pulse is changed according to the battery voltage only when the current is equal to or less than a predetermined value. It is.

FIG. 7 is a circuit diagram of a power supply circuit according to a fifth embodiment of the present invention. Drawing, in FIG. 6, the photocoupler PC _FB emitter and a resistor R26 is inserted between the negative pole of the primary side, the resistor R the current flowing through the photo coupler PC _FB
At 26, the voltage is converted and detected. The voltage V _FB detected by the resistor R26 is input to the non-inverting terminal of the operational amplifier OP2, while the reference voltage V _{REF obtained by} dividing the Vcc voltage by the resistors R27 and R28 is input to the inverting terminal of the operational amplifier OP2. I have. And the operational amplifier OP
The output of 2 is input to the SOFT terminal via the diode D23.

In the above configuration, the photocoupler PC _FB
, A current corresponding to the output current of the conversion circuit section 3 flows, and this current is converted into a voltage V _FB by the resistor 26 and detected. The output terminal of the operational amplifier OP2 is at a low level when the voltage V _FB is equal to or lower than the reference voltage V _REF ,
When the voltage exceeds the reference voltage V _REF , it goes high.

When a high level is output from the operational amplifier OP2, the voltage of the resistor R12 increases, and the input voltage V _SOFT of the SOFT terminal increases to the value of the output voltage from the REG terminal. As a result, the frequency of the switching pulse output from the VOUT terminal becomes the maximum frequency.

On the other hand, when the low level is output from the operational amplifier OP2, that is, when the output current of the conversion circuit unit 3 is smaller than a predetermined value, the photo coupler PC _SFT
A current corresponding to the battery voltage flowing through the resistor R12 flows into the resistor R12, and the voltage V _SOFT is determined by the voltage at the resistor R12. As a result, the voltage V _{SOFT of the} SOFT terminal varies according to the battery voltage, and the frequency of the switching pulse output from the VOUT terminal is suitably adjusted. In addition,
The current corresponding to the battery voltage is blocked by the diode D23, and does not flow to the feedback current detection circuit including the operational amplifier OP2 and the like.

As described above, in the fifth embodiment, the switch
Pulse on-duty ratio falls below a predetermined reference value.
When the output current falls below a predetermined value , the frequency of the switching pulse is changed according to the magnitude of the battery voltage, so that the on-duty ratio of the switching pulse does not become smaller than the predetermined reference value. In addition, it is possible to reliably prevent the occurrence of intermittent oscillation due to the narrow pulse width of the switching pulse.

FIGS. 8A and 8B are views showing the structure of the AC line of the power supply circuit according to the present invention. FIG. 8A is a perspective view showing a state before a ferrite core is attached to an AC input terminal, and FIG.
It is a perspective view showing the state where a ferrite core was attached to an input terminal.

In the figure, 41, 42 and 43 are connection terminals, F is a fuse, 44 and 45 are ferrite cores, 46
Is a substrate that supports the connection terminals 41 to 43. The terminals 41 and 42 correspond to the terminal a and the terminal a 'in FIG. 1, respectively.

As shown in FIG. 6B, the ferrite cores 44 and 45 are attached so that a magnetic path is formed on the outer periphery of the terminals 41 and 42. By doing so, the energy of the high frequency component contained in the AC line is consumed by the eddy current flowing through the ferrite cores 44 and 45 and does not flow into the power supply circuit.

[0068]

As described above, according to the present invention,
The DC voltage flowing into the primary winding of the oscillation transformer is intermittently switched at predetermined intervals by a switching means to output a desired output current from the secondary side of the oscillation transformer.
A power supply for detecting a secondary output current and changing the on-duty ratio of a switching pulse for controlling the driving of the switching means in accordance with the secondary output current, thereby maintaining the secondary output current at a desired current value In the circuit, when the on-duty ratio of the switching pulse becomes equal to or less than a preset reference value, the frequency of the switching pulse is reduced according to the secondary output voltage of the oscillation transformer. Even when the voltage is low and the on-duty ratio of the switching pulse is reduced in order to control the secondary output current at a constant current, the frequency of the switching pulse is reduced in accordance with the decrease in the secondary output voltage. The width does not become smaller than the predetermined width. This makes it possible to reliably control the driving of the switching means without causing intermittent oscillation for a wide range of output voltages.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a power supply circuit according to the present invention.

FIG. 2 is an external view of a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a main part circuit diagram of a second embodiment of the power supply circuit according to the present invention.

4A and 4B are diagrams for detecting the type of a battery pack from the output voltage of a temperature sensor built in the battery pack, wherein FIG. 4A is a circuit diagram for a 2.4V battery pack, and FIG. 4B is a diagram for a 7.2V battery; FIG. 2 is a circuit diagram for a pack, (c) is a circuit diagram for a 9.6 V battery pack, (d) is a circuit diagram for a 12 V battery pack, and (e) is a circuit diagram for a 24 V battery pack.

FIG. 5 is a diagram illustrating output voltage characteristics of a temperature sensor output from a battery pack.

FIG. 6 is a circuit diagram of a power supply circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a power supply circuit according to a fifth embodiment of the present invention.

FIG. 8 is a diagram showing a structure of an AC line of a power supply circuit;
(A) is a perspective view showing a state before a ferrite core is attached to an AC input terminal, and (b) is a perspective view showing a state where a ferrite core is attached to an AC input terminal.

[Explanation of symbols]

1, 1 ', 1 "drive circuit section 11 PWM control circuit 2, 2', 2" control circuit section 21 secondary side power supply circuit 22 constant current control circuit 23 battery pack detection circuit 24 secondary side control circuit 3 conversion circuit section Reference Signs List 4 rectifying and smoothing circuit section 41, 42, 43 terminal 44, 45 ferrite core 46 substrate 5 main body 51 battery pack mounting section 52 display section 53 switch group 6 temperature sensor 7 forward amplification circuit D21 to D23 diodes R _{OFF1 to} R _OFF5 , R _SFT1 , R _SFT2 resistors RB1, RB2, RT1 to RT5, R12, R21 to R
28 Resistance PC1 to PC5, PC _SFT , PC _FB Photocoupler T1, T2 Transformer SW1 to SW6 Switch OP1, OP2 Operational amplifier

Continuation of the front page (56) References JP-A-4-84672 (JP, A) JP-A-56-36716 (JP, A) JP-A-2-151266 (JP, A) Jpn. , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H02M 3/28

Claims (1)

(57) [Claims] An oscillation transformer and one of the oscillation transformers
A switching means connected in series to the secondary winding for interrupting a DC voltage applied to the primary winding; a pulse generating means for generating a switching pulse to drive the switching means on and off; Current detection means for detecting the secondary output current of the above, and turning on of the switching pulse in accordance with the secondary output current detected by the current detection means to maintain the secondary output current at a desired current value. In a power supply circuit having a PWM control unit for changing a duty ratio, a voltage detection unit for detecting a secondary output voltage of the oscillation transformer, and a frequency of the switching pulse is changed according to a detection result of the voltage detection unit. Frequency control means for detecting that the on-duty ratio of the switching pulse has fallen below a predetermined reference value; A duty ratio detecting means, and characterized in that on-duty ratio of the switching pulse and a control means for reducing according to the frequency of the switching pulses in the secondary output voltage when it is below the reference value Power supply circuit.