JP2685979B2 - Power supply - Google Patents

Description

TECHNICAL FIELD The present invention relates to a feedback control type power supply device.

[Prior Art] A conventional analog switching control type power supply device is disclosed, for example, in "High Speed Switching Regulator;
A digitally controlled power supply device as shown in the figure is known.

In FIG. 4, the output voltage V _IN of the DC voltage source 1 is switched into a rectangular wave by a switch 2 such as a transistor, and this rectangular wave is a low-pass filter (LPF) 3.
Is smoothed by the DC voltage. This DC voltage becomes the power supply voltage of the load 4. That is, the output voltage V _IN of the DC voltage source 1 is dropped by the switch 2 and LPF 3 and applied to the load 4 as a power supply voltage having a desired value.

In this case, the DC voltage output from LPF3 is also A /
The digital data is converted by the D converter 5 and applied to one input terminal of the comparator 8. On the other hand, the target DC voltage that specifies the value of the power supply voltage applied to the load is supplied from the control terminal 7, and this target DC voltage is converted into digital data by the A / D converter 6 and the other side of the comparator 8 is supplied. Applied to the input terminal of. The comparator 8 calculates the difference between these current voltages and outputs a difference signal.

The pulse width modulation (PWM) circuit 9 outputs a pulse having a width proportional to the difference between the DC voltage output from the LPF 3 and the target DC voltage input from the control terminal 7 according to the difference signal output from the comparator 8. Then, the switch 2 is turned on and off according to this pulse width.

Therefore, the above circuit constitutes a negative feedback loop, is stable when the output voltage of the LPF 3 and the input voltage from the control terminal 7 match, and a DC voltage of a desired value is applied to the load 4.

[Problems to be Solved by the Invention] However, in the above-described conventional power supply device, the output of the comparator 8 is digital data, and the pulse width of the switching pulse output from the PWM circuit 9 depends on this digital data. Therefore, if the number of bits of this digital data is N, the minimum change rate of the output voltage of LPF3, that is, the quantization error of the power supply voltage applied to the load 4 is V _IN / 2N. Therefore, in order to reduce the quantization error, there is only a method of increasing the number of bits of digital data handled by the PWM circuit 9, which causes a problem of increasing the circuit scale.

An object of the present invention is to provide a power supply device capable of reducing the quantization error of the power supply voltage applied to the load without increasing the circuit scale in view of the above problems of the prior art.

[Means for Solving the Problems] In order to achieve the above object, the present invention divides a voltage value of an output DC voltage of a DC voltage source into a plurality of voltage ranges, and sets a plurality of voltage ranges in advance and applies the voltage to a load. The control unit that detects the voltage range to which the target value of the power supply voltage belongs and turns on the switch at a predetermined cycle for a time corresponding to the lower limit voltage of the detected voltage range, and is generated by the smoothing circuit and applied to the load. A drive circuit is provided that calculates a difference between the power supply voltage and the target value, and turns on the switch at a predetermined cycle during a period in which the control unit turns off the switch and a time period according to the difference.

[Operation] According to the present invention, with the above configuration, the power supply voltage applied to the load is controlled by the control unit so that the target value of the power supply voltage applied to the load becomes the lower limit voltage value of the voltage range to which the target value belongs. On the other hand, the drive circuit controls so as to eliminate the difference between the target voltage and the power supply voltage controlled to the lower limit voltage value.

Therefore, since the drive circuit can control the power supply voltage within a voltage range narrower than the voltage value of the output DC voltage of the DC voltage source, the quantum of the power supply voltage applied to the load can be increased without increasing the number of bits in the drive circuit. The conversion error can be reduced.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a power supply device according to the present invention, FIG. 2 (a) is an explanatory view showing a partial pressure of the power supply device of FIG. 1, and FIG. 2 (b) is a view of FIG. FIG. 3 is a waveform chart showing the voltage applied to the switch, and FIG. 3 is a flow chart for explaining the operation of the control unit in FIG.

In FIG. 1, the + terminal (voltage V _IN ) of the DC voltage source 11
Is one end of the resistor 12 and the emitter of the pnp transistor 13 and n
It is connected to the collector of the pn transistor 14. Resistance 12
The other end of is connected to the base of the transistor 13, and the collector of the transistor 13 is connected to the base of the transistor 14. Therefore, these resistors 12 and transistors 13,1
4 is a DC voltage source 11 depending on the base voltage of the transistor 13.
The switches (12 to 14) that turn on and off the output voltage V _IN of

The emitter of the transistor 14 of this switch (12-14) is connected to the cathode of the diode 15 and the coil 16 once, and the other end of the diode 15 is grounded. The other end of the coil 16 is connected to one ends of a capacitor 17 and a load 18, respectively, and the other ends of the capacitor 17 and the load 18 are both grounded. Therefore, the coil 16 and the capacitor 17 form a smoothing circuit (16, 17) that smoothes the emitter voltage of the transistor 14 and outputs the voltage V _out .

The other end (output voltage V _out ) of the coil 16 is also the A / D converter 19
Of the A / D converter 19 and the output terminal of the A / D converter 19 is connected to one input terminal of the comparator 20. A target DC voltage V _t that specifies the value of the power supply voltage V _out applied to the load 18 is input from the control terminal 21, and this target DC voltage V _t is
A / D converter 22 converts to digital data and comparator 20
Is applied to the other input terminal and the control unit 23.

The pulse width modulation (PWM) circuit 24 receives a DC voltage V output from the smoothing circuit (16, 17) according to the output signal of the comparator 20.
A pulse having a width proportional to the difference between _out and the DC voltage V _t input to the control terminal 21 is output and applied to the base of the npn transistor 26 via the base resistor 25. Further, as will be described later, the control unit 23 controls the DC voltage V _IN of the DC voltage source 11 from the voltage 0.
Up to this, a plurality of voltage ranges obtained by equally dividing the above range are set in advance. The control unit 23 detects which voltage range the target voltage V _t belongs to, and has a width corresponding to the lower limit voltage of the detected voltage range. A pulse is output and applied to the base of the npn transistor 28 via the base resistor 27.

The collectors of the transistors 26 and 28 are both switches (12 to 1
4) is connected to the base of the transistor 13 and the emitters are both grounded. Therefore, when one of the transistors 26 and 28 is turned on, the switch (12
~ 14) are turned off and both transistors 26, 28 are turned off, the switches (12-14) are turned on.

In this way, the feedback loop is constructed, and when the switches (12-14) are on, as shown by the solid line in the figure,
Depending on the output voltage V _IN of the DC voltage source 11, the switch (12 to 1
4), current flows through the smoothing circuit (16, 17), and when the switches (12 to 14) are off, the energy accumulated in the coil 16 causes the diode 15 and the coil A current flows through 16 which causes a voltage V _out to be applied to load 18.

Here, for example, as shown in FIG. 2A, the range from the voltage 0 to the value of the output voltage V _IN of the DC voltage source 11 is V _a ,
Divide into 4 equal parts by V _b , V _c (however, V _IN > V _a > V _b > V _c > 0),
It will be described for controlling the output voltage V _out of the power supply voltage or the smoothing circuit of the load 18 (16, 17) in the range of the voltage range V _a ~V _b.

Generally, the input voltage V _i is switched on and off,
The output of this switch is smoothed by a smoothing circuit to obtain a DC voltage V _o.
When the switch ON / OFF cycle is T and the ON period time length is V _ON , It is.

FIG. 2 (b) shows the waveform of the switch pulse of the switch (12 to 14) by the PWM circuit 24 and the control unit 23, and the switch (12 to 14) is at "L" (low level) of this waveform. Turn on, and turn off at "H" (high level). Therefore, the width of the "L" period of this waveform is the pulse width of the switching pulse.

Now, assume that the power supply voltage V _out applied to the load 18 is set to a predetermined value within the voltage range V _{a to} V _b as shown in FIG. 2 (a). Control unit 23, the output data of the A / D converter 22, the voltage range target DC voltage V _t is V _a ~V _b
Detects that is within, generates a pulse having a pulse width T _b which corresponds to the lower limit value V _b of the voltage range V _a ~V _b. The period of this pulse is T. Therefore, in the above equation (1), if V _o is V _b , T _ON is V _b , and V _i is V _IN , Thus, the pulse width T _b is obtained, and as described above, the control unit 23 generates a pulse having the period T and the pulse width T _b and supplies it to the base of the transistor 28.

The on / off operation of the switches (12 to 14) by such a pulse sets the voltage V _out to the voltage value V _b .

On the other hand, the comparator 20 detects the difference between the voltage V _out and the target DC voltage V _t within the voltage range V _{a to} V _b . This voltage V _out is controlled by the control unit 23 as described above. since is controlled as determined in the lower limit value V _b in the range V _a ~V _b, comparator 2
0 detects the difference between this lower limit value V _b and the target DC voltage V _t . The PWM circuit 24 generates a PWM signal having a pulse width corresponding to this difference and supplies it to the base of the transistor 26. The ON / OFF operation of the switches (12 to 14) by the PWM signal is performed during the period in which the pulse from the control unit 23 is "H" (T- _Tb ).

Here, the period of the PWM signal is T _p , and the time length of “L” is T _PWM
In the above formula (1), V _o is (V _t −V _out ),
If T _ON is T _PWM , T is T _P , and V _i is V _IN , Accordingly, although the pulse width T _PWM is determined, as described above, since the voltage V _out is controlled to by connexion voltage V _b to the control unit 23, the voltage V _out in equation (3), by the comparator 20 By the control of the PWM circuit 24, the target voltage V _{t is changed} from the voltage value V _b.
Equal to.

That is, switches (12 to 14), comparator 20, PWM circuit 24
The negative feedback loop consisting of the voltage V _out changes the voltage range V _{a to} V a.
Control in _b .

Therefore, if the number of bits of the digital data from the comparator 20 is N, the quantization error of the power supply voltage V _out by the PWM circuit 24 becomes (V _a −V _b ) / 2N, which is the conventional voltage range V.
Compared with the case of controlling by the _IN ~0, when equal the number of bits N, it will be reduced to _{(V a -V b) / V} IN times.

The same applies to the voltage ranges V _{IN to} V _a , V _{b to} V _o , and V _{c to} 0.

Next, the operation of the above embodiment, particularly the operation of the controller 23 will be described with reference to FIG.

The control unit 23 is composed of, for example, a microcomputer and has a voltage value V obtained by dividing the voltage V _IN of the DC voltage source 11 into four equal parts in advance.
_a , V _b , V _c , and control period T and voltage range V _IN ~ V _a , V _a ~
V _b, V _b ~V _c, the time interval corresponding to V _c ~0 T _a,
T _b , T _c , T _o are set.

In step 31, the target DC voltage V _t of the load 18 is input through the control terminal 21, A / D converter 22, at next step 32, it is determined whether V _t> V _a, V _t If> V _a , go to step 33 to set the pulse width to T _a and turn transistor 28 off for this pulse width T _a and on for the rest of the time (T−T _a ).

If V _a > V _t > V _b (step 34), the process proceeds to step 35, where the pulse width is set to T _b , the transistor 27 is turned off for this pulse width T _b , and the remaining time ( T
To turn on between the -T _b).

Similarly, when V _b > V _t > V _c (step 36),
Proceed to step 37 to set the pulse width to T _c , turn transistor 27 off for this pulse width T _c , turn on for the rest of the time (T−T _c ), and if V _c > V _t . the (step 36), sets the pulse width to T _o proceeds to step 38, it is always on the transistor 27.

Therefore, according to the above-mentioned embodiment, when the voltage ranges V _{IN to} V _a , V _{a to} V _b , V _{b to} V _c , V _{c to} 0 are set, PW
The M circuit 24 has a voltage range V _IN to which the set voltage V _t of the load 18 belongs.
~ V _a , V _a ~ V _b , V _b ~ V _c , V _c ~ 0 is controlled between the upper limit value and the lower limit value, so compared with the case of using the PWM circuit 24 of the same bit number as the conventional example. , Quantization error can be reduced to 1/4.

Further, since the number of divisions up to the voltage value of the output voltage V _IN of the DC voltage source 11 can be programmed in the control unit 23, the quantization error can be obtained by further dividing the range up to the voltage V _IN of the DC voltage source 11. Can be further reduced.

In the above embodiment, the switch (12
14 to 14) are pulse-driven, but it goes without saying that they may be driven by other pulse-modulated signals.

[Effects of the Invention] As described above, according to the present invention, the voltage range up to the DC voltage of the DC voltage source is divided into equal parts in advance to set a plurality of voltage ranges. The lower limit voltage of the voltage range is controlled by the control unit, while the voltage difference between the target voltage and the lower limit voltage is controlled by the pulse drive circuit. Since the voltage can be controlled in a voltage range narrower than the DC voltage, the quantization error of the power supply voltage with respect to the load can be reduced without increasing the number of bits in the pulse drive circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply device according to the present invention, FIG. 2 (a) is an explanatory diagram showing the operation of a control unit and a PWM circuit in FIG. 1, and FIG. 2 (b) is a first diagram. FIG. 3 is a waveform diagram showing the drive voltage of the switch in the figure, FIG. 3 is a flow chart for explaining the operation of the control unit in FIG. 1, and FIG. 4 is a circuit diagram showing a conventional power supply device. 11 …… DC voltage source, 13,14,26,28 …… Transistor, 15
…… Diode, 16 …… Coil, 17 …… Capacitor, 18
...... Load, 19,22 …… A / D converter, 20 …… Comparator, 21 ……
Control terminal, 23 ... Control section, 24 ... Pulse width modulation (PWM)
circuit.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masanori Inada 5-22-1 Kamimizuhoncho, Kodaira-shi, Tokyo Inside Hitachi Microcomputer System Co., Ltd. (72) Masashi Takamiya 2-15 Nishishinbashi, Minato-ku, Tokyo No. 12 Hitachi High-Technology Division, Home Appliance Business Headquarters (72) Inventor Masaharu Shimizu 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi Video Engineering Co., Ltd. (56) Reference JP-A-2-74152 ( JP, A) JP-A-59-76171 (JP, A) Jitsukaihei 2-91487 (JP, U)

Claims (2)

(57) [Claims] 1. A direct-current voltage source, a switch for turning on and off an output direct-current voltage of the direct-current voltage source, and a smoothing circuit for smoothing the output voltage of the switch to generate a direct-current voltage which becomes a power supply voltage of a load. , A plurality of voltage ranges are preset by dividing the voltage value of the output DC voltage of the DC voltage source into a plurality of values, and the voltage range to which the target value of the power supply voltage applied to the load belongs is detected and detected. A control unit that turns on the switch at a predetermined cycle for a time corresponding to the lower limit voltage of the voltage range, calculates a difference between the DC voltage generated by the smoothing circuit and the target value, and the control unit controls the switch. The power supply device is characterized in that a drive circuit is provided for turning on the switch at a predetermined cycle for a period corresponding to the difference during the turning off. 2. The power supply device according to claim 1, wherein the drive circuit is a pulse width modulation circuit.