JPH0284060A - Switching power supply - Google Patents

Abstract

PURPOSE:To reduce the number of parts of an apparatus and to contrive to lower its cost by broadening the width of an ON pulse to a switching means, when an input voltage is low, and on the other hand, by narrowing the width of said on pulse to the switching means, when said input voltage is high. CONSTITUTION:When a diode bridge 11 rectifies an input voltage, the rectified voltage is intermittently supplied to a transformer T by a transistor 12 and, after voltage transformation, is supplied to the secondary side. In this case, an ON-pulse width controller 13 controls the ON-pulse width of said transistor 12 on the basis of an electric current flowing through the transistor 12, a voltage Vc1 rectified by said diode bridge 11 and an output voltage VIN on the secondary side. Therefore, the width of an ON pulse to the transistor 12 is broadened when an input voltage from an AC input power supply 10 is low, and on the other hand, the width of said ON pulse to the transistor 12 is narrowed when said input voltage is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an input power factor improved switching power supply used as a power supply for office automation (OA) equipment and the like.

(Prior Art) Conventionally, there is an input power factor improving type switching power supply as shown in FIG. 112, which has been used as a power supply for OA equipment and the like.

The switching power supply shown in the figure is one in which a voltage supplied from an alternating current (AC) input power supply 1 is full-wave rectified by a rectifier 2, and then an on-pulse width control section 3 controls the on/off operation of a transistor 4. .

In such a switching power supply, energy is stored in the choke coil L when the transistor 4 is turned on. Then, when the transistor 4 turns off, the voltage VL becomes high, which causes the voltage to pass through the diode D1.
Energy of voltage VDC (direct current) is stored in capacitor CI.

The energy stored in the capacitor Ct is transformed by the transformer T and then supplied to the secondary side load. At this time, the voltage VI which is the +5VDC (direct current) output on the secondary side
Since N is fed back to the on-pulse width control circuit 5, the DC output voltage on the secondary side is stabilized by setting the on-pulse width of the transistor 6 based on this voltage VIN.

Here, the iJi control of the operation of the transistor 4 by the on-pulse width control section 3 includes detection of the output voltage v1 of the rectifier 2 by the rectification voltage detection circuit 3a, detection of the voltage VDC by the VDC voltage detection circuit 3b, and voltage detection by the current detection circuit 3d. V
This is done by detecting the current from R. That is, when these detection results exceed the reference value, the on-pulse width control circuit 3C determines the on-pulse width and frequency of the transistor 4.

Then, when the transistor 4 is switched from on to off, the energy stored in the choke coil L is stored in the capacitor C1 via the diode DI.

However, in such a switching power supply, in order to improve the power factor of the input from the AC input power supply 1, choke coil L1 diode Dl, transistor 4, and on-pulse width control section 3 are required, which not only complicates control but also The cost is high.

(Problems to be Solved by the Invention) As described above, in the conventional switching power supply described above, not only the control is complicated but also the cost is high.

The present invention was made under these circumstances, and an object of the present invention is to provide a switching power supply that can reduce the number of parts and reduce costs.

[Structure of the Invention] (Means for Solving the Problems) The switching power supply of the present invention includes a rectifying means for rectifying an input voltage, and a transforming means for transforming the voltage rectified by the rectifying means and supplying it to the secondary side. and a switching means for intermittent voltage rectified by the rectifying means, and an on-pulse width for controlling the on-pulse width of the switching means based on the current flowing through the switching means, the voltage rectified by the rectifying means, and the output voltage of the secondary side. and control means.

(Function) In the switching power supply of the present invention, when the rectifying means rectifies the input terminal, this rectified voltage is supplied to the transforming means while being interrupted by the switching means, and after being transformed by the transforming means, the voltage is applied to the secondary side. supplied to At this time,
The on-pulse width control means can control the on-pulse width of the switching means based on the current flowing through the switching means, the voltage rectified by the rectifying means, and the output voltage on the secondary side.

Thereby, when the input voltage is low, the on-pulse width to the switching means can be widened, and when the input voltage is high, the on-pulse width to the switching means can be narrowed.

As a result, in the conventional switching power supply shown in FIG. 12, for example, the choke coil L1 diode D1, the transistor 4, and the on-pulse width control section 3 that controls the on-pulse width of the transistor 4 are no longer necessary.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 shows an input power factor improving switching power supply showing an embodiment of the present invention.

As shown in the figure, the switching power supply is equipped with a diode bridge 11 as a rectifier for rectifying the voltage from an AC input power supply 10.

A capacitor CI that stores the voltage rectified by the diode bridge 11 as a charge is connected in parallel to the diode bridge 11.

A resistor R1 and the emitter side of a transistor 12 serving as a switching means for performing a switching operation are connected in series to the capacitor Ct.

Further, a snubber circuit 12A for recovering switching noise caused by the transistor 12 is connected in parallel to the capacitor Ct.

A primary coil TI of a transformer T serving as a voltage transformation means is connected in parallel to the snubber circuit 12A. The transformer T transforms the voltage rectified by the diode bridge 11 and supplies the transformed voltage to the secondary side.

This transistor 1 is connected to the base side of the transistor 12.
An on-pulse width control section 13 as an on-pulse width control means for controlling the on-pulse width of No. 2 is connected. The on-pulse width control section 13 is connected to a point G between the diode bridge 11 and the capacitor CI and 0, a point E between the capacitor CI and the resistor R1, and a point F between the resistor R1 and the emitter of the transistor 12. There is.

A diode D2 is connected in series to the secondary coil T2 of the transformer T. Further, a capacitor C2 is connected in parallel to the secondary coil T2 of the transformer T to smooth the voltage rectified by the diode D2. Output terminals A and B are connected to the capacitor C2.

Similarly, to the secondary coil T3 of the transformer T, a diode D3 is connected in series and a capacitor CB is connected in parallel. Output terminals C and D are connected to the capacitor C3.

FIG. 2 shows details of the on-pulse width control section 13 shown in FIG. 1.

As shown in the figure, the on-pulse width control section 13 includes an analog/digital (A/D) converter 14 that converts an analog signal into a digital signal. The A/D converter 14 has the above secondary side VIN7:+<resistance R2.
, 7t tokabura 15, a resistor R3, and a resistor R4 connected to the internal power supply VCC. The photocoupler 15 is electrically insulated and optically connected.

Further, the A/D converter 14 is connected to the above points G, E, and F, and the digital data converted by the A/D converter 14 is set in the A/D converter 14. 8
A bit register 15A is connected.

A bus 16 for transferring data is connected to the 8-bit register 15A. The bus 16 has a read-only ROM 17 that stores a control program and a writable RAM 18 that temporarily stores data.
A microcomputer 19 is connected which performs control based on the program of M17.

Also connected to the bus 16 is an 8-bit register 20 for on/off control of the k land destar 12. The base side of a transistor 21 is connected to the 8-bit register 20 via a resistor R5. The collector side of the transistor 21 is connected to the internal power supply Vcc and the base side of the transistor 12 via a resistor R6.

Next, the operation of the switching power supply having such a configuration will be explained.

First, in explaining the operation of the switching power supply of this embodiment, the relationship between AC input voltage and current consumption will be explained using FIGS. 3 and 4.

FIG. 3 shows the case of a conventional switching power supply. In FIG. The circuit has a circuit configuration that controls the width of the on-pulse applied to the circuit. It is also assumed that the capacitance of the capacitor CI is sufficiently large, and the voltage rectified by the diode bridge 11 is sufficiently smoothed.

In a switching power supply with such a configuration, Fig. 3 (C)
As shown in Figure 3(a) and (b), the current if flows where the absolute value of the input voltage is large, so when these switching power supplies are used a lot, the hc input voltage becomes sln as shown by the broken lines in Figure 3(a)(b). Distortion increases in areas where the absolute value of the waveform is large. Therefore, the sine waveform becomes flat, resulting in an overall waveform close to a trapezoid.

On the other hand, as shown in Figure 4(c), the ACC input improvement power supply constantly consumes power from when the AC input voltage is low to when the AC input voltage is high.
Distortion occurs as shown by broken lines in Figures (a) and (b). However, if many ACC input improvement power sources are used, the broken line portions will not be synchronized, resulting in an s1n waveform with very little distortion of the AC input voltage as a whole, making it possible to improve the AC input.

Based on these considerations, the operation of this embodiment will be explained using the jIJ diagram and FIG. 5.

First, when a voltage having the waveform shown in FIG. 4(a) is applied from the AC input power source 10, this applied voltage is full-wave rectified by the diode bridge 11 as shown in FIG. 4(b). . However, in this case, the capacitor CI-(+,
In other words, there is no CI.

At this time, the on-pulse width control section 13 controls the voltage Vc at point G.
Detect l. Further, the on-pulse width control unit 13 detects the voltage VIN in order to know whether the voltage at the secondary side DC output terminal A is +5V or more. Furthermore, the on-pulse width control section 1
3 detects the current flowing through the resistor R1 by detecting the voltage at point F.

Then, the on-pulse width of the transistor 12 is determined based on the values of these voltages.

That is, the on-pulse width control 113 corrects the current flowing through the transistor 12 to the actually predicted value when the on-pulse width is predicted, and performs overcurrent protection (improves accuracy) on the current value.

FIG. 4(C) shows that when the on-pulse width controller 13 controls the transistor 1 when the current value becomes constant,
2 shows a current waveform when controlled to turn off 2. In addition, the broken line portions shown in (a) and (b) of the same figure indicate distortions due to power consumption, but these distortions are caused by distortion of the peak portion of the waveform as shown in Fig. 3. It does not change the shape, but causes slight distortion throughout.

The waveform of FIG. 4(c) will be explained in more detail as shown in FIG. 5.

As can be seen from the figure, when the waveform after full-wave rectification is low, the on-pulse width is large. That is, the on-pulse width of the transistor 12 is, for example, tl.

t10. t11. It is enlarged as shown in t 19...

On the other hand, when the waveform after full-wave rectification is low, the current width is small. That is, the on-pulse width of the transistor 12 is
For example, t8, tl5... are made very small.

In this way, the on-pulse width of the transistor 12 is controlled, and the on-off period of the transistor 12 is controlled to be constant, so that the current value is kept at a certain constant value as shown in the figure! Turn it off when it reaches. In other words, this indicates that the amount of energy supplied to the primary side of the transformer T is I in a certain period of time. This is the power consumption on the secondary side (in this case, DC output terminal A
- B current consumption) is constant.

When the current consumption increases, the on-pulse width control section 13
By detecting the VIN that has decreased, the on-pulse width of the transistor 12 is increased, so that the current value I increases.

That is, considering the case of t4, the current waveform becomes a waveform corresponding to aS which is larger than I, and the on time is also longer, not t4 but T4. As a result, the supply of energy to the negative side is increased, and the voltage between the DC output terminals A-8 on the secondary side is stabilized.

Conversely, when VIN is high, the on-pulse width of transistor 12 becomes narrow. That is, considering the case of t8, the current waveform becomes the waveform shown by the broken line smaller than I, and the on time is also shortened to T8 instead of t8. This results in
- The supply of energy to the secondary side is reduced and the DC of the secondary side
The voltage between output terminals A-8 becomes stable.

Such control of the on-pulse width of the transistor 12 is as follows:
This is done as follows.

That is, voltage VIN is input to A/D converter 14 via resistor R2, photocoupler 15, and resistor R3.

Next, the microcomputer 19 reads the digital data of the voltage VIN set in the 8-bit register 15A via the bus 16.

At this time, voltages VIN, Vcl, and F are simultaneously A/
Since the voltage is input to the D converter 14, the microcomputer 19 specifies to the selector S which voltage is to be A/D converted.

The microcomputer 19 then stores ti in the ROM 17.
Based on the 1gI program, the voltages V IN, V c
The on-pulse width of the transistor 12 is calculated based on the information of l.

Here, the rising current value t in FIG. 5 is stored in the ROM 17.
The current values are stored as 20 at l, 21 at t2, 22 at t3, and so on. Also ROM17
Also stored is data on the time required to increase the current to the current value I.

In order to turn on the transistor 12, the microcomputer 19 sets the 8-bit register 20 to 00° via the bus 16. As a result, 8
The output from the bit register 20 becomes low level, and this low level output turns off the transistor 21 via the resistor R5. At this time, internal power supply Vcc
is applied to the database of the transistor 12 via the resistor R6, thereby turning the transistor 12 on.

Conversely, in order to turn off the transistor 12, the microcomputer 19 sets "80" in the 8-bit register 20 via the bus 16. This results in
The output from the 8-bit register 20 becomes high level,
This high level output turns on the transistor 21 via the resistor R5. At this time, internal power supply vC
The voltage from c is not applied to the database of the transistor 12 through the resistor Re, so that the transistor 12 is turned off.

Note that the capacitor CI shown in FIG. 1 is connected to the broken line x in FIG.
, is used to prevent y from falling to OV, but it does not need to be used if it is not necessary.

However, if the capacitor CI is used, control becomes easier. That is, in FIG. 5, tl.

t2, t9, t10. t II
, t 12 . . . when the AC voltage is low, it is possible to compensate for the difficulty in supplying energy. Further, by using this capacitor C1, it is possible to reduce the capacitance of the secondary side capacitors C2 and C3.

Next, the control characteristics of this embodiment will be explained.

First, as shown in Fig. 6, when the input voltage of the boost converter is e1 and the output voltage is EO (ignoring the voltage drop of diode D), (i) the on-period of switch S (0≦t≦ T on), △i=e/L-Ton - (1) (n) In the off period of switch S (Ton≦t≦T), △i - (EO-e) / L-Tart -- (2)
becomes. Therefore, eT-EO-Torr (
3) Tol'r -e / EO life T
---(4) In addition, T-Ton+Tof'f --・----
(5) Therefore, input voltage e and switching period T or
The relationship between r and Ton is calculated from the above equation (4) to Fig. 7 (a
)(b) holds true.

Next, using FIG. 8, the relationship between the peak value Ip and the average value of the input current i is determined.

Ip-11+ΔI (6) Therefore, from the above formulas (1), (4), and (5), Ip-1
1+e/L (T-e/Eft φT)・・・・・・(
7) Ip-If +T/L・1/EOe (EO
-e) ...... (8) From the same figure, the average value IAV of input current i is IAV = 1
/2 (I l + Ip) -----
--(9) From the above equation (8) If = Ip -T/L #1/EO-e (EO-e
)・・・・・・(10) Therefore, IAV-1p -T/ 2L -1/EOe (EO-
e) −(11) Actually, the input voltage e
changes with the sln wave, IAV changes according to the change in e. Now, if we assume that there are 2N switching pulses (period T) within one cycle of the input commercial power supply (50/80H2), there are N switching pulses within a half cycle, and the switching current within a half cycle is The phase of the angle θ (0≦θ≦π)
Expressed as: i = Ip - (T/2L EO) Es s
ln θ (EO−Es sin θ)
−・−・−(12) The average input power P of a half cycle (logs or 8.3g5) of a commercial power supply is expressed as P −1/πei ・idθ − ------(13
) However, el-Eg+sln θ −−−−・−
(14) i-1p-(T/2LED)Els
In θ(EO−Ew sln θ>
・−・−・ (15) i −Ip −(TEm /
2L) sln θ+ (T/ 2LEO) Em
2s1n 2θ− (16). Therefore, ei ・1−Ea Ipslnθ−Es (TEw
/2L) sin 2 θ+T/2LEOEI −
81n3θ...---(17) Here, AI = EII I p , A2 -- (T/
2L) Es 2A3-TEm3/2LEO...
・If we set (18), ei ' i −At sln θ +A2
sin 2 θ+A3 sln 3 θ
−−−−−(19), and by substituting this equation (19) into the above equation (14), we get P−(AI/π)11+(A2/π)I2+(A3/
π) 13 ・・・・・・(20)・・・・・・
(21) Therefore, 11=[-cosθ]. -2・・・・・・(22)I2
-[θ/2-1/45ln2θ]n-π12...
・(23) 13- [-17a cosθ(sin 2θ+2)]
.

-413... (24) Therefore, P-(2/π) E+g Ip -TEi 214L,
+(2T/3π)EII31LEO・・・(25
) Here, PK −T Es 2/ L (1/4−2/3π・E
m/EO) ...... (26
)) i:6 -'l/rr ・E---(27) Then, I p-P/Ec +Pk/Ec ・・
(28) And FIG. 9 shows the relationship of equation (28).

Therefore, after the output P is applied, by controlling the peak current xp of the boost converter, the output voltage EO
can be kept constant.

Note that when the relationship between the input terminal Ets/J2 and Ip is calculated using equation (28) in the case of L-1sH, T=10 μs, and P-100v, the result is as shown in FIG.

This is expressed graphically in Figure 11 (however, the output voltage E
The display is for two cases of O-160 and 200V). As can be seen from the same figure, E t
It can be seen that s/J''T and Ip are expressed in a substantially linear relationship.

In this way, in this embodiment, when the diode bridge 11 rectifies the input terminal, this rectified voltage is supplied to the transformer T while being interrupted by the transistor 12.
After being transformed by this transformer T, it is supplied to the secondary side. At this time, the on-pulse width control unit 13 can control the on-pulse width of the transistor 12 based on the current flowing through the transistor 12, the voltage Vcl rectified by the diode bridge 11, and the output voltage VIN on the secondary side.

As a result, when the input voltage from the AC input power source 10 is low, the on-pulse width to the transistor 12 can be widened, and when the input voltage is high, the on-pulse width to the transistor 12 can be narrowed.

Furthermore, although the switching power supply of this embodiment is an input power factor correcting type, it also includes a choke coil L1 diode DI, a transistor 4, and a transistor 4 shown in FIG.
Since the on-pulse width control unit 3 that controls the on-pulse width of the on-pulse width is not required, cost reduction and control can be simplified.

[Effects of the Invention] As explained above, according to the switching power supply of the present invention, it is possible to reduce the number of parts and reduce costs.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a switching power supply showing an embodiment of the present invention, Fig. 2 is a block diagram showing details of the on-pulse control section of Fig. 1, and Fig. 3 is a circuit diagram of a switching power supply of non-input power factor correction type. Figure 4 is a diagram showing voltage or current waveforms in an input power factor correcting switching power supply; Figure 5 is a diagram showing on-pulse applied to a transistor by the on-pulse control section in Figure 1; Figure 6 is a circuit diagram that simply shows a boost converter to explain the control characteristics of the switching power supply shown in Figure 1, and Figure 7 (a) (
b) is a diagram showing the relationship between the input voltage and the on/off period in the boost converter circuit of FIG. 6, and FIG. 8 is a diagram showing the current waveform in the boost converter circuit of FIG. 6;
9 to 11 are diagrams showing the relationship between input power and peak current in the boost converter circuit of FIG.
FIG. 2 is a circuit diagram showing a conventional switching power supply with improved input power factor. 10... AC input power supply, 11... Diode bridge, 12... Transistor, 13... On-pulse width control section, 14...^/D converter, 15... Photo coupler, 16...・Bus, 17...ROM, 18...
RAM, 19...Microcomputer, 20...
8 bit register. Applicant Toshiba Corporation Patent Attorney Satoshi Suyama - IN Fig. 2 Fig. 3 Fig. 4 Fig. 7 Fig. 8 Fig. 9 Fig. 11 Procedural amendment written form) January 18, 1999 1. Display of the case Japanese Patent Application No. 63-234041 No. 2, Name of the invention Switching power supply 3, Person making the amendment Relationship to the case Patent applicant 72 Horiyo-cho, Saiwai-ku, Yozaki City, Kanagawa Prefecture (307) Toshiba Corporation 4 , Agent Address: 2-1 Kanda Tamachi, Chiyoda-ku, Tokyo 101 December 20, 1983 (Shipping date) Figure 7

Claims (1)

[Claims] (1) a rectifying means for rectifying the input voltage; a transforming means for transforming the voltage rectified by the rectifying means and supplying it to the secondary side; and a switching means for intermittent the voltage rectified by the rectifying means; A switching power supply comprising: on-pulse width control means for controlling the on-pulse width of the switching means based on the current flowing through the switching means, the voltage rectified by the rectifying means, and the output voltage on the secondary side.