JPS6036605B2 - switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a switching regulator that outputs a voltage stabilized DC output from a DC input.

A switching regulator is generally configured as shown in FIGS. 1A and 1B, and includes a switching element 2 that periodically turns on and off an unstable DC power source 1, and a rectifying element 3.
, an inductance device consisting of a choke coil 4a (in the case of FIG. 1A) or a transformer 4b (in the case of FIG. 1B), and a rectifying and smoothing circuit constituted by a capacitor 5, and detecting the voltage applied to the load 6, It consists of a pulse modulation circuit 7 that converts the pulse into a pulse having a predetermined duty. The switching element 2 repeats ON and OFF operations according to the output of the pulse modulation circuit 7, that is, according to the duty of the output pulse (ratio of ON time to pulse period). In this way, the duty is changed according to fluctuations in the output voltage to stabilize the DC output. By the way, the output voltage P of this switching regulator is determined by the following equation.

P = droplet 2T...m However, efficiency Ei: DC input voltage D: output duty T: period L: inductance of the inductance device It is desirable that the control range of this output P be wide, but 4. When controlling the output power (ie, when the load is light), the following problems arise.

In other words, if Ei and T are constant, the output voltage P can be reduced by increasing L or decreasing D. However, a large L inductance device has a large weight and volume, and is also expensive, so it is not practical.
Economic efficiency is low. On the other hand, in order to reduce D, it is necessary to shorten the ON time of the switching element 2 such as a transistor. 2 to O
It is difficult to operate N. In other words, when controlling the load voltage in the duty range near 0% (for example, 0 to 20%), a large load voltage change occurs in response to a subtle change in the load current, and it is difficult to follow the large load voltage change and to control the load voltage in a non-field manner. A sophisticated in-pulse modulation circuit is required to provide short output pulses in the pulse. Furthermore, the minimum ON time of the semiconductor switching element 2 such as a transistor is limited due to the essential characteristics of the element such as the charge accumulation effect, and is driven by short to medium pulses using a high performance pulse modulation circuit. However, control with a D value of about 20% or less becomes extremely unstable due to time delays caused by the rise and fall of the pulse signal. Note that the maximum load range can be expanded relatively easily by, for example, making the above-mentioned L small.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching regulator that can reduce the maximum value of the duty variable range with a simple configuration and further reduce the minimum value of the output voltage control range. do.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

2A and 2B are block circuit diagrams showing the first embodiment, and parts equivalent to those in FIGS. 1A and 1B are given the same numbers.

A switching circuit 20 is connected to the unstabilized DC power supply 1, in which two switching elements 21 and 22, each of which is independently controlled to open and close (ON, OFF), are connected in series. The output of this switching circuit 20 is a rectifying and smoothing circuit constituted by a rectifying element 3, an inductance device consisting of a choke coil 4a (in the case of FIG. 2A) or a transformer 4b (in the case of FIG. 2B), and a capacitor 5. smoothed by This smoothed output is given to the load 6.
The pulse modulation circuit 7 detects the smoothed output voltage and outputs a pulse having a predetermined duty according to this output voltage. This output pulse controls ON/OFF of the switching element 21 of the switching circuit 20. Further, the output pulse of the pulse modulation circuit 7 is turned into a pulse with a predetermined phase shift by the phase shifter 8, and the switching element 22 is turned on.
OFF control. In FIG. 3, ``A'' indicates the ON/OFF operation of the switching element 21, and ``A'' indicates the switching element 22.
C is a time chart showing the ON and OFF operations of the switching circuit 20 in which these two switching elements 21 and 22 are connected in series.

In the case of the switching regulator having the configuration shown in FIG. 2, ``A'' in FIG. 3 represents the output pulse of the pulse modulation circuit 7, and ``A'' represents the output pulse of the phase shifter 8, respectively. The period of the output pulse I of the modulation circuit 7 during the pulse is T, and the period during the pulse is t.
, when the phase difference of the phase shifter 8 is 0, the switching circuit 20
The ON time 7 of is t-0, and the cycle of ON and OFF operations is T. Now the duty D of the output pulse current (=t'
The variable range of T) is set to 20 to 80%, and the phase difference 8 between the pulse and the mouth is set to 20% of the period T. When t during the output pulses is 20% of the period T which is the minimum value, the ON time T of the switching circuit 20 is 0% of the period T, that is, the switching circuit 20 is in a completely non-conducting state. Also, when t is the maximum value (80% of T) during the output pulse I and the mouth pulse, the ON time is 7.
is 60% of the period T. Therefore, the variable range of the duty (units/T) of the switching circuit 20 is 0% to 60%.
becomes. That is, during the output pulse of the pulse modulation circuit 7
By making the minimum value tmin and the phase difference 8 equal, the duty of the switching circuit 20 can be varied down to a minimum of 0%. FIG. 4 is a block circuit diagram showing the second embodiment.

In this figure, the oscillator 10 outputs a pulse having a constant period and pulse length, and the switching element 21 is controlled to turn on and off by this power pulse (corresponding to pulse waveform A in FIG. 3). The variable phase shifter 9 shifts the phase of the oscillator 10 according to the output voltage applied to the load 6, and turns on the switching element 22 using the phase-shifted pulse.
, OFF control. This pulse corresponds to the mouth in Figure 3,
The phase difference a changes depending on the detected load voltage. Therefore, the ON operation of the switching circuit 20 is as follows.
Determined by the rise of pulse slow and the fall of pulse swing,
The operating waveform is as shown in FIG. 3C. Further, when the phase difference of 0 becomes equal to the pulses of the first and second pulses, the duty of the switching circuit 20 becomes 0%. Note that the maximum value in the pulses is 50% of T, and if the phase difference is changed to 50% of T at this time, the duty of the switching circuit 20 becomes 0%. The other configurations and operations are the same as those of the first embodiment, so their explanation will be omitted. FIG. 5 and FIGS. 6A and 6B show a third embodiment.

In this embodiment, two in-pulse modulation circuits 71 and 72 with equal output pulse periods and different in-pulse variable rates are used,
The output pulse 2 of one of the pulse modulation circuits 71 is directly connected to the switching element 21, and the other pulse modulation circuit 72
The output pulses HO control other switching elements 22 to turn on and off, respectively, via a phase shifter 8. The variable range of the duty of these output pulses 2 and 5 is 20%~
100%, 20% to 80%, and the phase difference is 20% of the period T.
%. The duty of pulse 2 and e are both 20% (
(minimum value), the switching circuit 20 is completely OFF as shown in FIG. 6A, and the duty is 0%. Next, when the duty of pulses 2 and 5 is the maximum value of 100% and 80%, respectively, the duty of the switching circuit 20 is 8 as shown in FIG. 6B.
It becomes 0%. Therefore, the duty variable range of the switching circuit 20 is 0% to 80%. 7 and 8 show a fourth embodiment, in which both the ON time and the phase difference between the ON times of the switching elements 21 and 22 of the switching circuit 20 are changed according to the output voltage applied to the load 6. There is.

FIG. 7 shows a concrete block circuit diagram, and FIG. 8 shows signal waveforms of each signal transmission path T to W. 7 and 8, the comparator 11 compares the output voltage applied to the load 6 and the reference voltage from the reference voltage generation circuit 12. In FIG. This compared output is the pulse modulation circuit 1
3, a variable phase shifter 14, and a pulse modulation circuit 15 composed of a monostable multi-layer. The oscillator 16 generates a pulse with a predetermined period T, and this pulse is differentiated and rectified to become a trigger pulse, which is sent to the pulse modulation circuit 13 and the variable phase shifter 14, respectively. The in-pulse modulation circuit 13 generates a pulse in response to a trigger pulse, and the in-pulse t of this pulse in changes in accordance with the output from the comparator 11. From this pulse river, switching element 21 power N, OFF
controlled. Further, the variable phase shifter 14 generates a pulse null in response to the trigger pulse pulse, and changes in accordance with the comparison output from the comparator 11 during the pulse null. The pulse null is differentiated and rectified to become a trigger pulse, and the pulse modulation circuit 15 generates a pulse in response to this trigger pulse. The output pulse of this pulse modulation circuit 15 changes in pulse t according to the comparison output from the comparator 11, and this pulse modulation circuit 1
The output pulse of 3 is set equal to the pulse of 3.
In other words, the output pulse is the same as the phase a.
This pulse is shifted by a certain amount, and this pulse controls the ON/OFF state of the switching element 22. Therefore, the ON/OFF operation of the switching circuit 20 is expressed as a pulse wave, which is an overlapping portion of pulse-ri and pulse-wo. In the case of this fourth embodiment, if the variable range in the pulses of Pulse-ri and Pulse-wo is, for example, 20% to 80%, the variable range of the ON duty of the switching circuit 20 is 0 to 80%.
Up to 0%. As is clear from the above explanation, by using the switching circuit 20 in which two switching elements 21 and 22 are connected in series, the switching circuit 2
The duty of 0 can be changed from a minimum of 0%.

Furthermore, commercially available transistors and the like can be used as the switching elements 21 and 22, and are easily available. Furthermore, since an inductance device with a large L value is not required, the structure can be made small and inexpensive. Note that the present invention is not limited to the above-mentioned embodiments, and for example, the number of switching elements forming the switching circuit 20 may be any number from 2 to 2. Furthermore, the configuration of the first embodiment shown in FIG. 2B is also possible for the second, third, and fourth embodiments. Further, although an NPN transistor is illustrated as a switching element, a series-connected switching circuit such as a PNP transistor, a thyristor, a UJT, or a combination thereof may also be used.

[Brief explanation of the drawing]

Figures 1A and B are block circuit diagrams showing conventional examples, Figure 2A
, B is a block circuit diagram showing the first embodiment of the present invention, FIG. 3 is a time chart for explaining the embodiment, FIG. 4 is a block circuit diagram showing the second embodiment, and FIG. is a block circuit diagram showing the third embodiment, and FIGS. 6A and 6B are block circuit diagrams showing the third embodiment.
7 is a concrete block circuit diagram showing the fourth embodiment, and FIG. 8 is a time chart for explaining the fourth embodiment.
2 is a time chart for explaining an embodiment of the present invention. 1...DC electric wire, 2, 21, 22...
Switching element, 20... Switching circuit, 3... Rectifying element, 4... Choke coil, 4b... Transformer, 5... Smoothing capacitor, 6...Load, 7,71,72...
... Pulse modulation circuit, 8... Phase shifter, 9, 1
6...Oscillator, 10...Variable phase shifter, 11
...Comparator, 12...Reference voltage generation circuit,
13, 15... Pulse modulation circuit, 14...
・Variable phase shifter. Many diagrams, many 2 diagrams, many 3 diagrams, many 9 box diagrams, many diagrams, many diagrams, many 8 diagrams.

Claims (1)

[Claims] 1. A switching circuit in which at least two switching elements are connected in series, each of which is controlled to open and close independently, a drive circuit that periodically turns ON and OFF in a different phase from each of these switching elements, and a smoothing circuit that smoothes the output of the switching circuit. and detects the output voltage of the smoothing circuit, and controls the overlapping time of conduction times of the plurality of switching elements based on the detected output voltage to keep the output of the smoothing circuit constant. Switching regulator.