JPH04251522A - Electric power averaging circuit - Google Patents

Abstract

PURPOSE:To increase a strength of a power supply against an overload. CONSTITUTION:When driving a load 4 from a dc supply 1 as shown by the Figure 1, a capacitor auxiliary to overload C1 is preliminarily charged by the dc supply and when an overload occurs, the capacitor C1 is inserted between the dc supply 1 and the load by a changeover switch 6 and the load 4 is supplied with power by the discharging of the capacitor C1. By this method, the power supply voltage as seen from the load is about twice as large as the dc supply 1 in the event of an overload. Since a capacitor C2 is inserted in series with the dc supply in the event of an overload, an electric charge of the capacitor 2 is entirely utilized effectively and thereby an overload strength of the power supply is increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply circuit that can handle even large short-term overloads.

0002

[Prior Art] Some loads require a large amount of power at startup but only require a small amount of power in a steady state, or are used by applying peak power intermittently. Although the temporally average power supplied to the load is small, a large amount of power is required in the short term. If the power supplied to such a load exceeds the load fluctuation tolerance of the power supply even in the short term, the capacity of the power supply must be larger than the average power requirement of the load, which is uneconomical.

Conventionally, in order to increase the resistance of a DC power supply to load fluctuations, a method has been used in which a large capacitor is connected in parallel with the load, but in this method the capacitor is charged up to the power supply output voltage. When the load power is large and the voltage across the load drops slightly below the power supply voltage, only the charge corresponding to the charging voltage difference from the power supply is added to the load, and the full charge of the capacitor cannot be utilized. The effect of increasing the power supply's resistance to overload is not very large.

0004

[Problems to be Solved by the Invention] The present invention attempts to significantly improve the overload resistance of the power supply by making it possible to use all of the charge in the capacitor inserted in the power supply circuit to supplement power supply in the event of an overload. It is something.

[0005]

[Means for solving the problem] A DC power supply and an overload auxiliary capacitor are connected in parallel with the load during normal load or when the load is stopped, and when the load is overloaded, the above capacitor is connected between the DC power supply and the load. A power averaging circuit is constructed by connecting the power source and the connection switching means connected in series with the load between the power source and the load.

[0006]

[Operation] Since the overload auxiliary capacitor is normally connected in parallel with the load, it is charged to the voltage across the load, that is, close to the output voltage of the DC power supply. At peak load, the above capacitor is inserted between the power supply and the load and the three are connected in series, so immediately after the connection is switched, the output voltage of the series connection of the power supply and the above capacitor is equal to the power supply voltage and the capacitor charge. This is the sum of the voltage and the power supply voltage, which is approximately twice the power supply voltage. Since the capacitor discharges through the load until the charging voltage becomes 0, all of the charged charge can be used to assist in overloading.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit according to an embodiment of the present invention. In the figure, 1 is a DC power source, which may be a rectifier circuit that rectifies commercial AC, or a battery. A + terminal of DC power supply 1 is connected to output terminal 3 through diode D1, switching regulator 2, and resistor R1. The - terminal of the DC power supply 1 is connected to the output terminal 3' and also to ground. 4 is the load. The output voltage of the DC power supply 1 is approximately 25V, and normally this power supply supplies power to the load 4 through a diode D2 in parallel with the switching regulator 2. C2 is a smoothing capacitor which, together with a resistor R1, smoothes the current that is turned on and off by the switching regulator 2 during overload, and supplies the smoothed current to the load. Voltage dividing resistors R2 and R3 for detecting inter-terminal voltage are connected in parallel with the output terminals 3 and 3', and the voltage at the voltage dividing point is compared with a reference voltage by a comparator 5, and the output of the comparator 5 determines switching. The regulator 2 is turned on and off so that the voltage between the terminals 3 and 3' is adjusted to 23.5V. However, under normal conditions, the voltage across the load is about 24V, which is higher than the reference voltage of 23.5V, and the switching regulator 2 is in a continuous off state.

In the figure, C1 is an overload auxiliary capacitor which is a feature of the present invention, and its + terminal is connected to the + side output line of the power supply 1 between the diode D1 and the regulator 2, and its - terminal is connected to the common switch 6. connected to the terminal. One contact b of the changeover switch 6 is connected to the negative output line of the power source 1, that is, the ground, and the other contact a is connected between the positive terminal of the power source 1 and the diode D1. The changeover switch 6 is normally switched to the contact b side, and the capacitor C1
is charged to the output voltage of power supply 1 of 25V. Reference numeral 7 denotes a control device for operating the switch 6, which switches the switch 6 to the contact a side when the load 4 becomes overloaded depending on the operating state of the load 4. Then, the negative pole of capacitor C1 is the power supply 1.
The + terminal of the switching regulator 2 is connected to the + terminal of the switching regulator 2 . When overload occurs, output terminals 3 and 3'
Since the voltage between them drops below 23.5V, switching regulator 2 is turned on, and when looking at power supply 1 from load 4, the voltage that the load receives is the sum of the 25V output of power supply 1 and the charging voltage of capacitor C1, 25V. The voltage becomes approximately 50V, and the capacitor C2 is charged by the discharge current of the capacitor C1, and current is also supplied to the load 4, and the + terminal voltage of the comparator 5 exceeds the standard 23.5V, so
The switching regulator 2 is immediately turned off, and thereafter the switching regulator 2 repeatedly turns on and off, discharging the charge in the capacitor C1 to the load 4.

When the changeover switch 6 is switched to the contact a side, a closed circuit is created that connects the contact a, the diode D1, and the capacitor C1, and the charge in the capacitor C1 attempts to discharge counterclockwise through this closed circuit. This discharge is blocked by diode D1. Diode D2 is connected in parallel with the series connection of diode D1, switching regulator 2, and resistor R1, but the output of the switching regulator is controlled so that the voltage on the load side does not become higher than that on the power supply 1 side of D2. is always conductive and current flows from the power source 1 to the load. Furthermore, when the voltage at the terminal 3 falls below the specified value, the switching regulator 2 is turned on again. In this way, while the changeover switch 6 is switched to the contact a side, power is supplied to the load from both the DC power supply 1 and the capacitor C1.

FIG. 2 shows a time chart of the above-mentioned operation. In this figure, a indicates the voltage at terminal 3 in Fig. 1, and b indicates x on the input side (power supply 1 side) of switching regulator 2.
The voltage at the point c is shown, and c shows whether the switching regulator 2 is turned on or off. In the figure, load 4 is a normal load until point t,
From point t, the load changes to excessive load. At point t, the changeover switch 6 switches from contact b to a. The voltage at the terminal 3 is approximately 24V up to t, and if an overload occurs, it will drop as shown by the dotted line. When the voltage drops below 23.5V, switching regulator 2 turns on, so power supply 1
The voltage obtained by adding the charging voltage of capacitor C1 to the voltage is applied to the load and capacitor C2, and the voltage at point The capacitor C2 is discharged, and the x-point voltage drops. Accordingly, the voltage at terminal 3 rises with a certain time constant determined by the sizes of resistor R1, capacitor C1, and load 4, and when it exceeds the reference value, switching regulator 2 is turned off and the voltage drop at point x stops. ,
The voltage at terminal 3 decreases, regulator 2 is turned on again, the voltage at point x decreases, and the voltage at terminal 3 increases. In this way, the switching regulator 2 is repeatedly turned on and off, while the capacitor C1 is intermittently discharged to supply power to the load. When the load returns to normal load, switch 6
is switched to the contact b side, and the capacitor C1 is charged up to the voltage of the power supply 1.

The control method for the changeover switch 6 is arbitrary; for example, if the manner in which the load fluctuates is known in advance, the changeover switch 6 may be controlled in accordance with time according to the time schedule of the load. Alternatively, the current flowing through the load is detected and the changeover switch 6 is automatically activated when the current exceeds the standard value.
may be switched from contact b to contact a.

[0012] When the capacity of the DC power supply is 25V12A, the load is intermittently energized for 0.5 ms, and the current during instantaneous energization is 24.5A, a sufficient effect can be obtained by using 4700 μF as the capacitance of C1. was there.

An application example of the above-mentioned device will be described. This application example concerns power supply to a thermal head of a printer using a thermal line head. The thermal line head divides all dot rows into several blocks and prints one dot row by energizing each block several times. The load is defined as a normal load when up to half of the dots in one block are energized, and an overload when more than half of the dots are energized. Normal load and overload can be determined from the printed pattern.
Since it can be determined whether the block to be energized next to the thermal head is in a normal load state or an overload state, the selector switch shown in FIG. 1 is switched to the contact a side before energizing that block. And the energization time is uniformly 0.5ms regardless of the weight or weight of the load.
Therefore, the current when all dots in one block are energized is 24.5A. Specifically, as shown in Figure 3, there are 2 line dot rows.
It is divided into blocks, and 4 ms is allotted for printing one dot row. In other words, each line is printed at a speed of 4ms. And during this 4ms, at the beginning, 0.5
Power is applied for ms×2=1 ms, and the remaining 3 ms is used for inputting the next print data to the thermal head. Recovery of the charging voltage of capacitor C1 in case of overload mainly takes place during this 3 ms period. When all one dot row is energized, the amount of energization is 24.5A x 1ms, which is approximately 0
．． 025 coulombs. Capacitor C1 is 4700μ
F, so a discharge of 0.025 coulombs will result in approximately 5.3V.
The voltage drops. Power supply 1 has a capacity of 12A, so C1
It takes about 2 ms to raise the charging voltage of 5.3 V. On the other hand, as mentioned above, one week of printing is 4
ms and 3 ms can be taken as a recovery period, so the circuit in the actual example has sufficient margin in this case.

[0014]

[Effects of the Invention] According to the present invention, the overload auxiliary capacitor is normally connected in parallel with the power supply and charged to the power supply voltage, and when overloaded, it is connected in series with the power supply and discharged to the load. In principle, the entire charge can be supplied to the load (in reality, the overload condition is usually resolved before the entire charge is discharged), and the short-time load is much larger than the capacity of the power supply. It will be possible to supply the required power to.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a time chart of operations in the above embodiment of the present invention.

FIG. 3 is a time chart showing a power supply schedule for a thermal printer when the above embodiment is used as a power source for the thermal printer.

[Explanation of symbols] 1 DC power supply 2 Switching regulator 3 Output terminal 3’ Output terminal 4 Load 5 Comparator 6 Selector switch 7 Control device C1 Overload auxiliary capacitor C2 Smoothing capacitor

Claims (3)

[Claims] [Claim 1] A DC power supply, an overload auxiliary capacitor,
Switching means connects the capacitor in parallel with the DC power supply during normal load or load stoppage, and connects the capacitor in series with the load between the DC power supply and the load during overload. A power averaging circuit characterized by: 2. The switching means is activated when the printing density is equal to or higher than a predetermined value, and the capacitor is connected between the DC power source and the load so as to be connected in series with the load. Power averaging circuit for thermal printers. 3. The apparatus according to claim 2, further comprising a means for detecting a printed information portion having a print density equal to or higher than a predetermined value, and the switching means is operated in response to this detection signal.
The described power averaging circuit for thermal printers.