JPH01186135A - Power source circuit with backup function - Google Patents

Abstract

PURPOSE:To obtain a backup compensating function by a capacitor of a less electrostatic capacity than a conventional one by transmitting charge obtained from a power source to charge storage means by charge supply means having no intrinsic threshold level of an element at a forward voltage drop. CONSTITUTION:A series circuit of a resistor 11 and a capacitor 12 is connected to the anode of a diode 13. Thus, the capacitor 12 is completely charged to a stabilized power source voltage V2. When a stabilized power source 10 is normally operated, a load 15 is energized by a load current I13 from the diode 13 at a load voltage V3. Assume now that the power source 10 is defective so that the voltage V2 is dropped to zero. Then, the current I13 does not flow. Insteads, a backup current I14 from the capacitor 12 charged up to an output voltage corresponding to the output from the power source 10 flows through a diode 14 to the load 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in a power supply circuit with a backup function.

(Prior art) -The TTL control Fuji 12 circuit semiconductor integrated circuit requires a stable low voltage (approximately 5V) power supply.In addition, it is necessary to use a stable low voltage (approximately 5V) power supply. In order to prevent the function of the control logic circuit from being damaged due to a failure or the like, this type of power supply device is often equipped with a large capacity capacitor or a rechargeable battery for power backup.

A conventional power supply circuit with a backup function has a circuit configuration as shown in FIG. 3, for example. In the figure, 10 indicates a regulated power supply with a voltage regulator, an unregulated D
The C input voltage (1) is obtained from an AC4 current circuit (not shown). The power supply 10 outputs a stabilized DC voltage 2.

A load (not shown) such as a RAM board or a TTL logic board is connected to the output circuit of the power supply 10 via a forward biased diode 13. In this case, the load voltage
3 is the voltage drop of the forward bias diode 13 as VFlB
Then, V3=V2-VFlB.

A series circuit of a resistor 11 and a capacitor 12 is connected in parallel to the load circuit of voltage 3. A diode 14 is connected in parallel to the resistor 11, and when the power supply 10 is operating normally, the diode 14 is reverse biased. The resistance value of the resistor 11 is usually several ohms to several tens of ohms.

When the power supply 10 is shut down and current flows from the capacitor 12 to the load, the diode 14 acts to lower the parallel combined resistance value with the resistor 11. Further, the diode 13 prevents the charge in the capacitor 12 from escaping to the power supply 10 side.

Now, diodes 13 and 14 are Schottky barrier diodes, and their forward voltage drop VF13. VFI4
Suppose that both are 0.4V. In addition, the allowable voltage range of load voltage ■3 is 5■±5% (4,75V to 5.25V)
Assume that the reference value of the voltage (3) is 5.2 (2). In this case, the output voltage v2 from the stabilized power supply 10 is 5.6■
(=5.2V+0.4V=VF13).

(Problem to be solved by the invention) FIG. 4 shows the output voltage characteristics of the power supply circuit of FIG. 3.

When the power supply IO fails and the voltage ■2 becomes zero at time t1,
Correspondingly, voltage ■3 is 5.2V (capacitor 12
charge-up voltage) to 4.8V (5,2V-0
, 4V=VF14). Next, capacitor 1
2 is mainly discharged to the load side via the diode 14. Along with this discharge, the load voltage (3) gradually decreases from 4.8 (4.8) toward the lower limit of the load voltage of 4.75 V (t1 to t2 in FIG. 4).

Here, the capacitance of the capacitor 12 is C, and the load current is 1
Let the allowable fluctuation range of load voltage ■3 be Δ■, and ■3≧4.
．． Assuming that the compensation period during which 75V is ensured is T (=tl to t2), the following relationship is obtained.

C=(IxT)/ΔV ---(1)th (1
) By applying the above assumption to the equation, C= (IxT)/(
0,05) = 20 (IxT) ---(2), T in equation (2) is usually a little over 0.1 seconds, and the coefficient "2
0'' indicates that a large capacity capacitor 12 must be used. This is a problem with the conventional circuit shown in FIG. 3, and it is an object of the present invention to solve this problem.

That is, an object of the present invention is to provide a power supply circuit that can have a sufficient backup function without using a large-capacity capacitor or a large-capacity battery unlike conventional circuits.

[Structure of the Invention] (Means for Achieving the Problems of the Invention) A power supply circuit with a backup function according to the present invention includes a power supply (
10) A capacitor (
12) etc., a resistor (11) etc. which sends the charge obtained from the power supply (10) to the capacitor (12) and whose forward voltage drop does not have an element-specific threshold level, and a power supply (10) etc. ) from the load (
15) - a first diode (13) etc. that allows the direction to flow;
A second diode (14) that allows the second current (114) from the capacitor 12) to flow in one direction to the load (15), etc. is provided.

(Function) According to the configuration of the present invention described above, the capacitor (12) can be charged up to the full output voltage (v2) of the power source (10). The reason for this is that as the charging voltage to the capacitor (12) approaches the output voltage (v2) of the power supply (10), the charging current to the capacitor (12) approaches zero, so the forward voltage drop has a threshold level unique to the element. This is because the voltage drop across a resistor (11) that does not have a
and the square of its charging voltage. In the conventional circuit shown in FIG. 3, the charging voltage for the capacitor 12 becomes lower than the output voltage 2 of the power supply 10 by the forward voltage drop VF13 of the diode 13, so the conventional circuit cannot obtain the same charging energy as the present invention. ) capacitor (12) must be used.
2) can be charged up to the full output voltage (v2) of the power supply (lO), which means that the allowable fluctuation width Δ■ in equation (1) can be made larger than in the conventional circuit (see Figure 2 and (see Figure 4), and as Δ■ increases, the second
) becomes small, and the capacitor 12 with a relatively small capacity is sufficient.

(Embodiment) Hereinafter, a power supply circuit with a backup function according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the basic configuration of a power supply circuit with a backup function according to an embodiment of the present invention. The difference between the embodiment circuit of FIG. 1 and the conventional circuit of FIG. 3 lies in the connection state of the Schottky barrier diodes 13 and 14 to the resistor 11. In FIG. 3, a series circuit of resistor 11 and capacitor 12 is connected to the cathode side of diode 13, and capacitor 12 is only charged up to a maximum of V2-VF13. In contrast, in FIG. A series circuit is connected to the anode side of the diode 13, and the capacitor 12 is completely charged to 2.

The output voltage characteristics of the power supply circuit shown in FIG. 1 are as shown in FIG. 2, for example. When the stabilized power supply 10 is working normally (before time t1), the load 15 is powered by the load current 113 from the diode 13 at voltage 3.

Now, suppose that the power supply 10 fails and the voltage 2 drops to zero (time tl). Then, current 113 stops flowing, and instead, backup current 114 from capacitor 12 charged up to 5.6V flows to load 15 via diode 14. At this time, part of the charge in the capacitor 12 leaks to the power supply side via the resistor 11, but by appropriately selecting the value of the resistor 11, the current value due to this leakage can be made sufficiently smaller than the current 114. .

For example, if the rated load current H3 is 60A and the value of the resistor 11 is 10Ω, the leakage current is 0.56A at maximum.
(=5.6V/10Ω), which is 0.56A, which is sufficiently smaller than 60A.

The initial value of the load voltage (3) obtained by the charge on the capacitor 12 is 5.2 (2). In this case, as can be seen from Figure 2, Δ■ in equation (1) is 0.45V (=5.2
V-4,75V), and this ΔV=0.45V is
1) By substituting into the equation, the following equation is obtained.

C= (IxT>/(0,45>=2.2 (IxT) ---(3).The coefficient r2.2J of equation (3) is the first The figure shows that the capacitance of the capacitor 12 in the figure is only about 1/9 of that in the case of Figure 3.This is a feature of the present invention compared to the prior art.

FIG. 5 shows a first modification of the basic configuration of FIG.
In the figure, diodes 13 and 14 are placed on the negative voltage side of the power supply circuit. Note that the capacitor 12 may be replaced with a rechargeable battery as appropriate.

FIG. 6 shows a second modification of the basic configuration of FIG.
In the figure, diodes 13 and 14 are replaced by diode-connected bipolar transistors Q13 and Q14, respectively. For devices made of the same material (for example, Si), between the collector and emitter (or between the base and emitter) of a diode-connected transistor
Since the forward voltage drop between the anode and the cathode of a normal diode is also small, the configuration shown in FIG. 6 allows Δ■ in equation (1) to be larger than that in FIG. 1. In other words, the configuration of FIG. 6 allows the capacitance of the capacitor 12 to be smaller than that of FIG. 1.

FIG. 7 shows a third modification of the basic configuration shown in FIG. 7th
The figure shows two diodes 13 and 14 in FIG.
The collector-base PN junction and the emitter-base PN junction of two bipolar power transistors Q134 are used instead.

FIG. 8 shows a fourth modification of the basic configuration of FIG.
In the figure, the resistor 11 in Figure 1 is replaced by a depression type FET Q1.
This is replaced with a constant current circuit using 1. This constant current circuit can also be constructed using elements other than FETQII, such as constant current diodes.

In the circuit refinement shown in FIG. 8, since the internal resistance value of the constant current element Qll is large, when the power supply device (not shown) fails and the power supply voltage 2 becomes zero, a discharge current flows from the capacitor 12 to the power supply device side. The size of is much smaller than in the case of FIG. Therefore, when the allowable load voltage fluctuation range ΔV and the voltage compensation period t1 to t2 (=T) in FIG. 2 are constant, the capacitance of the capacitor 12 required in FIG. It can be made smaller than.

FIG. 9 shows a fifth modification of the basic configuration shown in FIG. 9th
The figure shows a parallel circuit in which the resistor 11 of FIG. 1 having a medium resistance value (for example, 10Ω) is connected to a series circuit of a resistor 11a having a large resistance value (for example, 100Ω), a resistor 11b having a small resistance value (for example, 1Ω), and a diode llc. This is the case when replaced with .

In this configuration, when the power supply device (not shown) is operating normally, the capacitor 12 is rapidly charged through the series circuit of the small resistor 11b and the forward biased diode llc. The potential difference between the power supply voltage 2 and the charging voltage of the capacitor 12 is the threshold voltage of the diode LLC (
(approximately 0.6V for Si), the diode llc cuts off, and the capacitor 12 becomes the large resistance 11a.
It is slowly charged via .

When the power supply device (not shown) fails and the power supply voltage 2 becomes zero, the magnitude of the discharge current flowing from the capacitor 12 to the power supply device side is greater than that in the case of FIG. 1 because the resistance value of the resistor 11a is large. Can be made smaller. Therefore, the capacitance of the capacitor 12 required in FIG. 9 can be made smaller than that in FIG. 1.

FIG. 10 shows a sixth modification of the basic configuration shown in FIG.

In FIG. 10, the RC series circuit (11+1
2) is the first RC series circuit (11X+12X) and the second
is replaced with a parallel circuit with an RC series circuit (11y+12y). Further, the diode 14 in FIG. 1 is replaced with a bipolar transistor Q14.

The collector of transistor Q14 is connected to the node between resistor 11x and capacitor 12x, and the base of transistor Q14 is connected to the node between resistor 11y and capacitor 12y. The emitter of transistor Q14 is connected to the cathode of diode 13.

FIG. 11 is a diagram illustrating the voltage characteristics of the circuit of FIG. 10. If the current amplification factor hfe of transistor Q14 is 100, its base current is 1/10 of its collector current.
It becomes a small value of 0. Therefore, the capacitor 12y
Even if the capacitance is as small as 1/10 of the capacitor 12x.

The attenuation rate of voltage vy due to discharge of capacitor 12y is smaller than the attenuation rate of voltage Vx due to discharge of capacitor 12x. Then, as shown in FIG.
The voltage vy on the capacitor 2y is always higher than the voltage Vx on the capacitor 12x.

During a period in which the voltage Vy is higher than the voltage Vx by the base-emitter threshold voltage Gh of the transistor Q14, the transistor Q14 is completely turned on, and the collector-emitter voltage drop (=Vx - V3) is relatively small. - Emitter saturation voltage VCe (Sat).

Therefore, even in the circuit shown in FIG. 10, a large allowable load voltage fluctuation range Δ■ can be obtained.

In addition, other voltages (1) or (2) in Figure 1 are for commercial AC
There is no problem in obtaining the voltage 1 or V2 from a DC power source such as a battery, a DC generator, or any other DC power source, which is not limited to a rectified power source.

[Effect of the invention 1 As described above, according to the present invention, although the capacitor 12 can be charged up to a higher voltage than the conventional one, the same backup compensation function as the conventional one can be achieved with the capacitor 12 having a smaller capacitance than the conventional one. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the basic configuration of a power supply circuit with a backup function according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the output voltage characteristics of the power supply circuit of FIG. 1, and FIG. A circuit diagram showing a power supply circuit with backup function, Fig. 3
5 is a diagram illustrating the first modification of the basic configuration of FIG. 1, and FIG. 6 is a diagram illustrating the output voltage characteristics of the power supply circuit shown in FIG.
7 is a diagram showing a third modification of the basic configuration of FIG. 1; FIG. 8 is a fourth modification of the basic configuration of FIG. 1. , FIG. 9 is a diagram showing a fifth modification of the basic configuration of FIG. 1, FIG. 10 is a diagram showing a sixth modification of the basic configuration of FIG. 1, and FIG. FIG. 3 is a diagram illustrating voltage characteristics of the circuit shown in the figure. 10---Stabilized power supply (electricity 1), 11. lla, llb
. 11x, 1ly--One resistor (charge supply means), 12.1
2x, 12y - 11 capacitor or battery (charge storage means), 13, 1lc - m - diode (11th circulation means), H3 - m - load current (first current), 14...
・Diode (second current passing means), 114-・Backup current (second current), 15-m-load, Q13. Q
14. Q134--Transistor, ■1--Unregulated DC input voltage, v2...Stabilized DC voltage, ■3--
load voltage. Application agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 5 Figure 7 11 No. 9 Prisoner No. 6 [! I Figure 8 Figure 10

Claims (1)

[Claims] A charge storage means for storing charge obtained from a power supply; and a charge supply means for sending the charge obtained from the power supply to the charge storage means and having no element-specific threshold level for forward voltage drop thereof. , comprising a first current passing means for causing a first current from the power source to flow one-way to the load, and a second current passing means for causing a second current from the charge storage means to flow one-way to the load. Power supply circuit with backup function.