JP3215020B2 - Battery circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply which can be supplied by an external AC power supply and an internal rechargeable battery.
In a battery circuit that switches to supply power by discharging a secondary battery when the voltage of a power supply drops, a battery circuit capable of keeping the output voltage fluctuation within a predetermined range for the operation stability of the next stage circuit About.

[0002]

2. Description of the Related Art FIGS. 3 and 4 are views for explaining a conventional technique. FIG. 3 is a diagram showing a conventional battery circuit, and FIG. 4 is a diagram showing voltage and current waveforms during operation of the circuit.
(a) is the voltage of the power output unit 32, (b) is the p-channel FET
37 represents a current flowing from the source terminal 37b to the drain terminal 37a. In FIG. 3, where the wiring crosses in a cross shape, the circuit does not branch in four directions, but the wiring extending vertically and the wiring extending left and right simply cross without electrical connection. Indicates a state. Electrically connected branches are only when represented by a T.

In FIG. 3, a power input unit 31 is connected to an external A
Power is supplied from the C power source. The input power is rectified by the first diode 38 and sent from the power output unit 32 to the next-stage circuit existing outside.

[0004] The charger 34, which receives power supply from the power input unit 31, operates at a voltage higher than the supplied voltage.
Charge 3 The reason why the charging voltage is made higher than the supply voltage is to make the output voltage when using the AC is close to the output voltage when using the secondary battery 33, and to ensure the stable operation of the next-stage circuit. .

[0005] In order to make the discharge voltage of the secondary battery 33 close to the voltage at the time of steady use of AC, the charge voltage must be higher than the steady voltage of AC at least at the end of charging. Here, the p-channel FET 37 is incorporated as a discharge switch that connects the secondary battery 33 to the power output unit 32 when the AC voltage drops. When the p-channel FET 37 is turned off during charging, the output of the charger outputs the power output unit. We prevent going out to 32. Without this, the rechargeable battery 33 cannot be charged, and the use efficiency of the circuit is deteriorated.

The output of the comparator 36 takes a predetermined value when the voltage of the power input section 31 falls below the reference voltage 35. This output is the gate terminal 3 of the p-channel FET 37.
7c, the p-channel FET 37 is turned on, and the power from the secondary battery 33 is supplied to the second diode 39.
The power is supplied to the power output unit 32 via the power supply.

[0007]

However, according to the above-mentioned prior art, the voltage drop on the AC power supply side remains unchanged until the p-channel FET 37 is turned on and the power supply is switched to the secondary battery 33 side. The information is transmitted from the output unit 32 to the next device.

As shown in FIG. 4A, when the AC voltage which has started to fall falls below the threshold value 41, the detection delay 42
After a lapse of time, the p-channel FET 37 is turned on, and the discharge of the secondary battery 33 is started. Thereafter, the voltage starts to gradually increase and recovers to the battery discharge voltage 43.

Therefore, a DC-DC converter or the like connected to the next stage of the battery circuit must be able to operate stably in a wide voltage range in which the potential difference 44 can be tolerated. Conversely, if the potential difference 44 is reduced in order to use a device having a narrow voltage range,
The detection delay 42 must be shortened. However, for noise that is longer than the time width of the detection delay 42,
The p-channel FET 37 is turned on, and the discharge of the secondary battery 33 starts. In other words, there is a problem in that a separate noise countermeasure is required to shorten the detection delay 42, and the circuit becomes complicated.

Further, as shown in FIG.
The current flowing through 37 is "0" while the p-channel FET 37 is off while the AC power supply is normal. When a voltage drop is detected and the p-channel FET 37 is turned on, a large current temporarily flows as the peak current 45,
Eventually, the steady current 46 falls. Therefore, the p-channel FET 37 is not a steady current 46 but a peak current 45.
It was required to be able to withstand the heat.

The present invention satisfies the above noise immunity when the voltage of the AC power supply is close to the battery discharge voltage,
It is another object of the present invention to provide a battery circuit that suppresses a voltage drop due to a switching time delay.

[0012]

FIG. 1 is a diagram showing a battery circuit according to the present invention. The battery circuit of the present invention comprises an external A
A power input unit 1 that receives power supply from a C power source, a power output unit 2 that outputs power to a circuit in the next stage, a rechargeable secondary battery 3, and a power higher than that supplied from the power input unit 1. A charger 4 that charges the secondary battery 3 with a voltage, and a comparator that receives the voltage of the power input unit 1 at a positive terminal and compares the voltage with a reference voltage 5 connected to a negative terminal to detect a voltage drop of the AC power supply. 6, a first diode 8 connected in a forward direction from the power input unit 1 to the power output unit 2, and a secondary battery 3
And a second diode 9 connected in a forward direction from the output of the switch circuit to the power output unit 2. An n-channel FET 7 connects the drain terminal 7a to the positive terminal of the secondary battery 3 and connects the source terminal 7b to the power output unit 2 via the second diode 9, and a circuit from the drain terminal 7a to the gate terminal 7c. A third diode 10 connected in the forward direction, a fourth diode 11 connected in the forward direction to the gate terminal 7c, and terminals 12a and 12b on the light emitting side from the output terminal of the comparator 6 to the power output unit 2. Are connected in the reverse direction, the light receiving side terminals 12c and 12d are connected in the reverse direction from the source terminal 7b to the fourth diode 11, and the comparator 6 And Hotoborukapura 12 which is turned on when detecting the voltage drop of the source, and a.

[0013]

The power supplied from the external AC power supply is transmitted from the power input unit 1 to the power output unit 2 via the first diode 8. At this time, if the voltage of the AC power supply is sufficiently high,
Since the discharge switch including the n-channel FET 7, the photovoltaic coupler 12, and the third to fourth diodes 10 to 11 is in the off state, the secondary battery 3 is charged by the charger 4 without being discharged.

When the AC voltage falls below the threshold value, it is detected by a detection unit including the reference voltage 5 and the comparator 6, but the discharge switch is not immediately switched. The voltage continues to decrease and is clamped to this value when it reaches a predetermined voltage. This predetermined voltage value is determined by the characteristics of the gate threshold voltage of the n-channel FET 7 and the forward voltage drop of the third diode 10, and the battery discharge voltage of the secondary battery 3.

When a predetermined detection delay time elapses after the voltage drop is detected, the n-channel FET 7 turns on, and the discharge of the secondary battery 3 starts. The voltage held at the clamped value rises to the discharge voltage of the secondary battery 3.

[0016]

In FIG. 1, power input from a power supply unit 1 is output to a power output unit 2 through a first diode 8. At this time, when a drop in the power supply voltage is detected by the voltage drop detection unit, the discharge switch circuit switches accordingly, and the secondary battery 3 connected to the power output unit 2 starts discharging.

The voltage drop detecting section includes a reference voltage 5 and a comparator 6. The voltage of the power input section 1 is applied to the plus terminal of the comparator 6, and the reference voltage 5 is connected to the minus terminal. Here, while the input voltage is higher than the reference voltage 5, the output of the comparator 6 is kept at "H". On the other hand, when the input voltage falls below the reference voltage 5, the output becomes “L” after a predetermined delay time. This delay time is for confirming that the voltage drop is not instantaneous due to noise.

The switch circuit comprises an n-channel FET 7, a photovoltaic coupler 12, a third diode 10, and a fourth diode 11. In response to the "L" output from the comparator 6, the photovoltaic coupler changes the light emitting side terminal 12c.
And a voltage between 12d and an n-channel FET
Turn 7 on. When the n-channel FET 7 is turned on,
A current flows between the source terminal 7b and the drain terminal 7a, and flows into the power output unit 2 via the second diode 9. That is, the secondary battery 3 starts discharging and supplies power to the power output unit 2.

Here, the photovoltaic coupler is an element that generates a voltage between the terminals 12c and 12d on the light receiving side when the diode between the terminals 12a and 12b on the light emitting side emits light. With this voltage, the n-channel FE
The potential of the gate terminal 7c of T7 can be higher than that of the source terminal 7b. Further, the n-channel FET 7 is turned on when the potential of the gate terminal 7c becomes higher than a predetermined threshold with respect to the source terminal 7b.

By using a photovoltaic coupler, an n-channel FET having a small on-resistance can be used. n
When the channel FETs have the same cell area, that is, the same chip size, the on-resistance is lower than that of the p-channel FET. With the same on-resistance, smaller chips can be used.

This switch circuit has two functions, n
Drain terminal 7a and source terminal 7b of channel FET 7
And a power zener and a switch have a function equivalent to a circuit connected in parallel. The function of the power zener is constituted by the n-channel FET 7 and the third diode 10, and the function of the switch is constituted by the n-channel FET 7, the photovoltaic coupler 12 and the fourth diode 11.

By the function of the power zener, the potential of the source terminal 7b can be clamped to a predetermined value. When the voltage at the gate terminal 7c exceeds a predetermined threshold value V _TH with respect to the voltage at the source terminal 7b, the n-channel FET 7 turns on. The potential of the drain terminal 7a to the source terminal 7b becomes higher by an amount obtained by adding the voltage V _F and V _TH that is determined by the characteristics of the third diode 10, a current toward the drain terminal 7a to the source terminal 7b Flows. That is, to operate the circuit in the same way that there's containing the (V _F + V _TH) of the Zener diode.

Here, the drain terminal 7a of the n-channel FET 7 has the same potential as the positive terminal of the secondary battery 3, and the source terminal 7b has the same potential as the power output unit 2. this is,
Reduces the potential of the power output section 2, the difference between the battery discharge voltage of the secondary battery 3 is greater than (V _F + V _TH), means that the current flows from the secondary battery 3 to the power output unit 2 However, the voltage will be clamped so as not to drop below that value.

On the other hand, the power of the secondary battery 3 is supplied to the power output unit 2 by the switch function. When the photovoltaic coupler 12 is turned on by the output from the comparator 6, the gate terminal 7c is held at a potential higher than the source terminal 7b by V _TH . This situation does not change even if the potential of the power output unit 2 exceeds the clamped value, the n-channel FET 7 continues to be turned on, and the potential of the power output unit 2 rises to the battery discharge voltage 23 of the secondary battery 3. I do.

As described above, since the power Zener and the switch are formed using the same FET, an n-channel FET having a low on-resistance can be used.

FIGS. 2A and 2B are diagrams showing voltage / current waveforms of the circuit of the present invention. FIG. 2A shows the voltage of the power output unit 2 and FIG. 2B shows the voltage from the drain terminal 7a to the source terminal 7b of the n-channel FET 7.
It shows the current flowing to

As shown in FIG. 4A, when the starting AC voltage falls below the threshold 21, the detection delay 22
After a lapse of time, the n-channel FET 7 is turned on, and the discharge of the secondary battery 3 is started. Thereafter, the voltage gradually starts to increase and recovers to the battery discharge voltage 23. However, even if the voltage attempts to decrease during the detection delay 22, the potential difference 24 from the battery discharge voltage 23 becomes (V _F +
V _TH ).

As shown in (b), the current flowing through the n-channel FET 7 is the same as that of the n-channel FET 7 while the AC power supply is normal.
Is "0" because is off. When the voltage decreases and the potential difference 24 from the battery discharge voltage 23 tries to expand beyond (V _F + V _TH ), a current 25 flows. Eventually, the n-channel FET 7 is completely turned on, and finally falls to the steady current 26.

[0029]

As described above, in the present invention,
Since the supply voltage to the power output unit can be clamped to a predetermined value, a sufficient detection delay can be taken. Therefore, a microprogram or the like can be interposed for detection or switching. Further, since there is enough time for the detection delay, the surge current can be reduced by gradually increasing the voltage when the discharge switch is turned on, and the withstand capacity of the semiconductor used can be reduced.

In the present invention, an n-channel FET can be used as the FET used as the discharge switch. here,
Since an n-channel FET can use a smaller on-resistance than a p-channel FET, a voltage drop can be suppressed for the same size, and a smaller size can be used for the same voltage drop. Are available. Therefore, according to the present invention, cost and space can be reduced as compared with the prior art in which only the p-channel type can be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a battery circuit of the present invention.

FIG. 2 is a waveform diagram of the circuit of the present invention.

FIG. 3 is a diagram showing a conventional battery circuit.

FIG. 4 is a waveform diagram of a conventional circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power input part 2 Power output part 3 Secondary battery 4 Charger 5 Reference voltage 6 Comparator 7 N-channel FET 8 1st diode 9 2nd diode 10 3rd diode 11 4th diode 12 Photovoltaic coupler

Claims (1)

(57) [Claims] A power input unit for receiving power from an external AC power supply; a power output unit for outputting power to a next-stage external circuit; A possible rechargeable battery (3), connected between the power input (1) and a positive terminal of the rechargeable battery (3) and higher than the power supplied from the power input (1) A charger (4) for charging the secondary battery (3) with a voltage, and a voltage of the power input unit (1) received at one input terminal;
Compare with the reference voltage (5) connected to the other input terminal,
A comparator for detecting a voltage drop of the AC power supply;
A first diode (8) connected in a forward direction from the power input unit (1) to the power output unit (2); and a discharge power of the secondary battery (3), a comparator (6).
And a second diode (9) connected in a forward direction from the output of the switch circuit to the power output section (2). The switch circuit includes a drain terminal (7) connected to a positive terminal of the secondary battery (3).
a) and an n-channel FET (7) connecting a source terminal (7b) to the power output section (2) via a second diode (9); and a drain terminal ( A third diode (10) connected in a forward direction from 7a) to a gate terminal (7c), and a fourth diode connected in a forward direction to a gate terminal (7c) of the n-channel FET (7). (11), the light-emitting-side terminals (12a, 12b) are connected in the opposite direction from the output terminal of the comparator (6) to the power output section (2), and the source terminal of the n-channel FET (7) A photovoltaic coupler (12) is connected from 7b) to the fourth diode (11) and connected to the light receiving side terminals (12c, 12d) and turned on when the comparator (6) detects a voltage drop of the AC power supply. When Battery circuit, characterized in that they are composed of.