JPH043555Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a charging circuit for a rechargeable secondary battery such as a nickel-cadmium battery.

[Technical background of the invention]

Conventionally, this type of circuit, as shown in Figure 2,
For example, the AC voltage input from the input terminal 11
AC100V is stepped down by a transformer 12, rectified by a rectifier diode 13, and further connected to a capacitor 14.
The alternating current component is smoothed to reduce so-called ripples, and a direct current voltage of, for example, DC12V can be obtained at point A. The diode 15 is for obtaining a constant voltage by utilizing forward voltage drop, and adjusts the voltage value according to the number of elements connected in series. Further, the resistor 16 is used to determine the value of the charging current output to the nickel cadmium (NiCd) battery 17 from the above-mentioned constant voltage. Note that 18 and 19 are NiCd
A connection terminal for connecting the battery 17 to the charging circuit,
20 is a diode for preventing reverse connection of the NiCd battery.

In addition, the connection terminals 18 and 19 each have a resistor 2.
An inverter 23 is connected via terminals 1 and 22, and the inverter 23 is connected to connection terminals 18 and 19.
Detection is being made as to whether or not the NiCd battery 17 is connected.

A voltage regulator 24 is connected to point A,
The DC voltage is stabilized and the output constant voltage is supplied to the inverter 23 and other circuits.

Here, when charging the NiCd battery 17 at about 1/10C at the start of charging and about 1/25C at the end of charging, the capacity C of the NiCd battery is assumed to be 200 [mAH], for example. Also,
The voltage drop across each diode 15, 20 is approximately
0.72 [V], and when the capacity of the NiCd battery 17 is exhausted, the voltage becomes about 1.2 [V] per cell, and 4
In the cell, it is 4.8 [V]. When the capacity is satisfied (when fully charged), the voltage is 1.5 [V] per cell.
The voltage will be approximately 6V for 4 cells.

Therefore, the charging current when the capacity is exhausted is 1/10C = 200/10 = 20 [mA], and if the resistance value of the resistor 16 is R ₁₆ [Ω], then 20 [mA] = 12 [V]. ]-0.72[V]×7-4.8[V]/R ₁₆ [Ω] Therefore, the resistance value R ₁₆ becomes R ₁₆ 110[Ω].

Also, when the resistance value R ₁₆ is R ₁₆ = 110 [Ω], the charging current in a fully charged state is 12 [V] - 0.72 [V] x 7-6 [V] / 110 [Ω] = 8.7 [mA] ] becomes. Therefore, it becomes 8.7 [mA] 1/25C.

Next, connect the inverter 23 shown in Figure 2 to the CMOS
When an inverter is used and the output voltage of the voltage regulator 24 is 8 [V], the threshold value of the inverter 23 is 8 [V]/2=4 [V]. In addition, in order to detect that the NiCd battery 17 is being charged, it is sufficient to detect that the voltage at the connection terminals 18 and 19 changes from 12 [V] to 6 [V]. Resistance value
When R ₂₁ and R ₂₂ are each set to R ₂₁ =R ₂₂ =100 [kΩ], the voltage at point C is 6 [V]×R ₂₂ /R ₂₁ +R ₂₂ =3 [V].

Since this detection voltage of 3V is lower than the threshold value of 4V of the inverter 23, the inverter 17 outputs an H level voltage and lights up a lamp such as a light emitting diode (not shown) connected to the output terminal 25.
It displayed that the NiCd battery 17 was being charged. In addition, the NiCd battery 17 is connected to terminals 18 and 19.
When the battery is removed from the battery, charging ends and the voltage at point C becomes higher than the threshold value of the inverter 23, so the inverter 23 outputs an L level voltage and turns off the lamp.

[Problems with background technology]

However, with the above circuit, if the load current of other circuits of the device that incorporates this charging circuit changes significantly, for example due to switching of a switch, the current will fluctuate.
The rectified output changes, for example, from 10 [V] to 16 [V]. Along with this, the charging current of the NiCd battery 17 also changes, so when the rectified output is 16 [V], a large current can flow, which shortens the life of the NiCd battery, and when the rectified output is 10 [V], a large current can flow. On the contrary
There was a problem that NiCd batteries could not be charged sufficiently.

[Purpose of invention]

This invention was created in view of the above problems.
It is an object of the present invention to provide a charging circuit that can obtain a stable desired charging current and accurately detect the charging state of a battery (whether or not it is being charged).

[Summary of the idea]

The present invention includes a stabilizing circuit and an impedance element with high impedance to stabilize the DC voltage and supply charging current to the secondary battery.
The above objective is achieved by stably performing detection during charging.

[Example of idea]

An embodiment of the present invention will be described in detail based on the drawing of FIG.

The difference between FIG. 1 and FIG. 2 is that the DC voltage smoothed by the capacitor 14 is stabilized to a constant voltage by the voltage regulator 26, and other circuits of the device incorporating the charging circuit of the present invention are controlled by switching with a switch or the like. Even when the load current changes significantly, diode 2
7. Allow a stable charging current to flow to the connection terminal 18 via the resistor 16, and connect point A and the connection terminal 18 with a resistor 28 to stabilize the detection output for detecting the state of charge of the battery 17. The point is to do it.

Here, when charging the NiCd battery 17 at about 1/10C at the start of charging as in FIG. 2, and assuming that the capacity C of the NiCd battery is 200 [mAH], the charging current when the capacity is exhausted is: Same as Figure 2 20 [mA]
Therefore, the resistance value R ₁₆ of the resistor 16 is R ₁₆ = 8 [V] - 0.72 [V] x 2 - 4.8 [V] / 20 [mA] ∴R ₁₆ 82 [Ω].

Also, when the resistance value R ₁₆ is R ₁₆ = 82 [Ω], the charging current in a fully charged state is: 8 [V] - 0.72 [V] x 2-6 [V] / 82 [Ω] = 7 [mA] ] becomes. Therefore, it becomes 7 [mA] 1/25C.

By the way, when the above-mentioned resistor 28 is not connected, the connection terminal 18 has a voltage of 5.5 [V] to 6.7 during charging.
A voltage of [V] is applied, and a voltage of 8 [V] is applied when the NiCd battery 17 is not connected, so in order to detect whether or not it is being charged, it is necessary to There arises a need to distinguish between 8V and 8V. Therefore, assuming that the resistance value R ₂₁ of the resistor 21 is 100 [kΩ], the threshold values of the inverter 23 are 8 [V] and 6.7 [V].
Find the resistance value R 22 of the resistor ₂₂ so that it is the median value of R ₂₂ /100 [kΩ] + R ₂₂ × 8 [V] + 6.7 [V] / 2 = 4 [V] ∴R ₂₂ 120 [ kΩ]. Therefore, the voltage at point C is 8 [V] × 120 [kΩ] / 120 [kΩ] + 100 [kΩ] = 4.35 [V] to 6.7 [V] × 120 [kΩ] / 120 [kΩ] + 100 [kΩ] = 3.65 [V]. That is, the change is in the range of 4±0.35 [V]. However, in CMOS inverters, the threshold value generally varies, and the threshold value exceeds at least ±10% from the reference value. Therefore, with the voltage value at the point C, the state of charge of the battery 17 may not be detected correctly due to variations in the threshold value of the inverter 23. Therefore, as in the present invention, A
When a resistor 28 is connected between the point and the connecting terminal 18, the voltage applied to the connecting terminal 18 changes from 12 [V] to 6.7
Since it will be possible to change up to [V],
The resistance value R ₂₂ of the resistor 22 is R ₂₂ 75 [kΩ]. Therefore, the voltage at point C is 12 [V] × 75 [kΩ] / 75 [kΩ] + 100 [kΩ] 5.1 [V] to 6.7 [V] × 75 [kΩ] / 75 [kΩ] + 100 [kΩ] 2.9 It changes up to [V]. In other words, the change is in the range of 4±1.1 [V], so the detected voltage at point C during charging, 2.9V, is a value lower than the threshold value of the inverter 23, 4±0.4V, so the inverter 23 detects the H level voltage. It is possible to detect that the NiCd battery 17 is being charged, and after charging is completed, the voltage at point C when not charging is higher than the threshold value of the inverter 23, so the inverter 23 It outputs an L level voltage and can perform good detection of non-charging.

Note that the diode 27 is used to obtain a constant voltage and to prevent current from flowing from the 12 [V] power supply to the 8 [V] power supply. If a shot barrier diode with a small voltage drop (voltage drop: about 0.14 V) is used as the diode 27, the voltage value can be precisely matched by adjusting the number of elements. Also, resistance value R ₂₈ ≫R ₁₆
By doing so, the charging current suppresses the current flowing from the resistor 16 side, and furthermore, the resistance value R ₂₁ ,
By setting R ₂₂ >>R ₁₆ , unnecessary current can be prevented from flowing through the resistors 21 and 22.

[Effect of idea]

As explained above, the present invention is equipped with a stabilizing circuit that stabilizes the DC voltage and an impedance element that stabilizes the detection of charging, so that it can supply a stable desired charging current and the state of charge of the battery. can be detected accurately.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is an example of a conventional circuit diagram. 13... Rectifier circuit, 16, 21, 22, 28...
...Resistor, 17...Battery, 18, 19...Connection terminal, 20, 27...Diode, 23...Inverter, 26...Voltage regulator.

Claims (1)

[Scope of utility model registration request] A stabilizing circuit that stabilizes the output voltage of the rectifying circuit is connected to the output of a rectifying circuit that rectifies an alternating current power source into a direct current voltage, and the output of the stabilizing circuit is charged via a first impedance element. connected to a secondary battery, and a threshold circuit having a predetermined threshold value is connected to a connection terminal for the secondary battery via a second impedance element having a higher impedance than the first impedance element; A charging circuit characterized in that the output of the rectifier circuit is connected to a connection terminal for the secondary battery via a third impedance element having a higher impedance than the first impedance element.