JPH0640711B2 - Peak detection circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a peak detection circuit having a peak holding capacitor.

[Conventional technology]

When charging Ni-Cd batteries (nickel-cadmium batteries), etc., in order to shorten the charging time, when the battery is charged rapidly with a relatively large current, the charging is likely to be 100% or more and the storage battery is destroyed. There is a risk of Therefore, it is necessary to detect full charge (100% charge) and prevent the storage battery from being destroyed.

By the way, it is known that among the storage batteries, the Ni-Cd battery shows a charging characteristic in which the charging voltage Eo (terminal voltage) reaches its peak at full charge t ₀ as shown by the solid line in FIG. ing. Therefore, in the case of Ni-Cd batteries, it is possible to detect full charge by utilizing this property.
As a detection circuit, for example, a circuit as shown in FIG. 8 has been proposed.

In the figure, (1) is a charging line, and a Ni-Cd battery (not shown) is, for example, subjected to constant current charging through the charging line (1). The voltage of this charging line (1), that is, the charging voltage Eo of the Ni-Cd battery, is constant voltage ΔV.
After being lowered only by this, it is supplied to a peak detection circuit (4) having an operational amplifier (2) and a peak holding capacitor (3). The detection output Ep of the peak detection circuit (4) is supplied to the negative input terminal of the operational amplifier (5) for comparison. The charging voltage Eo is detected by the capacitor (6) and supplied to the positive side input terminal of the operational amplifier (5). Then, the output terminal (7) is derived from the operational amplifier (5).

In the example of FIG. 8, the detection output Ep of the peak detection circuit (4) changes at a value lower than the charging voltage Eo by ΔV until full charge t ₀ , as shown by the broken line in FIG.
After ₀ , the charging voltage Eo drops, so that it remains at the value at the time point t ₀ . Therefore, after full charge, charge voltage E
The charging voltage Eo is higher than the detection output Ep until the time point t ₁ when o decreases by ΔV, and a signal of high level “1” is obtained at the output terminal (7). After _1, the charging voltage Eo becomes lower than the detection output Ep, and the output terminal
In (7), a low level “0” signal can be obtained. Therefore, full charge is detected. Although not described above, the voltage ΔV is selected to be small enough not to impair the detection accuracy so that the time point t ₁ becomes close to the full charge time t ₀ .

[Problems to be solved by the invention]

In order to maintain the characteristics of this charge detection circuit in good condition, it is essential that the peak detection circuit (4) performs peak detection correctly. However, this peak detection circuit
As the peak-holding capacitor (3) that constitutes (4), a large-capacity electrolytic capacitor is usually used because of the holding time.If this electrolytic capacitor is not activated, for example, it has not been charged for a long time. However, since the leak current is large, the peak detection circuit (4) cannot correctly detect peaks. Therefore, the characteristics of the charge detection circuit are also insufficient.

The present invention has been made in view of the above points and enables accurate peak detection.

[Means for solving problems]

In order to solve the above problems, the present invention is to perform peak detection with the peak holding capacitor (3) being activated. That is, the present invention provides a charging and discharging path for the peak holding capacitor (3) in addition to the peak detection path, and charges the capacitor (3) with the charging path before starting peak detection, and also discharge path. With this, the peak detection is started after the capacitor (3) is discharged.

[Action]

Since the peak holding capacitor (3) is charged before the peak detection is started, it is always kept in the activated state before the peak detection is started. Therefore, the leak current of the capacitor (3) at the time of peak detection is reduced, and the peak can be detected accurately.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 8 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the voltage of the charging line (1), that is, Ni
The charging voltage Eo of the −Cd battery is reduced by a constant voltage ΔV and then supplied to the terminal on the A side of the changeover switch (8).
Further, the voltage E ^* is supplied from the battery (9) to the B side terminal of the changeover switch (8). The value of the voltage E ^* is set to a value substantially equal to the maximum value of the voltage held in the peak holding capacitor (3) at the time of peak detection. The output of the changeover switch (8) is supplied to the peak detection circuit (4).
In this case, the changeover switch (8) is controlled so as to be connected to the B side before the start of charging and connected to the A side after the start of charging.

In this example, the output side of the peak detection circuit (4),
That is, the non-grounded side of the peak holding capacitor (3) is grounded through the series circuit of the connection switch (10) and the resistor (11). In this case, the connection switch (10) is controlled to be in the ON state for the predetermined time TA after the start of charging. This time TA is, for example, a time during which the charged capacitor (3) is sufficiently discharged before the start of charging.

Others are the same as in the example of FIG.

In this example, since the changeover switch (8) is connected to the B side before the start of charging, the capacitor (3) is kept charged with the voltage E ^* . Then, the connection switch (10) is turned on for a predetermined time TA after the start of charging. Therefore, at this time TA, the capacitor (3) is sufficiently discharged by the series circuit of the connection switch (10) and the resistor (11). Since the changeover switch (8) is connected to the A side after the start of charging, after the time TA has elapsed, the peak detection circuit (4) operates in the same manner as in the example of FIG. 8 to perform peak detection.

Thus, according to this example, the peak holding capacitor (3)
Is charged before peak detection and this capacitor (3)
The peak detection is started after the discharge of
This capacitor (3) is always kept activated at the start of peak detection. Therefore, the leakage current of the capacitor (3) during peak detection is reduced, and the peak detection circuit
The peak detection in (4) can be performed more accurately than in the conventional example. As a result, the characteristics of the charge detection circuit are also good.

Next, FIG. 2 shows a specific example of the example shown in FIG. 1, and corresponding parts are designated by the same reference numerals. In the example of FIG. 2, the Zener diode (12), the resistors (13), (1
Due to 4), a voltage difference of ΔV is formed. In the case of this example, a voltage Eo ′ lower than the charging voltage is supplied to the positive input terminal of the operational amplifier (5), and the peak detection circuit
This voltage Eo 'is supplied to (4) and a voltage lower than this voltage Eo' by .DELTA.V is supplied to the peak detection circuit (4), which is basically the same as that of FIG. .

In FIG. 2, the terminal (15) has a high level “1” (for example, 5 V) before the start of charging and a low level “0” after the start of charging, as shown in FIG. 3A. A signal S _{1 of} (for example, 0 V) is supplied from a charge control unit (for example, a microcomputer), and this signal S ₁ is transmitted through a diode (16) to a peak detection circuit
Supplied to (4). The operation of the diode (16) or the like is substantially the same as that of the changeover switch (8) in FIG. That is, since the signal S ₁ is at the high level “1” before the start of charging, the diode (16) is turned on and the capacitor (3) is charged by the signal S ₁ . In addition, since the signal S ₁ becomes low level “0” after the start of charging, the diode (1
6) is turned off and the charging line (1) is connected to the peak detection circuit (4).
Signal to be detected is supplied.

Further, in FIG. 2, the terminal (17) has a low level “0” (for example, 0 V) before the start of charging, as shown in FIG. 3B.
After the start of charging, a signal S ₂ that becomes a high level “1” (for example, 5 V) is supplied from the charging control unit, and this signal S ₂ is supplied to the connection switch via the capacitor (18) and the resistor (19). It is supplied to the base of the npn-type transistor (20) which constitutes it.
In this case, since the signal S ₂ has a high level “1” after the start of charging, the transistor (20) has a capacitor after the start of charging.
It is turned on for a predetermined time TA determined by (18) and the resistor (19). This time TA depends on the capacitor (18) and the resistor.
It is adjusted by changing the value of (19).

Then, at this time TA, the capacitor (3) is sufficiently discharged by the series circuit of the resistor (11) and the transistor (20). Incidentally, the diode (21) and the resistor (22)
The path formed by means of forms a discharge path for the capacitor (18).

As described above, also in the specific example of FIG. 2, the same operation as described in FIG. 1 is performed, the peak holding capacitor (3) is charged before the peak is detected, and the discharge of this capacitor (3) is performed. The peak detection is started after the peak detection is performed, and since the capacitor (3) is always kept in the activated state at the start of the peak detection, the same effect can be obtained.

Next, FIG. 4 shows another embodiment of the present invention.
Portions corresponding to those in FIGS. 1 and 8 are designated by the same reference numerals.

In this example, the charging voltage Eo is reduced by ΔV and then supplied to the peak detection circuit (4). Also the peak detection circuit
The output side of (4), that is, the non-ground side of the peak holding capacitor (3) is connected to the movable terminal of the changeover switch (23). The voltage E ^* is supplied from the battery (9) to the fixed terminal on the A side of the changeover switch (23), and the fixed terminal on the B side is grounded via the resistor (11). In this case, the changeover switch (23) is connected to the A side before the start of charging, and is B for a predetermined time TA after the start of charging.
It is connected to the side and then controlled to be in an electrically floating state. Here, the voltage E ^* and the time TA are set in the same manner as in the example shown in FIG. 1, and the others are set in the example shown in FIG.
The configuration is the same as the example shown.

In this example, since the changeover switch (23) is connected to the A side before the start of charging, the capacitor (3) is kept charged with the voltage E ^* . Then, the changeover switch (23) is connected to the B side for a predetermined time TA after the start of charging. Therefore, at this time TA, the capacitor (3) is sufficiently discharged by the series circuit of the changeover switch (23) and the resistor (11). After the predetermined time TA, the changeover switch
Since (23) is in an electrically floating state, the peak detection circuit (4) operates in the same manner as in the example of FIG. 8 to perform peak detection.

Thus, also in this example, the peak holding capacitor
(3) is charged before peak detection, and this capacitor (3) is discharged before peak detection is started.This capacitor (3) is always activated at the start of peak detection. Be put in a state. Therefore, also in this example, it is possible to obtain the same effect as that of the first example.

Incidentally, the peak detection circuit (4) of the above-mentioned FIG. 1 example is an operational amplifier (2)
Although it is constructed by using
As shown in the figure, a diode (24) or transistor
The present invention can be similarly applied to the one configured by using (25). In addition, the peak detection circuit of the above-mentioned FIG. 4 example
(4) is also configured using the operational amplifier (2),
The present invention can be similarly applied to a device which is similarly configured by using a diode or a transistor (not shown).

〔The invention's effect〕

According to the present invention described above, the peak holding capacitor is always activated at the start of the peak. Therefore, the leak current of the peak holding capacitor at the time of peak detection is reduced, and the peak detection in the peak detection circuit can be performed more accurately than in the conventional example.
Therefore, the peak detection circuit according to the present invention is suitable for application to, for example, a charge detection circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a specific circuit diagram thereof, FIG. 3 is a waveform diagram for explaining the example of FIG.
4 to 6 are configuration diagrams showing another embodiment of the present invention, FIG. 7 is a characteristic diagram showing charging characteristics of a Ni—Cd battery, and FIG. 8 is a configuration diagram of a conventional example. (1) is a charging line, (2) and (5) are operational amplifiers, (3) is a peak holding capacitor, (4) is a peak detection circuit, (7) is an output terminal, (8) is a changeover switch, ( 10) is a connection switch.

Claims (1)

[Claims] 1. A peak detection circuit having a peak holding capacitor, wherein a charging and discharging path for the capacitor is provided in addition to the peak detecting path, and the capacitor is charged through the charging path before starting peak detection. A peak detection circuit, wherein peak detection is started after the capacitor is discharged through the discharge path.