JPH09308125A - Charge circuit of storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To charge a storage battery efficiently according to the change of the starting voltage of a thermocouple, and not to give excessive load to a boosting circuit. SOLUTION: When the starting voltage of a thermocouple is low, a judging circuit 16 judges it and outputs the signal to an oscillating circuit 15. The oscillating circuit 15 outputs a pulse signal of large duty ratio to a switching element 14, and by the on-and-off of the switching element 14, the stating voltage is boosted greatly, so the charge of the storage battery can be performed with small starting voltage. When the staring voltage of the thermocouple 21 goes higher than the specified value, the judging circuit 16 judges it and outputs the signal to the oscillating circuit, and the oscillating circuit outputs the pulse signal of small duty ratio to the switching element. By the on-and-off of the switching element, the boosting of the starting voltage is suppressed, so the charge current is raised all the more, and the charge of the storage battery can be performed efficiently, Moreover, since the load added to the coil 13, a switching element, etc., is suppressed, the fault of these parts can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage battery charging circuit for charging a storage battery by boosting an electromotive voltage from a thermoelectric generator such as a thermocouple.

[0002]

2. Description of the Related Art
As shown in FIG. 2, the charging circuit of the storage battery of this type turns on and off the switching element 3 of the booster circuit 2 by a pulse signal from the oscillation circuit 4 to induce a voltage in the coil 5 to generate a voltage in the thermocouple 1. The electromotive voltage VI is boosted. Then, the boosted voltage is rectified by the diode 6, and the storage battery 7 is charged by the rectified output voltage VO. Here, the relationship between the electromotive voltage VI and the output voltage VO is given by the following mathematical expression 1.

[0003]

## EQU1 ## VO = {(TON + TOFF) / TOFF} VI-VF

However, TON is the ON time of the switching element 3, TOFF is the OFF time of the switching element 3, and V
F is the forward voltage of the diode 6.

As is clear from the above equation 1, the degree of boosting can be increased by increasing TON, that is, the duty of the oscillation pulse. Here, when this charging circuit is used for a burning appliance such as a water heater, charging efficiency is good if charging is performed from a time when the electromotive voltage of the thermocouple 1 is small at the beginning of combustion of the appliance. In this case, since the electromotive voltage is small, it is necessary to increase the duty of the switching element 3 in order to obtain a large output. However, if the duty remains high, when the output of the thermocouple 1 increases with the passage of time, as shown in FIG. 3, when the duty is small with a predetermined electromotive voltage VT as a boundary (D1> D2). ), The charging current will be lower and charging efficiency will be lower. Further, since the electromotive voltage becomes excessively large, a load higher than the rating is applied to the switching element 3, the coil 5 and the like of the booster circuit 2, so that there is also a problem that these components are likely to fail. The present invention is intended to solve the above problems, and provides a storage battery charging circuit that efficiently charges a storage battery according to a change in electromotive voltage of a thermoelectric generator and does not give an excessive load to a booster circuit. The purpose is to do.

[0006]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the structural feature of the invention according to claim 1 is that the input voltage is changed by inducing a voltage in a coil by turning on and off a switching element. In the charging circuit of the storage battery that boosts the electromotive voltage input from the thermoelectric generator using the booster circuit that boosts the voltage and charges the storage battery with the boosted output voltage, the on / off duty of the switching element depends on the value of the electromotive voltage. Is to change.

According to the invention according to claim 1 as described above, when the electromotive voltage of the thermoelectric generator is low, the duty of the switching element is increased, that is, the ON time is lengthened to increase the electromotive voltage. Therefore, the storage battery can be charged with a low electromotive voltage.
Further, when the electromotive voltage of the thermoelectric generator becomes high, the duty of the switching element is made small, that is, the boosting of the electromotive voltage is suppressed by shortening the ON time, so that the charging current is increased and the storage battery is charged. It can be done efficiently. Further, since the electromotive voltage is suppressed, the load applied to the switching element of the booster circuit is suppressed, so that the failure of these components can be prevented.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a charging circuit for a storage battery for a water heater according to the embodiment. The charging circuit has a booster circuit 10. Boost circuit 10
Includes a diode block 11, a capacitor 12, a coil 13 and a switching element 14 using a MOS field effect transistor connected in parallel, and an oscillation circuit 15 is connected to a gate terminal of the switching element 14. There is.

The booster circuit 10 is provided with a decision circuit 16 connected between the input terminal and the oscillator circuit 15. The determination circuit 16 compares the input voltage VI with the reference voltage VT and outputs the comparison result to the oscillation circuit 15. The oscillator circuit 15 receives the input voltage VI from the determination circuit 16.
When the signal that is smaller than the reference voltage VT is received,
When a pulse signal having a large duty D1 is transmitted and a signal that the input voltage VI is larger than the reference voltage VT is received from the determination circuit 16, a small duty D2 (<D1)
Is configured to emit a pulse signal of. However, the reference voltage is not limited to one type, and a plurality of types may be provided to change the duty of the pulse signal at each stage. Further, the oscillator circuit 15 has the input voltage V
It is also possible to change the duty continuously according to I.

A thermocouple 21 is connected to the input terminal of the booster circuit 10. The + terminal of the rectifying diode 22 is connected to the output terminal between the coil 13 and the switching element 14, and the capacitor 23 and the storage battery 24 via the resistor R are connected to the − terminal of the diode 22. , The other end is grounded. Terminal voltage VO of capacitor 23
The relationship between the input voltage VI and the input voltage VI is as shown in Equation 1 above. In this charging circuit, the output terminal of the storage battery 24 is connected to another booster circuit 30 via a switch 31. In the present embodiment, the output of the booster circuit 30 is used not only as a power source for electronic control of the water heater, but also as a power source for the oscillation circuit 15 and the determination circuit 16.

Next, the operation of the embodiment configured as described above will be described. First, when the electromotive voltage of the thermocouple 21 at the beginning of combustion of the water heater is low, the determination circuit 16 outputs a signal to the oscillation circuit 15 that the input voltage VI is smaller than the reference voltage VT. In response to this, the oscillation circuit 1
5 outputs a pulse signal having a large duty D1 to the gate of the switching element 14. Switching element 14
However, it turns on and off according to this pulse signal. When the switching element 14 is turned on, a current flows through the coil 13 and a voltage is induced in the coil 13, thereby boosting the voltage. As a result, as shown in Equation 1, the thermocouple 2
Since the electromotive voltage of 1 is greatly boosted, the storage battery 24 can be charged with a low electromotive voltage.

Further, as the combustion of the water heater progresses, the thermocouple 21
When the electromotive voltage of is higher than a predetermined value, the determination circuit 1
6, a signal that the input voltage VI is higher than the reference voltage VT is output to the oscillation circuit 15. In response to this, the oscillator circuit 15 outputs a pulse signal having a small duty D2 (<D1) to the gate of the switching element 14. Since the switching element 14 is turned on / off in response to the pulse signal, boosting of the electromotive voltage is suppressed as shown in Formula 1, so that the charging current is rather increased and the storage battery is charged as shown in FIG. It can be done efficiently. Further, since the boosting of the electromotive voltage is suppressed, the load applied to the coil 13, the switching element 14, and the like of the booster circuit 10 is suppressed, so that the failure of these components can be prevented.

Although a thermocouple is used as the thermoelectric generator in the above embodiment, a semiconductor thermoelectric generator using the Seebeck effect may also be used.
Further, in the above-mentioned embodiment, the charging circuit for the storage battery is applied to the water heater, but it can be applied to other combustion equipment and the like.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a charging circuit for a storage battery according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a charging circuit for a conventional storage battery.

FIG. 3 is a graph showing the relationship between the electromotive voltage of the thermocouple and the charging current of the storage battery when the duty of the pulse signal of the oscillation circuit is large or small.

[Explanation of symbols]

10 ... Booster circuit, 12 ... Capacitor, 13 ... Coil, 1
4 ... Switching element (field effect transistor), 15
... Oscillation circuit, 16 ... Judgment circuit, 21 ... Thermocouple, 22 ... Diode, 23 ... Capacitor, 24 ... Storage battery, 30 ... Booster circuit, 31 ... Switch.

Claims (1)

[Claims] 1. A booster circuit for boosting an input voltage by inducing a voltage in a coil by turning on / off a switching element is used to boost an electromotive voltage input from a thermoelectric generator element, and a boosted output voltage is used to charge a storage battery. A charging circuit for a storage battery to be charged, wherein a duty of turning on and off the switching element is changed according to a value of the electromotive voltage.