JPS6355298B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field] The present invention relates to a charging circuit.

[Background Art] Generally, in rechargeable electrical equipment that uses a storage battery to drive a load, a so-called floating charging circuit (hereinafter abbreviated as a charging circuit) that can drive the load even while the storage battery is being charged is often used. It is being For example, Figure 5 shows a conventional example of a charging circuit used in a rechargeable electric shaver, in which a DC power source obtained by rectifying and smoothing a commercial AC power source AC in a rectifier circuit 1 is stepped down in an inverter type DC-DC converter 4. Then, turn the power switch SW on DC motor M.
A storage battery B such as a nickel cadmium battery connected via the battery is floatingly charged. By the way, in such a conventional example, charging current is always supplied to the storage battery B while the commercial AC power supply AC is applied, regardless of the usage status of the DC motor M. , a charge control unit 2 is provided to prevent overcharging, so that storage battery B will not be overcharged and the charging characteristics of storage battery B will deteriorate, or storage battery B will be damaged due to gas generation inside storage battery B. The set voltage applied to the base of transistor _Q4 is compared with the terminal voltage of storage battery B applied to the emitter, transistor _Q4 turns on and off transistor _Q5 , and the terminal voltage of storage battery B is lower than the set voltage. When the voltage rises, the oscillation of the DC-DC converter 4 is stopped. However, such a conventional charging control unit 2 has a disadvantage that the configuration is complicated and the charging circuit becomes large, and the output current of the DC-DC converter 4 fluctuates due to changes in input voltage. Therefore, when the input voltage is high, the rotation speed of the DC motor M increases, causing noise and vibration, and as the output current increases, the components of the DC-DC converter 4 generate more heat. There was a problem in that a heat sink was required, which increased the size of the entire device.

A circuit configuration shown in FIG. 6 can be considered as a solution to such problems. This is DC-DC
A transistor Q 3 as a switch element that bypasses the base current is connected to the base of the oscillation transistor Q ₁ of the converter ₄ , and a Zener diode ZD ₂ as a constant voltage element is inserted in the emitter of this transistor Q ₃ . The protection circuit 6 is configured to detect the terminal voltage of the series circuit of the emitter resistor _R6 and the storage battery B at the base of _Q3 . That is, the emitter resistance R ₆
The terminal voltage of the series circuit of and storage battery B is the threshold voltage of Zener diode ZD ₂ and transistor Q ₃
When the base-emitter voltage exceeds the sum of the base-emitter voltage, transistor _Q3 becomes conductive and bypasses the base current of transistor _Q1 . In this configuration, when the input voltage increases, the on-period of the oscillation transistor _Q1 is shortened to reduce the charging current, while when the load is large, the oscillation output is increased to increase the current supplied to the load. Although it has a simple circuit configuration, it has the effect of stabilizing the current supplied to the load. However, when transistor Q ₃ conducts and bypasses the base current of transistor Q ₁ , this current also flows through Zener diode ZD ₂ at the same time, so the voltage across Zener diode ZD ₂ increases due to the DC resistance of Zener diode ZD ₂ . This causes a problem in that transistor _Q3 no longer responds as sharply as the operating voltage increases. In other words, the response to load fluctuations is rather slow and cannot follow the rapidly changing load of the DC motor M.

Furthermore, when the polarity of the transformer T is reversed during oscillation, a reverse bias voltage is applied between _the emitter and base of transistor _Q1 ; Since _{only the} diode that is It will take time.

[Object of the Invention] The present invention has been made in view of the above points, and its purpose is to prevent overcharging of a storage battery and to obtain a stable output current even when the input voltage fluctuates. It is an object of the present invention to provide a charging circuit which has a simple configuration and has good responsiveness to load fluctuations.

[Disclosure of the Invention] (Structure) The charging circuit according to the present invention supplies a DC power source obtained by rectifying a commercial AC power source to a collector winding of an oscillation transformer between the collector of a first transistor and one end of the DC power source. At the same time, the voltage is stepped down by a ringing chain-yoke converter type DC-DC converter, which has a configuration in which the base winding of an oscillation transformer is inserted between the base and emitter of the first transistor, and the storage battery connected to the load is In the charging circuit for charging, a series circuit of an emitter resistor and a storage battery is inserted between the emitter of the first transistor and the other end of the DC power supply, and a series circuit of an emitter resistor and a storage battery is inserted between the emitter of the first transistor and the other end of the DC power supply. a second transistor whose collector-emitter is inserted between the base and the emitter of the first transistor and the base of the second transistor, and a series circuit of the emitter resistor and the storage battery; A protection circuit is constituted by a constant voltage element that turns on a second transistor when the voltage exceeds a predetermined threshold voltage, and is able to follow load fluctuations with good responsiveness. .

(Example) In this example, a charging circuit used for a rechargeable electric shaver is illustrated. Further, an example will be shown in which a transistor _Q2 serves as both a switch element and a rectifier element. In FIG. 1, 1 is a rectifier circuit, which includes current-limiting resistors R ₁ , R ₂ , a capacitor C ₁ , a bidirectional threshold element Z, and a diode bridge D.
It is designed to rectify and smooth the commercial alternating current power source AC to obtain a direct current power source. 4 is a ringing chain yoke converter type DC-DC converter, which includes a base feedback line L ₁ , a collector winding L ₂ ,
An oscillation transformer T formed by winding the output winding L ₃ around the same ferrite core, a transistor Q ₁ , and a resistor.
The DC-DC converter 4 is composed of R ₃ to R ₆ , capacitors C ₂ , C ₃ , and diode D ₁ , and the rectifier circuit 1
It is designed to generate high-frequency oscillation modulated by the ripple component of the DC power supply output. A stepped-down high frequency voltage is induced in the output winding _L3 of the oscillation transformer T, and the high frequency voltage induced in the output winding _L3 is rectified by the diode _D1 to charge the storage battery B. DC power from rectifier circuit 1
When supplied to the DC-DC converter 4, the resistance R ₃
As a result, a starting current flows to the base of the transistor _Q1 , the transistor _Q1 turns on, and current flows to the collector winding _L2 of the oscillation transformer T, and the collector winding _L2 and base winding _L1 become positive. Since it is connected as a feedback, it starts oscillating. At this time, no current flows in the output winding L ₃ because a voltage in the opposite direction of the diode D ₁ is generated, and as shown in FIG. 2, the collector current I _L of the transistor Q ₁ increases linearly. A terminal voltage V _R is generated across the emitter resistor R ₆ due to the emitter current I _E flowing due to the base current I _B and collector current I _L of the transistor Q ₁ .
When the sum of the terminal voltage V _R of the emitter resistor R ₆ and the terminal voltage of the storage battery B exceeds the set voltage V set by the Zener voltage of the Zener diode ZD ₁ of the protection circuit 6, the transistor Q ₂ turns on. hand
The base current I _B of the transistor Q ₁ of the DC-DC converter 4 is bypassed as the collector current I _C of the transistor Q ₂ to quickly turn off the transistor Q ₁ . At this time, the current flowing through the Zener diode ZD ₁ hardly changes before and after the transistor Q ₂ turns on, and the set voltage of the Zener diode ZD ₁ does not change. Here, resistor R ₇ is a Zener diode ZD ₁
This is provided for the purpose of preventing malfunction of transistor _Q2 due to leakage or the like.

The operation will be explained in more detail. transistor
When Q ₂ conducts and bypasses the base current of transistor Q ₁ , the collector current of transistor Q ₁ can no longer increase as before, and the current flowing through the base winding L ₁ no longer increases and the base The polarity at both ends of winding L ₁ is reversed, so that
The polarity at both ends of the collector winding L ₂ is also reversed. Therefore, a reverse bias is applied between the emitter and base of the transistor _Q1 due to the voltage induced in the collector winding _L2 , and the transistor _Q1
Since the excess electrons existing in the base region of Q1 are extracted, the collector current decreases and the transistor _Q1
is turned off. Here, the time from when the base current begins to decrease until when the collector current begins to decrease is called the accumulation time of the transistor, and in the present invention, this accumulation time is shortened.

In other words, a Zener diode ZD ₁ is connected between the emitter and base of transistor Q ₁ , and
The base and collector of transistor Q ₂ are connected in series, and the base and collector of transistor Q ₂ act as a diode with the base as an anode. Therefore, the above reverse bias voltage becomes the forward voltage for the series circuit of the Zener diode ZD ₁ and the diode formed by the transistor Q ₂ , and since this is applied between the emitter and base of the transistor Q ₁ , the high reverse bias voltage causes the transistor to
This allows the charge in the base region of Q ₁ to be removed. Therefore, the switching speed of transistor _Q1 becomes faster and the loss during switching is reduced.

As mentioned above, the emitter of transistor _Q1
By inserting _a series circuit between the base of the Zener diode ZD ₁ and the diode consisting of the collector and base of the transistor
The reverse bias voltage between the emitter and base of Q ₁ is set high to protect the emitter and base, and the transistor Q ₁ is protected from polarity reversal of the transformer T.
This can shorten the time it takes for the device to turn off.

The energy stored in the oscillation transformer T during the period when transistor _Q1 is _on is
When _Q1 is turned off, a voltage is induced in the output winding _L3 in the opposite direction to that when it is on, and current is supplied to the storage battery B and the DC motor M through the diode _D1 . The period T _OFF during which current is supplied to storage battery B and DC motor M is the collector winding.
It is determined by the impedance of _L2 , the collector peak current of transistor _Q1 , the turns ratio between collector winding _L2 and output winding _L3 , and the output voltage. When the energy stored in the oscillation transformer T is released, the current stops, a surge voltage is generated, and is fed back to the base winding _L1 , turning on the transistor _Q1 again and repeating the same process. Therefore, as the charging of storage battery B progresses and the terminal voltage of storage battery B increases, the sum of the terminal voltage of emitter resistor R ₆ and the terminal voltage of storage battery B also increases, making it easier to reach the set voltage V, and as a result, the transistor The period T _ON during which Q ₁ is on becomes shorter, the energy stored in the oscillation transformer T decreases, and the charging current decreases. That is, when the input voltage to the DC-DC converter 4 increases, the emitter current I _E of the transistor Q ₁ increases, so the terminal voltage V _R of the emitter resistor R ₆ increases, and as shown in FIG. When the input voltage exceeds a predetermined value, the charging current is saturated and the charging current is prevented from increasing. In addition, as shown in Fig. 4, the terminal voltage of storage battery B and the emitter resistance R ₆
When the sum of the terminal voltage and the set voltage reaches the set voltage, DC-
The oscillation of the DC converter 4 is stopped and no charging current flows, preventing overcharging.

Incidentally, a nickel cadmium battery is mainly used as the storage battery B, and since the terminal voltage of this type of storage battery B generally has a temperature coefficient of about -3 mV/°C, the Zener diode ZD ₁ of the protection circuit 6 is If the set voltage of the protection circuit has a temperature coefficient of about -3 mV/° C. by utilizing the temperature characteristics, the influence of temperature on the charging characteristics can be reduced.

[Effects of the Invention] As described above, the present invention provides DC power obtained by rectifying a commercial AC power source by inserting a collector winding of an oscillation transformer between the collector of the first transistor and one end of the DC power source. At the same time, the voltage is stepped down by a DC-DC converter of the ringing chain converter type, which has a configuration in which the base winding of an oscillation transformer is inserted between the base and emitter of the first transistor, and the storage battery connected to the load is charged. In the charging circuit, a series circuit of an emitter resistor and a storage battery is inserted between the emitter of the first transistor and the other end of the DC power supply, and the base of the first transistor and the other end of the DC power supply are connected. A second transistor is inserted between the collector and emitter of the first transistor, and a voltage across the series circuit of the emitter resistor and the storage battery is inserted between the emitter of the first transistor and the base of the second transistor. A protection circuit consists of a constant voltage element that turns on the second transistor when the voltage exceeds a predetermined threshold voltage, and when the oscillation transistor of the DC-DC converter is on, the emitter When the current increases and the sum of the voltage across the emitter resistor and the terminal voltage of the storage battery exceeds a predetermined voltage set in the protection circuit, the base current of the transistor is bypassed and the transistor is turned off. Here, since the constant voltage element is connected to the control terminal of the switch element, when the switch element becomes conductive, a bypass current is not passed to the constant voltage element, and the operating voltage of the constant voltage element changes. Therefore, the switch element can be expected to operate rapidly. In other words, the protection circuit has good responsiveness and a high ability to follow load fluctuations. Furthermore, the oscillation transistor is quickly switched from on to off, reducing loss in the oscillation transistor and improving the efficiency of the charging circuit. Moreover, the 6th
Similar to the circuit shown in the figure, when the input voltage increases, the emitter current of the oscillation transistor of the DC-DC converter increases, so the sum of the voltage across the emitter resistor and the terminal voltage of the storage battery increases. The increase in charging current is suppressed, and when the input voltage decreases, the charging current increases, and the protection circuit has the effect of keeping the charging current approximately constant.
Therefore, even when connected to a load with large changes in drive current and performing floating charging, a stable drive current can be supplied to the load, preventing unstable load operation due to input voltage fluctuations. It has the advantage of being able to Also,
When the storage battery approaches full charge and the terminal voltage of the storage battery increases, the on period of the oscillation transistor becomes shorter and the charging current gradually decreases, making it impossible to supply a charging current that matches the charging characteristics of the storage battery. As a result, there is an advantage that overcharging is prevented and deterioration of the storage battery can be prevented. Moreover, the emitter of the oscillation transistor
Since a constant voltage element and a rectifier are inserted between the bases to bypass the reverse bias voltage between the emitter and the base, the protection circuit not only helps detect full charge, but also protects the DC-DC inverter. This shortens the time from when the base current of the transistor is reversed to when the collector current stops for the oscillation operation, and the loss in switching can be reduced.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is an explanatory diagram showing the operation of each part of the same as above, Figure 3 is an explanatory diagram of operation showing the relationship between the input voltage and output current of the DC-DC converter used in the above, and Figure 4 is the terminal voltage of the storage battery and An operation explanatory diagram showing the relationship with the charging current, Fig. 5 is a circuit diagram showing a conventional example, and Fig. 6 is a circuit diagram showing the conventional example.
The figure is a circuit diagram showing another conventional example. 1 is a rectifier circuit, 4 is a DC-DC converter, 6 is a protection circuit, AC is a commercial AC power supply, B is a storage battery, M
is a DC motor, Q ₁ and Q ₂ are transistors, R ₆ is an emitter resistor, V is a set voltage, and ZD ₁ is a Zener diode.

Claims (1)

[Claims] 1. A DC power source obtained by rectifying a commercial AC power source is inserted into the collector winding of an oscillation transformer between the collector of the first transistor and one end of the DC power source, and the DC power source is connected between the base and emitter of the first transistor. This is a ringing chain yoke converter system with a configuration in which the base winding of an oscillation transformer is inserted into the
In a charging circuit in which voltage is stepped down by a DC-DC converter to charge a storage battery connected to a load, a series circuit including an emitter resistor and a storage battery is connected between the emitter of the first transistor and the other end of the DC power supply. is inserted, a second transistor having a collector-emitter interposed between the other end of the DC power supply and the base of the first transistor, and a connection between the emitter of the first transistor and the base of the second transistor. A protection circuit is formed by a constant voltage element inserted between the emitter resistor and the storage battery to make the second transistor conductive when the voltage across the series circuit of the emitter resistor and the storage battery becomes equal to or higher than a predetermined threshold voltage. charging circuit.