JPH0261224B2 - - Google Patents

Description

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

[Background Art] As shown in Figure 1, a conventional charging circuit connects the primary coil _L10 of a transformer T' to the collector of a transistor _Q0 .
Connect the secondary coil L ₂₀ of the transformer T′ to the base.
is connected to the polarity that forward biases the base to form an oscillation circuit, and a series circuit of a rectifier diode D ₁₀ and battery B is connected across the tertiary coil L ₃₀ of the transformer T' to convert the output of the oscillation circuit into a tertiary one. The voltage was obtained from coil L ₃₀ and rectified by rectifier diode D ₁₀ to charge battery B. R ₁₀ is the oscillation starting resistor, C ₁₀ is the oscillation capacitor, D ₂₀ is the reverse bias diode of transistor Q ₀ , C ₂₀ and R ₃₀ are the spike voltage absorption capacitor, resistor R ₂₀ is the current limiting resistor, and SW is a switch that turns the load L on and off. DB is a diode bridge, and E is an AC power supply.

In this case, the transformer T′ requires three coils L ₁₀ , L ₂₀ , and L ₃₀ , so the transformer
T′ and the circuit become complicated, making it unsuitable for miniaturization. Furthermore, the thin coil of the transformer T′ tends to cause disconnection, and the polarity of each coil may be incorrectly processed, making the transformer T′ unreliable. It had the disadvantage of low performance.

In addition, since the coil of transformer T' has three windings, the coupling coefficient between coils L ₁₀ and L ₃₀ shown in Figure 1 deteriorates, leakage inductance increases, and the spike voltage when transistor Q ₀ is cut off becomes very large. becomes higher, so the transistor Q ₀
This required parts such as a resistor R ₃₀ and a capacitor C ₂₀ to increase the breakdown voltage of the collector-emitter voltage V _CE and to absorb spike voltages, which caused the problem that it was not possible to create a small and inexpensive product.

Therefore, the second circuit is an improvement on the circuit shown in Figure 1.
This is the circuit shown in the figure, in which the coil of the oscillation transformer has two windings, resulting in a small and inexpensive quick charging circuit configuration with no loss and no need to take measures against loss.

That is, in this other conventional example, as shown in FIG. 2, it is composed of an oscillation circuit, a charging block including a battery to be charged B, and a charging control block. The charging block is constructed as follows. Connect the primary coil _L1 of the oscillation transformer T to the collector of the transistor Q, and
The base of is connected to the polarity that forward biases the secondary coil _L2 of the transformer T. Transformer T is 1
A two-winding coil consisting of a secondary coil _L1 and a secondary coil _L2 is used. At both ends of the secondary coil _L2 ,
A series circuit of battery B and rectifier diode _D2 is connected. E is an AC power supply, and _D1 is a power rectification diode. Although half-wave rectification is performed here, full-wave rectification may also be performed. C ₁ is a capacitor for noise prevention, R ₁ is a resistor for starting oscillation, R ₂ is a base forward bias limiting resistor, R ₃ is a charging current limiting resistor,
_C2 is a capacitor for oscillation, _D3 is a light emitting diode for displaying power, and SW is a switch, which is inserted and connected between battery B and load L.

The charging control block includes a reference voltage generation block 1 that generates a reference voltage _V1 , a battery voltage comparison block 2 that compares the reference voltage _V1 and the voltage of battery B,
The oscillation starting current bypass block 3 bypasses the base current of the transistor Q to stop oscillation when the voltage of the battery B is higher than the reference voltage _V1 .

Now, when AC power supply E is half-wave (or full-wave) rectified by diode D ₁ and a base current is supplied to transistor Q through resistor R ₁ , collector current i _C starts flowing through primary coil L ₁ and 1 A voltage is generated in the next coil _L1 . This voltage generates a voltage in the secondary coil L ₂ that forward biases the transistor Q.
turns on rapidly and the collector current i _C is i _C =
(V _L1 /X ₁ ) increases by t. Note that V _L1 is the voltage applied to the primary coil L ₁ , and X ₁ is the inductance of the primary coil L ₁ . Then, i _C = h _FE・I _B (h _FE is the current amplification factor of transistor Q, I _B is the base current)
When the current increases to , the current change in the primary coil _L1 stops. Then, in an attempt to cause more current to flow, the polarity of the voltage generated in the primary coil _L1 is reversed, and this voltage is induced in the secondary coil _L2 as described above.
Transistor Q is reverse biased
is turned off. At this time, the voltage generated in the secondary coil _L2 is passed through the diode _D2 to charge the battery B. Similarly, a current is shunted to the light emitting diode _D3 , and the light emitting diode _D3 is turned on to indicate energization.

Here, the current i flowing through battery B is i=-
(V ₂ /X ₂ ) flows by t. Here, V ₂ is the primary coil L ₁ generated when transistor Q is turned off.
L ₂ /L ₁ of the voltage, and X ₂ is the inductance of the secondary coil L ₂ . Then, when the energy stored in the primary coil _L1 is released, oscillation starts again and continues in the same manner as described above. The resistor R ₃ controls the base potential of the transistor Q at a potential of R ₃ ×i _C by the current i _C that flows when the transistor Q is turned on, and adjusts the energy stored in the primary coil L ₁ for charging. It controls the current i. Figures 3a to 3d show the voltage and current waveforms of various parts during the above operation, and Figure 3a shows the collector-emitter voltage V _CE of the transistor Q,
The figure b shows the base-emitter voltage of the transistor Q, the figure c shows the collector current i _C of the transistor Q,
d in the figure is the charging current of battery B.

As battery B is charged in the manner described above, the voltage of battery B exhibits characteristics as shown in FIG. When rapidly charging battery B, unless charging is stopped at 80 to 100% of its capacity, battery B will enter the overcharge region, causing deterioration of battery B. Charging control is required to control this, and this is the charging control block shown in FIG. Generate a DC reference voltage V ₁ in the reference voltage generation block 1,
The battery voltage comparison block 2 compares the reference voltage V ₁ and the battery voltage V _B , and when V ₁ > V _B , the oscillation starting current bypass block 3 does not operate, and the above operation is repeated to charge the battery. The current continues to flow. Then, when V ₁ ≦ V _B , the oscillation starting current bypass block 3 operates, and the starting current of the transistor Q does not flow to the transistor Q, but is bypassed by the oscillation starting current bypass block 3, and the oscillation of the transistor Q is stopped. This prevents overcharging by stopping charging of battery B. In the circuit shown in FIG. 2, in the event of an abnormality when battery B becomes open, the oscillation starting current does not flow and oscillation does not start because transistor Q and battery B are connected in series. Therefore, the circuit will not be destroyed.

In this conventional example, by adopting the configuration shown in Fig. 2, the transformer T of the charging block is connected to the primary coil _L1 and the secondary coil, compared to the case shown in Fig. 1.
As 2 windings with L ₂ , less than 3 windings,
The transformer T can be easily manufactured, reliability is improved, and the transformer T can be made smaller and costs can be reduced. Furthermore, since the transformer T consists of only the primary coil _L1 and the secondary coil _L2 , the leakage inductance of the coil is reduced, the back electromotive force generated in the primary coil _L1 is reduced, and its energy is absorbed. The resistor and capacitor used in parallel with the primary coil for this purpose are no longer required, and transistors with low breakdown voltage can be used, making it possible to construct a smaller and cheaper circuit.

However, the circuit shown in FIG. 2 also has the following problems. That is, transistor Q
Due to the carrier accumulation effect when is on,
There is a problem that the transition time from on to off of the transistor Q is delayed, and the loss generated by the transistor Q is large.

In addition, when the switch SW was turned on, battery B was over-discharged, and when the battery voltage was low, the oscillation start voltage decreased, the charging current became extremely large, and the circuit generated heat. That is, in the conventional circuit shown in FIG. 2, oscillation begins only when the base current flows from the voltage rectified by the diode _D1 to the transistor Q through the resistor _R1 . The voltage is determined by the sum of the voltage V _B of battery B and the base-emitter voltage V _BE of transistor Q. If the oscillation start voltage is Vs, then Vs=V _B +V _BE , and V _BE is constant, but if the battery voltage V _B changes, the oscillation start voltage Vs also changes. Therefore, if the battery voltage V _B is low, the oscillation start voltage Vs will be lowered. In FIG. 2, if battery B is connected to load L and left as it is to be over-discharged, battery voltage V _B will become almost 0V. If it is charged in that state, Vs≒ _VBE , and the oscillation start voltage Vs will be lower than in normal conditions.

When the oscillation start voltage is low, the output of the oscillation circuit that can be extracted increases accordingly, and the rectifier diode
Exceeding the rating of D ₂ will lead to problems such as heat generation and destruction, and the time it takes for the battery voltage to return to the normal level of approximately 1.2 to 1.3V, or due to battery abnormality, may occur. When charging a battery, the above-mentioned problems occur, and furthermore, there is a problem that leads to the destruction of the charger.

[Object of the Invention] The present invention has been provided in view of the above-mentioned points.
The object of the present invention is to provide a quick charging circuit that prevents a drop in oscillation start voltage and eliminates an extreme increase in charging current.

[Disclosure of the Invention] Examples of the present invention will be described below with reference to the drawings. A specific circuit diagram is shown in Fig. 5, and 2 of the transformer T.
A series circuit consisting of a secondary coil L ₂ , a rectifier diode D ₂ and a battery B is connected in parallel to the base-emitter of transistor Q and a resistor R ₃ , and a charging current rectifying diode D ₄ is connected to the base-emitter of transistor Q. and resistor _R3 are connected in parallel to the circuit. Incidentally, members having the same reference numerals perform the same functions as in the case of FIG. 2. Further, the negative electrode of battery B is connected to the ground line of the entire circuit, and the emitter of transistor Q is connected to the ground line via resistor _R3 .

Here, when the transistor Q is turned off and the energy of the secondary coil L ₂ is rectified by the diodes D ₂ and _{D 4} to charge the battery B, the transistor Q is Since the base and emitter of the transistor are reverse biased, carrier accumulation when transistor Q is on can be quickly canceled out, so the transition time from transistor Q on to off is faster, and the loss that occurs in transistor Q is reduced. It has its advantages. Figure 6a shows the base-emitter voltage V _CE of transistor Q, and Figure 6 b shows the collector current of transistor Q. In the period t ₁ in the figure, a loss of V _CE ×i _C occurs. Therefore, the shorter this period (time) is, the better. Therefore, the loss of the transistor Q can be reduced by quickly canceling the carrier accumulation and quickly transitioning the transistor Q from on to off.

In addition, in Fig. 2, when the switch SW is turned on and battery B is over-discharged and the battery voltage V _B is low, the oscillation start voltage decreases and the charging current i becomes extremely large, causing heat generation in the circuit, etc. In the embodiment shown in FIG. 5, since the oscillation starting voltage is prevented from decreasing, there is no extreme increase in the charging current and it is safe.

The reason why the oscillation start voltage does not decrease even if the battery voltage V _B is low, that is, it is not affected by the battery voltage V _B will be explained below. In other words, in Fig. 5, when the input voltage is applied through the resistor _R1 , the internal resistance of battery B causes the diode to
Since the total voltage of D ₂ and the battery voltage V _B is greater than the base-emitter voltage V _BE of transistor Q, oscillation starts when the input voltage exceeds the base-emitter voltage V _BE of transistor Q. . In other words, the oscillation start voltage of the oscillation circuit is not affected by the battery voltage V _B. Also, when battery B is shorted, due to the forward voltage drop of diode _D2 ,
The base potential of transistor Q is kept low, and transistor Q does not start oscillating. Here, for example, if a shot key barrier diode with a low forward voltage drop is used as the rectifier diode _D2 , the forward voltage drop of this diode is equal to the base-emitter voltage _VBE of the bipolar transistor Q. Since it is smaller, the base potential of the transistor Q does not rise even when charging the battery B that has been shot, so the start of oscillation can be reliably prevented and safety can be maintained.

Here, in this embodiment, the diode D ₄ reverse biases between the base and emitter of the transistor _Q to quickly cancel out the carrier accumulation. The reverse bias is even smaller than in the example, and there is a risk that the effect of diode _D4 may be unclear. Therefore, in order to resolve this question, the following explanation will be given.

That is, in the case of the conventional example shown in FIG. 2, the reverse bias voltage of the transistor Q is the voltage between the diode _D2 and the battery voltage _VB , and the diode of the present invention
It becomes larger than D ₄ , and the transistor Q
The reverse bias between the base and emitter becomes deeper.
However, if the reverse bias is applied deeply, the forward bias current for turning on the next transistor Q must also be increased. Therefore, in the conventional example, the reverse bias voltage is affected by the battery voltage _VB .

Also, as the battery voltage V _B increases, the reverse bias voltage increases, but in the conventional example, the forward bias of the transistor Q is determined by the secondary coil L ₂ and the resistor R ₂ , and the battery voltage V _B Since the current is constant regardless of the current, the turn-on speed of the transistor Q becomes slow and the heat generation of the transistor Q becomes large. In the case of the present invention, the forward bias is determined by the secondary coil L ₂ and the resistor R ₂ and is constant as in the conventional example, and the reverse bias of the transistor Q is limited to a constant by the diode D ₄ as described above. For,
The problem is improved as described above without being affected by the battery voltage _VB .

Furthermore, as the number of charged batteries increases and the battery voltage V _B increases, the withstand voltage between the emitter and base of transistor Q (approximately 7V) will be exceeded during reverse bias. In this example, a protective element (diode) is required between the emitter and base of transistor Q. However, in the present invention, since the diode _D4 also serves this role, the charger can be manufactured at low cost.

Furthermore, in the conventional circuit shown in FIG. 2, the on-time of the transistor Q is determined by the secondary coil L2 and the _hFE of the transistor Q, as explained in the explanation of the operation of the conventional example, and this is determined by the secondary coil _L2 and hFE of the transistor Q. Although it is not affected by the battery voltage _VB , since the charging current i shown in FIG. 3d can be expressed as the following equation, the off-time toff is greatly influenced by a change in the battery voltage _VB .

i = - (V _B + V _D2 ) / L ₂ toff where V _B is the battery voltage, V _D2 is the forward drop voltage of diode D ₂ , L ₂ is the inductance of secondary coil L ₂ , and toff is the off-state of transistor Q. It's time. Here, for example, if a shot key barrier diode is used as diode _D2 , its forward drop voltage V _D2 is approximately 0.3 to 0.4V, and the charged voltage varies from 1.0 to 1.5V, so This has a large effect on the off-time toff of the transistor Q. Therefore, the oscillation frequency changes depending on the battery voltage V _B ,
Changes in the charging current used to charge the battery become large.

In the case of the present invention, the on time of the transistor Q is the same as in the conventional example. However, unlike the conventional example, the off time is not easily affected by the battery voltage V _B. That is, as is clear from FIG. 5, the charging current i
is expressed by the following equation.

i=−(V _B +V _D2 +V _D4 )/L ₂ toff where V _D4 is the forward voltage drop of the diode D ₄ . Therefore, from the above equation, since the diode _D4 is included, changes in the battery voltage _VB have less influence on the off time than in the conventional example, and changes in the battery voltage _VB have less effect on the charging current i. It has little impact.

Although the battery voltage V _B changes as it is charged, the charging current is less affected by this, and charging with a constant current is more stable against battery deterioration, shorting, and battery shorting in the case of multi-cell batteries. For this reason, if the diode _D4 of the present invention is provided, the influence of the battery voltage _VB on the charging current will be improved compared to the conventional example.

[Effects of the Invention] As described above, the present invention connects the primary coil of the oscillation transformer to the collector of the transistor, connects one end of the secondary coil to the base of the transistor, and connects the other end of the secondary coil to the base of the transistor. It is connected to the positive electrode of the battery to be charged via a rectifying element, and the negative electrode of the battery is connected to the ground line of the entire circuit, and the emitter of the transistor is connected to the ground line, so that when the transistor is turned off, the transistor's A charging block connects a diode between the base and emitter of the transistor to reverse bias the base and emitter, and when the voltage of the battery is detected and becomes higher than a predetermined voltage, the base current of the transistor is bypassed and charged. Since it is equipped with a charge control block that stops the oscillation of the block, the forward voltage drop of the diode reverse biases the base-emitter of the transistor, preventing carrier accumulation when the transistor is on. This has the effect that the transition time from on to off of the transistor becomes faster, and the loss generated in the transistor is reduced. In addition, the reverse bias diode reverse biases the transistor at a constant value without being affected by the battery voltage, unlike conventional examples where the reverse bias is deep.
The turn-on speed of the transistor is also faster, which prevents the transistor from generating heat.
Additionally, as the number of batteries increases and the battery voltage increases, the withstand voltage between the emitter and base of the transistor will be exceeded during reverse biasing. Conventionally, a corresponding protection element is required, but with the present invention, By using a diode to fulfill this role, it can be constructed at low cost. Moreover, when charging a battery, the battery, rectifying element, and diode are connected in series, and the battery voltage can be determined from the above charging current equation. By reducing changes in charging current due to changes in
Since it can be charged with a current close to a constant current, it is stable against battery deterioration, shorting, and battery shorting in the case of multiple cells. In addition, since the total voltage of the rectifying element and the battery is greater than the potential between the base and emitter of the transistor, oscillation starts when the input voltage exceeds the voltage between the base and emitter of the transistor, so the battery voltage Not affected by
Therefore, since the oscillation start voltage does not drop, there is no extreme increase in charging current as in the conventional case, and it is safe. Furthermore, since the negative terminal of the battery is connected to the ground line of the entire circuit, when performing charge control such as battery voltage detection, the ground line is shared, simplifying the circuit configuration. .

[Brief explanation of drawings]

Fig. 1 is a specific circuit diagram of a conventional example, Fig. 2 is a specific circuit diagram of another conventional example, Fig. 3 is an operational waveform diagram of the same as above,
FIG. 4 is a charging characteristic diagram of the same battery as above, FIG. 5 is a specific circuit diagram of an embodiment of the present invention, and FIG. 6 is an operation waveform diagram of the same as above. T is a transformer, L ₁ is a primary coil, L ₂ is a secondary coil, Q is a transistor, B is a battery, and D ₄ is a diode.

Claims (1)

[Claims] 1 Connect the primary coil of the oscillation transformer to the collector of the transistor, connect one end of the secondary coil to the base of the transistor, and connect the other end of the secondary coil to the positive electrode of the battery to be charged via a rectifier. At the same time, the negative electrode of the battery is connected to the ground line of the entire circuit, the emitter of the transistor is connected to the ground line, and a diode is connected to the transistor, which reverse biases between the base and emitter of the transistor when the transistor is off. A charging block connected between the base and emitter of the battery, and a charging control block that detects the voltage of the battery and, when the voltage becomes higher than a predetermined voltage, bypasses the base current of the transistor and stops the oscillation of the charging block. A quick charging circuit made up of