JPH0576254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a charging circuit including an inverter circuit.

[Background Art] Conventionally, this type of charging circuit equipped with an inverter circuit has a switching element as shown in FIG.
Q ₁ , primary winding L ₁ , secondary winding L ₂ and feedback winding
An inverter circuit 1 that oscillates at a predetermined frequency is configured by a transformer T equipped with L ₃ , a diode D ₁ and resistors R ₁ and R ₂ , and the output of the secondary winding L ₂ is rectified by a rectifier circuit 2. In addition to charging a storage battery 3 such as a CD battery, an automatic voltage oscillation control circuit 4 that varies the ON time of the switching element _Q1 according to the power supply voltage is provided to keep the charging current constant. Here, the voltage detection control circuit 6
When the battery voltage is detected and the battery voltage reaches a predetermined charge completion voltage, a charge end signal is output, and when this charge end signal is input, the automatic voltage oscillation control circuit 4 starts charging. Control is performed such that the ON time of switching element _Q1 is shortened so as to reduce the current, thereby transitioning to trickle charging mode to prevent overcharging. Further, the inverter circuit 1 is applied with a DC power source obtained by rectifying the AC power source AC in a rectifier circuit 7, and the voltage detection control circuit 6 is connected to a transformer T.
DC power is supplied by rectifying and smoothing the voltage induced in the power supply winding _L4 wound in the rectifying and smoothing circuit 5.

By the way, the automatic voltage oscillation control circuit 4 requires a certain amount of time (for example, the time for charging the smoothing capacitor of the constant voltage circuit provided on the power input side) for its operation to stabilize after power is supplied. be. Therefore, when current flows through switching element _Q1 of inverter circuit 1 at the same time as the power is turned on,
Since normal control is not possible until the automatic voltage oscillation control circuit 4 operates, the
A problem arises in that a large current I flows through the switching element Q 1 from t ₀ to a time t ₁ when the automatic voltage oscillation control circuit 4 operates normally, and a large amount of stress is applied to the switching element Q ₁ . In particular, when rapid charging is being performed, the charging current is large, so a greater stress is applied and the switching element _Q1 may be destroyed. Therefore, conventionally, even when the power is turned on, the switching element _Q1 is not turned on until the automatic voltage oscillation control circuit 4 operates.
A delay power supply circuit 10 is provided for turning on the switching element _Q1 after the automatic voltage oscillation control circuit 4 is supplied with an operable power. This delayed power supply circuit 10 is formed of a Zener diode ZD, a transistor Q ₄ , a diode D ₂ , and resistors R ₇ and R ₅ , and as shown in FIG.
The switching element _Q1 is not turned on for a certain period of time from _t0 to _{t2 '} (where _t1 < _t2 ').
However, even in such a conventional example, in the case of automatic voltage switching, for example,
If the turns ratio of the primary winding L ₁ and the feedback winding L ₃ of the transformer T is set to match AC100V, there is a problem that the current limiting resistor R ₁ will generate more heat at AC240V; When the turns ratio of the transformer T is set, the number of turns of the feedback winding _L3 decreases, resulting in insufficient energy (feedback energy) generated at 100 VAC, and current is supplied from the delayed power supply circuit 10, so the current limiting resistor is _R7 ,
There was a problem that the _R6 generated a lot of heat.

[Object of the Invention] The present invention has been made in view of the above points, and its object is to be able to reduce the stress applied to the switching element when the power is turned on, and to reduce the heat generated by the stress reduction means. The object of the present invention is to provide a charging circuit that does not cause this problem.

[Disclosure of the Invention] (Structure) The present invention includes a switching element, a primary winding, and a secondary winding.
A transformer equipped with a secondary winding and a feedback winding constitutes an inverter circuit that oscillates at a predetermined frequency.
In a charging circuit that rectifies the output of the next winding to charge the storage battery, and also includes an automatic voltage oscillation control circuit that varies the ON time of the switching element according to the power supply voltage to keep the charging current constant. a detection means for detecting the end of charging; a power supply winding for the control switch circuit wound around the transformer; and a voltage induced in the power supply winding when the switching element is turned off is smoothed to operate the control switch circuit. a rectifying and smoothing circuit that obtains a signal; and when receiving a charging end signal from the detection means, or in a non-operating state where no power is supplied from the rectifying and smoothing circuit, the current to the switching element is reduced, and power is supplied from the rectifying and smoothing circuit. A control switch circuit that increases the current in a certain operating state is provided, and when the switching element is turned on immediately after power is turned on, the rectifying and smoothing circuit does not supply power and the control switch circuit is placed in a non-operating state. By reducing the current to the switching element, it is possible to reduce the stress applied to the switching element when the power is turned on, and to provide a charging circuit that does not generate heat due to the stress reduction means.

(Example) Figures 1a and 1b show an example of the present invention.
Switching element _Q1 , primary winding _L1 , secondary winding
_L2 and a transformer T equipped with a feedback winding _L3 constitute an inverter circuit 1 that oscillates at a predetermined frequency, and rectifies the output of the secondary winding _L2 to fill a storage battery 3, and also In a charging circuit similar to the conventional example in which an automatic voltage oscillation control circuit 4 for varying the on-time of the switching element _Q1 is provided to keep the charging current constant, the current to the switching element _Q1 is reduced. When the control switch circuit 7, the power supply winding _L4 for the control switch circuit wound around the transformer T (wound in the opposite direction to the primary winding _L1 ), and the switching element _Q1 are turned off, A rectifying and smoothing circuit 5 smoothes the voltage induced in the power supply winding _L4 to obtain an operating signal for the control switch circuit 4, and a detection means (voltage detection control circuit 6 and timer circuit 8) that detects the completion of charging of the storage battery 3. control switching circuit 7 which reduces the current to the switching element _Q1 when receiving a charging end signal from ) and in a specific operating state without power supply from the rectifying and smoothing circuit 5, and increases the current in an operating state. When the switching element _Q1 is turned on immediately after the power is turned on, the rectifying and smoothing circuit 5 does not supply power, and the control switch circuit 7 is brought into a non-operating state, thereby reducing the current to the switching element _Q1 . That is. In the embodiment, the switching element _Q1 is formed of an FET, and the rectifying and smoothing circuit 5 includes a diode _D0 , a smoothing capacitor _C0 ,
It is formed by a constant voltage circuit VR. Further, the control switch circuit 7 is formed of transistors Q ₂ and Q ₃ , a photocoupler PC, and resistors R ₄ and R ₅ . End signal (H→L)
and the time-up signal (H→L) output from the timer circuit 8. The voltage detection control circuit 6 prevents overcharging based on the battery voltage, and the timer circuit 8 This is to prevent overcharging, where rapid charging is stopped after a certain period of time. That is, when the voltage detection control circuit 6 outputs a charge end signal or the timer circuit 8 outputs a time-up signal, the transistor _Q3 turns off and the photocoupler PC
Transistor Q ₂ is turned off via Q 2 , disconnecting resistor R ₄ which was connected in parallel with resistor R ₂ in normal fast charging mode, and switching from fast charging mode to trickle charging mode to prevent overcharging. The government is beginning to aim to achieve this goal.

The operation of the embodiment will be described below. now,
As shown in Fig. 2, when the power is turned on at time _t0 , a current flows through the switching element _Q1 through the primary winding _L1 of the transformer T and the resistor _R2 . The voltage induced in L ₄ is
Since the signal is blocked by the diode _D0 in the rectifying and smoothing circuit 5 and is not used as an operating signal, the control switch circuit 7 is in a non-operating state. Therefore, immediately after the power is turned on, the switching element
When Q ₁ is on, transistor Q ₂ of control switch circuit 7 remains off, so
The resistor _R4 and the resistor _R2 are not connected in parallel but are separated, and the current I flowing through the switching element _Q1 is in the trickle charging mode as shown in the section _t0 to _t2 in Fig. 2. The current is small, and the switching element _Q1 is not destroyed even if the automatic voltage oscillation control circuit 4 is not operating normally. In other words, the present invention is directed to a device in which the operation of the automatic voltage oscillation control circuit 4 is stabilized during the period in which the switching element _Q1 is turned on and then turned off once after power is supplied.For example, the time for the circuit to stabilize is t _x Then, set t ₂ so that t _x t ₂ . That is, by changing the capacitor C ₀ shown in FIG. 1b of the rectifying and smoothing circuit 5, t ₂ is set. In the method of creating the power supply for the automatic voltage oscillation control circuit 4, it may be stabilized after one on/off time, or it may take two or three times. However, it is unlikely that it is already stable when it is first turned on. In order to achieve stable oscillation faster, t ₂ is made as small as possible.

Now, immediately after the power is turned on, the automatic voltage oscillation control circuit 4
is not operating stably as shown in Figure 3d, and when switching element _Q1 is turned on in this unstable state, if resistor _R4 is not disconnected from resistor _R2 , the broken line in Figure 3b As shown, the current flowing through the switching element _Q1 increases, but in the present invention, when the switching element _Q1 is on, no voltage is induced from the winding _L4 of the transformer T, as shown in FIG. 3a. Therefore, power is not supplied to the control switch circuit 7, and the transistor
Q ₂ remains off. In other words, since the resistor R ₂ is not short-circuited, the current flowing through the switching element Q ₁ is larger than the current during trickle charging due to the increased input voltage, but smaller than the current during normal charging.

And when switching element _Q1 is off,
An induced voltage is generated from the winding _L4 of the transformer T as shown in FIG. 3a, and the induced voltage is rectified and smoothed by the rectifier and smoothing circuit 5 as shown in FIG. Ru. As a result, transistor Q ₂ turns on, shorting out resistor R ₂ . In other words, the transistor Q ₂ starts turning on after the first switching element Q ₁ turns off, so when the power is turned on when the automatic voltage oscillation control circuit 4 is in an unstable operating state, a large No current flows through the switching element _Q1 . When switching element Q ₁ is turned on for the second time, automatic voltage oscillation control circuit 4 is already in a stable operating state, so transistor Q ₂ of control switch circuit 7 is turned on by power supply from rectifier and smoothing circuit 5, and resistor Even if _R2 is short-circuited, the automatic voltage oscillation control circuit 4 is stable in the switching element _Q1 , so that a current during normal charging will flow through the switching element Q1.

Incidentally, FIG. 3d shows the voltage across the switching element _Q1 . In addition, in this case, stress is prevented by not supplying power to the control switch circuit 7 forming the stress prevention means, so that heat generation by the stress prevention means does not occur as in the conventional example. It's getting old.

On the other hand, the voltage induced in the power supply winding L ₄ when the switching element Q ₁ is turned off is rectified and smoothed by the rectification and smoothing circuit 5 and supplied as an operating signal to the control switch circuit 7, which operates the control switch circuit 7. Then, transistor _Q2 is turned on (if the charging end signal is not output), so resistor _R4 is connected in parallel with resistor _R2 , and normal charging (quick charging) occurs.
will be carried out. In other words, at this time, the automatic voltage oscillation control circuit 4 is in a stable operating state, so the input voltage is constant, and the switching element is connected with the resistor _R2 and the resistor _R4 connected in parallel.
Even if Q ₁ is turned on, the input power to switching element Q ₁ does not become abnormally large, so the switching element
When _Q1 is turned off, the output voltage induced in the transformer T also becomes a stable voltage, and the charging current also becomes a normal current value. Next, when the battery voltage reaches the predetermined charge completion voltage due to rapid charging, the voltage detection control circuit 6 outputs the charge completion signal (L level) as described above, and the transistor _Q3 is turned off to turn off the photocoupler. Transistor Q ₂ , controlled via the PC, is turned off and resistor R ₄ is disconnected to switch from fast charging mode to trickle charging mode to prevent overcharging. In addition, even if the voltage detection control circuit 6 does not operate normally due to changes in battery characteristics, control is performed when a time-up signal is obtained from the timer circuit 8, which performs a time-limited operation from the time the power is turned on. Since the switch circuit 7 operates and stops rapid charging after a certain period of time, deterioration of the storage battery 3 can be prevented.

[Effects of the Invention] As described above, the present invention includes a switching element,
A transformer equipped with a primary winding, a secondary winding, and a feedback winding constitutes an inverter circuit that oscillates at a predetermined frequency, and rectifies the output of the secondary winding to charge the storage battery. The charging circuit is provided with an automatic voltage oscillation control circuit that varies the on-time of the switching element to keep the charging current constant, and the charging circuit includes a detection means for detecting the end of charging of the storage battery, and a control switch wound around the transformer. a power supply winding for the circuit, and a rectification and smoothing circuit that smooths the voltage induced in the power supply winding when the switching element is turned off to obtain an operating signal for the control switch circuit;
When receiving a charging end signal from the detection means or in a non-operating state with no power supplied from the rectifying and smoothing circuit, the current to the switching element is reduced, and in an operating state with power supplied from the rectifying and smoothing circuit, the current is reduced. When the switching element is turned on immediately after the power is turned on, the rectifying and smoothing circuit does not supply power, and the control switch circuit is brought into a non-operating state, thereby reducing the current to the switching element. Therefore, the stress applied to the switching element when the power is turned on can be reduced.
Moreover, the operation of the control switch circuit is controlled by the output of the power supply winding wound around the transformer to reduce stress, making it possible to prevent heat generation from occurring due to the stress reduction means as in the conventional case. There is an effect.

[Brief explanation of the drawing]

Figure 1a is a circuit diagram of an embodiment of the present invention, Figure 1b
is a circuit diagram of the same main part as above, Fig. 2 is a diagram explaining the operation of the same as above, Fig. 3 is a timing chart for explaining the operation of the same as above, Fig. 4 is a circuit diagram of the conventional example, and Figs. 5 and 6 are the same as above. It is an operation explanatory diagram. 1 is an inverter circuit, 2 is a rectifier circuit, 3 is a storage battery, 4 is an automatic voltage oscillation control circuit, 5 is a rectifier smoothing circuit, 7 is a control switch circuit, Q ₁ is a switching element, T is a transformer, L ₁ , L ₂ , L ₃ and L ₄ are windings.

Claims (1)

[Claims] 1. An inverter circuit that oscillates at a predetermined frequency is configured by a switching element and a transformer including a primary winding, a secondary winding, and a feedback winding, and rectifies the output of the secondary winding. Detection means for detecting the end of charging of the storage battery in a charging circuit that charges the storage battery and is provided with an automatic voltage oscillation control circuit that varies the ON time of the switching element according to the power supply voltage to keep the charging current constant. and a power supply winding for a control switch circuit wound around the transformer;
a rectifier and smoothing circuit that smooths the voltage induced in the power supply winding when the switching element is turned off to obtain an operating signal for the control switch circuit; A control switch circuit is provided that reduces the current to the switching element in a non-operating state where there is no power supply, and increases the current in an operating state where power is supplied from a rectifier and smoothing circuit, so that the switching element is turned on immediately after the power is turned on. In the charging circuit, the rectifying and smoothing circuit does not supply power and the control switch circuit is put into a non-operating state to reduce the current flowing to the switching element. 2. The charging circuit according to claim 1, wherein the switching element is formed of an FET.