JPH0755029B2 - Charger - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a charger using a switching regulator circuit having a step-up transformer.

BACKGROUND ART Conventionally, there is a charger of this type shown in FIG. 2, which has a series circuit of a primary winding L ₁ of a step-up transformer T and a switching transistor Q ₁ at both ends of a DC power source E. Connect a series circuit of a feedback winding L ₃ , which is the tertiary winding of the step-up transformer T, a capacitor C ₃ , and a base resistance R ₃ between the base and emitter of this switching transistor Q ₁ , and supply the DC power supply E. Then, the switching transistor Q ₁ is started by the starting resistor R ₁ and the current flowing in the primary winding L ₁ is induced in the feedback winding L ₃ at this time to perform positive feedback to the switching transistor Q ₁ for switching. Transistor Q ₁
Of the step-up transformer T by the current flowing through the primary winding L _{1 due} to the oscillation of the switching transistor Q _1.
A voltage is induced in the secondary winding L ₂ , and this induced voltage is applied to the diode D ₁
The DC voltage is obtained by half-wave rectification at and smoothed by the capacitor C ₁ and voltage converted. Here, in the switching regulator circuit 1, the energy stored in the secondary winding L ₂ is discharged to the storage battery B ₁ when the switching transistor Q ₁ is turned off. Further, in the conventional example, the output opening protection circuit 3 for preventing the output of the switching regulator circuit 1 from abnormally rising when the storage battery B ₁ is disconnected, and the charging for preventing the storage battery B _{1 from} being overcharged And a control circuit 2 '. The output open protection circuit 3 is specifically a zener diode ZD and a capacitor for the output of the switching regulator circuit 1.
Connect a series circuit of a C _2, the switching transistor
It is formed by connecting the base of the transistor Q ₂ connected between the base and emitter of Q _{1 to} the connection point of the zener diode ZD and the capacitor C ₂ . In operation, when the storage battery B ₁ is disconnected and the output of the switching regulator circuit 1 is in a no-load state, the voltage between the open terminals rises abnormally. When the voltage between the open terminals rises above the Zener voltage of the Zener diode ZD, the capacitor C ₂ is charged, and when the voltage across the capacitor C ₂ rises above the threshold of the transistor Q ₃ , the transistor Q ₃ becomes conductive. by, in which it stops the switching of the switching transistor Q ₁ by bypassing the base current supplied by the feedback winding L ₃ to the switching transistor Q _1. Therefore, the switching regulator circuit 1 output is not generated due to the stop of the switching of the switching transistor Q ₁ . The charge control circuit 2'concretely includes a comparator CP that compares the output voltage of the switching regulator circuit 1 with a reference voltage, and a transistor Q ₂ that short-circuits the base and emitter of the switching transistor Q _{1 with} the output of this comparator CP. Since the charge control circuit 2'detects the output voltage of the switching regulator circuit 1, the power supply voltage of the comparator CP needs to be higher than the output of the switching regulator circuit 1. Therefore the 4 winding L ₄ provided in the step-up transformer T, this 4 winding L ₄
The boosted voltage was obtained at and the voltage that was rectified and smoothed by diode D ₂ and capacitor C ₅ was used as the power supply. The operation of the charging control circuit 2 ', the comparator CP output when rises above a predetermined voltage determined by the switching regulator circuit 1 outputs the reference voltage goes high, blocking of the switching transistor Q ₁ by conducting the transistor Q ₂ By shortening the ON period of the switching transistor Q ₁ by decreasing the charging speed, the charging current flowing in the storage battery B ₁ is reduced,
This is to prevent the storage battery B ₁ from deteriorating due to heat generation.

However, in the above-mentioned charger, since the quaternary winding L ₄ is required for the charge control circuit 2 ′, the size of the step-up transformer T becomes large, which leads to an increase in the size of the device and the charge control circuit 2 ′. It is necessary to include both the output opening protection circuit 3 and there is a problem that the circuit configuration becomes complicated.

[Object of the Invention] The present invention has been tried in view of the above points, and an object of the present invention is to share a charging control circuit and an output opening protection circuit to simplify the circuit configuration and reduce the size of the device. It is to provide a charger that can realize the following.

DISCLOSURE OF THE INVENTION (Embodiment) FIG. 1 is a diagram showing an embodiment of the present invention. In this embodiment, the output of a switching regulator circuit 1 similar to that of a conventional example includes resistors R ₄ and R _5. The voltage control circuit 4 is connected and the transistor Q ₂ is controlled by the output of the comparator CP which compares the voltage at the voltage dividing point of the resistors R ₄ and R ₅ of the voltage dividing circuit 4 with the reference voltage. The charging control circuit 2 ′ and the output opening protection circuit 3 are also provided to provide the charging control circuit 2. Specifically, a diode D ₄ is connected between the voltage dividing circuit 4 and the storage battery B ₁ . This diode D ₄ is a storage battery
A diode for preventing reverse flow for B ₁ is to prevent the charges charged in the storage battery B ₁ is being discharged through the resistor R _4, R ₅ of the voltage dividing circuit 4 when it is charged above a predetermined value is there. Also, a capacitor C ₄ is connected to both ends of the resistor R ₅ of the voltage dividing circuit 4, and the comparator CP may malfunction or may not operate stably due to noise such as ripple components contained in the output of the switching regulator circuit 1. To prevent that. Further, the power supply of the comparator CP uses the voltage of the DC power supply E because the charge control circuit 2 monitors the output of the voltage dividing circuit 4 to detect an overcharged state and the like, so that it is not necessary to increase the power supply voltage. .

The operation will be described below. At the same time that the voltage boosted by the switching regulator circuit 1 is applied to both ends of the storage battery B ₁ , this voltage is also applied to the voltage dividing circuit 4. Therefore, the voltage divided by the resistors R ₄ and R _{5 of the} voltage dividing circuit 4 is monitored by the comparator CP, and when the divided voltage becomes higher than the reference value, the output of the comparator CP becomes high level and the transistor Q _{By making 2} conductive, the base current of the switching transistor Q ₁ is bypassed, and the switching transistor Q ₁ is cut off to perform switching control of the switching transistor Q ₁ .

Now, assuming that the storage battery B ₁ is connected to the output of the switching regulator circuit 1 to be charged, and if the storage battery B ₁ has almost reached the fully charged state, the voltage dividing circuit 4 and the switching control circuit 2 operate as described above. the base current of the switching transistor Q ₁ are bypassed, the switching transistor Q ₁
Of the switching regulator circuit 1 is made faster than the switching cycle of the normal switching regulator circuit 1. For this reason, the energy stored in the secondary winding L ₂ of the step-up transformer T becomes small, and the charging current of the storage battery B ₁ also becomes small. Therefore,
The storage battery B ₁ is no longer overcharged.

Next, with the storage battery B ₁ disconnected from the output of the switching regulator circuit 1, the switching regulator circuit 1
Is operating, the output of the switching regulator circuit 1 is detected by the voltage dividing circuit 4 in the same manner as above, and since the storage battery B ₁ is not connected to the output of the switching regulator circuit 1 this time, the reference voltage is constantly set to The exceeded divided voltage is applied to the comparator CP. Therefore, the output of the comparator CP maintains the high level state, and the transistor Q ₂ maintains the conductive state, so that the switching of the switching transistor Q ₁ is completely stopped. Therefore, it is possible to prevent the output voltage of the switching regulator circuit 1 from rising abnormally and damaging the circuit components. By thus monitoring the voltage obtained by dividing the output voltage of the switching regulator circuit 1 by the voltage dividing circuit 4, for example, the battery voltage is
When the power supply of the comparator is 10V at 12V, 1 / in the voltage divider circuit 4
When the voltage is divided into 2, the reference voltage can be set to 6V, and it is not necessary to further increase the voltage voltage of the comparator CP. Therefore, it is not necessary to provide the step-up transformer T with the quaternary winding L ₄ . Further, by using the charge control circuit 2 that also performs the charge control and the output opening protection operation, the circuit configuration can be simplified, which is effective for downsizing the device and reducing the cost.

Incidentally, in the conventional example of FIG. 2, when shared with output open protection circuit charging control circuit 2 ', the battery B ₁ is disconnected, the voltage between the open terminals are increased in the output of the comparator CP, the transistor Q ₂ conducts, turning off transistor Q ₁ and stopping oscillation. But the comparator
Since the power supply of CP is taken from the fourth winding L ₄ , the power supply of the comparator CP is lost when the oscillation stops. For this reason,
The output of the comparator CP disappears and the oscillation restarts. Then, when the operation of the switching regulator circuit 1 is started, the voltage between the open terminals rises, and the above operation is repeated. Therefore, the function of the output opening protection is not fulfilled. Oscillation and stop are repeated even in the case of charge control. In this case, the battery is intermittently charged to be supplemented, but when the charging current is not large, there is little risk of overcharging.

[Advantages of the Invention] As described above, the present invention turns on and off the switching element connected in series with the primary winding of the step-up transformer in the DC power supply to rectify the step-up voltage induced in the secondary winding of the step-up transformer. A switching regulator circuit that obtains an output that smoothes and charges a storage battery, a voltage divider circuit that includes a resistor that divides the output voltage of the switching regulator circuit, and a switching element of the switching regulator circuit that compares the voltage divider circuit output with a reference voltage. The charging control circuit that controls the switching of the charging control circuit is obtained directly from the DC power supply, so the voltage obtained by dividing the output voltage of the switching regulator circuit by the voltage dividing circuit is monitored by switching control. Therefore, if the voltage dividing ratio of the voltage dividing circuit is properly selected, the voltage of the charging control circuit must be made even higher. Since there is no need to obtain the power supply voltage of the charge control circuit by providing a quaternary winding in the step-up transformer as in the conventional case, and the charge control circuit has both charge control and output opening protection operation, The structure can be simplified, and an effect is obtained that is effective in downsizing the device and reducing the cost.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram showing a conventional example. 1 is a switching regulator circuit, 2 is a charge control circuit, 4 is a voltage dividing circuit, E is a DC power supply, T is a step-up transformer,
L ₁ is a primary winding, L ₂ is a secondary winding, Q ₁ is a switching transistor, Q ₂ is a transistor, CP is a comparator, D ₁ and D ₄
Is a diode, C ₁ and C ₄ are capacitors, and R ₄ and R ₅ are resistors.

Claims (3)

[Claims] An output for charging a storage battery by rectifying and smoothing a boost voltage induced in a secondary winding of a step-up transformer by turning on and off a switching element connected in series to a DC power source and a primary winding of the step-up transformer. And a voltage divider circuit consisting of a resistor that divides the output voltage of the switching regulator circuit, and a charge control that controls the switching of the switching element of the switching regulator circuit by comparing the output of the voltage divider circuit with a reference voltage. And a circuit, wherein the charging control circuit is directly powered by a DC power source. 2. The charger according to claim 1, wherein a diode for preventing backflow is inserted between the voltage dividing circuit and the storage battery. 3. The charger according to claim 1, wherein a capacitor is inserted between the voltage dividing point of the voltage dividing circuit and the negative electrode of the storage battery.