JPH08163791A - Charging circuit - Google Patents

Abstract

PURPOSE: To provide a charging circuit capable of reducing the variation of a charging time even when there is variation in the characteristics of a control switch element. CONSTITUTION: A charging circuit has an A/D conversion circuit 10 for converting AC voltage into DC voltage, a transformer 13 with a primary coil 13N, to which the DC voltage of the A/D convesion circuit 10 is applied, a secondary side coil 13M, to which a battery charger 19 is connected, and an auxiliary coil 13H, a switching element Q1 for allowing a current to flow through the primary coil 13N and a transistor Q2 for turning the switching element Q1 off. A transistor Q3 is connected to the transistor Q2 in a cascade manner, and the base potential of the switching element Q1 is lowered by the conduction of the transistor Q3 and the conduction of the switching element Q1 is cut off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit used for, for example, an electric shaver.

[0002]

2. Description of the Related Art Conventionally, a charging circuit shown in FIG. 2 has been known as a charging circuit used for an electric shaver.

In FIG. 2, reference numeral 1 is a rectifier for AC voltage.
Rectifying circuit consisting of two diodes, 2 is a smoothing capacitor for converting the voltage rectified by the rectifying circuit 1 into a DC voltage,
3 is a transformer. One end 3Na of the primary coil 3N of the transformer 3 is connected to the plus terminal 2a of the smoothing capacitor 2, and the other end 3Nb of the primary coil 3N is connected to the collector of a switching element Q1 formed of a field effect transistor. The emitter of the switching element Q1 is connected to the minus terminal 2b of the smoothing capacitor 2 via the resistor 4.

Base (gate) of switching element Q1
Is connected to the collector of the transistor (control switch element) Q2, is also connected to one end 3Na of the primary coil 3N of the transformer 3 via the resistor 6, and is also the auxiliary coil 3H of the transformer 3 via the capacitor 7 and the resistor 8.
Connected to the terminal. The base of the transistor Q2 is connected to the emitter of the switching element Q1, and the emitter of the transistor Q2 is connected to the minus terminal 2b of the smoothing capacitor 2.

On the other hand, a rechargeable battery 9 is connected to the secondary coil 3M of the transformer 3 via a diode D.

[0006] Now, when a DC voltage is applied to the primary coil 3N of the transformer 3 by the smoothing capacitor 2, a positive potential is generated at the terminal 3Ha of the auxiliary coil 3H, and this potential is generated via the resistor 8 and the capacitor 7 as a switching element. Q
Applied to the base of 1. As a result, as shown in FIG. 3, the switching element Q1 becomes conductive and current starts to flow.

Since the primary coil 3N and the auxiliary coil 3H are oriented in the same direction, positive feedback is applied to the terminal 3Na of the primary coil 3N, and the current flowing through the switching element Q1 increases.

As the current of the switching element Q1 increases, the voltage generated in the resistor 4 also increases, and when this voltage exceeds 0.6 [V], the control transistor Q2 becomes conductive. The conduction of the transistor Q2 lowers the base potential of the switching element Q1 and the current flowing through the switching element Q1 decreases. This decrease further lowers the base potential of the switching element Q1 by the positive feedback action of the transformer 3 and cuts off the switching element Q1.

When the switching element Q1 is cut off, a counter electromotive voltage is generated in the secondary coil 3M of the transformer 3 and a current (charging current) I flows. When this current I has finished flowing, the switching element Q1 is turned on in the same manner as above. Then, these operations are repeated and the rechargeable battery 9 is charged.

Here, if the primary current flowing through the primary coil 3N of the transformer 3 is a flyback type, the power supply voltage (voltage of the smoothing capacitor 2) and the primary coil 3N of the transformer 3 are used.
It rises with a slope determined by the inductance of. When the transistor Q2 is a junction type, the collector potential of the transistor Q2 is equal to the base potential of the transistor Q1 and has a value obtained by adding 0.6 [V] to the emitter potential of the transistor Q1.

Further, the emitter potential of the switching element Q1 changes with the voltage generated in the resistor 4, and therefore has a waveform similar to the waveform of the emitter current of the switching element Q1. Since the emitter current is the sum of the collector current and the base current that increase linearly, it changes depending on the voltage applied to the primary coil 3N of the transformer 3 and the induced voltage of the auxiliary coil 3H.

[0012]

In such a charging circuit, the base potential of the switching element Q1 is controlled by turning on / off the transistor Q2, thereby controlling the on / off of the switching element Q1. So
Due to variations in the characteristics of the transistor Q2, the conduction time of the switching element Q1 greatly differs.

That is, the transistor Q2 has a junction capacitance between the terminals, and in a transistor having a grounded-emitter operation, the direction of change in collector voltage is opposite to the direction of change in base potential. Therefore, the apparent junction capacitance between the emitter and the base (mirror effect) increases. This depends on the current amplification factor of the control transistor Q2. The increase in the junction capacitance causes the speed of the switching operation of the switching element Q1 to decrease.

This is because when the junction capacitance increases, this junction capacitance can be regarded as a battery. Therefore, even if the transistor Q2 becomes conductive, the collector potential does not immediately drop, and as a result, the transistor Q2 becomes conductive. Therefore, it takes a long time to turn off the switching element Q1.

For this reason, even if the same type of transistor Q2 is used, the variation in the current amplification factor is large, so that the switching operation of the switching element Q1 varies from product to product, and a large difference in switching speed occurs between products. It will be.

This is because the transistor Q2 detects the voltage of the resistor 4 which rises linearly, and therefore the difference in the switching operation time is caused by the primary coil 3N of the transformer 3.
The difference is the primary current that flows through. This is equal to the difference in the average value of the primary current, and increases the variation of the secondary current flowing in the secondary coil 3M of the transformer 3, that is, the charging current I, which causes a problem that the charging time varies from product to product. there were.

In particular, the transistor Q2 has a MOS-FET
When using, the gate current hardly flows, and since the MOS-FET is driven by the voltage between the gate and the source, the change in the collector potential of the transistor Q2 is larger than that when using the junction type transistor, so that the mirror effect is obtained. It becomes bigger and this problem becomes more prominent.

The present invention has been made in view of the above problems, and an object thereof is to provide a charging circuit capable of reducing the variation in charging time even if the characteristics of the control switching element vary. It is in.

[0019]

In order to achieve the above object, the present invention comprises an AC / DC converter circuit for converting an AC voltage into a DC voltage, and a primary coil to which the DC voltage of the AC / DC converter circuit is applied. The transformer includes a secondary coil to which a battery is connected, an auxiliary coil, a switching element for supplying a current to the primary coil, and a first control switch element for turning off the switching element. The voltage generated in the coil is applied to the gate of the switching element to make the switching element conductive, and after a lapse of a predetermined time from this conduction, the first control switch element is made conductive to lower the gate potential and cut off the conduction of the switching element. By repeating these operations, an intermittent current is caused to flow in the primary winding, and the rechargeable battery is generated by the voltage generated in the secondary coil. A charging circuit for charging, wherein a second control switch element is cascade-connected to the first control switch element, and conduction of the second control switch element lowers a gate potential of the switching element to cut conduction of the switching element. It is characterized by turning off.

[0020]

According to the present invention, the second control switching element is cascade-connected to the first control switching element, and the conduction of the second control switching element lowers the gate potential of the switching element to cut off the conduction of the switching element. Therefore, the mirror effect of the first control switch element can be suppressed, and as a result, the conduction time of the switching element can be made constant even if the characteristics of the first control switch element vary.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a charging circuit for an electric shaver according to the present invention will be described below with reference to the drawings.

In FIG. 1, 11 is a rectifying circuit composed of four diodes for rectifying an AC voltage, and 12 is a rectifying circuit 1.
It is a smoothing capacitor that converts the voltage rectified by 1 into a DC voltage. Then, the rectifying circuit 11 and the smoothing capacitor 1
An AC / DC conversion circuit for converting an AC voltage into a DC voltage is constituted by 2 and.

Reference numeral 13 is a transformer, and this transformer 13
One end 13Na of the primary coil 13N is a smoothing capacitor 1
The other end 13Nb of the primary coil 13N is connected to the positive terminal 12a of the second switching element 12a, and is connected to the collector of the switching element Q1 formed of a field effect transistor. On the other hand, the rechargeable battery 19 is connected to the secondary coil 13M of the transformer 13 via the diode D.

The emitter of the switching element Q1 is a resistor 1
4 is connected to the negative terminal 12b of the smoothing capacitor 12. The base (gate) of the switching element Q1 is connected to the primary coil 13 of the transformer 13 via the resistor 16.
It is connected to one end 13Na of N. The emitter of the switching element Q1 is connected to the base of a transistor (first control switch element) Q2, and the emitter of the transistor Q2 is connected to the negative terminal 12b of the smoothing capacitor 12.

The collector of the transistor Q2 is connected to the emitter of the transistor (second control switch element) Q3, and the collector of the transistor Q3 is connected to the base of the switching element Q1. The base of the transistor Q3 is the smoothing capacitor 1 via the Zener diode 20.
It is connected to the second negative terminal 12b. That is,
The transistor Q2 and the transistor Q3 are cascade-connected.

On the other hand, the series circuit of the diode 21 and the capacitor 22 is connected between the terminals 13Ha and 13Hb of the auxiliary coil 13H of the transformer 13, and the diode 21 and the capacitor 22 are connected to the base of the transistor Q3 via the resistor 25. Has been done. The terminal 13Hb of the auxiliary coil 13H of the transformer 13 is connected to the negative terminal 12b of the smoothing capacitor 12.

Next, the operation of the above embodiment will be described.

When a DC voltage is applied to the primary coil 13N of the transformer 13 by the smoothing capacitor 12, a positive potential is generated at the terminal 13Ha of the auxiliary coil 13H, and this potential is applied to the switching element Q1 via the resistor 18 and the capacitor 17. Apply to the base. As a result, the switching element Q1 becomes conductive and current starts to flow.

Since the primary coil 13N and the auxiliary coil 13H are oriented in the same direction, the terminal 13 of the primary coil 13N is
Positive feedback is applied to Na, and the current flowing through the primary coil 13N and the switching element Q1 increases.

A voltage proportional to the primary current flowing through the primary coil 13N of the transformer 13 is generated in the resistor 14. When the voltage generated in the resistor 14 exceeds 0.6 [V], the transistor Q2 becomes conductive, and the conduction of the transistor Q2 decreases the emitter potential of the transistor Q3.

When the emitter potential of the transistor Q3 becomes lower than the base potential of the transistor Q3 by 0.6 [V] or more, the transistor Q3 becomes conductive and lowers the base potential of the switching element Q1. Due to the positive feedback action of the transformer 13, the potential of the auxiliary coil 13H decreases, and the switching element Q1
Cuts off.

When the switching element Q1 is cut off, a counter electromotive voltage is generated in the secondary coil 13M of the transformer 13 and a charging current I flows. When the charging current I has finished flowing, the switching element Q1 is turned on in the same manner as above. Then, these operations are repeated and the rechargeable battery 19 is charged.

By the way, since the transistors Q2 and Q3 are cascade-connected, the collector potential of the transistor Q2 is fixed to the emitter potential of the transistor Q3. Also, since the base of the transistor Q3 is fixed by the voltage of the Zener diode 20,
The emitter potential of the transistor Q3 is also fixed.

As a result, if the transistors Q2 and Q3 are turned on, the emitter potential of the transistor Q2 is fixed to the base potential of the transistor Q3, and even if the base potential of the transistor Q2 changes, the emitter potential does not change. Therefore, the mirror effect will be suppressed. And
Since the emitter potential of the transistor Q3 is also fixed to the base potential of the transistor Q3, if the transistor Q3 conducts, the base potential of the switching element Q1 immediately becomes the base potential of the transistor Q3 regardless of the collector-base capacitance of the transistor Q2. Switching element Q1
Will cut off immediately.

Therefore, variations in the switching speed of the switching element Q1 due to the difference in the current amplification factor of the transistor Q2 can be suppressed, and as a result, variations in the charging time can be reduced.

In the above embodiment, the normal transistor Q2
I explained the case of using MOS-FE.
The same effect can be obtained by using T. Also,
Although the charging circuit for the electric razor has been described, other charging circuits may be used.

[0037]

As described above, according to the present invention, even if the characteristics of the control switch element vary, it is possible to suppress the variation of the switching speed of the switching element and reduce the variation of the charging time. You can

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a charging circuit according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional charging circuit.

FIG. 3 is a time chart of the main part of FIG.

[Explanation of symbols]

 10 AC / DC conversion circuit 13 Transformer 13N Primary coil 13M Secondary coil 13H Auxiliary coil 19 Rechargeable battery Q1 switching element Q2 transistor (first control switch element) Q3 transistor (second control switch element)

Claims (1)

[Claims] 1. An AC-DC converting circuit for converting an AC voltage into a DC voltage, a primary coil to which the DC voltage of the AC-DC converting circuit is applied, a secondary coil connected to a rechargeable battery, and an auxiliary coil. A transformer, a switching element for supplying a current to the primary coil, and a first control switch element for turning off the switching element, and a voltage generated in the auxiliary coil is applied to the gate of the switching element to switch the switching element. Is turned on, and after a lapse of a predetermined time from this turning on, the first control switch element is turned on to lower the gate potential to cut off the conduction of the switching element, and these operations are repeated to apply an intermittent current to the primary winding. A charging circuit for charging the rechargeable battery with a voltage generated by flowing the secondary coil, the first control switch element A second control switch element is cascade-connected to the second control switch element, and the conduction of the second control switch element lowers the gate potential of the switching element to cut off the conduction of the switching element.