JP2566289B2 - Charging circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a charging circuit for a rechargeable electric device such as an electric razor.

[Prior Art] As an example of this type of conventional charging circuit, there is a converter type charging circuit configured as shown in FIG. 5, which includes a resistor 1, a capacitor 2, a rectifier 3, a smoothing capacitor 4, a resistor 5,
7, 9, 11, capacitor 6, diodes 8, 12, 16, transistors 10, 13, capacitor 14, storage battery 15, transformer 18
Primary winding 18a, drive winding 18b, and secondary winding 18 of
It consists of c and load 17.

An AC voltage of an AC power supply (not shown) is converted into a DC voltage by the resistor 1, the capacitor 2 and the rectifier 3. The DC voltage converted here is applied to the primary winding 18a of the transformer 18, and the DC voltage is applied to the primary winding 18a when the transistor 10 is on and the transistor 10 is off. At this time, the DC voltage is not applied to the primary winding 18a.

Transistor 10 is driven by the voltage appearing on drive winding 18b of transformer 18. That is, the resistor 11 and the transistor 13 form a control circuit. In this control circuit, a voltage proportional to the current flowing through the transistor 10 via the resistor 11 is generated, and this voltage is the threshold voltage of the base of the transistor 13. When (≈0.6v) is reached, transistor 13
Becomes conductive, the base voltage of the transistor 10 is lowered, and the transistor 10 becomes non-conductive. Therefore, the primary winding
The current flowing from the transistor 18a to the transistor 10, that is, the emitter current waveform does not exceed a constant value, that is, the peak current IP as shown in FIG. 7 (a), and the current waveform of the secondary winding 18c of the transformer 18 is It does not exceed the peak current Iop like the output current of FIG.

However, when the power supply voltage applied to the primary winding 18a changes, the rising rate changes in the emitter current waveform of FIG. 7 (a), and even if the peak value IP of the emitter current is the same, the peak current IP The time τ1 required to reach it changes. Therefore, even if the off period τ2 is the same, the period τ1 + τ2
Changes to .tau.1 '+. Tau.2 as shown in FIG. 7 (b), and eventually the average value of the emitter current fluctuates. Therefore, the output current also fluctuates as shown in FIG. 7 (b).

FIG. 6 shows another example of the conventional charging circuit.
FIG. 9 is a circuit diagram showing only a main part in the case where only a portion corresponding to the output circuit of the figure is of a forward converter type, and the primary current in this case has a trapezoidal waveform as shown in FIG. The value IS at the shoulder of this waveform changes depending on the power supply voltage, and the output current is not constant even if the peak current Ip is constant. FIG. 8A shows a current waveform when the power supply voltage is constant, and FIG. 8B shows a current waveform when the power supply voltage changes.

[Problems to be Solved by the Invention] In the conventional converter-type charging circuit described above, the fluctuation of the output current due to the fluctuation of the power supply voltage cannot be sufficiently suppressed. In addition, almost no effect can be obtained with the forward converter type charging circuit.

Therefore, an object of the present invention is to provide a charging circuit in which the output current does not fluctuate even when the power supply voltage fluctuates, and the same effect can be obtained regardless of the type of the output circuit.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention relates to a transformer having a drive winding that generates an output according to DC input power, and receiving DC input power to obtain AC output power. , A switching element for stopping the supply of DC input power input to the transformer, the switching element being turned on and off by a control current flowing from the drive winding to a control terminal provided therein, and an AC output of the transformer A rectifier circuit that rectifies a current and charges a storage battery, a control circuit that detects a current flowing in the switching element from the DC input power of the transformer, and that applies a current limit when the detected current value exceeds a predetermined value, The control current from the drive winding to the control terminal of the switching element is shunted and added to the detected current value detected by the control circuit.

[Operation] The present invention adds the current shunted from the drive winding of the transformer to the detected current value detected by the control circuit to change the limit value of the control circuit when the power supply voltage rises. Little change in output current. Therefore, the above object can be achieved.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the first embodiment of the present invention, in which a DC power supply voltage obtained by a resistor 1, a capacitor 2, a rectifier 3 and a capacitor 4 is turned on / off by a transistor 10 so that the primary winding of a transformer 28 is turned on. The line 28a can be applied or stopped. The base of the transistor 10 is connected to the output side of the rectifier 3 via the starting resistor 7, and the timing capacitor 14 that determines the off time of the transistor 10 is connected in series to the parallel circuit of the base current limiting resistor 9 and the speed-up diode 8. Is connected to one end of the drive winding 28b via a series circuit formed by. Also transistor 10
The emitter of is connected to the output terminal of the rectifier 3 via the resistor 11, and is also connected to the output terminal of the rectifier 3 and the other end of the drive winding 28b via the resistor 21, the diode 22 and the resistor 24 in series. . Base of transistor 10 and resistor 9
Control transistor 25 via diode 30 at the connection point
Of which is connected to the connection point between the resistor 24 and the diode 22, and the emitter of the transistor 25 is connected to the connection point between the resistor 24 and the drive winding 28b.
A series circuit of a diode 29 and a capacitor 27 is connected in parallel to the drive winding 28b, a resistor 26 is connected in parallel to the capacitor 27, and a connection point between the capacitor 27 and the diode 29 and a connection point between the diode 22 and the resistor 24 is connected. Resistor 20 is connected to. The resistor 11, resistor 21, diode 22, resistor 24,
The transistor 25 constitutes a control circuit. Then, the storage battery 32 and the load 31 are connected in parallel to the secondary winding (output winding) 28c of the transformer 28, and the rectifier circuit 33 is provided between the one end side of the secondary winding 28c and the connection point of the storage battery 32. The storage battery 32 and load
The load drive switch 34 is connected between the connection point with 31.

The operation of the charging circuit thus configured will be described below. The emitter current of the transistor 10 is shunted to the resistor 11 side, the resistor 21, the diode 22, and the resistor 24 side.
When the voltage generated at 24 reaches the threshold value (≈0.6v) of the base potential of the transistor 25, the transistor 25 becomes conductive, which lowers the base current of the transistor 10 and turns off the transistor 10.

On the other hand, in the drive winding 28b of the transformer 28, the transistor 10
Forming a current loop composed of a capacitor 14, a resistor 9 and a diode 8 for driving the diode, and a current loop shunted by the diode 29. The voltage of the drive winding 28b is generated by the action of the transformer 28 in proportion to the voltage of the primary winding 28a. Since the base-emitter voltage of the transistor 10 and the voltage generated in the resistor 11 are sufficiently smaller than the power supply voltage, that is, the voltage applied to the secondary winding 28a, the voltage of the primary winding 28a is almost equal to the power supply voltage. Therefore, the voltage of the drive winding 28b is approximately proportional to the power supply voltage.

The current shunted by diode 29 is
It is smoothed by 27 and resistor 26 and added to resistor 24 through resistor 20. Therefore, the current flowing through the resistor 24 is the current shunted from the emitter current of the transistor 10 and the transformer.
It is the sum of the currents shunted from the 28 drive windings 28b. A diode 29, a capacitor 27, connected to the drive winding 28b,
The resistors 26 and 20 are almost constant resistance circuits, and the current flowing through them is proportional to the voltage of the drive winding 28b. Therefore, the peak value Ip of the emitter current of the transistor 10 can be changed by the power supply voltage.

For this reason, the peak value IP of the emitter current fluctuates so as to cancel the change in the output current due to the fluctuation in the power supply voltage, so that the output current can be kept constant. .

This situation will be described with reference to FIG. FIG. 3 (a) shows the waveforms of the emitter current and the output current when the power supply voltage hardly changes, and FIG. 3 (b) shows the waveforms when the power supply voltage is higher than that in FIG. 3 (a). It is a waveform of an emitter current and an output current. The emitter current peak IP in FIG. 3 (a) is reduced to the emitter current peak value IP 'in FIG. 3 (b). Primary windings 28a and 2 of transformer 28
Since the ampere arn is the same between the next windings 28c,
The peak value Iop of the current in the secondary winding 28c in FIG. 3 (a) decreases to IOP 'as shown in FIG. 3 (b). Therefore, the average value Io 'of the output current becomes the same as Io.

FIG. 2 is a circuit diagram showing only an essential part of another embodiment of the present invention, which is a circuit of a forward converter system connected to the secondary winding 28c of the transformer 28 of FIG. , A storage battery 36, a reactor 37, a rectifying circuit 38, a diode 39, and a load drive switch 40.

The current waveform in the case of such a configuration is as shown in FIG. 4, and the peak value IP of the emitter current in (a) is set to compensate for the increase in the value IS 'of the trapezoidal shoulder portion as shown in (b). Since the peak value Ip 'decreases, the output current becomes constant.

The control circuit of the embodiment described above is composed of the resistor 11, the resistor 21, the diode 22, the resistor 24, and the transistor 25, but the diode 22 and the resistor 21 are not always necessary. Further, in the embodiment, the drive winding 28 of the transformer 28 is
Although the current obtained by shunting the current from b is applied to the control circuit via the smoothing circuit including the resistor 26 and the capacitor 27, the smoothing circuit is not always necessary.
Further, the transistors 10 and 25 of the embodiment may be any switching elements such as thyristors having a control terminal such as a gate terminal. In short, according to the present invention, the current flowing through the switching element such as the transistor 10 is changed to the resistance 11
Resistor 21, diode that limits the current value by detecting
If the control circuit is composed of 22, the resistor 24, the transistor 25, etc., the current shunted from the drive winding 28b by the diode 29, etc. is added by the resistor 20, etc., and the limit value depends on the power supply voltage. Anything is fine.

[Effect of the Invention] According to the present invention, when the power supply voltage rises by applying the current shunted from the drive winding of the transformer to the control circuit, the limit value of the control circuit changes, so the output current There is little fluctuation. Therefore, even if the power supply voltage fluctuates, the output current hardly fluctuates, and it is possible to provide a charging circuit that can obtain the same effect regardless of the type of the output circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a charging circuit according to the present invention, FIG. 2 is a circuit diagram showing only essential parts of another embodiment of the present invention, and FIGS. 3 and 4 are FIG. 1 and FIG. 5 is a diagram for explaining the operation of FIG. 2, FIGS. 5 and 6 are diagrams for explaining different conventional charging circuits, and FIGS. 7 and 8 are the operations of FIGS. 5 and 6. It is a figure for explaining. 1 ... Resistance, 2 ... Capacitor, 3 ... Rectifier, 5 ...
Resistance, 6 ... capacitor, 7 ... resistor, 8 ... diode, 10 ... transistor, 11 ... resistor, 12 ... diode, 14 ... capacitor, 20,21,24,26 ... resistor, 25 ... …
Transistor, 27 ... Capacitor, 28 ... Transformer, 28a
…… Primary winding, 28b …… Drive winding, 28c …… Secondary winding, 29
...... Diode, 33,38 rectifier circuit, 32,36 …… storage battery, 31,35 …… load.

Claims (1)

(57) [Claims] 1. A transformer having a drive winding that generates an output according to a DC input power, which receives the DC input power to obtain an AC output power, and a supply stop of the DC input power input to the transformer. A switching element that is turned on and off by a control current flowing from the drive winding to a control terminal of the drive winding; a rectifying circuit that rectifies an AC output current of the transformer to charge a storage battery; A control circuit for detecting a current flowing in the switching element from the DC input power of the power supply device and limiting the current when the detected current value exceeds a predetermined value, and a control flowing from the drive winding to the control terminal of the switching element. And a charging circuit that adds a current to the detected current value detected by the control circuit.