JP2566566B2 - Charging circuit with automatic voltage switching function - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit with an automatic voltage switching function for charging a charged battery such as an alkaline storage battery incorporated in a small electric device such as an electric razor.

(Prior Art) Conventionally, as a charging circuit having a voltage switching function for automatically detecting a different power supply voltage and keeping the charging current constant, for example, as disclosed in Japanese Patent Laid-Open No. 61-1228. The one using an inverter circuit as shown is known.

FIG. 1 shows the circuit configuration of the above-mentioned conventional device. Hereinafter, with reference to FIG. 1, reference numeral 1 is a power supply circuit, and an AC input from a commercial power supply Vs passes through a protection resistor R1 and is rectified and smoothed by a diode D1 and a capacitor C1. The DC voltage Vin is supplied to the inverter circuit 2 and the like. Reference numeral 2 is an inverter circuit. The primary winding L1 of the transformer is provided at the collector of the switching transistor Q1, and the feedback winding is provided at the base via the base resistor R3 and the speed-up capacitor C3.
L3 are connected to each other, and a battery B to be charged is inserted in series to the emitter via a current detecting resistor R5.
Also, a diode D5 and a capacitor C4 are provided on both ends of the primary winding L1.
And a spike absorption circuit consisting of resistor R4 is connected. Reference numeral 4 is an output circuit, and the voltage induced in the secondary winding L2 of the transformer is applied to both ends of the battery B through the diode D2.

Reference numeral 5 is a stabilizing circuit, which is composed of a bypass transistor Q2 and a Zener diode D4 as a constant voltage element. 6 is an automatic voltage switching circuit, which has a current limiting resistor R6,
It is composed of a Zener diode D3 as a voltage detecting means and a switching element Q3.

The collector and base of the bypass transistor Q2 are connected to the base and emitter of the switching transistor Q1, respectively, and further, the base and emitter of the bypass transistor Q2 are connected in series with a constant voltage element to perform the switching. It is connected in parallel to the current detection resistor R5 inserted in the emitter of the transistor Q1, and with this configuration, when the peak of the collector current of the switching transistor Q1 exceeds a certain value, the bypass transistor Q2 becomes conductive and the base of the switching transistor Q1. By drawing in the current, the collector current is reduced and oscillation can be sustained stably.

More specifically, in the above configuration, if the collector current of the switching transistor Q1 increases for some reason, the emitter potential Ve of the switching transistor Q1 rises due to the voltage drop in the current detection resistor R5. When this potential Ve is larger than the sum of the voltage drop Vdz in the Zener diode D4 and the voltage drop Vbe between the base and emitter of the transistor Q2, and Ve> Vbe + Vdz, the transistor Q2 becomes conductive and bypasses the base current of the switching transistor Q1. , Collector current Ic
To reduce. In reality, the collector current is a high-frequency pulsating flow, and when the peak value of the collector current waveform starts to exceed a certain value, the base current is suppressed and the collector current is controlled so as not to rise above a certain value.

Further, the Zener diode D3 as a voltage detecting means detects that the voltage across the feedback winding L3 exceeds a certain value and makes the switching element Q3 conductive, and when used in a 100 to 120 V power supply. The switching element Q3 does not conduct, and when used in a 200 to 240 V power supply, the switching element Q3 conducts and short-circuits the Zener diode D4. After the voltage switching circuit 6 operates in this way, the voltage drop Ve of the current detection resistor R5
Is larger than the base-emitter voltage drop Vbe of the transistor Q2, that is, Ve> Vbe, the base current of the switching transistor Q1 is bypassed. In this way, when the power supply voltage used is high, the collector current is suppressed to a low value, and an almost constant average output current is obtained on the secondary side of the transformer for any power supply. .

FIG. 2 shows the operation of the stabilization circuit 5, and Vce, I
c and Ib are the collector-emitter voltage, collector current, and base current of the switching transistor Q1, respectively, and Io is the secondary current of the transformer, that is, the output current. In the figure, Ic increases linearly while Vce is zero, and Ic is Icp = h
_When reaching _FE × Ib, the transistor Q1 is cut off, and the energy accumulated in the transformer is released as the output current Io. When the input voltage rises for some reason, the rate of rise of Ic increases as shown on the right side of the figure.
When Ic reaches a constant value as described above, transistor Q2
Since Ic is cut off by bypassing
The ON period Ton of Q1 is shortened, and therefore the energy stored in one cycle is also reduced, and as a result, the average value of the output current Io is maintained substantially constant.

FIG. 3 shows the operation of the voltage switching circuit 6.
Now, assuming that the input voltage is Vin, a voltage corresponding to Vin × (turning ratio of L3 and L1) is induced in the feedback winding L3. Therefore, it has a function of switching the constant voltage element in the vicinity of a certain input voltage by the set voltage of the Zener diode D3 as the voltage detecting means. Therefore, by appropriately selecting the values of the current detection resistor R5 and the Zener diode D4 as a constant voltage element,
It is possible to reduce the difference in output current in a ~ 240V power supply. The characteristics a, b and c in FIG. 3 will be described later.

However, since the actual input voltage is the rectified AC input voltage, the voltage across the feedback winding L3 is
The waveform is as shown in FIG. Therefore, in the case of a voltage such as D3-1 (set the voltage higher than the voltage when AC120V is input), as shown in FIG. 4, depending on the set voltage of the constant voltage element composed of the Zener diode D3. ,
The output will be as shown in characteristic b in Fig. 3, and AC100V, 120V
Then, the required output can be taken out, but when AC 220V or higher,
This time the output will be too high.

Further, this time, when the set voltage of the Zener diode D3 is a voltage like D3-2 in FIG. 4 (a set voltage that can be controlled even when AC120V is input), the characteristic c shown in FIG. 3 is obtained. It becomes an output, and the AC100V system and the AC200V system have almost the same output, but when the AC100V, 120V input is applied, there is a place where the set voltage of the Zener diode D3 is exceeded, so it is partially controlled and the output current is reduced. It will decrease and the required output will not be output.

As described above, it has been difficult for the conventional device to stably and reliably keep the output current constant for different AC inputs.

(Object of the Invention) The present invention solves the above problems, and can stabilize the oscillation of the inverter for different power supply voltages with a circuit configuration as simple as possible, and automatically switch the output current corresponding to the power supply voltage. It is an object of the present invention to provide a charging circuit with an automatic voltage switching function that is capable of charging.

(Structure of the Invention) According to the present invention, a primary winding of a transformer is connected to a collector of a switching transistor, a primary winding and a feedback winding that are positively feedback-coupled are connected to a base, and a collector and a collector are respectively connected to a base and an emitter of the switching transistor. And the base of the bypass transistor connected to the base and the constant voltage element are connected in series, and are connected in parallel to the current detection resistor inserted in the emitter of the switching transistor, and the voltage across the feedback winding is constant. Voltage detection means for detecting that the value is exceeded,
It is equipped with a switching element that short-circuits the constant voltage element or a part of the constant voltage element divided into a plurality according to its detection output, and the voltage induced in the secondary winding of the transformer is charged through a diode. In an inverter type charging circuit applied to a battery, means for rectifying and smoothing the voltage across the feedback winding is provided, and the voltage detecting means is adapted to perform voltage detection on the rectified and smoothed voltage. A charging circuit with an automatic voltage switching function, which is characterized in that

With this configuration, when the power supply voltage is different, the rectified and smoothed voltage of the voltage across the feedback winding can be clearly distinguished, and the automatic voltage switching can be performed accurately.

(Embodiment) FIG. 5 shows a circuit configuration according to an embodiment of the present invention. In the figure, only the points different from the above will be described. D6 is a rectifying diode for the voltage induced in the feedback winding L3, C2 is a smoothing capacitor for the voltage rectified by the diode D6, and diode D6 is a voltage switching The capacitor C2 is inserted in series in the circuit 6, and the capacitor C2 is connected in parallel to the series path of the Zener diode D3 and the base emitter of the switching element Q3.

The diode D6 and the capacitor C2 constitute means for rectifying and smoothing the voltage across the feedback winding L3, and the voltage switching circuit 6 serves as means for detecting that the smoothed voltage has exceeded a certain value. The element Q3 constitutes a switching means for short-circuiting the Zener diode D4 which is a constant voltage element by the detection output.

The other configuration is the same as that shown in FIG. 1, and the operation of this inverter circuit 2 is the same as that described above. Therefore, here, the output current control operation by the voltage switching circuit 6 at the AC100V system and AC200V system inputs is performed. Will be described only.

A voltage having a waveform as shown in FIG. 4 is output to both ends of the feedback winding L3. This output is actually the number 10
Since it is switched at KHz, the voltage of both poles is output, but it is shown by the envelope of the output when the resistance R3 side of the feedback winding L3 is +. And
This output is rectified by diode D6, resistor R6 and capacitor
By smoothing with C2, a DC voltage is generated across the capacitor C2 as shown in Fig. 6, and the AC100V input (AC
100V, 120V) and AC200V input (AC220V, 240V), DC voltages V1 and V2 that can be clearly distinguished are obtained.

Therefore, the set voltage of the constant voltage element of Zener diode D3
By setting VD3 so that V2>VD3> V1, since VD3> V1 when AC100V, 120V input, the base current does not flow in switching element Q3, so Zener diode D4 switches switching element Q3 Therefore, Ic of the switching transistor Q1 does not decrease. On the other hand, AC200V, 220
In the case of V, 240V input, the base current is supplied to the switching element Q3 through the Zener diode D3 to turn on the switching element Q3, so that the Zener diode D4 is short-circuited and the Ic flowing through the switching transistor Q1 is controlled.

In this way, since the control ON / OFF is clearly distinguished between the AC100V system and the AC200V system, the output current (charging current) characteristic is the third.
As shown by the characteristic a in the figure, when the power supply voltage is different, the automatic voltage switching is appropriately performed and a stable output can be obtained.

Although only one Zener diode D4 is short-circuited by the switching element Q3 in the above embodiment, it is possible to short-circuit only a part of the plurality of constant voltage elements. Good.

(Effects of the Invention) As described above, according to the present invention, the voltage across the feedback winding of the inverter type charging circuit can be clearly distinguished and detected when the power supply voltage is different. By simply adding such a circuit configuration, it is possible to accurately and automatically switch the voltage for differences and fluctuations in the power supply voltage, and to stabilize the charging current that is the output. Further, the output does not become excessive even with a large difference in power supply voltage depending on the region, and an automatic voltage switching circuit with less loss can be realized.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a conventional charging circuit, FIG. 2 is a waveform diagram of each part for explaining the operation of the circuit, FIG. 3 is an explanatory diagram showing a voltage switching operation of the circuit, and FIG. FIG. 5 is a waveform diagram of the voltage across the feedback winding of the circuit, FIG. 5 is a circuit configuration diagram of the charging circuit according to an embodiment of the present invention, and FIG. 6 is a waveform diagram of the rectified and smoothed output of the voltage across the feedback winding of the circuit. Is. 2 ... Inverter circuit, 4 ... Output circuit, 5 ... Stabilization circuit, 6 ... Automatic voltage switching circuit, B ... Charged battery, L1
...... Primary winding of transformer, L2 …… Secondary winding of transformer,
L3 ... Feedback winding, Q1 ... Switching transistor, Q2 ... Bypass transistor, Q3 ... Switching element, D2 ... Diode, D3 ... Zener diode, D4 ... Zener diode (constant voltage element), D6 ...
… Diode (rectifier means), C2… Capacitor (smoothing means), R5… Current detection resistor.

Claims (1)

(57) [Claims] 1. A primary winding of a transformer is connected to the collector of a switching transistor, a primary winding is connected to a feedback winding that is positively feedback-coupled to the base, and a collector and a base are connected to the base and emitter of the switching transistor, respectively. The base emitter of the bypass transistor and the constant voltage element are connected in series and connected in parallel to the current detecting resistor inserted in the emitter of the switching transistor, and the voltage across the feedback winding exceeds a certain value. Voltage detection means for detecting that
It is equipped with a switching element that short-circuits the constant voltage element or a part of the constant voltage element divided into a plurality according to its detection output, and the voltage induced in the secondary winding of the transformer is charged through a diode. In an inverter type charging circuit applied to a battery, means for rectifying and smoothing the voltage across the feedback winding is provided, and the voltage detecting means is adapted to perform voltage detection on the rectified and smoothed voltage. Charging circuit with automatic voltage switching function.