JPH0130372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit, and more particularly to a charging circuit that charges a battery by rectifying the output of an oscillation circuit including a plurality of coils and transistors wound around a transformer.

In the conventional charging circuit, as shown in Fig. 1, the primary coil _L1 of the transformer T is connected to the collector of the transistor Q.
Connect the secondary coil L ₂ of the transformer T to the base.
is connected to the polarity that forward biases the base to form an oscillation circuit, and a series circuit of rectifier diode D ₁ and battery B is connected across the tertiary winding L ₃ of transformer T to convert the output of the oscillation circuit into a tertiary The voltage was obtained from coil L ₃ and rectified by rectifier diode D ₁ to charge battery B.
R ₁ is the oscillation starting resistance, C ₁ is the oscillation capacitor, D ₂
is the reverse bias diode of transistor Q,
C ₂ and R ₃ are capacitors and resistors for absorbing spike voltages, R ₂ is a current limiting resistor, and SW is a switch that turns the load L on and off. A is a charging control block which detects the voltage of battery B using a battery voltage detection resistor _R4 and controls the oscillation circuit. In this case, since the transformer T requires three coils, the transformer T and the circuit become complicated, making it unsuitable for miniaturization. By the way, in the circuit configuration shown in Figure 1, while transistor Q is on, the potential between the collector and emitter is approximately
OV, and when the transistor Q is off, the potential difference between the collector and emitter is maximum, but the collector current is approximately 0. Therefore, regardless of whether transistor Q is on or off,
Power consumption in transistor Q is extremely low.
However, during the transition period from on to off of the transistor Q, there is a state in which there is a potential difference between the emitter and the collector and a collector current is flowing, and a large amount of power is consumed during this transition period. In other words, the carriers accumulated between the base and emitter during the ON period of transistor Q remain and carry charges even after the base current is stopped, so the collector current flows until the carriers disappear, and the collector current decreases. As a result, the potential difference between the emitter and collector increases.

Therefore, in order to reduce the heat generation of the transistor Q, it is necessary to shorten the transition period as much as possible. In other words, when the capacity of battery B is sufficient to drive load L and the charging circuit is operating normally, when transistor Q is turned off,
The polarity of the induced voltage in the secondary coil _L2 is reversed, a reverse bias is applied between the base and emitter of the transistor Q through the capacitor _C1 and the reverse bias diode _D2 , and the carrier is canceled almost instantaneously. Therefore, power consumption during the transient period is not a problem. However, assuming that the battery B is empty and the switch SW is turned on, when the impedance of the load L is small (if the load is a motor or the like), the voltage across the tertiary coil _L3 becomes approximately OV. Here, if the number of turns of the secondary coil L ₂ and the tertiary coil L ₃ are n ₂ and n ₃ , respectively, the voltage V _L2 across the secondary coil L ₂ during the off period of the transistor Q is as follows. Become.

V _L2 = V _L3 ·n ₂ /n ₃ However, V _L3 is the voltage across the tertiary coil L ₃ . In other words, the voltage V _L3 across the tertiary coil L ₃ is approximately
If it is OV, the voltage V _L2 across the secondary coil L ₂ is also approximately
OV, and the voltage across the secondary coil _L2
This means that the effect of canceling out the carrier by V _L2 cannot be expected. As a result, the transient period becomes relatively long, the power consumption in the transistor Q increases, heat is generated, the safety temperature fuse Fth is activated, and the operation of the circuit is stopped. Furthermore, since battery B is connected in series with transistor Q, it is difficult for leakage current to flow between the collector and emitter of transistor Q, and if the oscillation starting resistor _R1 is eliminated, oscillation will not start unless the applied voltage is increased. Also, since the potential generated in the tertiary coil _L3 viewed from the emitter of transistor Q does not affect the potential of battery B, oscillation continues even if the potential of battery B is extremely low, causing the phenomenon described above. It had the disadvantage that it occurs.

The present invention has been made in view of these points, and its purpose is to simplify the creation of a transformer by reducing the number of coils in the transformer, to make the circuit configuration simple, compact, and inexpensive, and to reduce the battery voltage. The purpose is to stop oscillation when the temperature is extremely low to prevent circuit damage. The present invention will be explained in detail below with reference to Examples.

As shown in Fig. 2, a series circuit in which the primary coil _L2 of a transformer T is connected to the collector of the transistor Q is connected across a DC power supply, and the base of the transistor Q is connected to the base of the transistor Q when the transistor Q is turned on. 2 of the transformer T to the polarity to which positive feedback is applied.
Connect one end of the secondary coil L ₂ and connect the secondary coil L ₂
An oscillation capacitor C is connected between the other end and the emitter of the transistor Q, and a reverse bias diode _D12 is connected between the base and the emitter of the transistor Q with a polarity opposite to that between the base and the emitter, A charging battery B is connected between the other end of the secondary coil L ₂ and the emitter of the transistor Q via a rectifier diode D ₁₁ . The DC power source is obtained by rectifying the AC power source E with an AC power rectifier diode D. Here, the DC power source may be half-wave rectified as shown in the figure, or may be full-wave rectified. Here, the oscillation starting resistor _R1 in the conventional example shown in FIG. 1 is not connected. The rest is the same as the conventional example.

Now, when the AC power supply E is applied, a voltage is applied to the transistor Q, and a leakage current flows between the collector and emitter of the transistor Q. When this leakage current flows through the primary coil _L1 , the voltage generated in the primary coil _L1 induces the secondary coil _L2 in a direction to forward bias the transistor Q, causing the base current of the transistor Q to flow. As a result, positive feedback occurs in which the collector current increases and the base current also increases, causing the transistor Q to rapidly turn on and increase to I _C =h _FE ·I _B . At this time, the oscillation capacitor _C1 is charged with a polarity such that the ground terminal becomes positive. Then, when I _C = h _FE・I _B , the current change in the primary coil L ₁ becomes 0, and the polarity of the voltage generated in the primary coil L ₁ changes as the primary coil L ₁ tries to pass current. Invert. This voltage is induced in the secondary coil _L2 , reverse biasing the transistor Q, and the transistor Q is rapidly turned off. At this time, the voltage generated in the secondary coil _L2 is passed through the rectifier diode _D11 , the battery B, and the reverse bias diode _D12 to charge the battery B. During this time, the oscillation capacitor _C1 is charged with a polarity such that the terminal on the secondary coil _L2 side becomes positive. and,
When the energy stored in the primary coil _L1 is released, the base current of the transistor Q begins to flow due to the charge in the oscillation capacitor _C1 , and oscillation occurs in the same manner as described above. FIGS. 3a to 3d show voltage and current waveforms at various parts during the above-described operation.

Next, battery B discharges while the switch SW remains on, and when AC power source E is applied in this state, the voltage in the primary coil _L1 is induced in the secondary coil _L2 due to the leakage current of the transistor Q. However, because the voltage of battery B is extremely low, the rectifier diode _D11 side of secondary coil _L2 is clamped at a low voltage, and the voltage induced in secondary coil _L2 causes the base current of transistor Q to flow. oscillation is not started. Therefore, no abnormal heat generation occurs, and the temperature fuse F _th does not blow out. and,
When the switch SW is turned off, the voltage of battery B self-recovers, and when it reaches normal voltage, oscillation starts as described above.

As described above, the present invention connects a series circuit in which a primary coil of a transformer is connected to the collector of a transistor between both ends of a DC power supply, and applies positive feedback to the base of the transistor when the transistor is turned on. connecting one end of the secondary coil of the transformer, connecting an oscillation capacitor between the other end of the secondary coil and the emitter of the transistor, and connecting a reverse bias diode between the base and emitter of the transistor; A battery for charging is connected between the other end of the secondary coil and the emitter of the transistor through a rectifier diode, and a leakage current between the collector and the emitter of the transistor is connected. 1 above
The oscillation is detected by the secondary coil and induced in the secondary coil to start oscillation, and the induced output of the secondary coil when the transistor is off is charged to the battery through the rectifier diode and the reverse bias diode. Since the battery is charged by the induced output of the secondary coil, there is no need for a tertiary coil and the number of coils in the transformer can be reduced, simplifying the circuit configuration and reducing the size.
This makes it possible to reduce costs. Furthermore, when the battery voltage is low, as mentioned above, the induced output of the secondary coil does not turn on the transistor, so oscillation does not start, and as a result, circuit damage and thermal fuse blowing can be prevented. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional charging circuit, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a voltage and current waveform diagram of the main parts of the same. Q...transistor, T...transformer, _L1 ...
...Primary coil, L ₂ ...Secondary coil, B...Battery,
D ₁₁ ... Rectifier diode, D ₁₂ ... Reverse bias diode, C ₁ ... Oscillation capacitor.

Claims (1)

[Claims] 1. A series circuit in which the primary coil of a transformer is connected to the collector of the transistor is connected between both ends of a DC power supply, and the polarity of the secondary coil of the transformer is set to the polarity to which positive feedback is applied to the base of the transistor when the transistor is turned on. An oscillation capacitor is connected between the other end of the secondary coil and the emitter of the transistor, and a reverse bias diode is connected between the base and emitter of the transistor, and the polarity is opposite to that between the base and emitter. connect to
A charging battery is connected between the other end of the secondary coil and the emitter of the transistor via a rectifier diode, and the leakage current between the collector and emitter of the transistor is detected by the primary coil and A charging circuit characterized in that the coil is induced to start oscillation, and the induced output of the secondary coil when the transistor is off is charged to a battery through the rectifier diode and the reverse bias diode.