JPH0130373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit using a transistor inverter.

FIG. 1 shows a general circuit example of a transistor inverter type predisposition circuit, which mainly consists of a rectifier circuit 3 that rectifies an AC power supply 1, an inverter 2 that operates with the output of this rectifier circuit 3, and two components of this inverter 2. Next winding L ₂ rectifies the output and charges rechargeable battery B 2
The inverter 2 includes a switch starting circuit 5, a switch section 6, and a power converter section 7. _R1 to _R4 are for oscillation startup, base current limit, and main transistor, respectively.
Tr ₁ is a resistor for collector current limitation, primary winding L ₁ is a resistor for back electromotive force absorption, C ₁ to C ₃ is a capacitor for power supply smoothing, primary winding L ₁ is for back electromotive force absorption, and base circuit. , and D ₁ D ₂ are diodes for absorbing the back electromotive force of the primary winding L ₁ and for high frequency rectification, respectively. Also
L ₁ to _{L 3} are primary to tertiary windings, respectively, and constitute an oscillation transformer.

Thus, in the conventional example circuit shown in FIG.
, the main transistor is connected through resistor _R1 .
The base current is supplied to Tr ₁ , and the main transistor
Tr ₁ turns on, and its collector current Ic generates a voltage of V=Ldi/dt in the primary winding L ₁ , which is positively fed back in the tertiary winding L ₃ , which further turns on the main transistor Tr _1. deepen. Then, when the collector current flows with respect to the base current I _B of the main transistor Tr ₁ until I _C = h _FE・I _B , the current change in the primary winding L ₁ disappears, and as a result, the primary winding L ₁ The polarity of the voltage across the transistor is instantaneously reversed, the potential is fed back to the tertiary winding _L3 , and the main transistor _Tr1 is reverse biased and turned off. Also, at this time, the primary winding L ₁
The energy is extracted from the secondary winding L ₂ and rectified by the diode D ₂ to charge the rechargeable battery. After this, the base potential of the main transistor Tr ₁ rises through the resistor R ₁ , and when this base potential reaches a predetermined voltage, a base current flows to repeat the above operation and continue the oscillation operation. Figure 2 shows the waveforms of each part of the above operation, where a is the main transistor Tr ₁
, b shows the collector current, and c shows the waveforms of the rectified current by the diode D ₂ .

However, in the conventional circuit as described above,
Since the circuit is designed according to the voltage rating of the AC power supply 1, when the power supply voltage differs depending on the country,
An adapter for this power supply voltage is required, which makes it difficult to miniaturize, and there is also the problem of damage to the equipment due to incorrect use of the adapter or switching error in power supply voltage switching types. When assuming two power supply voltages of 240V and 240V, the main transistor
In order to satisfy the stress on Tr ₁ , it is necessary to use a main transistor Tr ₁ with a high rating, which makes it necessary to use a large and expensive main transistor Tr ₁ , which makes the charger smaller. I have a problem that is difficult to solve.

Therefore, the oscillation frequency of the inverter 2 in the circuit shown in FIG. 1 is made constant, and the main transistor Tr ₁
There is a device in which the collector current of Tr 1 is limited to a permissible value or less, so that the charging current can be kept constant even if a small main transistor Tr ₁ is used. When a circuit is added to keep the oscillation frequency constant and limit the collector current in this way, a power supply circuit is required for these circuits. In this case, when a power supply circuit that makes the output of the rectifier circuit 3 a constant voltage is used, there is a problem that when the power supply voltage is high, the loss increases and heat generation occurs.

The present invention has been provided in view of the above points, and can be used in common with changes in power supply voltage in each country, can reliably limit the collector current of a transistor to a permissible value or less, and can reduce loss. less,
The object of the present invention is to provide a charging circuit that can use a small main transistor.

An embodiment of the present invention will be described in detail below with reference to the drawings.
Figure 3 shows a circuit according to an embodiment of the present invention, which includes a power supply circuit 8 that rectifies and smoothes the output of the fourth winding _L4 of the oscillation transformer, and an inverter 2 operated by the output of this power supply circuit 8, which is synchronized. an oscillation frequency control circuit 9 that makes the oscillation frequency constant regardless of the power supply voltage;
A peak collector current control circuit 11 which is also operated by the output of the power supply circuit 8 and which compares the voltage across the resistor R ₃ and the output of the reference voltage generation circuit 10 to ground the base of the main transistor Tr ₁ is connected to the conventional circuit shown in FIG. Added to the example circuit, and when the voltage across the resistor R ₃ exceeds a predetermined voltage, the main transistor Tr ₁ turns on.
In this embodiment circuit of FIG. 3, the collector current of the main transistor Tr ₁ is detected by the voltage across the resistor R ₃ . Here, the power supply circuit 8 is composed of a quaternary winding _L4 , a diode _D3, and a smoothing capacitor _C5 .
The oscillation frequency control circuit 9 is an IC-based oscillator 13
It consists of an external resistor R ₅ and a capacitor C ₄ , and its output turns on the transistor Tr ₃ '.
Turn off and synchronize inverter 2. The peak collector current control circuit 11 is composed of a comparator 14 which has a constant input as the output of the reference voltage generation circuit 10 consisting of a resistor R ₆ and a Zener diode D ₆ and the other input as the terminal voltage of the resistor R ₃ .
At the output of this comparator 14, a transistor
By turning on Tr ₃ , when the collector current of the main transistor Tr ₁ exceeds a predetermined value, the base of the main transistor Tr ₁ is grounded. The peak collector current limiting circuit 12 consists of a transistor Tr ₂ with a series diode D ₄ D ₅ connected in series to its emitter. By connecting the base to one end of the resistor R ₃ , the voltage across the resistor R ₃ is controlled by the transistor Tr ₂ . The base of the main transistor _Tr1 is grounded.

Thus, the circuit of the embodiment shown in FIG. 3 operates as follows. That is, at time t=0, the resistance
When a base current flows through R ₁ to the base of main transistor Tr ₁ , this main transistor Tr ₁ turns on and collector current I _C flows, and V _IN =L ₁ dic/ _dt ... (1) L ₁ : The inductance of the primary winding flows, so I _C (t)=V _IN /L ₁ ·t...(2) V _CE (sat) of _Tr 1≈0. On the other hand, the output current I ₀ is calculated as W _IN =∫ ₀ ^{TON V} IN , where F is the oscillation frequency, W _IN is the primary input, W ₀ is the secondary output, and η _is the conversion efficiency.

Claims (1)

[Claims] 1 Operates with a DC output obtained by rectifying an AC power source as a driving power source, and performs oscillation operation by positively feeding back the voltage induced in the tertiary winding of an oscillation transformer whose primary winding is connected in series with the main transistor to the base of the main transistor. a secondary output rectifier circuit that rectifies the high-frequency voltage induced in the secondary winding of the oscillation transformer of this inverter and charges a rechargeable battery, and a secondary output rectifier circuit that rectifies and smoothes the voltage induced in the 4th winding of the oscillation transformer. a power supply circuit that uses the output of this power supply circuit as a power supply to synchronize the inverter and keep the inverter's oscillation frequency constant, and a power supply circuit that detects the collector current of the inverter's main transistor. collector current detection means; a first peak collector current limiting circuit that operates using the output of the power supply circuit as a power source and grounds the base of the main transistor when the output of the collector current detection means rises above a first predetermined value; When the output voltage of the power supply circuit is low and the first peak collector current limiting circuit is inoperative, the output of the collector current detection means rises to a second predetermined value that is higher than the first predetermined value. and a second peak collector current limiting circuit that grounds the base of the main transistor.