JPS6337586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit using a switching power supply.

Figure 3 shows a conventional charging circuit using the so-called ringing chain converter system, _which is used to charge secondary batteries (hereinafter simply referred to as batteries) such as Nikkad batteries and lead- _acid batteries. is the input terminal of the commercial power supply, DB is the rectifier, C ₁ , C ₂ are capacitors, L ₁ , L ₂ , L ₃ are coils wound around the same core of transformer T, R ₁ , R ₂ , R ₃ are resistors, Q ₁ and Q ₂ are transistors, D is a diode, and B is a battery to be charged.

In this charging circuit, the coil of transformer T
A self-excited oscillation circuit consisting of L ₁ , L ₂ , L ₃ , transistor Q ₁ , resistors R ₁ , R ₂ , capacitor C ₂ , etc. drives transistor Q ₁ on and off, and when transistor Q ₁ is on, coil L ₁ The energy stored in the coil L ₂ is released by the coil L 2 when it is off, charging the battery B via the diode D, and the resistor detects the peak value of the current flowing through the coil L ₁ .
The voltage drop across R ₃ turns on transistor Q ₂ and allows the base current of transistor Q ₁ to be bypassed, thereby controlling the collector current of transistor Q ₁ , that is, the current of coil L ₁ , and controlling the charging current on the secondary side. control.

However, in this charging circuit, if the power supply voltage fluctuates greatly, for example from 100V to 200V,
If the _current changes to
Due to the relatively long operating time before flipping transistor _Q1 off through _Q2 , the transistor
The disadvantage is that the peak value of the current at the moment when _Q1 is turned off changes greatly due to fluctuations in the power supply voltage, and the average value of the charging current on the secondary side of the transformer T ends up fluctuating greatly. It was hot.

The present invention has been proposed in view of the above points, and its purpose is to maintain the average value of the charging current constant regardless of fluctuations in the AC power supply voltage in a charging circuit using a switching power supply. Another object of the present invention is to provide a charging circuit configured to control the on-time of a transistor as a switching element.

The present invention will be explained below with reference to the drawings.

Figure 1 shows an embodiment of the present invention. In the figure, A ₁ and A ₂ are input terminals of an AC power supply, DB is a rectifier such as a diode bridge, and C ₁ is a smoothing capacitor. At both ends of the capacitor C ₁ are the primary coil L ₁ of the transformer T, the collector and emitter of the transistor Q ₁ as a switching element,
Capacitor C ₃ and current detection resistor R ₃ are connected in series, and a resistor is connected in parallel to these.
A series circuit consisting of R ₆ and capacitor C ₄ is connected. A Zener diode ZD 1 is connected in parallel to the capacitor C ₃ with its cathode facing the emitter of the transistor Q ₁ , and a Zener diode _{ZD 2 is} connected in parallel to the capacitor C ₄ with its cathode facing the resistor R ₆ . .

The connection point between capacitor C ₄ and resistor R ₆ is connected to the positive power supply terminal of comparator CP, and the voltage across capacitor C ₄ is divided by resistors R ₄ and R ₅ , and the voltage division point is connected to the comparator CP. It is connected to the non-inverting input terminal of CP and is given a reference voltage. Note that the inverting input terminal of the comparator CP is connected to the connection point between the resistor R ₃ and the capacitor C ₃ , and the negative power supply terminal is connected to the earth line.

Between the base and emitter of the transistor Q ₁ are a capacitor C ₂ and a resistor that constitute a self-oscillation circuit.
R ₂ and the coil L ₃ of the transformer T are connected in series,
Further, a resistor R ₁ is connected between the base of the transistor Q ₁ and the connection point of the coil L ₁ and the capacitor C ₁ . Furthermore, the base of transistor _Q1 is connected to the output terminal of comparator CP.

Note that a battery B to be charged is connected to both ends of the secondary coil _L2 of the transformer T via a diode D.

However, in this embodiment, the self-excited oscillation circuit operates to turn on transistor Q ₁ and turn on coil L ₁
The charging current of the capacitor _C3 flowing through the transistor _Q1 causes a voltage drop in the current detection resistor _R3 , and when this voltage exceeds the reference voltage of the comparator, the output voltage of the comparator CP is turned to L level. At this time, a capacitor is connected between the emitter and base of transistor _Q1 due to the voltage of capacitor _C3 .
Reverse bias is applied through the circuit of C ₃ , resistor R ₃ and comparator CP, and the emitter-base charge of transistor Q ₁ is rapidly discharged by capacitor C ₃ , reducing the switching time when transistor Q ₁ is turned off. can.

In other words, due to fluctuations in the power supply voltage, the coil L ₁
The rate of increase in the current flowing through the capacitor _C3 changes, but this changes the time it takes for the voltage across the capacitor C3 to act as a reverse bias between the emitter and base of the transistor _Q1 , in other words, the supply voltage increases. Sometimes, the on-period of transistor _Q1 is controlled to be short, so that the peak value of the current flowing through coil _L1 can be kept constant, and the average value of the charging current of battery B through coil _L2 can be kept constant. It is something.

FIG. 2 shows another embodiment, in which a battery B to be charged is connected between the emitter of the transistor Q ₁ and the resistor R ₃ , and this battery B is connected in the opposite direction to the emitter of the transistor Q ₁ . It is shared as a bias power source, and a series circuit of coil _L2 and diode D is connected in parallel to battery B. This operation is almost the same as the previous embodiment, so its explanation will be omitted, but according to this embodiment, the capacitor C ₃ and the Zener diode ZD ₁
This has the advantage of reducing the number of parts and simplifying the circuit.

As described above, according to the present invention, the peak value of the current flowing through the primary coil of the transformer connected in series with the transistor is detected by the current detection resistor, and the transistor is turned off via the comparator. In addition, a DC power supply circuit consisting of a capacitor or a battery to be charged is provided to apply a reverse bias between the emitter and base of this transistor, which enables high-speed switching operation of the transistor and reduces switching loss of the transistor. In addition, even in the case of large fluctuations in the power supply voltage, the on-period of the transistor is detected by a current detection resistor to detect the peak value of the current flowing through the primary coil, and suitably controlled via a comparator to charge the secondary side of the transformer. This has the effect of keeping the flow constant.

Further, since the transistor is driven by a self-excited oscillation circuit, a power source for driving is not required, and there are advantages such as miniaturization and high efficiency.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the charging circuit of the present invention, FIG. 2 shows another embodiment, and FIG. 3 shows a conventional charging circuit. A ₁ , A ₂ ... Input terminal, DB ... Rectifier, C ₁ ...
C ₄ ... Capacitor, R ₁ to R ₆ ... Resistor, L ₁ to _{L 3} ...
...coil, T...transformer, ZD ₁ , ZD ₂ ...Zener diode, Q ₁ ...transistor, D...
Diode, CP... comparator, B... battery.

Claims (1)

[Claims] 1. A series circuit consisting of a DC power source that applies a reverse bias between the primary coil of the transformer, a transistor, and the emitter-base of this transistor and a current detection resistor is connected to the DC power source obtained by rectifying the AC power source, and By driving the transistor on and off by the self-excited oscillation circuit, the power obtained in the secondary coil of the transformer is rectified to charge the secondary battery, and the current detection resistor is used to
In the charging circuit, the output terminal of the comparator is connected to the base of the transistor, and the output terminal of the comparator is connected to the base of the transistor, and the output terminal of the comparator is connected to the base of the transistor. input the reference voltage, connect the inverting input terminal to the connection point between the power supply that applies reverse bias and the current detection resistor,
A charging circuit using a switching power supply, characterized in that a reverse bias is applied between the emitter and base of the transistor in accordance with a change in the voltage drop of the current detection resistor.