JPH0333178Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a charging control circuit used for charging a main capacitor in a camera flash device.

[Conventional technology]

This type of charging control circuit has a flyback transformer that boosts the charging voltage to a predetermined value with respect to the power supply voltage, and an oscillation circuit provided on the primary side of the transformer, and is roughly configured as shown in Figure 3. Ta.

In FIG. 3, 11 is a transformer, which has a primary winding 11P, a feedback winding 11F, and a secondary winding 11S, and the secondary winding 11S has a diode 12.
A main capacitor (not shown) is connected via. 13 is a capacitor for the oscillation circuit, and resistor 14
and connected to both ends of a DC power source 16 via a power switch 15. 17 is a driving transistor;
Between the collector and emitter is the primary winding 11P.
It is connected between both ends of the DC power supply 16 via. Further, its base is connected to one end of the capacitor 13 via a resistor 18 and a feedback winding 11F. Reference numeral 19 denotes an oscillation stop transistor whose collector and emitter are connected in parallel with the base and emitter of the drive transistor 17, and whose base is connected to a main transistor (not shown) connected to the secondary winding 11S side. When the charging voltage of the capacitor rises to a predetermined value, a current is applied, bypassing the base current of the driving transistor 17 and turning it off.

In the above configuration, when the power switch 15 is closed, a bias current I _B flows through the resistor 14, the feedback winding 11F, and the resistor 18 to the base of the driving transistor 17. Therefore, the transistor 17 turns on and excites the primary winding 11P. Accordingly, a slight voltage is induced in the feedback winding 11F, thereby positively biasing the transistor 17. As a result, a collector current I _C flows, increasing the induced voltage in the feedback winding 11F. This tendency is then reinforced, causing the transistor 17 to switch dramatically so that its collector current increases. The collector current of this transistor 17 increases as described above, and the supply of the base bias current I _B necessary to drive it reaches a saturated state (I _C
>I _B ·h _FE ), the base bias current I _B tends to decrease with respect to a constant base-emitter voltage V _BE , and this tendency is exacerbated. Therefore, transistor 17 is instantaneously cut off.

When transistor 17 is turned off in this way, a current _ID flows through the secondary side, which decreases linearly with time. After this secondary current I _D =0, a kick voltage that turns on the transistor 17 is generated, and the transistor 17 starts to turn on again. In this way, oscillation is sustained and the main capacitor on the secondary side is charged.

When the terminal voltage of the main capacitor on the secondary side rises to a predetermined value, the base of the oscillation stop transistor 19 is positively biased, and the drive transistor 1
The base bias current I _B of 7 is bypassed to turn it off. This stops oscillation and the main capacitor is not charged.

[Problem that the invention attempts to solve]

However, in the above configuration, the base bias current required to drive the collector current is
The I _B supply reaches saturation and the base bias current
When I _B goes in the direction of decreasing, not only does I _B = 0, but the base of transistor 17 is
As shown in the figure, it becomes reverse biased. For this reason, the transistor 17 is reverse biased between its base and emitter, so the transient time during which it turns off is shortened, and the spike caused by the back electromotive force in the primary winding 11P that occurs thereby increases, and the transistor 17 Therefore, one with a large V _CES rating must be used. Further, as described above, since the reverse voltage applied between the base and emitter is not suppressed, a transistor with a high V _EBO rating must be used as the transistor 17.

Further, as described above, the transistor 19 is turned on, and the base bias current of the transistor 17 is
Even if I _B is bypassed and the oscillation operation is stopped, current flows from the capacitor 13 to the feedback winding 11F due to the kick voltage after the secondary current I _D =0, and the transistor 17 is connected again via the resistor 18. may turn on, and the oscillation operation may not stop reliably. This is considered to be because a current that becomes IFC flows from the feedback winding 11F toward the capacitor 13, and the capacitor 13 is charged. If such unnecessary oscillation continues, a problem arises in that the voltage on the secondary side becomes abnormally higher than the specified value.

An object of the present invention is to provide a charge control circuit that suppresses spike voltages occurring on the primary side and prevents overcharging of the main capacitor by reliably stopping the oscillation operation after charging is completed.

[Means for solving problems]

The present invention has a primary winding 11 as shown in FIG.
A charging control circuit includes a transformer 11 having a feedback winding 11F and a secondary winding 11S, and charges a main capacitor 21 connected to the secondary winding 11S of the transformer 11 via a diode 12. , an oscillation circuit capacitor 13 connected to both ends of this DC power supply 16 via a resistor 14, and a collector/emitter connected to the primary winding 11.
A driving transistor 17 is connected to both ends of the DC power supply 16 via P, and its base is connected to one end of the oscillation circuit capacitor 13 via the feedback winding 11F, and the secondary winding 11S side. When the terminal voltage of the main capacitor 21 reaches a predetermined value, the transmission stop transistor 19 is turned on and bypasses the base current of the drive transistor 17.
and a diode 22 provided between the feedback winding 11F and one end of the oscillation circuit capacitor 13 in a direction to block current flowing from the feedback winding 11F to the capacitor 13.

[Effect]

The present invention uses a diode 22 provided between the feedback winding 11F and the oscillation circuit capacitor 13 to
When the driving transistor 17 turns off, the base
It prevents reverse bias between the emitters and suppresses spike voltage, and also connects the feedback winding 11F to the capacitor 1.
By blocking the current flowing toward 3, unnecessary oscillation operation after oscillation is stopped is prevented.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. Note that the same reference numerals are given to the parts corresponding to those shown in FIG. 3, and the explanation thereof will be omitted.

In FIG. 1, the configuration of the primary side of the transformer 11 is almost the same as that shown in FIG.
The difference is that a diode 22 is provided between the feedback winding 11F and the capacitor 13 in the illustrated direction.

Further, a main capacitor 21 is connected to the secondary winding 11S of the transformer 11 via a diode 12. 24 is a neon tube for indicating charging completion, and resistor 2
5, 26, and 27 to both ends of the main capacitor 21. The base of the transmission stop transistor 19 is connected between the resistors 26 and 27. Reference numeral 29 denotes an arc tube, which is connected to both ends of the main capacitor 21. 3
0 is the trigger coil, capacitor 31, resistor 3
The main capacitor 2 is connected in parallel to the arc tube 29 via the main capacitor 2, and when the trigger switch 33 connected in parallel is turned on, the arc tube 29 is triggered.
Light is emitted by the charge charged to 1.

In the above configuration, when the power switch 15 is turned on, the transistor 1 is connected via the resistor 14, the diode 22, the feedback winding 11F, and the resistor 18.
Bias current I _B flows through the base of transistor 17, turns on transistor 17, excites primary winding 11P, and causes transistor 1 to flow due to the induced voltage in feedback winding 11F.
It is the same as the conventional method that 7 is positively biased and switched in a jumping manner. Furthermore, when the supply of the base bias current I _B necessary to drive the collector current I _C increased in this way is saturated, the base bias current decreases,
This tendency is also exacerbated and leads to the transistor 17 being cut, but in this case, because the diode 22 is provided, the base bias current I _B remains at 0 as shown in Fig. 2, and unlike the conventional The base and emitter of transistor 17 are not reverse biased. Therefore, transistor 17
Since the transient time when the primary winding 11P is turned off can be taken, the spike voltage caused by the back electromotive force of the primary winding 11P is sufficiently suppressed and small compared to the conventional case.

The main capacitor 21 provided on the secondary side is charged by the above-mentioned oscillation operation on the primary side, and when the terminal voltage reaches the specified voltage, the neon lap 24 lights up.
Displays that charging is complete. At the same time, the base of the transistor 19 is positively biased, bypassing the base bias current I _B of the driving transistor 17, turning off the transistor 17, and stopping the oscillation operation.

At this time, the current in the reverse direction from the feedback winding 11F to the capacitor 13 is blocked by the diode 22, and even after a kick voltage occurs after the secondary current _ID = 0, the feedback winding continues as before. No current flows from the line 11F toward the capacitor 13, so the transistor 17 is not turned on, and unnecessary continuation of oscillation can be reliably prevented.

[Effect of idea]

As described above, according to the present invention, a diode is provided between the feedback winding and the oscillation circuit capacitor to prevent current from flowing in the opposite direction. It is possible to ensure that the oscillation operation is stopped, and to suppress the spike voltage during oscillation, and it is possible to prevent overcharging due to abnormal oscillation and to have good results in extending the life of the power supply battery.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the charging control circuit according to the present invention, FIG. 2 is a waveform diagram explaining the operation of FIG. 1, FIG. 3 is a circuit diagram of a conventional example, and FIG.
FIG. 3 is a waveform diagram illustrating the operation shown in the figure. 11...Transformer, 11P...Primary winding, 11
F...Feedback winding, 11S...Secondary winding, 12...
Diode, 13...Capacitor for oscillation circuit, 1
4...Resistor, 16...DC power supply, 17...Drive transistor, 19...Oscillation stop transistor, 21...Main capacitor, 22...Diode.

Claims (1)

[Claims for Utility Model Registration] In a charging control circuit that includes a transformer having a primary winding, a feedback winding, and a secondary winding, and charges a main capacitor connected to the secondary winding of the transformer via a diode. , a DC power supply, an oscillation circuit capacitor connected to both ends of the DC power supply via a resistor, and a collector.
The emitter is connected to both ends of the DC power supply via the primary winding, and the base is connected to a driving transistor connected to one end of the oscillation circuit capacitor via the feedback winding, and to the secondary winding side. A transmission stop transistor that is turned on when the terminal voltage of the main capacitor reaches a predetermined value and bypasses the base current of the drive transistor, and a feedback winding between the feedback winding and one end of the oscillation circuit capacitor. A charging control circuit characterized by comprising a diode provided in a direction to block current flowing toward the capacitor.