JPS627777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit that charges a storage capacitor to a high voltage by boosting a low voltage DC power supply using a DC-DC converter circuit.

A flashlight emitting device in which a storage capacitor is charged using the above-mentioned charging circuit and the charge is discharged by a discharge tube to emit light is used for various purposes. In such charging circuits, many techniques are already known for controlling the charging voltage of the storage capacitor to be constant in order to keep the amount of emitted light constant. The control circuit that keeps the charging voltage of the storage capacitor constant turns on a transistor using a voltage detection element such as a Zener diode that becomes conductive when the charging voltage of the storage capacitor reaches a certain predetermined voltage. The operation of the DC-DC converter circuit is stopped. DC-DC
As is well known, the converter circuit consists of an oscillation transistor and an oscillation transformer having three coils, so when the transistor is turned on, the base and emitter of the oscillation transistor are short-circuited, and the DC-DC converter circuit is completed. operation is stopped.

As the voltage detection element, a detection element such as a Zener diode or a neon tube is often used.
These elements operate as switching elements to apply a base bias to the base of the transistor. However, unlike mechanical switches, these devices tend to cause the voltage to gradually rise over time. That is, before a base bias sufficient to saturate the base of the transistor is applied, a bias voltage that causes the transistor to operate in an unsaturated region is applied. If this period is extremely short, there will be no particular problem. In the above control circuit, since the voltage is detected in order to stop charging the storage capacitor, the detection element is usually turned on at the end of charging. As is well known, the charging characteristic of a capacitor is such that the voltage rises slowly at the end of charging. For that purpose,
The transient state of the detection element becomes slightly longer.

Furthermore, if the transistor for stopping the operation of the DC-DC converter circuit moves from the cut-off region to the unsaturated region by applying a base bias, the base-emitter region of the oscillating transistor in the DC-DC converter circuit will become unsaturated. Since the impedance between the collector and emitter of the transistor in the transistor is short-circuited, the operation becomes slower and the charge to the storage capacitor becomes weaker. Therefore, the rising speed of the charging voltage of the storage capacitor becomes extremely slow from the time when the detection element starts to be turned on, and the transient state of the element continues lazily.

As a result, the transistor that keeps the DC-DC converter circuit inactive has to operate in the unsaturated region for a longer period of time, generating heat and, in the worst case, damaging the transistor. Furthermore, the drift of the charging voltage also increases.

The object of the present invention is to provide a charging circuit for a storage capacitor that avoids such drawbacks.

The present invention achieves the above object by connecting a low voltage power source to a transistor that is turned on by a voltage detection element that detects the voltage of a storage capacitor and stops the operation of a DC-DC converter circuit, and a low voltage power source. The device is characterized by the connection of a differentiating circuit that increases the base bias voltage of the transistor when the voltage increases. The connection of this differentiator circuit is between the positive side of the power supply and the base of the transistor if the transistor is of the NPN type, and the negative side of the power supply if the transistor is of the PNP type. and the base of the transistor.

As the low voltage power supply, a normal electric power source is used. Therefore, when charging a storage capacitor using a DC-DC converter circuit, the voltage of the low-voltage power supply is reduced while the DC-DC converter circuit is operating. As the storage capacitor charges up, it gradually rises and the sensing element begins to turn on, causing the DC
-It increases further when the current flowing through the primary coil of the oscillation transformer of the DC converter suddenly decreases. When this increased amount is applied as a differential pulse to the base of the transistor, the base bias current of the transistor increases rapidly and shifts to the saturation region.
Therefore, the operation of the DC-DC converter circuit is completely stopped. In this way, the period of operation of the transistor in the unsaturated region for stopping the operation of the DC-DC converter circuit can be shortened, and the oscillation operation can be reliably stopped. Therefore,
Accidents such as damage to control transistors caused by heat generation can be completely eliminated, and in addition, sloppy charging of the storage capacitor can be stopped, resulting in a so-called clean circuit.

The illustrated embodiment will be described below. The low voltage DC power supply 1 is made up of four AA size dry batteries connected in series, and the voltage is applied to the DC-DC converter circuit 3 via the switch 2. The DC-DC converter circuit 3 is conventionally well-known and includes an oscillation transistor consisting of two transistors 4 and 5, an oscillation transformer 9 having a primary coil 6, a secondary coil 7, and a feedback coil 8, and a diode 10. The storage capacitor 11 is charged with its output. A Zener diode 13 as a voltage detection element is connected to a sliding piece of a variable resistor 12 connected in parallel to the storage capacitor 11, and a transistor 14 is connected to which a base bias is applied when the Zener diode 13 is turned on. It is connected to the Zener diode 13. This transistor 14 is Darlington connected to the transistor 15, and its collector is connected to the base of the transistor 16. This transistor 16
It is used to stop the operation of the DC-DC converter circuit, and its collector and emitter are connected between the base and emitter of the oscillation transistors 4 and 5.

The charging circuit for the storage capacitor 11 and the circuit for detecting the voltage and stopping the charging, which have these configurations, are well known in the art, so no special explanation is necessary.

In this embodiment, a capacitor 17 forming a differential circuit is connected between the base of the transistor 14 and the positive terminal of the power supply 1. Therefore, when the voltage of the storage capacitor 11 increases and the Zener diode 13 starts to turn on at the set voltage, a bias is applied to the base of the transistor 16 via the transistors 14 and 15, and each transistor is cut off. The primary side current of the oscillation transformer 9 is decreased. As a result, the voltage of the power supply 1 increases, and the change is transferred to the transistor 14 via the capacitor 17.
added to the base of. Therefore, transistor 1
4 and 15 reach the saturation region, and similarly the transistor 16 also reaches the saturation region. Since the bases and emitters of the oscillation transistors 4 and 5 are completely short-circuited, the oscillation operation is reliably stopped and charging of the storage capacitor 11 is stopped.

A capacitor 18 indicated by a dotted line is another example of a differentiating circuit, and is designed to increase the base bias of the transistor 16 by the amount of the voltage rise of the power supply. Its operation is the same as above.

[Brief explanation of the drawing]

The figure is a circuit diagram of an embodiment of the present invention. 1: Low voltage DC power supply, 3: DC-DC converter circuit, 4, 5: Oscillation transistor, 9: Oscillation transformer, 13: Zener diode, 14, 1
5, 16: Transistor, 17, 18: Capacitor.

Claims (1)

[Claims] 1 Low voltage DC power supply, oscillation transistor,
It oscillates using an oscillation transformer with three coils (primary, secondary, and return coils) and a low-voltage DC power supply as a power source.
A connection circuit that connects the secondary coil of the oscillation transformer to generate high voltage, a storage capacitor that is charged by rectifying the voltage generated in the secondary coil of the oscillation transformer, and a storage capacitor whose voltage has reached the expected value. In a charging circuit for a storage capacitor, which has a voltage detection element that sometimes conducts, and a transistor circuit that turns on when the voltage detection element conducts and stops the operation of the oscillation transistor, a low-voltage DC power supply and a transistor circuit are used. A charging circuit for a storage capacitor, characterized in that a differentiating circuit is connected therebetween for adding a voltage increase of a low-voltage DC power supply to increase a base bias current of a transistor circuit.