JP2844481B2 - Power supply voltage monitoring device for flyback converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply voltage monitoring device of a flyback converter used as a power supply circuit of a flash discharge light emitting device for photography, for example.

"Conventional technology" The flash discharge light emitter used as a certifier for photography is equipped with a DC-DC converter as a power supply circuit, the DC voltage of the battery power is boosted by this converter, and the electric energy stored in the main capacitor is triggered by a trigger. It is configured to discharge through a xenon discharge tube and convert it to light energy.

Many of the above-mentioned DC-DC converters use a blocking oscillation circuit, but recently, a DC-DC converter using a flyback converter circuit provided with a flyback transformer having a small input voltage fluctuation has been developed.

In the case of a flash discharge light emitter incorporated in a camera, one battery power supply is commonly used for the camera side circuit and the flash discharge light emitter. In this case, the flyback converter circuit described above is advantageous. This is because it is necessary to supply a stable constant voltage to a microcomputer incorporated as a camera-side circuit.

[Problems to be Solved by the Invention] When the battery power is shared with other load circuits including a microcomputer, such as a flash discharge illuminator built in a camera, the DC voltage of the battery power is increased by the charging operation of the flash discharge illuminator. Since the voltage fluctuates considerably, power is supplied to another circuit via a regulator.

However, there is a problem in that a sufficient constant voltage cannot be supplied even with the provision of the regulator, and there is a problem that if the accuracy of the regulator is increased, the circuit configuration becomes complicated, and furthermore, the production cost increases accordingly.

In view of the above circumstances, the present invention guarantees the power supply pressure of other load circuits that require a constant voltage, such as a computer,
It is an object of the present invention to develop a power supply voltage monitoring device for a flyback converter that allows fluctuation in a range exceeding the power supply pressure.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a step-up transformer for stepping up a DC voltage of a battery power supply and a switching element for intermittently oscillating a primary coil current of the transformer. A flyback converter that charges a capacitor load by an output of a boosting transformer, detects a charging voltage of the capacitor load, and regulates the switching element to non-conduction when charged to a predetermined charging voltage; and an oscillation start signal. To enter the monitoring mode, and when the DC voltage of the battery power supply drops to a predetermined voltage value, the state is switched from the first state to the second state in response to the DC voltage to operate the monitor circuit, And a monitoring circuit for restricting the switching element to non-conduction. A source voltage monitoring device is proposed.

[Operation] The monitoring circuit enters the monitoring mode in response to the input of the oscillation start signal, and monitors the voltage change of the battery power supply.

This monitoring circuit keeps the first state as long as the DC voltage of the battery power supply fluctuates in a range exceeding a predetermined voltage value, and does not regulate the switching element that oscillates.
Therefore, a normal oscillation operation of the converter is performed.

When the DC voltage of the battery power source changes to a predetermined voltage value, the monitoring circuit switches from the first state to the second state, and operates the monitor circuit. Then, the monitor circuit restricts the switching element for oscillation operation to non-conduction to stop the oscillation of the converter.

Since the input current of the converter is interrupted by the non-conduction regulation of the switching element, the battery power supply keeps a voltage equal to or higher than a predetermined voltage value.

"Example" Next, an example of the present invention will be described with reference to the drawings.

The drawing is a circuit diagram of a flyback converter implemented as a power supply circuit of a flash discharge light emitting device.
11 is a step-up transformer having a flyback transformer structure, two primary coils 11P ₁ and 11P ₂ , a secondary coil 11S, and a feedback coil 1
It is equipped with 1F.

The primary coils 11P ₁ and 11P ₂ are connected in parallel, one of the connecting portions a is connected to a transistor 12 for oscillation, and the other connecting portion b is connected to a negative wiring 14 of a battery power supply 13. .

The secondary coil 11S has an output terminal on the winding start side connected to a main capacitor 16 and other light emitting circuits via a rectifying diode 15.

The feedback coil 11F has one end connected to a capacitor 17 and a resistor 18.
Is connected to the base of the transistor 19, and the other end is connected to the negative wiring 14 together with the primary coil.

The transistor 19 controls the base current of the oscillation transistor 12, and the flyback converter circuit is formed by the transistors 12, 19, the step-up transformer 11, and the choke coil 20 provided between the battery power supply 13 and the transistor 12. Is formed.

A series circuit of a zener diode 21, a resistor 22, and a capacitor 23 connected in parallel to the main converter 16 is a charge detection circuit that detects that the main capacitor 16 has been charged to a predetermined voltage value Vc. , A charge completion signal Sc is output from the connection point c between the resistor 22 and the capacitor 23.

Further, the base of the transistor 25 is connected to the connection part d between the Zener diode 21 and the resistor 22 via the Zener diode 24, and the transistor 25 is turned on by the detection operation of the charge detection circuit. That is, when the main capacitor 16 is charged to the predetermined voltage value Vc, the transistor 25 is turned on, and the voltage between the base and the emitter of the transistor 19 is extinguished. As a result, the transistor 19
By turning off, the transistor 12 is turned off and the oscillation of the converter is stopped.

That is, the charge detection circuit and the transistor 25 form a monitor circuit that brakes the oscillation of the converter.

On the other hand, a series circuit composed of a resistor 26, a Zener diode 27, a transistor 28, and a resistor 29 connected in parallel to the battery power supply 13, a transistor 30 base-connected to a connection part e of the transistor 28 and the resistor 29, and an oscillation start signal So input end f
The resistor 31 and the diode 32 connected more toward the base of the braking transistor 25 form a power supply voltage monitoring circuit. The configuration of the monitoring circuit formed in this manner is simplified because it uses the transistor 25 for braking.

Note that the oscillation start signal So is input to the base of the transistor 19 via the resistor 33, and the transistor 28 of the monitoring circuit is
Of the brake transistor 25 when the monitoring circuit operates.

In addition, 34 is a capacitor for stabilizing the power supply voltage, and 35 is an internal resistance of the battery power supply 13.

The flyback converter circuit described above starts oscillating when the battery power supply 13 has a voltage value equal to or higher than a predetermined value when the oscillation start signal So is input. That is, the oscillation start signal So is input to the base of the transistor 19, and the transistor 19 shifts from OFF to ON. Thus, the oscillating transistor 12 is turned on by the base current flowing from the battery power supply 13 and starts oscillating. The voltage induced in the feedback coil 11F by the start of the converter oscillation is fed back to the transistor 19, and this transistor 19
In order to increase the base current of the transistor 12, the transistor 12 gradually increases the primary coil current of the step-up transformer 11.

When the transistor 12 enters the saturation region, the voltage of the feedback coil 11F induced at this time is applied to the base of the transistor 19 in the opposite direction, and the transistor 19 is turned off.
Then, the transistor 12 is turned off accordingly.

When the transistor 12 is turned off, the step-up transformer 11
The flyback voltage generated in the secondary coil 11S is output, and the flyback voltage
Is charged.

When the voltage induced in the feedback coil 11F changes to turn on the transistor 10 due to vibration, the transistor 19 is turned on by the induced voltage and the base input of the oscillation start signal So.
Is turned ON again, and the transistor 12 is turned ON.

Thereafter, in the same manner, the transistor 12 is repeatedly turned on and off to continue the oscillation, and the main capacitor 16 is charged by the flyback voltage of the secondary coil 11S generated at each oscillation.

When the main capacitor 16 is charged to the predetermined voltage value Vc, the Zener diode 21 conducts, the charge detection circuit outputs the charge completion signal Sc, and the transistor 25 is turned on to keep the transistor 19 in the off state. . As a result, the oscillation is stopped while the transistor 12 remains in the OFF state.

When the charged voltage of the main capacitor 16 is discharged and the Zener diode 21 of the charge detection circuit becomes non-conductive, the transistor 25 returns to OFF, so that the transistors 19 and 12 repeat ON and OFF as described above. Oscillation starts.

On the other hand, the transistor 28 of the monitoring circuit that inputs the oscillation start signal So at the base is turned on, and the monitoring mode is set.

When the battery power supply 13 is equal to or higher than a predetermined voltage value,
Since the Zener diode 27 that detects this voltage value conducts, the voltage generated at the resistor 29 is applied to the base of the transistor 30, and the transistor 30 is turned on. That is,
Under the condition that the battery power supply 13 is equal to or higher than a predetermined voltage value, the transistor 30 is turned on, and the oscillation start signal So passes through the resistor 31 and the transistor 30, so that the oscillation start signal So is not applied to the braking transistor 25. As described above, when the monitoring circuit is in the first state, the converter oscillates as described above because the oscillating transistor 12 and the braking transistor 25 are not involved at all. Stops.

When the voltage of the battery power supply 13 drops and reaches a predetermined voltage value, the Zener diode 27 that detects this voltage value becomes non-conductive, and the transistor 28 receives the oscillation start signal So as the base input. Switch from ON to OFF,
As a result, the voltage of the resistor 29 disappears and the transistor 30 is turned on.
OFF from.

As a result, when the battery power supply 13 reaches a predetermined voltage value, the monitoring circuit changes from the first state to the second state, the transistor 30 is turned off, and the oscillation start signal So is braked via the resistor 31 and the diode 32. To the base of the transistor 25.

Thus, since the transistor 25 is turned on, the transistor 12 is turned off as the transistor 19 is turned off.

Therefore, since there is no power consumption by the converter thereafter, battery power supply 13 can be maintained at a predetermined voltage value.

Specifically, the battery power supply is 6 V, and the internal resistance 36 is set to 0.
5 Ω, predetermined voltage value of battery power supply 13 (keep voltage) 4.2
Assuming that V is 6-4.2 = 1.8V, 1.8 / 0.5 = 3.6A, the current can be input to the converter up to 3.6A. If the battery current changes within the range of 3.6A, the converter will operate normally. Oscillate.

When the above battery current 3.6A tries to increase, the battery power 13
, The monitoring circuit enters the second state, the transistor 12 is turned off, and the battery current is maintained at 3.6 A.

As a result, the voltage value of the battery power supply 13 is maintained at 4.2 V, and when power is supplied to another load circuit by the battery power supply 13, power can be supplied to the other load circuit with a battery voltage of 4.2 V or more.

Note that the choke coil 20 shown in the above embodiment works to prevent a ripple transmitted from the step-up transformer 11 side to the battery power supply side. Therefore, when the ripple is not a problem, it is not necessary to provide the choke coil 20.

Further, the present invention is not limited to a flyback converter provided in a flash discharge light emitting device, but can be similarly applied to a flyback converter used as a power supply circuit of another electric device.

[Effects of the Invention] As described above, according to the present invention, when the battery power supply drops to a predetermined voltage value, the monitoring circuit regulates the oscillation switching element to be non-conductive, so that the battery voltage drops or the converter Even if the input voltage fluctuates, the power supply voltage does not drop below a predetermined voltage value. Therefore, when sharing the battery power of the converter with other load circuits,
Regardless of the converter load, another load circuit can be supplied with a battery voltage that is equal to or higher than a predetermined voltage value.

In particular, according to the present invention, the above effects can be obtained by a simple monitoring circuit having a configuration using a monitoring circuit for monitoring a capacitor load, so that a practically excellent power supply voltage monitoring device for a flyback converter can be obtained.

[Brief description of the drawings]

The drawing is a circuit diagram showing an example in which the power supply voltage monitoring device of the present invention is applied to a flyback converter provided in a flash discharge light emitting device. 11 Boost transformer 12 Oscillation transistor 13 Battery power supply 16 Main capacitor 19 Transistor for base current control 25 Transistor for brake 27 Zener diode for monitoring 28 Monitoring Circuit transistor 30 Transistor for oscillation start signal path

Claims (1)

(57) [Claims] 1. A flyback converter comprising: a boosting transformer for boosting a DC voltage of a battery power supply; and a switching element for intermittently oscillating a primary coil current of the transformer, and charging a capacitor load by an output of the boosting transformer. A monitoring circuit that detects a charging voltage of a capacitor load and regulates the switching element to non-conduction when charged to a predetermined charging voltage, and enters an oscillation start signal to enter a monitoring mode, in which the DC voltage of the battery power supply is set in advance. A monitoring circuit that switches from the first state to the second state in response to the DC voltage when the voltage drops to a predetermined value, operates the monitor circuit, and regulates the switching element to be non-conductive. A power supply voltage monitoring device for a flyback converter.