JPH0320988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a power supply device used, for example, as a discharge lighting device.

[Technical background of the invention]

Conventionally, various power supply devices such as discharge lighting devices using a blocking type single-stone self-excited inverter have been proposed.

FIG. 1 is a circuit diagram (unknown) of a power supply device previously proposed by the applicant and others. In the figure, 1 is a full-wave rectifier circuit, which converts an AC power source such as a commercial power source into a DC voltage, and then connects an inductor 2 and a capacitor 3.
an L-type low-pass (high-pass rejection) filter consisting of;
The DC voltage is applied to a single transistor transistor inverter 6 via a power storage means consisting of a power storage capacitor 4 and an isolation diode 5. Here, the high frequency component of the rectified output is removed by a capacitor 3 and then applied to a capacitor 4. The capacitor 4 stores power from the L-type filter via the inverter 6, and supplies power to the inverter 6 while the output of the L-type filter is lower than a predetermined voltage. Also, this inverter 6
is the output transformer 7 and 1 of this output transformer 7.
It includes an output transistor 8 that switches the current of the next winding ₇₁ at high frequency, and a drive circuit 9 that drives this transistor 8. The drive circuit 9 is a base winding (feedback winding) of the output transformer 7.
A drive capacitor 10 connected between 7 ₃ and the base side of the transistor 8, a resistor 11 and a diode 12 that are connected in parallel to the capacitor 10 and discharge the charge of the capacitor 10, and a capacitor that is connected in parallel to the resistor 11. It is composed of a reset switching element, for example a transistor 13, which shortens the discharge time of the transistor 10, and a bias resistor 14 connected between the base and emitter of the transistor 13. This drive circuit 9 feeds back the electromotive force induced in the base winding ₇₃ of the output transformer 7 to the base of the transistor 8 via the capacitor 10 to turn the transistor 8 on and off at high frequency, and the waveform shaping capacitor A high frequency voltage is applied to a load 100 such as a discharge lamp through a resonant circuit constituted by a primary winding 7 ₁ and a secondary winding 7 ₂ .
In FIG. 1, an inductor 16 connected in series with the capacitor 4 limits the charging current of the capacitor 4 flowing through the capacitor 4 and the diode 17, thereby regulating the power stored in the capacitor 4. Furthermore, a bias resistor 18 is connected between the (+) side of the L-type filter and the base side of the transistor 8.
and a parallel circuit of an inductor 19 and a resistor 20 for improving the turn-off characteristics of the transistor 8 are connected in series. Also transistor 8
A diode 21 connected to the emitter of the transistor 8 is for protecting the transistor 8 from emitter-base reverse voltage.

FIG. 2 is an explanatory diagram of the operation of the power supply device configured as described above. Here, when the AC voltage Vin is input, this AC voltage Vin is full-wave rectified by the full-wave rectifier circuit 1 and is applied to the L-type filter and the power storage means. The power storage capacitor 4 is charged in a predetermined direction by a current flowing in a closed loop of the rectifier circuit 1 → L-type filter → inductor 16 → capacitor 4 → diode 17 → transistor 8 every time the transistor 8 of the inverter 6 is turned on. The capacitor 4 is discharged via the isolation diode 5 when the rectified output given through the L-type filter becomes less than a predetermined voltage (that is, the charging voltage of the capacitor 4) every half cycle, and this discharge output is sent to the inverter 6. (Refer to the voltage V _C4 waveform across capacitor 4 in Figure 2). The voltage V _ab across the power storage means is the inverter 6
When the current is applied to the base current i B1 , a base current i _B1 flows in a loop of resistor 18 → inductor 19 and resistor 20 → the base of transistor 8, and transistor 8 is turned on. Then, due to the resonance of the inductor 19 and the capacitor 10, a base current flows through the transistor 8 in the direction opposite to the forward bias, turning off the transistor 8 (point c on the emitter side and point d on the base side of the transistor 8 in Fig. 2). Voltage at point V _cd waveform,
When the time axis of this voltage V _cd waveform is lengthened, c
(See the voltage V _cd waveforms at points and d points and the voltage V _ed waveform across the capacitor 10). When the transistor 8 is turned off, an electromotive force is generated in the base winding ₇₃ in the direction of the dashed arrow, and as a result, a base current i _B2 flows through the bias resistor 14, and the transistor 13 is turned on. Therefore, the charge in the capacitor 10 is rapidly discharged through the transistor 13, and the transistor 8 is reset. In this way, the transistor 8 is turned on and off, and the high frequency voltage _Vput is applied to the load 100 via the output transformer 7.

In such a power supply device, since the rectifier circuit 1 is non-smooth, the input power factor is high, and in a section where the output voltage of the rectifier circuit 1 is lower than a predetermined voltage, a DC voltage V _C4 is applied from the power storage capacitor 4 to the inverter 6. Therefore, even though a non-smooth current output is used, there is no rest period and a high frequency output with little ripple is generated. In addition, since the rectified output is supplied to the power storage means and the inverter 6 via the L-type filter, the terminal voltage of the capacitor 4 is low when the power is turned on or when the discharge lamp of the load 100 is dimmed by phase control. At times, the rush current flowing through the capacitor 4 to the primary winding 7 ₁ and the collector of the transistor 8 can be reduced. That is, capacitor 4
Since the current is mainly supplied from capacitor 3,
For example, even if a rush current attempts to flow through the capacitor 4 at startup, the voltage across the capacitor 3 decreases, thereby suppressing the rush current. Therefore, the output transistor 8 with a small rated current can be used. Furthermore, since the high frequency component of the input current of the power supply device is removed by the L-type filter, there is an advantage that the high frequency current flowing to the capacitor 4 can be prevented from having an adverse effect on the AC power supply, and the input power factor of the power supply device is also improved. Furthermore, since the drive circuit 9 is provided with the reset transistor 13, the charge in the capacitor 10 is rapidly discharged, thereby shortening the recovery time and advantageously increasing the oscillation frequency of the inverter 6. Therefore, if a discharge lamp is lit using the high frequency output of this power supply device, it will be lit with good luminous efficiency, and by rectifying the high frequency output, it will be possible to obtain a DC output with less ripple.

[Problems with background technology]

In this type of power supply device, an inductor 19 is provided at the base of the transistor 8 in order to improve the turn-off characteristics of the transistor 8. When a phase-controlled AC voltage Vin as shown by the broken line in FIG. 2 is applied as an input to this power supply for dimming, when the transistor 8 is turned on, the inductor 19 and the capacitor 10 resonate and the 2
A base voltage waveform V _vd and this waveform V _cd appear as shown in Figure a.

V _cd in FIG. 2a has a waveform V _cd1 that has a high peak when transistor 8 is off, and
There are two types of waveforms, V _cd2 and V cd2, which have a low peak when turned on. Utilizing the difference between these peak voltages, the transistor 13 is operated only when the transistor 8 is off to reset the capacitor 10.
The voltage V _Z is chosen at the level shown in Figure 2a.
Here, the voltage V _Z is a Zener voltage of a Zener diode 30, which will be described later.

When the relationship is V _cd1 >V _Z >V _cd2 , transistor 13 turns on only when transistor 8 is off, resets capacitor 10, and enables continuous oscillation.

However, when dimming is performed, the voltage at the valley part decreases as shown in the waveform V _cd in Figure 2b, so V _cd1
＞V _Z ＞V _cd2 It becomes impossible to select a voltage V _Z that satisfies the condition. That is, transistor 13
does not operate only when transistor 8 is off, but does not operate when transistor 8 is off and operates when transistor 8 is on, so the reset of capacitor 10 becomes uneven and oscillation partially stops. . Note that I _C in FIG. 2b indicates the waveform of the collector current of the transistor 13.

The Zener diode 30 inserted on the base side of the transistor 13 in FIG. 1 originally functions to effectively prevent such intermittent oscillation during dimming.

When using such a Zener diode 30, considering ripples in the power supply frequency, at the maximum peak value V ₁ of the voltage waveform V _cd2 , the transistor 1
It is necessary to select the Zener voltage V _Z so that the voltage waveform V _cd1 does not turn on, and the outer transistor 13 turns on at the minimum peak value V ₂ of the voltage waveform V cd1.

V ₂ > V _Z > V ₁ However, when a discharge lamp is dimmed and lit using a phase-controlled AC power source, this conditional expression cannot be satisfied because the ripple becomes large. Therefore, even if the Zener diode 30 is used, intermittent oscillation cannot be effectively prevented.

[Purpose of the invention]

The present invention has been made in order to eliminate the drawbacks of the prior art as described above, and an object of the present invention is to provide a power supply device that does not cause intermittent oscillation during dimming.

[Summary of the invention]

To achieve this objective, the present invention discharges the charge in the drive capacitor using a reset switching element in the drive circuit that turns on only during the off period of the transistor, which is the main switch of the inverter, in response to the inverter output. I try to let them do it.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, in the following drawings, the first
Elements that are the same as those in the figures and FIG. 2 are given the same reference numerals.

FIG. 3 is a circuit diagram of the power supply device according to this embodiment. The difference between this power supply device and the one shown in FIG. 1 is that the configuration of the drive circuit is different.

That is, in the drive circuit 39 of this power supply device, the base winding (feedback winding) 7 is connected to the output transformer 7.
An auxiliary winding 7 ₄ connected in _series with the primary winding 7 ₁ is wound in the opposite direction to the base winding 7 ₃ and the auxiliary winding 7 ₄ . and auxiliary winding 7
₄ is connected to the (-) side of the rectifier circuit 1, and the other end of the base winding ₇₃ is a switching element for resetting,
For example, it is connected to the base of a PNP transistor 43 via a bias resistor 44. transistor 4
The emitter of transistor 43 is connected to the junction of base winding ₇₃ and auxiliary winding ₇₄ , and the emitter of transistor 43
A series circuit of a drive capacitor and a diode 52 and a resistor 51 are connected between the emitter and collector of the
are connected in parallel. and transistor 43
The emitter-collector of the diode 52 and the capacitor 50 form a discharge loop of the capacitor 50. Further, a junction between the cathode of the diode 52 and the capacitor 50 is connected to the base side of the transistor 8.

In the power supply device configured in this way, when the input power is turned on, the transistor 8 is turned on,
This results in capacitor 15 and primary winding 7 ₁
A collector current flows between the resonant circuit and the emitter and collector of the transistor 8. Then, an electromotive force is induced in _the base winding 7 ₃ and the auxiliary winding 7 ₄ in the direction of the solid arrow in FIG. At the same time, the capacitor 50 is charged by the electromotive force generated in the auxiliary winding ₇₄ .
Then, due to the resonance of the inductor 19 and the capacitor 50, a base current in the direction opposite to the forward bias flows through the transistor 8, and when the transistor 8 turns off, the collector current of the transistor 8 is suddenly cut off, and the base winding 7 ₃ An electromotive force is induced in the auxiliary winding ₇₄ in the direction of the dashed arrow in FIG. ₃ , and the electromotive force generated in the base winding 73 forward biases the transistor 43, turning it on. The charge in the capacitor 50 is discharged and reset in a closed loop from the emitter and collector of the transistor 43 to the diode 52. In this way, when the reset transistor 43 is reverse biased during the ON period of the transistor 8, the transistor 43 becomes OFF state, and since only the ON period of the transistor 8 is reliably reset, oscillation occurs in the low voltage section during dimming. can be easily and accurately prevented from stopping.

FIG. 4 is a circuit diagram of a power supply device according to another embodiment of the present invention. This power supply device differs from the previous embodiment in that the configuration of the drive 39' is different.
That is, in this drive circuit 39', a photocoupler 53 is used instead of the auxiliary winding ₇₄ of the above embodiment, and a series circuit of a light emitting element, such as a light emitting diode 54 and a current limiting resistor 56, constituting the photocoupler 53 is connected to a base winding. A light receiving element, for example PNP, connected in parallel to the line ₇₃ and paired with the light emitting diode 54.
A type phototransistor (second switching element) 55 is connected in parallel to the resistor 51. In this way, the electromotive force of the base winding ₇₃ induced when the transistor 8 is turned on is transferred to the light emitting diode 55.
is applied in the opposite direction, the phototransistor 55 is turned off, and only the on period of the transistor 8 is reliably reset.

〔Effect of the invention〕

As explained above, according to the present invention, the charge in the drive capacitor is discharged by a switching element that is turned on only during the off period of the transistor in response to the inverter output, so that the switching element is reliably discharged only during the off period of the transistor. Intermittent oscillation during dimming can be easily and accurately prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power supply device, FIG. 2 is a diagram explaining the operation of FIG. 1, FIG. 3 is a circuit diagram of a power supply device according to an embodiment of the present invention, and FIG. 4 is a circuit diagram of another power supply device of the present invention. FIG. 2 is a circuit diagram of a power supply device according to an example. 1... Rectifier circuit, 2... Inductor, 3... Capacitor, 4... Capacitor for power storage, 6...
…Inverter, 7…Transformer, 7 ₁ …Primary winding, 7 ₂ …Secondary winding, 7 ₃ …Base winding (feedback winding), 7 ₄ …Auxiliary winding, 8… transistor,
9, 39, 39'...drive circuit, 10, 50
...Drive capacitor, 13, 43, 55
... Switching element, 19 ... Inductor, 5
3...Photocoupler, 54...Light emitting element, 100...
…load.

Claims (1)

[Claims] 1. A transistor, a feedback winding provided between the base and emitter of the transistor, which generates a voltage based on whether the transistor is turned on or off, and controls the transistor by positive feedback; and a feedback winding between the feedback wire and the base of the transistor. A series resonant circuit of a capacitor and an inductor is provided, and a switching element is connected in parallel with the capacitor, and the switching element is activated only when the transistor is off in response to a voltage based on whether the transistor is on or off. A power supply device comprising a drive circuit that turns on.