JPH0667208B2 - Power supply circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power supply circuit used in a lighting device for a discharge lamp or the like.

[Background technology]

FIG. 1 shows a conventional example of a power supply circuit used as a discharge lamp lighting device, FIG. 2 (A) shows a time chart at the time of full lighting, and FIG. 2 (B) shows a time chart at the time of dimming. In Figure 1, E is an AC power source, DB full-wave rectifier, C ₁ smoothing capacitor, I _n is separately excited full-bridge inverter, a discharge lamp as L _o is the load, L ₁ is an inductor, C is a capacitor, Tr _{1 to} Tr ₄ are transistors as switching elements,
D _{1 to} D ₄ are feedback diodes. I _C1 , I _C2 and V _CE1 ,
V _CE2 is the collector current and collector-emitter voltage of the transistors Tr ₁ and Tr ₂ , I _D1 and I _D2 are the forward currents of the diodes D ₁ and D ₂ , I _L is the load current, and V _L is the load voltage, that is, the inductor. L _1, the discharge lamp L ₀ and a both sides pressurized Ruru voltage of the load circuit consisting of capacitor C, a voltage appearing at the output terminal of the separately-excited full-bridge inverter I _n.

The transistors Tr _{1 to} Tr ₄ are on / off controlled by a control circuit (not shown). The transistors Tr ₁ and Tr ₄ are on and the transistors Tr ₂ and Tr ₃ are off.
A second state in which r ₁ and Tr ₄ are off and transistors Tr ₂ and Tr ₃ are on is alternately repeated. Transistor
Since Tr ₁ and Tr ₄ have the same operation, the transistors Tr ₂ and Tr ₃ have the same operation, the diodes D ₁ and D ₄ have the same operation, and the diodes D ₂ and D ₃ have the same operation. In the figure, regarding transistors and diodes, only the operation waveforms of the transistors Tr ₁ and Tr ₂ and the diodes D ₁ and D ₂ are representatively shown.

Separately-excited full-bridge inverter I _n are well known, to start the lamp by the series resonance of the inductor L ₁ and capacitor C, after the lighting is for the inductor L ₁ is flow a lamp current provisions serve as stabilizing element , Becomes a lag load.

When dimming, each transistor Tr _{1 to} Tr _{4 is} used as a means.
The on-duty of is controlled. If the on-duty of the transistors Tr ₁ to Tr ₄ is reduced during dimming, even if the load is a lagging load due to the inductor L ₁ and the discharge lamp impedance, for example, after the current flows through the diodes D ₁ and D _4. , appears interval transistor Tr _2, Tr ₃ are turned on, the diode D _1, occurs momentarily supply short-circuit state by the D reverse recovery time of ₄ tau, momentarily transistor Tr _1, Tr ₄ and the diode D _1, D _4, inrush An electric current flows. Therefore, in the conventional example, there is a problem that the circuit element may generate heat and may be destroyed.

Such a problem is not limited to the one having the separately excited full bridge inverter shown in the figure, but is a problem occurring in the one having an inverter with a switch element and a feedback diode.

[Object of the Invention]

An object of the present invention is to provide a power supply circuit in which a rush current is suppressed from flowing in a circuit element including a switch element and a feedback diode when an output is adjusted.

[Disclosure of Invention]

A power supply circuit according to the present invention includes an inverter having a switch element and a feedback diode connected to a direct current or a rectified power source, a control circuit for controlling ON / OFF of the switch element, and an inverter interposed between an output terminal of the inverter and a load. Saturable inductor that increases or decreases the amount of phase delay of the load current with respect to the load voltage by means of adjusting the on-duty of the switch element, and in conjunction with this on-duty adjustment, the saturable inductor Control means for controlling the load current so that the polarity of the load current is reversed after the switching element is turned on by decreasing or increasing the amount of phase delay of the load current phase with respect to the load voltage phase by decreasing or increasing the inductance value. It is a thing.

According to this configuration, when the on-duty of the switch element is adjusted to be long or short in adjusting the output, the phase delay amount of the load current phase with respect to the load voltage phase is automatically decreased or increased accordingly. Since the saturable inductor is controlled so that the load current reverses polarity after it is turned on, reverse recovery of the feedback diode is suppressed, and therefore a momentary short circuit of the power supply is avoided, and inrush current flows through the transistor and feedback diode. It is also suppressed.

An embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 shows a basic circuit as a whole, and FIG. 4 shows a more specific circuit. DB is a full-wave rectifier (diode bridge) connected to the AC power supply E, C ₁ is a rectifier DB
A smoothing capacitor connected to the output terminal of the rectifier DB together with the rectifier DB. Tr ₁ and Tr ₂ are transistors as first and second switching elements connected in series with each other connected to the output terminal of the capacitor C ₁ , and Tr ₃ and Tr ₄ are transistors of the first and second transistors Tr ₁ and Tr ₂ . Transistors serving as third and fourth switching elements, which are connected in series to each other in parallel in a series circuit, D ₁ and D
₂ , D ₃ , D ₄ are first to fourth transistors Tr ₁ , T
r _2, Tr _3, Tr ₄ connected in parallel to feedback diodes, L _o is the discharge lamp as a load, C is a capacitor for connecting both ends filament of the discharge lamp L _o, L is series to one of the filaments of the discharge lamp L _o It is a saturable inductor for current limiting as a connected phase variable element.

The four transistors Tr ₁ to Tr ₄ and four feedback diodes D ₁ to D ₄ constitutes a full-bridge inverter I _n,
The midpoint of the first and _second diodes D ₁ and D ₂ (the midpoint of the first and second transistors Tr ₁ and Tr ₂ ) and the third and fourth transistors T
Between the middle point of r ₃ and Tr ₄ (the middle point of the third and fourth diodes D ₃ and D ₄ ), the discharge lamp _Lo , the capacitor C, the saturable inductor L
Is connected to the load circuit. The load voltage is a voltage applied to the load circuit, and the load current is a current flowing through the load circuit.

T is a transformer connected to the power source E, DB ₁ is a full-wave rectifier (diode bridge) connected to the secondary side of the transformer T, C ₂
In smoothing capacitor connected to an output terminal of the rectifier DB _1, constituting the rectified power with the rectifier DB _1. CC is a control circuit connected to this rectified power supply, and is the first and fourth transistor
The first state in which Tr ₁ and Tr ₄ are turned on and the second and third transistors Tr ₂ and Tr ₃ are turned off, and the first and fourth transistors Tr ₁ and Tr ₄ are turned off, and the second and third transistors are turned on. Each of the transistors Tr _{1 to} Tr ₄ so as to alternately repeat the second state of turning on the transistors Tr ₂ and Tr ₃ of
A control signal is sent between the base and emitter of the. That is, the pulse transformer PT ₁ connected to the output end of the control circuit CC
The secondary side is the base of the _first and _fourth transistors Tr ₁ and Tr ₄ .
The secondary side of the pulse transformer PT ₂ connected between the emitters and separately connected to the output terminal of the control circuit CC is connected between the base and emitter of the second and third transistors Tr ₂ and Tr ₃ .

CCC is a load current phase control circuit to which the rectification power source and the control circuit CC are connected, and the output side thereof is connected to the saturable inductor L. This load current phase control circuit CCC
Is in conjunction with the adjustment of the on-duty of the transistor Tr ₁ to Tr ₄ ON ON duty length, reducing the inductance value of with saturable inductor short, the phase delay amount with respect to the load voltage phase of the load current phase by increasing After the switching element is turned on by decreasing or increasing, the load current method is controlled so that the polarity is reversed.

More specifically with reference to FIG. 4, the control circuit CC
Is composed of an integrated circuit IC (μPD1042 manufactured by NEC Corporation), and a resistor R ₆ and a capacitor C ₆ connected to its terminals. The terminals, which are the output terminals of the integrated circuit IC, are connected to the pulse transformers PT ₁ and PT ₂ , respectively, and alternately output a rectangular wave control signal. Terminal is a terminal for adjusting the on-duty of the control signal from the terminal, the resistor R ₁ is connected to the rectified mains, is connected to the midpoint of the series circuit of the variable resistor R _2, the variable resistor R ₂ The adjustment changes the input voltage to adjust the on-duty. The oscillation frequency of the control signal is determined by the resistor R ₆ and the capacitor C ₆ .

The load current phase control circuit CCC is configured as follows.
Connect the base of transistor Tr ₅ via resistor R ₃ to the middle point of resistor R ₁ and variable resistor R ₂ , and connect the collector of transistor Tr ₅ to transistor T 5.
The emitter of r ₆ is connected to the negative terminal of the rectifying power supply through the reverse bias Zener diode D _Z2 . Resistance R ₄
The series circuit of the reverse bias Zener diode D _Z1 and the rectified power source is connected, and the middle point is connected to the transistor Tr via the resistor R _5.
It is connected to the base of ₆ . The transistor Tr ₆ has its collector connected to the positive terminal of the rectified power supply together with the collector of the transistor Tr ₇ and its emitter connected to the base of the transistor Tr ₇ . The emitter of the transistor Tr ₇ is connected to the parallel circuit of the saturable inductor MAG (corresponding to the saturable inductor L in FIG. 3) and the capacitor C ₅ , and the parallel circuit and the capacitor C ₄ connected to the base of the transistor Tr ₆ are It is connected to the negative terminal of the rectified power supply.

Next, the operation will be described.

After power-on, for the aforementioned reason, the operation is full-bridge inverter I _n, the discharge lamp L _o is igniting. Variable resistance
When R ₂ = 0, the on-duty of the rectangular wave control signal output from the terminal is maximum, and the discharge lamp _Lo is in the full lighting state. At this time, the base current does not flow in the transistor Tr ₅ and is in the off state, sufficient base current is supplied to the transistors Tr ₆ and Tr ₇ through the resistors R ₄ and R ₅ , and the transistor Tr ₇ is in the on state (saturation region). ), The control current flowing through the saturable inductor MAG becomes the maximum, and the inductance value of the saturable inductor MAG becomes the minimum.

On the other hand, when the value of the variable resistor R ₂ is gradually increased, the input voltage of the terminal of the integrated circuit IC rises, and accordingly,
Since the on-duty of the rectangular wave control signal from the terminal is reduced, a so-called dimming state is set. As the on-duty is decreased, as described in [Background Art], a phenomenon occurs in which an inrush current flows through the transistors Tr ₁ , Tr ₄ , Tr ₂ , Tr ₃ , but to prevent this phenomenon, the phase of the load current I _L shown in FIG. 5 which is reused the necessary portions of the second view (B) (a) forcibly delayed, the transistor Tr
For example, in the case of the transistor Tr ₁ , a forward current is applied to the diode D ₂ before it is turned on so that the load current _IL is zero-crossed, that is, the polarity is inverted after the transistors ₁ and ₄ or the transistors Tr ₂ and Tr ₃ are turned on. It is only necessary that the flow does not flow, and such control is performed in this embodiment. That is, by decreasing the on-duty and delaying the phase of the load current I _{L at} the same time, a waveform as shown in FIG. 5B can be obtained, and the reverse recovery time of the diodes D _{1 to} D ₄ can be obtained. It is possible to prevent the inrush current due to. Therefore, while controlling the on-duty of the transistors Tr _{1 to} Tr ₄ , the saturable inductor MAG
By controlling the inductance value of, the transistor Tr ₁ ~T
r _4, thereby preventing the inrush current of the diode D ₁ to D _4.

That is, when the value of the variable resistor R ₂ is zero, the on-duty becomes maximum (<50%).
₅ is turned off, and transistors Tr ₆ and Tr _{7 are connected} through resistors R ₄ and R _5.
To the saturable inductor MAG, the control current flowing through the saturable inductor MAG is maximized, the inductance value thereof is minimized, and the discharge lamp _Lo is in a so-called full lighting state. On the other hand, as the value of the variable resistor R ₂ is increased, the voltage of the terminal of the integrated circuit IC rises, which reduces the on-duty of the rectangular wave control signal from the terminal. At the same time, increases the base current of the transistor Tr ₅ is, the transistor Tr ₅ starts to conduct, the base potential of the transistor Tr ₆ is Yuki lowered, since the base current of the transistor Tr _6, Tr ₇ decreases, The transistor Tr ₇ operates in the unsaturated region. Therefore, the control current of the saturable inductor MAG decreases, its inductance value increases, and the load current I
It works to further delay the phase of _L. As described above, by controlling the on-duty of the transistors Tr ₁ to Tr ₄ and controlling the inductance value of the saturable inductor MAG, the phase of the load current I _L is delayed, as shown in FIG. 5 (B). Moreover, for example, since the current is prevented from flowing to the diode D ₂ before the transistor Tr ₁ is turned on and the collector current flows, stable dimming lighting can be performed without the rush current flowing. Note that it is possible to perform the same control by using a signal from the outside instead of the variable resistor R ₂ .

〔The invention's effect〕

According to the present invention, when adjusting the output, it is possible to suppress the inrush current from flowing through the switch element, the feedback diode, and other circuit elements that form the inverter, and extend the life thereof.
This has the effect of improving the reliability of the device.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a conventional example, FIG. 2 (A) is a time chart of waveforms of respective parts at full lighting, (B) is a time chart of waveforms of respective parts at dimming, and FIG. 4 is an electric circuit diagram of an embodiment of the invention, FIG. 4 is a more specific electric circuit diagram thereof, FIG. 5A is a time chart of waveforms in which necessary portions of FIG. ) Is a time chart of operation waveforms in the embodiment. Tr _{1 to} Tr ₄ …… Transistors (switch elements), D _{1 to} D ₄ …
... feedback diode, I n _...... inverter, CC ...... control circuit, L ...... saturable inductor, MAG ...... saturable inductor, R ₂ ...... variable resistor (on-duty of the adjusting means), CC
C: Load current phase control circuit (means)

Claims (1)

[Claims] 1. An inverter having a switch element and a feedback diode connected to a DC or rectified power source, a control circuit for controlling ON / OFF of the switch element, and a load inserted between an output end of the inverter and a load. A saturable inductor that increases or decreases the phase delay amount of the load current with respect to the voltage; and an on-duty adjusting means of the switch element,
In conjunction with this on-duty adjustment, the inductance value of the saturable inductor is decreased or increased according to the on-duty length and the on-duty, thereby decreasing or increasing the phase delay amount of the load current phase with respect to the load voltage phase. And a control means for controlling the load current so that the polarity of the load current is reversed after the power is turned on.