JPH033669A - power supply - Google Patents

Abstract

PURPOSE:To contrive to simplify the circuits of an apparatus and to decrease the cost thereof by providing a control circuit for controlling the output of an inverter circuit according to DC voltage and a rush current preventing circuit to give the apparatus the function of making a soft start and preventing a rush current. CONSTITUTION:As the power control circuit 6 for an inverter circuit 7, a circuit for controlling the output of the inverter circuit 7 on the basis of the operating supply voltage of the circuit itself is used in the manner of raising the DC power 5 of control circuit 6 by a specified time constant immediately after closing of an AC power supply 1. Further, the switching means 42 of a rush current preventing circuit 4 is turned ON, when the DC power 5 voltage reaches a specified voltage. That is, not only a soft start for reducing the output of the inverter circuit 7 but also the prevention of rush current to a smoothing capacitor 3 are realized by the use of the rise of the DC power 5. Thus, only one system of time constant circuit, i.e., timer circuit is sufficient so that it is possible to realize the simplification of circuits and the decrease in cost of an apparatus.

Description

Detailed Description of the Invention [Field of Application in Industry A] The present invention rectifies an AC power source such as a commercial power source to generate a DC output, and converts this DC output into a power source with a frequency higher than that of the AC power source, for example, This invention relates to a power supply device that converts to 100kHz AC output. Such a power supply device is particularly suitable for use as a discharge lamp lighting device (electronic ballast) for lighting a discharge lamp such as a fluorescent lamp at a so-called high frequency.

Generally, a so-called soft start function is provided in which the voltage applied to the lamp is lowered below the discharge starting voltage of the lamp until the lamp is sufficiently heated. In addition, for rectifier circuits that generate DC output from an AC power supply, especially if this rectifier circuit is of a capacitor input type, generally, in order to prevent rush current to the smoothing capacitor immediately after the power is turned on,
A rush current prevention circuit is provided, which includes a parallel circuit of a resistor and a switching element, and a timer circuit that turns on the switching element after a predetermined time has elapsed after the power is turned on.

In conventional discharge lamp lighting devices, two systems of timer circuits are provided for these soft start functions and inrush current prevention functions.

[Prior Art] In this type of discharge lamp lighting device, in order to prevent a so-called cold start, in which the filament of the discharge lamp (lamp) lights up before it is sufficiently heated when the power is turned on, the filament is turned on immediately after the power is turned on. [Problems to be Solved] The present invention aims at simplifying the circuit and reducing the cost in a power supply device having functions of soft start and inrush current prevention.

[Means for Solving the Problems] In order to achieve the above problems, a first aspect of the present invention includes a rectifier circuit that generates a smooth rectified output from an AC power source, and an inverter that generates an AC output from the smooth rectified output. a soft start circuit that reduces the AC output from a normal state for a predetermined period of time immediately after the power is turned on, and an inrush current prevention circuit that prevents an inrush current from flowing through the smoothing capacitor of the rectifier circuit immediately after the power is turned on. In the device,
The soft start circuit includes a DC power supply that generates a DC voltage that rises with a predetermined time constant from the smoothed DC output;
and a control circuit that operates when supplied with this DC power and controls the output of the inverter circuit according to this DC voltage, and the inrush current prevention circuit is connected to the inrush current prevention circuit connected in series to the smoothing capacitor. It consists of a prevention resistor and a switching means that turns on when the DC voltage exceeds a predetermined voltage to short-circuit the inrush current prevention resistor.

[Function] According to the configuration of the first aspect of the present invention, the output control circuit of the inverter circuit is one that controls the output of the inverter circuit based on its own operating power supply voltage, and this control is performed immediately after the AC power is turned on. The DC power supply for the circuit is started up at a predetermined time constant. Further, the switching means of the rush current prevention circuit is turned on when the DC power supply voltage reaches a predetermined voltage. That is, the soft start that reduces the output of the inverter circuit and the prevention of rush current to the smoothing capacitor are realized by utilizing the rise of the DC power supply. Therefore, one system of time constant circuits, that is, timer circuits is sufficient, and the circuit can be simplified and the cost of the device can be reduced.

By the way, some conventional discharge lamp lighting devices are equipped with a so-called safety circuit function that cuts off or reduces the output of the device by detecting malfunctions caused by the discharge lamp not being installed, its life, or one-way discharge at the end of its life. It is being In a device equipped with a control circuit that controls the output of the inverter circuit according to the power supply voltage, this function is achieved by switching the power supply of the control circuit 6 to the second switching means 45 as shown in FIG. (hereinafter referred to as the NEB method).

However, in a device that employs such an NEB system, if the first aspect is applied and the switching means 42 of the inrush prevention circuit is driven by the control circuit DC power supply, when the safety circuit function is activated, the control circuit DC power supply 5, that is, the drive voltage of the switching means 42 becomes zero, and the switching means 42 of the inrush current prevention circuit 4 does not turn on (or turns off), so the inrush current prevention resistor 41 is connected in series with the smoothing capacitor 3. There is a problem in that the device remains inserted and generates heat.

A second object of the present invention is to provide a control circuit that controls the output of an inverter circuit based on its own operating power supply voltage, a switching means for a safety circuit function that is turned on in an emergency such as when an abnormality occurs in a device or a load, and In a power supply device having an inrush current prevention function means and a soft start function means,
The purpose is to simplify the circuit configuration and reduce the cost of the device.

In order to achieve this second object, in a second aspect of the present invention, in contrast to the first aspect, the DC power supply is configured with a resistor and a capacitor that serve as the decoupling and time constant functions. The voltage between the terminals of this capacitor is then supplied to the control circuit, and the voltage between the terminals is divided by a first and second resistor, and the voltage between the terminals of the second resistor is used to short-circuit the inrush current prevention resistor. A second switching means is connected in parallel with the first resistor, and operates in response to a predetermined signal, such as the safety circuit function operation signal, which serves as a drive signal for the first switching means.

According to the configuration of the second aspect, the soft start immediately after power is turned on and the inrush current prevention effect are realized in the same manner as in the first aspect, and the second switching means is turned on by the safety circuit function operation etc. When the first
Since the resistor is short-circuited, the DC power supply voltage becomes a voltage obtained by dividing the smoothed DC output voltage by the decoupling resistor and the second resistor. This voltage is lower than the steady state DC power supply voltage and higher than the voltage obtained by dividing the steady state DC power supply voltage by the first resistor and the second resistor. Therefore, the power supply voltage of the control circuit can be lowered, the inverter output can be reduced or cut off, and the drive signal of the first switching means can be maintained at a sufficient voltage. In particular, when an element with a low drive signal voltage such as an SCR or a transistor is used as the first switching means, the voltage of the control circuit becomes substantially zero when the second switching means is turned on, and the voltage of the control circuit becomes substantially zero when the second switching means is turned on. This control circuit can be used without any modification.

[Example] Hereinafter, this invention will be explained based on examples.

FIG. 1 shows a circuit of a power supply device according to an embodiment of the present invention. In the figure, 1 is an AC power supply, and the AC input terminal of a full-wave rectifier circuit 2 is connected to this AC power supply 1, and the full-wave rectifier is Between the DC terminals a and b of the circuit 2, there is a series circuit including a smoothing capacitor 3 and a rush current prevention resistor 41 of the rush current prevention circuit 4;
A control circuit DC power supply 5 consisting of a series circuit of a decoupling resistor 51 and a decoupling capacitor 52 and an inverter circuit 7 are connected in parallel.

The inrush current prevention circuit 4 includes a 5CR 42 connected in parallel to the inrush current prevention resistor 41, a voltage dividing circuit that is a series circuit of voltage dividing resistors 43 and 44 connected in parallel to the capacitor 51 of the DC power supply 5, etc. Equipped with. Resistor 43 is 5CR
42, and a resistor 44 is connected in parallel between the gate and cathode of 5CR42.

The control circuit 6 receives power supply from between the terminals of the capacitor 51 of the DC power supply 5 and controls the output of the inverter circuit 7 according to this power supply voltage, and is connected to the base drive circuit of the main transistor 71 of the inverter circuit 7. A capacitor 61 and an FET 62 are provided.

The inverter circuit 7 uses a so-called secondary current feedback self-help transistor inverter. In the inverter circuit 7, 71 is a main transistor, 72 is a leakage type output transformer, and one end of the primary winding 72p of the output transformer 72 is connected to the smoothed DC output positive side terminal a, and the other end is connected to the smoothed DC output positive side terminal a. A resonance capacitor 73 is connected to the collector and in parallel with this primary winding 72p.
The output transformer primary winding 72p and the resonant capacitor 73 form a parallel resonant circuit. Furthermore, a discharge lamp (lamp) 75 such as a fluorescent lamp serving as a load is connected to the secondary winding 72s of the output transformer 72, and both filaments fl and f2 of the lamp 8, a starting capacitor 76, and a load current are detected. A primary winding 77p of a saturable current transformer (CT) 7 that provides positive feedback to the base of the transistor 71 is connected to a secondary winding 72s of the output transformer 72 to form a series circuit.

Further, the secondary winding 77s of the CT77 has one end connected to the base of the transistor 71 to apply a positive voltage when the load current flows from the lamp 8 toward the secondary winding 72s of the output transformer 71 when the transistor 71 is turned on. transistor 71
and the other end is connected to the negative side DC terminal (common terminal) b via a switching improvement capacitor 79.
Furthermore, the emitter of the transistor 71 is connected to the negative side DC terminal, and the base of the transistor 71 is connected to the negative side DC terminal.
A capacitor reset circuit consisting of a series circuit of a resistor 74 and a diode 75 in the opposite direction with respect to the base and emitter is connected between the emitters. Furthermore, a series circuit consisting of the capacitor 61 and FET 62 of the control circuit is connected in parallel with the switching improvement capacitor 79.

Next, the operation of the apparatus shown in FIG. 1 will be explained.

When the AC power supply 1 is turned on, it is rectified by the rectifier circuit 2, smoothed by the smoothing capacitor 3, and a smoothed DC output is generated between the DC terminals a and b.

In the inverter circuit 7, when the smoothed DC output is applied, the transistor 71 is supplied with a minute negative current from a starting circuit (not shown), and becomes slightly conductive. As a result, the primary winding 72p of the output lance 72 is slightly driven, and the secondary winding 72S is connected to both filaments f of the lamp 8.
l, f2, starting capacitor 76 and CT77 1
Next winding? Load current flows through 7p. This load current is detected by the CT 77 and fed back positively to the base of the transistor 71. The positive feedback loop from the base of transistor 71 to the base of transistor 71 via the collector, output transformer 72 and CT77 turns on transistor 71 rapidly.

During the ON period of the transistor 71, the capacitor 79
is charged by the base current for driving the transistor 71, and the voltage between the terminals increases. Rise. C
The magnetic flux density of the core of T77 is determined by the time integral value of the output voltage of CT77, and when this magnetic flux density exceeds the maximum magnetic flux density of the core, CT77 is saturated and the induced output of the secondary winding 7s becomes zero. As a result, the transistor 71 is turned off, and the capacitor 79 is discharged (reset) via the reset resistor 74, the diode 75, and the secondary winding 77s of the CT 77. At this time, the forward voltage of the diode 75 becomes a reverse bias between the base and emitter of the transistor 71, so that the accumulated carriers are extracted from the transistor 71 and the transistor 71 is smoothly turned off.

Note that the discharge current of the capacitor 79 flows through the secondary winding 77s of the CT77 in the opposite direction to when it is turned on, so the saturation state of the CT77 is immediately released, but after that, the positive feedback in the opposite direction to that when it is turned on as described above occurs. The operation turns off transistor 71 completely.

When the transistor 71 is off, the output voltage of the output transformer 72 is
Due to the resonance of the resonant system consisting of the next winding 72p, the resonant capacitor 73, the load circuit, etc., the load current once reverses its polarity and then rotates in the normal direction again. Then, the voltage applied to the base of the transistor 71 becomes positive, and the transistor 71 is turned on again due to the positive feedback. Thereafter, due to such positive feedback and parallel resonance, the inverter circuit of the device shown in FIG. 1 continues to oscillate.

In this device, when the power is cut off, the capacitor 52 of the DC power supply 5 is discharged, and the DC output voltage of the DC power supply 5, which is the voltage between the terminals of the capacitor 52, is zero. Then, when the AC power supply 1 is turned on and a smoothed DC output is generated between the DC terminals a and b, the capacitor 52 is charged via the resistor 51 by this smoothed DC output, and the voltage between the terminals of the capacitor 52, that is, the DC power supply 5. The DC output voltage increases with a time constant determined by these resistors 51 and capacitors 52. In this case, immediately after the AC power source is turned on, the capacitor 52 is discharged as described above, and the DC output voltage of the DC power source 5 is zero. Therefore, 5C of inrush current prevention circuit 4
Since R42 has a gate potential of zero and is off,
The current flowing through the smoothing capacitor 3 is limited by the inrush current prevention resistor 41, and inrush current is prevented.

In addition, the control circuit 6 that operates by being supplied with the output voltage of the DC power supply 5 operates during a period in which the output voltage is lower than a predetermined voltage.
The gate drive output voltage of ET81 is zero.

On the other hand, in the inverter circuit 7, since the lamp 8 is off immediately after the power is turned on, both filaments f1 of the lamp 8. A series resonant circuit is formed by f2, the starting capacitor 76, the secondary winding 72s of the output transformer 72, etc., and the filaments fl and f2 are heated by this resonant current. Here, in this inverter circuit 7,
During the off period of the transistor 71, the resonance capacitor 7
It is determined by the resonance frequency f0 between 3 and the inductance of the primary winding 72p of the output transformer 72, and the on period is mainly determined by C
It is determined by the magnetic flux density of the T77 core and therefore by the capacitance of the switching improvement capacitor. Immediately after the AC power source 1 is turned on, as described above, the output of the DC power source 5 is zero, the output of the control circuit 6 is zero, and the FET 61 is turned off. In this case, since the only switching improvement capacitor connected in series to the base circuit of the transistor 71 is the capacitor 79, the off period of the transistor 71 is short, and the oscillation frequency f of the inverter circuit 7 is considerably higher than the resonant frequency f0. , the voltage applied to the lamp 8 is lower than the discharge start voltage of the lamp 8. In this state, the lamp 8 is sufficiently preheated over a predetermined period of time.

After the AC power is turned on, the terminal voltage of the capacitor 52 of the DC power supply 5 rises, and in the inrush current prevention circuit 4, the terminal voltage of the capacitor 52 is divided by the resistor 43 and the resistor 44, resulting in a voltage between the terminals of the resistor 44. When the voltage reaches the gate-on voltage of 5CR42, 5CR42 turns on and short-circuits the inrush current prevention resistor 41. Thereby, the rectifier circuit 2 generates a smoother DC output as a capacitor input type rectifier circuit in which a smoothing capacitor is connected between the DC output terminals.

When further time passes and the terminal voltage of the capacitor 52 (output voltage of the DC power supply 5) exceeds the voltage set in the control circuit 6, a gate drive signal is supplied from the control circuit 6 to the FET 61. This turns on the FET 61, and the capacitor 62 is connected in parallel to the switching improvement capacitor 79. When the capacitance of the switching improvement capacitor increases in this way, the on-period of the transistor 71 in the inverter circuit 7 becomes longer, and the oscillation frequency f decreases and approaches the resonant frequency f0, so the secondary winding of the output transformer 72 The induced voltage increases. As a result, a voltage higher than the discharge starting voltage is applied to the lamp 8, and the lamp 8 starts discharging. After the discharge starts, the impedance of the lamp 8 decreases, so the Q of the series resonant circuit decreases, and the cage inductance of the output transformer 72 becomes a ballast impedance, so that the lamp 8 is stably lit.

As described above, according to this embodiment, a time constant is provided for the rise of the DC power supply for the control circuit, and this time constant is used as a timer circuit for both the inrush current prevention circuit 4 and the control circuit. , it was possible to simplify the circuit configuration of the device and reduce costs.

FIG. 2 shows a schematic circuit configuration of a discharge lamp lighting device according to another embodiment of the present invention. This device differs from the one in FIG. 1 in that it uses the aforementioned NEB system control circuit that stops the oscillation of the inverter circuit when the power supply voltage is approximately zero as the control circuit 6, and also drives the gate of 5CR42 of the inrush current prevention circuit 4. In parallel with the voltage dividing resistor 43, a phototransistor 45 is connected which constitutes a photocoupler together with an LED placed in a safety circuit (not shown) and is turned on by a signal from the safety circuit when an abnormality is detected.

In the device shown in FIG. 2, the operation of inrush current prevention and lamp start-up (soft start) at power-on starts after the power supply voltage to the control circuit 6 exceeds approximately 1.5V. Rice removal is carried out in exactly the same manner as in the apparatus shown in FIG.

In the safety circuit, when an abnormality such as a lamp malfunction or one-way discharge is detected and the LED is turned on, the phototransistor 45 is turned on.

In this case, the voltage between the terminals of the resistor 44 becomes the gate-on voltage (about IV) of the 5CR42. This inter-terminal voltage is supplied to the control circuit 6 as the output voltage of the DC power supply 5. As a result, in the inverter circuit 7, the base drive signal for the transistor 1 from the control circuit 6 is cut off, and oscillation is stopped.

Such abnormality detection is also performed when the power is turned on, and when the abnormality is detected before 5CR42 of the inrush current prevention circuit 4 is turned on, and the phototransistor 45 is turned on, the power supply of the control circuit 6 is short-circuited. There was a problem in that the gate voltage of the inrush current prevention resistor 41 became zero and the 5CR42 could not be turned on, causing the inrush current prevention resistor 41 to generate heat.

This resistor 41 is originally provided to operate for a short period of time immediately after the AC power is turned on, but if a low-power resistor is used with only normal operation in mind, it may burn out, etc. There was a problem.

In the device shown in FIG. 2, only the resistor 43 is short-circuited, so the voltage supplied to the control circuit 6 is the gate voltage of the 5CR42.
The voltage between the cathodes can be lowered to below. Furthermore, even if an abnormality is detected when the AC power is turned on and the phototransistor 45 is turned on, the voltage between the gate and cathode of the 5CR42 will remain at the resistor 5 until it reaches the gate-on voltage.
1 and the resistor 44, and in a steady state, a sufficient voltage can be applied via the resistors 51 and 44. Therefore, in a steady state, 5CR42 can always be turned on, and the resistor 41 will not generate heat.
The capacity of the resistor 42 can be set at a short-time rating, and the resistor 42 can be made smaller, thereby reducing the cost of the device.

[Effects] As explained above, according to the power supply device of the present invention, the time constant for the inrush current prevention circuit and the time constant for soft start can be used together, and the circuit configuration can be simplified to reduce the power consumption of the device. can be converted into

In addition, even when using the NEB method, which cuts off or reduces the output of the device by lowering the power supply of the control circuit when an abnormality in the device or load is detected, it is also possible to Since the voltage dividing resistor on the side is short-circuited, the switching means is not turned off when an abnormality is detected, and therefore the inrush current prevention resistor does not generate heat.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a power supply device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a modification of the device in FIG. 1, and FIG. 3 is a conventional power supply device. FIG. 1: AC power supply 2: Full wave rectifier circuit 3: Smoothing capacitor 4: Inrush current prevention circuit 41: Inrush current prevention resistor 42: SCR (first switching means) 43: Voltage dividing resistor (first resistor) 44 : Resistor for voltage division (second resistance) 5: DC power supply 51: Comin capacitor for decoupling 52: Resistor for decoupling 6: Control circuit 7: Inverter circuit

Claims (2)

[Claims] (1) an AC power source; a rectifier circuit that includes a smoothing capacitor and generates a smoothed rectified output from the AC power source; an inverter circuit that generates an AC output from the smoothed rectified output; and a rectifier circuit that generates an AC output from the smoothed DC power source at a predetermined time constant. A DC power supply that generates a rising DC voltage, a control circuit that operates when supplied with this DC power and controls the inverter circuit to generate an output according to the DC voltage, and a control circuit connected in series to the smoothing capacitor. A power supply device comprising: an inrush current prevention resistor; and switching means that turns on when the DC voltage exceeds a predetermined voltage to short-circuit the inrush current prevention resistor. (2) an AC power source; a rectifier circuit that includes a smoothing capacitor and generates a smoothed rectified output from the AC power source; an inverter circuit that generates an AC output from the smoothed rectified output; and a rectifier circuit that generates an AC output from the AC power source through a decoupling resistor. a DC power supply that includes a decoupling capacitor that is charged with a decoupling capacitor and generates a DC voltage that rises at a predetermined time constant as the voltage between the terminals of this capacitor; an inrush current prevention resistor connected in series with the smoothing capacitor and with one end connected to a common ground with the control circuit; The circuit includes a first switching means connected in parallel, and a series circuit of a first resistor and a second resistor connected to the DC power source, and divides the DC voltage to convert the voltage across the terminals of the second resistor to the second resistor. 1. A power supply device comprising: a voltage dividing circuit that applies a driving signal to a first switching means; and a second switching means that short-circuits the first resistor in response to a predetermined signal.