JPH0241667A - Inverter circuit for lighting fluorescent lamp - Google Patents

Abstract

PURPOSE:To reduce switching loss by supplying start pulses properly only when it is found necessary to supply them to switching transistors. CONSTITUTION:A diode D1 to constitute a discharging circuit in an inverter circuit is provided. In order further to constitute a bias circuit, a resistance R2, a diode D2, a capacitor C6 and a resistance R3, a diode D3 and a capacitor C7 are connected between each transistor(Tr) Q1 to Q2 and windings M2 to M3. In putting the power supply AC to work, start pulses are applied to the base of the Tr Q2 from a starter circuit by a time constant circuit, etc., by which the inverter circuit starts operation and turns on a fluorescent lamp FL. In addition, when the operation is started, with the Tr Q2 ON the energized electric charge of a capacitor C5 in the starter circuit is discharged through the diode D1 and Tr Q2. During the operation of the inverter circuit no start pulses will be applied to the Tr Q2 as a result.

Description

DETAILED DESCRIPTION OF THE INVENTION fa) Industrial Application Field This invention relates to a half-bridge type inverter circuit for lighting a fluorescent lamp.

(b) Conventional technology The inverter circuit for lighting fluorescent lamps uses a push-pull method.
There are forward methods, half bridge methods, etc. Third
The figure shows a schematic diagram of a half-bridge system, which is the premise of this invention. In this half-bridge type inverter circuit, a switch 5WISW2 that alternately switches the fluorescent lamp FL is connected in a half-bridge manner.

The bridge circuit is composed of these two switches SWi SW2, capacitors C1 and C2, fluorescent lamp FL, and capacitor C3 and inductor L that constitute a resonant circuit. A large capacity capacitor C4 is connected to the input side of the electric current aE. In this half-bridge inverter circuit, the switches SWI and SW2 are turned on and off alternately, and the current 'l' is turned on and off alternately.
+ '2 alternately flows to the fluorescent light FL. Since the capacitor C1 exists in series on each current path, the current flow stops as soon as the capacitor ClC2 becomes fully charged. In reality, as soon as one current stops flowing, the switch is turned on and off, and the other current starts flowing. In such a half-presociable inverter circuit, since a capacitor is connected in series to the path through which the Ja+ load current flows, the moment when the load current becomes 0 is steep. Therefore, when switching elements such as transistors are used for the switches SWI and SW2, the switching can be made steep, and therefore, when both switching elements are switched on and off, both switching elements are not turned on. Therefore, there is no need to connect an inductor to the power input side to prevent a large current from flowing when both switching elements are turned on. Furthermore, in push-pull type inverter circuits, a voltage that is at least twice the input power supply voltage is applied to the switching element when the switching element is switched, or in the case of a half-bridge type inverter circuit, a voltage that is at least twice the input power supply voltage is applied to the switching element, or in the case of a half-bridge type inverter circuit, a voltage that is at least twice the input power supply voltage is applied to the switching element.
Since there is no large inductor in the path through which current flows, a large voltage is not applied to the switching element as in the push-pull method. That is, there is an advantage that the switching element has a low breakdown voltage.

A conventional configuration of the half-bridge type inverter circuit as described above is as shown in FIG. 4, for example.

In this inverter circuit, the transistor QIQ2 constitutes the switches SWI and SW2, and the lance TR alternately supplies bias voltages from the bias windings M2 to M3 to each of the switching transistors Q1 to Q2. In this half-bridge type inverter circuit, if there is no scooter circuit, the Swiss transistor Ql will be activated when the power is turned on.
, Q2 cannot be turned on. Therefore, a stark circuit is required in a half-bridge inverter circuit, but this normal stark circuit is
A well-known pulse generation circuit using a time constant circuit is used. In the circuit shown in Fig. 4, a time constant circuit is constructed with a resistor R1 and a capacitor C5, and a capacitor C is connected via a diac DA.
A start pulse based on the charge of 5 is applied to the switching transistor Q2. However, in this starter circuit, although the switching transistor Q2 is reliably activated when the power is turned on, a start pulse is not supplied when the inverter circuit is operating. But fluorescent light I? If L is used in a stand-type fluorescent lamp device, for example, and the fluorescent lamp FL has a structure that allows it to be easily removed while it is on, the moment it is removed while it is on, Since the oscillation stops, even if the fluorescent lamp is returned to its original state, the inverter circuit will not be restarted because the starter circuit no longer generates pulses as described above. With stand-type fluorescent lamp devices, etc., the fluorescent lamp FL is often operated while it is on, so
Such problems must be solved by some means. Therefore, a method has been considered in which a series circuit of a capacitor C6 and a diac DA is directly connected to the AC power source as shown in FIG. In this circuit, since a starting pulse is supplied to the transistor Q1 every cycle, restarting of the transistor Q2 is guaranteed even if the fluorescent lamp FL is temporarily removed and then put back together while the inverter circuit is operating. Ru.

(C) Problems to be Solved by the Invention However, in the circuit shown in FIG.
Since a start pulse is supplied to the transistor Q2 every cycle, the start pulse is also supplied during the oscillation operation of the inverter circuit, and the continuous oscillation operation is restarted when the start pulse is generated. This has the drawback that the lighting state of the fluorescent lamp FL flickers in synchronization with its start pulse. In addition, in the half-bridge type inverter circuits shown in FIGS. 4 and 5, some accumulation gear remains when the switching transistor switches from the on state to the off state, so the accumulated carriers are divided into steep on/off states. There was a problem in that the switch was not in an off state, resulting in a large amount of switching loss.

The purpose of this invention is to correctly supply a starter pulse to the switching transistor when it is necessary to supply star 1 to pulses to the switching transistor, such as when the power is turned on or when the fluorescent lamp is turned on again while the inverter circuit is operating. To provide an inverter circuit that does not supply an unnecessary start panel that causes flickering of lights.

Furthermore, it is an object of the present invention to provide an in-hark circuit in which accumulated carriers are eliminated when the switching transistor is switched from the on state p3 to the off state, and the switching loss is extremely reduced.

(Means for Solving the d1 Problems) This invention provides an inverter circuit for a fluorescent lamp in which two switching transistors are connected in a half bridge. a transformer having two bias windings for supplying a voltage; a bias circuit connected between each of the switching transistors and the bias windings and biasing the bias winding output input to each switching transistor to the negative side; CR when two switching transistors are not operating
It consists of a starter circuit that outputs star 1 to pulse to one of the switching transistors using the capacitor charging charge of the time constant circuit, and a closed circuit of one of the switching transistors and the capacitor of the CR time constant circuit, and the capacitor's charge is A discharge circuit for discharging electricity.

FIG. 1(A) is a diagram showing the configuration of an inverter circuit for lighting a fluorescent lamp according to the present invention, and FIG. 1(B) is a diagram showing the configuration of a bias circuit according to the present invention.Discharge circuit according to the present invention is between the capacitor C5 of the scooter circuit, the collector-emitter of switching 1 and transistor Q2, and the diode.
1'DI. Further, as shown in FIG. 1(B), the bias circuit of the present invention has a bias S line M2M3 of each switching transistor Ql, Q2 and a transformer TR.
connected between. These bias circuits are connected to winding M2. M
Bias the output voltage of 3 to the negative side.

(81 action) In the inverter circuit of this invention, a starter pulse ist flows from the starter circuit when the power is turned on.
is started, but once the inharter circuit operates, the charge in the capacitor C5 of the starter circuit is transferred to the diode D.
I and the collector-emitter of the switching transistor Q2 as a discharge current i. Since this discharging occurs during the operation of the impark circuit, the charge charged in the capacitor C5 is almost 0. Therefore, in that state, if the fluorescent lamp FI is once removed and returned to its original state, the 'ζ capacitor C
Since the charging current flows to the transistor Q2, the start pulse current isr flows again to the transistor Q2. That is, the inverter circuit starts operating. On the other hand, during the operation of the inverter circuit, the charge charged in the capacitor is O, so no start pulse is generated.

Further, during operation of the inverter circuit, the bias circuit connected to each transistor Ql, Q2 is connected to the winding M2. M
3 outputs are biased to the negative side, transistor Q1. The base potential of Q2 is as shown in FIG. 1(C). Here, Δ■ indicates the amount of negative bias. Therefore, each transistor is on in the region A and off in the region B, but when switching from A to B, when switching from on to off, A<
B, the accumulated carriers rapidly disappear. As a result, the switching loss of the switching transistor is reduced (and the efficiency is improved) (fl Embodiment) Fig. 2 shows an embodiment of the present invention. The circuit is twisted.The difference in configuration from the circuit shown in FIG. A resistor R2, a diode D2, a capacitor C6, a resistor R3, a diode D3, and a capacitor C7 are connected between each transistor Ql, Q2 and the windings M2 and M3.

In FIG. 2, when the power supply AC is turned on, a start pulse is applied to the base of the transistor Q2 from a starter circuit composed of a time constant circuit of a resistor R1 and a capacitor C5, and a diac DA. This activates the 1-transistor Q2, and the impark circuit starts operating. The inductor connected in series to the fluorescent lamp F L and the conching °C3 connected between the filament of the fluorescent lamp F L form a resonant circuit, supplying preheating current to the filament and generating current at both ends of the capacitor C3. The fluorescent lamp FL is ignited by the resonant voltage. The transformer 1'R is excited by the load current flowing through the winding M1, and the winding M2. The M3 outputs are respectively applied as transistor drive voltages (bias voltages) to the bases of transistors Ql and Q2. This winding M2. M3 constitutes a bias winding, and the output of each winding is applied to the base in the form of a waveform shown in FIG. 1(C) by the action of capacitors C6 and C7 and resistors R2 and R3. . Therefore, the carriers accumulated in each transistor disappear rapidly during switching operation, and the loss during switching becomes extremely small.

When the in-hark circuit starts operating as described above,
When the transistor Q2 is on, the charge in the capacitor C5 of the starter circuit is discharged through the diode D1 and the collector-emitter of the transistor Q2. On the other hand, after the discharge, the current passing through the resistor R1 flows between the diode D1 and the collector-emitter of the transistor Q2, so that the capacitor C5 is not charged. That is, while the inverter circuit is in operation, capacitor C5 is hardly charged.

Therefore, no activation pulse is applied to the switching transistor Q2 during operation of the inverter circuit.

Once the fluorescent lamp FL is pulled out while the inverter circuit is operating, the oscillation operations of the transistors Ql and Q2 naturally stop. At this time, capacitor C5 is charged via resistor R1. The charging charge is diac DA and volume vAM3
°ζ is discharged through the capacitor C, but once it is discharged, the capacitor C
Charging is performed at 5. That is, the capacitor C5 is constantly charged while the oscillation operation is stopped. In this state, when the fluorescent lamp FL is connected as before, the charge in the capacitor C5 is discharged through the diac DΔ, and at this time, the star I pulse is transmitted to the transistor Q2.
added to. Then, the operation of the inverter circuit is started again.

As described above, since the star 1 pulse is applied only when necessary, no flickering occurs during lighting of the fluorescent lamp. Furthermore, since a bias circuit is provided in the base circuit of each transistor, accumulated carriers disappear rapidly, and losses during switching operations are extremely reduced.

(g1 Effects of the Invention As described above, according to the present invention, a start pulse is supplied to the switching transistor only when necessary, and a start pulse is not supplied when unnecessary. It is possible to prevent flickering even when the lamp is on, and in many cases, such as with a stand-type fluorescent lamp device, the fluorescent lamp is operated while it is on (although it is possible to prevent flickering even when the lamp is removed). This can prevent a situation where the light does not turn on again when the original state is restored.

Additionally, a negative circuit is provided between each switching transistor and the bias winding of the transformer to bias the bias winding output input to each switching transistor to the negative side, making it possible to eliminate the effects of accumulated carriers that can cause problems during switching. , switching efficiency can be increased.

[Brief explanation of the drawing]

FIGS. 1(A) and 1(B) are diagrams for explaining the present invention in detail, and FIG. 1(C) is a diagram for explaining the operation of the bias circuit. Fig. 2 shows a circuit diagram of an embodiment of the present invention, Fig. 3 is a schematic diagram of a half-bridge inverter circuit before the present invention, and Figs. 4 and 5 show a conventional half-bridge inverter circuit. The circuit diagram is shown. I R1゜I R M2゜L C5 - CR time constant circuit, C5, DA - scooter circuit, C2 - switching transistor, transformer, M3 - bias winding, fluorescent lamp.

Claims (1)

[Claims] (1) An inverter circuit for a fluorescent lamp in which two switching transistors are connected in a half-bridge, and has two bias windings that are excited by the load current and alternately supply bias voltage to each of the two switching transistors. a transformer; a bias circuit connected between each of the switching transistors and the bias winding to bias the bias winding output input to each switching transistor to the negative side; and a CR when the two switching transistors are not in operation.
It consists of a starter circuit that outputs a start pulse to one of the switching transistors based on the capacitor charging charge of the time constant circuit, and a closed circuit that includes one of the switching transistors and the capacitor of the CR time constant circuit, and discharges the charge of the capacitor. An inverter circuit for lighting a fluorescent lamp, comprising a discharging circuit and a discharge circuit.