JPS63136494A - Load controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a load control device using semiconductor switches.

(Background technology) FIG. 5 shows a circuit diagram of a conventional load control device.

The load control circuit 5 connects the AC power supply 1 to a diode bridge D.
A DC voltage is created by full-wave rectification by B + and smoothed by capacitor C5, and this DC voltage is inducted with transistor Q and stepped down by a step-down chopper including diode D+ to discharge lamp 2. is supplied to. A detection resistor Rs for current detection is connected in series to the discharge lamp 2, and a capacitor C2 that operates like a direct current is connected in parallel to both ends of the series circuit of the discharge lamp 2 and the detection resistor Rs. . ■・The transistor Q operates on and off at high frequency. When the transistor Q1 is turned on, a current flows from the capacitor C1 through the series circuit of the transistor Q1, the inductance L1, the discharge lamp 2 and the resistor Rs, and the parallel circuit of the capacitor C2, and returns to the capacitor C7. When the transistor Q is turned off, the energy stored in the inductance L1 flows from the inductance L1 through the series circuit of the discharge lamp 2 and the resistor Rs, the parallel circuit of the capacitor C2, and the diode D. Current flows in the path that returns to .

The on/off operation of the transistor Q in the load control circuit 5 is PWM controlled by the switching control circuit 6. This switching control circuit 6 is the PWM control circuit 3
and a base drive circuit-1. The pwM control circuit 3 detects the lamp current of the discharge lamp 2 with a resistor Rs, controls the on-time of the transistor Q according to the magnitude of the detected current, and supplies stable power to the discharge lamp 2. be. P
WM control inscription 3 includes comparators CPI and CP2 for providing signals to reset/reset the flip-flop FF and the flip-flop FF, and comparators CPL and CP2 to provide a triangular wave voltage as a voltage. It has a triangular wave generation circuit O8C that provides a triangular wave generation circuit O8C. The voltage detected by the current detection resistor Rs is input to the comparator CPl, and is compared with the triangular wave voltage. A voltage obtained by dividing the reference voltage RE' is inputted to the comparator CP2 and compared with the triangular wave voltage.The output of the flop FF is sent to the base drive circuit 4 (
') is input to the base of I transistor Q2.

The base drive circuit 4 supplies the output current of the transistor Q2 between the base and emitter of the transistor Q1 via the transformer Tf.

When the AC power supply 1 is turned on, the transistor Q1 is turned on and off at high frequency, but since the discharge lamp 2 has not yet started discharging, the voltage of the capacitor C2 rapidly increases. When the voltage 2 of the capacitor C2 increases to the discharge starting voltage of the discharge lamp 2, the discharge lamp 2 starts discharging and a lamp current flows.

The ON time of the transistor Q1 is controlled by the PWM control circuit I33 so as to keep this lamp current at a predetermined value. In other words, when the lamp current increases, the on time of transistor Q is shortened, and when the lamp current decreases,
Perform the opposite action.

In such an operation, when there is no load, such as when the discharge lamp 2 is not removed, the voltage 2 of the capacitor C2 remains at a high voltage. Figure 6 shows capacitor C at no load and when lighting.
2 voltage ■2 is shown. As is clear from the figure, when there is no load, the voltage of capacitor C2 2 becomes high, and if the voltage is maintained as it is, the output voltage at no load will be high, so there will be an emergency when replacing the discharge lamp 2, etc. is dangerous. Furthermore, even if the power source 1 is turned off, the charge in the capacitor C2 remains stored, which is not desirable from a safety standpoint.

(Object of the invention) The present invention has been made in view of the above-mentioned points,
The purpose is to provide a load control device that can reduce the output voltage during no-load conditions.

(Disclosure of the Invention) Figure 1 is a basic configuration diagram of the present invention. As shown in the figure, in the load control device of the present invention, the semiconductor switch Q
A load control circuit 5 having a load control circuit 5 and a capacitor C2 of the output terminal of the load control circuit 5 connected in parallel with a load such as a discharge lamp 2, and a switch element S connected in parallel with the capacitor C2. and a no-load detection circuit 7 that turns on the switch element S1 when a no-load condition is detected.
and connect this inductance. and capacitor C2 to cause vibration and change the voltage across capacitor C2 from DC voltage to AC voltage, thereby lowering the effective value and substantially reducing the output voltage at no-load. be.

FIG. 2 shows an example of the voltage 2 of the capacitor C2 when the switch element S1 is turned on in the circuit of FIG. Figure 2 (a) shows the inductance L0
When resistor R8 is not connected in series with
oscillates with the same amplitude, but the same [1 (1,) is when the resistor R6 is connected in series with the inductance L0, and there is power loss due to the resistor R8, so the amplitude of the voltage V2 changes over time. It is attenuating with As shown in FIG. 2 (1)), even the slight presence of the resistance component R8 causes the voltage V2 to undergo damped oscillation, and the output voltage under no load decreases with the passage of time.

In the circuit shown in FIG. 1, when the no-load detection circuit 7 operates, it gives a stop signal to the switching control circuit 6 to turn off the semiconductor switch Q of the load control circuit 5, so that the capacitor C2 is turned off. Vibration occurs due to the residual charge, and power is not supplied from the load control circuit 5, but even if this semiconductor switch Q is not stopped, the resonance frequency due to the inductance L0 and capacitor C2 can be set far away from the operating frequency of the semiconductor switch Q. If the frequency is set to a certain frequency, the voltage V2 of the capacitor C2 will not increase.

Examples will be described below. In the example circuit, parts having the same functions as those of the conventional example circuit are given the same reference numerals, and redundant explanation will be omitted.

Large 1,000 [L FIG. 3 is a circuit diagram of a first embodiment of the present invention.

In this embodiment, an I transistor Q is used as a switching element, and a diode D2 is connected in antiparallel to this transistor Q4. The no-load detection circuit 7 determines the no-load state based on the presence or absence of a voltage across the detection resistor Rs. The detection voltage VR5 of the detection resistor Rs and the reference voltages V F and EF are input to the comparator CP, and when VRs>VRεF, it is determined that the lighting is on, and when VRs<REF, it is determined that there is no load. It is determined that the state is When it is determined that there is no load, the output of comparator CP becomes 'II' level,
When transistor Q4 turns on, resistor R+, capacitor C3, and resistor R2 cause a predetermined time delay to turn on transistor Q, which short-circuits the base and emitter of transistor Q2, turning transistor Q2 off. Therefore, the l transistor Q1 is turned off. As a result, the charge accumulated in the capacitor C2 is discharged through the inductance L, and an oscillating current flows. In other words, from capacitor C2 to inductance L0, and transistor Q.

When a current flows in the path returning to capacitor C2 via capacitor C2 and the voltage polarity of capacitor C2 is reversed, an inductance is generated from capacitor C2 to diode D2.

Current flows in the opposite direction via the path returning to capacitor C2. As a result, the voltage V2 of the capacitor C2 is converted into an alternating current, so its effective value decreases, and the output voltage at no-load time substantially decreases. That is, since the output voltage under no load is converted from the DC voltage Vm (the effective value is also +n) to the AC voltage, the effective value becomes Vm/L', and can be substantially lowered.

In the circuit shown in FIG. 3, the detection resistor Rs for PWM control is also used as a resistor for detecting a no-load state, so that a simple no-load detection circuit 7 can perform no-load detection. In addition, since the resistor R1, capacitor C3, and resistor R2 provide a predetermined time delay for the turn-on operation of the transistor Q, the discharge lamp 2
It is possible to apply the high voltage necessary to start the lamp, and it is possible to smoothly transition to a steady lighting state.

Husband 1 Ren 1 FIG. 4 is a circuit diagram of a second embodiment of the present invention.

In this embodiment, the inductance L0 in the step-down chopper is commonly used as the inductance L0 of the circuit shown in FIG. 3, and the diode D1 is also commonly used as the diode D2 of the circuit shown in FIG. The configuration and operation of the control circuit 8 are similar to those shown in FIG.

In this embodiment, when transistor Q4 is turned on,
Current flows from capacitor C2 through inductance 0, transistor Q, and returns to capacitor C2,
When the voltage polarity of capacitor C2 is reversed, capacitor C
Current flows in the opposite direction from C2 to capacitor C2 via diode D5 and inductance L+. As a result, the voltage V2 of the capacitor C2 is changed to alternating current, so its effective value decreases, and the output voltage under no load substantially decreases.

In the above description of the embodiment, a step-down chopper was used as the load control circuit 5, but a step-up chopper and other load control circuits can also use a similar configuration to control the output voltage at no-load. Can be lowered.

Further, in the embodiment, the no-load state is detected by detecting the presence or absence of load current, but it may also be detected by detecting voltage.

Furthermore, in the embodiment, the discharge lamp 2 is used as a load, but it goes without saying that similar effects can be obtained even if a load other than the discharge lamp is used.

(Effects of the Invention) As described above, the present invention connects an inductance element in parallel to the output smoothing capacitor of the load control circuit connected in parallel with the load via a switch element that is turned on when there is no load. When there is no load, the capacitor voltage oscillates due to the resonance between the inductance and the capacitor, and by converting the capacitor voltage from DC voltage to AC voltage, the effective value decreases, and the output under no load suddenly changes. Since the voltage can be lowered, there is an effect that a highly safe load control device can be provided.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the basic configuration of the present invention, Figure 2 (a)
(b) is an explanatory diagram of the same operation as above, FIG. 3 is a circuit diagram of the first embodiment of the present invention, FIG. 4 is a circuit diagram of the second embodiment of the present invention,
FIG. 5 is a circuit diagram of a conventional example, and FIG. 6 is an explanatory diagram of the same operation. 1 is a power source, 2 is a discharge lamp, 5 is a load control circuit, 7 is a no-load detection circuit, Q, , Q are transistors, c2 is a capacitor, and L, , L are inductances.

Claims (1)

[Claims] (1) a load control circuit having a semiconductor switch; a capacitor for smoothing the output of the load control circuit connected in parallel with the load; and an inductance element connected in parallel with the capacitor via a switch element; A load control device comprising: a no-load detection circuit that turns on the switch element when a no-load state is detected.