JPS6149570A - Power supply device for display device - Google Patents

Abstract

PURPOSE:To avoid superposing a rush current and make it possible that power is turned on again immediately after power switch is opened, by flowing the rush current to a degaussing circuit when the rush current to a capacitor disappears and using a fixed resistance to disconnect the degaussing circuit after a prescribed time. CONSTITUTION:When power is turned on by closing of a power switch 2, a timer 16 is started and is operated after t1-number of seconds to close a switch 13. When this switch 13 is closed, the charging current to a capacitor 6 is charged through a ripple suppressing resistance 12 having a small resistance value, and therefore, a rush current suppressing resistance 11 is not overheated unnecessarily. A timer 17 is operated simultaneously with coming of the output of the timer 16 to close a switch 14, and a degaussing circuit 9 is operated. Thus, the rush current for power-on is flowed to the circuit 9 when the rush current to the capacitor 6 disappears, and the rush current is not superposed to that to the capacitor 6. Since a resistance circuit 10 is the fixed resistance, the stable rush current suppressing operation is secured even if the switch 2 is opened in the state, where the circuit is warmed up sufficiently after power on, and is closed again immediately.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a power supply device used in a display device such as a CRT (cathode ray tube) monitor or television;
In particular, the present invention relates to a power supply device for a display device that suppresses inrush current when the power is turned on.

[Prior Art] Fig. 1 is a circuit diagram showing a conventional power supply device of this kind, in which (1) is an AC power supply, (2) is a power switch, (
3) is a power supply circuit connected to the AC power supply (1) through this power switch, which includes a rectifier circuit (4) for full-wave rectification of the AC power supply (1), and a negative characteristic thermistor (3) for suppressing inrush current. 5), a power supply stabilizing capacitor (6), and a power transformer (7).

(8) is an output terminal of this power supply circuit (3), which is connected to and drives a display device (not shown). (
Reference numeral 9) is a demagnetizing circuit consisting of a demagnetizing coil, a positive temperature coefficient thermistor, etc. for removing magnetization of the display device, and is connected to the AC power source (1) via the power switch (2). Note that this degaussing circuit (9) is, for example,
Since it is a well-known circuit as shown in Japanese Patent No. 9-16486, detailed explanation thereof will be omitted here.

The operation shown in FIG. 1 will be explained. The magnitude of the rush current when the power is turned on by opening the power switch (2) is determined mainly by the resistance values of the degaussing circuit (9) and the negative characteristic thermistor (5). Now, if we replace the negative characteristic thermistor (5) with a fixed resistor R1 that has no temperature characteristics, we get
The resistance value of R1 needs to be greater than the lower limit value RL and smaller than the upper limit value RH.

This is because if the resistance value of R1 becomes smaller than the lower limit value RL, the ripple current of the circuit becomes too large and the ripple current specification cannot be satisfied.
This is because if it becomes larger than H, the rise of the power supply voltage will be too slow and one circuit will not operate properly. Ideally, the resistance value of R1 should be as large as possible without exceeding the upper limit value RH when the power is turned on, and on the other hand, after the power supply stabilizes, the resistance value of R1 should be as large as possible without exceeding the upper limit value RH.
It is desirable that it be as small as possible within a range not less than L. In other words, it is most desirable to be able to change the resistance value R1 from the upper limit value RH to the lower limit value RL. Because of this requirement, a negative characteristic thermistor (5) is used. In other words, if you choose a negative characteristic thermistor (5) whose resistance value at room temperature (when the power is turned on) is RH, whose resistance value is reduced by self-heating after the power is turned on, and whose resistance value after the power supply is stabilized is R1, You can achieve your purpose.

However, this conventional device has the following disadvantages. In other words, since the negative characteristic thermistor (5) is used as a resistance for suppressing inrush current, when the power is turned off, the negative characteristic thermistor (5)
Until the temperature returns to room temperature, the resistance value is small and the inrush current suppression function cannot be achieved. In other words, when the power is turned off, it takes several tens of minutes for the negative characteristic thermistor (5) to return to room temperature, and during that time, the inrush current cannot be sufficiently suppressed, and the power cannot be turned on again immediately after the power is turned off. There was this inconvenience.

[Summary of the Invention] This invention has been made to solve the above-mentioned inconveniences, and includes a timer circuit that is activated when the power is turned on and operates after a predetermined period of time. By reducing the resistance value of the circuit, the inrush power can be sufficiently suppressed even if the power is turned on again immediately after being turned off.In addition, the degaussing circuit is connected to the power supply when the above-mentioned timer circuit is activated. This is intended to further suppress the inrush current by shifting it from the time of turning on.

[Embodiment of the Invention FIG. 2 is a circuit diagram showing an embodiment of the invention.
0) is a resistance circuit consisting of a parallel circuit of a high-resistance inrush current suppression resistor (1]) and a low-resistance ripple suppression resistor (+-2), and (13) is a resistance circuit in which the ripple suppression resistor (12) is inserted. A switch for degaussing, (4) is a switch provided at the input end of the degaussing circuit (9), (j5) is a first timer (16) that is activated when the power is turned on and operates after a predetermined time; This is a timer circuit consisting of a second timer (17) that operates simultaneously with the arrival of the output of the first timer and returns after a predetermined time, and the output of the first timer (16) activates the switch (13). The resistor (12) is inserted into the circuit, and the output of the second timer (17) drives the switch (14) to connect the degaussing circuit (9) to the AC power source (1).
Connect to. (18) is a degaussing start switch, and by closing this, the switch (14) is closed at any time via the second timer (17), and the degaussing path (9) is operated.

The operation shown in FIG. 2 will be explained. When the power is turned on by opening the power switch (2), the switches (13) and (14) are both open. The first timer (
16) starts and operates after t1 seconds and switches (1
3) Close. Since the capacitor (6) is charged only through the inrush current suppressing resistor (11) having a sufficiently large value until the switch (13) is closed after the power is turned on, the inrush current when the power is turned on is a small value. If the switch (13) is closed after t1 seconds have elapsed, the charging current to the capacitor (6) will be charged through the ripple suppression resistor (12) with a small resistance value, and the inrush current suppression resistor (11) will be charged. No unnecessary overheating.

The second timer (17) operates simultaneously with the arrival of the output of the first timer (16), that is, t1 seconds after the power is turned on, to close the switch (14) and operate the degaussing circuit (9). Due to the above operation, the inrush current when the power is turned on is reduced by the resistance (1
1), and by delaying the operation time of the degaussing circuit (9) by 1 second from the time of power-on, the inrush current to the capacitor (6) is suppressed to the minimum value. Since the current flows, the rush currents of the power supply circuit (3) and the degaussing circuit (9) are not superimposed, and the rush current when the power is turned on can be further suppressed. In addition, since the resistance circuit (lO) is a fixed resistance, the power switch (
2) Stable inrush current suppression operation is guaranteed even if it is opened and then immediately re-closed.

By the way, the second timer (17) is reset when 2 seconds have elapsed due to the degaussing time by the degaussing circuit (9), and the switch (14) is activated.
The degaussing circuit (9) is disconnected from the circuit by opening the circuit, but this also eliminates unnecessary power consumption caused by the degaussing circuit (9) and extends the life of the positive temperature coefficient thermistor used in the degaussing circuit (9). It can be made longer. Furthermore, the degaussing circuit (9)
By disconnecting the degaussing circuit (9) from the circuit, the positive temperature coefficient thermistor in the degaussing circuit (9) can be kept at room temperature.
Complete degaussing can be performed even if the power switch (2) is turned on again immediately after being opened, and the second timer (17
) demagnetization can be performed at any time.

In the above embodiment, the first timer (1G) and the second timer (
17) were made the same, but the second timer (17)
) by delaying the operating point of the first timer (16), the turning point of the degaussing circuit (9) and the resistor circuit (
By shifting the switching point in step 10), it is possible to further reduce the rush current when the degaussing circuit (9) is turned on. Second
The following two methods can be considered to make the operation of the timer (17) later than the first timer (16). One is that the second timer (17) is also started when the power is turned on, like the first timer (16), and its operating time is set longer than that of the first timer (I6). The other one starts the second timer (17) by the output of the first timer (16),
It is assumed that the operation starts after a predetermined time. Further, in the above embodiment, the resistance circuit (10) is configured as a parallel circuit with a high resistance, and the low resistance is inserted/removed by the switch (13), but it is configured as a series circuit with a high resistance and a low resistance. A similar effect can be expected by connecting a switch (13) in parallel with the high resistance to insert and remove the high resistance.

[Effects of the Invention] As described above, according to the present invention, the resistance value of the fixed resistor is reduced by the output of the timer circuit that is activated when the power is turned on and operates after a predetermined period of time, and the degaussing circuit is also turned on. Inrush current suppression operation is possible, and since a fixed resistor is used and the degaussing circuit is disconnected from the circuit after a predetermined time, it is possible to immediately turn on the power again after turning off the power.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional device, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, (1) is an AC power supply, (2) is a power switch, and (3) is a power supply circuit. ,(4)
is a rectifier circuit, (6) is a power supply stabilization capacitor, (7) is a power transformer, (8) is its output terminal, (9) is a degaussing circuit, (10) is a high resistance (11), a low resistance (12) ), (13) and (14) are switches, (
15) is a timer circuit, (1G) is the first timer, (I7
) is a second timer, and (18) is a degaussing start switch. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (7)

[Claims] (1) A display device having a power supply circuit connected to an AC power source and consisting of a rectifier circuit, a resistance circuit, and a power supply stabilizing capacitor, and a degaussing circuit that removes magnetization from a display device driven by the output of this power supply circuit. a timer circuit that is activated when the power supply circuit is connected to the AC power source and operates after a predetermined time; first and second switches driven by the output of the timer circuit; A power supply device for a display device, characterized in that the resistance value of the resistance circuit is reduced by driving the switch, and the degaussing circuit is connected to the AC power source by driving the second switch. (2) The power supply for a display device according to claim 1, wherein the resistance circuit is made up of a parallel circuit of a high resistance and a low resistance, and the low resistance is inserted and removed by a first switch. Device. (3) The power supply for a display device according to claim 1, wherein the resistance circuit is composed of a series circuit of a high resistance and a low resistance, and the high resistance is inserted and removed by a first switch. Device. (4) The timer circuit is composed of a first timer and a second timer that operates later than the first timer,
2. The power supply device for a display device according to claim 1, wherein the first timer drives the first switch, and the second timer drives the second switch. (5) The power supply device for a display device according to claim 4, wherein the second timer is activated by the output of the first timer. (6) A power supply device for a display device according to claim 4 or 5, characterized in that the second timer is reset after a predetermined period of time after activation. (7) The power supply device for a display device according to claim 6, characterized in that the second timer can be restarted at any time after recovery.