JPH04353897A - Voltage switching device - Google Patents

Abstract

PURPOSE:To obtain two different DC voltages with one rectifying and smoothing circuit by providing terminals which differ in ratio of the number of turns on the cold side of the secondary winding of a power transformer in a power circuit which drives the deflecting circuit of a multi-mode cathode-ray tube display monitor which has several different deflection frequencies, and switching the terminals by a relay. CONSTITUTION:The terminals (g) and (f) which differ in ratio of the number of turns are provided on the cold side of the secondary winding of the power transformer 6 and connected to switching contacts f' and g' of the relay 11. A rectifying diode 1 and a smoothing capacitor 3 are connected to the hot side of the transformer and then connected to a DC power output terminal (c). When a deflection frequency detection signal is applied to a voltage switching control terminal (d) for the base of a transistor 10 for voltage switching control, the relay 11 operates to switch the terminals (g) and (f) of the transformer and the two different DC voltages are led out to the output terminal (c) by the one rectifying circuit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power line voltage switching device for driving a deflection circuit of a multi-mode cathode ray tube display monitor having several different deflection frequencies.

0002

[Prior Art] In recent years, cathode ray tube display monitors, which have been used as display terminals for personal computers, have not only a single display capability that is deflected at a single deflection frequency, but also deflections that vary depending on the type of displayed characters and graphics. In order to switch the frequency on the personal computer side and display it on a single CRT display monitor,
Multi-mode support has become common, and the deflection circuit drive voltage must also be switched due to differences in deflection frequency, and various methods have been adopted for voltage switching devices.

[0003] Below, a method of switching the voltage of a power supply line for driving a deflection circuit of a conventional multi-mode cathode ray tube display monitor will be described. FIG. 2 shows an example of a circuit configuration of a conventional deflection circuit drive voltage switching device.

In FIG. 2, 1 and 2 are rectifier diodes whose anodes are connected to the hot side terminal and intermediate tap terminal of the secondary winding of the transformer 6, and 3 and 4 are connected to the cathodes of diodes 1 and 2. Smoothing capacitor 5 is a backflow prevention diode whose anode is connected to the cathode of diode 2; 7 and 8 are resistors connected in series to the cathode of diode 1; 9 is a diode whose emitter is connected to the cathode of diode 1; A voltage switching transistor whose collector is connected to the cathode and whose base is connected to the connection point of resistors 7 and 8, 10 is the resistor 8
This is a voltage switching control transistor with a collector connected to the other end, and a switching control voltage is applied to the base of the transistor 10, and a rectified voltage is switched and output to the cathode side of the diode 5.

The operation of the voltage switching device configured as described above will be explained below. First, the hot side output of the transformer 6 is rectified by the diode 1, smoothed by the capacitor 3, and a direct current is output to point a at the rectified output end. Similarly, the intermediate tap side output of the transformer 6 is rectified by the diode 2, smoothed by the capacitor 4, and a direct current is output to the other rectified output end at point b. In this case, it is assumed that the voltage at point a is higher than the voltage at point b.

On the other hand, the deflection circuit of a cathode ray tube display monitor has different deflection frequencies, and in order to make the amplitude size of the display screen the same, the impedance of the deflection coil is the same, so the driving voltage of the deflection circuit is A common method is to switch the voltage, and the voltage switching method described here is used. For example, when the deflection frequency becomes high and a high deflection drive voltage is required, the transistor 10 becomes conductive by setting the voltage switching control terminal d point to a high level, and as the transistor 10 becomes conductive, the transistor 9 also becomes conductive. The voltage at point is outputted to point c of the DC power output terminal via the emitter and collector of transistor 9, and is supplied as a drive voltage for the deflection circuit.

Next, when the deflection frequency becomes low and a low deflection driving voltage is required, the transistor 10 is cut off and non-conducting by setting the point d to a low level, and the transistor 9 is also cut off and non-conducting. The voltage at point a, which is about to become conductive, will no longer be output to point c, and from now on, the voltage at point a will be output to point b.
The voltage at point C is outputted to point c via diode 5, and a low deflection drive voltage is supplied to the deflection circuit, and this automatic voltage switching device makes the deflection amplitude constant even in deflection circuits using the same deflection coil. be able to.

[0008]

However, the conventional configuration described above requires two series of rectifier diodes, smoothing capacitors, and backflow prevention diodes, which increases the number of parts and increases the cost. had.

The present invention solves the above-mentioned conventional problems, and is a voltage switching method that can obtain a plurality of DC voltages with different voltage values by switching the cold side (ground side) of the transformer in one series of rectifier circuits. The purpose is to provide a device.

0010

[Means for Solving the Problem] In order to solve this problem, the voltage switching device of the present invention does not switch between two rectified and smoothed DC voltages obtained from the secondary winding, but instead switches between two rectified and smoothed DC voltages obtained from the secondary winding. The ratio is switched by a plurality of terminals on the ground side, so that a plurality of different DC voltages can be obtained with one series of rectifier circuits.

[0011]

[Operation] With this configuration, there is no need for rectification and smoothing circuits with multiple series as in the past, and with a small number of parts, multiple different DC voltages can be easily controlled by switching the transformer turns ratio on the ground side. Output can be switched.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a rectifying diode, 3 is a smoothing capacitor, 6 is a transformer, and 10 is a voltage switching control transistor, which have the same functions as conventional ones. 11 is a relay whose relay winding is connected to a power supply terminal e for driving the relay and a transistor 10 for voltage switching control.
and its relay contacts f', g
' is connected to two terminals f and g provided on the cold side to set the ground level of the secondary winding of the transformer 6, and when the relay 11 selects either of the cold side terminals f or g, , the secondary windings of the transformer 6 are set to have different winding ratios.

The operation of the voltage switching device configured as described above will be explained with reference to FIG. First, when a high deflection drive voltage is required at a high deflection frequency, when a high-level control voltage is applied to point d of the voltage switching control terminal, the transistor 10 becomes conductive, the relay 11 operates, and the contact point goes to the f' side. It is connected to the f terminal side of the transformer, which has a large turns ratio, and a circuit of ground-i-f'-f-rectifier diode 1 is formed, and a rectifier diode 1 and a smoothing diode are connected to point c of the DC power output terminal. A high voltage rectified and smoothed by the capacitor 3 is output.

Next, when a low deflection drive voltage is required at a low deflection frequency, when the point d is set to a low level, the transistor 10 is cut off and becomes non-conductive, and the relay 11 becomes inoperable, so the contact is switched to the g' side, connected to the g terminal side with a small turns ratio of the transformer, and a circuit of ground-i-g'-g-rectifier diode 1 is formed, and the DC power output terminal c is connected to the f terminal side. A lower voltage is output than when connected, and the voltage is switched.

As described above, according to this embodiment, outputs of two different voltage values can be easily switched with one rectifier circuit.

[0016]

As described above, according to the present invention, the transformer winding ratio is changed by switching the ground side terminal of the transformer. It becomes possible to further reduce the number of rectifier diodes, smoothing capacitors, backflow prevention diodes, and voltage switching transistors, thereby realizing an excellent voltage switching device that can reduce the number of parts and cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a voltage switching device according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional voltage switching device.

[Explanation of symbols]

1 Rectifier diode 3
Smoothing capacitor 6 Transformer 10 Voltage switching control transistor 11 Relay c DC power output terminal d
Voltage switching control terminal e
Relay f', g' Relay contact f, g Cold side terminal

Claims (1)

[Claims] [Claim 1] A plurality of cold side terminals with different turns ratios provided on the cold side of a power transformer secondary winding;
A voltage switching device comprising a relay for switching the cold side terminal and means for driving the relay, and configured to switch and obtain a plurality of different output voltages by switching the cold side terminal.