JPH0666892B2 - Power supply circuit for multi-scan display - Google Patents

Description

The present invention relates to horizontal deflection of a horizontal deflection circuit according to the frequency of a horizontal synchronizing signal in a composite video signal including a video signal and a horizontal synchronizing signal. The present invention relates to a power supply circuit of a multi-scan display that displays an image corresponding to a video signal included in a composite video signal of horizontal synchronizing signals of various frequencies on a screen by switching the frequency of current.

(Prior Art) A television scanning display is widely used as a display device, and inputs a composite video signal (composite video signal) including a video signal, a horizontal synchronization signal, a vertical synchronization signal, and the like,
Scanning is performed according to the horizontal synchronizing signal and the vertical synchronizing signal to display the image represented by the image signal on the screen. Currently, a display such as a television receiver or a personal computer is required to have an excellent image quality for more finely displaying an image, a character, a figure and the like. Generally, the frequency of the horizontal synchronizing signal is increased and the number of scanning lines in the vertical direction of the screen is increased to improve the image quality, but it is very inconvenient to replace the display for each video signal having a different image quality. Therefore,
There has been proposed a multi-scan display capable of displaying a video signal in which the frequency of the horizontal synchronizing signal takes various values within a predetermined range with one device. In this multi-scan display, horizontal scanning is performed by causing a sawtooth deflection current generated by a horizontal deflection circuit to flow in a horizontal deflection coil, and the frequency of the deflection current matches the frequency of the horizontal synchronizing signal. In the multi-scan display, the horizontal sync signal has various frequencies. When the frequency of the horizontal sync signal increases, the frequency of the deflection current also increases. However, if the power supply voltage of the horizontal deflection circuit is constant, the amplitude of the deflection current becomes small. turn into. However, since it is necessary to keep the amplitude of the deflection current constant, the power supply voltage of the horizontal deflection circuit must be increased as the frequency of the horizontal synchronizing signal increases.

FIG. 2 is a diagram showing a power supply circuit of a conventional multi-scan display. The DC power supply 51 is a general switching power supply and supplies a DC voltage to the horizontal deflection circuit 70. The frequency-voltage conversion circuit 52 converts the input horizontal synchronizing signal into a voltage corresponding to the frequency and outputs the voltage to the amplifier 57, and the amplifier 57 amplifies the output voltage of the frequency-voltage conversion circuit 52 with a certain amplification factor. A VCO (voltage controlled oscillator) 58 generates a reference signal having a frequency according to the output voltage of the amplifier 57. The output voltage of the amplifier 57 is proportional to the frequency of the horizontal synchronizing signal, and the frequency of this reference signal follows so as to match the frequency of the horizontal synchronizing signal. The horizontal deflection circuit 70 generates a sawtooth-shaped deflection current according to the reference signal output from the VCO 58 and supplies the deflection current to the deflection coil 68. The generation of the deflection current will be described in detail below.

The deflection current flowing in the deflection coil 68 is
It is generated by switching the npn-type bipolar transistor 64 according to the reference signal output from O58. Since the frequency of the deflection current is determined by the switching operation of the transistor 64, it has a proportional relationship with the frequency of the reference signal, that is, the frequency of the horizontal synchronizing signal.
Further, the VCO 58 extracts the voltage component of the deflection current from the FB point, which is the connection point between the capacitors 66 and 67 in the horizontal deflection circuit 70,
By inputting the voltage component, the phases of the reference signal and the deflection current are aligned.

Here, the amplitude of the deflection current must be constant,
In order to keep the amplitude constant, np is increased as the switching operation of the transistor 64 increases, that is, as the deflection current becomes higher in frequency.
It is necessary to increase the voltage Vcc output from the emitter of the n-type bipolar transistor 61. Therefore, the higher the deflection current frequency, the higher the Vcc voltage value must be, and the deflection current frequency, that is, the reference signal frequency and Vcc
Must be proportional to the voltage value of. This means that the frequency of the horizontal synchronizing signal and the voltage value of Vcc need to be proportional to each other. Transistor
61 converts the output voltage of the DC power supply 51 input to its collector into a voltage value instructed by the control circuit 60, and outputs the converted voltage as Vcc from the emitter. The control circuit 60 indicates the voltage value of Vcc according to the output voltage of the amplifier 57,
Since the output voltage of the amplifier 57 is proportional to the frequency of the horizontal sync signal, the voltage value of Vcc is proportional to the frequency of the horizontal sync signal.

Transistor 61 operates as a series power supply and voltage Vcc
Therefore, the output voltage of the DC power supply 51 must have a voltage value higher than Vcc. Therefore, DC power supply 51
The output voltage of is constant at a voltage value that can generate Vcc corresponding to the highest frequency horizontal synchronizing signal input to the frequency-voltage conversion circuit 52, and the transistor 61 is connected to the DC power supply 51.
Vcc corresponding to the frequency of the horizontal synchronizing signal is generated from the output voltage which is a constant value of.

(Problems to be Solved by the Invention) However, in the power supply circuit of the conventional multi-scan display described above, the output voltage of the DC power supply 51 is constant at a high value corresponding to the horizontal synchronizing signal of the highest frequency. In such a power supply circuit, when the frequency of the horizontal synchronizing signal is low and a low voltage value is required for Vcc,
Since the transistor 61 increases its heat loss and sets Vcc to a low value, the power loss increases.

Therefore, an object of the present invention is to provide a power supply circuit for a multi-scan display which can supply power of a required voltage to a horizontal sync signal having an arbitrary frequency within a predetermined range with a small loss, and has a simple structure and is inexpensive. Especially.

(Means for Solving the Problem) A power supply circuit for a multi-scan display according to the present invention includes a frequency-voltage conversion circuit (25) that generates a voltage proportional to the frequency of a horizontal synchronization signal, and a frequency-voltage conversion circuit (25). The control circuit (32) that receives the frequency proportional voltage and generates a control signal according to the frequency proportional voltage, the horizontal deflection coil (41), and the horizontal deflection coil (41) that are connected in series A voltage control transistor (34) that generates a voltage (Vcc) by giving a voltage drop according to the control signal to the power voltage, and a voltage (Vcc) as a power supply voltage, which is synchronized with the horizontal synchronization signal to produce a horizontal signal. Deflection coil (4
1) is provided with a circuit for supplying a horizontal deflection current, and if the frequency of the horizontal synchronization signal is within a predetermined range, the voltage (Vcc is set to keep the horizontal deflection current constant regardless of the frequency of the horizontal synchronization signal. ) Is provided in the multi-scan display to generate DC power having a voltage corresponding to the frequency proportional voltage, and the DC power is generated by the voltage control transistor (3
4) a power supply circuit for a multi-scan display, which is supplied as the input power to a DC power supply for generating first to nth DC voltage (n is a positive integer of 2 or more), and the frequency proportional A selection circuit that selects one of the first to nth DC voltages as an input voltage of the voltage control transistor according to the voltage.

(Operation) The power supply circuit of the multi-scan display of the present invention converts the horizontal synchronizing signal into a voltage according to the frequency, and determines the value of the output voltage of the DC power supply by the voltage. The value of the power supply voltage of the horizontal deflection circuit that generates the horizontal deflection current having a frequency proportional to is set to a value corresponding to the frequency of the horizontal synchronization signal.

(Examples) Next, the present invention will be described in more detail with reference to Examples.

FIG. 1 is a diagram showing an embodiment of the present invention. The switching power supplies 1, 2, 3, 4 are DC power supplies that output a DC voltage, and the switching power supplies 1, 2, 3, 4 are connected in series to supply the DC voltage to the horizontal deflection circuit 43. The frequency-voltage conversion circuit 25 converts the input horizontal synchronization signal into a voltage according to the frequency and outputs the voltage. The amplifier 30 amplifies the output voltage of the frequency-voltage conversion circuit 25 with a certain amplification factor. A VCO (voltage controlled oscillator) 31 generates a reference signal having a frequency according to the output voltage of the amplifier 30. Since the output voltage of the amplifier 30 is proportional to the frequency of the horizontal synchronizing signal, the frequency of this reference signal fluctuates in proportion to the frequency of the horizontal synchronizing signal. The horizontal deflection circuit 43 generates a sawtooth-shaped deflection current according to the reference signal output from the VCO 31, and outputs the deflection current to the deflection coil 41.
Supply to. The horizontal deflection circuit 43 operates in the same manner as the horizontal deflection circuit 70 of FIG. 2, and the drive circuit 36 switches the npn-type bipolar transistor 37 according to the reference signal output from the VCO 31 to generate a deflection current. To do. Since the frequency of the deflection current is determined by the switching operation of the transistor 37, it matches the frequency of the reference signal, that is, the frequency of the horizontal synchronizing signal. Similarly to FIG. 2, the VCO 31 extracts the voltage component of the deflection current from the FB point that is the connection point between the capacitors 39 and 40, inputs the voltage component, and aligns the phases of the reference signal and the deflection current. There is. The operation inside the VCO is as follows:
It operates according to 0, and the fine tracking depends on the horizontal synchronizing signal and the FB voltage. Here, since the amplitude of the deflection current must be constant regardless of its frequency, the horizontal deflection circuit 43 changes the deflection voltage Vcc of the emitter of the npn-type bipolar transistor 34 according to the output voltage of the amplifier 30. Keeps the amplitude of. The voltage Vcc needs to have a higher voltage value as the frequency of the deflection current is higher. less than,
The supply of the DC voltage to the horizontal deflection circuit 43, that is, the collector of the transistor 34, and the generation of the voltage Vcc by the transistor 34 by the switching power supplies 1, 2, 3, 4 will be described.

The output voltage supplied to the collector of the transistor 34 by the switching power supplies 1, 2, 3, 4 is determined by the conduction state of the field effect transistors 5, 6, 7. When the transistors 5, 6, 7 are all off, the voltage of only the switching power supply 1 becomes the output voltage. When only the transistor 5 is turned on, the voltage obtained by adding the voltages of the switching power supplies 1 and 2 becomes the output voltage. When the transistors 5 and 6 are turned on, the voltage obtained by adding the voltages of the switching power supplies 1, 2 and 3 becomes the output voltage. When all the transistors 5, 6, 7 are turned on, the voltage obtained by adding the voltages of the switching power supplies 1, 2, 3 and 4 becomes the output voltage. Ie transistor
The output voltage becomes the lowest when all 5,6,7 are in the off state, and the output voltage increases every time the transistors 5,6,7 are turned on in sequence, and all the transistors 5,6,7 become The highest output voltage is obtained when it is turned on. Here, the diodes 11, 12, 13, and 14 are backflow prevention diodes, respectively. Control of the conduction states of the respective transistors 5, 6, 7 is performed by comparators 18, 19, 20 via npn-type bipolar transistors 15, 16, 17, respectively. Each transistor 5,6,
7 is turned on when each of the transistors 15, 16 and 17 is off. The comparators 18, 19 and 20 use the voltage V for the four resistors 2
The voltage value divided by 1, 22, 23, 24 is input as a reference voltage, and the reference voltage and the output voltage of the amplifier 30 are compared with each other. The reference voltage of the comparator 18 is the lowest and the reference voltage of the comparator 20 is the highest. When the output voltage of the amplifier 30 is low, none of the comparators 18, 19, 20 operate and the
Since 15, 16, 17 are all on and transistors 5, 6, 7 are all off, the collector voltage of the transistor 34 is the lowest voltage of only the switching power supply 1.
When the output voltage of the amplifier 30 rises and the comparator 18 operates,
Since the transistor 15 is turned off and the transistor 5 is turned on, the collector voltage of the transistor 34 becomes a voltage obtained by adding the voltage of the switching power supply 2 to the voltage of the switching power supply 1. When the output voltage of the amplifier 30 further increases, the comparators 19 and 20 sequentially operate, the transistors 16 and 17 sequentially turn off, the transistors 6 and 7 turn on, and the collector voltage of the transistor 34 also changes. It rises sequentially. That is, the voltage of the collector of the transistor 34 is sequentially switched to four levels of voltage according to the output voltage of the amplifier 30, and the voltage value increases. Further, since the output voltage of the amplifier 30 is proportional to the frequency of the horizontal sync signal, the voltage of the collector of the transistor 34 rises in four steps as the frequency of the horizontal sync signal rises.

Here, the transistor 34 converts the voltage of its collector into a voltage designated by the control circuit 32 and outputs it as Vcc from the emitter. As described above, since Vcc is required to have a voltage value proportional to the frequency of the horizontal synchronizing signal, the control circuit 32 increases the designated voltage in proportion to the output voltage of the amplifier 30.
Therefore, the voltage at the collector of transistor 34 is
Output voltage, that is, it increases according to the required Vcc voltage value. As described above, the collector voltage of the transistor 34 is low when generating a low voltage value Vcc, and the collector voltage of the transistor 34 is high when generating a high voltage value Vcc. The power lost in the form of loss is almost constant regardless of the voltage value of Vcc.

(Effects of the Invention) As described in detail above, according to the present invention, the voltage of the collector of the transistor 34, that is, the power supply circuit Since the output voltage changes, the power loss wasted in the transistor 34 is small when the frequency of the horizontal synchronizing signal is low. Further, in the present invention, since a general-purpose switching power supply is connected in series and various voltages are obtained by switching the combined voltage of the switching power supplies by the conducting operation of the transistor, the circuit configuration is simple and the circuit can be manufactured at low cost. .

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a power supply circuit of a conventional multi-scan display. 1,2,3,4… Switching power supply, 18,19,20… Comparator, 25,52
… Frequency voltage conversion circuit, 30,57… Amplifier, 31,58… VCO
(Voltage controlled oscillator), 32,60 ... Control circuit, 36,63 ... Drive circuit, 41,68 ... Deflection coil, 43,70 ... Horizontal deflection circuit, 51
… DC power supply.

Claims (3)

[Claims] 1. A frequency-voltage conversion circuit (25) for generating a voltage proportional to the frequency of a horizontal synchronizing signal, and a control signal corresponding to the frequency-proportional voltage received from the frequency-voltage conversion circuit (25). A control circuit (32) for generating
A horizontal deflection coil (41) and a voltage control transistor connected in series to the horizontal deflection coil (41) and generating a voltage (Vcc) by giving a voltage drop according to the control signal to the voltage of the input DC power. (34) and a circuit that receives a voltage (Vcc) as a power supply voltage and supplies a horizontal deflection current to the horizontal deflection coil (41) in synchronization with the horizontal synchronization signal, the frequency of the horizontal synchronization signal being within a predetermined range. Within the range, the multi-scan display that controls the voltage (Vcc) so as to keep the horizontal deflection current constant regardless of the frequency of the horizontal synchronizing signal is provided, and a voltage having a magnitude corresponding to the frequency proportional voltage. DC power of the voltage control transistor (3
4) in the power supply circuit of the multi-scan display for supplying as the input power, a direct current power source for generating first to nth direct current voltage (n is a positive integer of 2 or more); And a selection circuit for selecting one of the first to nth DC voltages as an input voltage of the voltage control transistor. 2. The direct current power supply comprises first to nth switching power supplies connected in series with each other and n-1 switching power supplies of the second to nth switching power supplies among these n power supplies. N-1 switches respectively connected to the output terminals, and n backflow prevention diodes respectively connected to the output terminals of these switches and the output terminal of the first switching power supply. The output terminal of the backflow prevention diode is connected to the DC power input terminal of the voltage control transistor, and the selection circuit controls opening and closing of the switch according to the frequency proportional voltage. 1. A power supply circuit for the multi-scan display according to 1. 3. The selection circuit divides a range of frequencies to be planned as the frequency of the horizontal synchronizing signal into n number of frequency bands from the first to the nth in order from the lowest to the second to the nth. N-corresponding to each frequency band up to
A circuit that generates one reference voltage, n-1 comparators that receive these n-1 reference voltages as one comparison voltage and the frequency proportional voltage as the other comparison voltage, and these n -1 depending on the output of one comparator
The power supply circuit of the multi-scan display according to claim 2, further comprising: n-1 switch control transistors that respectively control opening and closing of one switch.