JPS5913748B2 - Capacitive display element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit that efficiently applies alternating voltage to elements of capacitive display elements such as EL and PDP.

Display elements such as EL, PDP, etc. are capacitive loads, and there is a certain threshold voltage Vt in the relationship between applied voltage and luminance.
h exists and has a steep rise characteristic.

As a method of efficiently applying an alternating voltage to such a capacitive display element, a resonant circuit is formed by the capacitive component and inductance of the capacitive display element, and a switching element is used to maintain the potential of the capacitive component of the capacitive display element. A method has been proposed. Figure 1 shows a conventional drive circuit using this method, where C is the equivalent capacitance of the capacitive display element, D, ,D
2 is a diode, SW4 and SW2 are switches, and E is a power supply. In this circuit, first, when the switch SWI is turned on and the switch SW2 is turned off, a charging current ic from the power source E flows. In this case, the potential between the terminals of the equivalent capacitor C after 51/2 periods of the resonant frequency due to the inductance Li and the equivalent capacitor C becomes a potential V1 higher than the power supply voltage E, and the diode D0 becomes reverse biased and held at this voltage V1. Ru. Next, when switch SWI is turned off and SW2 is turned on, the charge charged in equivalent quantity C is released 10
When a discharge current id flows and 1/2 period of the resonant frequency due to the inductance L2 and the equivalent capacitance C has passed, the diode D2 becomes reverse biased and the equivalent capacitance C is held at the voltage V2 at that time. The values of the voltages V, , V2 held in the equivalent capacitance C gradually increase after the start of operation.
Due to resistance such as I, S%, etc., it becomes a certain constant value and becomes a steady state. The values of V4 and V2 at this time are several times the power supply voltage E. However, this circuit has two switches SW and SW2.
Since only the 0- side can be grounded, the configuration of the control section for switches SWI and SW2 becomes complicated. In addition, different inductances are used depending on the direction of the current flowing through the equivalent capacitance, so there is a drawback that two inductances are required. Ta.
25 The present invention has been made to eliminate these drawbacks, and is characterized in that the switch used in the circuit can be grounded, and only one inductance is used, and its purpose is to The reason lies in the simplification of the drive circuit.

30 Figure 2 shows an embodiment of the present invention. In the figure, E is a DC power supply, SWI and SW2 are two switches that are opened and closed alternately, and D, D2 are switches in the forward direction with respect to the power supply. The switches SW, , S
A series circuit of a capacitive display element C and an inductance L is connected between the connection midpoint of W2 and the connection midpoint of the diodes D1 and D2.

In this circuit, when the switch SWl is first turned on and the switch SW2 is turned off, a charging current 1c from the power source E flows.

In this case, after 1/2 period of the resonant frequency due to the inductance L and the equivalent capacitance C of the capacitive display element has elapsed, the amount of charge in the equivalent capacitance C reaches its maximum, and the voltage between the terminals reaches its maximum value V
It becomes 1. After that, the equivalent capacitance C enters the process of discharging, but since the direction of this current is opposite to Ic, the diode D1
will be blocked. Therefore, the voltage induced in the inductance L becomes O, and the voltage between the terminals of the equivalent capacitance C is maintained at V1. Next, turn off switch SWl, switch SW
When 2 is turned on, the charge stored in the equivalent capacitance C becomes L.
It is discharged during the first 1/4 period of the resonant frequency of C, and a current flows in the same direction as the discharge during the next 1/4 period (indicated by Id in FIG. 2). Therefore, the potential between the terminals of the equivalent capacitance C reaches its maximum value V after 1/2 period of the resonant frequency of LC.
It becomes 2. After that, the equivalent capacitance C enters the process of discharging, but the direction of the current here is opposite to Id, so the diode D
, and the potential between the terminals of the equivalent capacitance C is held at 2. Next, when switch SWl is turned on and switch SW2 is turned off, the period shown in Fig. 2
A current flows in the direction shown by c, and after 1/2 period has elapsed, the potential between the terminals of the equivalent capacitance C is held at the highest potential V3. This process differs from the process at the start of operation in that there is first a process of discharging the equivalent capacitance C. Similarly, switches SWl, S
When W2 is turned on and off alternately, the same operation is repeated, and the voltage between the terminals of the equivalent capacitance C becomes Vl, 2, 3, 4, 5,
It is maintained at the value of V6... At this time V1
V3, V5..., V2〈V4〈V6...
・However, each has a certain value Vc depending on the resistance of the circuit etc.
, Vd, resulting in a steady state. As is clear from the above description, Vc and d are potentials in opposite directions, and an alternating voltage with a potential difference of VC+Vd can be applied between the terminals of the equivalent capacitance C. Although it is difficult to accurately determine the values of C and d, experiments have shown that approximately c+3E1d+1.5E can be obtained, and it is possible to apply a voltage approximately five times the power supply voltage between the terminals of the equivalent capacitance C. did it. FIG. 3 is a diagram showing another embodiment of the present invention.

In other words, the switch SWl is activated by the transistors Trl and Tr2.
, SW2, and the transistors Tr4 and Tr3 constitute a pulse conversion circuit that converts the control pulse 1 input from the terminal 2 into a pulse varying between +V and -V, and the output of this circuit is used to convert the control pulse 1 into a pulse that changes between +V and -V. Tr2 is controlled to be turned on alternately. Other operations are similar to those in the previous embodiment. In this way, one of the switches SWl and SW2 can be grounded, so the respective switches can be connected to NPN and PN.
By using P transistors, a drive circuit for a capacitive display element can be easily realized. As explained above, according to the present invention, one terminal of the switch that controls the direction of the current flowing in the series resonant circuit of the capacitive display element and the inductance can be grounded. A driving circuit for a display element can be realized. Further, since the inductance used to form the series resonant circuit with the capacitive display element is shared regardless of the current flowing, there is an advantage that only one inductance is used.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram of a conventional drive circuit, FIG. 2 is a circuit diagram showing an embodiment of the invention, and FIG. 3 is a circuit diagram showing another embodiment of the invention. C: equivalent capacitance of capacitive display element, Dl, D2: diode, Ll, L2, L: inductance, SWl, SW2
: switch, E: DC power supply, Trl to Tr4: transistor, 1: control pulse.

Claims (1)

[Claims] 1 A DC power source, two switching elements, and two diodes oriented in the forward direction with respect to the power source are connected in a circle in the above order, and the middle of the switching element and the middle of the two diodes are connected in the above order. A drive circuit for a capacitive display element, wherein a series circuit of a capacitive display element and an inductance is connected between the two switching elements, and the two switching elements are alternately opened and closed.