SU563931A3 - Liquid crystal device provided with protection circuit - Google Patents

Description

(54) LIQUID-CRYSTAL DEVICE WITH A CIRCUIT

PROTECTION

one

The invention relates to a class of indicator devices for displaying information on liquid crystals, such as digital indicators, which are controlled by integrated circuits and used in electronic clocks.

Liquid crystal display devices are known, using the effect of dynamic dispersion, in which either the transparency or the intensity of the radiation changes. One of the electrodes can be solid, and the second, forming the image, is figured. For example, a digital indicator consists of 7 segments. When the voltage is switched, a milky-white image of the corresponding digit is obtained.

It is also known to include a device comprising a liquid crystal indicator — with electrodes, a generator generating a unipolar alternating voltage, a control circuit connected to a constant voltage source and converting a unipolar alternating voltage of the generator into a bipolar alternating voltage supplied to indicator electrodes. The indicator signal plate can receive, for example, a relatively low-frequency unipolar voltage of one phase, and the segments can receive a signal of the same frequency that is either in phase or out of phase with the signal applied to the signal plate.

A disadvantage of the known devices is that in case of failure of the generator of a low-frequency unipolar voltage controlling the integrated circuit, the battery serving as a power source for the winding elements of the liquid crystals still provides a significant level of constant voltage. In this case, the constant voltage on some segments and the signal plate of the indicator may increase and

These static voltages can lead to the destruction of liquid 1 crystals and thereby shortening their service life.

The aim of the invention is to increase the service life and reliability of the liquid crystal display device. This goal is achieved by introducing a sensitive element in the liquid crystal device, which reacts to the presence of a polarized alternating voltage, and an element associated with a sensitive element, which removes the constant voltage from the control circuit, when

alternating unipolar voltage disappears.

Said sensor element may comprise a switch, or an alternating current element and an alternating current controlled switch associated with it, the alternating current element being used to connect a unipolar alternating voltage to a switch that opens when the alternating voltage disappears. The alternating current element may be a capacitor, and the switch-transistor, the control electrode of which must be connected to this capacitor, one of the supply electrodes with a constant voltage source, and the second supply electrode with one of the terminals of the second capacitor, the other pin of which must be connected to the point of the reference potential. In another embodiment, the source of the DC voltage for the control circuit can be a capacitor, which can be charged with a unipolar alternating voltage, and the switch, which is part of the sensing element and that reacts to the presence or absence of a unipolar alternating voltage, must be in the same circuit with this capacitor.

Thus, the circuit being described is a storage capacitor connected via a conductive transistor circuit to a power supply source. The control electrode of the transistor receives oscillations from the generator output. When oscillations occur, the storage capacitor is charged for each oscillation period and acts as a source of supply voltage. When the oscillation stops, the transistor closes and the charge from the storage capacitor flows from it for a short period of time, thereby removing the source of supply voltage.

The drawing shows the scheme of the proposed device.

The circuit includes a generator 1, which is supplied from source 2 by a voltage Uss - 5 | Volt and which supplies a unipolar alternating voltage to the integrated circuit 3. This voltage may be, for example, 30 Hz and amplitude - 5 V, t. . it can vary from 0 to -5 volts. P1 integral circuit 3 can be a standard element containing a device for shifting the level of susceptibility (sensitivity) of the oscillations produced by generator 1, and the binary-decimal code input signal. The circuit inputs receive four binary decimal coded voltages and oscillations from generator 1. A level shifter within circuit 3 is connected to a binary output decider of seven output slots, and the decoder is connected to display control transistors. The outputs of the integrated circuit 3 are connected to the seven segments of the digital indicator 4. One of the outputs is connected to the signal plate of the digital indicator 4. When the circuit operates, amplified oscillations are supplied from the level shifter inside the circuit 3. These oscillations can have amplitudes up to 5V. The level shifter also transmits

the binary-decimal code to the decoder of the seven segments in response to four control voltages applied to the circuit inputs, and the decoder sends signals to the input of the control unit of the display device inside

schemes 3. Last, in accordance with the decimator signals and amplified oscillations of the level shifter, applies a voltage of 15 V amplitude (ranging from 0 to 15 V) with a frequency of 30 Hz to the corresponding segments, which is either in phase or out of phase with the signal voltage plates. When it is required that the indicator be some digit, the display control unit BLOC supplies a voltage of 30 Hz in phase with the voltage on the signal plate to the segments that should not be visible, and the voltage of 30 Hz shifted by 180 ° out of phase with respect to the voltage of the signal plate, to the corresponding segments that should be visible. As a result, a bipolar alternating voltage with an amplitude of 30 V is applied to the rendered segments. The zero voltage is applied to the remaining segments. An excitation voltage of 30 volts causes the liquid crystal, if it is of the type of crystals with dynamic scattering, to be excited and scatter light. For these purposes can also be used and

Other types of crystals that darken in the excited state and light in the non-excited state.

If the supply voltage ss drops significantly, then generator 1 stops working. However, the constant voltage and EE. may still have a significant level - the order of Yu.v. When the generator is turned off, the voltage on the signal plate drops to 0. In this case, the control transistors will not perceive oscillations of the generator. However, the state they assume — conductive or non-conductive — will depend on the levels of the DC control voltages coming from

binary decimal. Some of these transistors will be in the conducting state (open), but before they apply unipolar voltage to the corresponding segments, a constant

voltage close to the value of voltage UEE- Thus, when the generator is turned off, the voltage on the signal plate drops to O, is grounded, while some of the segments are also grounded, while others have a potential close to / OEE due to the conduction of the circuit through the control transistor. This component of a constant voltage, if it is not excluded, can take out a liquid crystal. To eliminate this drawback, a transistor 5 is introduced into the circuit, the collector of which 5 is connected to the power source 7 (UEE), and its emitter 8 is connected to the output of the circuit for the supplying constant voltage. The base 9 of the transistor is connected via a capacitor 10 to the output of the generator 1. Base 9 is also connected via a resistor 11 to the emitter 8 of the transistor. A capacitor 12 is connected between the emitter 8 and the second output of the circuit for the supply voltage. This conclusion has the potential of the earth. When the circuit operates, when the generator is turned on, the oscillations are supplied through the capacitor 10 to the base 9. Each period when the generator voltage reaches -5 V, the transistor 5 opens and the current flows from the ground through the capacitor 12 to the source voltage f / EE- After a very short period of time, the capacitor 12 is charged to - 15 V, supplying these - 15 V to the output of the integrated circuit. In effect, the resistor And and the opsensor 12 act as a low-pass filter and create a constant voltage close in level to the voltage LJ EE. When the voltage Uss drops significantly, so that the generator turns off, a constant voltage is applied to its output. This constant voltage cannot pass through the capacitor 10. Through the resistor. And a certain bias voltage is applied to the base of the transistor, so that transistor 5 is closed. The charge from capacitor 12 flows through one of the transistors in integrated circuit 3 in a short period of time (about 10 seconds) and the value at the output of the integrated circuit for the supply voltage drops to zero. In this way, any DC components through the liquid crystal are eliminated.

In practice, such schemes as described above, in most cases, have separate power supply batteries with voltage Uss and EE electric capacity of these batteries is chosen so that they have the same service life, but it rarely happens that both batteries are worn out at the same time. If the LEE battery fails first, there will be no serious consequences. However, if the Uss power battery fails, the oscillations arriving at the pick-up device will cease and damage to the liquid crystal, as described above, is inevitable. In practice, the generator is turned off when the pressure drops - 2 volts.

Claims (5)

1. A liquid crystal device with a protection circuit containing a liquid crystal indicator with at least two electrodumps, a generator that produces a unipolar alternating voltage, a control circuit connected to a constant voltage source that converts a unipolar alternating voltage of the generator into a bipolar alternating voltage, supplied to the electrodes of the indicator, which is different from the fact that, in order to increase the service life and reliability of operation, it contains a critical element that reacts to the presence of a unipolar variable voltage, and an element associated with a sensitive element, which removes the constant voltage from the control circuit when the alternating unipolar voltage disappears. 2. A device according to claim 1, characterized in that the sensitive element contains a switch. 3. An Icho device, item I, characterized in that the sensitive element contains an alternating current element and an AC-controlled switch associated with it, the alternating current element being used to connect a unipolar alternating voltage to a switch that opens the alternating current variable voltage. 4. The device according to claim 3, noting that the alternating current element is a capacitor, and the switch is a transistor whose control electrode is connected to this capacitor, one of the supply electrodes is connected to a constant voltage source, and the second supply electrode is connected to one of the terminals of the second conductor, the other terminal of which is connected to the point of the reference potential. 5. The device according to claim 1, characterized in that a constant voltage capacitor for the control circuit is used as the constant voltage, which is charged by an unpolar alternating voltage, and the switch, which is part of the sensitive element and re-reacting to the presence or absence of an alternating alternating voltage, is located in the same circuit with this (capacitor.