SU434616A1 - DEVICE PROTECTION OF OUTPUT CASCADE OF MASTERTRADING AMPLIFIER FROM SHORT CIRCUIT IN A LINE - Google Patents

Description

one

The invention can be used in automation, computing and communication devices.

The known 1ML091 chip, having at the input a matching circuit for positive signals, is intended for use as a trunk amplifier operating on a cable line with a characteristic impedance of 75 ohms. In this chip integrated short-circuit protection (short circuit) on the line.

However, with a stable short circuit on the line, the power of the short-circuit currents is released in the chip, causing it to overheat and fail. In this case, after eliminating the short-circuit fault in the line, the device restores operation only after replacing the trunk amplifier.

The aim of the invention is to automatically restore the health of the trunk amplifier after eliminating the short circuit in the line.

This is achieved by the fact that in the proposed device the information input of the protection device is connected to the first input of the main amplifier through the input and output of the delay element, the first input and output of the logic circuit is AND is NOT connected to the second input of the main amplifier, the output of which is through the input and output of the inverter connected to the second input of the logic circuit "AND-NOT.

FIG. I shows the scheme of the proposed protection device and the method of its connection.

to protected main amplifier; in fig. 2 - time diagram of the protection device.

Protection device 1 contains information input 2 connected via the first

the input and output of the trunk amplifier (MU) 3 to the input of line 4, the delay element (EZ) 5, the inverter 6 and the AND-HE logic 7, performing the function AND for positive signals.

The security device operates as follows.

In the initial state, a low voltage level is applied to the first input of the trunk amplifier 3 and to the information input 2 of the protection device 1. At the same time, the input of line 4 also has a low voltage level, which is fed to the input of inverter 6, which forms a high level at its output. The low level from the information input 2 through the input and output of the delay element 5 is fed to the first input of the logic circuit AND-NOT 7, so that at its output a high (permitting) voltage level is supplied to the second

input power amplifier 3.

When applied to the first input of the trunk amplifier 3 and to the information input 2 of the high-level protection device 1, a high level is also formed at the input of the line 4, which is converted by the inverter 6, which forms a low voltage level at the second input of the AND-HE circuit 7. Delay element 5 is designed to maintain a low level at the first input of the AND-NOT 7 logic circuit when applied to high level information input 2 until a low level appears at the output of the inverter 6 and the second input of the AND-7 logic circuit. delay 5 should slightly exceed the time of signal propagation through the trunk amplifier 3 and inverter 6.

In the event of a short circuit in the line when a high level voltage is applied to the input of the main amplifier 3, the voltage at the input of the line 4 remains low. Since the input of the inverter 6 connected to the input of line 4 remains low, the output level connected to the second input of the AND-HE circuit 7 maintains a high voltage level. After a time determined by the delay time of element 5, a high level of voltage is applied to the first input of the AND-HE circuit 7. As a result of the coincidence of the high levels of the AND-HE 7 circuit at both inputs, a low level is formed at its output. Since at the input of the trunk amplifier 3 there is a coincidence circuit for positive signals, when appearing at the second input

trunk amplifier 3 low level from the output of the circuit "IS-NOT 7" turns off the amplifier 3. Thus, in the output circuit of the amplifier 3 the short circuit current flows only the time determined by the signal passing through the delay element 5, and does not exceed the permissible one for the 1IL091 chip.

When the short circuit in the line is eliminated in the initial state, the trunk amplifier is prepared for operation.

The protection device of the output stages of the main amplifier against short circuits in the line can be used to protect any main amplifier having the logic AND input circuit.

Subject invention

A device for protecting the output stages of a trunk amplifier from a short circuit in a line, containing an information input connected through the first input and output of the trunk amplifier to the line input, a delay element, an inverter and an AND-NIC logic circuit, in order to automatically restore performance the main amplifier after the elimination of the short circuit in the line, the information input through the input and output of the delay element the first input and output of the logic "AND IS NOT connected to the second input main amplifier, the output of which through input and output of the inverter is connected to the second input of the logic circuit "AND-NO.

FIG. 2