JPS5996826A - Protecting circuit of device controlled by electric signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for a device controlled by electrical signals, whose input side is protected by the protection circuit against positive and/or negative overvoltages.

Integrated units with narrow operating voltage tolerances are generally used in electrical control systems used, for example, for gasoline injection systems in motor vehicles.

An operating voltage of 1d5V±10% is normal. The signal at the input side of the unit must also be from Ov to 5V'ff, if full functionality is to be guaranteed in this case. To avoid any damage to the unit,
The input signal is usually -0.3V ([must not fall below,
Must not exceed +7V.

During operation of the motor vehicle, high positive or negative voltage peaks repeatedly occur in the signal Iw of the control device, for example due to switching off of the ignition, inductive loads and other low-resistance loads.

The object of the invention is to limit the voltage to an acceptable level at the input of the entire unit without distorting the signal itself.

What are the features indicated in claims 1 and 2 for solving this problem? A configuration is provided.

Protection circuits for analog signals, in which the desired limit voltage is adjusted by a voltage divider connected between the positive and negative wires or earth of the operating voltage, ensure that the analog signal does not distort its value. It is particularly well suited for this purpose. For the protection of digital signals where the absolute height of the signal voltage is not critical or essential, according to the invention forward-poled diodes are provided in place of the first and third resistors, respectively. is provided. In both cases, the entire circuit is
It is particularly advantageous to integrate the control device with two transistors of opposite conductivity type into an integrated circuit in which the other units of the control device are integrated.

DESCRIPTION OF EMBODIMENTS Two embodiments of the present invention will be described in detail below with reference to the drawings.

Protection circuit for digital signals in FIG.
= "f-1i gh" must be detected. A general TTL circuit detects a voltage smaller than 3.7V as ``Ii OW'', 2.4V,
l: Larger voltage k Detected as ``High''. Therefore, the input signal is just thicker than QV (limited to less than 5V).

The circuit according to FIG. 1 has an input voltage Ueini, a lower voltage iQV
and +0.3V, and above I['<Ugrenz−
It is limited between 0.3V and '[Jgrenz. The variation of the limit value depends on the temperature, the current flowing through the diodes D1 and DZk, and the current flowing in the bases of the transistors T1 and T2. Ugrenz is usually the operating voltage UB of the integrated component.

Function: Diode Di, D2. A voltage of approximately 0.7 V appears at the base of transistor T1 via a voltage divider consisting of resistor R, and approximately TJgrenz at the base of transistor T2.
A voltage of -0.7V occurs.

1Jein falls to approximately (IV), current flows into the base of T1, making it conductive. This causes current to flow from Ugrenz through T1 to In connection with the preresistors R, V connected to the signal supply lines, the voltage at '[Jein] no longer drops.

'[When the voltage applied to Jein rises to Ugrenz, the base current flows through T2i, so that this transistor limits the voltage upwards.

The difference between the protection device for analog signals and the protection device for digital signals according to FIG. The point is that it is a pure 11. Therefore, the protection function for analog signals below 10V and
The first step is to perform it higher up. This limits the input signal to 10,3V ・QV and Ugrenz-U
It becomes a box of grenz+0.3 V.

This can be accomplished as follows: When using all small diodes (eg Schottky diodes) with the same forward voltage as the diode voltage and D2, use the circuit shown in FIG.

Resistors (as shown in FIG. 2) are used to adjust the base-bias voltage for transistors T1 and T2.

The circuit for functional analog signals operates in the same way as the circuit for digital signals, and the difference from the circuit for digital signals is that the transistor T
The voltage at the base of the transistor T2 is raised to near Ov by the resistor R,3, and the voltage at the base of the transistor T2 is raised by the resistor R1 to near Ov.

ADVANTAGES OF THE INVENTION The protection circuit of the present invention is limited only when the operating range is above or below a certain voltage (mainly the diode voltage), and is not limited to f'L, but rather to the open circuit. Direct is any value near the limit value, limit value, and is determined between the limit values.

This allows safe operation of the protected circuit even during the occurrence of fault voltages.

Another advantage is that only one connection is required for the line to be protected during the integration of the circuit.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of a protection circuit for digital signals according to the present invention, and FIG. 2 is a complete circuit diagram of a protection circuit for analog signals according to the present invention.

Claims (1)

[Claims] 1. In a protection circuit of a device controlled by an electrical signal, whose input side is protected by a protection device against positive and/or negative overvoltages, two transistors of mutually opposite conductivity types (Tl , T2) are provided, the transistors are connected in series with each other to the operating voltage of the device, and at the mutually connected emitters of the two transistors a pre-resistor () (, ■) is provided. ? Indirectly to the signal voltage via f, the input of the interviewing device 11't! The first resistor (R1) is connected to the second resistor (R,2
) and a third resistor (11,3), the first transistor (
The base of T1) is connected to the connection point between the second resistor CJJL2) and the third resistor (C3).
2) A protection circuit for a device controlled by an electric signal, wherein the base is connected to a connection point between the first resistor (R1) and the second resistor (R2). 2. In the protection circuit of a device controlled by an electrical signal, whose input side is ρ-protected by a protection device against positive and f or negative overvoltages, two transistors of mutually opposite conductivity types (Tl, T2) are provided, the transistors being connected in series with each other to the operating voltage of the device, and with the mutually connected emitters of the two transistors being indirectly connected via a preresistor (RV')'v. The signal voltage is directly connected to the input side (E) of the device,
Furthermore, a first diode (Di) connected in the forward direction,
A voltage divider consisting of a second diode (D2) and a resistor (R2) connected between the two diodes is connected to the operating voltage and the current flow, f'L, is connected in the direction. The base of the first transistor (T1) connected to the resistor (
R2) and the second diode (D2), and the base of the second transistor (T2) is connected to the connection point between the first diode (Dl) and the resistor (R2). A protection circuit for devices controlled by electrical signals. 3. A protection circuit for a device controlled by an electrical signal according to claim 2, wherein the diode has a particularly low forward rising voltage.