JPS6326012A - Protective circuit device against overload of push-pull output stage - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a protection circuit device against overload of a transistorized push-pull output stage, the output side of the push-pull stage having a load impedance connected to a reference potential. and at least one calibration element connected to ρ, said bush, and at least one calibration element for measuring the output current flowing in the pull output stage.

A circuit for protection against overload of the output stage is described, for example, in German Patent Specification No. 33 11 955. In this specification, a voltage proportional to the output current is tapped off via a detection resistor in the output stage, and by this voltage, when a predetermined output current is exceeded, the switching device is fully activated and the output stage is deactivated. It will be destroyed. In that case the circuit described there evaluates only half of the output current. The circuit described above therefore does not operate with sufficient precision and is unsuitable for high quality output stages, such as hi-fi equipment. Furthermore, the known circuit has considerable tolerances, so that a predetermined cut-off point of the output stage cannot be achieved.

OBJECT OF THE INVENTION What is the purpose or problem of the invention: precisely defined cut-off point of the output stage in case of overload? It's about achieving.

The problems related to grooves and bites of the invention are solved by the constituent elements described in the claims. Other embodiments are disclosed in the dependent claims.

Fu example Next, one embodiment will be fully explained using FIG. 1a and FIG. 1b.

In the circuit arrangement shown in FIG. 1, a known configuration of a push-pull output stage is used, which has termination transistors 1, 2 whose emitters are interconnected. The converter of these transistors is operating voltage +UBl,
- Connected to the UBl terminal. A load impedance 3, for example in the form of a loudspeaker, is connected to the output side (C) of the push-pull output stage. The other end of the load impedance is connected to a reference potential, for example earth. For measuring the flowing dark current, one resistor 4, 5 is inserted in each emitter line.

To adjust the dark current, a transistoro inserted and connected between the bases of the termination transistors 1 and 20 is used. An input signal is supplied via the terminal 7, which controls the push-pull output stage via the preamplifier 8 and the driver translator 9. A voltage determined individually with respect to the reference potential can be taken out from the resistors 4.5 fJ'. The voltage that can be extracted through the resistor 4 (which is formed by the dark current and the load current superimposed on it and flowing through the load impedance 3) is supplied to the non-inverting input side of the differential amplifier 10. , and the voltage taken out by the resistor 5 is supplied to the inverting input side of the differential amplifier stage 10.

A signal as shown is generated at the output side of the differential amplifier stage 10. This signal consists of a dark current (() corresponding value UR and a value TJ3 corresponding to the signal current.

By supplying the negative signal component to the 1st input input side of the differential amplifier 10, the above signal is output! It appears after 1800 phase rotations at fi11. The supply voltage t for the differential amplifier 10 is UB 2
is smaller than the supply voltage UB1 for the push-pull output stage, so the signal voltage supplied to the differential amplifier 10 is determined by the frequency division coefficient (this is the ratio of the respective resistances of the resistors (R11+R12
)/R11]. The differential amplifier stage 10 has an amplification degree of ⋅=R12/total.

The output signal of differential amplifier 10 is applied to the positive input of comparator 20. The negative input of this comparator is placed at the reference potential Uref (which is generated using a voltage divider formed by resistors 21 and 22), said voltage divider being inserted between the operating voltage +UB2 and the reference potential. It is connected. As soon as the output voltage of the differential amplifier stage 10 exceeds the reference potential, the output side of the comparator 20 is placed at a high potential, and this high potential causes, for example, a transistor 25 connected to the input side of the push-pull output stage to controlled. This transistor 25 short-circuits the input signal OEi, thereby eliminating the overload. Upon removal of the overload condition, transistor 25 is immediately placed in the blocking state again;
A clock-controlled activation and disconnection of the output stage takes place. Muting control can also take place elsewhere in the circuit, for example by blocking the driver transistor 9.

Therefore, at the output of the comparator 20, a reference potential appears in the normal operating state of the output stage in question, whereas in the case of an overload, the potential is given by the value of the resistor 28 connected to the terminal of the operating voltage UB2. The amount increases. This jump in potential is transmitted via resistor 23 and capacitor 24 to the base of transistor 25, rendering it conductive. This flanges the reference voltage input side of the comparator 20 to the reference potential, so that the output side of the comparator is reliably held at a high potential. So'f
``LvC charges the capacitor 24, the charging being carried out while the transistor 25 is kept conductive by controlling its base.

Only when the capacitor 24 is placed in a charged state does the base-emitter voltage across the resistor 27 of the transistor 25 drop to such an extent that the transistor 25 becomes non-conducting and the reference voltage Uref again acts on the comparator. descend. In an instant, the overload is no longer present due to the mute signal, so that the comparator output is placed at the reference potential. Thereby capacitor 24
is fully discharged through all of the diodes 26, thus creating the initial conditions for a new cycle.

If an overload event occurs, the comparator output is immediately brought back to the +UB2- potential and the operating process is repeated until the overload disappears. This process is illustrated in diaphragms 1b (a), (b), and (c) of the figure.

The dark current control during overload of the push-pull amplifier can be influenced via the line 29 by means of a corresponding signal for switching off the dark current control, which is not shown in detail in the push-pull configuration.

Effects of the Invention In view of the fact that it has been difficult to obtain a predetermined cutoff point in the past, the present invention provides an accurate cutoff point k'! of the output stage in the event of an overload! 2
The effect of knowing and achieving is achieved.

[Brief explanation of drawings]

FIG. 1a is a schematic diagram of an embodiment of the present invention, and FIG. 1b is an explanatory diagram of waveform changes during overload.

Claims (1)

[Scope of Claims] 1. A protection circuit device against overload of a push-pull output stage made of transistors, wherein a load impedance connected to a reference potential is connected to the output side of the push-pull stage, and With at least one sensing element for measuring the output current flowing in the push-pull output stage, one sensing element (4, 5) is provided in each branch of the push-pull output stage (1, 2). A voltage measured with respect to a reference potential can be extracted from the detection element, and the voltage is applied to one input side (+/-) of the differential amplifier stage (10). , the output side of the amplifier stage is connected to one input side of a comparator circuit (20), the other input side of the comparator circuit is placed at a reference potential (Uref), and further supplied to the comparator circuit (20). The input voltage is the reference potential (Uref
) is exceeded, the signal for blocking the push-pull output stage (1, 2) can be taken from the output side of the comparator circuit (20). 2. The circuit arrangement according to claim 1, wherein the signal for blocking the push-pull output stage is configured to be applied directly to the input side of the push-pull output stage. 3. The circuit arrangement according to claim 1 or 2, wherein the signal for blocking the push-pull output stage is supplied to the driver stage (9). 4. When the push-pull output stage is overloaded, the output signal of the comparator circuit (comparator circuit) (20) causes the time-limiting element (2
3, 24, 27) and an electronic switch (25) controlled by the timing element.
3. The circuit device according to claim 1, wherein the reference voltage input side of the circuit is clamped to a reference potential. 5. The timing element is a series connection of a resistor (23) and a capacitor (24), which is provided between the output side of the comparator circuit (20) and the control electrode of the electronic switch (25).
5. The circuit arrangement according to claim 4, further comprising a resistor (27) inserted and connected between the control electrode of the electronic switch (25) and the reference potential. 6. A diode (26) is connected in series to the resistor (23) of the time element, and the parallel connection configuration is such that the cathode of the diode is connected to the output side of the comparator circuit (20). A circuit device according to claim 5.