JPS607550Y2 - Amplifier protection circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a protection circuit used in an amplifier.

Currently, many 5EPP type amplifiers that operate in class B are used, but in so-called direct-coupled amplifiers that do not use a DC blocking capacitor at the output end, in order to ensure that the DC potential at the output end is zero, A dual power supply circuit, positive and negative, is used.

However, in this type of amplifier, due to the influence of temperature and other causes, accidents are likely to occur, such as direct current flowing to the output terminal and damaging the speaker as a load.

Therefore, conventional amplifiers are configured to detect positive and negative DC outputs greater than a predetermined value and activate a protection function when positive and negative DC outputs of a predetermined value or higher occur at the output end of the amplifier.

However, conventional DC detection circuits tend to be complicated, and therefore, there is a desire for a protection circuit that can provide sufficient protection with a relatively simple configuration.

This invention was developed in view of the above-mentioned demands, and will be described below with reference to illustrated examples.

That is, FIG. 1 shows a state in which a B class 5EPP amplifier is connected to a power supply circuit having two positive and negative power supplies.

T is a power transformer whose primary side T□ is connected to AClooV, and the secondary side T2 is configured with a tap at the center point, and the center point is connected to the ground E.

And diodes D□~D are connected between both winding ends of the secondary side T2.
.

A bridge type rectifier circuit is connected, and its rectified output is applied to the other ends of smoothing capacitors C1 and C2, one end of which is connected to earth E, thereby forming a two-power supply circuit, positive and negative.

The collector of one power transistor Q□ of the 5EPP amplifier is connected to the positive power supply, and the collector of the other power transistor Q2 is connected to the negative power supply, and their emitters are connected in common, and between the emitter and ground. For example, a speaker is connected to the load RL.

Note that eg is a signal source applied to the bases of power transistors Q□ and Q2.

In the circuit shown in Fig. 1, if the capacitances of capacitors C1 and 02 are almost the same, the ripples at points a and b have an anti-phase relationship with each other as shown in Fig. 2, and the ripples are almost the same. There are ripple precepts with values VaE, VbE.

However, such a state is caused by the power transistors Q□ and Q
This is a case where the B class amplifier according to No. 2 is operating normally, and when the operational balance of the power transistors Q□ and Q2 is disrupted and direct current is flowing to the negative IL, the ripple values VaE and VbE will not be equal.

The protection circuit of the present invention is developed by focusing on such points, and an example thereof is shown in FIG.

That is, points a, b, and E in FIG. 3 are connected to a, b, and E in FIG. 1, respectively,
From points a and b, capacitors C of the same capacity are connected.
3 and C2, and the respective ripple components are added by addition resistors R1 and R2,
Added to Amplifier A.

The output of amplifier A is rectified by diode D5,
The rectified output is applied to an integrating circuit including a resistor B3 and a capacitor C5, and is further amplified by a predetermined amount by a relay drive amplifier A3 before being applied to a relay coil Z.

Furthermore, the ripple component at point b obtained by capacitor C4 is added to potentiometer vR1, and its divided voltage output is amplified by an amplifier and then rectified by diode D5, and then connected to the above-mentioned integration circuit by resistor R3 and capacitor C5. added to.

In the above configuration, B due to transistors Q□ and Q2
When the class amplifier is operating normally, as mentioned above, from points a and b, there are ripples that are in opposite phase to each other and have almost the same ripple values VaE and VbE as shown in Figure 2. brought about.

Since the ripple fractions are added by the resistors R1 and R2, they cancel each other out and the input to the amplifier A□ becomes zero.

However, as described above, when the operational balance of power transistors Q1 and Q2 is disrupted and direct current flows through load RL, the magnitudes of ripple values VaE and VbE are different, and therefore the difference component is applied to amplifier A□. That will happen.

Its output is therefore rectified by diode D5 and charges up capacitor C6.

Furthermore, the DC output is amplified by a relay drive amplifier, and applied to the relay coil Z. The relay is operated by the output above a predetermined value applied to the relay coil Z, and B
It operates to activate well-known protection functions such as disconnecting the load RL from the class amplifier or disconnecting the collectors of transistors Q□ and Q2 from the DC power supply.

Furthermore, when an overcurrent flows through the load RL, the ripple component at point a or point b increases.

Therefore, the voltage b divided by the potentiometer VR□
A part of the ripple signal at the point is amplified by the amplifier, rectified by the diode D6, and operates to charge up the capacitor C5, so even if an overcurrent flows through the load RL, the same protection as above is provided. function is activated.

As is clear from the above explanation, this invention takes into account the protection function according to the amount of ripple components present in the positive and negative dual power supply circuit, so it can be constructed with a relatively simple circuit, and the DC detection Since there is no need to provide extra circuits such as an overcurrent detection circuit or an overcurrent detection circuit, practical effects such as the ability to simplify the amplifier circuit can be expected.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the basic configuration of a positive and negative power supply circuit and an amplifier connected to it, Figure 2 is a waveform diagram showing the ripples that exist in the power supply circuit, and Figure 3 is the protection circuit of the present invention. FIG. C≦;C1...Capacitor, R□, R2...
...Additional resistor, A3...Relay drive amplifier, Z...Relay coil.

Claims (1)

[Scope of utility model registration request] The ripple component is extracted from each of the smoothing capacitors of the two positive and negative power supplies added to the 5EEP direct-coupled core that operates in class B, and the ripple components are added together. An amplifier protection circuit characterized by activating a protection function.