JPS5852728Y2 - Click prevention circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a click prevention circuit in audio equipment such as a magnetic recording/playback device. This paper proposes an anti-click circuit that reduces clicks by pre-charging.

Various countermeasure circuits of this type have been proposed in the past, and each has its own effects, but none of them are perfect because they require many external components and are often subject to strict conditions.

Figure 1 shows a recording head drive amplifier as a conventional example.
The figure shows the output DC voltage characteristics of Figure 1.

1 and 2 are resistors, 3 to 6 are capacitors, T is a power supply, 8 is a power switch, 9 and 10 are PNP transistors, 11 is a muting NPN) transistor, 12 is an input terminal,
13 is the recording head.

14 is a recording head drive circuit, and a resistor 1 and a ripple capacitor 3 constitute a ripple filter.

Case, resistor 2, capacitor 5, NPN) transistor 11
serves to increase the output impedance as the frequency increases, and supplies a constant current to the recording head 13.

The operation after the power switch 8 is turned on will be explained with reference to FIG.

When the power switch 8 is turned on 15, the ripple capacitor 3 of the ripple filter is charged through the resistor 1, and the voltage across both ends Vc3 changes as shown in FIG. 2a, and Vl
When the level is reached, a normal bias is applied to the recording head drive circuit 14, and then a bias voltage as shown by the broken line of the output voltage VC in FIG. 2 is applied to the PNP transistor 9, and the muting transistor 11 is becomes the collector voltage.

At this time, the capacitor 5 is connected to the Vc of FIG. 2C through the resistor 2.
5, and when it reaches VBH, the transistor 11 is turned on and works to lower Vc, producing a rising portion of Vc as shown by the solid line and generating a click sound 17.

The transistor 10 is provided to prevent clicking, and when the relationship between the voltage Vc applied to the ivy and the voltage Vc3 applied to the base is V-Vc3>VBE,
When transistor 10 is turned on, the ICQIO shown in FIG.
A collector current flows, and the output is V.

However, □ neat is applied only to the rising portion of Vo, and a sufficient effect cannot be obtained.

The present invention has been made to eliminate the above-mentioned drawbacks, and is to precharge the capacitor 5 with a voltage close to a normal bias for a certain period of time, thereby eliminating the clicking sound.

An embodiment of the present invention will be described below based on the drawings.

In Figure 3, 20-23 are resistors, 24-26 are NP
N) Lanozister, 27 is PNP) Lanozister, 28.2
9 is a diode, and the components with other symbols are the same as those in FIG.

One end of the resistor 1 is connected to a power switch 8, and the other end is grounded through a ripple capacitor 3 and connected to a recording head drive circuit 14 to provide normal bias to the circuit 14.

One NPN) run raster 240 base of the differential amplifier is connected to a resistor 20, 2 interposed between the power switch 8 and ground.
The collector of the other NPN transistor 25 of the differential amplifier is connected to the power switch 8, and its emitter is connected to the power switch 8, and its collector is connected to the power switch 8 through a resistor 22.
It is grounded through a resistor 23 together with the 4th vine, and its base is further connected to the output terminal of the recording head drive circuit 14.

The collector of the NPN transistor 24 is connected to the base of the PNP transistor 21, and the transistor 2T
Its emitter is connected to the power switch 8 and its collector is grounded through diodes 28 and 29.

Further, the collector of the PNP) transistor 2T is connected to the base of the NPM) transistor 26, and the collector thereof is connected to the power switch 8.
4 is connected to the base of a PNP transistor 9, the emitter of the transistor 9 is connected to the power switch 8, and its collector is connected to the collector of a muting NPN transistor 11. The emitters are grounded, and the collectors of both transistors 9 and 11 are connected to the recording head 13 through a capacitor 6 and to the base of an NPN transistor 110 through a resistor 2.

The base of the transistor 110 is further connected to the emitter of the NPN transistor 26 and grounded through the capacitor 5.

Next, its operation will be explained.

The base voltage VBI of the NPN transistor 24 determined by the resistor 20.21 is PNP) The base voltage VBI of the transistor 9
Set lower than B2.

When the power switch 8 is turned on 15, VBI is applied to the base of the NPN transistor 24, and the recording head drive circuit 14 becomes normally biased because no pressure is applied to the base of the NPN transistor 25. During that period, current flows only through the transistor 24, the PNP) transistor 27 and the NPN) transistor 26 are turned on, and a voltage close to normal bias is applied to the capacitor 5 from the power supply γ.
Preliminary charging is performed on VC5 as shown by the solid line in FIG. 4C.

Therefore, after VC5 reaches VBE, VC3 reaches vLubernis as shown in FIG. 4a.

When VC3 reaches Vl, a bias is applied to transistor 9 as in the conventional case.

However, since the transistor 11 is already normally biased as shown by the solid line for VC5 in Figure 4C, VC does not rise suddenly as shown by the broken line in Figure 4C, but rises as shown by the solid line, and the click sound disappears. 6 Next, the ripple capacitor 3 is fully charged and the recording head drive circuit 1
4 is normally biased, VB2 is added to the NPN transistor 25, and since VB2>VBl is set,
NPN) transistor 25 is turned on, and NPN transistor 24 is turned off.

Transistors 26 and 27 are off and do not affect steady state bias.

In a normal steady state, the base current of the NPN) Rangemetal 250 flows, so in order not to disturb the bias condition of the recording head drive circuit 14, the transistors 24 and 25 are
may be connected to Darlington.

The base of the transistor 250 may be any point that is biased with a time delay, for example at the midpoint between the resistor 1 and the ripple capacitor 3.

At the time of sprouting, the resistance is 2 as in the above condition VBI < VB2.
0.21 may be selected.

As described above, according to the present invention, an extremely effective circuit that can take countermeasures against clicks without affecting the bias circuit in a steady state can be obtained, and especially when used in integrated circuits, the number of transistors and resistors will not increase. This is an extremely effective circuit that requires fewer components than individual components.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram of a conventional head drive amplifier, Fig. 2 is a waveform diagram of each part of Fig. 1, Fig. 3 is a circuit diagram showing an embodiment of the present invention, Fig. 4 are waveform diagrams of various parts in FIG. 3. 5...Capacitor, 7...Power supply, 8.
...Power switch, 13...Recording head, 14...Recording head drive circuit, 17...
...Click sound, 20~23...Resistance, 24~
26...NPN) transistor, 27...
・PNP) transistor, 28, 29... diode.

Claims (1)

[Scope of utility model registration request] A DC voltage VBI is applied to one input terminal of the differential amplifier at the same time when the audio equipment to be processed is energized.The DC voltage VBI is applied to the input terminal of the differential amplifier when the audio equipment to be processed reaches a normal bias state after a delay from the energization. DC voltage V higher than voltage VBI
B2 is configured to be applied from the to-be-processed audio equipment side,
The output of the differential amplifier (YPNP) is applied to the base of the transistor, the emitter of the PNP transistor is connected to a power supply, and the collector is connected to one end of a series circuit consisting of at least one diode, the other end of which is grounded; A capacitor connected to the base of the NPN transistor at one end of the series circuit, connecting the collector of the NPN transistor to a power supply, having an emitter installed in a bias circuit in the device to be processed, and having the other end grounded. An anti-click circuit connected to one end of the.