JPS599449Y2 - Switching circuit between BTL circuit speaker and external output - Google Patents

Description

[Detailed explanation of the invention] This invention is based on BTL (Balance Transf.
It is related to the switching circuit between the speaker and external output of the BTL circuit, which reduces the number of parts compared to conventional switching circuits of this type, and eliminates the influence of the phase conversion circuit in the BTL circuit on the external output. To provide a switching circuit which has advantages in terms of circuit operation, does not interrupt the sound from a speaker even if the externally exposed part of an external output jack is grounded, and does not require any protective means. With the goal.

In a so-called BTL output circuit, the signal output between output terminal a and ground shown in Figure 1 and the signal output between output terminal b and ground have the same voltage but a 180° difference in phase. By connecting a speaker or the like between the output terminals a and l), it is possible to extract four times the power output.

Figure 1 shows a conventional switching circuit between a speaker and an external output in such a BTL circuit. Contacts c and d of the external output jack 1 are normally closed, and the output terminal a
, l), a speaker 2 is loaded between them.

Note that 3 is a BTL power amplifier. In addition, by inserting an earphone or headphone plug into the external output jack 1, the speaker 2 and these loads are switched, and a direct current blocking device is installed between the jack fitting e of the external output jack 1 and the output terminal b. The reason why the resistor R1 is connected in addition to the capacitor C1 is to correct the level since the permissible input of earphones or headphones is smaller than that of the speaker 2.

In addition, the jack fitting e is normally exposed to the outside of the device, but since this part is a conductive part of the output signal, if it is shorted to ground when the external output jack 1 is not in use. This causes problems such as the sound from the speaker 2 being interrupted during that time, and measures to prevent this are troublesome, especially in devices using metal panels.

FIG. 2 shows an external output switching circuit showing an embodiment of this invention, in which the same parts as in FIG. 1 are denoted by the same reference numerals.

The external output is the jack fitting e of the jack 1, that is, the non-switching side terminal of this jack is grounded through the capacitor C1.

Therefore, the earphones or headphones connected to external output jack 1 will be loaded with half the voltage and quarter of the power of the signal output of the BTL circuit. Then, there is no need to use the correction resistor R1.

In this case, the output from output terminal a of the BTL circuit is BT
The circuit structure is such that only the output from output terminal b becomes an opposite phase signal that passes through the phase conversion circuit without passing through the phase conversion circuit in the L circuit.

In other words, earphones, headphones, etc. that are connected to the external output jack 1 have various impedances.
Since the load condition cannot be made constant, if this load is applied to the output signal from output terminal b that has passed through the phase conversion circuit, it is likely to cause an increase in distortion. It is arranged to take out only from the output terminal a which is not connected.

As described above, in a circuit configured to switch the output of a BTL circuit between a speaker and an external output, this invention provides that one signal output that does not pass through the phase conversion circuit in the BTL circuit is output to the speaker. and the switching side terminal of the external output jack, and the other signal output, which outputs the opposite phase signal that has passed through the phase conversion circuit in the BTL circuit, is connected to the non-switching side terminal of the speaker, Both of the two terminals of the above speaker are not grounded, and the non-switching side terminal of the external output jack is grounded through a capacitor, so that only one signal output of the above BTL circuit is used as an external output. Therefore, its implementation has the following effects.

(1) The cost is reduced because the level correction resistor R1 can be omitted.

(2) Since the capacitor C1 can be grounded, pattern design of the printed circuit board is easy.

(3) It is possible to eliminate the influence of increased distortion that occurs when the output signal that has passed through the phase conversion circuit in the BTL circuit is loaded with various impedances connected to external outputs.

(4) The externally exposed part of the jack metal fitting of the external output jack has zero potential with respect to DC and signals when not in use, so even if it is grounded, the sound from the speaker will not be interrupted. No protection is required.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for switching between a speaker and an external output in a conventional BTL circuit, and FIG. 2 is a circuit diagram for switching between a speaker and an external output in a BTL circuit according to the invention. 1... External output jack, 2... Speaker, 3... BTL power amplifier, a, l) output terminal, c, d... External output jack contact point,
e...Jack metal fitting of external output jack, C1
・・・・・・Capacitor.

Claims (1)

[Scope of utility model registration request] In a circuit that switches the output of the BTL circuit between a speaker and an external output, one signal output that does not pass through the phase conversion circuit in the BTL circuit is output, and the signal output is switched between the speaker and the external output jack. Connect to the terminal,
The other signal output, which outputs the opposite phase signal that has passed through the phase conversion circuit in the BTL circuit, is connected to the non-switching side terminal of the speaker, so that neither of the two terminals of the speaker is grounded, and the external Connect the above BTL by grounding the non-switching side terminal of the output jack through the capacitor.
A switching circuit between a BTL circuit speaker and an external output, in which only one signal output of the circuit is used as an external output.