JPH03216007A - Protection circuit for switching amplifier - Google Patents

Abstract

PURPOSE:To prevent a faulty current from flowing to a switching element for a long time in advance by providing an overcurrent detection section and turning off all switching elements of a power amplifier section forcibly at a faulty state. CONSTITUTION:An overcurrent detection section 4 is provided with a secondary winding L0 coupled electromagnetically with a choke coil L3 of a power amplifier section 3, a resistor R1 converting a secondary current flowing to the secondary winding L0 into a voltage V1 and a transistor(TR) T1 turned off when the voltage V1 exceeds a prescribed value and an emitter voltage V2 of the TR T1 is given to a fault sensing terminal 25 of a driver section 2. In such a case, the voltage V1 is higher than the prescribed value at a faulty state where a current i1 flowing to the power amplifier section 3 exceeds the maximum current level, the TR T1 is turned off and the voltage V2 reaches a high level. In such a case, the driver section 2 brings the level of output terminals 21-24 forcibly to an L level, thereby turning off switching elements Q1-Q4. Thus, even when the current i1 is large, since the continuous flowing of it to the elements Q1-Q4 is not caused, the thermal destruction of the elements Q1-Q4 is prevented in advance.

Description

[Detailed Description of the Invention] [Summary] Regarding the protection circuit of a switching amplifier that receives a digital signal as input, the purpose is to prevent the switching element of the power amplifier section from being destroyed by overcurrent. A protection circuit for a switching amplifier that selectively drives a switching element of a power amplification section with a drive signal provided by the power amplification section, wherein a secondary winding is provided in a choke coil of the power amplification section, and the current value flowing through the secondary winding is The device is configured to include an overcurrent detection unit that fixes all of the drive signals to a non-drive level when the drive signal exceeds a certain value.

[Industrial Field of Application] The present invention relates to a protection circuit for a switching amplifier that receives a digital signal as input.

In recent years, as the source (sound source) of audio equipment has been digitized, each part has also been digitized. One example is the power amplifier that drives a speaker, and if a digital amplifier called a switching amplifier is used here, it is possible to achieve high output with high efficiency.

[Conventional technology]

Figure 4 is an explanatory diagram of the switching amplifier, where SP is the speaker, Q, ~Q are the switching elements of the power amplification section, G,
~G4 is a drive signal, VCC is a power supply, and GND is a ground. Element Q, . Q. For example, it is turned on when the signals G+ and G4 are H (high), and a drive current flows through the speaker SP with the polarity indicated by the solid line arrow. On the other hand, elements Q2, Q. is the signal G2,G
．． is turned on when SPY is H, and a current of opposite polarity (indicated by a broken line arrow) flows through the speaker SPY.

For example, as shown in FIG. 5, the drive signals G l and G z are generated using PWM (Pulse Width Modulation) with mutually opposite phases, in which the duty of each pulse of a pulse train with a constant frequency T (carrier) is changed according to the amplitude of the audio signal. ) signal, and the amplitude of G2 is ■. , the amplitude of G1 is set to 2VCC. Similarly, the drive signal G, is a PW with an amplitude of 2Vcc, which is the inversion of G1.
M signal, and drive signal G4 has amplitude ■ which is the inversion of G2. , is the PWM signal of . With this PWM signal, element Q1
When ~Q4 is driven, a pulse voltage having an amplitude of VCC is applied to the speaker SP, and thereby a driving current having an average amplitude according to the duty of the PWM signal flows. An audio signal restored to its original analog value by this drive current is reproduced from the speaker SP.

[Problem to be solved by the invention] The above-mentioned switching amplifier is a switching element':F-
Q1 to Q4 and choke coils L, -L. It is composed of a power amplification section that includes components, etc., and a dryer section that drives the elements.
If an abnormality occurs such as a short circuit between the terminals of the element Q, -
Q. There is a problem that an abnormal current flows through the device and thermally destroys the device.

The present invention attempts to prevent thermal destruction of the power amplifier by forcibly turning off all switching elements of the power amplifying section in the event of such an abnormality.

[Means to solve the problem]

The present invention is a protection circuit for a switching amplifier that selectively drives a switching element of a power amplification section with a drive signal output from a driver section, in which a secondary winding is provided in a choke coil of the power amplification section. The present invention is characterized in that it includes an overcurrent detection section that fixes all of the drive signals to a non-drive level when the current value flowing through the secondary winding exceeds a certain value.

[Function] The current flowing through the switching element directly flows through the choke coil of the power amplification section. Therefore, when a secondary winding is provided in this choke coil, a secondary current proportional to the current flowing through the switching element flows through the secondary winding, so that when an overcurrent flows through the switching element, it is transferred to the secondary winding. Can be detected as electric current. This overcurrent detection method does not cause a voltage drop due to the insertion of a current detection resistor, which is a drawback of the current detection method used in analog amplifiers, so it does not interfere with the high efficiency of the switching amplifier.

When an overcurrent detecting section using a secondary winding detects an overcurrent, all outputs (drive signals) of the dryer section are fixed to a non-driving level, and all switching elements are put into a non-energized state. As a result, even if a power supply fault or a ground fault occurs in the power amplifying section or a short circuit occurs between the speaker terminals, the switching element will not be destroyed.

〔Example〕

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and 1 is a PWM
This is a signal generator. This PWM signal generator [is a PCM/PWM signal generator that receives a PCM signal that has been pulse code modulated using amplitude information of an audio signal as input, and converts it into a PWM signal that has been pulse width modulated using a carrier of a constant frequency.
It is a conversion circuit. 2 is a driver section of the switching amplifier, 3 is a power amplification section thereof, and 4 is an overcurrent detection section.

The dryer section 2 receives a drive signal G. which is in phase with the PWM signal. G4,
and an opposite phase drive signal G. , G3 and output them from the output terminals 21 to 24 to selectively drive the switching elements Q, to Q4 of the power amplifying section 3.

The power amplifying section 3 includes a switching element Q. - In addition to Q4, the choke coil L. which constitutes the output smoothing filter. , LX, capacitors C1 to C3, and a choke coil L3 for removing power supply noise.

The overcurrent detection section 4 includes choke coils 1 to 1 of the power amplification section 3.
Secondary winding L electromagnetically coupled to one of L3 (L3 in this example)
0 and this secondary winding L. A resistor R, which converts the secondary current flowing into a voltage V, into a voltage V, a transistor T1, which turns off when this voltage vl exceeds a certain value, and its human resistors R2, R3, and a transistor T, which turns on. A resistor R4 is provided to limit the current flowing between the emitter and the collector, and the emitter voltage V2 of the transistor T1 is applied to the abnormality detection terminal 25 of the dryer section 2.

When the level of this terminal 25 is L (normal), the tricycle part 2 can switch the outputs G and -G4 from the terminals 21 to 24 to H and L according to the input, but when the level of the terminal 25 is H (abnormal), ), the output from terminals 21 to 24 becomes G. -G. Forcibly rub all L6 regardless of the input number.

FIG. 2 is an operating waveform diagram, with the left half showing normal conditions and the right half showing abnormal conditions. Under normal conditions, the value of the current 11 flowing through the choke coil L and into the power amplifying section 3 is below the allowable maximum current level, and at this time, the voltage 1 is also low, so the transistor T1 is turned on. Therefore, dryer section 2
When the voltage V2 is applied to the abnormality detection terminal 25, the drive signals 01 to G4 from the output terminals 21 to 24 change to H and L in synchronization with human power. For this reason, the suinoting element Q
．． -Q. Q. ,Q. and Q. ,Q. Each set is turned on and off to drive the subica SP.

On the other hand, when the current l1 exceeds the maximum current level, the voltage ■1 becomes higher than the constant value, so the transistor T
1 turns off, and voltage 2 becomes H.

At this time, the driver unit 2 forcibly sets the output terminals 21 to 24 to L, so that the switching elements Q1 to Q are all turned off. As a result, even if the current 11 is large, it is
Since the current does not continue to flow to elements Q, -Q,.
can prevent thermal damage.

The driver section 2 has a configuration for each terminal as shown in FIG. 3, for example, in order to forcibly set the output terminals 2n (n=1 to 4) to L. T z and T 3 in the same figure are human PWM
A series transistor of the reverse type driven exclusively by the signal, the common transmitter of which is connected to the output terminal 2n of the drive signal Gn. R is a Heas current limiting resistor, and up to this point is the existing driver configuration. This configuration includes a transistor T4 and a Hess input resistor R. , R, and abnormality detection terminal 2. When the voltage v2 of the transistor T4 becomes H, the transistor T4 is turned on, the bases of the transistors Tz and Ts are forcibly grounded, and the output On is fixed at L.

In the above explanation, the secondary winding L0 was provided in the choke coil L3 of the power supply section, but this is the same as that of the choke coil L. of the output smoothing filter section. Or it may be L2.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent abnormal current from flowing for a long time in the switching element for power amplification of a switching amplifier, thereby preventing short circuits from occurring in the power amplifier section or ground faults, and There is an advantage that even if there is a short circuit between the two, the switching element will not be destroyed.

Furthermore, since no inserted resistor that causes a voltage drop is used for overcurrent detection, the high efficiency of the switching amplifier is not compromised.

[Brief explanation of drawings]

Figure L is a configuration diagram showing an embodiment of the present invention, Figure 2 is its operating waveform diagram, Figure 3 is a circuit diagram of eight parts of the try, Figure 4 is an explanatory diagram of the switching amplifier, and Figure 5 is its operation waveform diagram. It is an operation waveform diagram. In the figure, 2 is a dryer section, 3 is a power amplification section, 4 is an overcurrent detection section, Q1 to Q4 are switching elements, and L. -L. is a choke coil, and L0 is a secondary winding. People Fujitsu Ten Ltd.

Claims (1)

[Claims] 1. Drive signal (G_1) output from the driver section (2)
~G_4), the switching element (Q) of the power amplification section (3)
A protection circuit for a switching amplifier that selectively drives a switching amplifier (_1 to Q_4), wherein a secondary winding (L_0) is provided in the choke coil (L_1 to L_3) of the power amplification section, and a current flowing through the secondary winding is provided. When the value exceeds a certain value, the drive signal (G_1 to G_
Overcurrent detection section (4) that fixes all 4) at the non-drive level
A protection circuit for a switching amplifier, comprising: