JPH01129515A - Protecting circuit for pwm amplifier - Google Patents

Abstract

PURPOSE:To prevent the breakdown of a power element by providing a control means for cutting off power source supply to a power amplifying circuit by a fact that a state that a detection voltage by a monitor means is in a prescribed value has continued for a prescribed time. CONSTITUTION:A monitor means is constituted of resistances 18-26, comparators 12, 13 and an OR gate 14. Also, a control means is constituted of a reference signal generating circuit 15, a counter 16 and a power source cutting-off circuit 17. When an 'H' level voltage is applied to an enable(EBL) terminal, the counter 16 counts a clock of a prescribed period supplied from the reference signal generating circuit 15. When an 'H' level voltage is outputted continuously from an OR gate 14, and during that time, the counter 16 has counted up to a count value which is set in advance, the counter 16 counts up, and also, generates an 'H' level signal. The power source cutting-off circuit 17 which received this signal cuts off electrifying to power elements 4-7 for forming a power amplifying circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PWM modulated signal that is used for current amplification of a PWM modulated signal.
The present invention relates to a protection circuit for a PWM amplifier that protects the amplifier from excessive current.

Conventional technology FIG. 3 shows P W M (P u 1
FIG. 2 is a circuit diagram showing a circuit of a pulse width modulation (pulse width modulation) amplifier.

In Figure 3, ■ is a preamplifier that amplifies the analog input signal, 2 is a triangular wave generation circuit that generates a triangular wave signal, and 3
is a PWM circuit that compares the output signal of the preamplifier 1 with the triangular wave signal output from the triangular wave generating circuit 2 and modulates the analog input signal into a PWM signal according to the amplitude thereof.

The PWM circuit 3 generates PWM signal signals whose phases are mutually inverted, a pair of power elements 4 and 5 are connected to the power terminal for the PWM signal signal, and a pair of power elements 4 and 5 are connected to the power terminal for the PWM signal signal.
A pair of power elements 6 and 7 are connected, and these power elements form a power amplification circuit. The pair of power elements are connected in series between a power supply Vcc and ground, and the intermediate connection point serves as a signal input/output point. Inductors 8 and 9 are connected to each of the output end of power element 4.5 and the output end of power element 6.7, and a capacitor (C) 1.0 is connected between the other ends of inductors 8 and 9. and resistance (RL)
Eleven parallel circuits are connected.

Next, proceed to 3-7 for the operation of the PWM amplifier with the above configuration. This will be explained with reference to the waveform diagram in FIG.

When an analog input signal as shown in FIG. 4 is input to the preamplifier 1, the preamplifier 1 amplifies it to a level that allows comparison with a triangular wave signal and outputs it.

This amplified signal is compared with the triangular wave signal output from the triangular wave generating circuit 2 by the PWM circuit 3, and a rectangular wave signal in a state where the points where both signals intersect is connected and the level is alternately converted is generated by the PWM circuit 3. It is generated as a PWM signal from The PWM signal simultaneously outputs a positive polarity signal Q and a negative polarity signal Q obtained by inverting the positive polarity signal Q, and the signal Q is outputted from the power elements 4 and 5.
The signal Q is current amplified by the power elements 6 and 7. Each of the current amplified PWM signals is smoothed by a smoothing circuit consisting of an inductor 8.9 and a capacitor 10, and then combined and applied to a low resistance load resistor 11. The signal supplied to the load resistor 11 is
Since it is smoothed by a smoothing circuit, it becomes an analog signal with the same frequency and similar to the analog input signal.

Problems to be Solved by the Invention However, in the conventional configuration as described above, if an excessive voltage is input for a long time, or if the PWM circuit 3 malfunctions, the voltage at a constant level of XXH or js L /L level is applied to the power element. If it is input for a long time, a current exceeding the maximum rating will flow through the power device, which may cause damage to the power device.

The present invention solves the conventional problems as described above.
A PW that protects the PWM amplifier by preventing damage to the power element due to excessive input or malfunction of the preceding stage circuit.
The purpose of this invention is to provide a protection circuit for M amplifiers.

Means for Solving the Problem In order to solve the above problem, the present invention performs pulse width modulation (pulse width modulation) by comparing an analog input signal with a reference triangular wave signal
PWM) which generates a signal and drives the power amplification circuit.
It is equipped with a monitor means for detecting the output voltage of the M circuit, and a control means for cutting off the power supply to the power amplification circuit when the voltage detected by the monitor means continues to be at a constant value for a predetermined period of time. be.

5・\-7 action The present invention has the following effects due to the above configuration.

In other words, excessive voltage is input to the PWM amplifier for a long time,
Or the PWM circuit malfunctions and the power element becomes 'H/l.
Or, if a constant voltage at NL level is input for a long time,
This is detected by the monitoring means, and if it continues for a certain period of time or more, the power supply to the power element is cut off. Therefore, excessive current will not flow through the power device, and the power device can be protected from destruction.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a protection circuit for a PWM amplifier in an embodiment of the present invention.

In this embodiment, the same parts as those of the PWM amplifier shown in FIG. 3 are given the same reference numerals, and the explanation thereof will be omitted, and the different configuration will be explained. A feature of the present invention is that a protection circuit 100 consisting of monitor means and control means is added to the PWM amplifier shown in FIG.

Monitoring means include resistors 18 to 26 and comparators 12.1
3 and an or gate 14. The control means is still composed of a reference signal generation circuit 15, a counter 16, and a power cutoff circuit 17.

The resistors 18, 21, and 24 are connected in series between the power supply Vcc and the ground, and the resistors 20 and 22 have one end connected to the Q output terminal of the PWM circuit 3. The other end of the resistor 20 is connected to one input terminal of the comparator 12.
The other end of 2 is connected to one input terminal of the comparator 13. The other input terminal of comparator 12 and resistor 1
A resistor 19 is connected between the connection point of the resistor 8.21 and a resistor 23 is connected between the other input terminal of the comparator 13 and the connection point of the resistor 21.24. Comparator 12
Resistors 25 and 26 are connected between the output terminals of and 13 and the power supply Vcc.

Each output of comparators 12 and 13 is connected to an OR gate 140.
When there are two human forces and a signal is applied to either of the two human forces, an output signal is generated from the OR gate 14, and the counter 1
6 is applied to the enable (EBL) terminal of 7...-7.

The counter 16 counts the clock signal input to the clock (CLK) terminal when a signal of (k J (l/level) is applied to the EBL terminal. The clock signal is provided from the reference signal generation circuit 15.

The output signal of the output terminal Q of the counter 16 is the power cutoff circuit 1
7, and when the output signal of the output terminal Q is \\H, the power supply to the power element group is turned off.Next, the operation of the above configuration will be explained with reference to Fig. 2. . Note that the operation of the PWM amplifier is the same as that described in FIG. 3, so the explanation here will be omitted.

If excessive voltage is input to the PWM amplifier for a long time, or if the PWM
Suppose that the output Q of the PWM circuit 3 remains at the tt H/7 level due to a malfunction of the M circuit 3, etc.
The voltage is applied to the comparator] 2 via the resistor 20, and since this voltage is higher than the voltage applied via the resistor 19, the output voltage of the comparator 12 is ss Hl/
become the level. The OR gate 14 that receives this \\H level outputs a \\H level voltage, which is sent to the counter 1.
6 to the EBL terminal.

When the IS Hn level voltage is applied to the EBL terminal, the counter 16 counts the constant cycle clock supplied from the reference signal generation circuit 15. From orgate 14
If the t Hn level voltage is continuously output and the counter 16 counts up to a preset count value during that time, the counter 16 will count up and ts Htt.
A level signal S is generated. The power cutoff circuit 17 receiving this signal S is connected to the power elements 4 to 7 forming a power amplification circuit.
Cut off the power to.

If the output Q of the 'I PWM circuit 3 reaches the tt L l/level, the detection voltage applied to the comparator 13 through the resistor 23 is lower than the reference voltage applied through the resistor 22. Comparator 13 is \\
Outputs H level voltage. As a result, the output voltage of the OR gate 14 reaches the 1\H level in the same manner as described above, the counter 16 generates the signal S, and the power cutoff circuit 17 can be activated.

9. / As is clear from the above, the output voltage of the PWM circuit 3 is determined by the comparators 12 and 13 by 'Hl/level and ss
The state of the L l/level is compared with the reference voltage, a detection signal is generated according to the continuation of the output of the PWM circuit 3, and the counter 1 determines whether this detection state has continued for a certain period of time or more.
6, and the current supply to the power element group is cut off if the current supply continues longer than the set time, so it is possible to prevent the power elements from being destroyed due to excessive current supply.

Effects of the Invention As described above, according to the present invention, even if an excessive input voltage is applied to the PWM amplifier for a long time, or if the PWM circuit malfunctions and an excessive current exceeding the maximum rating flows through the power element, the power can be maintained. It is possible to cut off current supply to the element, prevent damage to the power element, and protect the PWM amplifier.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a protection circuit for a PWM amplifier according to an embodiment of the present invention, Fig. 2 is a waveform diagram of each part of the circuit shown in Fig. 1, and Fig. 3 is a block diagram of a protection circuit for a conventional PWM amplifier. , FIG. 4 is an operational waveform diagram of each part of the amplifier shown in FIG. 3. 2 Triangular wave generation circuit, 3-PWM circuit, 4-7... Power element, 8.9...-Inductor, 10... Capacitor, 11.18-26... Resistor, 12.13... Comparator, 14 ...OR gate, 15..Reference signal generation circuit, 16 counter.

Claims (1)

[Claims] A monitor means for generating a pulse width modulation (PWM) signal by comparing an analog input signal with a reference triangular wave signal and detecting an output voltage of a PWM circuit that drives a power amplification circuit; 1. A protection circuit for a PWM amplifier, comprising: control means for cutting off power supply to the power amplifier circuit when a state at a constant value continues for a predetermined period of time.