JP2504698Y2 - Inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention uses a signal from an oscillation circuit or a microcomputer to alternately drive two switching elements using, for example, a power MOS-FET to generate an AC voltage. The present invention relates to a generated inverter, and more particularly to protection of a circuit when a signal from an oscillation circuit or a microcomputer is fixed to one level due to a malfunction of a supply voltage or noise.

<Prior Art> FIG. 4 shows a configuration of a conventional example of an inverter that drives two switching elements alternately to perform DC / AC conversion, and FIG. 5 shows a signal time chart. The signal waveforms at points (a) and (b) in FIG. 4 are represented by (a) and (b) in FIG.

Reference numeral 1 is a drive signal for generating a signal for driving the switching element, which is, for example, an oscillation circuit or a microcomputer. Q1 and Q2 are CMOS for driving switching elements
A buffer composed of gates, Q3 and Q4 are switching elements used in the power MOS-FET, and 2 is a transformer. The signal from the oscillation circuit 1 at this time is (a) and (b) in FIG.
It is assumed that it is a rectangular wave of opposite phase as shown by. Where time t
After that, if the signal from the oscillator circuit 1 stops,
Since Q3 remains ON, the impedance of transformer 2 disappears and Vcc and GND are short-circuited, causing an overcurrent to flow in the transformer and transistor. When (a) stops at H level, Q4 remains ON and the same phenomenon as above occurs.

<Problems to be solved by the invention> It is extremely dangerous if the transformer of the power supply is short-circuited in this way.

The present invention has been made to solve such a problem, and when the drive signal of the switching element is stopped, both switching elements are turned off and an overcurrent flows in the transformer and the transistor. The purpose is to realize a preventive inverter.

<Means for Solving the Problems> According to the present invention, two buffers receive drive signals generated by a drive signal source and having opposite phases to each other, and two switching elements are alternately provided at the outputs of these buffers. In an inverter that drives and converts a DC voltage into an AC voltage, a differentiation circuit that is provided for each of the buffers and that includes a resistor and a capacitor, and that is connected between the output end of the drive signal source and the input end of the buffer. , The input terminal has a diode having an anode connected to the input terminal of the buffer, the cathode connected to the power supply potential point, the anode having a common potential point, and the input protection diode connected to the cathode input terminal of the buffer. The output of the differentiation circuit, which is provided and is connected to the buffer that outputs the H level signal when the level of the drive signal is fixed, is a resistor and a capacitor. It is an inverter characterized in that the output of this buffer is dropped to an L level signal by changing it with a time constant given by.

<Operation> When the drive signal source of the switching element stops its operation, if one of the reverse-phase signals output from this is fixed at the L level, the switching element before this turns on. Up to. To avoid this,
Even if a capacitor is attached to the input stage where a drive signal is given and the output is pulled up by a resistor and the signal stops at L level, it becomes H level after a certain period of time and both switching elements are turned off. . Therefore, the power supply (Vcc and GND) of the transformer is not short-circuited.

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 4 are designated by the same reference numerals. Second
The figure is an illustration of the CMOS gates Q1 and Q2 shown in FIG.

One end of C1 and C2 is connected to the drive signal source 1 and the other end is connected to the input terminals of the buffers Q1 and Q2, respectively. R1 and R2 are connected to the potential point Vcc and the other end to the input terminals of the buffers Q1 and Q2, respectively. The connected resistors Q1 and Q2 are buffers composed of CMOS gates for driving switching elements.
In addition, D1 and D2 in FIG. 2 are clamp diodes, and by AC coupling of the capacitors C1 and C2, (c) of FIG.
It prevents the output of (d) from becoming the center of GND.

FIG. 3 is a time chart of each signal of the inverter shown in FIG. The signals (a) to (f) in FIG. 2 correspond to the signals at points (a) to (f) in FIG. The signal from the driving signal source 1 is a signal having a rectangular wave of opposite phase as shown in (a) and (b) of FIG. 2, and the capacitors C1 and C2.
After passing through, the differential waveforms (c) and (d) are as shown in (c) and (d).
It depends on the constant of 2. At the frequency of (a), a constant that does not reach the threshold level must be selected. The outputs of the CMOS buffers Q1 and Q2 are (e) and (f).

Here, after the time t, when the signal level from the oscillation circuit 1 is fixed, (a) is fixed to the L level. At this moment (e), it is at H level, but (c) is a constant of the resistor R1 and the capacitor C1, and gradually approaches H level. When (c) reaches the threshold level of CMOS buffer Q1, (e) becomes L level, so power MOS-FET Q3
Is turned off and no current flows through transformer 2, so Vcc and GND
Does not short.

<Effect of the device> As explained in detail above, even when the drive signal source stops operating, both switching elements are off, so Vcc and GND of the transformer do not short-circuit and overcurrent in the transformer and transistor. Is safe because it does not flow.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the CMOS gates Q1 and Q2 shown in FIG. 1, and FIG. 3 is a time chart showing the operation of FIG. FIG. 4 is a circuit diagram of a conventional example, and FIG. 5 is a time chart showing the operation of FIG. 1 ... Driving signal source, 2 ... Transformer, C1, C2 ... Capacitor, R1, R2 ... Resistor, Q1, Q2 ... Buffer, Q3, Q4
...... Switching element, D1, D2 …… Protection diode ,.

Claims (1)

(57) [Scope of utility model registration request] Claims: 1. Two buffers receive drive signals generated by a drive signal source and having opposite phases to each other, and the two switching elements are alternately driven by the outputs of these buffers to convert a DC voltage into an AC voltage. In the inverter that converts to
A differentiation circuit, which is provided for each buffer and includes a resistor and a capacitor, is connected between the output end of the drive signal source and the input end of the buffer, and the input part, the anode is the input end of the buffer, and the cathode is the A diode connected to the power supply potential point, a buffer having an input protection diode connected to the common potential point at the anode and a cathode at the input end of the buffer, and when the level of the drive signal is fixed, An inverter characterized in that the output of a differentiating circuit connected to a buffer that outputs an H level signal changes with a time constant given by a resistor and a capacitor to drop the output of this buffer into an L level signal.