JPS598473Y2 - frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency conversion device, and more particularly to a control circuit for a frequency conversion circuit that converts DC power into high-frequency power using an LC resonant circuit.

Conventionally, a transistor inverter circuit using an LC resonant circuit has been used as a high frequency power source for an induction heating cooker that heats a household metal pot or the like.

FIG. 1 shows an example of a transistor inverter device applied to an induction heating cooker.

Conventionally, the inverter circuit shown in Figure 1 was controlled by detecting the load current or by detecting the conduction of a diode connected in anti-parallel with a transistor to control oscillation, but the control circuit was extremely difficult to control. There was a high possibility that the system would become complicated or the oscillation would become unstable, resulting in malfunction.

The present invention provides an improved control circuit for a transistor inverter circuit using LC resonance.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an inverter device to which a control circuit according to the present invention is applied.

FIG. 2 shows one embodiment of the control circuit according to the present invention;
The figure shows a concrete implementation circuit.

FIG. 4 shows waveforms of various parts of the control circuit according to the present invention.

In FIG. 1, an AC voltage is applied from a low frequency AC power source 1 to a rectifier circuit 2 and converted into a DC voltage.

The output DC voltage of the rectifier circuit 2 is applied to the inverter circuit 3.

The inverter circuit 3 is oscillated under control by the control circuit 4 and converts DC power into high frequency power.

The inverter circuit 3 connects an input capacitor 30 between the DC voltage terminals and the resonant inductor 3 from the DC voltage terminal.
1 and a parallel connection body consisting of a resonance capacitor 32 and a power switching semiconductor 33 are connected in series.

The resonance inductor 31 also serves as a heating coil.

As the power switching semiconductor 33, a transistor or a gate turn-off thyristor can be considered, for example.

FIG. 1 shows an embodiment using a transistor.

The emitter of the transistor 33 is connected to one DC voltage terminal, and a diode 34 is connected in antiparallel.

The resonance capacitor 32 is a power switching semiconductor 33
may be connected in parallel.

The control circuit 4 includes a current detection current transformer 400 for controlling the input or output of the inverter circuit 3, its input detection terminals 401a and 401b, and a voltage detection terminal 402 of the power switching semiconductor 33 and the power switching semiconductor 33. A drive output terminal 40 to which a control signal is applied
3a and 403b.

FIG. 2 shows a block diagram of the control circuit 4. As shown in FIG.

The control circuit 4 controls the pulse width of the conduction of the power switching semiconductor 33 in synchronization with the resonance of the load resonance circuit.

The signal from the voltage detection terminal 402 is sent to the synchronous pulse generation circuit 4.
1, when the voltage of the power switching semiconductor 33 changes from positive to negative, a synchronizing pulse signal Vt is generated and applied to the pulse width control circuit (PWM circuit for short) 42.

On the other hand, the signal from the current transformer 400 is applied to an input detection circuit 43, which takes out a voltage signal p corresponding to the input current of the inverter circuit 3 and applies it to the PWM circuit 42.

The PWM circuit 42 generates a pulse synchronized with the synchronizing pulse signal Vt, and its pulse width is controlled by a pulse width control signal p.

The output signal VW of the PWM circuit 42 is added to the gate circuit, and the oscillation start/stop control circuit 45 controls the output signal VW of the PWM circuit 42.
The output signal (e) of the gate circuit controlling the output signal is applied to a pulse drive circuit 46 and a synchronization pulse generation circuit 41 that turn on and off the power switching semiconductor 33.

The synchronous pulse generation circuit 41 receives the output signal of the PWM circuit 42,
Alternatively, it is controlled by the output signal ``e'' of the gate circuit, and has a prohibition circuit that prevents the synchronization pulse signal ``t'' from being output when the power switching semiconductor 33 is in a conductive state.

In other words, when the synchronization signal Vt is applied to the PWM circuit 42, the power switching semiconductor 33 becomes conductive for a certain period of time, but when the synchronization pulse signal Vt is input while the power switching semiconductor 33 is conductive, the power switching semiconductor 33 becomes conductive. This eliminates the drawback of widening the conduction period.

Figure 3 shows the synchronous pulse generation circuit 41 and PWM according to the present invention.
This is a specific example of a circuit 42 and a gate circuit.

From the voltage detection terminal 402, resistors 410a and 410b
The voltage is lowered from D and applied to the inverter 411.

A diode 412 is connected to the control circuit DC power supply VCC from the input of the inverter 411 to provide overvoltage protection.

A differential capacitor 413 and a differential resistor 414 are connected to the output terminal of the inverter 411 to form a differential circuit, and the differential signal is connected to one input of a NAND gate 415.

The output of the NAND gate 415 is connected to the cathode of a diode 416, and the anode of the diode 416 is connected to the connection point of the resistors 420a and 420b.

A synchronous pulse signal V which is the output of the NAND gate 415
t is shown in FIG.

That is, VC in FIG. 4 is the power switching semiconductor 33.
At a voltage VC of , IC is the current of the power switching semiconductor 33 and the anti-parallel diode 34.

The moment VC becomes zero, the output signal of inverter 411 becomes H.
i level, differential capacitor 413 and differential resistor 4
14, the output signal V of the NAND gate 415
t becomes the LO level.

The PWM circuit 42 consists of a ramp generator and a comparator.

The lamp generator includes an output resistor 422 of the first comparator 421 of the open collector, a charging resistor 423,
A discharge resistor 424, a discharge diode 425, and a reset diode 426 are connected to the output side of the comparator 421, and the voltage of the timer capacitor 427 is connected to the comparator 4.
Add to the input terminal of 21.

The tenth input terminal of the comparator 421 is connected to the resistor 420 a
, 420b, that is, a set voltage is applied.

The operation of the lamp generator starts with the comparator 42.
When output 1 is off, output resistance 422 and charging resistance 423
When the voltage r of the timer capacitor 427 becomes higher than the input voltage of the comparator 421, the output of the comparator 421 becomes LO level and is charged to the timer capacitor 427 via the discharge resistor 424 and the discharge diode 425. discharge.

During this discharge, the comparator 4 is connected by the diode 426.
21 to prevent comparator 421 from entering the latched state.

FIG. 4(r) shows the ramp waveform Vr of the timer capacitor 427.

In addition to the ramp signal ■r being sent to the single-power terminal of the second comparator 428, the pulse width control signal ■p is also sent from the input detection circuit 43.
A PWM signal VW is obtained.

Comparator 428 is an open collector, and resistor 429 is a load resistor.

The PWM signal VW is applied to the second NAND gate 440 and is NANDed with the output signal of the oscillation start/stop control circuit 45.
The signal Ve is the NAND gate 4 of the synchronization pulse generation circuit 41.
Added to 15.

The output signal Ve of the NAND gate 440 is sent to the inverter 44.
1 to the pulse drive circuit 46, and when the signal Ve is at the LO level, the power switch semiconductor 33
A drive signal is applied to the

When the signal Ve is at the I, o level, the NAND gate 4
Since the output signal Vt of No. 15 is always at Hi level, PW
No synchronizing signal is applied to M circuit 42.

The lamp generator shown in FIG.
Synchronous oscillation is performed by forcibly setting the input terminals of 10 to I and o levels.

In addition, in FIG. 3, the + of the second comparator 428
, one power is connected in reverse and its output signal is directly connected to the first N
It is clear that it may be applied directly to AND gate 415.

As described above, the present invention stably obtains a synchronizing signal for a PWM circuit that performs synchronous oscillation. In particular, the PWM pulse width can always be kept constant, and the oscillation of an inverter circuit can be stabilized.

Especially in inverter circuits using LC resonance, LC
It is necessary to oscillate in synchronization with resonance, and there is a risk of destruction if the pulse width of the power switching semiconductor 1 widens due to malfunction, but it is extremely superior in terms of improved reliability.

In particular, conventional oscillation control circuits directly detect the load current and control the load current, but the present invention uses a pulse width control circuit that includes a synchronous signal generation circuit and a lamp generator that oscillates in synchronization with the synchronous signal. Since the oscillation is controlled, the circuit can be simplified, the cost can be reduced, and the reliability can be improved, and an inexpensive frequency conversion device can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a frequency conversion device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a control circuit used in the device.
3 is a specific circuit diagram of FIG. 2, and FIG. 4 is a waveform diagram of each part of the circuit of FIG. 2. 1...Low frequency AC power supply, 2...Rectifier circuit, 3...Inverter circuit, 4...Control circuit, 31...Resonance Inductor for 32...
... Resonance capacitor, 33... Power switching semiconductor.

Claims (1)

[Scope of utility model registration request] The inverter circuit is composed of an inverter circuit that converts DC power into high-frequency power, and its control circuit. The inverter circuit is composed of a resonant inductor, a resonant capacitor, and a power switching semiconductor, and the control circuit is synchronized with the resonant waveform of the inverter circuit. a synchronous pulse generation circuit that generates a pulse, a pulse width control circuit that is connected to the output of the synchronous pulse generation circuit and controls the pulse width, and a pulse that is connected to the output of the pulse width control circuit that turns on and off the power switching semiconductor. a drive circuit, connected to feed back the output signal of the pulse width control circuit or the pulse drive circuit to the synchronization pulse generation circuit,
A frequency conversion device configured to prohibit the synchronization pulse when the power switching semiconductor is in a conductive state.