JP2000004589A - Resonance-type dc-to-ac converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the output of a DC/AC converter. SOLUTION: Switches S1 and S2 of a power switch 1 connected to a switching power supply 3, which is a voltage resonance type DC/AC converter via an inductor 2 are driven to be alternately turned on and turned off. A voltage detection circuit 4 detects the output voltage of the switching power supply 3, and the detection output is supplied to a control circuit 5 (IC) which controls the turning on/off of the power switch 1. The power switch 1 is controlled intermittently by the pulse signal of a PWM 5B of the control circuit 5 so as to obtain a constant AC signal or a rectified DC voltage from the switching power supply. The inductor 2 which is the component of the switching power supply 3 is used in common as a part of a down converter, and since the switching period and the on/off period of the power switch are synchronized with each other, a constant voltage can be o utputted for a DC voltage Vin of wide range with a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resonance type DC-AC.
In particular, the present invention relates to a resonance type DC-AC converter suitable for obtaining a constant output voltage with respect to an arbitrary driving power supply.

[0002]

2. Description of the Related Art For example, a fluorescent display device that displays various information by exciting a fluorescent substance applied to an anode electrode enclosed in a vacuum vessel has a heater voltage for generating an electron beam. In order to make this electron beam incident on a desired electrode, a drive power supply, a relatively high DC power supply for supplying an anode electrode, and the like are required,
Such a power source is conventionally supplied by a converter that converts a DC voltage into a predetermined DC voltage and an AC voltage.

FIG. 3 shows a DC-DC system proposed by the present applicant.
The figure shows a converter, which is a resonance type converter so that a sine wave AC signal can be output from the secondary winding of the transformer, and is hereinafter referred to as a resonance type DC-AC converter. In this figure, Vin is a drive DC power supply, C1 is a capacitor, and L is a current limiting inductor (coil). T is an output transformer which is a primary winding NP and a secondary winding N
S, and a center tap CT is provided for each. A resonance capacitor C ₀ is connected in parallel to the primary winding NP to form a resonance circuit, and two field-effect transistors (FETs) Tr 1 and Tr 2 are connected to supply a drive current to the resonance circuit. You. A driving DC power source Vin is connected via an inductor L between a connection point of the transistors Tr1 and Tr2 and a center tap of the primary winding.

Further, the voltage induced in the primary winding NP, ie, the resonance circuit, is fed back to the gate electrodes of the two transistors so as to be positively fed back to form an oscillation circuit. That is, waveform diagrams A, D, and
As seen from E, M, and N, during the period when the transistor Tr1 is on, the voltage at the point E has a positive polarity, the voltage at the point D becomes 0, and the transistor Tr2 is turned off. Also,
During the period when the transistor Tr2 is on, the voltage at the point D has a positive polarity, and the voltage at the point E becomes 0, thereby forming a push-pull type voltage resonance type oscillation circuit in which the transistor Tr1 is driven off. Therefore, transformer T 2
From the secondary winding, 4√2 proportional to the winding ratio NP / NS
An AC voltage with (NS / NP) Vin substantially peak-to-peak is obtained. The resonance frequency f ₀ is f ₀ = 1.
/ 2π (L _P C ₀₎ is set at ^-1/2 (H _Z), L _P denotes an inductance component of the transformer primary for one transistor.

In the above circuit, since the gate electrode of each transistor is directly driven by the resonant sine wave voltage of the primary winding NP, no extra circuit element is required, and the switching voltage is substantially half sine wave. , The switching loss is reduced, and the converter can be sufficiently practically used as a small power converter for a fluorescent display device or the like. In addition, since the output voltage also has a sinusoidally changing waveform, an accurate output voltage can be obtained by setting the winding of the transformer, which is useful as a multi-output power supply.

[0006]

However, this resonance type DC-AC converter requires a DC voltage V
Because the circuit is designed by setting the voltage value of in,
If the device is used for a device in which the driving DC power source Vin deviates from this set value, the output voltage also changes, and in the case of a fluorescent display device, the display content becomes unstable. Therefore, it is conceivable to perform feedback control such as detecting the output voltage on the secondary side and changing the switching frequency as is commonly used in ordinary DC-DC converters. In this case, the switching frequency is set by the resonance element, and the output is a sinusoidal wave. Therefore, a feedback control circuit cannot be easily added.

Therefore, for example, it is set so as to operate at a DC voltage higher than the set value, and the input power supply Vin is supplied to the resonance type DC-AC converter via a series regulator, or the DC power supply Vin and the resonance type DC-AC converter are connected. It has been considered that a DC-DC converter is interposed between AC converters to drive at a constant voltage.

However, if a voltage conversion circuit or a voltage conversion device for converting the voltage value of the driving power supply is interposed on the input side of the resonance type DC-AC converter, the circuit configuration becomes complicated, and the power conversion is performed. The problem of reduced efficiency arises. In addition, there is a disadvantage that the cost is increased as a general-purpose power supply device.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an output transformer in which a primary winding and a secondary winding are wound, and a parallel connection to the primary winding of the output transformer. And a resonance capacitor forming a resonance circuit, and first and second switching transistors connected in series between both terminals of the resonance circuit. Each control of the first and second switching transistors Forming a converter by forming a feedback circuit for feeding back the voltage between both ends of the resonance circuit to the electrode, and connecting the intermediate point of the primary winding and a driving power supply via a power switch and an inductor; A constant output voltage is obtained from the secondary winding by controlling the intermittent ratio of the power switch in accordance with the power supplied to the converter.

The above-mentioned resonance type DC-AC converter is configured such that a DC voltage Vin for driving a power supply is supplied via a power switch and an inductor. This power is converted into a voltage or a current and detected. In addition, by performing on / off control of the power switch in synchronization with the oscillation frequency of the converter, the amount of power supplied to the primary winding is controlled. As a result, the AC voltage output from the secondary winding or the rectified DC voltage can be maintained at a constant value.

[0011]

FIG. 1 shows a resonance type DC-AC according to the present invention.
FIG. 2 shows a basic block diagram of a converter.
In this figure, reference numeral 1 denotes a power switch configured so that switches S1 and S2 are alternately turned on / off, and the output thereof is a switching power supply that is a voltage resonance type DC-AC converter via an inductor 2. 3 are provided. The voltage resonance type switching power supply 3 is constituted by a push-pull type switching transistor as shown in FIG. 3, and the inductor 2 is shared with an impedance for limiting the driving current.

Reference numeral 4 denotes a voltage detection circuit for detecting the output voltage of the switching power supply. The detection output is supplied to a control circuit 5 (IC circuit) for controlling opening and closing of the power switch 1.

The control circuit 5 includes an error amplifier 5A for comparing the detection voltage of the voltage detection circuit 4 with the reference voltage of the reference voltage generation circuit 5B, a synchronization circuit 5C for synchronizing the oscillation circuit 5D with the switching frequency of the switching power supply 3, and,
A PWM modulator 5E is provided which converts the output of the oscillation circuit 5D into a rectangular wave and modulates the pulse width by the output of the error amplifier 5A. Then, this PWM modulator 5B
By controlling the opening and closing of the power switch 1 by the pulse signal, a constant AC signal or a rectified DC voltage can be obtained from the switching power supply 3.

That is, in the present invention, the DC power source Vin supplied to the terminal Tin is supplied to the switching power source 3 via the power switch 1 and the inductor 2.
Then, an output signal converted into an AC voltage by the switching power supply 3 is output from the terminal Tout, and a signal corresponding to the output voltage of the switching power supply 3 is fed back to the control circuit 5 via the voltage detection circuit 4, and the power switch 1
Is controlled to keep the output voltage constant even when the DC voltage Vin fluctuates.

For example, when the DC voltage Vin supplied to the terminal Tin decreases, the output voltage usually decreases. At that time, the output of the error amplifier 5A is different from the reference value, and is output from the PWM modulation circuit 5E. Is controlled so that the pulse width of the power switch 1 is increased.
Control is performed such that the ON period of 1 is prolonged. as a result,
As the power stored in the inductor 2 increases, the power supplied to the switching power supply 3 is controlled to increase. The switch S2 is connected to the switch S1
When the switch is turned off, a current path for supplying the power stored in the inductor L to the switching power supply 3 is formed.

The present invention provides a power switch 1 as described above.
And a simple configuration in which the inductor 2 constituting a part of the switching power supply 3 is arranged on the power supply side, so that voltage control of a resonance type switching power supply that converts a DC voltage into a sinusoidal AC signal is performed. With a relatively simple control circuit, a wide-range drive power supply can be used. For example, a power supply that is useful when applied to an in-vehicle electronic device or display device using a 12V battery as an operation power supply. Become.

FIG. 2 shows a specific circuit example of the resonance type DC-AC converter of the present invention constructed by the above block diagram. In this figure, a portion surrounded by a dashed line indicates the same operation as that of the block diagram of FIG. 1, and 1 indicates a MOS transistor Tr3 and a commutation diode DS.
A power switch section, and 2 is an inductor L
Is a voltage resonance type switching power supply. This switching power supply 3 performs DC-AC conversion in the same operation state as the circuit shown in FIG. 3 previously, and alternately conducts transistors Tr1 and Tr2, a primary winding Np, and a secondary winding Ns1. , Ns2 and Ns3, and a resonance capacitor Co.

Reference numeral 4 denotes a voltage detection circuit, which rectifies a sine wave pulsating current on the primary side supplied to the switching power supply 3 by a diode D10 and divides it by resistors R4 and R5. The capacitor C8 is provided for smoothing and preventing noise. Reference numeral 5 denotes a control circuit (IC circuit) having a control function as shown in FIG.
A detection voltage is supplied to one terminal, and a synchronization signal corresponding to the switching cycle of the switching power supply 3 is supplied to two terminals.
Then, a PWM signal is supplied to the MOS transistor Tr3 constituting the power switch 1 in accordance with the detected voltage.

It is important that the cycle of the PWM signal is synchronized with the switching frequency of the switching power supply 3, and when the two are not synchronized, it is difficult to expect a smooth voltage control function. Note that the detection of the switching cycle and the detection of the switched output voltage do not necessarily need to be taken out from the primary side, and it goes without saying that the secondary side alternating signal can be taken out and inputted to the control circuit 5. Absent.

In the embodiment of the present invention, the output of the switching power supply 3 is used as a driving power supply for a fluorescent display tube. That is, the output transformer T is a primary winding Np, the secondary side of the output transformer T is an anode of a fluorescent display tube, a secondary winding Ns1 for supplying a bias voltage, and rectifying and smoothing circuits (D1, D2, D3, D4, C4, L
2) is provided. Further, a secondary winding Ns2 for outputting a heater voltage of the fluorescent display tube, and a secondary winding Np3 for power supply of a signal system of the fluorescent display tube are provided. Diodes D5 to D5 also serve as rectifying and smoothing elements in secondary winding Np3.
8, choke coils L3 and L4, and capacitor C6,
C7 is provided and supplied to other circuits such as an amplification circuit other than the fluorescent display tube as needed.

The full-wave rectified output of the secondary winding Ns1 is output from the smoothing capacitor C4 as a voltage Vcc-Vee applied to the anode. Also, this voltage Vcc-Ve
e is divided by a resistor R3 and a Zener diode Dz1,
It is connected to the center tap CT of the secondary winding Ns2 as a bias voltage for the cathode. Therefore, a positive bias voltage is applied to the filament voltage Ef to the IC circuit for driving the fluorescent display tube VFD described later.

The MPU operates an I / O for driving the display tube VFD.
This is a C circuit (drive control unit CPU), and a circuit of a positive power supply system and a circuit of a negative power supply system are adopted depending on the type of the IC circuit. Although not shown, the IC circuit MPU includes a signal terminal to which information for display is input as data and a signal input terminal for operation according to the number of electrodes of the fluorescent display tube. The fluorescent display tube VFD has a heater H, a grid electrode G, and an anode electrode P coated with a fluorescent substance disposed in a vacuum container in a segment system or a dot matrix system. 1 shows a well-known fluorescent display device.

In the present invention, the power is supplied to the inductor L constituting the switching power supply 3 via the power switch 1. For example, when the output of the switching power supply 3 is reduced, the power is supplied to the inductor L. The voltage is detected by the voltage detection circuit 4, and the control circuit 5 controls the MOS transistor of the power switch 1 to increase the conduction period. As the conduction period becomes longer, the power stored in the inductor L increases, and this power flows through the switching power supply via the diode Ds even when the MOS transistor Tr3 is off.

As described above, since the MOS transistor Tr3, the inductor L, and the commutation diode Ds operate as a down converter, for example, when the input side DC voltage Vin is 12V, control is performed so that the output side of the inductor becomes 5V. The switching power supply 3 operates at this voltage and can be used as a driving power supply for the MPU. The down converter has an advantage that the power conversion efficiency is extremely high, so that the power consumption does not increase, and that the down converter does not have a complicated circuit configuration unlike a general DC-DC converter. In particular, in the present invention, since the inductor L required as a voltage resonance type DC-AC converter is shared as it is with a down converter, there is an effect that the circuit configuration can be extremely simplified.

Further, since the control circuit 5 for controlling the down converter is synchronized with the switching cycle of the switching power supply 3, the step-down control is extremely stable and the voltage control capability is high. In addition, the resonance type DC of the present invention
-Needless to say, the AC converter can be used besides the drive power supply of the VFD.

[0026]

As described above, the resonance type D of the present invention is used.
Since the C-AC converter performs feedback control using an inductor constituting a switching power supply so that the output voltage is constant, the AC output is always constant even when the input-side power supply voltage fluctuates greatly. Is obtained. Further, when driving a fluorescent display tube or the like with a resonance type switching power supply, it is important to control the heater voltage. In the case of the present invention, such a power supply device is small and has a small mounting area. It can be constituted by a circuit, and can provide a practically excellent effect. Further, since DC-AC conversion is performed by power conversion using a resonance circuit, switching loss of the transistor is reduced, and the withstand voltage of the transistor as a switching element can be reduced.

[Brief description of the drawings]

FIG. 1 is a basic circuit configuration diagram of a resonance type DC-AC converter of the present invention.

FIG. 2 is a circuit diagram showing an embodiment when the circuit of FIG. 1 is used as a power supply of a fluorescent display tube.

FIG. 3 is a diagram showing a basic circuit of a resonance type DC-AC converter.

FIG. 4 is an explanatory diagram of a resonance waveform and a switching waveform.

[Explanation of symbols]

1 power switch, second inductor, third switching power supply, 4 voltage detection circuit, 5 a control circuit, L inductor, C ₀ resonance capacitor, Tr1, Tr2 switching transistor (MOSFET), T the output transformer,
Vin DC power supply

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H007 BB03 CA02 CB06 CB09 CC12 CC32 DA06 DB03 DC05 EA02 5H730 AA14 AA15 AS11 BB25 BB72 CC25 DD04 EE04 EE73 FD01 FG05

Claims (5)

[Claims] 1. An output transformer having at least a primary winding and a secondary winding wound thereon, a resonance capacitor connected in parallel with the primary winding of the output transformer to form a resonance circuit, First and second switching transistors connected in series between both terminals of the circuit, and a voltage at both ends of the resonance circuit is fed back to each control electrode of the first and second switching transistors. A feedback circuit is formed to form a converter, and an intermediate point of the primary winding and a drive power supply are connected via a power switch and an inductor, and the power switch of the power switch is connected to the power supplied to the converter. A constant output voltage is obtained from the secondary winding by controlling an intermittent ratio.
AC converter. 2. A cycle in which the power switch is turned on and off,
The resonant DC-AC converter according to claim 1, wherein the converter is synchronized with a switching cycle of the converter. 3. The resonant DC-AC converter according to claim 1, wherein the power supplied to the converter is detected by an output of the inductor. 4. The resonance type DC-AC converter according to claim 1, wherein the output of said output transformer is used as a driving power source for a fluorescent display tube. 5. The resonance type DC-AC according to claim 1, wherein said switching transistor and said power switch are constituted by MOS transistors.
converter.