JP3355867B2 - Class C amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a class C amplifier circuit, and more particularly to a class C amplifier circuit used for narrow band power amplification.

[0002]

2. Description of the Related Art As conventional amplifier circuits, class A, class B, and class C amplifier circuits have been proposed depending on how an input signal is applied. The class A amplifier circuit has low efficiency instead of linear amplification, and the class C has high efficiency but is not suitable for linear amplification.
Class B is intermediate between the two. Therefore, for linear amplification, A
Class and class B amplifier circuits are used, and class C is often employed for narrow band power amplification. FIG. 6 shows an operation waveform diagram of the class C amplifier circuit, and FIG. 7 shows transistors. The class C amplifier circuit will be briefly described below. FIG. 6 (a)
Is the base-emitter voltage of the transistor (= input signal)
FIG. 6B shows a relationship between the collector current Ic and the base current IB of the transistor, and FIG. 6C shows a relationship between the collector-emitter voltage VCE and the collector current Ic of the transistor. The relationship is shown below.

A class C amplifier circuit is a circuit that operates at a transistor operating point VBB below a point where the collector current Ic becomes zero (hereinafter, referred to as a cutoff point). Even if the input signal is only a part of the vibration waveform for a period shorter than half a period, the output waveform is the output of a substantially sinusoidal resonance vibration waveform of the entire period Can be obtained.

[0004] This resonance vibration waveform is obtained as follows. In the steady state, the current Ic has a sawtooth waveform. When the switching element is turned off, the current Ic is cut off, but the current flowing through the inductance element does not immediately become zero, and a charging current flows from the inductance element to the capacitance element. Eventually, the charging current to the capacitance element becomes zero, and conversely, a discharging current flows from the capacitance element to the inductance element. The frequency of vibration due to the repetition of such an operation becomes the resonance vibration frequency.

[0005]

However, the conventional class C amplifier circuit has the following problems.

In a conventional class C amplifier circuit, since the resonance circuit and the driving frequency of the switching element are substantially the same, a resonance voltage is applied to the switching element and the current is applied to the switching element near the ON time of the switching element. , The switching loss occurs in the switching element, and the circuit efficiency decreases.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a class C amplifier circuit capable of improving circuit efficiency by reducing switching loss.

[0008]

In order to solve the above problems, according to the first aspect of the present invention, a series circuit of a switching element and an inductance element and one of the switching element and the inductance element are provided. A class C amplifier circuit having a capacitance element connected in parallel, and forming a resonance circuit with the inductance element and the capacitance element, wherein when the voltage across the switching element is zero, the switching element is turned on. It is characterized by doing.

According to the second aspect of the present invention, the resonance frequency of the resonance circuit is about 1.10 times the drive frequency of the switching element.
It is characterized in that it is 5 times and the Q (quality factor) of the resonance circuit is about 3.

According to the third aspect of the present invention, the output end of the resonance circuit matches the impedance of the electrodeless discharge lamp, the induction coil for applying a high-frequency electromagnetic field to the electrodeless discharge lamp, and the impedance of the induction coil and the resonance circuit. And a load having at least a matching circuit for connection.

[0011]

According to the first aspect of the present invention, when the switching element is turned on when the voltage across the switching element becomes zero, the slope of the voltage across the switching element at that time is zero. The flowing current becomes substantially zero, and the switching loss becomes substantially zero.

According to the second aspect of the present invention, the frequency of the resonance circuit is set to about 1.5 times the driving frequency of the switching element, and the Q (quality factor) of the resonance frequency is set to about 3 times.
Then, when the voltage across the switching element becomes zero, the switching element is turned on. At that time, the current flowing through the switching element becomes substantially zero, the switching loss becomes substantially zero, and the circuit efficiency becomes 89%.

According to the third aspect of the present invention, when starting and lighting the electrodeless discharge lamp, when the switching element is turned on when the voltage across the switching element becomes zero,
At that time, the current flowing through the switching element becomes substantially zero, so that the switching loss becomes substantially zero.

[0014]

【Example】

(Embodiment 1) A circuit diagram of a first embodiment according to the present invention is shown in FIG.

In this circuit, a series circuit of an inductance element L1 and a MOSFET (S1) (hereinafter referred to as a switching element S1) is connected in parallel to both ends of a power supply E, and a capacitance element C1 is connected in parallel to both ends of the switching element S1. A class C amplifier circuit in which a series circuit of a capacitance element C2 and a load Z is connected in parallel to both ends of the capacitance element C1 and an input signal is input to the switching element S1 to extract an amplified signal to the load Z.

Here, power source E = 100 V, inductance element L1 = 760 nH, capacitance element C1 = 7
0 pF, capacitance element C2 = 3000 pF, load Z = 150Ω, switching frequency f = 10 MHz (d
uty 46%), the parasitic capacitance Cd of the switching element S1
When s = 68 pF, the resonance frequency fo of the resonance circuit including the inductance element L1, the capacitance element C1, and the parasitic capacitance Cds is:

[0017]

(Equation 1)

, That is,

[0019]

(Equation 2)

The resonance frequency fo is set at about 1.5 times the switching frequency f. The Q (quality factor) when the capacitance element C2 and the load Z are connected is set to be about 3.

With this setting, as shown in FIG. 2, the switching element S1 can be turned on when the voltage Vds across the switching element S1 becomes zero due to resonance oscillation, and in this case, the switching element S1 is turned on. Since the slope of the voltage Vds across S1 is zero, the current flowing through the switching element S1 also becomes substantially zero, and the switching loss in the switching element S1 can be reduced. Switching element S1
Duty, the value of X, Q (quality factor),
Table 1 shows the relationship between the circuit efficiencies.

From Table 1, it can be seen that the switching element S1 has a dut.
A maximum efficiency of 89% was obtained when y was 46%, X was 1.55 times, and Q (quality factor) was about 3.

[0023]

[Table 1]

In order to obtain an input signal having an arbitrary duty, the driving circuit of the switching element S1 becomes complicated, and the overall efficiency including the driving circuit is reduced. Therefore, the input signal is generally biased by a sine wave. Often do not call. When no bias is applied, the duty is about 42%, X = 1.45, Q (quality factor)
Is about 3, a circuit efficiency of 88% is obtained.

(Embodiment 2) FIG. 3 is a circuit diagram of a second embodiment according to the present invention.

The first embodiment shown in FIG. 1 is different from the first embodiment in that the load Z is an electrodeless discharge lamp La that excites and emits a discharge gas sealed in the bulb when a high frequency electromagnetic field is applied from the outside. In order to match the impedance of the dielectric coil 1 wound around the electrodeless discharge lamp La and applying a high-frequency electromagnetic field to the electrodeless discharge lamp La by applying a high-frequency current thereto, and the dielectric coil 1 and the resonance circuit. And the same components as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

In general, the matching circuit 2 is used to match the impedance between the resonance circuit and the dielectric coil 1 when the electrodeless discharge lamp La is turned on, but the load is set before and after the discharge lamp is started. Since the impedance greatly changes, the impedance of the resonance circuit and the dielectric coil 1 cannot be matched at the time of starting the electrodeless discharge lamp La,
As a result, in other zero-volt switching amplifier circuits, a high voltage is applied to the switching element, and stress is applied to the switching element.

However, in the class C amplifier circuit according to the present invention,
Since the resonance circuit is used as the output circuit, the voltage applied to the switching element is reduced, and the stress applied to the switching element can be reduced irrespective of the load impedance fluctuation.

It should be noted that an electroded discharge lamp may be used instead of the electrodeless discharge lamp La. Further, in all the above embodiments, the MOSFET is used as the switching element S1, but a transistor may be used. Further, as a circuit for realizing a class C amplifier circuit, a series connection of a parallel circuit of an inductance element L11, a capacitance element C11 and a load Z and a switching element S1 as shown in FIG. As shown in FIG. 5, a series circuit of a load Z and a capacitance element C12 may be connected in parallel to both ends of the switching element S1.

[0030]

According to the first and second aspects of the present invention, a class C amplifier circuit capable of improving circuit efficiency by reducing switching loss can be provided.

According to the third aspect of the present invention, there is provided a class C amplifier circuit capable of reducing the stress applied to the switching element when starting and lighting the electrodeless discharge lamp and improving the circuit efficiency. it can.

[Brief description of the drawings]

FIG. 1 is a circuit diagram according to a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram according to the embodiment.

FIG. 3 is a circuit diagram according to a second embodiment of the present invention.

FIG. 4 is another circuit diagram according to the present invention.

FIG. 5 is still another circuit diagram according to the present invention.

FIG. 6 is an operation waveform diagram of the class C amplifier circuit.

FIG. 7 is a circuit diagram illustrating a transistor.

[Explanation of symbols]

 S switching element L inductance element C capacitance element La electrodeless discharge lamp Z load 1 induction coil 2 matching circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeki Matsuo 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. Inventor Shohei Yamamoto 1048 Kadoma, Kazuma, Osaka Pref. Matsushita Electric Works, Ltd. (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 3/20

Claims (3)

(57) [Claims] 1. A switching element and an inductance element
And a switching element and an inductor
Capacitor connected in parallel with one of the sensing elements
An inductance element, and the inductance element and the capacitor
Class C amplifier circuit that constitutes a resonance circuit with the capacitance element
A class C amplifier circuit, wherein the switching element is turned on when the voltage between both ends of the switching element is zero. 2. The resonance frequency of the resonance circuit is about 1.5 times the drive frequency of the switching element.
The class C amplifier circuit according to claim 1, wherein a Q (quality factor) of the resonance circuit is about 3. 3. An electrodeless discharge lamp, an induction coil for applying a high-frequency electromagnetic field to the electrodeless discharge lamp, and a matching circuit for matching impedance of the induction coil and the resonance circuit at an output terminal of the resonance circuit. The class C amplifier circuit according to claim 1 or 2, wherein a load having at least the following is connected.