JPH0454719A - Frequency control circuit - Google Patents

Abstract

PURPOSE:To easily secure a minimum ON or OFF width with simple constitution by using a diode so as to control the discharge of a capacitor in a time constant circuit. CONSTITUTION:When a charging voltage of a capacitor 3 exceeds an error signal voltage being a difference between an input voltage Vin from an amplifier 1 and a reference voltage, the output signal of a comparator 4 is inverted and a monostable multivibrator 5 outputs a pulse signal with a prescribed pulse width. The capacitor 3 is discharged via a diode 6 during the period when the pulse width exists and the output of the comparator 4 is restored to the original state. When a prescribed pulse width period elapses, the charging of the capacitor 3 is restarted via a resistor 2. Thus, a pulse signal having a frequency corresponding to that of the voltage Vin is outputted, the charting is started to the capacitor 3 after lapse of the prescribed pulse width period. Then a prescribed OFF or ON width is ensured in the case of applying this circuit to a converter, and a minimum ON or OFF width is surely ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency control circuit whose output frequency is controlled in response to input voltage.

Frequency control circuits whose frequency is controlled by voltage are known in various configurations such as voltage controlled oscillators (VCOs) and voltage frequency converters (VFOs or VFCs), and are used in various control devices and voltage measurement devices. Applied.

In addition, a resonant converter compares the output DC voltage from the rectifying and smoothing circuit on the secondary side of the transformer with a set reference voltage to form an error signal, and adjusts the switching frequency of the switching element on the primary side of the transformer according to the error signal. A frequency control circuit that outputs a signal with a frequency according to an error signal is used, and the output DC voltage is stabilized by controlling resonance conditions. Further, there are two types of resonant converters: a voltage resonant type and a current resonant type, and configurations in which they are combined are also known.

[Conventional technology]

Various configurations of conventional frequency control circuits have already been proposed. For example, when controlling switching elements such as transistors, the configuration shown in FIG. 3 is known. In the figure, 21 is a frequency generator such as a voltage controlled oscillator (VCO) or a voltage frequency converter (VFC), 22 is a monostable multivibrator, 23 is a driver, and 24 is a field effect transistor (FET).

The frequency generator 21 uses a signal with a frequency corresponding to the input voltage Vin as a trigger signal for the monostable multivibrator 22, and includes, for example, an integrating circuit that integrates the input voltage Vin and a terminal voltage of a capacitor of this integrating circuit. It is possible to use a voltage-frequency converter consisting of a comparator that compares the voltage and a reference voltage, and a discharge circuit that discharges the capacitor when the comparison matches.

The monostable multi-bi break 22 uses the signal from the frequency generator 21 as a trigger signal to output a pulse signal with a constant pulse width according to a time constant, and uses this output pulse to drive the transistor 24 by the driver 23. It is turned off only during the period of the pulse width set by the monostable multivibrator 22.

The resonant converter has, for example, the configuration shown in FIG. 4, where 31 is a transformer, 32 is a switching transistor, 33 is a rectifier diode, 34 is a flywheel diode, 35 is a smoothing circuit, and 36 is a frequency control circuit. ,3
7 is a capacitor constituting a primary side resonant circuit, 38 is a DC power supply, 39 is an output capacitance between the drain and source of the switching transistor 32, 40 is a smoothing coil, 41 is a smoothing capacitor, and 42 is a load.

The excitation inductance of the primary winding of the transformer 31, the capacitance of the capacitor 37, and the switching transistor 32
A resonant circuit is formed by the output capacitance of Also, during the ON period of the switching transistor 32, current is supplied from the DC power source 3 to the primary winding of the transformer 31, and the induced voltage in the secondary winding due to this is rectified by the rectifier diode 33, and the rectified output voltage is passed through the smoothing circuit. 35 and is applied to the load 42.

The output DC voltage applied to the load 42 is compared with a set reference voltage in the frequency control circuit 36, and a signal with a frequency according to the error signal is outputted to control the switching frequency of the switching transistor 32. The output DC voltage is stabilized.

FIG. 5 is an explanatory diagram of the operation of the resonant converter shown in FIG. 4, in which (a) shows the voltage vcs applied from the frequency control circuit 36 to the gate of the switching transistor 32, and (b)
is the train-source voltage of the switching transistor 32 ■. 8, (C) shows the drain current In, (d) shows the voltage Vat applied to the rectifier diode 33, and (e) shows the current IDI flowing through the rectifier diode 33.

When the gate-source voltage VGS of the switching transistor 33 reaches the Roni level, the switching transistor 32 is turned off, and the half-wave resonant voltage of the sine wave due to the resonant circuit on the primary side of the transformer 31 becomes the switching transistor.
The voltage is applied to the transistor 32 as shown in (b), and the rectifier diode 33 has a flywheel diode 34.
A half-wave voltage (1) of the sine wave shown in (d) is applied through the circuit. Further, when the gate-source voltage ves becomes high level, the switching transistor 32 is turned on,
Drain current shown in (C) 1. flows. Thereby,
The rectifier diode 33 receives a current 1. shown in (e). flows.

Therefore, the switching transistor 32 operates as a negative side voltage resonance type, and the off-width of the switching transistor 32 is kept constant and the on-width is varied to control the switching frequency and stabilize the output DC voltage. When the output DC voltage rises above the set reference voltage, the frequency control circuit 36 operates to increase the switching frequency of the switching transistor 32. Conversely, when the output DC voltage falls below the set reference voltage, the frequency control circuit 36 operates to increase the switching frequency of the switching transistor 32. 32 switching frequency.

[Problem to be solved by the invention]

The conventional frequency control circuit shown in FIG. 3 uses the monostable multivibrator 22 and can perform switching control while keeping the off-width of the transistor 24 constant. It can be applied as a control circuit. Also, if the output signal of the monostable multivibrator 22 is inverted, the transistor 24
Since switching control can be performed with the 0-on width constant, it can be applied as a frequency control circuit of a current resonance type converter.

However, in order to ensure a constant off width or on width and to ensure a minimum on width or off width, the frequency generation section 21
It is necessary to make the time constant of the time constant circuit larger than the output pulse width of the monostable multivibrator 22, and therefore there is a drawback that the frequency generating section 21 is severely restricted.

An object of the present invention is to easily ensure a minimum on-width or off-width with a simple configuration.

[Means to solve the problem]

The frequency control circuit of the present invention causes the capacitor of the time constant circuit to start charging after a predetermined period of discharge time, and will be explained with reference to FIG.

The input voltage Vin from the terminal 8 is the reference voltage of the reference power supply 7.
an error amplifier 1 that outputs an error signal by comparing the
A comparator 4 compares the charging voltage obtained by charging the capacitor 3 of the time constant circuit consisting of the capacitor 3 with the output error signal of the error amplifier l, and the comparison output signal of the comparator 4 generates a constant pulse width. This device includes a monostable multivibrator 5 that outputs a pulse signal of .

[Effect]

The capacitor 3 of the time constant circuit is connected to the voltage VC through the resistor 2.
C, and the charging voltage of the capacitor 3 increases exponentially. Furthermore, the input voltage Vin and the reference voltage of the reference power supply 70 are compared by the error amplifier 1, and the error signal of the difference therebetween and the charging voltage of the capacitor 3 are compared by the comparator 4. When the charging voltage of capacitor 3 rises and exceeds the error signal, the output signal of comparator 4 is inverted. The inversion of the output signal of the comparator 4 triggers the monostable multivibrator 5 to output a pulse signal with a constant pulse width. During this period of constant pulse width, the capacitor 3 is discharged via the diode 6, so the charging voltage of the capacitor 3 becomes lower than the error signal, and the output signal of the comparator 4 returns to its original state. I'll have to go back. Then, after a period of a certain pulse width has elapsed, charging of the capacitor 3 is restarted via the resistor 2, and the above-described operation is repeated.

Therefore, a pulse signal with a frequency corresponding to the input voltage Vin is output, and since the capacitor 3 of the time constant circuit starts charging after a period of a certain pulse width has elapsed, it is not necessary to apply it to the converter. In some cases, it is possible to ensure a constant off width or on width, and also to ensure a minimum on width or off width.

〔Example〕

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

FIG. 1 is a block diagram of an embodiment of the present invention, showing a case where switching control is performed by giving a constant off width to a field effect transistor (FET) 12, 1 is an error amplifier, 2 is a block diagram of an embodiment of the present invention.
3 is a resistor, 3 is a capacitor, 4 is a comparator, 5 is a monostable multivibrator, 6 is a diode, 7 is a reference power supply, 8 is an input terminal, 9 is a driver, and 10.11 is an inversion drive element. The input voltage Vin can be, for example, the output DC voltage of a resonant converter, and the field effect transistor 12 can be a switching transistor on the primary side of a transformer of the resonant converter.

The driver 9 is shown as having an inversion drive element 10 for driving the field effect transistor 12 and an inversion drive element 11 for discharging the capacitor 3 via the diode 6. It is also possible to configure it with a driving element.

FIG. 2 is an explanatory diagram of the operation of the embodiment of the present invention, (Figure 2 shows the input voltage Vin, (b) shows the error signal a input to the comparator 4 and the charging voltage b of the capacitor 3, and (c) shows the comparison. The output signal C of the device 4, (b) shows the output pulse signal d of the monostable multivibrator 5, and (e) shows the output signal e of the driver 9.

The input voltage Vin applied to the terminal 8 is applied to one terminal of the error amplifier 1, and a reference voltage set in advance from the reference power supply 7 is applied to the child terminal of the error amplifier 1. When this input voltage Vin is shown in (a), the output signal a of the error amplifier 1 becomes as shown in the curve a in (b), and is applied to the child terminal of the comparator 4.

Also, the capacitor 3 of the time constant circuit receives the voltage v via the resistor 2.
It is charged by ec, and the charging voltage S is as shown in the curves 3 and 4, and is applied to one terminal of the comparator 4. When this charging voltage S rises and matches the error signal a, the output signal C of the comparator 4 is inverted as shown in (C).

The monostable multi-bi break 5 receives the output signal C of the comparator 4.
is triggered by the falling edge of , and outputs a pulse signal d with a constant pulse width t1 as shown in (6). As the pulse signal d rises, the output signal of the inversion driving element 11 becomes low level, and the charging voltage of the capacitor 3 is discharged through the diode 6 and rapidly lowers. Then, during the period of the pulse width t of the pulse signal d, the capacitor 3 is in a discharging state, and the charging voltage S of the capacitor 3 becomes almost zero. After the period of constant pulse width tl has elapsed, the pulse signal d falls and the output signal of the inversion drive element 11 becomes high level, so the diode 6 becomes reverse biased.
Charging of the capacitor 6 is restarted, and the charging voltage S rises. When it matches the error signal a, the output signal C of the comparator 4 causes the monostable multi-bi break 5 to output the pulse signal d of the constant pulse l1tl, and the capacitor 3 is discharged.

Therefore, the next pulse signal d is output after a time t2 from the start of charging of the capacitor 3 until the charging voltage matches the error signal a, and the period 'r (
=t+ +t4) changes according to the error signal a.

In this case, since the capacitor 3 of the time constant circuit is not charged during the period when the pulse signal d from the monostable multivibrator 5 is output, a rest period t must be ensured between the pulse signals 6. I can do it. Therefore, driver 9
When the field effect transistor 12 is driven by the output signal e of the inverting drive element 10, a constant off width t can be secured without particularly increasing the time constant of the time constant circuit, and the minimum on width tg can be maintained. The field effect transistor 12
Switching control can be performed.

Therefore, it can be applied as a frequency control circuit of a voltage resonance type converter.

Furthermore, if the inverting driving element 10 of the driver 9 is a non-inverting driving element, the field effect transistor 12 can be driven with a constant ON width, and therefore it can be applied as a frequency control circuit of a current resonance type converter.

Further, the present invention is not limited only to the above-described embodiments, and various additions and changes can be made.

〔Effect of the invention〕

As explained above, in the present invention, the capacitor 3 of the time constant circuit is charged via the resistor 2, the charging voltage S and the error signal a are compared by the comparator 4, and the comparison output signal C is used to The multi-by-break 5 is triggered to output a pulse signal d with a constant pulse width tl, and the pulse signal d
During the period of constant pulse width 11, the capacitor 3 of the time constant circuit continues discharging via the diode 6, and when switching control is performed by the output signal,
To secure a minimum off width or on width by ensuring a constant on width or off width using the monostable multivibrator 5, and by starting charging the capacitor 3 after the elapse of the certain time t1. Because it becomes possible to
This can be applied to a frequency conversion circuit of a resonant converter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the embodiment of the present invention, and FIG. 3 is a block diagram of a conventional example.
FIG. 4 is a circuit diagram of a main part of the resonant converter, and FIG. 5 is an explanatory diagram of the operation of the resonant converter. 1 is an error amplifier, 2 is a resistor, 3 is a capacitor, 4 is a comparator, 5 is a monostable multivibrator, 6 is a diode,
7 is a reference power supply, 8 is a terminal, and 9 is a driver. Patent Applicant Fujitsu Denso Co., Ltd. Representative Patent Attorney Akira Aitani Representative Patent Attorney Hiroshi Watanabe - Lid Block diagram of conventional example Figure 3 Block diagram of embodiment of the present invention Figure 1 Operation of embodiment of the present invention Explanatory diagram: Figure 2: Main circuit diagram of a resonant converter: Figure 4: Operational diagram of a resonant converter: Figure 5:

Claims (1)

[Claims] An error amplifier (1) that compares an input voltage with a reference voltage and outputs an error signal; and charging of a capacitor (3) of a time constant circuit consisting of a resistor (2) and a capacitor (3). voltage and the error amplifier (1
), a monostable multivibrator (5) that outputs a pulse signal with a constant pulse width based on the comparison output signal of the comparator (4), and the monostable multivibrator (5) A frequency control circuit comprising a diode (6) for discharging the capacitor (3) of the time constant circuit during the pulse width of the output pulse.