JPH063990B2 - Intermittent control type power supply circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intermittent control type power supply circuit.

<Prior Art> A conventional intermittent control type power supply circuit has a configuration as shown in FIG. AC voltage between input terminals 1 and 1 ', or
Apply non-smooth full-wave or half-wave rectified voltage. While the instantaneous value of the input voltage is small, the switching transistor is in the conductive state, and if the capacitor 8 is not connected to the output side, a voltage proportional to the input voltage is output between the output terminals 9 and 9 '. To be done. However, the instantaneous value of the input voltage rises and the output voltage reaches a predetermined value accordingly, that is, the output voltage level exceeds the sum of the zener voltage V _DZ and the base-emitter voltage V _BE5 of the transistor 5. At that moment, the Zener diode 6 is energized, and the transistor 5 becomes conductive. Therefore, the transistor 3 is short-circuited between its base and emitter and its collector circuit is cut off, so that the switching transistor 2 is cut off and the output voltage is cut off. However, since the output voltage is cut off, the Zener current is reduced at the next moment, and the transistor 5
Is again cut off, a base current flows through the transistor 3, and the collector circuit is rendered conductive, so that the switching transistor 2 is also rendered conductive and an output voltage is generated again. When the output voltage is generated, the Zener diode becomes conductive again,
As long as the input voltage (instantaneous value thereof) exceeds a predetermined value (V _DZ + V _BE + collector-emitter voltage of the switching transistor 2 at the time of energization), the above intermittent action is repeated. FIG. 2 explains the above-mentioned operation when the input is an unsmoothed full-wave rectified voltage. When the input voltage changes like the curve ABPCQDP'E in the figure,
A voltage equal to the input voltage is output during P, but
When the change of input voltage reaches point P, Zener diode 6
Is activated, the switching transistor 2 is cut off, and the output voltage drops to 0 level. After that, the output voltage is intermittently repeated as described above until the change of the input voltage reaches the point Q. A voltage equal to the input voltage corresponding to ABP is obtained during QDP ', but the output voltage is repeated intermittently after reaching the point P'.

The voltage which changes intermittently in this way is ABP, QDP '.
Is smoothed by the output-side capacitor 8 including the drop portion due to the waveform of the input voltage like the section of
A DC voltage between 9'is obtained.

By the way, in such a system, the intermittent control cycle is determined by the response speed of semiconductor elements such as zener diodes and transistors, so electromagnetic noise with a very high frequency is generated from the circuit, which adversely affects other electronic devices in the vicinity. In addition to the possibility, the period of the intermittent control signal is too short, so that the switching action of the power transistor used as the switching transistor cannot sufficiently respond to the intermittent control signal, and the class C operation cannot be performed.
Therefore, the average power consumption of the switching transistor increases, which may cause thermal breakdown.

<Object of the Invention> An object of the present invention is to provide an intermittent control type power supply circuit in which a switching transistor operates in complete response to an intermittent control signal, and the above-mentioned drawbacks of the prior art are eliminated.

<Structure of the Invention> In order to achieve the above object, the circuit according to the present invention comprises a switching transistor inserted between an input side and an output side, and a series connection of a zener diode and a resistor, which is operated by a voltage on the output side. A DC power supply circuit for outputting an intermittent DC voltage to the output side by utilizing the Zener current characteristics of the Zener diode, wherein the Zener diode and either one of the output side positive and negative terminals are provided. A collector-emitter circuit of a grounded-collector type transistor is inserted between the two, and the unsaturated characteristic of this grounded-collector type transistor is used to add hysteresis to the conduction / cutoff function of the switching transistor. There is.

<Examples> Examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of an embodiment of the present invention. The circuit configuration is such that the circuit 10 in the dotted line is added to the circuit according to the prior art of FIG. 1, and the basic operation of oscillation is the same as that of FIG. 1, but there is a hysteresis in the detection voltage level. different. The outline of the operation will be described below.

The transistor 11 is grounded at the collector, and the voltage drop between the collector and the emitter depends on the base potential.
When the output voltage Vout is equal to or lower than the specified value, the zener current does not flow through the zener diode 6 as described with reference to FIG. 1, so that the transistor 5 is off and the transistors 3 and 2 are on. Base potential V of transistor 11 at this time
_B11 is given by the following equation.

Where V _D14 : forward voltage of diode D ₁₄ , V _CE3 : collector-emitter saturation voltage of transistor 3,
Rv: resistance value of the volume 12, R ₁₃ : resistance value of the resistance 13. Since the collector of the transistor 11 is grounded, its emitter potential is V _B11 + V _BE11 = V _E11 . Where V _BE11 is the base-emitter voltage of transistor 11. Therefore, the voltage detection level V _ON when the transistor 2 is on is given by the following equation.

V _ON ≈ V _E11 + V _D6 + V _BE5 (2) where V _BE5 : Base-emitter voltage of transistor 5.
However Between the values _{R 7} and ₇ 'value _R' of the resistor 7 resistor 7 R '
_The resistance division ratio was ignored because of the relationship of ₇ << R ₇ .
When Vout becomes higher than the above voltage detection level V _ON , a zener current flows through the zener diode 6 and the transistor 5
Is turned on, so that the transistors 3 and 2 are turned off and the supply of energy to the Vout side is stopped. Considering the base potential _V'B11 of the transistor 11 at this time, it is given by the following equation.

Here, R _CE3 (0) is a collector-emitter equivalent resistance when the transistor 3 is OFF. Therefore transistor 2
The voltage detection level V _{OFF when} is _off is given by the following equation.

Since a _{V OFF ≒ V 'B11 + V} BE11 + V D6 + V BE5 V' B11 ≒ 0, the hysteresis of _{V OFF ≒ V BE11 + V D6} + V BE5 ...... (3) Therefore the ON voltage of the transistor 2 and the off voltage (2) Since it is given by the formula − (3), Therefore, it is understood that the hysteresis can be arbitrarily set by selecting the resistance values of the resistors 12 and 13. That is, when the switching transistor 2 is on, the voltage dropped by the volume 12 is supplied to the base of the transistor 11, and the voltage of the Zener diode 6 passes through the transistor 11 having the unsaturated characteristic. Is detected. On the other hand, when the switching transistor 2 is off, the transistor 11 is on, so that the output side voltage is applied to the zener diode 6 via the collector of the transistor 11. Therefore, Zener
Depending on whether the diode 6 is turned on or off,
With respect to the output side voltage, there is a difference of V _B11 corresponding to the voltage drop in the volume 12.

That is, there is a margin of time for the output side voltage to drop by V _{B11 from} the time when the Zener diode 6 is turned on to the time when it is turned off. As a result, the intermittent period can be extended as compared with the case where the Zener diode 6 is turned on and off at substantially the same voltage as in the conventional circuit shown in FIG.

In the case of the above configuration, the period of voltage 0 between PQ in FIG. 2 becomes long.

As described above, the hysteresis characteristic can be set to any continuous point by utilizing the unsaturated characteristic of the grounded-collector type transistor. Further, since the transistor 11 has the collector grounded configuration, the transistor 11 does not overdrive due to input and output voltage fluctuations, and therefore the negative feedback operation from the voltage detection to the transistor 2 has almost no delay and the intermittent control type power supply circuit. The greatest feature of this circuit configuration is that it achieves the high feedback speed and the elimination of feedback delay, which are especially required in.

Incidentally, FIG. 4 shows the circuit configuration when a C-type transistor is used as the transistor 2, and FIG. 5 shows the transistor 2 as an N-channel power MOS FET.
The circuit configuration implemented in place of the above is shown. The circuit operation is the same as that of the embodiment shown in FIG. In both cases, the same reference numerals used in FIG. 3 are used for the portions corresponding to the circuit components shown in FIG.

<Effects of the Invention> As is apparent from the above description, according to the present invention, the intermittent period can be arbitrarily set, so that an inexpensive switching element can be used in accordance with the load condition, and the unsaturated due to the excessive response capability of the switching element. The problem of efficiency reduction and heat generation due to the increase of the degree is solved, and the intermittent period can be adjusted, so that the amount of noise flowing out to the outside can be reduced. Since the transistor 11 has a collector-grounded circuit configuration, there is no overdrive of the transistor and the operation delay of the voltage detection circuit is small in principle.

[Brief description of drawings]

FIG. 1 and FIG. 2 are a block diagram and an operation explanatory view of an intermittent control type power supply circuit according to the prior art, respectively. FIG. 3 is a circuit configuration diagram of an embodiment of the present invention. 4 and 5 are circuit configuration diagrams when the above embodiment is modified. 2, 2a ... Switching transistor 2b ... Switching transistor (MOS FET type) 3, 3a, 3b, 5, 5a, 5b, 11, 11a, 11
b ... transistor 6,6a, 6b ... zener diode 7,7a, 7 '... resistor 8 ... output capacitor 10,10a, 10b ... intermittent period adjusting circuit 14 ... diode

Claims (1)

[Claims] 1. A switching transistor inserted in series between an input side and an output side, a series circuit of a Zener diode and a resistor inserted on the output side, and a voltage divided and output from the series circuit. In a power supply circuit consisting of a transistor for controlling on / off of the switching transistor by means of and a capacitor inserted in parallel relationship with the series circuit on the output side, in series between the Zener diode and the output side. An intermittent control transistor having an unsaturated characteristic that constitutes a collector-grounded circuit is inserted, and a control resistor is inserted between the transistor for controlling ON / OFF of the switching transistor and the output side. It controls conduction and supplies a predetermined voltage division output by the control resistor to the base of the intermittent control transistor. Off control power supply circuit, characterized in that remembering hysteresis conduction, the blocking function of the switching transistor.