JPH0330894Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a DC power supply circuit that obtains a DC voltage by transforming, rectifying and smoothing a commercial power supply voltage using a power transformer, and its purpose is to reduce the size of the power transformer, It is an object of the present invention to provide a DC power supply circuit which can achieve weight reduction, has good regulation due to commercial power supply voltage fluctuations and load fluctuations, and has a configuration in which changes in magnetic flux of a power transformer are stabilized.

In order to achieve this purpose, in this invention,
The primary side of the power transformer is equipped with a line filter and a circuit that controls the conduction angle using the commercial power supply voltage, and the secondary side is equipped with a circuit that controls charging of the smoothing capacitor based on changes in output voltage due to load fluctuations. It was established.

An embodiment of the present invention will be described below with reference to the drawings.
Fig. 1 shows an embodiment of the present invention, in which 1 is a line filter that removes noise from a commercial power supply;
Tr 1 is a phase advancing circuit that advances the output voltage of the line filter, Tr ₁ is a triax that is provided in series with the primary winding of the power transformer 7 and divides the output voltage of the line filter 1 with the primary winding, and Tr 3 is a triax that advances the output voltage of the line filter 1. Phase advance circuit 2
A level detection and trigger circuit, _D7 to _D10 , generates a trigger pulse to the triac Tr ₁ at a reference level with a falling edge of the phase-advanced voltage that is the output of the
are diodes that constitute a rectifying bridge that rectifies the secondary voltage of the power transformer 7, and C ₁₃ and C ₁₄ are smoothing capacitors installed between the positive and negative output terminals Eo ⁺ ut, Eo ^- ut and the ground terminal GND. , SCR ₁ and SCR ₂ are thyristors inserted between the smoothing capacitors C ₁₃ and C ₁₄ and the output side of the diode bridge, and 4 is a DC regulator that obtains a constant DC voltage from the secondary voltage of the power transformer 7. Voltage circuits 5 and 6 are comparison and trigger circuits that compare the DC constant voltage and the output voltage, amplify the error voltage as necessary, and generate trigger pulses for the thyristors SCR ₁ and SCR ₂ .

FIG. 2 shows a detailed example of the circuit shown in FIG. 1, in which the line filter 1 is composed of capacitors C ₁ to C ₃ , and the phase advance circuit is composed of capacitor C ₄ and resistor R ₁ ,
The level detection and trigger circuit ₃ includes diodes _D1 to _D4 , Zener diodes _D5 and _D6 , resistors _R3 to _R8 , and a capacitor.
C ₆ , C ₇ , transistors Q ₁ , Q ₂ , and diac
It consists of Dia ₁ and Dia ₂ . Further, the DC constant voltage circuit 4 includes diodes D ₁₁ and D ₁₂ ,
capacitors _C9 to _C12 , transistors _Q3 to _Q6 ,
Zener diodes _D13 , _D14 and resistors _R10 to _R15
It is composed of Toni Ni. Further, the comparison and trigger circuits 5 and 6 each include a transistor Q ₇ and a resistor R ₁₆ , and a transistor Q ₈ and a resistor R ₁₇ .

Next, the operation of this circuit will be explained. Figure 3 is the second
This shows the primary voltages of points a, b, and c in the figure and the power transformer 7. The power supply voltage Va from which noise has been removed by the line filter is phase-advanced by the phase advance circuit 2 to Vb. Now, if we consider the case where the voltage at point b increases from zero to positive, capacitor C ₆ is charged via diode D ₁ , resistor R ₃ and diode D ₃ , and the voltage Vb is charged through Zener diode D. When the Zener voltage Ve of ₅ + the voltage drop of the diode D ₁ and the resistor R ₃ due to the current flowing through the resistor R ₅ is reached, charging of the capacitor C ₆ stops. the voltage
Vb reaches the falling part, Zener voltage Ve + resistance R ₅
When the voltage drop across diode D ₁ and resistor R ₃ due to the current flowing through transistor Q ₁
Because the base voltage of the capacitor C6 is lower than the emitter voltage, the base current of the transistor _Q1 flows through the resistor _R5 due to the capacitor _C6 , so the charge of the capacitor _C6 is transferred to the transistor _Q1 , the dielectric _Dia1 ,
It is discharged through the gate of triac Tr ₁ , and triac Tr ₁ becomes conductive. In other words, since there is a resistor R ₅ , the terminal voltage of the Zener diode D ₅ is the third
As shown by Vz in FIG. b, the time h becomes earlier than in the case without the resistor _R5 , and the range of change in the conduction angle due to power supply fluctuations becomes wider. Therefore, the regulation is better than without the resistor _R5 . Even when the voltage Vb becomes negative, the same operation is performed by the actions of the diodes D ₂ and D ₄ , the resistors R ₄ and R ₆ , the Zener diode D ₆ , the capacitor C ₇ , the transistor Q ₂ and the diagonal Dia ₂ .

Here, if the power supply voltage Va increases,
The time point h when the voltage Vb becomes smaller than the Zener voltage Ve at the time of falling moves in the B direction, and therefore the conduction angle θ of the power transformer 7 becomes large. On the other hand, when the power supply voltage Va decreases, the point h shifts to the direction A, which serves to reduce the conduction angle θ of the power transformer, resulting in good regulation against power supply fluctuations.

Generally, the magnetic flux φ of a transformer is determined by integrating the primary voltage, but the magnetic flux φ′ when the conduction angle θ is set as described above is compared to the case of 100% conduction, as can be seen from the formula below. decreases to

φ′／φ＝∫Vad dt／∫Va dt＝∫πVa dt／∫πVa dt In this way, by reducing the magnetic flux compared to a normal transformer, the margin up to the saturation magnetic flux density is increased, and the winding It promotes a reduction in the number of wire turns and a smaller core size, and stabilizes magnetic flux changes in the transformer.

In the secondary circuit, when the voltage across capacitor C ₁₁ decreases and the voltage across resistor R ₁₄ decreases to below the sum of the Zener voltage of Zener diode D ₁₃ and the base-emitter voltage of transistor Q ₅ , transistor Q ₅ turns off, which causes a base current to flow through the resistor R ₁₀ to the transistor Q _{3 ,} turning it on and transferring the charge on the capacitor C ₉ through the transistor Q ₃ to the capacitor C ₁₁
, the voltage across capacitor C ₁₁ increases. This turns on transistor _Q5 , which turns off the base current of transistor _Q3 and flows across the capacitor.
C ₁₁ stops charging and the voltage V ₅ across capacitor C ₁₁ remains constant. Similarly, the voltage Vg of capacitor C ₁₂ is also connected to transistors Q ₄ , Q ₆ and Zener diode.
It is kept constant by the action of D ₁₄ , etc.

Here, due to load fluctuations and ripple voltage, transistors Q ₇ and Q ₈ whose output voltage Eou ⁺ t (Eo ^- ut) is smaller than the constant voltage Vf (Vg) are turned on, so
Thyristors SCR ₁ , SCR ₂ are triggered, and capacitors C ₁₃ , C ₁₄ are charged and held at a constant voltage via diodes D ₇ , D ₈ , D ₉ , D ₁₀ and thyristors SCR ₁ , SCR ₂ . Therefore, regulation due to load fluctuations is also improved.

FIG. 4 shows another embodiment of the present invention, in which the diagonals Dia ₁ and Dia ₂ of FIG. 2 are replaced with transistors, and the comparison and trigger circuits 5 and 6 of FIG.
This is a simplified version of the embodiment shown in FIG. 2, and the basic operation is the same as that of the embodiment shown in FIG.

According to the present invention, regulation against power supply voltage fluctuations and load fluctuations can be significantly improved compared to the conventional case where the conduction angle is controlled only on the primary side, and compared with the case where the conduction angle is controlled only on the secondary side, the regulation of the power supply transformer can be improved. can reduce heat generation,
The number of windings can be reduced, the core size can be reduced, making the power transformer smaller and lighter, the magnetic flux changes in the power transformer can be stabilized, and there is no need to provide an intermediate terminal on the primary winding of the power transformer. There is no feedback circuit or electrical or optical coupling between the primary and secondary circuits of the power transformer, so there is no isolation. It has the following advantages: it is very good, requires fewer parts, and can be implemented at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a detailed circuit diagram thereof, FIG. 3 is an operation waveform diagram thereof, and FIG. 4 is another embodiment. 1... Line filter, 2... Phase advancing circuit, 3...
...Level detection and trigger circuit, 4...DC constant voltage circuit, 5, 6...Comparison and trigger circuit, 7...
…Power transformer, Tr ₁ …Triack, D ₇ ~
D ₁₀ ... Diode composing the bridge, SCR ₁ ,
SCR ₂ ...Thyristor, _C13 , _C14 ...Smoothing capacitor.

Claims (1)

[Scope of utility model registration request] A line filter that removes noise from the power supply,
An energizing path that divides the output voltage of the line filter between the primary winding of the power transformer and the triax, a phase advance circuit that advances the phase of the output voltage of the line filter, and a diode and a resistor connected in series to the output of the phase advance circuit. a level detection and trigger circuit that detects the level at both ends of a parallel circuit of a Zener diode and a resistor connected through the circuit, and outputs a trigger pulse to the triax when the level falls below a predetermined level; A bridge rectifier circuit using diodes that rectifies the secondary side voltage, a thyristor inserted between the output side of the bridge rectifier circuit and a smoothing capacitor at the output end, and a direct current that rectifies and stabilizes the secondary side voltage. A DC power supply circuit comprising: a constant voltage circuit; and a comparison and trigger circuit that compares an output voltage of the DC constant voltage circuit with an output voltage at an output end and outputs a trigger pulse to the thyristor.