JPS5840797Y2 - DC-DC converter - Google Patents

Description

[Detailed description of the invention] This invention automatically changes the time constant of the time constant circuit including the element by changing the impedance of the light-receiving element in accordance with changes in the DC output voltage, and thereby The present invention relates to a circuit configuration of a DC stabilized power supply device characterized in that the DC output is stabilized by controlling the conduction time of the DC power supply.

Conventional DC-D in which the input and output sides are electrically isolated from each other
In the C converter, the detection circuit on the output side and the control circuit on the input side are coupled in an alternating current manner using a pulse transformer, etc.
The switching transistors were controlled by varying the output of the input-side control circuit in response to fluctuations in the DC output voltage.

In such conventional converters, noise on the input side adversely affects the output side, making it difficult to obtain a device with extremely stable output characteristics.

The present invention aims to eliminate these drawbacks by combining a time constant circuit and an optical coupling element to create highly reliable DC stabilization that is extremely stable against noise and has an extremely simple circuit configuration. There is a power supply provided.

The present invention will be explained below with reference to the drawings. In FIG. 1, if the switching element connected in series to the primary winding N□ of the transformer T, here the transistor Q□, is in a conductive state, then the transformer T□ Voltage is induced in the primary winding N□, the degaussing winding N3, the secondary winding N, and the detection circuit power supply winding N4, which are respectively wound on the secondary winding. The alternating current voltage is converted to direct current by rectifier D2,
Next, it is smoothed through a smoothing circuit consisting of an inductor L and a capacitor C2, and appears at the output terminals o and o' as a DC voltage with a small ripple.

On the other hand, the AC voltage between the detection circuit power supply winding N4 is applied via the rectification/smoothing circuit B as the power supply voltage of the detection circuit C that detects the output voltage.

When the switching transistor Q0 becomes non-conductive, the output rectifier D2 becomes non-conductive, but the energy stored in the inductor L0 during the rectifier's conductive period is transferred to the load F via the freewheeling diode D3. As the load current is discharged, the load current is sustained as shown in FIG. 2d.

At this time, a voltage that forward biases the diode D0 is induced in the degaussing winding N3, so a current flows through the demagnetizing winding N3 through the diode D3, and the energy is transferred to the DC. It returns the energy to the power source E and also absorbs the energy stored in the core of the transformer T□, thereby preventing magnetic saturation of the core.

The operation of the main circuit accompanying the conduction and non-conduction of the transistor Q0 has been described above. Next, the control operation, detection operation, etc. will be described in detail with reference to FIG.

A is an oscillator such as a multivibrator,
Its output terminal A.

The oscillation voltage becomes a rectangular wave as shown in FIG. 2a.

This oscillator A constitutes a variable pulse width oscillator with a time constant circuit I consisting of a capacitor C0, a resistor R1, and a light receiving element Q5 that provides variable impedance, and this constitutes a drive circuit with a semiconductor element such as a transistor Q2. ing.

At time 1=0, the voltage at the output terminal Ao of the oscillator A is almost equal to the voltage e2 of the DC bias power supply E2, and the terminal Ao side of the capacitor C has a positive polarity and the point X side has a negative polarity. Assume that it is charged to voltage e2.

In this state, a sufficient drive current is flowing from the DC power source E2 through the resistor R0 and point X to the base of the transistor Q2.

Therefore, the transistor Q2 is in a saturated state, and its collector voltage is at almost zero potential as shown in FIG.
Transistor Q0 is in a non-conducting state.

At this time, the voltage at point X is at the base potential of transistor Q2.

Next time 1=1. At output terminal A of oscillator A.

is grounded and its voltage drops to zero, the capacitor C0, which is charged to approximately the voltage e2 with the polarity described above,
Since the positive polarity side of is zero potential, the negative polarity side, that is, the voltage at point X is approximately -02.

Therefore, the transistor Q2 becomes non-conductive, and the collector voltage of the transistor Q2 rises to approximately the voltage e□ of the DC power supply E□, as shown in FIG.

Therefore, the switching transistor Q□ becomes conductive and becomes saturated.

Also, capacitor C0 is the integration time constant of time constant circuit I, and the point
is terminal A.

, the voltage at point X gradually rises, and at time t-t2 transistor Q2
When the base-emitter saturation voltage E 2 of Q1 is exceeded, the transistor becomes conductive, rendering transistor Q1 non-conductive.

Then, at time 1=1, the output terminal A of oscillator A.

Even if the voltage increases to approximately e2, the above state is maintained.

On the input side, the sensor performs the control operation as described above, while on the DC output side, the resistor R6tR7 of the detection circuit C
detects the output voltage and compares the reference voltage of the constant voltage diode D with the voltage across the resistor R6, that is, the detected voltage. Based on the deviation voltage, the light emitting diode connected in series to the transistor Q4 A light emitting element D5 like
changing the current flowing through the

When the output voltage increases and the voltage drop across the resistor R6 becomes larger than the reference voltage of the constant voltage diode D40, the transistor Q4 becomes conductive and current flows through the light emitting element D5.

This light-emitting element is optically coupled to a light-receiving element Q5, such as a phototransistor, in the drive circuit, and typically generates an optical signal proportional to the current flowing through it.

Therefore, this light emitting element D5 sends an optical signal approximately proportional to the deviation value between the detected value of the DC output voltage and the above reference voltage to the light receiving element Q.
Send to 5.

Since the light receiving element usually changes its impedance depending on the magnitude of the optical signal, the impedance of the light receiving element Q5 decreases as the output voltage increases.

Therefore, the time constant formed by the resistor R1, the light receiving element Q5, and the capacitor C0 becomes small, and the charging of the capacitor C0 is accelerated.

Along with this, the conduction time t5 of the transistor Q2 is advanced as shown in FIG.
conduction period becomes shorter, lowering the output voltage.

Conversely, even when the output voltage becomes lower than the set value, the above-described operation is performed to lengthen the conduction period of the transistor Q0 and increase the output voltage.

By repeating such operations, a stable DC output voltage is supplied to the load.

Here, resistor R0 determines the maximum pulse width.

As mentioned above, this invention uses a light emitting element provided on the output side, which is DC isolated from the input side, to change the time constant of the time constant circuit using a light emitting signal generated in response to fluctuations in DC output. Controls on/off of element Q2,
It is characterized by stabilizing the DC output voltage by controlling the conduction period of the switching element, and by controlling the time constant of the time constant circuit using an electrically independent light emission signal to adjust the pulse width of the drive signal. Since it is made variable, it is extremely stable against noise, and since it is controlled by a combination of a time constant circuit and an optical coupling element, the number of circuit components can be reduced and reliability can be extremely improved.

Therefore, this DC stabilized power supply device is very suitable as a power supply for information equipment such as computers.

Although the embodiment has been described using a single transistor inverter, a separately excited inverter using a plurality of transistors may of course be used.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a DC stabilized power supply device according to the present invention, and FIG. 2 shows voltage waveforms at various parts. A: Oscillator, C: Detection circuit, ■
... Time constant circuit, Q ... Switching element, Q5 ... Light receiving element, D ... Light emitting element, T□ ... Transformer.

Claims (1)

[Scope of utility model registration request] a switching element connected to the primary winding of the output transformer;
In the DC power supply device, the DC power supply device includes a drive circuit that includes an oscillator and applies a drive signal to the switching element, and a detection circuit that detects DC output on a DC output side that is DC-isolated from the input side of the transformer. The detection circuit is provided with a light emitting element that emits an optical signal corresponding to the deviation value between the detected value of the DC output and the reference value, and the drive circuit having a time constant circuit receives the optical signal and determines the intensity of the optical signal. By providing a light receiving element whose impedance changes according to the change in impedance of the light receiving element, and automatically changing the time constant of the time constant circuit according to the change in the impedance of the light receiving element, the pulse width of the oscillation signal of the oscillator can be changed according to the deviation value. A DC stabilized power supply device characterized in that the conduction period of the switching element is controlled by varying the period of time of the switching element.