JPS6027407B2 - Stabilized power supply circuit - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for rectifying alternating current voltage to obtain direct current voltage.
The present invention relates to a stabilized power supply circuit that can automatically correct fluctuations in output DC voltage, and is particularly designed to be insulated from the input side to the output side.

Conventionally, as this type of stabilized power supply circuit, one using a switching element as shown in FIG. 1 is known.

For example, an AC input voltage from a commercial power supply is rectified by a rectifier circuit 3 consisting of a diode bridge circuit 1 and a capacitor 2, and this rectified voltage is applied to a switching element such as a thyristor 4. is controlled on/off by the rectangular wave signal Sc from the pulse width modulator 8, so that a rectangular voltage is obtained on the cathode side of the thyristor 4, and this rectangular voltage is applied to the diode 6, choke coil 7 and The DC voltage is smoothed by a smoothing circuit 9 consisting of a capacitor 8 and taken out from the output terminal 10. By controlling the pulse width of the rectangular wave signal Sc from the pulse width modulator 5, the DC voltage is output from the output terminal 10. The DC voltage taken out is controlled.

However, this has the drawback that the input side and output side cannot be insulated.

Therefore, it was considered that insulation could be achieved by using a transformer.

Figure 2 shows an example of a stabilized power supply circuit using the transformer, where the output end of the rectifier circuit 3 is connected to the primary winding 11 of the transformer 11.
grounded through a series circuit of a and the switch circuit 12,
This switch circuit 12 is turned on and off by a constant period rectangular wave signal from a pulse width modulator 113, and in response, a substantially rectangular voltage is obtained on the secondary winding 11b side of the transformer 11, which is a diode. 14 and capacitor 5
The voltage is rectified by a rectifier circuit consisting of the following, and is output as a DC voltage to the output terminal 16.

In this case, fluctuations in the DC output voltage are detected by the fluctuation detection circuit 17, and the detected output controls the pulse width modulator 13 to change the pulse width of the output rectangular wave signal. The conduction time is controlled, thereby controlling the voltage obtained at the secondary winding 11b of the transformer 11, so that the voltage obtained at the output terminal 16 is always kept constant. However, in the one shown in FIG. 2, the primary winding 11a and the secondary winding 11b of the transformer 11 must be placed in close contact due to leakage inductance.

In addition, since control to stabilize the output voltage is performed on the primary side, the control signal must be isolated and supplied from the secondary side. For example, a photocoupler or the like is used in the control signal transmission path. There was a drawback that it had to be. The present invention aims to provide an isolated stabilized power supply circuit that can eliminate the above-mentioned drawbacks.

Hereinafter, an example of the stabilized power supply circuit according to the present invention will be described with reference to FIGS. 3 and 4, taking the case of a television receiver as an example.
Let me explain with reference to the diagram.

In FIG. 3, 20 is a converter transformer, for example, a horizontal output transformer, and the output end of the rectifier circuit 3 is connected to this transformer 2.
The connection point between the primary winding 20a of the transformer 20 and the capacitor 21 is the collector terminal of the switching transistor 23. grounded through the transmitter.

Reference numeral 24 denotes an oscillator from which a pulse of, for example, a horizontal frequency is obtained, which is supplied to the base of the transistor 23, thereby controlling the transistor 23 on and off.

In addition, 25 is an overload protection circuit, which detects when a large current flows during an overload such as discharge of a cathode ray tube, and stops the oscillation of the oscillator 24 using the detected output.The oscillator 24 When the switching transistor 23 is turned on and off by the output of A pulse-like voltage is obtained, which is transmitted to the secondary side of the transformer 20, and the
A similar pulsed voltage EP (FIG. 4A) is obtained on the next side.

Then, this voltage EP is integrated by an integrating circuit 28 consisting of a resistor 26 and a capacitor 27, and the output E, (FIG. 4B) of this integrating circuit is passed through a capacitor 29 and a resistor 30 to a PNP type transistor 31 as a comparator. supplied to the base of The emitter voltage of this transistor 31 is
The Zener diode 32 keeps the Zener voltage Vz constant, and this voltage V2 is compared with the integral output EI. Note that 41 and 42 are resistors for connecting the base bias of the transistor 31, and in this example, the stabilized output voltage obtained from the output terminals 4 is connected to the resistors 41 and 4.
2, and this divided voltage is coupled to the base of a transistor 31 via a resistor 30.

When the voltage obtained on the secondary side of the converter transformer 20 is a pulsed voltage EP as shown by the solid line in FIG. 4A, the integral output B of the integrating circuit 28 is shown as the solid line in FIG. 4B. The sawtooth wave voltages E and M are as follows, and this voltage E
1, is lower than the voltage Vz (strictly speaking, a value lower than Vz by the base-emitter voltage VB8 of the transistor 31), the transistor 31 becomes conductive, and the collector of this transistor 31, and thus the inverting NPN transistor 3
A rectangular voltage S as shown in FIG. 4C is obtained at the base of transistor 33, and this is inverted on the collector side of transistor 33 to obtain a rectangular voltage S as shown in FIG. 4D. The rising pulse of S is supplied to the gate of a thyristor 35 as a switching element via a capacitor 34 to turn it on.

On the other hand, this thyristor 35 is turned off when the voltage EP obtained on the secondary side of the transformer 20 falls to negative. In this case, since the voltage EP falls negatively when the transistor 23 is turned off, the time point at which the thyristor 35 is reversed from on to off is at a constant period determined by the oscillation frequency of the oscillator 24. Therefore, thyristor 35
On the cathode side of , there is a rectangular voltage E as shown in FIG. 4E.

, is smoothed by a smoothing circuit 39 consisting of a diode 36, a choke coil 37, and a capacitor 38, and a voltage corresponding to the on/off period of the thyristor 35 is extracted from the four output terminals. Next, for example, when the power supply voltage fluctuates and the voltage obtained on the secondary side of the transformer 20 becomes a pulsed voltage EP2, which is larger than the pulsed voltage EP2 as shown by the broken line in FIG. 4A, the integral output E,2 is the voltage E, . as shown by the broken line in FIG. 4B. This results in a sawtooth wave voltage E,2 with a larger slope. At this time, as is clear from the figure, during the period when the voltage E12 is lower than the voltage Vz, the voltages E, . is longer than the period during which the voltage V2 is lower, and the transistor 31 is connected to the collector side as shown in FIG.
A rectangular voltage S2 as shown in is obtained, and the transistor 3
9, an inverted voltage S2 as shown in FIG. 4G is obtained. That is, the rise of the voltage S2 is delayed from the rise of the voltage S, and therefore the time when the thyristor 35 is turned on from off is also delayed. The time when the oscillator 35 is turned off is determined by the oscillator 24 as described above.
Since this is a fixed point in time determined by the oscillation frequency of 4th on cathode side
A voltage Eo2 as shown in Figure H' is obtained. If the voltage obtained on the secondary side of the transformer 20 is the same as EP, the output voltage obtained by smoothing this in the smoothing circuit 39 should be lower because the period during which the thyristor 35 is on is shorter. However, the voltage obtained on the secondary side is EP
, to EP2, the voltage obtained at the output terminal 40' remains unchanged.

Although not shown, when the voltage EF obtained on the secondary side of the transformer 20 becomes smaller than EP due to fluctuations in the power supply voltage,
The integral output EI has an even smaller slope than E1. At this time, the period during which the thyristor 35 is on becomes longer, and the output voltage obtained from the output state 401 does not change.

In this way, the output voltage obtained from the output terminal 401 is stabilized.

According to the stabilized power supply circuit according to the present invention, a converter transformer is used and the voltage can be controlled on the secondary side of the transformer, so that complete insulation can be achieved.

Further, according to the present invention, since the primary side has a resonant circuit and this resonance is used to obtain a voltage on the secondary side, the second
Compared to the case where energy is transmitted only by a transformer, as in the secondary example in the figure, there is no need to consider the influence of leakage inductance, and therefore the primary and secondary windings do not need to be in close contact with each other. This is advantageous in terms of noise.
In addition, this invention stores energy in the transformer and
The current flowing to the secondary side, such as the one that converts to the next side,
Compared to the case where all the DC components are superimposed, there is less DC component superimposition, so there is an advantage that the transformer can be made smaller and the cost can be reduced. Furthermore, by providing a resonant circuit on the primary side of the transformer and utilizing its resonance, it is possible to obtain a negative pulse voltage on the secondary side as shown in Figure 4A. This makes it easy to turn off.

Furthermore, in this invention, the impedance seen from the switching element to the input side is high due to the use of a transformer, and the constant current property is large, so that rush current does not easily flow into the switching element or the smoothing choke coil. There is also this effect.

In the example shown in FIG. 3, since the overload protection circuit 25 is provided, oscillation stops and current stops flowing in the event of an overload, so that the smoothing choke coil 37 does not become saturated.

That is, conventionally, it was necessary to use an expensive coil as the coil 37 that does not saturate even when overloaded, but in the example shown in the figure, there is no such need, and an inexpensive coil can be used as the coil 37. . Note that the control switching element is not limited to a thyristor, but a transistor or other switching element can be used.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of an example of a conventional stabilized power supply circuit, FIG. 3 is a circuit diagram of an example of a stabilized power supply circuit according to the present invention, and FIG. 4 is a waveform diagram for explaining the same. . 3 is a rectifier circuit, 20 is a converter transformer, 22 is a resonant circuit, 28 is an integration circuit, 31 is a comparison transistor, 3
2 is a Zener diode, 35 is a thyristor, and 39 is a smoothing circuit. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 has a converter transformer, a resonant circuit is provided on the primary side of this converter transformer, DC voltage is supplied in the primary order of this converter transformer, and a switching element and a smoothing element are provided on the secondary side of the converter transformer. A circuit, an integrator, and a comparator are provided, the voltage obtained on the secondary side of the converter transformer is integrated by the integrator, the integrated output and a reference voltage are compared in the comparator, and the comparison output is A stabilized power supply circuit in which the switching element is controlled so that the voltage obtained on the output side of the switching element is smoothed by the smoothing circuit to obtain an output voltage.