JPH06335241A - Transformer-coupled secondary dc power-supply forming device - Google Patents

Abstract

PURPOSE:To stabilize a protective function against overcurrent and at the same time miniaturize a device and reduce its weight and cost by forming an overcurrent detection circuit by connecting a time-constant circuit consisting of a charging resistor and a capacitor for charging in parallel with the auxiliary winding of a transformer. CONSTITUTION:An overcurrent detection circuit 50 is formed of a charging resistor R51 and a charging capacitor C51 connected in series between the positive pole side of an auxiliary winding L12 of a transformer 20 and the negative pole side of a rectification circuit 14 and a discharging resistor R52 connected in parallel with the charging capacitor C51 and in series with the charging resistor R51. Then, the point between the charging resistor R51 and the charging capacitor C51 is connected to an element 16 for protection against overcurrent, thus indirectly detecting overcurrent from a control voltage VC and an oscillation frequency, thus miniaturizing the overcurrent detection circuit 50, achieving stabilization against the voltage fluctuation of an AC power supply 11 by adding a constant current circuit, and further easily coping with the change-over of the voltage of the AC power supply 11.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a primary DC power supply circuit and a secondary DC power supply circuit.
The present invention relates to a transformer-coupled secondary DC power generation device that is connected and coupled to a secondary DC power supply circuit via a transformer and has an overcurrent protection function.

[0002]

2. Description of the Related Art In FIG. 7, a primary DC power supply circuit 10 and a secondary DC power supply circuit 30 are connected via a transformer 20. The primary DC power supply circuit 10 includes an AC power supply 11,
Switch 12, noise filter 13, rectifier circuit 14,
The smoothing capacitor C10, the switching element (transistor) 15, and the control circuit (40) are included and formed, and the switching element 15 is connected between the primary winding L11 of the transformer 20 and the negative side of the rectifier circuit 14. In addition, the control voltage Vc is induced from the auxiliary winding L12 and the diode D10
Is oscillated and generated through and is supplied through the resistor R10.

The secondary DC power supply circuit 30 includes a diode D21 connected to the secondary winding L21 of the transformer 20,
The load 3 is formed by including the smoothing capacitors C21 and C22.
Connected to 5. A stabilizing circuit 45 inputs a voltage detection signal to a feedback signal generating circuit 46 including a photo coupler.

Thus, in such an RCC type self-oscillation type (frequency fluctuation type) transformer-coupled secondary DC power supply generator, the control circuit (transistor 40) is turned on / off by a feedback signal to control the control voltage Vc. ON-OFF control the switching element 15 using
Electric power energy is supplied from the secondary winding L11 to the secondary winding L21. In the secondary DC power supply circuit 30, the diode D21
Is rectified and smoothed by the smoothing capacitors C21 and C22 to generate a secondary DC power supply and supply it to the load 35. Load 35
Fluctuation of the secondary DC power supply voltage as a fluctuation of the stabilization circuit 4
The signal is detected at 5 and is output to the feedback signal generation circuit 46. This stabilizes the secondary DC power supply voltage.

Therefore, when the load 35 is light, the current flowing through the switching element 15 decreases and the oscillation frequency increases. On the other hand, when the load 35 becomes heavy, the current flowing through the switching element 15 increases and the oscillation frequency decreases. O of the switching element 15 by the control circuit (40)
This is because the N duty is constant.

In the separately-excited flyback type fixed frequency type shown in FIG. 8, the control circuit 40 is formed of a PWM IC, and when the load 35 is light, the switching element 15 is used.
The current flowing through the device decreases, and the energizing time becomes shorter. on the other hand,
When the load 35 becomes heavy, the current flowing through the switching element 15 increases, and the energization time becomes longer accordingly. This is because the oscillation frequency is constant. The drive power source (voltage Vd) of the control circuit 40 is induced to oscillate in the secondary winding L12 and supplied through the diode D10. That is, this drive voltage Vd is generated similarly to the control voltage Vc in the case of FIG.

By the way, in either case, in order to protect the switching element 15 from overcurrent, 1
An overcurrent detection circuit (R50) and an overcurrent protection element 16 are provided on the side of the next DC power supply circuit 10. The overcurrent detection circuit is formed of a resistor R50 connected between the switching element 15 and the negative side of the rectifier circuit 14, and the overcurrent protection element 16 is a base of the switching element 15 and the rectifier circuit 1.
4 is connected to the load side. Then, between the switching element 15 and the resistor R50 and the overcurrent protection element (MO
It is connected to the drive terminal (gate) of the S.FET) 16.

Therefore, when the current flowing through the switching element 15 increases, the overcurrent detection circuit (R50) increases the detection voltage Va. Then, the overcurrent protection element 1
Since 6 is turned on, the current flowing into the switching element 15 is drawn into the overcurrent protection element 16. Therefore, the switching element 15 can be turned off to protect it from an overcurrent.

[0009]

When the load 35 on the secondary DC power supply circuit 30 side becomes larger, the current flowing through the switching element 15 on the primary DC power supply circuit 10 side also becomes larger. Then, of course, a large current stress is applied to the resistor R50 forming the overcurrent detection circuit, so that the resistor R50 itself must have a large capacity, and the shape becomes large. However, further weight reduction, downsizing and cost reduction are strongly desired, and an overcurrent detection circuit (resistor R50)
Has become one of the factors that hinder the achievement.

The voltage of the AC power source 11 (for example, AC
100V) fluctuates (for example, 85 to 138V),
It is difficult to set a constant because the overcurrent protection point changes. Further, in order to expand the applicability, when the AC power supply 11 is constructed so that it can be selectively used in either AC100V or AC200V, the resistance value of the resistor R50 must be exchanged, which is troublesome.

It is an object of the present invention to provide a transformer-coupled secondary DC power supply generator capable of achieving a light weight / miniaturization and cost reduction while stably exhibiting an overcurrent protection function.

[0012]

A transformer-coupled secondary DC power supply generator according to the invention of claim 1 is a primary DC power supply circuit including a rectifier circuit, a smoothing capacitor, a switching element, and a control circuit, and a stabilizing circuit. A secondary DC power supply circuit including a switch is connected and coupled through a transformer, and a switching element is turned on while applying a feedback signal from the stabilizing circuit to the control circuit.
It is formed so as to generate a secondary DC power source by N-OFF control, and when the overcurrent is detected by the overcurrent detection circuit, the switching element is turned off via the overcurrent protection element.
In the transformer-coupled secondary DC power supply generator formed so as to perform overcurrent protection, the overcurrent detection circuit is connected in series between the positive side of the auxiliary winding of the transformer and the negative side of the rectifier circuit. A charging resistor and a charging capacitor connected to each other, and a discharging resistor connected in parallel with the charging capacitor and in series with the charging resistor, and between the charging resistor and the charging capacitor and for protecting the overcurrent. It is characterized in that it is connected to the drive terminal of the element.

According to a second aspect of the present invention, a constant current circuit is provided which receives the voltage generated from the auxiliary winding of the transformer as an input and makes the current flowing through the charging resistor and the charging capacitor constant. Characterize.

[0014]

In the case of the first aspect of the present invention having the above structure, for example, in the case of the frequency fluctuation type, when the load of the secondary DC power supply circuit becomes heavy, the current flowing through the switching element increases and the oscillation frequency becomes low. That is, the oscillation frequency of the control voltage decreases. If the cycle corresponding to this oscillation frequency becomes longer than the cycle of the charging time constant of the charging resistor and the charging capacitor, the voltage of the charging capacitor rises to the set voltage, and the overcurrent protection element is turned on. Therefore, the switching element can be turned off to protect from overcurrent. After that, the electric charge accumulated in the charging capacitor is discharged through the discharging resistor in a timely manner. When the load is light and the oscillation frequency is high, the voltage of the charging capacitor does not reach the set voltage, and the overcurrent protection element remains OFF, so normal control operation can be continued.

In the case of the fixed frequency type, when the load of the secondary DC power supply circuit becomes heavier, the current flowing through the switching element increases and the energization time becomes longer. That is, the oscillation time of the drive voltage of the control circuit becomes long. Therefore,
When the energization time becomes longer than the charging time constant of the charging resistor and the charging capacitor, the voltage of the charging capacitor rises to the set voltage, so that the overcurrent protection element can be turned on. Therefore, the switching element can be turned off to protect from overcurrent. The overcurrent protection element remains off when the load is light.

According to the invention of claim 2, in addition to the function of claim 1, a control voltage or a drive voltage is input to a constant current circuit, and a constant current is caused to flow from this constant current circuit to a charging resistor and a charging capacitor. . Therefore, the overcurrent protection point can be kept constant even when the AC power supply is used in a state in which the voltage fluctuations or the AC power supply is switched between high and low.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) As shown in FIG. 1, the transformer-coupled secondary DC power source generator is a self-excited oscillation type (frequency fluctuation type) of the same RCC method as the conventional example (FIG. 7). Moreover, the overcurrent detection circuit 50 is formed to indirectly detect the overcurrent by utilizing the oscillation frequency of the control voltage Vc.

The same parts as those of the conventional example (FIG. 7) are designated by the same reference numerals, and the description thereof will be simplified or omitted.

In FIG. 1, a diode D10 for oscillating and generating a control voltage Vc on the positive side of the auxiliary winding L12 and a resistor R are provided.
An overcurrent detection circuit 50 of a frequency detection method is provided between the output terminal 10 and the negative electrode side of the rectifier circuit 14. The overcurrent detection circuit 50 is formed by connecting a charging resistor R51 and a charging capacitor C51 in series, and connecting a discharging resistor R52 in parallel to the charging capacitor C51. Then, the charging resistor R51 and the charging capacitor C51
Between, and the overcurrent protection element 1 consisting of MOS FET
The drive terminal (gate) of 6 is connected by an electric path.

The waveform of the voltage applied to the switching element 15 and the flowing current are as shown in FIG. That is, when the load 35 of the secondary DC power supply circuit 30 is light [same (A)], the oscillation frequency f1 (cycle T1) is high (short), but when the load 35 is heavy [same (B)], oscillation occurs. The frequency f2 (cycle T2) becomes low (long). That is,
The oscillation frequency f2 (cycle T2) of the control voltage Vc becomes low (long).

Thus, assuming that the overcurrent detection value required to protect the switching element 15 is the value shown by the dotted line in FIGS. 2A and 2B, the oscillation frequency f of the control voltage Vc is shown in FIG. The overcurrent detection value can be indirectly detected by detecting that the oscillation frequency (f2 + α) corresponds to a period (T2 + α) longer than the period T2 shown in (B).

Here, the fixed time (T) of the charging resistor R51 and the charging capacitor C51 is selected and set to be equal to the period (T2 + α).

In the embodiment having such a configuration, when the load 35 of the secondary DC power supply circuit 30 is light, the voltage waveform and the current waveform of the switching element 15 have a high oscillation frequency f1 as shown in FIG. T1 is short. Therefore, part of the oscillation-generated control voltage Vc flows through the charging resistor R51 and the charging capacitor C51, but its cycle (T2) is shorter than the set cycle (T2 + α), so the overcurrent protection element 16 is turned on. The set voltage Va for driving is not established. That is, the overcurrent protection element 16 is OF
Since it remains F, the switching element 15 is turned ON-O.
Normal operation can be performed by FF control.

However, since the load 35 becomes heavy,
As shown in (B), when the oscillation frequency f2 is low, the cycle T2 is long, and when the oscillation frequency f2 is higher and the cycle is longer (T2 + α), the set voltage Va set in the charging capacitor C51 is established. The overcurrent protection element 16 is turned on. Therefore, the switching element 1
Since 5 can be turned off, the switching element 15 can be protected from overcurrent.

The charge accumulated in the charging capacitor C51 is discharged by the discharge resistor R when the control voltage Vc disappears.
It is discharged through 52.

Therefore, according to this embodiment, the overcurrent detection circuit 50 is connected in series between the positive side of the auxiliary winding L12 of the transformer 20 and the negative side of the rectifier circuit 14 and the charging resistor R51 and the charging. Capacitor C51 and a discharging resistor R52 connected in parallel with the charging capacitor C51 and in series with the charging resistor R51, and between the charging resistor R51 and the charging capacitor C51 and the overcurrent protection element 16 Drive terminal (gate) of the control voltage Vc is connected via an electric path, and the overcurrent is indirectly detected from the oscillation frequency of the control voltage Vc. Compared to the conventional example (Fig. 7), a large capacity and large resistance (R50) can be wiped out, so the device is lightweight and compact while maintaining its overcurrent protection function. It is possible to achieve a reduction.

(Second Embodiment) This second embodiment is shown in FIGS. 3 and 4. In FIG. 3, the transformer-coupled secondary DC power supply generator is of a fixed frequency type in which the same basic control circuit 40 as that of the conventional example (FIG. 8) is formed from a PWM IC, and an overcurrent detection circuit 50 is provided. (R51,
C51, R52) have the same structure as in the first embodiment.

That is, in this fixed frequency type, the load 3
When 5 is light, the waveforms of the current and its voltage flowing through the switching element 15 are as shown in FIG. 4 (A), and the oscillation frequency f is constant and the energization time T1 is short. On the other hand, the load 35
When the voltage is heavy, the voltage / current waveform has the same oscillating frequency f as shown in FIG. That is,
The oscillation time of the drive voltage Vd of the control circuit 40 generated by oscillation from the auxiliary winding L12 is short (T1) when the current flowing through the switching element 15 is small, and long (T1) when it is large.
2)

Therefore, if the time constants of the charging resistor R51 and the charging capacitor C51 are selectively set so as to be a time (T2 + α) longer than the energization time T2 shown in FIG. The overcurrent detection value indicated by the dotted line can be detected as the energization time.

The time constant (R
51 × C51) is the time constant (R51 in the case of the first embodiment.
The same code is used as that of (XC51), but its absolute value is different.

Even in the case of the second embodiment, however, the first
It is possible to obtain the same effect as that of the embodiment.

(Third Embodiment) The third embodiment has the same basic configuration as that of the first embodiment (FIG. 1) and supplies a constant current to the overcurrent detection circuit 50. Is provided so that the overcurrent protection operation point can be kept constant even if the control voltage Vc changes.

That is, in the first embodiment (FIG. 1),
When the AC power supply 11 is AC100V and the predetermined control voltage Vc is generated, the charging voltage of the capacitor C51 is as shown in FIG.
Since the curve rises with a solid line in (A), the set voltage Va
The time until it becomes is "T" shown in FIG.

When the AC power supply 11 drops in voltage from AC100V to AC85V, for example, the control voltage becomes "Vc2" which is lower than the predetermined control voltage Vc due to the characteristics of the transformer 20. This control voltage Vc2 is the same (A)
It rises in the curve shown by the dotted line. Therefore, the time required to reach the same set voltage Va is "T2", which is longer than the predetermined time T. On the other hand, for example, AC13
When the voltage rises to 8V, the control voltage Vc1 changes to the control voltage Vc.
Therefore, the voltage reaches the set voltage Va in a time T1 shorter than the predetermined time T in order to rise in the curve indicated by the one-dot chain line.

That is, the input voltage (AC power supply → control voltage)
If f changes, the overcurrent protection operation point changes, and appropriate overcurrent protection cannot be performed. This means that the current flowing through the charging circuit (R51, C51) corresponds to the control voltages Vc1, Vc, Vc2 shown in FIG.
This is because it changes to Ic1, Ic, and Ic2 shown in (B).

Thus, in the third embodiment, since the control voltage Vc may be detected by the time management, the constant current circuit 60 supplies the constant current to the charging circuit (R51, C51) regardless of the fluctuation of the control voltage Vc. (Ic) is supposed to flow.

Therefore, according to the third embodiment, the first
In addition to the same effects as those of the embodiment,
Further, even if the AC power supply 11 has a voltage fluctuation, and even if the AC power supply 11 is switched from AC100V to AC200V for use, proper current protection can be surely and stably performed, and the applicability can be remarkably expanded.

In the third embodiment, the constant current circuit 60 is provided in the first embodiment (FIG. 1), but the constant current circuit 60 is provided in the second embodiment (FIG. 3). However, the same effect can be obtained.

[0039]

According to the invention of claim 1, the overcurrent detection circuit is connected in series between the positive side of the auxiliary winding of the transformer and the negative side of the rectifying circuit, and a charging resistor and a charging capacitor. The charging capacitor is formed in parallel with the discharging resistor connected in series with the charging resistor, and the driving resistor and the driving terminal of the overcurrent protection element are connected between the charging resistor and the charging capacitor. Since the overcurrent is detected indirectly from the oscillation frequency in the variable type and from the energization time in the fixed frequency type, it has a larger capacity than the conventional example consisting of a resistor connected in series with a switching element. Since the large resistance can be wiped out with, it is possible to reduce the size and weight of the device while ensuring the overcurrent protection function.

According to the invention of claim 2, claim 1
In addition to the above effect, a constant current is made to flow from the constant current circuit to the charging resistor and the charging capacitor, so even if the AC power supply voltage changes, the AC power supply voltage can be switched between high and low. However, since the reliable overcurrent protection can be guaranteed, the applicability can be significantly expanded.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is also a timing chart for explaining the operation.

FIG. 3 is a circuit diagram showing a second embodiment.

FIG. 4 is also a timing chart for explaining the operation.

FIG. 5 is a circuit diagram showing the third embodiment.

FIG. 6 is also a diagram for explaining the operation in comparison with the examples of the room for improvement of the first and second embodiments.

FIG. 7 is a circuit diagram showing a conventional frequency variation type example.

FIG. 8 is a circuit diagram showing a conventional fixed frequency type example.

[Explanation of symbols]

 10 Primary DC power supply circuit 11 AC power supply 12 Switch 13 Noise filter 14 Rectifier circuit 15 Switching element 16 Overcurrent protection element 20 Transformer 30 Secondary DC power supply circuit 35 Load 40 Control circuit 45 Stabilization circuit 46 Feedback signal generation circuit 50 Overcurrent Current detection circuit 60 Constant current circuit C10 Smoothing capacitor C51 Charging capacitor L12 Auxiliary winding R51 Charging resistance R52 Discharging resistance Va Set voltage Vc Control voltage Vd Driving voltage

Claims (2)

[Claims] 1. A primary DC power supply circuit including a rectifying circuit, a smoothing capacitor, a switching element, and a control circuit, and a secondary DC power supply circuit including a stabilizing circuit are connected and coupled via a transformer, and control is performed from the stabilizing circuit. It is formed so as to generate a secondary DC power source by ON / OFF controlling the switching element while applying a feedback signal to the circuit, and through an overcurrent protection element when an overcurrent is detected by the overcurrent detection circuit. A transformer-coupled secondary DC power supply generator formed to turn off the switching element to protect against overcurrent, wherein the overcurrent detection circuit includes a positive side of an auxiliary winding of the transformer and a negative side of the rectifier circuit. A charging resistor and a charging capacitor connected in series between the charging resistor and a charging resistor, and a discharging resistor connected in parallel with the charging capacitor and in series with the charging resistor. And trans-coupled secondary DC power generating apparatus being characterized in that connecting the drive terminal of the overcurrent protection element and between the charging capacitor and the charging resistor. 2. A constant current circuit for inputting a voltage generated from the auxiliary winding of the transformer and for making a current flowing through the charging resistor and the charging capacitor constant, is provided. Transformer-coupled secondary DC power generator.