JPS63178762A - Switching power supply device - Google Patents

Abstract

PURPOSE:To prevent an influential accident from happening, by interrupting the outflow of secondary current for output at a switching transistor, when a load short-circuiting accident happens. CONSTITUTION:A switching power supply device is composed of a DC power source 1, an input capacitor 2, a switching transformer 3, a switching transistor 4, a control circuit 5 generating the output of drive signal 5a, a rectifying transis tor 7 for a secondary winding 36 for output, a smoothing circuit 23, an arithme tic circuit 14, and the like, and specified DC voltage E0 is fed to a load 13. In this case, in place of smoothing coils, a current transformer 16 is set, and an excess current monitoring circuit 17 including the transformer 16 is set. At the transformer 16, a primary winding 16a having a winding N1 is set to be worked in the same manner as the smoothing coils are worked, and to both the ends of a secondary winding 16b, a resistor R3 is connected. As a result, when a secondary current value exceeds a specified value to get excessive, then the flowing passage of secondary current at the rectifier circuit 23 is inter rupted, and an influence accident is prevented from happening.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a switching power supply device that outputs DC voltage;
In particular, even if a load short-circuit accident occurs, a ripple accident may occur in the circuits that make up the switching power supply.
Concerning power supply equipment.

[Conventional technology]

With the development of microelectronics, the number of various digital control circuits using microcomputers is increasing, and the switching regulator power supply that drives these microcomputer circuits is effective as a small, highly efficient power supply circuit, and the frequency of use is decreasing. It is on the rise.

Under these circumstances, it is important to improve the reliability of switching regulator power supplies. For example, it is desired to protect power supply circuits from overcurrents caused by short-circuit failures in load circuits connected to switching regulator power supplies.

Figure 2 is a block diagram of a conventional switching power supply.

In Fig. 2, l is a DC power supply input to this power supply device, 2 is an input capacitor for smoothing the output voltage of the power supply 1, 3 is a switching transformer, and the primary winding 3a of the transformer 3 and A series circuit consisting of a switching transistor 4 and a resistor Ro is connected to both ends of the capacitor 2. 5 is the control signal 6 and the voltage V across the resistor Ro.
is input, and when the voltage V is less than the predetermined value Vs, the drive signal 5a corresponding to the signal 6 is output.
The drive signal 5 which has a predetermined constant mode when the value exceeds s
The drive signal 5a is a signal that adjusts the duty ratio of the switching operation of the transistor 4. Signal 5a indicates that when voltage V is less than Vs,
As will be described later, the value of the signal 6 is set to a predetermined value via the duty ratio of the transistor 4.

Further, the signal 5a has resistance when the voltage V becomes equal to or higher than Vs.

7 is a transistor that rectifies the current flowing through the output secondary winding 3b of the transformer 3, and the on/off operation of the transistor 7 is driven by the output voltage of the transistor driving secondary winding 3c of the transformer 3. It is supposed to be done. 8 is a reverse current prevention diode, 9 is a smoothing coil through which the output current of transistor 7 flows, IOt! This is a smoothing capacitor that constitutes a smoothing circuit 11 together with the coil 9.

The smoothing circuit 11 is provided to smooth the output voltage of the series circuit consisting of the secondary winding 3b and the transistor 7 so that the DC voltage Eo is outputted to both ends of the capacitor IO. From now on, electric current may be referred to as secondary current. 1
2 is the output terminal for outputting EO, I3 is the terminal 12
is the load connected to the The graphical voltage E o is resistor R,
, R2 to form a divided voltage Ea, and the voltage Ea is designed to be input to the arithmetic circuit 14. Then, the voltage Ea is input to the arithmetic circuit 14, and this voltage Ea
is compared with a built-in reference voltage Ek and a control signal 6 corresponding to Ea-Ek is output.

As described above, when the voltage V is less than Vs, the control circuit 5 outputs the drive signal 5a so that the value of the signal 6 becomes a predetermined value.

It is to be controlled by the control circuit 5vc so that the value Es becomes the predetermined value Es.

Since the device shown in FIG. 2 is configured as described above, when the impedance fluctuation of the load 13 and the voltage fluctuation of the DC power source 1 are within predetermined ranges, the output DC voltage Ho always becomes the predetermined value BS. This means that a situation occurs in which the power P sent from the primary side to the secondary side of the transformer 3 exceeds the predetermined value PS.

[Problem that the invention seeks to solve]

In FIG. 2, the power supply operates as described above, but if an accident occurs in which the load 13 is short-circuited, the voltage E
. becomes almost zero, so the arithmetic circuit 14 outputs a signal 6 corresponding to the voltage Eo, and the control circuit 5 outputs a signal 6 corresponding to the voltage Eo.
It operates so that the value of voltage Eo recovers to Es by outputting a drive signal 5a that increases the duty ratio of the switching operation. Therefore, the voltage V across the resistor R0 increases, but in this case, V exceeds the predetermined value Vs, so the vehicle power P sent to the secondary side of the transformer 3 is reduced to the predetermined power value Ps by the power suppression circuit 15. limited to.

Therefore, a predetermined non-zero voltage appears across the secondary winding 3b. However, at this time, the transistor 7 and coil 9, which have small current impedance, are connected to the secondary winding 3b+c&ji.
Therefore, an excessive secondary current exceeding their rated values flows through the transistor 7 and the coil 9. In other words, in the case of FIG. 2, when the load 13 is short-circuited, the power P t sent from the primary side to the secondary side of the transformer 3
Although it is limited by the power suppression circuit 15, an excessive current flows through the transistor 7 and the coil 9. If this state continues, a short circuit failure will occur in the transistor 7 and the coil 9, and as a result, an even larger current will flow. This causes a dielectric breakdown failure in the transformer 3. If such a failure occurs in the transformer 3, the impedance of the primary winding 3a will drastically decrease, and when the transistor 724 turns on, an excessive current will flow through the primary circuit of the transformer 3, resulting in the destruction of the transistor 4. Accidents that happen occur.

In other words, in the switching power supply shown in Fig. 2, when a load short-circuit accident occurs, the impedance read from the output secondary winding 3b of the switching transformer 3 becomes extremely small, so that the secondary current There is a problem in that the voltage becomes too large, and as a result, the transistor 7, the coil 9, the transformer 3, and the transistor 4 may sequentially fail, resulting in many spillover accidents.

The purpose of the present invention is to solve the problem when a load short circuit accident occurs.

The purpose of this invention is to prevent the above-mentioned spillover accident from occurring by blocking the outflow of the output secondary direct current in the switching transformer.

[Means for solving problems]

In order to solve the above problems, the present invention provides a switching transformer and a secondary current flowing through the output secondary winding of the switching transformer. A rectifier circuit that cuts off the secondary DC when a rectification and cutoff signal is input, and a smoothing coil through which the secondary current outputted from the rectification circuit flows, and a smoothing capacitor, and a smoothing coil that outputs a smoothed DC voltage. A smoothing circuit that outputs the DC voltage, and an overcurrent monitoring circuit that detects the secondary current and outputs the cutoff signal when the value of the secondary current exceeds a predetermined value, and outputs the DC voltage as an output voltage. A switching power supply shall be configured.

[Effect]

When the value of the secondary current exceeds a predetermined value and becomes excessive, the flow path of the secondary current in the rectifier circuit is cut off by the overcurrent monitoring circuit and the rectifier circuit, so when a load short circuit accident occurs, the secondary current There is no need to worry about situations where the amount of damage becomes excessive and spillover accidents occur.

〔Example〕

FIG. 1 is a configuration diagram of an embodiment of the present invention. The difference from FIG. 2 is that a current transformer 16 is provided in place of the smoothing coil 9 in FIG. An overcurrent monitoring circuit 17 including a transformer 16 is provided. In the DC transformer 16, a primary winding 16a having a number of turns Nm is arranged to function similarly to the smoothing coil 9, and a resistor R8 is connected to both ends of a secondary winding 16b having a number of turns N2. Therefore, in this case, the smoothing circuit 11 of FIG.
A smoothing circuit 23 corresponding to the above is formed.

18 is a rectifying and smoothing circuit consisting of a diode 19 and a capacitor 20, which converts the alternating current voltage VrQ generated across the resistor R8 into a direct current, 2N'! This is a transistor whose base is driven by the DC voltage output from the circuit 18.

The collector of this transistor 21 is connected to the base Ic of the transistor 7, and the emitter of the transistor 21 is connected to the negative electrode of the capacitor 20 via the resistor R4, and to the capacitor l.
Connected to the negative electrode of O. Overcurrent monitoring circuit 18 &X
b It is composed of the above-mentioned transformer 16, resistor R3°R4, rectifying and smoothing circuit 18, transistor 21, and base resistor R3 of the transistor.

Since FIG. 1 is constructed as described above, when the secondary DC current flows through the transistor 7, the voltage at both ends of the resistor R3 (N1
/Nt)・Engine・A voltage Vr proportional to R8 appears. In FIG. 1, when the current is below a predetermined upper limit current value Ih that will not cause a short-circuit accident in the transistor 16 or the transformer 16, the transistor 21 is turned on due to the generation of the voltage Vr. It is configured so that it does not.

However, in FIG. 1, the voltage V exceeds a predetermined value and the transistor 21 is turned on when the current exceeds Ih. 7 is turned off and the secondary current is cut off. Therefore, in FIG. 1, when the load 13 is short-circuited, %Eo becomes almost equal to zero and the switching transistor 4 returns E to the original value. However, the power suppression circuit 15 operates and the power sent to the secondary side of the °C transformer 3 is not suppressed to the predetermined value Ps.Therefore, the secondary winding 3bvc of the transformer
A finite predetermined voltage appears, and as a result, an excessive secondary current ■ tries to flow through the secondary winding 3b, the transistor 7, and the primary winding 16aI/c of the transformer 16, but the overcurrent monitoring circuit 17 operates. Therefore, the current ■ is cut off. Therefore, the voltage Vr becomes small -10- so that the transistor 21 is turned off and the transistor 7 is turned on. When transistor 7 is turned on, the current flow increases, so transistor 7 is turned off again. Therefore, an intermittent current will eventually flow through the transistor 7 and the winding IF1a. It is clear that the maximum value of this electric current is Ih. Therefore, in Fig. 1, when a short circuit accident occurs in the load 13,
Transistor 7, winding 16a% transformer 3. A spillover accident such as burnout of the transistor 4 does not occur.

In FIG. 1, each part operates as described above, so the overcurrent monitoring circuit 17 detects the secondary current ■ and sends a voltage to the cutoff signal 22 to turn off the transistor 7 when the value of the secondary current exceeds a predetermined value. The transistor 7 is a rectifier circuit that rectifies the secondary current flowing through the secondary winding 3b and cuts off the secondary current I when the cutoff signal 22 is input. You can say that.

〔Effect of the invention〕

As described above, the present invention includes a switching transformer, a rectifier circuit that rectifies the secondary current flowing through the output secondary winding of the switching transformer, and cuts off the secondary current when a cutoff signal is input; A smoothing circuit includes a smoothing capacitor and a smoothing coil through which a secondary current outputted from a rectifier circuit flows, and outputs a smoothed DC voltage; and a smoothing circuit that outputs a smoothed DC voltage, and detects a secondary current and adjusts the value of the secondary current to a predetermined value. The switching power supply device is equipped with an overcurrent monitoring circuit that outputs a cutoff signal and a cutoff signal, and is configured to output the DC voltage as an output voltage. Therefore, in the present invention [&1, when the value of the secondary current exceeds a predetermined value and becomes excessive, the flow path of the secondary current in the rectifier circuit is cut off by the overcurrent monitoring circuit and the rectifier circuit, thereby preventing a load short circuit accident. This is effective because it prevents the secondary DC from becoming excessive and causing spillover accidents when such occurrence occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional switching power supply device. 3...Switching transformer, 3b...
...Secondary winding, 7...Transistor, 9...
...Smoothing coil, 1.0...Smoothing capacitor% 11.23...Smoothing circuit, 16a...
...-Next winding, 17... Overcurrent monitoring circuit, 2
2... Cutoff signal, ■... Secondary current, E
o...DC voltage.

Claims (1)

[Claims] a switching transformer, a rectifier circuit that rectifies the secondary current flowing through the output secondary winding of the switching transformer and cuts off the secondary current when a cutoff signal is input; a smoothing capacitor; a smoothing circuit for outputting a smoothed DC voltage, the smoothing coil having a smoothing coil through which the secondary current flows; A switching power supply device comprising: an overcurrent monitoring circuit that outputs the DC voltage as an output voltage.