JPH06225534A - Power-supply circuit - Google Patents

Abstract

PURPOSE:To protect a rectifier diode from an excessive induced voltage, at a transformer, which is generated when a power supply is cut off and a load is released. CONSTITUTION:A transformer T transforms an AC input AC according to the turn ratio of a primary winding L1 to a secondary winding L2 and outputs it to the secondary side. A secondary output is full-wave-rectified by diodes D1, D2, and it is supplied to a laod RL. A current loop is composed of a tertiary winding L3 and of Zener diodes D3, D4. Individual cathodes for the Zener diodes D3, D4 are connected to both ends of the tertiary winding L3, and both anode sides are connected via a resistance R1. Zener voltages for the Zener diodes D3, D4 are at an induced voltage or higher which is generated in the tertiary winding L3 during the ordinary operation of the transformer T, and they are set to a level which is turned on with reference to an induced voltage, for spike, which is generated when the AC input AC is cut off or the load RL is released.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a charging adapter for a storage battery, transforms an AC input with a transformer, rectifies the obtained secondary output, and supplies it to various loads such as a battery and a motor. Regarding the power circuit.

[0002]

2. Description of the Related Art Conventionally, there is known a charging adapter which is detachably connected between an AC input and a load such as a storage battery or a drive motor and supplies a DC output to the load when necessary.

The power supply circuit shown in FIGS. 4 (a) and 4 (b) transforms the AC voltage input between the input terminals 1 and 1'with a transformer T, and further rectifies the diodes D1 and D2 (see FIG. 4).
In (b), it is rectified by the diode D) and the obtained DC voltage is supplied to the load RL via the output terminals 2 and 2 '. 4A is a full-wave rectification type, and FIG. 4B is a half-wave rectification type.

The operation will be described with reference to FIG. 4A. The diodes D1 and D2 are alternately turned on and off by an alternating voltage generated on the secondary side of the transformer T. That is, when the anode side of the diode D1 becomes positive, the diode D1
1 is turned on, the diode D2 is turned off, and the current flows from the secondary winding of the transformer T through the diode D1 to the output terminal 2,
The current flows from the load RL, the output terminal 2 ', the center tap loop of the transformer T, and in the next half-wave period, the current flows from the secondary winding of the transformer T through the diode D2 to the output terminal 2 and the load R.
L, the output terminal 2 ', and the center tap loop of the transformer T flow. Now, when the AC input voltage is cut off while the diode D1 is on, the secondary winding of the transformer T induces a voltage in a direction to maintain the current, so that the diode D2 in the off state is reversely driven. A spike-shaped voltage is applied, and a leakage current I _R (see FIG. 5) flows. As the leakage magnetic flux of the transformer T increases, the counter-induced voltage of the secondary winding increases,
The larger the load RL, the larger the value. That is, at the moment when the supply of the AC input voltage is interrupted, or at the same time when the load RL is removed, the reverse voltage is applied to the diode by the counter electromotive force generated in the secondary winding of the transformer T, and this reverse voltage is applied. There is a problem that the diode is deteriorated or destroyed when the voltage is excessive.

In the case of the half-wave rectification type shown in FIG. 4 (b), even if the AC input voltage is cut off while the diode D is on, no reverse induced voltage is applied to the diode D, but the diode D is off. When the AC input voltage is turned off at
A back electromotive force is applied, and the same problem as described above occurs.

Conventionally, in order to protect the diode from such a phenomenon, measures such as adoption of a high breakdown voltage diode and reduction of magnetic flux leakage even if the structure of the transformer is improved have been taken.

[0007]

However, the conventional countermeasures have a problem that the high withstand voltage diode and the transformer having the improved structure lead to an increase in the size of parts and an increase in the cost of parts.

Further, since the induced voltage in the secondary winding of the transformer when the power is cut off or when the load is released is proportional to the magnitude of the load current immediately before that and the leakage flux of the transformer, it is difficult to quantitatively predict. Is. Therefore, it is difficult to predict how large the breakdown voltage of the diode will be. On the other hand, a diode having a higher breakdown voltage has a larger forward voltage, which causes a problem of power loss during normal operation and heat generation associated therewith.

The present invention has been made in view of the above,
An object of the present invention is to provide a power supply circuit that protects a rectifier diode from an excessive induced voltage of a transformer that occurs when the power is cut off and when the load is opened.

[0010]

According to the present invention, a transformer for transforming an AC input applied to a primary winding and outputting the transformed AC input to a secondary winding and a secondary winding of the transformer are connected. And a diode for rectifying an AC output from the secondary winding, and in a power supply circuit for supplying the rectified output to a load, a voltage level induced in the secondary winding has a predetermined level equal to or higher than a transformation level during normal operation. A current loop for releasing the energy of the transformer when the voltage exceeds the current loop is provided (Claim 1).

Further, the current loop is provided with a tertiary winding in the transformer, and a series circuit composed of first and second Zener diodes each having a cathode connected to each terminal of the tertiary winding is connected. It may also be configured (claim 2).

Further, the current loop may be constructed by connecting a series circuit composed of first and second Zener diodes having anodes connected to each other in parallel to the diode (claim 3).

The current loop may be constructed by connecting a series circuit composed of first and second Zener diodes whose anodes are connected to each other in parallel to the secondary winding (claim 4).

[0014]

According to the invention described in claim 1, during normal operation, the AC input applied to the primary winding is transformed by the transformer, and the AC output of the secondary winding is rectified by the diode and supplied to the load. To be done. Now, when the AC input is cut off or the load RL is opened, the voltage level induced in the secondary winding tends to rise in a spike shape over a predetermined level that is equal to or higher than the transformation level during normal operation. However, when this voltage exceeds the predetermined level, the current loop operates to release the residual energy of the transformer. For this reason,
The reverse voltage above a predetermined level is not applied to the diode.

According to the second aspect of the invention, when the spiked voltage is about to exceed a predetermined level, the induced voltage in the tertiary winding of the transformer at this time causes the first and second spikes.
Zener diode turns on, and the third winding, the first and second
The residual energy of the transformer is released by the current loop composed of the Zener diode of.

According to the third aspect of the present invention, when the spiked voltage is about to exceed a predetermined level, the first and second Zener diodes are turned on and the secondary winding, the first and the second windings are turned on. The residual energy of the transformer is released by the current loop composed of the Zener diode. When applied to the full-wave rectification type, when the first and second zener diodes are turned on, one of the secondary winding and the rectifying diode which is in the forward direction, the first and second diodes. The residual energy of the transformer is released by the current loop composed of the Zener diode of.

According to the fourth aspect of the invention, when the spiked voltage is about to exceed a predetermined level, the first and second Zener diodes are turned on and the secondary winding, the first and the second windings are turned on. The residual energy of the transformer is released by the current loop composed of the Zener diode.

[0018]

1 is a circuit diagram showing a first embodiment of a power supply circuit according to the present invention. Reference numerals 1, 1'are input terminals to which an AC input AC such as a commercial power source is connected, and the primary winding L1 of the transformer T is connected to the input terminals 1, 1 '. This transformer T uses an AC input AC as a primary winding L1 and a secondary winding L2.
It is transformed according to the winding number ratio and output to the secondary side. A circuit for rectifying the secondary output and a load RL to which the rectified output is supplied are connected to the secondary winding L2 of the transformer T. Circuits for rectification are diodes D1 and D2
The anodes are connected to both ends of the secondary winding L2, while the cathodes are connected to each other, and further connected to the output terminal 2 of the power supply circuit. The output terminal 2'is connected to the center tap of the secondary winding L2. The load RL is detachably connected between the output terminals 2 and 2 '.

The transformer T also has a tertiary winding L3. D3 and D4 are Zener diodes, and each cathode is connected to both ends of the tertiary winding L3.
Both anodes are connected via a resistor R1. The Zener voltages of the Zener diodes D3 and D4 do not turn on due to the induced voltage generated in the tertiary winding L3 during normal operation, and considering the breakdown voltage of the rectifying diodes D1 and D2, the tertiary winding It is decided together with the number of turns of L3.
The resistor R1 may have a small resistance value and may not be used depending on each of the above elements.

The circuit operation on the side of the tertiary winding L3 will be described below. AC input is cut off or load R
When L is opened, the induced voltage in the secondary winding L2 of the transformer T becomes large in a spike shape, and along with this, the tertiary winding L2 is increased.
The induced voltage of 3 also becomes large. If the induced voltage at this time exceeds the Zener voltage of the Zener diodes D3 and D4,
A current starts to flow in the tertiary winding L3. For example, diode D
If the AC input AC is cut off or the load RL is opened when 1 is on, current flows from the tertiary winding L3 through the loop of the Zener diode D3, the resistor R1, and the Zener diode D4, and the residual energy of the transformer T is increased. Is consumed in the low impedance loop of the tertiary winding L3 including the resistor R1. Therefore, no further reverse voltage is applied to the diode D2 connected to the secondary winding L2, so that no current flows.

In this embodiment, by reducing the number of turns of the tertiary winding L3 of the transformer T, the Zener voltage of the Zener diodes D3 and D4 can be reduced, and the size of the element can be reduced accordingly. It can also be built into a transformer.

FIG. 2 is a circuit diagram showing a second embodiment of the power supply circuit according to the present invention. In this embodiment, the circuit and load part for rectification are the same as in the first embodiment.

In FIG. 2, Zener diode D5,
D6 forms a series circuit in which the anodes are connected to each other, and is connected in parallel to the diode D1. The Zener diodes D7 and D8 form a series circuit in which the anodes are connected to each other and are connected in parallel to the diode D2. Zener voltage Vz of the Zener diodes D6 and D8
6, Vz8 are set to values slightly larger than the induced voltage generated in the secondary winding L2 of the transformer T during normal operation. The Zener diodes D5 and D7 are for preventing current from flowing in the forward direction of the Zener diodes D6 and D8 due to the induced voltage generated in the secondary winding L2 of the transformer T during normal operation.

Here, the Zener diode D6
The operation of D8 will be described. Zener diode D5
Since the Zener voltages D8 to D8 are both higher than the induced voltage generated in the secondary winding of the transformer T during normal operation, the output current due to the induced voltage is applied to the diodes D1 and D2 which are circuits for rectification. Each half wave alternately flows (full-wave rectification) and is supplied to the load RL.

On the other hand, when the AC input AC is cut off or the load RL is opened, the induced voltage in the secondary winding L2 of the transformer T rises in a spike shape and the Zener diode D6
Or D8 turns on. That is, for example, when the diode D1 is on, the AC input AC is cut off or the load RL is cut off.
When the induced voltage of the secondary winding L2 starts to rise like a spike and exceeds the Zener voltage Vz8 of the Zener diode D8, the Zener diode D8 is turned on and the diode D1 from the secondary winding L2 is turned on. , The Zener diode D8 and the Zener diode D7 flow a current, and the residual energy of the transformer T is consumed by the low impedance component of this loop. For this reason, the spike voltage does not rise any further, and therefore the reverse voltage of the Zener voltage Vz8 or higher is not applied to the diode D2. Similarly, when the induced voltage of the secondary winding L2 exceeds the Zener voltage Vz6 even when the diode D2 is on, a current is generated in the loop of the diode D2, the Zener diode D6, and the Zener diode D5 from the secondary winding L2. Since it flows, the Zener voltage Vz6 is applied to the diode D1.
The above reverse voltage is not applied.

In this second embodiment, the diodes D1 and D
Depending on which of 2 is on, the current emission loop is used properly, so the current sharing in each loop is halved,
Parts are degraded and reliability is improved.

FIG. 3 is a circuit diagram showing a third embodiment of the power supply circuit according to the present invention. In this embodiment, the circuit and load part for rectification are the same as those in the first embodiment, and in addition to this, Zener diodes D9 and D10 in which anodes are connected to both ends of the secondary winding L2 of the transformer T are provided. A serial circuit consisting of is connected and added. The Zener diodes D9 and D10 have their Zener voltage set to be slightly higher than the induced voltage generated in the secondary winding L2 of the transformer T during normal operation, and are not operated during normal operation.

Next, the Zener diodes D9 and D
The operation of 10 will be described. When the AC input AC is cut off or the load RL is opened, the induced voltage in the secondary winding L2 of the transformer T rises in a spike shape, and when it exceeds the Zener voltage, the Zener diode D9 or D10.
Turns on. That is, for example, when the diode D1 is on, the AC input AC is cut off or the load RL is opened, the induced voltage in the secondary winding L2 rises, and exceeds the Zener voltage of the Zener diode D9. D9 is turned on, current flows from the secondary winding L2 through the loop of the Zener diode D9 and Zener diode D10, and the residual energy of the transformer T is consumed by the low impedance component of this loop. For this reason, the spike voltage does not rise any further, so that a reverse voltage higher than the Zener voltage of the Zener diode D9 is not applied to the diode D2. Similarly, when the induced voltage of the secondary winding L2 exceeds the Zener voltage of the Zener diode D10 even when the diode D2 is turned on, a current is generated in the loop of the Zener diode D10 and the Zener diode D9 from the secondary winding L2. Since it flows, diode D
No reverse voltage higher than the Zener voltage of the Zener diode D10 is applied to the 1st line.

By carrying out the above-mentioned first to third embodiments, it becomes possible to use, as the rectifier diodes D1 and D2, elements having a small reverse voltage withstand voltage, for example, Schottky type diodes. Is getting smaller,
Since heat generation can be suppressed, it is suitable for downsizing of equipment.

Although the first to third embodiments have been described with reference to the full-wave rectification type power supply circuit, for example, FIG.
It is also applicable to the half-wave rectification type power supply circuit shown in (b).

[0031]

As described above, according to the present invention,
Since a current loop set to operate in consideration of the reverse voltage of the rectifier diode is set, the rectifier diode is applied regardless of the timing of AC input cutoff or load opening, and the lightness or weight of the load. The reverse voltage can be limited to a certain level, which deteriorates the rectifier diode,
Reliable protection from destruction. Further, since an element having a small reverse voltage withstand voltage can be used as the rectifier diode, the size can be reduced, and the forward voltage loss during the normal operation can be reduced to reduce heat generation. Further, since the influence of the induced voltage due to the variation of the leakage magnetic flux of the transformer is eliminated, the burden of consideration such as the tight winding of the winding when manufacturing the transformer can be reduced, and the productivity in mass production can be improved.

According to the second aspect of the invention, by reducing the number of turns of the tertiary winding of the transformer, the Zener voltage of the first and second Zener diodes can be low, and the size of the element can be reduced accordingly. It is possible to make it possible, and it is possible to manufacture it in a transformer.

Further, when the invention according to claim 3 is applied to the full-wave rectification type power supply circuit, the current loop can be selectively used depending on the timing exceeding the level in the normal operation. Is halved, parts are degraded, and reliability is improved. Further, according to the invention described in claim 4, the current loop can be easily configured, so that the current loop can be built in the transformer.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply circuit according to the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the power supply circuit according to the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the power supply circuit according to the present invention.

FIG. 4 shows a conventional power supply circuit, FIG. 4 (a) is a full-wave rectification type, and FIG. 4 (b) is a half-wave rectification type.

FIG. 5 (a) is a diagram showing a case where the diode D1 is turned on when the AC input voltage is cut off when the diode D1 is turned on.
FIG. 6 is a diagram for explaining an operation in which a leak current IR (see FIG. 5) in the opposite direction flows to 2;

[Explanation of symbols]

 T transformer L3 tertiary winding (current loop) D1, D2 rectifying diode D3 to D10 Zener diode (current loop) AC AC input RL load R1 resistance 1, 1'input terminal 2, 2'output terminal

Claims (4)

[Claims] 1. A transformer for transforming an AC input applied to a primary winding and outputting it to a secondary winding, and an AC output from the secondary winding connected to the secondary winding of the transformer. In a power supply circuit that includes a rectifying diode and supplies the rectified output to a load, when the voltage level induced in the secondary winding exceeds a predetermined level that is equal to or higher than the transformation level during normal operation, the energy of the transformer is reduced. A power supply circuit having a current loop for discharging. 2. The current loop is provided with a tertiary winding in the transformer, and a series circuit including first and second Zener diodes each having a cathode connected to each terminal of the tertiary winding is connected. The power supply circuit according to claim 1, wherein the power supply circuit is a power supply circuit. 3. The current loop is characterized in that a series circuit including first and second Zener diodes in which anodes are connected to each other is connected in parallel to the diode is connected. Power circuit. 4. The current loop is formed by connecting a series circuit including first and second Zener diodes whose anodes are connected to each other in parallel to the secondary winding. Power circuit.