JPH0515151A - Dc power supply - Google Patents

Abstract

PURPOSE:To provide a DC power supply which can produce a stabilized output over a wide range of input power supply including a vehicle mounted power supply and domestic power supply. CONSTITUTION:In a DC power supply comprising a transformer 3 and a switching element for producing a predetermined output voltage from an input power supply 1, the switching element is constituted of a FET Q1 and the DC power supply further comprises a detection resistor R3 connected in series between the source of the FET Q1 and the tertiary winding N3 of the transformer 3, and a Zener diode ZD1 connected between the gate of the FET Q1 and the joint of the tertiary winding N3 and the detection resistor R3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device used for a charger, etc.
The present invention relates to a DC power supply device suitable for use as a portable AC power supply for home use from 100 V to 240 V AC.

[0002]

2. Description of the Related Art Recently, portable telephones equipped with a rechargeable battery have become widespread, and such telephones require a large capacity DC power source. There are also those used in automobiles and the like, and there is a demand for something that can be charged from a household power source to an in-vehicle power source.

A conventional DC power supply device is shown in FIGS. 8 and 9.
Will be explained. FIG. 8 is a circuit diagram showing a first conventional example of a DC power supply device. The input power supply 11 is connected to the rectification bridge 12 via a terminal. Rectifier bridge 1
2 is a transformer 1 that rectifies the input voltage from the input power supply 11
3 to the primary winding N11. Transformer 1
3 is a primary winding N11, a secondary winding N12 and a tertiary winding N1
It consists of 3 and becomes 1 by turning on and off the transistor Q11.
The current flowing into the secondary winding N11 is switched, so that a voltage is induced in the secondary winding N12 and the tertiary winding N13.

A series circuit for oscillation consisting of the tertiary winding N13, a resistor R11 and a capacitor C11 is connected to the base of the transistor Q11, and the tertiary winding N13 is connected.
The base voltage is supplied to the transistor Q11 by the induced voltage to turn it on and off. The starting resistor R12 applies a voltage to the base of the transistor Q11 to start the transistor Q11.

A diode D11 is provided on the secondary winding N12.
Are connected in series, the power induced in the secondary winding N12 is rectified by the diode D11, and a DC power source is supplied from the output terminal.

This method has a drawback that the output capacity of the DC power supply cannot be increased because the oscillation frequency cannot be increased because a normal transistor is used as a switching element.

To increase the output capacity of the DC power supply, it is sufficient to make the transformer larger, but this leads to an increase in the size of the DC power supply device. Therefore, in order to increase the oscillation frequency, there is also a method of using a field effect transistor having a switching speed higher than that of the transistor.

FIG. 9 is a circuit diagram showing a second conventional example of a DC power supply device. The same contents as those of the first conventional example are designated by the same reference numerals and the description thereof will be omitted. The transistor is driven by current, whereas the field effect transistor is driven by voltage, and since a high voltage due to R12 is applied to the gate of the field effect transistor and exceeds the withstand voltage, simply replace with transistor Q11 in FIG. I can't. Therefore, as shown in FIG. 9, the switching control I
C is used.

In FIG. 9, the tertiary winding N of the transformer 13
13, diode D21, capacitor C21, resistor R2
Reference numeral 1 is a power supply circuit of the IC 1 for switching control. The capacitor C22 and the resistor R22 are an oscillation circuit of the IC1.

By applying the output of the IC1 for switching control to the gate of the field effect transistor Q21, the field effect transistor Q21 is turned on / off.

[0011]

However, if the above switching control IC is used in the DC power supply device, the circuit becomes complicated and large in size, which is not preferable especially in the demand for miniaturization.

When a transistor is used as in the first conventional example, an input voltage of about 60 V is required to supply the current required to drive the transistor. The input voltage-output voltage characteristic in the first conventional example is shown by the broken line in FIG. As can be seen from FIG. 2, the configuration of the first conventional example cannot support an on-vehicle power supply.

An object of the present invention is to solve the above problems, and to provide a DC power supply device capable of achieving a large capacity and miniaturization capable of accommodating a wide range of input power supplies.

[0014]

In order to achieve the above object, the present invention is to connect a series circuit of a primary winding of a transformer and a switching element to an input power source and drive the switching element on / off. The DC power is obtained by rectifying the electric power induced in the secondary winding of the transformer, and the tertiary winding of the transformer and the oscillation circuit are connected in series with the switching element, and the input power source is further connected. In a DC power supply device in which a starting resistor is connected in parallel with the primary winding of the transformer between the switching element and the switching element, a field effect transistor is used as the switching element, and the source of the field effect transistor and the 3 A detection resistor connected in series between the secondary winding, a gate of the field effect transistor, the tertiary winding, and the detection resistor. Is obtained by a first Zener diode is interposed between the connection points.

According to a second aspect of the present invention, in the DC power supply device according to the first aspect, the negative voltage generating means for generating a negative voltage according to the source current of the field effect transistor, and the collector and the emitter of the field effect transistor. The transistor includes a gate connected to the negative side of the negative voltage generating means, and a second Zener diode connected between the base of the transistor and the source of the field effect transistor.

[0016]

According to the DC power supply device having the above structure, the field effect transistor can be used because the gate voltage of the field effect transistor is controlled to the predetermined value or less regardless of the input voltage by the first Zener diode. As the source current of the field effect transistor increases, the source voltage generated across the detection resistor increases, and the field effect transistor turns off. Since the gate voltage of the field effect transistor is a predetermined value (zener voltage) or less, the source voltage quickly increases when the input voltage is high. Therefore, the field effect transistor is turned off faster, and the output voltage is suppressed. On the contrary, when the input voltage is low, the source voltage increases slowly, and the field effect transistor is turned off slowly, so that the output voltage increases. Therefore, a stable output can be obtained for a wide range of input power supplies.

According to the DC power supply device of claim 2,
The increase in the source voltage activates the second Zener diode, turning on the transistor. As a result, the gate voltage of the field effect transistor is reduced to the negative voltage generated by the negative voltage generating means, and the field effect transistor switches at high speed, so that a stable output can be obtained.

[0018]

1 is a circuit diagram showing a first embodiment of a DC power supply device according to the present invention. The input power supply 1 is connected to the rectification bridge 2 via a terminal. The input power supply 1 is shown as an AC power supply in the figure, but a power supply of AC100V to 240V or a vehicle-mounted power supply of DC12V can also be used. The rectifying bridge 2 rectifies the input voltage from the input power source 1 and outputs it to the primary winding N1 of the transformer 3. The transformer 3 includes a primary winding N1, a secondary winding N2, and a tertiary winding N3, and the current flowing into the primary winding N1 is switched by turning on and off the field effect transistor Q1. A voltage is adapted to be induced in the line N2 and the tertiary winding N3.

A diode D1 is connected in series to the secondary winding N2, the electric power induced in the secondary winding N2 is rectified by the diode D1, and a DC power source is supplied from an output terminal.

The gate of the field effect transistor Q1 is connected to an oscillation series circuit composed of the tertiary winding N3, a resistor R1 and a capacitor C1, and the induced voltage of the tertiary winding N3 causes the field effect transistor Q1. A gate voltage is supplied to the gate to repeatedly turn on and off in a predetermined cycle. Starting resistor R2 and Zener diode ZD
1 is to apply a voltage of a required level to the gate of the field effect transistor Q1 to activate the field effect transistor Q1. This Zener diode ZD1
Is interposed between a connection point between the tertiary winding N3 and a detection resistor R3 described later.

A detection resistor R3 is connected in series between the source of the field effect transistor Q1 and the tertiary winding N3.

Next, the operation of the circuit configured as described above will be described. When the input power supply 1 is connected, a voltage is applied to the gate of the field effect transistor Q1 through the starting resistor R2, and the field effect transistor Q1 starts to turn on. Therefore, a current flows through the primary winding N1 and the tertiary winding N1
3, a feedback voltage is induced, and the induced voltage is applied to the tertiary winding N3,
It rises with a time constant determined by the resistor R1 and the capacitor C1, increases the gate voltage Vg of the field effect transistor Q1, and increases the source current Is flowing from the source of the field effect transistor Q1.

On the other hand, by increasing the source current Is,
The source voltage Vs generated in the detection resistor R3 rises. Here, if the threshold voltage for turning on the field effect transistor Q1 is Vth and the Zener voltage of the Zener diode ZD1 is Vz, when Vz> Vg = Vs + Vth, the ON state continues, but this source voltage Vs
Rises and the gate voltage Vg becomes equal to or higher than the Zener voltage Vz, the field effect transistor Q1 is rapidly turned off. When the field effect transistor Q1 is turned off, the tertiary winding N3
A feedback voltage is induced in the field effect transistor, the induced voltage decreases with a time constant determined by the tertiary winding N3, the resistor R1 and the capacitor C1, the gate voltage Vg of the field effect transistor Q1 decreases, and the field effect transistor Q1 is turned off for a predetermined time. Let

Thereafter, when the gate voltage Vg of the field effect transistor Q1 rises again due to the starting resistor R2, the field effect transistor Q1 turns on. That is, the field-effect transistor Q1 repeats switching, electric power is induced in the secondary winding N2 by the switching, an output current flows, and a DC power supply is obtained.

Here, when the input voltage is high, the source current Is also immediately increases, so that the source voltage Vs increases in a short time. On the other hand, since the gate voltage Vg does not exceed the Zener voltage Vz, the field effect transistor Q1
The on time of will be shortened accordingly. Therefore, the output voltage can be stabilized against the level of the input voltage.

FIG. 2 shows the result of the above voltage stabilization in comparison with the conventional example. As shown in the figure, in the conventional example, the input voltage is 60 V and no output can be obtained.
In this embodiment, an output can be obtained up to an input voltage of around 12V.

Further, with the above configuration, even if the input power source is DC 12V for an automobile or the like, AC 100V-240 for household power source.
Even with V, for example, when a field effect transistor with Vth = 4V is used and a zener diode with zener voltage Vz = 8V is used, Vg ≦ 8V, which is sufficient for switching drive without exceeding the breakdown voltage of the gate of the field effect transistor. You can Therefore, it is not necessary to use an IC as in the conventional case, the size is small, and a stable DC power source can be realized at low cost.

FIG. 3 is a circuit diagram showing a second embodiment of the DC power supply device according to the present invention. It should be noted that those having the same functions as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted (the same applies to the following embodiments). As shown in FIG. 3, the Zener diode ZD in the first embodiment
A resistor R4 is connected in parallel with 1.

Next, the operation of the circuit configured as described above will be described. Since the voltage applied to the gate of the field effect transistor Q1 is divided by the starting resistor R2 and the resistor R4, the voltage applied to the gate of the field effect transistor Q1 decreases. Therefore, although the input voltage required to turn on the field effect transistor Q1 increases, a more stable output voltage can be obtained.

That is, this second embodiment is effective in the case of a household power source. FIG. 4 shows the result of voltage stabilization in this embodiment. As shown in the figure, a more stable power source can be obtained within the range of household power sources.

FIG. 5 is a circuit diagram showing a third embodiment of the DC power supply device according to the present invention. In the present embodiment, a capacitor C2 and a diode D2 as a negative voltage generating means for newly generating a negative voltage according to the source current of the field effect transistor Q1 are connected in parallel with the tertiary winding N3 and the positive electrode side of the capacitor C2. Is connected to the detection resistor R3. Further, the transistor Q2 is connected to the collector of the field effect transistor Q1.
To the gate of the capacitor C2 so that the emitter is on the negative electrode side of the capacitor C2. Further, a Zener diode ZD2 is connected between the base of the transistor Q2 and the source of the field effect transistor Q1.

Next, the operation of the circuit configured as described above will be described. The voltage across the resistor R3 is Vs, the voltage across the capacitor C2 is Vc, and the Zener diode ZD
2 Zener voltage is Vz2, the base of transistor Q2
The voltage between the emitters is Vbe.

Source current I of field effect transistor Q1
When s starts to flow, Vs + Vc ≦ Vz2 + Vbe, but when the source current Is increases to Vs + Vc> Vz2 + Vbe, the Zener diode ZD2 turns on, the base current of the transistor Q2 flows, and the transistor Q2 turns on. The gate voltage of the field effect transistor Q1 is lowered to the negative voltage of the capacitor C2.

That is, a reverse bias is applied to the gate of the field effect transistor Q1, the field effect transistor Q1 is turned off faster, and the DC power supply can be stabilized.

FIG. 6 is a circuit diagram showing a fourth embodiment of the DC power supply device according to the present invention. In the fourth embodiment, the series circuit of the resistor R5 and the transistor Q3 is connected in parallel with the capacitor C2 in the circuit of the third embodiment.

Next, the operation of the circuit configured as described above will be described. The voltage charged in the capacitor C2 is discharged by externally controlling and turning on the transistor Q3. This allows Zener diode ZD
2. The on / off of the transistor Q2 can be controlled. Therefore, the switching speed of the field effect transistor Q1 can be controlled.

That is, the switching speed is controlled depending on the level of the input voltage to obtain a more stable output.

FIG. 7 is a circuit diagram showing a fifth embodiment of the DC power supply device according to the present invention. In the fifth embodiment, in the circuit of the third embodiment, the transistor Q4 is connected between the negative electrode side of the capacitor C2 and the diode D2.

Next, the operation of the circuit configured as described above will be described. The voltage charged in the capacitor C2 is discharged by externally controlling and turning on the transistor Q3. Therefore, as in the fourth embodiment,
The switching speed of the field effect transistor Q1 can be controlled.

That is, the switching speed is controlled by the level of the input voltage to obtain a more stable output.

[0041]

According to the present invention, the field effect transistor is used as the switching element, the first Zener diode is connected to the gate of the field effect transistor, and the detection resistor is connected to the source of the field effect transistor and the tertiary. By connecting in series with the winding, the voltage applied to the gate of the field effect transistor is limited, while the source voltage rises according to the input voltage, and the off time of the field effect transistor is changed. As a result, the input power source can be changed from in-vehicle DC12V to household AC100
A stable output voltage can be supplied even if the voltage is changed from V to 240V.

Also, a negative voltage generating means for generating a negative voltage according to the source current of the field effect transistor, and a transistor whose collector and emitter are connected to the gate of the field effect transistor and the negative side of the negative voltage generating means. By providing a second Zener diode connected between the base of the transistor and the source of the field effect transistor, a negative voltage is applied to the gate of the field effect transistor by turning on the transistor and the second Zener diode. Can be lowered to
The switching speed of the field effect transistor can be increased, and the output voltage can be stabilized.

[Brief description of drawings]

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

FIG. 2 is a graph showing input voltage-output voltage characteristics in the first, fourth, fifth embodiments and the first conventional example.

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

FIG. 4 is a graph showing an input voltage-output voltage characteristic in the second embodiment.

FIG. 5 is a circuit diagram showing a third embodiment of the DC power supply device according to the present invention.

FIG. 6 is a circuit diagram showing a fourth embodiment of the DC power supply device according to the present invention.

FIG. 7 is a circuit diagram showing a fifth embodiment of a DC power supply device according to the present invention.

FIG. 8 is a circuit diagram showing a first conventional example of a DC power supply device.

FIG. 9 is a circuit diagram showing a second conventional example of a DC power supply device.

[Explanation of symbols]

1 input power 2 rectifying bridge 3 transformers C1, C2 capacitors D1, D2 diode N3 tertiary winding R1, R4, R5 resistance R2 starting resistance R3 detection resistor Q1 field effect transistor Q2, Q3, Q4 transistors ZD1, ZD2 Zener diode

Claims (2)

[Claims] 1. A series circuit of a primary winding of a transformer and a switching element is connected to an input power source, and the switching element is driven on / off to rectify the electric power induced in the secondary winding of the transformer. A DC power source is obtained, a tertiary winding of the transformer and an oscillation circuit are connected in series with the switching element, and a primary winding of the transformer is further provided between the input power source and the switching element. In a DC power supply device in which a starting resistor is connected in parallel, the switching element is configured by a field effect transistor, and a detection resistor connected in series between the source of the field effect transistor and the tertiary winding, A field effect transistor having a gate and a first Zener diode provided between a connection point of the tertiary winding and the detection resistor. And a DC power supply device. 2. The DC power supply device according to claim 1,
Negative voltage generating means for generating a negative voltage according to the source current of the field effect transistor, a transistor whose collector and emitter are connected to the gate of the field effect transistor and the negative electrode side of the negative voltage generating means, and a transistor of the transistor. A DC power supply device comprising a base and a second Zener diode connected between the sources of the field effect transistors.