JPH0429565A - Switching power circuit - Google Patents

Abstract

PURPOSE:To reduce a loss brought forth when a semiconductor switch is put in continuity, by generating a driving waveform of a voltage being higher than an input voltage by rectifying a voltage generated in a tertiary winding of which the number of windings is larger than that of a primary winding. CONSTITUTION:A voltage VIN of an input DC power source 1 is supplied to an output voltage control circuit 2 and a bypass capacitor 3 through a diode 8. Since the number N3 of windings of a tertiary winding of a voltage conversion transformer 5 is larger than the number N1 of windings of a primary winding, on the other hand, a voltage between a terminal 5C1 and a terminal 5C2 of the transformer 5 is larger than the one between a terminal 5A1 and a terminal 5A2. Accordingly, an inter-terminal voltage of the bypass capacitor 3 is higher than the voltage VIN of the input DC power source 1 and a voltage VG of a terminal 2D of the output voltage control circuit 2 is higher than the voltage VIN of the input DC power source 1. In other words, a voltage for driving a semiconductor switch 4 turns to be high. Thereby a loss can be made low when the semiconductor switch is put in continuity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply circuit that receives direct current as input.

[Prior Art] Some switching power supply circuits of this type generate a voltage using a semiconductor switch drive circuit of a DC-DC converter that receives a low voltage power supply of around 5 volts (V) as an input. An example of such a switching power supply is shown in FIG.

As shown in FIG. 3, this switching power supply includes bypass capacitors 33. Trance 35. Semiconductor switch 34. Rectifier circuit 36. Output voltage detection circuit 37 and output voltage control circuit 3
The power source of the circuit that drives the semiconductor switch 34 is the input DC power source 1.

The semiconductor switch 34 is driven by the drive waveform output from the output voltage control circuit 32 as shown in the fourth section. The voltage 6 of this drive waveform is equal to the voltage VIN of the input DC power supply 31. Due to such a driving waveform, the waveform between the terminal 34A and the terminal 34B of the semiconductor switch 34 becomes an inter-terminal voltage waveform as shown in FIG.

[Problems to be Solved by the Invention] In the above-described conventional switching power supply circuit, when the input DC power supply is a low voltage power supply of around 5V, if an FET is used as a semiconductor switch, sufficient driving cannot be achieved. A semiconductor switch has a waveform like the one shown in , which tends to cause loss when conducting. This is because, as a D C-DC C' converter, the switching power supply is used because, firstly, the amount of heat generated increases and reliability decreases, and secondly, it is necessary to take a large amount of power from the input DC power supply. This has the disadvantage of increasing operating costs for the system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching power supply circuit that can eliminate such drawbacks and reduce the loss that occurs when a semiconductor switch is turned on.

[Means to solve the problem]

The switching power supply circuit of the present invention includes a transformer having a primary winding and a secondary winding, an input DC power supply that supplies DC input voltage to the primary winding of the transformer, and a DC power supply that supplies DC input voltage to the primary winding. In a switching power supply circuit that generates an output voltage based on the voltage generated in the secondary winding, the semiconductor switch is equipped with a semiconductor switch that switches the input voltage generated by the drive waveform, and generates an output voltage based on the voltage generated in the secondary winding. A tertiary winding with a number of turns, a rectifier circuit that rectifies the voltage generated in the tertiary winding, and is activated by the input voltage and operates by receiving the rectified voltage of the rectifier circuit.
It is characterized by having a control circuit that controls the output voltage to be constant and generates a drive waveform of a voltage higher than the input voltage and sends it to the semiconductor switch.

In the present invention described above, it is preferable that the control circuit has a diode that takes in the input voltage of the input DC power supply at the time of startup.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In addition to the conventional technology, this switching power supply has a circuit that supplies power for the output voltage control circuit from the input DC power supply through a forward-connected diode, and a winding in the voltage conversion transformer. and a circuit that supplies a voltage obtained by rectifying the output of the winding in a second rectifier circuit.

As shown in FIG. 1, such a switching power supply circuit includes an input DC power supply 1, an output voltage control circuit 2, a bypass capacitor 3, a semiconductor switch 4, and a voltage conversion transformer 5.
, a rectifier circuit 6 , an output voltage detection circuit 7 , and diodes 8 and 9 .

In such a switching power supply, the input DC power supply 1
is a low voltage power supply. Further, the voltage between the positive side and the negative side of this input DC power supply 1 is VIN.

The output voltage control circuit 2 has terminals 2A to 2D, and the terminal 2
The semiconductor switch 4 is driven at a constant cycle via D.

Terminal 2B is connected to the negative side of input DC power supply 1.

The bypass capacitor 3 is a power line bypass capacitor for the output voltage control circuit 2, and is connected between the terminal 2A and the terminal 2B of the output voltage control circuit 2.

The voltage conversion transformer 5 has terminals 5A, 5A2 and terminal 5.
B, 5B2 and terminals 5C, 5C2.

A primary winding is provided between the terminal 5 A + and the terminal 5 A z. The number of turns of this primary winding is N
It is 1. Between terminal 5B and terminal 5B2,
A secondary winding is provided. Also, terminal 5C, and terminal 5
A tertiary winding is provided between C and C. The number of turns of this tertiary winding is N3, and the number of turns N3 of the tertiary winding is greater than the number of turns N of the primary winding. A terminal 5 A + of the voltage conversion transformer 5 is connected to the plus side of the input DC power supply 1, and a terminal 5C2 is connected to the minus side of the input DC power supply 1.

The semiconductor switch 4 repeats conduction and non-conduction between the terminal 4A and the terminal 4B by the output voltage control circuit 2. The terminal 4A is connected to a terminal 5A of the primary winding of the voltage conversion transformer 5. Terminal 4B is connected to the negative side of input DC power supply 1.

The diode 8 is connected in the forward direction from the input DC power supply 1 to the output voltage control circuit 2. That is, diode 8
The anode is connected to the positive side of the input DC power supply 1, and the cathode is connected to the terminal 2A of the output voltage control circuit 2.

Diode 9 is a second rectifier circuit connected to the tertiary winding of voltage conversion transformer 50. That is, diode 9
The anode of is the terminal 5C of the tertiary winding of the voltage conversion transformer 5.
, and its cathode is connected to the terminal 2A of the output voltage control circuit 2.

The rectifier circuit 6 connects the terminal 5 of the secondary winding of the voltage conversion transformer 5.
The voltage generated between B and terminal 58z is rectified to produce an output voltage ■. Send out LIT.

The output voltage detection circuit 7 receives the output voltage ■ sent out by the rectifier circuit 6. Detect UT. Then, an output signal is sent to the terminal 2C of the output voltage control circuit 2.

Next, the operation of this switching power supply circuit will be explained.

First, the voltage VIN of the input DC power supply 1 is supplied to the output voltage control circuit 2 and the bypass capacitor 3 via the diode 8. Output voltage control circuit 2 is activated by voltage VIH. The output voltage control circuit 2 includes a semiconductor switch 4
is driven at a constant cycle.

As a result, the terminal 4A and the terminal 4B of the semiconductor switch 4 are repeatedly electrically connected and non-conductive.

By repeating conduction and non-conduction of the semiconductor switch 4, the voltage VIN of the input DC power supply 1 is converted between the terminals 5B and 5B2 of the voltage conversion transformer 5, and an electromotive force is generated. The rectifier circuit 6 rectifies this electromotive force and outputs voltage ■. , 41.

The output voltage detection circuit 7 detects the output voltage V from the rectifier circuit 6.

Detects UT and outputs the output signal to terminal 2 of voltage control circuit 2
Send to C. The output voltage control circuit 2 includes an output voltage detection circuit 7
After receiving the output signal, the output voltage ■. . The semiconductor switch 4 is driven so that , is constant.

At this time, the number of turns N of the tertiary winding of the voltage conversion transformer 5 is larger than the number of turns N1 of the primary winding, so the voltage between the terminal 5C+ and the terminal 5Cz of the voltage conversion transformer 5 is , becomes larger than the voltage between terminal 5 A l and terminal 5 A2. Therefore, the voltage between the terminals of the bypass capacitor 3 becomes higher than the voltage 3.4 of the input DC power supply 1, and the voltage V of the drive waveform sent from the terminal 2D of the output voltage control circuit 2 becomes as shown in FIG. , becomes higher than the voltage VIN of the input DC power supply 1. That is, the voltage for driving the semiconductor switch 4 becomes higher. With such a drive waveform,
The waveform between the terminal 4A and the terminal 4B of the semiconductor switch 4 becomes an inter-terminal voltage waveform as shown in FIG.

In this way, the present embodiment includes a transformer, a semiconductor switch,
A DC-DC converter that generates DC voltage by changing the voltage of an input DC power supply using a rectifier circuit, an output voltage detection circuit, and an output voltage control circuit, and is characterized by supplying power to the output voltage control circuit by the following two methods. shall be. First, it is supplied from an input DC power source via a forward-connected diode. Second, add a winding to the transformer,
A voltage obtained by rectifying the winding output in a second rectifier circuit is supplied.

In other words, in this embodiment, when the input DC power supply is low, around 5V, the power supply of the output voltage control circuit is firstly connected to a diode forwardly connected from the input DC power supply, and secondly, a winding is connected to the voltage conversion transformer. By additionally supplying the winding output from a circuit connected to the second rectifier circuit, the output voltage control circuit can drive the semiconductor switch so that the semiconductor switch has low loss when it is conductive.

[Effects of the Invention] As described above, according to the present invention, there is an effect that reliability can be improved by reducing the amount of heat generated, and operating costs can be reduced by reducing the power consumption of the input DC power source.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 1 is a waveform diagram of the embodiment, FIG. 3 is a circuit diagram showing an example of a conventional switching power supply circuit, and FIG. 4 is a waveform diagram. 1... 2... 3... 4... 5... 6... 7... 8.9. Waves of switching power supply circuit in Figure 3, input DC power supply, output voltage control circuit・Bypass capacitor ・Semiconductor switch ・Voltage conversion transformer ・Rectifier circuit ・Output voltage detection circuit ・Diode

Claims (2)

[Claims] (1) A transformer including a primary winding and a secondary winding, an input DC power supply that supplies a DC input voltage to the primary winding of this transformer, and an input DC power supply that supplies a DC input voltage to the primary winding. In a switching power supply circuit that includes a semiconductor switch that switches according to a drive waveform and generates an output voltage based on the voltage generated in a secondary winding, the transformer is provided with three
A rectifier circuit that rectifies the voltage generated in the secondary winding and the tertiary winding is activated by the input voltage and operates by receiving the rectified voltage of the rectifier circuit.
1. A switching power supply circuit comprising: a control circuit that controls an output voltage to be constant and generates a drive waveform of a voltage higher than an input voltage and sends it to a semiconductor switch. (2) The switching power supply circuit according to claim 1, wherein the control circuit includes a diode that takes in the input voltage of the input DC power supply at the time of startup.