JPH07337007A - Dc voltage supply circuit - Google Patents

Abstract

PURPOSE:To realize a DC voltage supply circuit having high power efficiency by detecting the load current flowing through an output terminal and controlling the current flowing through a bleeder circuit based on the load current value. CONSTITUTION:Under no-load or when the load is extremely light, a current larger than a prescribed level does not flow through a resistor R4. Consequently, a transistor TR1 is turned ON and a current flows through a bleeder resistor circuit R1 connected between the output terminals thus stabilizing the operation of a switching circuit. When the load current begins to flow, a potential corresponding to the quantity of current appears across the resistor R4. The potential is amplified through an operational amplifier IC1 and the base potential of the transistor TR1 is increased. When the current value of the bleeder resitstor R1 decreases and the load current exceeds the prescribed level, the transistor TR1 is turned OFF and a current does not flow through the bleeder resistor R1. This circuitry realizes a DC voltage supply circuit having high current efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC voltage source circuit for obtaining a DC high voltage by using a switching circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a schematic configuration of a conventional DC voltage source circuit of this type.
Is a switching circuit, 2 is a transformer, 3 is a load, 4 is P
WM, 5 is a DC power source, D1 is a rectifying diode, C1 is a ripple smoothing capacitor, R1 is a bleeder resistor circuit, and R2 and R3 are voltage detecting resistors.

A DC voltage source circuit of this type is generally well known, and a portion not directly related to the present invention is omitted in the drawings and the description thereof, but a DC current from a power source 5 is supplied to the switching circuit 1. It is converted into a switching current (AC), boosted to a desired high voltage by the transformer 2, converted into a DC voltage by the rectifying diode D1 and the ripple smoothing capacitor, and supplied to the load 3. The DC voltage is always detected by the voltage detection circuit composed of the resistors R2 and R3, and the information is fed back to the PWM4 to control the switching circuit 1 so that the constant voltage is maintained. Is configured.

In order to stabilize the operation of the switching circuit 1, the bleeder resistance circuit R is provided between the output terminals.
1 is inserted. That is, in this type of circuit, when there is no load or when the load is extremely light, the discharge from the ripple smoothing capacitor C1 takes a long time, and therefore the switching operation becomes intermittent, and audible noise is generated. When a heavy load is suddenly applied, the operation becomes unstable. Therefore, in order to perform the operation of the switching circuit 1 stably even in such a case, in the conventional circuit of this type, the bleeder resistor R1 is provided between the output terminals so that a predetermined voltage is applied to the output stage even when there is no load. It is inserted so that current is always applied.

[0005]

Since the conventional DC voltage source circuit is constructed as described above and the bleeder resistance is inserted between the output terminals to always flow the current, as shown in FIG. Even when the capacity is sufficiently large and the switching operation is stable, a current flows through the bleeder resistor as in the case of no load, and there is a problem in that power loss occurs correspondingly. In particular, this type of DC voltage source circuit uses a large-capacity ripple smoothing capacitor because it is intended to output a high voltage and a large amount of power, so the current flowing through the bleeder resistance is also relatively large. , This power loss cannot be ignored.

The present invention has been made to solve the above problems, and a bleeder resistance circuit is connected only when there is no load or when the load is extremely light by inserting a simple circuit. An object is to provide a DC voltage source circuit with good power efficiency.

[0007]

A direct current voltage source circuit according to the present invention comprises a switching circuit for boosting a direct current power source as a switching current by a transformer, and a ripple smoothing capacitor to obtain a desired high voltage direct current voltage source. In a DC voltage source circuit that inserts a bleeder resistance circuit between output terminals to stabilize the switching operation when the load connected is small, load current detection that detects the load current flowing through the output terminals Means for controlling the current flowing through the bleeder resistance circuit according to the load current value from the load current detecting means.

Further, the load current detecting means is carried out by inserting a resistor into one of the output terminals and detecting a potential difference between both ends of the resistor, and the bleeder resistor is detected by the load current value from the load current detecting means. The means for controlling the current flowing through the circuit is characterized in that the potential difference is amplified by an operational amplifier and the output is used to control the base potential of the gate transistor inserted in the bleeder resistance circuit.

Further, the means for controlling the current flowing through the bleeder resistance circuit according to the load current value from the load current detecting means comprises the bleeder resistance circuit as a voltage dividing resistor or a plurality of resistors having different resistance values. A potential difference is amplified by an operational amplifier, and the output is used to control the base potential of the gate transistor inserted in the bleeder resistance circuit while varying the resistance value of the bleeder resistance circuit.

[0010]

In the DC voltage source circuit of the present invention, the configuration described above limits the current flowing through the bleeder resistance circuit according to the load current amount, and the load current amount stabilizes the operation of the switching circuit. If the bleeder resistance circuit is turned off when sufficient, a circuit with high power efficiency can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
Only those portions corresponding to those shown in FIG. 3A that are directly relevant to the present invention are shown. In the figure, the same reference numerals as those in FIG. 3 indicate the same or corresponding parts, TR1 is a transistor inserted in a bleeder resistance circuit connecting output terminals, and IC1 is connected to the base of the transistor TR1 via a protection resistor R5. Operational amplifier, R4 is a resistor for detecting output current, R6
˜R9 are resistors for determining the amplification factor of the operational amplifier IC1.

Next, the operation will be described. When there is no load or when the load is extremely light, a current larger than the specified value does not flow in the resistor R4 and the transistor TR1 is in the ON state, so a current flows between the bleeder resistance circuit R1 connecting the output terminals, It stabilizes the switching operation of the switching circuit as in the conventional circuit. Then, when the load current starts flowing, a potential difference corresponding to the amount of the current is generated at both ends of the resistor R4. Therefore, the operational amplifier IC1 amplifies this potential difference and raises the base potential of the transistor TR1. Therefore, the current flowing through the bleeder resistance circuit R1 gradually decreases, and when the load current exceeds the specified value, the transistor TR
1 is turned off, and no current flows through the bleeder resistance circuit R1.

FIG. 2 is a diagram showing the operation of the present embodiment as described above. As shown in the figure, when the load is equal to or more than a specified value, that is, when the switching operation of the switching circuit becomes stable, the transistor TR1 is turned on. It is turned off, and it is possible to prevent useless power loss.

In the above embodiment, the bleeder resistance circuit is composed of one resistance, but a voltage dividing resistance is used and a plurality of transistors or diodes that are turned on / off by different load current amounts are provided. It is also possible to switch each tap of the voltage dividing resistor. Furthermore, a plurality of resistors having different resistance values are provided as a bleeder resistance circuit,
By adopting a configuration in which the bleeder resistance value is switched according to the amount of load current, for example, finer control can be performed.

[0015]

The DC voltage source circuit of the present invention limits the current flowing through the bleeder resistance circuit according to the amount of load current, and when the amount of load current is sufficient to stabilize the operation of the switching circuit, it is bleeder. With the configuration in which the resistance circuit is turned off, there is an effect that a circuit with a simple configuration and high power efficiency can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation and effect of the embodiment shown in FIG.

FIG. 3 is a block diagram showing an example of a conventional circuit of this type.

FIG. 4 is a diagram for explaining a defect of a conventional circuit.

[Explanation of symbols]

1 switching circuit 3 load D1 rectifier diode C1 ripple smoothing capacitor R1 bleeder resistance circuit R2, R3 voltage detection resistance TR1 transistor IC1 operational amplifier R4 output current detection resistance R6 to R9 resistance for determining the amplification factor of operational amplifier IC1

Claims (3)

[Claims] 1. A switching circuit boosts a direct current power supply as a switching current by a transformer, a ripple smoothing capacitor obtains a desired high voltage direct current voltage source, and stabilizes a switching operation when a connected load is small. For this purpose, in a DC voltage source circuit in which a bleeder resistance circuit is inserted between output terminals, a load current detecting means for detecting a load current flowing through the output terminal, and a load current value from the load current detecting means A DC voltage source circuit comprising: means for controlling a current flowing through the bleeder resistance circuit. 2. The load current detecting means is performed by inserting a resistor into one of the output terminals and detecting a potential difference between both ends of the resistor, and the bleeder resistance is determined by a load current value from the load current detecting means. The means for controlling the current flowing through the circuit is performed by amplifying the potential difference with an operational amplifier and controlling the base potential of the gate transistor inserted in the bleeder resistance circuit with this output. DC voltage source circuit. 3. The means for controlling the current flowing through the bleeder resistance circuit according to the load current value from the load current detection means comprises the bleeder resistance circuit as a voltage dividing resistor or a plurality of resistors having different resistance values, The direct current according to claim 1, wherein the potential difference is amplified by an operational amplifier, and the resistance of the bleeder resistance circuit is varied while controlling the base potential of the gate transistor inserted in the bleeder resistance circuit with this output. Voltage source circuit.