JPH0562189U - Power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a power supply device having an active dummy circuit that does not require a hysteresis circuit with a small number of components. A DC / DC converter 1 for generating a predetermined output voltage, a constant voltage control circuit 2 for detecting the output voltage of the DC / DC converter 1 and generating a control signal for voltage control, and a constant voltage control circuit. DC /
Provided with switching elements 1a, Q1 for controlling the output voltage of the DC converter 1, and an active dummy circuit 3 for receiving a control signal from the constant voltage control circuit 2 and flowing a dummy current between the outputs of the DC / DC converter 1. Power supply device characterized by.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a power supply device, and more particularly to improvement of an active dummy circuit in a switching regulator power supply.

[0002]

[Prior Art]

 Fig. 4 shows a power supply device using an active dummy circuit that has been generally used in the past. In the circuit shown in this figure, the pulse generated by the switching of the transistor Q1 is transformed by the transformer T, rectified by the diode D on the secondary side and output to the outside. The active dummy circuit 10 connected in parallel with this load detects a magnitude of the load current Io by the voltage VRS across the current detection resistor Rs and a point up to | VRS | <| Vref | It is composed of a control section for outputting a control signal for turning on the transistor Q2 when Io decreases and an operation section for supplying a dummy current ID to the dummy resistor RD.

If the minimum pulse width that can be controlled by the voltage control circuit of the switching regulator does not fall below the required pulse width, an overvoltage will be generated at the output when the load is light. To avoid this phenomenon, a dummy resistor is inserted at the output end, but this resistor always causes power loss. In order to reduce power loss, a circuit that allows dummy current to flow only when needed (light load) is required. The circuit for this is an active dummy circuit.

[0004]

[Problems to be solved by the device]

 Therefore, in order to configure the active dummy circuit, the elements shown in FIG. 4 are required at the minimum, and it is unavoidable to increase the cost due to the increase in the number of parts and the printed board area.

Further, in the circuit of FIG. 4, when the load current Io in the vicinity where | VRS | and | Vref | are equal to each other and the Io slightly fluctuates, the dummy current fluctuates with the fluctuation. There is also a problem that a phenomenon occurs. Therefore, it is necessary to provide a hysteresis circuit.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to realize a power supply device having a small number of components and an active dummy circuit that does not require a hysteresis circuit.

[0007]

[Means for Solving the Problems]

 Means for solving the above problems are a DC / DC converter that generates a predetermined output voltage, and a constant voltage control circuit that detects the output voltage of a DC / DC converter and generates a control signal for voltage control. , Receives a control signal from the constant voltage control circuit and controls the output voltage of the DC / DC converter, and receives a control signal from the constant voltage control circuit to generate a dummy current between the output of the DC / DC converter. It is characterized by having an active dummy circuit for flowing.

[0008]

[Action]

 In the present invention, since the control signal of the active dummy circuit is shared with the control signal of the constant voltage control circuit, the control signal dedicated to the active dummy circuit is unnecessary, and the active dummy circuit can be configured with a small number of parts. In addition, since the switching element for passing the dummy current starts operating from the active region, the dummy current does not suddenly turn on / off, and the hysteresis circuit is unnecessary.

[0009]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a principle configuration of an embodiment of the present invention, FIG. 2 is a configuration diagram showing a specific configuration, and FIG. 3 is a characteristic diagram showing characteristics of each part in an operating state.

In these figures, 1 is a DC / DC converter that transforms DC by a switching element Q1, 2 is a constant voltage control circuit for performing constant voltage control on the secondary side, and 3 is a control signal of the constant voltage control circuit. It is an active dummy circuit that receives and passes a dummy current. The cathode of the shunt regulator U1 is connected to the cathode of the photocoupler PC1, the anode is connected to GND, and the reference is connected to the midpoint of the output voltage adjusting resistors R1 and R2. The shunt regulator U1 has a function of comparing the voltage at the reference terminal with a reference voltage inside the IC and adjusting the cathode current IK which is a control signal of the constant voltage control circuit 2. The resistor RS is connected between the power supply voltage Vcc and the anode of the photocoupler PC1 and has the functions of limiting the cathode current IK and generating a voltage proportional to IK. The photocoupler PC1 has an anode connected to the resistor RS and a cathode connected to the cathode of the shunt regulator U1 to convert the control signal (cathode current) IK into an optical signal and electrically insulate the DC / DC converter 1. It has a function of transmitting to the primary side constant voltage control circuit 1a. The transistor Q2 is a switching element for flowing a dummy current ID, the emitter is connected to Vcc, the collector is connected to the dummy resistor RD, and the base is connected to the connection point between the resistor RS and the photocoupler PC1 node. The dummy resistor RD is for limiting the dummy current ID, and is connected between the collector of the transistor Q2 and GND.

The operation of the apparatus of this embodiment having the above-described configuration is as follows. When the load current I0 decreases, the constant voltage control circuit 2 operates to increase the control signal IK in order to narrow the pulse width of the switching element Q1.

Here, when the load current for which VBE (Q2) = IK × RS≈0.8 [V] is I0 ′, the transistor Q2 starts to turn on from the vicinity where the load current is I0 = I0 ′. Dummy current ID begins to flow. The value of ID at this time is ID = (VCC-VCE (Q2)) / RD.

When the load current is I0> I0 ′, VBE (Q2) = IK × RS <0.8 [V] and Q2 is turned off, so that the dummy current ID does not flow.

As a result of such a configuration, the following effects can be obtained. (1) Since the control signal of the active dummy circuit 3 is shared with the control signal of the constant voltage control circuit 2 (a signal proportional to the cathode current IK), the control signal dedicated to the active dummy circuit is not necessary and is small. An active dummy circuit can be configured with the number of parts.

Therefore, the area occupied by the printed circuit board can be suppressed. (2) In the active dummy circuit of this embodiment, since the switching element Q2 for flowing the dummy current starts operating from the active region, the dummy current does not suddenly turn on / off and the hysteresis circuit is unnecessary. Is.

As described in detail above, a power supply device having an active dummy circuit that does not require a hysteresis circuit can be realized with a small number of components.

[0017]

[Effect of the device]

 As described in detail with the embodiments above, a power supply device having an active dummy circuit that does not require a hysteresis circuit can be realized with a small number of components.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing a specific configuration of an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an operation in one embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration of a conventional device.

[Explanation of symbols]

 1 DC / DC converter 2 Constant voltage control circuit 3 Active dummy circuit

Claims (1)

[Scope of utility model registration request] 1. A DC / DC converter (1) which generates a predetermined output voltage, and a constant voltage control circuit which detects the output voltage of the DC / DC converter (1) and generates a control signal for voltage control. 2)
And a control signal from the constant voltage control circuit (2),
The switching element (Q1) that controls the output voltage of the C converter (1) and the control signal from the constant voltage control circuit (2)
A power supply device comprising: an active dummy circuit (3) for flowing a dummy current between the outputs of the C converter (1).