JP2584740Y2 - Power converter with constant current droop circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter with a constant current droop circuit.

[0002]

2. Description of the Related Art Conventionally, power conversion devices such as converters using semiconductor switch elements such as transistors and thyristors have been widely put into practical use. In general, power converters have an output voltage control function and an overcurrent protection function, and are widely used, including DC power supplies for communication devices and information devices.

An example of a power converter will be described with reference to a circuit diagram of FIG. FIG. 1 shows a ringing choke converter having an output voltage control function and an overcurrent protection function. A power conversion device including a power conversion circuit having a switching section and a rectification circuit section and an output voltage detection circuit as surrounded by a dotted line. It is.

(2) The output voltage detection circuit includes at least an output voltage detection resistor R1,
R2, a voltage detection unit IC1 incorporating a reference voltage, and a detection signal transmission unit PD. In FIG. 1, a shunt regulator using a semiconductor integrated circuit is used for IC1, and a PD is used.
A light emitting portion of a photocoupler, that is, a light emitting diode is used.

The switching section of the power conversion circuit stores energy in the transformer T when the main switch element Q1 is turned on,
This is known as a ringing choke converter that releases stored energy from T to the load side when turned off.
The output voltage control function is performed by applying an optical signal from a detection signal transmission unit PD (light emitting diode) of the output voltage detection circuit to a detection signal reception unit PT (phototransistor) of the switching unit. That is, the base current of the control transistor Q2 is made variable by an optical signal that has detected the output voltage, and the ON period of the main switch element Q1 is controlled to maintain a constant voltage. The rectifying circuit section of the power conversion circuit includes a rectifying diode D1 and a smoothing capacitor C2, and rectifies and smoothes the output of the switching section.

In the conventional device shown in FIG. 1, the load current I0 cannot increase beyond the maximum control width during the ON period of the main switch element Q1, and an overcurrent protection operation is performed. However, the relationship between the load current I0 and the load voltage V0 is As shown in the figure, the characteristic shows that I0 sharply decreases as V0 decreases from the point of the maximum load current.

However, for example, for communication, a power converter having a constant current drooping characteristic is required. That is, in a specific field, a characteristic is desired in which the load voltage droops at a substantially constant current at the maximum load current and rises at a substantially constant current even when the load voltage is increased again.

As a power converter having such a constant current drooping characteristic, there is a power converter as shown in the circuit diagram of FIG. A constant current drooping circuit (3) shown in a dotted frame is added to the load side of the output voltage detection circuit in FIG. 1, and the same reference numerals as those in FIG. 1 denote the same parts. The constant current drooping circuit includes an output current detection resistor R3 and a dropper transistor Q3 connected in series with a load, and further connects a dropper drive transistor Q4 and a drive resistor R4. Although the power conversion circuit is not shown particularly with the switching unit omitted, a ringing choke converter similar to that shown in FIG. 1 is used.

In FIG. 2, the relation between the maximum load current and the load voltage of the power conversion circuit controlled by the detection signal of the output voltage detection circuit is determined by the ON of the main switch element of the switching section.
It is realized by adding a constant current droop circuit without depending on only the width control. That is, when the load current I0 exceeds the set value, the voltage drop of the output current detection resistor R3 is increased, the transistor Q4 for dropper driving is controlled, and the base current of the transistor Q3 for dropper is bypassed. Had a characteristic of drooping at almost constant current.

[0010]

The power consumption of a dropper transistor in a conventional power converter having a constant current drooping circuit is determined by the constant current drooping circuit input voltage Vi and the load voltage V0.
Is substantially equal to a value obtained by multiplying the difference by the load current I0, it is necessary to select a transistor having a large permissible collector loss, and it is possible to solve the problem that the circuit configuration including heat dissipation means and the like becomes large and expensive. It is a problem to be solved.

[0011]

SUMMARY OF THE INVENTION The present invention provides an output voltage detecting resistor, a voltage detecting section having a built-in reference voltage, an output voltage detecting circuit having a detecting signal transmitting section, an output current detecting resistor connected in series with a load, and a dropper. In a power converter with a constant current drooping circuit comprising a constant current drooping circuit having a transistor and a power conversion circuit having a switching section controlled by a detection signal receiving section, division between an emitter and a collector of a dropper transistor is performed. A resistor is connected, and a part of the output voltage detection resistor is connected between the emitter and the collector of the bypass transistor.
It is characterized in that the dividing point of the dividing resistor and the base of the bypass transistor are connected via a reverse blocking diode, whereby low loss, small size,
An inexpensive power converter with a constant current droop circuit has been realized.

[0012]

FIG. 3 is a circuit diagram showing an embodiment of the present invention. The same reference numerals in FIGS. 1 and 2 denote the same parts. The emitter and the collector of the bypass transistor Q5 are connected to both ends of a part R5 of the output voltage detection resistor provided in the output voltage detection circuit, and the dividing point A is connected to both ends of the dropper transistor Q3 provided in the constant current drooping circuit. Are connected. The base of the dividing point A and the base of Q5 are connected via a reverse blocking diode D2.

Here, the output voltage detection resistors R1, R2, R
5. The input voltage Vi of the constant current drooping circuit at the reference voltage value VREF of the voltage detection unit IC1 is as follows: Vi = [(R1 + R2 + R5) / R2] · VREF Further, the load voltage V0 has a relationship of Vi0V0 in a load region where the droop operation is not performed. However, when the drooping operation starts and the load voltage V0 starts to decrease, the division resistance R6,
The voltage at the division point A of R7 also drops, and the bypass transistor Q5
When the base voltage falls below the emitter voltage, Q5 conducts. As a result, the resistance value of R5, which is a part of the output voltage detection resistor, decreases, and Vi also decreases.

When the constant current droop circuit operates due to a short circuit on the load side and enters a constant current region, the input voltage Vi of the constant current droop circuit
And the emitter of the dropper transistor Q3
The voltage drop between the collectors can be reduced, and as a result, the power consumption of Q3 can be reduced.

(5) The device of the present invention can make various circuit modifications within the scope of the present invention. For example, as a power conversion circuit,
In addition to the ringing choke converter illustrated in FIG.
The present invention can be applied to any power conversion circuit operated by a switching unit, such as an ON-ON converter. As the output voltage detection circuit, a shunt regulator using a semiconductor integrated circuit is used for the voltage detection unit.
Circuit may be formed by individual elements.
Further, although the detection signal transmitting unit PD and the detection signal receiving unit PT use a light emitting diode and a phototransistor using a photocoupler, the detection signal may be connected to the control circuit of the switching unit by a connection line regardless of the photocoupler. Good.
Further, the bypass transistor Q5 may be connected to the R1 side of the output voltage resistor. Either part can be equivalently modified, changed, added, deleted, etc. within the scope of the present invention.

[0016]

As described above, the power converter according to the present invention can reduce the power consumption of the dropper transistor of the constant current drooping circuit, thereby selecting a transistor having a small rated collector loss. It realizes a small and inexpensive circuit configuration, and has a large industrial use effect for communication and information processing.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a conventional power converter.

FIG. 2 is a circuit diagram of a conventional power converter with a constant current drooping circuit.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

 Q1 Main switching element Q2 Transistor for controlling Q1 Q3 Transistor for dropper (6) Q4 Transistor for driving dropper Q5 Transistor for bypass C1, C2, C0 Capacitor D1 Rectifying diode of rectifying circuit D2 Reverse blocking diode R1 , R2, R5 Output voltage detection resistor R3 Output current detection resistor R4 Dropper drive resistor IC1 Voltage detection unit with built-in reference voltage PD Detection signal transmission unit PT Detection signal reception unit Vi Input voltage of constant current droop circuit V0 Load voltage VREF reference Voltage value I0 Load current

Claims (1)

(57) [Scope of request for utility model registration] An output voltage detection circuit having an output voltage detection resistor, a voltage detection unit having a built-in reference voltage, and a detection signal transmission unit;
In a power converter with a constant current droop circuit comprising an output current detection resistor connected in series with a load, a constant current droop circuit having a dropper transistor, and a power converter circuit having a switching section controlled by a detection signal receiving section, A dividing resistor is connected between the emitter and collector of the bypass transistor, a part of the output voltage detecting resistor is connected between the emitter and collector of the bypass transistor, and the dividing point of the dividing resistor and the bypass transistor are connected. A power converter with a constant current drooping circuit, characterized in that the bases are connected via a reverse blocking diode.