JPH01140805A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To freely set the upper and lower bounds of an output voltage by providing the current switching type OR circuit of two inputs in a DC/DC conversion circuit and connecting a variable current source to the collector resistance of the OR circuit. CONSTITUTION:The upper bound of the input voltage in the DC/DC conversion circuit 1 is clipped by a voltage decided at the dynamic range of the current switching type OR circuit 2, namely, the voltage of a node between the collector resistance 4 and the input electrode of a second transistor 8. When the variable current source 3 connected to said node permits a current I to flow, the voltage of the node drops for the amount of voltage drop in the collector resistance 4, and said clip voltage changes. When a low DC voltage is given to an input terminal 10 by an adjusted voltage impressed on by an adjustment input 11 connected to the control electrode of a third transistor 6, the input voltage of the circuit 1 turns into the voltage decided by the adjusted voltage, whereby the lower bound of the input voltage in the circuit 1 is also restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to output voltage limiting means for a DC-DC conversion circuit.

〔overview〕

The present invention provides means for limiting the upper and lower limits of the output voltage of a DC-DC converter, by inserting a current switching type OR circuit and a variable current source into the input terminal of the DC-DC converter, thereby increasing the upper and lower limit limits. can be set freely.

[Conventional technology]

Although DC-DC conversion circuits have a wide range of uses, in recent years they have also been used as bias circuits for APDs, which are one of the light-receiving elements used in the field of optical communications. In the conventional circuit, a minimum output voltage setting circuit is provided at the input end of the DC-DC conversion circuit, and the APD
guaranteed minimum operating voltage.

[Problem that the invention seeks to solve]

However, the conventional circuit does not have a maximum output voltage clipping circuit, so if the input voltage of the DC-DC conversion circuit is set high by mistake, the bias voltage applied to the APD will become too high and destroy the APD. There are drawbacks that pose risks. On the other hand, a diode or Zener diode is generally used as voltage clipping means, but A
Although the maximum voltage that can be applied to the PD differs depending on each APD, the clipping voltage cannot be set freely, so there is a drawback that there is no flexibility in use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC-DC converter that can freely change and set the upper and lower limits of the voltage applied to the input terminal of a DC-DC converter circuit.

[Means for solving problems]

The present invention provides a first transistor having an input electrode connected to a common potential and a control electrode connected to an input terminal, an input electrode connected to a common potential via a resistor and connected to an input end of a DC-DC conversion means, a second transistor having a control electrode connected to a reference voltage source; a third transistor having an input electrode connected to the input electrode of the second transistor; and a third transistor having a control electrode connected to a level-adjustable voltage source; The present invention is characterized by comprising an OR circuit having a constant current source connected to the output electrodes of the second and third transistors, and a variable current source connected to the input electrode of the second transistor.

[Effect]

The upper limit of the voltage at the input terminal of the DC-DC conversion circuit is clipped by the input electrode potential of the second transistor determined by the dynamic range of the OR circuit, and the input electrode of the second transistor is further inserted between the input electrode of the second transistor and the common potential line. The level of this clipped voltage can be changed by applying a predetermined current from a variable current source to the clipped resistor to generate a voltage drop.

Further, even if a DC voltage lower than the adjustment voltage applied to the adjustment terminal of the third transistor is applied to the input terminal, the lower limit value of the voltage applied to the DC-DC conversion circuit is limited by the lower limit voltage determined by the adjustment voltage.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. 1st
The figure is a circuit diagram showing the configuration of this embodiment.

As shown in FIG. 1, this embodiment includes an input terminal 10 to which a DC voltage is applied, and a DC-DC conversion circuit that is a conversion means for converting the DC voltage applied to this input terminal into a DC voltage of a different level. 1, a first transistor whose input electrode is connected to the common potential and whose control electrode is connected to the input terminal 10, whose input electrode is connected to the common potential via the collector resistor 4 and connected to the input terminal of the conversion means; a second transistor 7 whose control electrode is connected to a reference voltage source; an input electrode of this second transistor 70 (=connected;
The current is an OR circuit with a third transistor 6 whose control electrode is connected to a level-adjustable voltage source and a constant current source 9 which is connected to the output electrodes of the first, second and third transistors 7.8 and 6. It comprises a switched OR circuit 2 and a variable current source 3 connected to the second trough 80 input electrode.

That is, a current switching type OR circuit (hereinafter referred to as an OR circuit) 2 is cascade-connected to the input side of the DC-DC conversion circuit 1.
A variable current source 3 is connected between the collector resistor 4 of the OR circuit 2 and the emitter power supply terminal 15.

As shown in FIG. 2, the input/output characteristics of the DC/DC conversion circuit 1 are such that the output voltage monotonically increases in accordance with the input voltage. On the other hand, when the OR circuit 2 is connected to the input side, the voltage determined by the dynamic range of the OR circuit 2, that is, the voltage at the 0 point becomes the ground potential, and the output voltage is clipped to this potential. This state is shown in the input/output characteristics in FIG.

Furthermore, when the variable current source 3 is connected between the collector resistor 4 and the emitter power supply terminal 15 and a current ■ is caused to flow, the voltage at the 0 point decreases by the voltage drop caused by the collector resistor 4, and the third
As shown in the input/output characteristic C in the figure, the maximum clip voltage decreases.

On the other hand, the voltage at the adjustment terminal 11 of the OR circuit 2 is set to VAnJ's
If the voltage of input terminal 10 is VB, then VIN>VAII
In the voltage range of J, V! The output voltage changes based on the voltage of Vt, but in the voltage range of I≦V A D J
Even if N changes, the output voltage remains constant, resulting in the input characteristics shown in FIG. Therefore, the minimum output voltage can be controlled by adjusting the voltage VADJ, and as shown in FIG. 4, when the voltage VADJ is increased, the input/output characteristic changes to the human output characteristic E.

〔Effect of the invention〕

As explained above, the present invention provides a two-input current switching type OR circuit at the input section of a DC-DC conversion circuit, and further connects a variable current source to the collector resistor of this OR circuit, thereby achieving a maximum output voltage. This has the effect of being able to freely adjust the minimum voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. 2 to 4 are characteristic diagrams showing the input/output characteristics of the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... DC-DC conversion circuit, 2... Current switching type OR circuit, 3... Variable current source, 4.5... Collector resistance,
6.7.8... Transistor, 9... Constant current source, 1
0...Input terminal, 11...Adjustment terminal, 12...Reference voltage terminal, 13...Output terminal, 14...Ground terminal, 15...Emitter power supply terminal.

Claims (1)

[Claims] (1) In a DC-DC conversion device comprising an input terminal (10) to which a DC voltage is applied, and a conversion means (1) that converts the DC voltage applied to the input terminal into a DC voltage of a different level, the input a first transistor (7) having an electrode connected to a common potential and a control electrode connected to the input terminal; an input electrode connected to the common potential via a resistor and connected to the input terminal of the converting means; a second transistor (8) whose input electrode is connected to a reference voltage source; a third transistor (6) whose input electrode is connected to the input electrode of this second transistor and whose control electrode is connected to a level-adjustable voltage source; An OR circuit having a constant current source (9) connected to the output electrodes of the first, second and third transistors, and a variable current source (3) connected to the input electrode of the second transistor. A DC-DC converter featuring: