JP2666497B2 - Variable voltage generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention divides a high voltage by a resistor,
The present invention relates to a variable voltage generation circuit that can output an arbitrary voltage.

[Prior art] As a variable voltage generating circuit, there is a method of using a multi-turn variable resistor and a vernier dial in a low voltage circuit, but in a high voltage circuit, when applying 500 V or more directly to both ends of the variable resistor, a large and special Variable resistors are required. Therefore, conventionally, in a high-voltage circuit, a fixed resistor is selected by a changeover switch, and the output is finely adjusted by a variable resistor connected to the changeover switch. In this conventional variable voltage generating circuit, as shown in FIG. 5, a plurality of fixed resistors R are connected to the positive and negative output terminals of a power supply voltage E of 40 V, and contacts OL to 3L of a rotary changeover switch SW are connected between the terminals of each resistor. , OH to 3H are connected. A resistance value R is provided at both ends of the changeover switch SW.
Are connected. To explain how to use this variable voltage output circuit, the two switching terminals of the changeover switch SW are switched in conjunction with each other, and when connected to the contacts OL and OH, the output terminal must be adjusted with a variable resistor VR. As a result, a voltage that can be finely adjusted from 0 to 10 V is obtained. Also,
10 to 20 V, 2 when connected to contacts 1, 2, and 3, respectively
Fine adjustable voltages of 0 to 30V and 30 to 40V can be obtained. At this time, since only one-fourth of the power supply voltage is always applied to both ends of the variable resistor VR, no special variable resistor is required for the variable resistor VR.

[Problem to be Solved by the Invention] In the conventional variable voltage generating circuit as described above, the output voltage is not determined during the switching of the changeover switch SW, and for example, the lower side (L) of the changeover switch SW is opened first. If the power supply voltage of 40V is output from the output terminal as it is,
It is dangerous because a high voltage is applied to the load. For this reason,
It is necessary to use a switch called a short type in which the switching terminal does not open at any position as the changeover switch. However, even if such a switch is used as the changeover switch, there is always a risk that an open state occurs due to a contact failure or the like, and an abnormal increase in output voltage cannot be reliably prevented.

The present invention has been made in order to solve the above-described drawbacks of the related art, and has provided a variable voltage generating circuit that can reliably limit an output voltage to a voltage equal to or less than a voltage before switching when a rotary switch is switched. The purpose is to provide.

[Means for Solving the Problems] To achieve the above object, a variable voltage generating circuit according to the present invention includes a means for detecting an open state of a rotary changeover switch, and a means for regulating an output voltage by an output of the detecting means. And

[Operation] In the variable voltage generator configured as described above, a variable resistor is inserted into a part of the series circuit of the fixed resistor by the rotary switch, and the variable resistor is adjusted so that each position of the rotary switch is adjusted. Get an output that can be fine tuned. Then, if the open state of the changeover switch occurs at the time of the changeover of the rotary changeover switch due to a contact failure or the like, this is detected by the detecting means, and the output voltage is limited to the voltage before the changeover of the rotary changeover switch.

Embodiment FIG. 1 is a basic circuit diagram of a variable voltage generator according to the present invention. Several positive and negative fixed resistors R are connected to positive and negative output terminals of a power supply voltage E of 40 V, and a rotary switch is made to a connection terminal of each resistor. The contacts OL to 3L and OH to 3H of the switch SW are connected. Also,
A variable resistor VR is connected to both ends of the changeover switch SW, a voltage detector VD is connected between the contacts 3L and OH, and a contact
The switch SW2 is connected between OH and the negative terminal of the power supply. The switching terminals of the changeover switch SW are switched in conjunction with each other, and a finely adjustable variable voltage is obtained at the output terminal as in FIG. At this time, at each switching position of the rotary selector switch, a voltage of 10 V is always applied to both ends of the variable resistor VR, and the voltage detector VD does not operate. Rotary changeover switch SW changeover switch
When a part of the SW, for example, the lower side (L) is opened, the power supply voltage is output to the output terminal as it is. Since this voltage is detected by the voltage detector VD and the switch SW2 is turned on, the voltage of the output terminal is limited to the voltage before the terminal is switched.

A specific embodiment of the present invention will be described with reference to FIG. 2. A fixed number of fixed resistors R are connected to the positive and negative output terminals of the power supply voltage E, and contacts OL to 3L of a changeover switch SW are connected between terminals of each resistor.
OH to 3H are connected. Further, a variable resistor VR is connected to both ends of the changeover switch SW which is switched in conjunction with each other, and a resistor 100R is connected to a sliding terminal of the variable resistor VR.
This resistor 100R is a protection resistor when both ends of the switch SW are open. When the circuit is normal, the voltage applied to the anode side of the Zener diode ZD through the emitter and base of the transistor Tr is the voltage across the variable resistor VR regardless of the position of the contact point of the changeover switch SW, and the power supply voltage is 40 V In this case, it is about 10V. At this time, the zener voltage of the zener diode ZD cannot exceed 12 V, and the transistor Tr does not turn on. On the other hand, part of the switch SW,
For example, when the lower side (L) is open, the transistor Tr
The emitter of is supplied with a power supply voltage of 40 V through 3 × R, and the base has an OV through a zener diode ZD and 3 × R.
, A current flows between the emitter and the base of the transistor Tr, and the emitter and the collector are turned on. In this case, assuming that the current amplification factor (h _FE ) of the transistor Tr is about 100, the voltage between the emitter and the collector of the transistor Tr is the voltage of the Zener diode ZD (12 V) and the voltage between the emitter and the base of the transistor Tr. About 12.6 of about 0.6V total
Clamped to V. Therefore, the output voltage differs depending on the switching position of the changeover switch SW.
A voltage that is always lower than the voltage that was output immediately before the SW was switched is output.

FIG. 3 shows another embodiment of the present invention, in which a current flowing through a lower resistor R is converted into a voltage by a current-voltage converter IVC and is input to a voltage comparator VC. In a normal circuit state, the output of the current-to-voltage converter IVC has a negative potential, the output of the voltage comparator VC has a negative value, and the transistor Tr does not turn on. On the other hand, if the lower side (L) of the switch is opened when the rotary changeover switch SW is switched, no current flows to the current-voltage converter IVC, the output of the voltage comparator VC becomes positive potential, and the transistor Tr is turned off. Turns on. Thereby, the potential of the sliding terminal of the variable resistor is clamped to the voltage of the ON potential of the transistor, and the output of the high potential is prevented.

FIG. 4 shows an application example of the high voltage generating circuit of the present invention, in which the variable voltage generating circuit of the present invention is used as a standard voltage source on the primary side of a DC-DC converter for generating a high voltage.

Describing the operation of this circuit, the output 0-10V of the variable voltage generating circuit of the present invention is inputted to the reference input terminal of the DC-DC converter, and 0-100KV is outputted from the output terminal. At this time, even if the changeover terminal of the changeover switch SW is opened, a voltage lower than the voltage which was output immediately before the switch is changed is always output to the reference input of the DC-DC converter, so that the voltage output is changed. An abnormal rise can be prevented.

[Effects of the Invention] As described above, the present invention detects the open state of the rotary changeover switch and limits the output voltage of the variable voltage output circuit. However, abnormal increase in the voltage output can be prevented.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of a variable voltage generating circuit according to the present invention, and FIG.
FIG. 3 shows an embodiment of the variable voltage generating circuit of the present invention.
The figure is a diagram showing another embodiment of the variable voltage generating circuit of the present invention,
FIG. 4 is a diagram showing an application example of the variable voltage generation circuit of the present invention,
FIG. 5 is a diagram showing a conventional variable voltage generating circuit. E: Power supply, R: Fixed resistance, VR: Variable resistance, SW:
Rotary changeover switch, VD …… Voltage detector, SW2…
... Switch, Tr ... Transistor, ZD ... Zener diode, IVC ... Current-voltage converter, VC ... Voltage comparator

Claims (1)

(57) [Claims] 1. A variable voltage generating circuit comprising: a rotary changeover switch for switching between connection terminals of a series circuit of fixed resistors connected to a power supply; and a variable resistor connected to an output terminal of the rotary changeover switch. A variable voltage generating circuit comprising: means for detecting an open state of a rotary changeover switch; and means for regulating an output voltage by an output of the detecting means.