JPH0195312A - Power circuit - Google Patents

Abstract

PURPOSE:To simplify the constitution of a power circuit by supplying either one of 1st and 2nd overvoltage detecting outputs to an overvoltage protecting circuit for protection of overvoltage. CONSTITUTION:When a plus DC voltage obtained between terminals 7 and 8 exceeds a prescribed level, a control transistor Q1 is turned on. Thus a thyristor 23 conducts and both terminals 7 and 8 are short-circuited. Then a fuse 4 is melted for protection of a load. While the level of a minus side terminal 9 of an operational amplifier 40 is increased more at the minus side in case the minus output voltage level obtained between the terminals 7 and 8 exceeds the prescribed level. Thus the plus detecting output is obtained from the amplifier 40 and applied to the gate of the thyristor 23. Then the thyristor 23 conducts and the fuse 4 is melted for protection of the load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply circuit having an overvoltage protection function.

[Prior Art] As a power supply circuit having an overvoltage protection function, for example, a multi-output type power supply circuit is known which is configured to obtain predetermined positive and negative direct current voltages as its output voltages, respectively.

This circuit can normally be used as a power supply circuit for obtaining the necessary DC voltage, for example, in a servo system, when the circuit is used for forward and reverse rotation of the drive motor.

FIG. 2 shows a power supply circuit 10 having this kind of overvoltage protection function.
FIG. 2 is a connection diagram of main parts showing an example of the above.

A commercial AC source 2 can be supplied to a primary coil 1a of a commercial power transformer 1 via a power switch 3 and a fuse 4.

A plurality of secondary coils lb and lc are provided on the secondary side, and one secondary coil 1b is connected to a positive side power supply terminal (the A positive voltage lead-out terminal (1) 7 is led out.

Further, a negative power terminal 9 is led out to the other secondary coil 1c via a rectifier circuit 11 consisting of a diode D2 and a capacitor C2. Diode D2
The terminal 8 to which is connected is a reference power supply terminal (OV).

In such a power supply circuit 10, each secondary coil lb,
The lc has positive side and negative side output voltages (+
Circuits 20 and 30 are provided to protect against overvoltage conditions (V, -V).

Starting from the positive overvoltage protection circuit 20, terminal 7
．． 8, a series circuit consisting of a Zener diode 21 for voltage detection and a resistor 22 is connected, and a control transistor Q1 is connected to the midpoint of the connection.

A thyristor 23 in this example, which roughly functions as a control element, is connected between the terminals 7 and 8, and its gate terminal is supplied with the output of the above-mentioned control transistor Q1.

Under normal conditions, the control transistor Q1 remains off, but for some reason the load connected between terminals 7° and 8 becomes heavy, and the positive voltage between terminals 7° and 8 exceeds the specified value. When the control transistor Q
1 is turned on, and based on this, the thyristor 23 is turned on.

As a result, the terminals 7 and 8 are short-circuited, and as a result, an excessive current flows through the primary coil la side of the commercial power transformer 1, and as a result, the fuse 4 is blown. This protects the load connected between the output terminals 7 and 8 from overvoltages.

Between terminals 8 and 9, there is a roughly negative overvoltage protection circuit 3.
0 is set. Therefore, in this example, the auxiliary power supply 31 consisting of the diode D3 and the capacitor C3 is connected to the secondary coil 1c, and the DC voltage obtained from this is connected to the photodiode 32a constituting the photocoupler 32 and the control device connected in series with it. It is supplied to the series circuit of transistor Q2.

A predetermined detection voltage obtained from a series circuit of a Zener diode 34 and a resistor 35 connected between terminals 8 and 9 is supplied to the control transistor Q2.

On the other hand, in the plus side overvoltage protection circuit 2o, the other phototransistor 32b constituting the photocoupler 32 is connected in parallel with the control transistor Q1 to the supply terminal of the DC voltage element B through respective resistance elements. This DC voltage element B has an intermediate tap derived from the secondary coil 1b, and the voltage obtained at the intermediate tap is rectified.

As a result, in the normal state, the control transistor Q2
maintains an off state, but when the negative DC voltage obtained between terminals 8 and 9 falls below a predetermined level, this is detected by control transistor Q2 and photodiode 32a is turned on.

When the photodiode 32a turns on, this is detected by the phototransistor 32b, and the thyristor 2
A predetermined gate signal is supplied to the gate No.3.

As a result, the terminals 7 and 8 are short-circuited, and the fuse 4 provided on the primary coil 1a side of the commercial power transformer 1 is blown out in the same manner as described above, and the load connected between the terminals 8 and 9 is exposed to the overvoltage. You will be more protected.

[Problems to be Solved by the Invention] Incidentally, in the power supply circuit 1o having an overvoltage protection function configured as described above, since it is necessary to detect negative overvoltage as well, a photocoupler 3 is installed as shown in FIG.
2, an overvoltage state on the negative side is detected, but when the overvoltage protection circuits 20 and 30 are provided on both the positive and negative sides, especially the overvoltage protection circuit 3o on the negative side is , an auxiliary power source 31 is required.

Moreover, it is necessary to transmit the negative side overvoltage state to the positive side overvoltage protection circuit 2o using a photocoupler.

As described above, the conventional configuration has the disadvantage that in addition to the photocoupler 32, the auxiliary power supply 31 is required to operate the negative side overvoltage protection circuit 30, making the circuit configuration complicated.

Therefore, the present invention proposes a power supply circuit having an overvoltage protection function that does not require a transmission means such as a photocoupler, and also eliminates the need for one auxiliary power supply and simplifies the circuit configuration. .

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, the first positive voltage is taken out from the secondary side of the transformer and supplied to the load, and the first positive voltage is A power supply circuit that performs an overvoltage protection operation of generating a first overvoltage detection output and supplying it to an overvoltage protection circuit when the voltage exceeds a predetermined level, and stopping supply of the first positive voltage to the load, the power supply circuit comprising: a transformer; extracting a negative voltage to be supplied to the load from the secondary side of the device, extracting a 20th positive voltage different from the first positive voltage, and dividing and extracting the differential voltage between the second positive voltage and the negative voltage; The configuration is configured to generate a second overvoltage detection output when the divided voltage becomes below a predetermined level, and to supply the second overvoltage detection output to the supply line of the first overvoltage detection output in the overvoltage protection circuit; Either the first or second overvoltage detection output is supplied to the overvoltage protection circuit to perform an overvoltage protection operation.

[Function] A positive voltage detection means 50a is connected to the thyristor 23, which is a control element, and a negative voltage detection means 50b can be connected in parallel thereto.

When the positive DC voltage becomes an overvoltage, the control transistor Q1 is turned on and the thyristor 23 is controlled to be in a conductive state.

Also, the fluctuation of the DC voltage on the negative side is caused by the operational amplifier 40.
and when this reaches a predetermined level or higher,
No. 48 is formed in which the output of the operational amplifier 40 is inverted and the thyristor 23 is turned on.

As a result, even if a negative overvoltage is detected, the load can be protected by, for example, blowing out the fuse 4 connected to the primary coil 1a.

[Embodiment] Next, an example of a power supply circuit having an overvoltage protection function according to the present invention will be explained in detail with reference to FIG. 1 and subsequent figures.

Also in this invention, the commercial power transformer 1 is used,
A commercial AC source 2 is supplied to the primary coil 1a side via a power switch 3 and a fuse 4. Also, part 2
A pair of secondary coils 1b and an IC are wound on the next side,
A positive side output terminal (first positive voltage deriving terminal) 7 is derived from one primary coil 1b.

Similarly, a terminal 9 for obtaining a predetermined negative DC voltage can be led out from the other secondary coil IC side.

Therefore, as in the past, a rectifier circuit 6 consisting of a diode D1 and a capacitor C1 is connected to the secondary coil 1b side, and a diode D is connected between the secondary coil IC and 1b.
2 is connected, and the rectifier circuit 11 is constructed by this diode D2 and capacitor C2. Then, a terminal 8 for obtaining a reference voltage (Ov) is led out from the cathode side of the diode D2.

In the present invention, an overvoltage protection circuit 50 is provided between the pair of output terminals 7 and 9, which operates in common against positive and negative overvoltages.

Therefore, in this example as well, the thyristor 23, which is a control element, is connected between the terminals 7 and 8, and the positive side detection means 50a and the negative side detection means 50b are connected to this gate.

As shown in the figure, the positive side detection means 50a includes a series circuit of a Zener diode 21 and a resistor 22 connected between terminals 7 and 8, and a control transistor Q1 connected to the midpoint of the connection.
It can be composed of

Similarly, the negative side detection means 50b has an operational amplifier 40,
The negative terminal has a predetermined divided voltage obtained from a voltage dividing resistor 41, 42 connected between the negative side terminal 9 and a predetermined DC power supply terminal (second positive voltage power supply terminal) 10B. Voltage is supplied.

The positive terminal is connected to the reference voltage from the reference terminal 8 (=O
V) is supplied. The output of the operational amplifier 40 is connected to the resistor 4
3 and a backflow blocking diode 44 to the gate of the thyristor 23.

Note that the detection means 50a provided in the overvoltage protection circuit 50
, 50b, the DC voltage element B explained in FIG. 2 is used for the DC voltage of one of them.

As this predetermined DC voltage element B, an intermediate tap can be derived from the secondary coil 1b, and a voltage obtained by rectifying the voltage obtained at the intermediate tap can be used.

The operation of the overvoltage protection circuit 50 configured in this manner will be described next.

In a normal operating state, the overvoltage state is not detected by the detection means 50a. Similarly, when the negative DC voltage obtained between the terminals 8.9 is within a predetermined range, the detection means 50. Since the detection output is not obtained from the terminal b, the thyristor 23 is kept in the off state in both cases.

However, for example, if the positive DC voltage obtained between terminals 7 and 8 exceeds a predetermined level, the control transistor Q1 is turned on, which makes the thyristor 23 conductive and the voltage between terminals 7 and 8 A short circuit occurs.

As a result, an overcurrent flows through the primary coil 1a and the fuse 4 is blown, so that the load connected between the terminals 7 and 8 can be protected from overvoltage.

Furthermore, if the negative output voltage obtained between the terminals 8 and 9 exceeds a predetermined level, the level of the negative terminal of the operational amplifier 40 increases roughly to the negative side.
A positive detection output is obtained from the operational amplifier 40.

Since this detection output is applied to the gate of the thyristor 23 via the resistor 43 and the diode 44, the thyristor 23 becomes conductive.

As a result, the fuse 4 is blown out in the same way as described above, and the load connected between the terminals 8 and 9 is protected from the overvoltage.

Furthermore, although the present invention has been applied to power supply circuits that do not have an output voltage stabilization function, the present invention can also be applied to power supply circuits that have a voltage stabilization function such as switching power supplies.

[Effects of the Invention] As described above, according to the configuration of the present invention, it is possible to correctly detect overvoltage of the negative DC voltage without using a photocoupler.

Furthermore, since the operational amplifier 40 is used to control the thyristor 23 based on its output, it is possible to use the same voltage as the DC voltage used by the positive side detection means 50a. As a result, there is no need to provide an additional auxiliary power source for the negative side detection means. As a result, the circuit configuration can be simplified.

Therefore, the power supply circuit having an overvoltage protection function according to the present invention is extremely suitable for application to the above-mentioned power supply circuit.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an example of a power supply circuit according to the present invention,
FIG. 2 is a connection diagram showing an example of a conventional power supply circuit. 1.φ.Commercial power transformer 2...Commercial AC source 4...Fuse 7...Plus side DC power terminal 9...Minus side DC power terminal 10...Power circuit 23...Control element 50 ...Overvoltage protection circuit 50a...Positive side detection means 50b...Negative side detection means Patent applicant Nippon Chemi-Con Co., Ltd.

Claims (1)

[Claims] (1) A first positive voltage is extracted from the secondary side of the transformer and supplied to the load, and when the first positive voltage exceeds a predetermined level, a first overvoltage detection output is generated to generate an overvoltage protection circuit. The power supply circuit performs an overvoltage protection operation of supplying the first positive voltage to the load and stopping the supply of the first positive voltage to the load, the power supply circuit extracting the negative voltage supplied to the load from the secondary side of the transformer and supplying the first positive voltage to the load. A second positive voltage different from the positive voltage is taken out, the difference voltage between the second positive voltage and the negative voltage is divided and taken out, and when the divided voltage becomes below a predetermined level, the second positive voltage is taken out. The overvoltage detection output is configured to generate an overvoltage detection output, and the second overvoltage detection output is supplied to a supply line of the first overvoltage detection output in the overvoltage protection circuit, and either of the first or second overvoltage detection output A power supply circuit characterized in that one of the two is supplied to the overvoltage protection circuit to perform an overvoltage protection operation.