JP2001025152A - Protection circuit against overcurrent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection circuit against overcurrent, which has a inverted deglegged-shape overcurrent protection property, so that the current value at which the protection circuit against overcurrent operates does not become a large value, as compared with a normal load current. SOLUTION: An inverted doglegged shape protective property against overcurrent is realized by combining a protective circuit Q3 against an overcurrent of constant power property, where when output voltage Vout is large, a protective circuit against overcurrent operates with a smaller load current, and when the output voltage Vout becomes small, the operation current of the protective circuit against overcurrent becomes large, and a protective circuit Q2 against overcurrent of 'Λ'-shaped property, where when the output voltage Vout is large, the protection circuit against overcurrent operates with a large load current, and when the output put voltage Vout is short-circuited to GND the protection circuit against overcurrent operates with a minimum load current with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit for a variable stabilized power supply circuit used in an ultrasonic diagnostic apparatus.
Particularly, the overcurrent protection circuit has an inverted character so that the current value at which the overcurrent protection circuit operates does not become larger than the normal load current.

[0002]

2. Description of the Related Art Conventionally, as a general characteristic of an overcurrent protection circuit of a stabilized power supply circuit, a U-shaped characteristic hanging type and a vertical hanging type are widely known.

In general, the load power of a stabilized power supply circuit is generally proportional to the output voltage. However, the load characteristics of a variable output stabilized power supply circuit used in an ultrasonic diagnostic apparatus are unique to the ultrasonic diagnostic apparatus. It has constant power load characteristics.

However, it is considered that the overcurrent protection circuit of the conventionally known general stabilized power supply circuit does not need the overcurrent protection having a constant power characteristic.

[0005]

Since the load of the variable output stabilizing power supply circuit of the ultrasonic diagnostic apparatus has the characteristic of a constant power load, the load current decreases when the output voltage is high.

On the other hand, the overcurrent protection circuit having a square-shaped characteristic operates such that the maximum load current flows when the output voltage is at the maximum value, as shown in FIG. For this reason, there is a problem in that the load power at the load current at which the overcurrent protection circuit having the foldback characteristic operates is larger than the load power at the normal time, compared to the load power at the maximum output voltage at the normal time. Was.

In order to solve the above problems, the present invention provides an overcurrent protection circuit having an inverted overcurrent protection characteristic so that the current value at which the overcurrent protection circuit operates does not become larger than a normal load current. It is intended to provide a circuit.

[0008]

In order to achieve the above object, an overcurrent protection circuit according to the present invention operates with a small load current when the output voltage is large, and operates when the output voltage is small. The overcurrent protection circuit has a constant power characteristic that increases the operating current of the protection circuit, and the overcurrent protection circuit operates with a large load current when the output voltage is large.
Combined with the over current protection circuit of the square-shaped characteristic that the over-current protection circuit operates with the minimum load current when short-circuited to GND, this allows the over-current protection characteristic to be inverted (see the right figure in Fig. 2). Is realized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a configuration of an overcurrent protection circuit according to a first embodiment of the present invention. As shown in FIG. The character-shaped overcurrent protection circuit 7 is characterized by comprising a combination of a constant-power overcurrent protection circuit and a square-shaped overcurrent protection circuit.

That is, in FIG. 1, the constant power overcurrent protection circuit compares the potentials at points b and d of the inverted overcurrent protection circuit 7 to determine whether the potential at point b is higher than the potential at point d. When the potential difference set in the overcurrent protection circuit 7 occurs, the constant power overcurrent protection function is set to operate.

The potential at point b is determined by the variable output voltage Vout and the load current flowing through R4 and R4 of the current detection resistor 4.
On the other hand, the potential at the point d is determined by the variable output voltage Vout, the input voltage Vin, and R5 and R6 of the constant power setting resistor 5.

When the variable output voltage Vout is large, the operation is performed such that the load current flowing through R4 of the current detection resistor 4 is a small value and the potential at point b becomes higher than the potential at point d. Variable output voltage Vout
Becomes smaller, the load current flowing through R4 of the current detection resistor 4 becomes larger and the potential at the point b becomes higher than the potential at the point d, thereby forming an overcurrent protection circuit with constant power characteristics.

The overcurrent protection circuit compares the potentials at points a and c of the inverted overcurrent protection circuit 7 and determines whether the potential at point a is higher than the potential at point c or vice versa. Character overcurrent protection circuit 7
When the potential difference set in the above is generated, it is set so that the foldback overcurrent protection function is activated.

The potential at the point a is determined by the variable output voltage Vout, the load current flowing through R4 of the current detection resistor 4, the load current flowing through R4 of the current detection resistor 4, and the R2 and R3 of the F-shaped characteristic setting resistor 3. Point c is the variable output voltage Vout itself.

When the variable output voltage Vout is large, the load current flowing through R4 of the current detection resistor 4 is large and the potential at point a is c.
It operates so as to be higher than the potential of the point. Variable output voltage Vo
When ut is short-circuited to GND, the operation is performed so that the load current flowing through R4 of the current detection resistor 4 is minimized, thereby forming an overcurrent protection circuit having a square-shaped characteristic.

The transistor Q1, the comparison amplifier 8, the R7 and R8 of the output voltage dividing resistor 9, and the variable reference power supply 10 constitute a variable output stabilized power supply. This variable output stabilized power supply may be any configuration, circuit, or component as long as it has the terminal and function of the overcurrent protection circuit.

FIG. 3 shows an actual circuit configuration of the inverted overcurrent protection circuit of FIG. As is clear from FIG. 3, a circuit is configured using two transistors. That is, the transistor Q2 operates as a square-shaped overcurrent protection circuit. Also, the transistor Q3 operates as a constant power overcurrent protection circuit. The transistor Q2 and the transistor Q3 operate as an inverted overcurrent protection circuit 7.

By using a circuit or a component having a function of comparing the potential difference between the points a and c and the points b and d of the inverted overcurrent protection circuit 7 other than the transistor, the inverted overcurrent can be obtained. It goes without saying that a protection circuit can be configured.

(Second Embodiment) FIG. 4 shows the configuration of an overcurrent protection circuit according to a second embodiment of the present invention. A stabilized power supply 11 is added to the configuration shown in FIG. By doing so, the condition for determining the potential by R5 and R6 of the constant power setting resistor 5 for setting the characteristics of the overcurrent protection circuit having the constant power characteristic is further simplified. In the present embodiment, by adding the stabilized power supply 11, even if the input voltage 1 fluctuates, stable constant power characteristics can be obtained.

[0020]

As described above, according to the present invention, since the load current of the variable output stabilized power supply of the ultrasonic diagnostic apparatus is controlled by the inverted characteristic, the power consumption when the variable output stabilized power supply is abnormal is reduced. This has the effect that heat generation at the time of abnormality can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an overcurrent protection circuit according to a first embodiment of the present invention;

FIG. 2 is a diagram showing overcurrent protection characteristics;

FIG. 3 is a diagram showing a more detailed circuit configuration of the overcurrent protection circuit according to the first embodiment of the present invention;

FIG. 4 is a diagram illustrating a configuration of an overcurrent protection circuit according to a second embodiment of the present invention.

[Explanation of symbols]

 3 F-shaped characteristic setting resistance (R2, R3) 4 Current detection resistance (R4) 5 Constant power setting resistance (R5, R6) 7 Reverse-shaped overcurrent protection circuit 8 Comparative amplifier 9 Output voltage dividing resistance (R7, R8) ) 10 Variable reference power supply 11 Stabilized power supply

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H02H 9/02 H02H 9/02 EF term (Reference) 5G004 AA04 AB02 BA03 BA04 DA02 DC10 FA01 5G013 AA02 AA04 AA09 BA01 CA10 5G053 AA01 AA02 BA01 BA04 CA04 CA07 DA01 EC03 FA07 5H430 BB01 BB09 BB11 BB12 BB13 EE02 EE12 FF04 FF08 FF13 GG08 HH03 JJ04 JJ07 LA01 LA06 LA13 LA15 LA17

Claims (3)

[Claims] 1. An overcurrent protection circuit for a variable stabilized power supply circuit used in an ultrasonic diagnostic apparatus, comprising a constant power overcurrent protection circuit and a square-shaped overcurrent protection circuit. An overcurrent protection circuit characterized by having an overcurrent protection circuit. 2. The constant power overcurrent protection circuit compares a potential between an input point of a current detection resistor and a middle point of a constant power setting resistor for setting a constant power characteristic, and determines that an input point of the current detection resistor has a constant power characteristic. The load current flowing through the current detection resistor is controlled so as not to become higher than the middle point of the constant power setting resistor. The middle point of the square-shaped characteristic setting resistor that sets the square-shaped characteristic is compared with the potential so that the middle point of the square-shaped characteristic setting resistor that sets the square-shaped characteristic is not higher than the output point of the current detection resistor. 2. The overcurrent protection circuit according to claim 1, wherein the overcurrent protection circuit controls a load current flowing through the current detection resistor. 3. The overcurrent according to claim 1, wherein a stabilized power supply is added to the input voltage to form a constant power overcurrent protection circuit that is not affected by the change in the input voltage. Protection circuit.