JPH0543129B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply circuit serving as a power supply section of a facial beauty device, a medical instrument, and the like.

[Prior Art] For example, in a facial beauty device, as shown in FIG. 4 or 5, a current-limited power source (stabilized power source) A is used, and an oscillation prevention capacitor B is connected to the output side of the power source A. As shown in Figure 6, when the load current is less than the set value _I1 , the power supply A outputs the maximum output voltage.
It has a characteristic that it becomes a constant voltage of Vmax, and becomes a constant current when the set value _I1 is reached.

The difference between FIG. 4 and FIG. 5 is in how the reference voltage points are taken; in FIG. 4, it is on the ground GND side, and in FIG. 5, it is on the voltage Vcc side.

By the way, in the facial beauty device, the load C is the human body, so when the output changes from constant voltage to constant current, the charge stored in the oscillation prevention capacitor is discharged through load C. A transient current may flow through the human body, giving a sensation of electric shock.

[Object of the Invention] An object of the present invention is to provide a power supply circuit that does not cause a sensation of electric shock to the human body, which is the load, in a facial beauty device or the like.

[Summary of the Invention] The present invention uses a current-limited power supply with a characteristic that the maximum output voltage is a constant voltage when the load current is smaller than a set value, and a constant current when the load current reaches the set value, and an oscillation prevention device is installed on the output side. In the power supply section of a facial beauty device, etc. connected to a capacitor, the transition of the output from the constant voltage region to the constant current region can be detected instantaneously by changes in the base voltage of the detection transistor and changes in the emitter voltage with a delay of a certain time constant. The present invention is characterized in that it is detected by the ON operation of the oscillation prevention capacitor, and instantaneously turns on a short circuit transistor serving as a discharge circuit for the oscillation prevention capacitor, thereby discharging the charge of the capacitor.

[Example] Figures 1 and 2 show an example of the present invention, where A is the maximum output voltage Vmax when the load (output) current is smaller than the set value _I1 as shown in Figure 6. A current-limited power supply (stabilized power supply) with an output voltage-current characteristic that becomes a constant voltage and becomes a constant current when the set value _I1 is reached. B is an oscillation prevention capacitor connected to the output side of this power supply A, and the output There is a load C between the terminals.
is connected. D is an instantaneous short circuit connected in parallel with the capacitor B, and has a configuration as shown in FIG.

That is, the emitter of the detection PNP transistor Q ₁ is connected to an output terminal different from the reference voltage point via the resistor R ₁ , and the collector is connected to the terminal on the reference point side via the resistor R ₂ . B
It is connected to the base of NPN type transistor Q ₂ for the short circuit, which is the discharge circuit of . The base of the transistor _Q1 is connected to the output terminal side of the resistor _R1 via the resistor _R3 . Further, a voltage Vcc is applied to the emitter via a capacitor _C1 . The collector of said transistor Q ₂ is resistor R ₄
is connected to one end of the oscillation prevention capacitor B, and the emitter is connected to the other end of the capacitor N (output terminal on the reference point side).

Next, the operation will be described. When the output of power supply A transitions from the constant voltage region at the maximum output voltage to the constant current region, the output voltage decreases. In this case, since the reference voltage point is on the ground GND side, the potential on the output (+) side decreases. At this time, the base potential of the transistor _Q1 decreases, and the emitter potential also decreases according to the time constant of the resistor _R1 and the capacitor _C1 . That is, during the time constant of resistor R ₁ and capacitor C ₁ , transistor Q ₁ is turned on and transistor Q ₂
Also turns on. As a result, the oscillation prevention transistor
The charge on Q ₂ is discharged into a discharge circuit containing resistor R ₄ .
After this, the output voltage increases to the voltage indicated by the constant current. In other words, the output voltage is applied to the human body of the load C without causing an electric shock sensation.

In addition, although the above embodiment is a case where the voltage reference point is on the ground GND side, it can be implemented similarly when the voltage reference point is on the voltage Vcc side.

In that case, as shown in Fig. 3, the instantaneous short circuit D' has an NPN type transistor for the detection transistor Q' ₁ and an NPN type transistor for the short circuit transistor Q' ₂ .
A PNP transistor is used, but the reference voltage is
This is the same as described above except that the change in Vcc and output voltage is performed on the output (-) side, and the explanation thereof will be omitted.

[Effects of the Invention] As described above, according to the present invention, when the output changes from the constant voltage region to the constant current region, that is, at the moment when the output terminal of the facial beauty device comes into contact with the human body, which is the load,
When this voltage change is detected, the transistor in the shot circuit, which serves as the discharge path for the oscillation prevention capacitor, is turned on instantaneously, so that most of the charge in the oscillation prevention capacitor is discharged into the discharge path that includes the transistor. , and the electric shock sensation given to the human body is almost eliminated.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the power supply circuit according to the present invention, Fig. 2 is a circuit diagram of an instantaneous short circuit in the same embodiment, and Fig. 3 is a circuit diagram of an instantaneous short circuit when the voltage reference points are different. Figures 4 and 5
Each figure is a circuit diagram showing a conventional example, and FIG. 6 is an output voltage-current characteristic diagram of a current-limited power supply. A...power supply with current limit, B...capacitor for oscillation prevention, C...load, D and D'...instantaneous short circuit,
Q ₁ , Q' ₁ and Q ₂ , Q' ₂ ...transistors, R ₁ to _{R 4} ...
Resistor, C ₁ ...Capacitor.

Claims (1)

[Claims] 1. When the load current is smaller than the set value, the maximum output voltage becomes a constant voltage, and when the set value is reached, the current becomes constant. In the power supply section, the transition of the output from the constant voltage region to the constant current region is detected by an instantaneous ON operation based on a change in the base voltage of the detection transistor and a change in the emitter voltage with a delay of a certain time constant. 1. A power supply circuit characterized in that a short circuit transistor serving as a discharge circuit for an oscillation prevention capacitor is turned on instantaneously to discharge the charge in the capacitor.