JPS6114275Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a starting circuit for a collector follower type stabilized power supply device, and its purpose is to improve the ripple suppression rate in a steady operating state.

FIG. 1 shows a conventional example. In the figure, 1 is a series control transistor used in the collector follower, 2 is an error detection amplification transistor, 3, 4,
5 is a resistor that divides the output voltage and applies it to the base of the error detection and amplification transistor 2, 6 is the emitter resistor of the error detection and amplification transistor 2, and 7 is a Zener diode. It constitutes the basic circuit of a stabilized power supply. This collector follower type stabilized power supply device is a well-known circuit, and a description of its steady operation and stabilizing action will be omitted. Here, 8 is a power switch, a-a' is an unregulated power supply input terminal, and bb' is a stabilized voltage output terminal.

It is well known that collector follower type stabilized power supply devices generally require a starting circuit in addition to the basic configuration described above. 1), or a resistor (not shown in Figure 1) between the base of the series control transistor 1 and the output terminal b.
(not shown in the figure) is used.

However, in this case, even in the event of an abnormality such as a short circuit in the load connected between output terminals b and b', input terminals a and
A problem arises in that current continues to be supplied from a.

In other words, in the case of the former starting circuit, when the load is short-circuited (i.e., short-circuited between output terminals b and b'), transistors 1 and 2 are cut off (this point is self-evident and will not be explained); Current continues to flow through the closed circuit of the power switch 8, the output terminal b-b', the resistor connected in parallel to the series control transistor 1, and the input terminal a'.

Furthermore, in the latter startup circuit, even if the error detection amplification transistor 2 is cut off when the load is short-circuited, the series control transistor 1 is controlled by the resistor connected between the base of the transistor 1 and the output terminal b.
Since the base current is supplied, there is some degree of conduction, and current continues to flow in the closed circuit of input terminal a, power switch 8, output terminals bb', collector-emitter of series control transistor 1, and input terminal a'. .

In order to eliminate this current after the load is short-circuited, a starting circuit as shown in FIG. 1 is used as an example of the conventional art. This startup circuit consists of resistors 9 and 1
0, a capacitor 11, and a diode 12, and is developed from the latter of the two startup circuits described above. That is, a resistor 9 is connected via a capacitor 11 between the base of the series control transistor 1 and the output terminal b.

To explain this startup circuit, when the power switch 8 is closed, the charging current of the capacitor 11 flows through the base-emitter of the resistor 9 - capacitor 11 - series control transistor 1, and this becomes the base current of the series control transistor 1. The series control transistor 1 is temporarily turned on. Therefore, a certain output voltage appears between the output terminals b and b', which causes the error detection amplification transistor 2 to conduct, supplying a base current to the series control transistor 1, and reaching a steady operating state.

When the power supply switch 8 is opened to stop the power supply, the charge of the capacitor 11 is transferred to the resistors 9 and 10.
The loop of diode 12 is discharged in preparation for the next power switch on.

That is, the resistor 10 and the diode 12 are a discharge loop of the capacitor 11, and when the power switch 8 is on, the diode 12 converts the charging current of the capacitor 11 into the base current of the series control transistor 1, and when the power switch 8 is off, capacitor 1
The purpose is to make the resistance value of the first discharge loop as small as possible to discharge quickly, and if this is not necessary, it may be replaced with a resistor.

In the conventional startup circuit shown in FIG. 1, when the load is short-circuited, the error detection amplification transistor 2 is cut off, cutting off the base current of the series control transistor 1. On the other hand, since the base current path of the series control transistor 1 consisting of the resistor 9 and capacitor 11 during switch-on is not connected in terms of direct current,
When the load is short-circuited, the base current of the series control transistor 1 is not applied. Therefore, even if the base current changes temporarily when the load is short-circuited, the current disappears after a certain amount of time. Note that there remains a current flowing through the resistor 10, but this current is compared to the current at the time of load short circuit in the case of the conventional startup circuit described above,
It can be made small enough to cause no practical problems.

However, in the conventional startup circuit shown in FIG. 1, during steady operation, the ripple voltage included in the input voltage is coupled to the base of the series control transistor 1 in an alternating current manner by the capacitor 11, so the performance of the stabilized power supply circuit is limited. A problem arises in that the ripple suppression rate (ratio of ripple voltages between input terminals a and a' and between output terminals b and b') is degraded.

The present invention eliminates the above-mentioned conventional drawbacks. The present invention will be explained below using FIG. 2 showing a specific example thereof.

FIG. 2 differs from FIG. 1 in that a diode 13 and a resistor 14 are added, and the other parts are the same as in FIG. 1, so a description thereof will be omitted. Here, the resistor 14 has a relatively high resistance.

To explain the operation of the starting circuit shown in Fig. 2,
The charging loop of the capacitor 11 when the power supply is switched on only includes the diode 13 mentioned above, and is composed of the resistor 9, the capacitor 11, and the diode 13 as in FIG.
becomes a temporary base current path for the series control transistor 1, and the series control transistor 1 becomes conductive, starting as a stabilized power supply circuit in the same way as in FIG. In Fig. 1, after the power is switched on, the capacitor 11 is finally charged to a voltage equal to the voltage drop between the base and emitter of the series control transistor 1 subtracted from the input voltage, but in the case of Fig. 2, a high resistance 14, the capacitor 11 is finally charged to the input voltage in the loop of the resistor 9, capacitor 11, and resistor 14. Therefore, diode 1
3 will eventually become reverse biased, and the series circuit of the resistor 9 and capacitor 11 of the starting circuit will be virtually disconnected from the base of the series control transistor 1, and the input voltage will not change as in the case of Figure 1. The included ripple voltage is not applied to the base of the series control transistor 1. Therefore, the ripple suppression rate can be improved compared to the conventional example.

Note that in the series circuit of the resistor 9 and capacitor 11, it goes without saying that the result will be the same even if the order of the resistor 9 and capacitor 11 is changed.

As is clear from the above explanation, according to the present invention,
When the load is short-circuited, current does not continue to flow in the power supply circuit, and ripple voltage is not applied to the base of the series control transistor during normal operation, which improves the ripple suppression rate, which is extremely advantageous in practice. becomes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power supply device, and FIG. 2 is a circuit diagram of a power supply device according to an embodiment of the present invention. 1... Series control transistor, 2... Error detection amplification transistor, 7... Zener diode, 9, 10... Resistor, 11... Capacitor, 1
2, 13...diode, 14...resistor.

Claims (1)

[Scope of utility model registration request] A series control transistor having an emitter connected in series to an input terminal and a collector connected to a load in series, an error detection amplification transistor for detecting an output voltage and controlling conductivity of the series control transistor, and a Zener diode, and A series circuit of a first resistor, a capacitor, and a first diode is connected between the base of the series control transistor and one output terminal to which the collector of the series control transistor is not connected, and a cathode of the first diode is connected. A second resistor having a relatively high resistance and a second diode are inserted so as to be connected to the base of the series control transistor, and between the anode of the first diode and the emitter of the series control transistor. A power supply device in which a parallel circuit is inserted in a direction in which the anode of a second diode is connected to the emitter of the series control transistor, and a third resistor is connected between the output terminal and the emitter of the series control transistor. .