JPH02219426A - Power circuit - Google Patents

Abstract

PURPOSE:To dispense with the provision of both of a load driving AC adapter and a charger and to allow the secondary current to be fully charged by using a constant voltage power supply section and a constant current power supply section depending on the output condition and further by providing a current limiting means. CONSTITUTION:After the input of commercial power supply was rectified by rectification circuits 15 and 16 in an AC/DC conversion section 2, it is converted into an almost constant DC value with capacitors C1 and C2 and inputted into the 1st and 2nd voltage sources 10 and 12 respectively. In charging a battery 7, no full charging will be made without giving the voltage higher than the battery rated voltage. The output voltage of an AC adapter 1 is detected by a battery voltage detection circuit 9. The constant current outputted from an impedance circuit 13 is then charged to the battery 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply circuit that enables power supply during driving of electronic equipment and charging of a secondary battery.

[Conventional technology]

AC adapters that convert commercial power to constant voltage used when driving portable electronic devices, etc. are used in place of secondary batteries (hereinafter referred to as batteries) such as nickel-cadmium batteries, so the output voltage is the battery voltage. It is desirable that the impedance is approximately equal to , and the impedance is low.

BACKGROUND ART As a charger for charging a battery, a charger is used in which an impedance element or the like is connected to a voltage source to limit the charging current of the battery. As the battery is being charged, the battery voltage increases and the charging current decreases, so in order to reduce this change, the voltage source must be set to a higher voltage (and the impedance must also be higher) than the rated voltage of the battery. There is.

In this way, the functions of an AC adapter and a charger are contradictory, so for electronic devices with built-in batteries, it is necessary to prepare an AC adapter and a charger separately, or to install a current limiting circuit to limit the charging current in the electronic device. The battery was being charged from the installed AC adapter.

[Problem to be solved by the invention]

In this way, in conventional electronic devices that use both an AC adapter and a charger, the AC adapter is used when using the electronic device, and the charger is used when charging the battery. It has to be replaced, which is very annoying.

In addition, electronic equipment with a current limiting circuit
In the case of nickel-cadmium batteries, the set voltage of the adapter is almost equal to the rated voltage of the battery.1. 2V/C
e1l), the voltage required for charging (1.5V/Ce1l
degree) is insufficient.

In view of the above points, the present invention provides a power supply circuit that satisfies the functions of both a constant voltage source and a charger.

[Means to solve the problem]

The present invention includes an AC/DC converter, a constant voltage power supply to which the output of the AC/DC converter is input and outputs a constant voltage output.
a constant current power supply section that receives the output of the AC/DC conversion section and outputs a constant current output, and connects the output of the constant voltage power supply section to the output of the constant current power supply section via a current limiting means for output. and a power supply circuit that prevents current from flowing from the constant current output to the constant voltage power supply section by the current limiting means when this output terminal becomes higher than a predetermined voltage.

[Effect]

With this configuration, when using electronic equipment, it is possible to supply almost the same voltage as the secondary battery to the load, and when charging the secondary battery, this power supply unit charges it up to the specified voltage, When the voltage exceeds the constant current power supply, the battery is fully charged by the constant current power supply, and current flow from the constant current power supply to the constant voltage power supply can be prevented by the current limiting means.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Figures 1 and 2 show a first embodiment of the present invention, in which 1 is an AC adapter (within this AC adapter 1, an AC/DC converter 2 for converting AC output into DC output is connected to a commercial power source). The output of the AC/DC converter 2 is connected to a constant voltage power supply 3 and a constant current power supply 4.The output of the constant voltage power supply 3 is connected to a switching element 5a, and the output of the constant voltage power supply 3 is connected to a switching element 5a. The output of 5a is connected together with the output of constant current power supply 4 to a load section 8, which is a portable electronic device having a load 6 and a battery 7. Here, the battery 7 is a secondary battery such as a nickel-cadmium battery. A battery voltage detection circuit 9 that detects the voltage of this load section 8 is connected to the input side of the load section 8 and controls switching of the switching element 5a.This switching element 5a and the battery voltage detection circuit 9 forms the switch means 5. Here, the switch means 5 is current limiting means.

The constant voltage power supply section 3 includes a first voltage source 10 and a first impedance circuit 11, and the constant current power supply section 4 includes a second voltage source 12 and a second impedance circuit 13.

FIG. 2 shows a specific embodiment of the present invention, in which the AC/DC converter 2 has the primary side of the transformer 14 detachably attached to a commercial power outlet with a power plug (not shown). The secondary side of the transformer 14 is connected to two rectifier circuits 15 and 16 in which four diodes are formed into a bridge, and smoothing capacitors CI and C2 are connected in parallel to the outputs of these rectifier circuits 15 and 16, respectively. It is connected.

The first voltage source lO and the second voltage source 12 have the same configuration,
A resistor R1 and a collector of an NPN transistor RI are connected to one output of the AC/DC converter 2, and a resistor R2 and a collector of an NPN transistor TR2 are connected, respectively. Further, the other of each of the resistors R1 and R2 is a transistor TRI.

Connected to the base of TR2. This transistor T
A Zener diode ZD1. is connected to the base of RI and TR2. Z
The cathode of D2 is connected, and the anode is connected to the other side of the AC/DC converter 2.

The emitters of the transistors TRI and TR2 are connected to the first impedance circuit 11 and the second impedance circuit 13 as outputs of the power supply circuit, respectively.

The first voltage source lO and the output are the first impedance circuit 1
1, and is connected to the collector of a PNP transistor TR3, which is a switching element 5a, through a resistor R3.

The emitter of the transistor TR2, which is the output of the second voltage source 12, is connected to the resistor R4 of the second impedance circuit 13 and the collector of the transistor TR4, and the other end of the resistor R4 is connected to the base of the transistor TR4 and the collector of the transistor TR5. The emitter of the transistor TR4 is connected to the base of the transistor TR5 and the resistor R5. The emitter of the transistor TR5 serves as an output of the second impedance circuit 13 together with one terminal of the resistor R5.

The output of the switching element 5a and the output of the second impedance circuit 13 are simultaneously detachably connected to the load section 8 by a connector (not shown) serving as an output end 17.

As described above, this load section 8 is an electronic device driven by the AC adapter 1 or the battery 7.

In addition, the battery voltage detection circuit 9 that detects the voltage of the battery 7 provided in the AC adapter 1 when charging the battery 7 detects the output voltage of the connector connected to the load section 8, so the battery voltage detection circuit 9 includes a resistor R6 and a resistor R7. The partial pressure of is input to the "+" input terminal of the comparator COM, and the "-j" of this comparator COM is input.
The reference voltage VRtF is input to each input terminal. The output of this comparator COM is input to the base of the transistor TR3 of the switching element 5. Here resistance R6
and R7 have relatively high resistance values, making it difficult for current to flow.

Next, the operation of this circuit will be explained. The input of the commercial power supply is rectified by the rectifier circuit Is, 16 of the AC/DC converter 2, and then converted to a substantially constant DC value by the capacitors CI, C2, and then the input voltage is transferred to the first voltage source IO and the second voltage source 12. is input.

This input voltage is applied to Zener diodes ZDI, ZD
Since it is larger than the zener voltage of 2, the zener diode Z
Zener current flows through the bases of transistors TRI and TR2 due to D1°ZD2, and they function as a constant voltage circuit.

The output of the first voltage source IO is connected to the first impedance circuit l
l, is supplied to the load section 8 through the switching element 5a.

The second voltage source 12 and the output are connected to the second impedance circuit 1
3 is input. This circuit constitutes a constant current circuit, and the current value is the base-emitter voltage V! of the transistor TR5! , E and resistor R5.
/ Becomes R5.

Then, the switch circuit 5 and the second impedance circuit 1
3 is simultaneously supplied to the load unit 8, but at this time, the impedance z1 of the first impedance circuit 11 and the impedance Z2 of the second impedance circuit 13 are Z2
>Zl, so when supplied to the load section,
The voltage becomes approximately equal to the voltage of the first voltage source IO.

When charging the battery 7, it cannot be fully charged unless a voltage higher than the rated voltage of the battery is applied, but the output voltage of the AC adapter l is detected by the battery voltage detection circuit 9, and the "+" input of the comparator COM is detected. When the voltage at the terminal becomes higher than the reference voltage V REF, the PNP transistor of the switching element 5a is turned off to prevent reverse current to the first voltage source. Then, the battery 7 is charged by the constant current output from the second impedance circuit 13. In this way, there is no leakage current from the output end to the constant voltage power supply section, and almost all the current flows to the battery 7. At this time, no voltage drop occurs due to leakage current. This constant current is the battery 7
The trickle current is approximately 1/20 to 1/30 c.

In this way, the battery is rapidly charged with a constant voltage until it reaches close to its rated voltage, and then charged with a weak current, so that it can be rapidly charged and the battery will not be destroyed even if it is charged for a long time.

In this way, by creating an AC adapter that has both a constant voltage source and a constant current source, it can fulfill the functions of an adapter for driving electronic devices and a battery charger at the same time, eliminating the need for a current limiting circuit in electronic devices. This allows portable electronic devices to be made smaller.

FIG. 3 shows another embodiment of the present invention, in which a diode DI is provided as current limiting means. By doing this, when the voltage of the load section 8 becomes higher than that of the constant voltage power supply section,
Cut off the electrical connection of the constant voltage source by diode DI,
Since the battery 7 is charged with a constant current, it is possible to provide an AC adapter that can drive a load and charge a battery with a very simple configuration.

The present invention is applicable not only to AC adapters but also to power supply circuits built into electronic devices.

〔Effect of the invention〕

As explained above, according to the present invention, a constant voltage power supply section and a constant current power supply section are used depending on the output state, so there is no need to prepare both an AC adapter and a charger for driving the load. By providing the current limiting means, when the voltage at the output terminal becomes higher than a predetermined voltage, there is no leakage current from the output terminal to the constant voltage power supply section, and all current from the constant current power supply section can be passed to the battery. Therefore, it is possible to provide a power supply circuit that can reliably charge the secondary current to full charge without causing voltage drop due to leakage current.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention, in which FIG. 1 is a block diagram, FIG. 2 is a circuit diagram, and FIG. 3 is a block diagram of another embodiment. l...AC adapter 2...AC/DC converter
3... Constant voltage power supply section 4... Constant current power supply section
5...Switch means (current limiting means)

Claims (2)

[Claims] (1) An AC/DC converter, a constant voltage power supply that receives the output of the AC/DC converter and outputs a constant voltage output, and a constant current power supply that receives the output of the AC/DC converter and outputs a constant current output. The output of the constant voltage power supply is connected to the output of the constant current power supply through a current limiting means to form an output terminal, and when the output terminal becomes higher than a predetermined voltage, the current limiting A power supply circuit characterized in that means prevents current from flowing into the constant voltage power supply section from the constant current output. (2) The power supply circuit according to claim 1, wherein the current limiting means is constituted by a diode.