JPH0919081A - DC power supply circuit using AC adapter and battery - Google Patents

Abstract

(57) [Abstract] [Purpose] To increase the usage efficiency of the DC-DC converter, which is the load of battery energy, and to extend the battery life. [Structure] Plug 1 for DC-DC converter 30
The first diode 32 is interposed in the voltage applying circuit 2 and the third diode 36 is interposed in the voltage applying circuit of the battery 28.
The third diode 36 and the P channel MOS type FET
The drain and source circuits of 42 are connected in parallel, the gate of the P-channel MOS FET 42 is connected to the negative terminal of the battery 28, and the gate resistor 44 is connected between the gate and the cathode connection points of the first and third diodes 36. Connect in between.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply circuit for electronic equipment which can use both an AC adapter and a battery for converting AC of a commercial power supply into DC for output.

[0002]

2. Description of the Related Art Conventionally, AC is used in a DC power supply circuit of electronic devices.
The one that uses both the adapter and the battery is used to cope with the blackout of the commercial power supply voltage. FIG. 3 is a circuit diagram showing an example of such a DC power supply circuit using an AC adapter and a battery. In the figure, 10 is an AC adapter / battery DC power supply circuit, 12 is a cylindrical plug that connects to the main body (rectifier) of the AC adapter, and 14 is a jack paired with the plug. The inner peripheral wall 16 of this plug 12 is normally +
The pole and the outer peripheral wall 18 are negative pole two pole plugs. In addition, 20
Is a cord connected to the body of the AC adapter. Then, when the plug 12 is inserted into the jack 14, it opens.
As a contact opening / closing mechanism that closes when the plug is pulled out, a movable contact 24 with a spring 22 that contacts the negative pole of the outer peripheral wall 18 when the plug is inserted and a fixed contact 26 are provided.

Further, 28 is a backup battery, 30 is a DC-DC converter for applying the voltage of the plug 12 or for applying the voltage of the battery 28, and 32 is the inner wall 1 of the plug.
The first diode, which is interposed in the connection circuit between the + pole of 6 and the + pole input terminal of the DC-DC converter 30, and the second diode, which is interposed in the voltage application circuit of the battery 28 and is connected in parallel with the contact circuit of the jack 14, The diode 36 is a third diode which is interposed in the voltage application circuit of the battery 28 and is connected in series with the second diode 34. The DC-DC converter 30 generates a constant voltage at the output terminal 38 irrespective of fluctuations in the voltage of the plug 12, the battery 28, and the like.

The first diode 32 protects the DC-DC converter 30 when the inserted plug has a reverse polarity. Some commercially available AC adapter plugs have a negative pole on the inner peripheral wall and a positive pole on the outer peripheral wall. The second diode 34 prevents the battery 28 from being charged and the plug 12
It enables the discharge from the battery 28 when a power failure occurs with the plug inserted. Note that when a power failure occurs with the plug 12 inserted, the contacts 24 and 26 remain open. The third diode 36 also prevents the battery 28 from being charged, but when the battery 28 is mounted with a reverse polarity, the reverse current is blocked to protect the DC-DC converter 30. Therefore, when such an AC adapter / battery DC power supply circuit 10 is used, charging of the battery 28 is prevented with a simple circuit configuration, backup is performed in the event of a power failure, and AC
The DC-DC converter 30 provided inside can be protected even when the adapter or the battery 28 is attached in reverse polarity.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
8 is always used, as shown in FIG.
Since the current I is supplied to the DC-DC converter 30 via 6, the power loss due to the third diode 36 becomes a problem. Therefore, the utilization efficiency η 0 consumed by the DC-DC converter 30, which is the load of the battery energy, is obtained and examined. This utilization efficiency η 0 can be expressed by Equation 1 where R is the load resistance and VF is the forward voltage of the third diode 36. Further, if the equation 1 is transformed, the equation 2 is obtained.

[Equation 1]

[Equation 2]

As is clear from the equation 2, the utilization efficiency η0
Decreases as VF increases and I decreases. Usually V
Since F is a logarithmic function of I, VF is regarded as a constant, and a typical utilization efficiency η 0 is VF when a silicon diode normally used as the third diode 36 is used.
= 0.7V, I = 80mA, R = 100Ω, η0 = 92%. Therefore, when the battery 28 is used, the third diode 36 always causes a large power loss. Moreover, since the minimum operating voltage of the DC-DC converter 30 is specified, the minimum operating voltage of the third diode 36 falls earlier than the minimum operating voltage by the forward voltage VF of the third diode 36, and the life of the battery 28 is shortened.

The present invention has been made by paying attention to such conventional problems, and DC, which is a load of battery energy, has been made.
-An object of the present invention is to provide an AC adapter / battery-using DC power supply circuit that can increase the utilization efficiency consumed by the DC converter and prolong the battery life.

[0008]

Means for achieving the above object will be described below with reference to FIG. 1 and the like corresponding to the embodiments. In this AC adapter / battery DC power supply circuit 40, a cylindrical inner peripheral wall 16 has a + pole and an outer peripheral wall 18 has a − pole.
AC adapter with pole plug 12 and the plug 12
As a contact opening / closing mechanism that opens when the plug 12 is inserted and closes when the plug 12 is pulled out, a jack 14 having a movable contact 24 with a spring 22 that contacts the negative pole of the outer peripheral wall 18 when the plug 12 is inserted and a fixed contact 26, and a backup battery 28. ,
The DC-DC converter 30 for applying the voltage of the plug 12 or the voltage of the battery 28, and the plug 1
+ Of the inner peripheral wall 16 of 2 and + of the DC-DC converter 30
First diode 32 interposed in connection circuit with pole input terminal
And the voltage application circuit of the battery 28, the jack 1
The second diode 34 connected in parallel with the contact circuit of No. 4 and the voltage application circuit of the battery 28 of the second diode 34.
4 and a third diode 36 connected in series.

The second diode 34 is connected to the battery 2
Between the negative pole of 8 and the negative input terminal of the DC-DC converter 30, and the third diode is the positive pole of the battery 28 and DC-D.
It is connected between the + pole input terminal of the C converter 30 and the third diode 36 and the P channel MOS type F
The drain and source circuits of ET42 are connected in parallel, and the P
The gate of the channel MOS type FET 42 is connected to the − of the battery 28.
Connected to the pole, and its gate resistor 44 is connected to the gate and the first and third
It is connected between the cathode connection points of the diodes 32 and 36.

[0010]

With the above construction, when the polarity of the two-pole plug 12 to be inserted into the jack 14 is appropriate, the plug 1
The voltage of 2 can be applied to the DC-DC converter 30 via the first diode 32. Moreover, the third diode 36
In parallel with the drain of the P-channel MOS type FET 42,
The battery 28 is not charged even if the source circuit is connected. Further, the DC-DC converter 30 can be protected by the first diode 32 even when the plug 12 has a reverse polarity.
On the other hand, when the polarity of the battery 28 is properly connected, when a slight discharge current first flows from the third diode 36 through the gate resistor 44, the P-channel MOS type FET 42 becomes conductive, and the battery 28 is connected to the P-channel MOS type FET 42.
The discharge current enters the DC-DC converter 30 through the drain and source having a small ON resistance.

Therefore, the P channel MOS type FET 42
A discharge current does not flow in the third diode 36 except when the operation of No. 3 is started, and no power loss occurs in the third diode 36. Moreover, with respect to the DC-DC converter 30, the third
There is no influence of the forward voltage VF of the diode 36. In addition,
The resistance value of the gate 44 is very large. In addition, even when the battery 28 is installed in reverse polarity, the P-channel MOS type FET
The DC-DC converter 30 can be protected because the gate and source of 42 are reverse-biased and cut off.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing an AC adapter / battery DC power supply circuit to which the present invention is applied. This AC adapter / battery DC power supply circuit 40 is a conventional AC adapter / battery DC power supply circuit 10 with a P channel MOS type FET.
42 and its gate resistance 44 are added. Therefore, the same reference numerals are used for the same components and locations as those constituting the conventional circuit 10 to indicate the corresponding relationship. However, the second diode 34 is connected to the negative pole of the battery 28 and DC-DC.
The third diode 36 is connected between the one pole input terminal of the converter 30 and the + pole of the battery 28 and the DC-DC converter 30.
Connect to each of the + pole input terminals.

Then, the P-channel MOS type FET 42
Is connected in parallel with the third diode 36, and the anode and drain thereof and the cathode and source thereof are coupled. Further, the gate of the P-channel MOS type FET 42 is connected to the negative terminal of the battery 28, and its gate resistance 44 is connected between the gate and both cathode connection points of the first and third diodes 32 and 36. At that time, since a current constantly flows through the gate resistor 44, a high resistance of several MΩ is used to minimize the idle current to several μA.

When the AC adapter is used, when the polarity of the plug 12 inserted into the jack 14 is proper, the inner peripheral wall 16 is the positive pole, and the outer peripheral wall 18 is the negative pole, the voltage of the plug 12 is the first.
DC-D via diode 32, spring 22, ground, etc.
Join the C converter 30. At that time, if the polarity of the battery 28 is appropriate and its + pole is connected toward the + pole input terminal of the DC-DC converter 30, first the third diode 3 is connected.
A slight discharge current flows from 6 through the gate resistor 44, the gate-source voltage of the P-channel MOS type FET 42 becomes higher than the threshold value, and the drain and source of the FET 42 become conductive. However, since the voltage of the plug 12 is usually set higher than the battery voltage, there is no discharge of the load current from the battery 28 through the second diode 34. Also, battery 2
8 is never charged. Then, even when the inner peripheral wall of the inserted plug has a negative pole and the outer peripheral wall has a positive pole and has a reverse polarity, the first diode 32 causes the DC-DC converter 30.
Can be protected. Further, when the battery 28 is mounted with the reverse polarity, the third diode 36 is reverse biased.
T42 becomes a reverse bias and is in a cutoff state, and the battery 28 is not discharged.

When the battery 28 is used, if the polarity of the battery 28 is properly connected, a slight discharge current still flows from the third diode 36 through the gate resistor 44 at the beginning of discharging the battery 28. Then, from the battery 28 to the P-channel MOS type F
A large discharge current flows between the drain and the source of the ET 42 having a small ON resistance, and is almost shunted to the gate resistor 44 to almost flow into the + pole input terminal of the DC-DC converter 30. The circuit configuration in that case is shown in FIG. If the plug 12 is unplugged, the jack 14
The contacts 24 and 26 are closed. Therefore, the load DC
-The utilization efficiency η of the battery energy consumed by the DC converter 30 is obtained. This utilization efficiency η is the load resistance R, F
The equivalent resistance when the drain and source of ET42 are conducting is RO
If N and the gate resistance are RG, it can be expressed by Equation 3.

(Equation 3)

Therefore, the utilization efficiency η decreases as the load resistance RG decreases and RON increases. Normal gate resistance R
If G is 1 MΩ, it works well, and MOS type FET4
The resistance RON during conduction of No. 2 is 0.5Ω or less. Then, R
When the utilization efficiency η is calculated with G = 1 MΩ, RON = 0.5 Ω and R = 100 Ω, η = 99.5%. Therefore, M
When the OS type FET 42 and its gate resistance 44 are added,
The utilization efficiency is improved by several% as compared with the conventional AC adapter / battery DC power supply circuit 10, and the loss is almost eliminated. Moreover, during the normal discharge, the discharge current is changed to the third diode 36.
Since the DC-DC converter 30 is not affected by the forward voltage VF of the third diode 36, the life of the battery 28 is extended. Even when the battery 28 is mounted in reverse polarity, a reverse bias is applied between the gate and the source of the P-channel MOS FET 42 and a cut-off state occurs, so that a reverse voltage may be applied to the DC-DC converter 30. Absent.

[0017]

According to the present invention described above, the conventional A
P-channel MO for DC power supply circuit using C adapter and battery
By adding the S-type FET and its gate resistance, the continuous power loss of the third diode and the influence of the forward voltage on the DC-DC converter are eliminated, and the energy of the battery is consumed by the DC-DC converter. Greater utilization efficiency and longer battery life.

[Brief description of the drawings]

FIG. 1 is a diagram showing a DC power supply circuit using an AC adapter / battery to which the present invention is applied.

[Fig. 2] P-channel MOS for battery discharge when the same AC adapter / battery-using DC power supply circuit is unplugged
It is a figure which shows the circuit structure at the time of type | mold FET conduction | electrical_connection.

FIG. 3 is a diagram showing a conventional AC adapter / battery DC power supply circuit.

FIG. 4 is a diagram showing a circuit configuration of battery discharge in a state where the AC adapter / battery-using DC power supply circuit is pulled out.

[Explanation of symbols]

12 ... AC adapter plug 14 ... Jack 16,
18 ... Inner and outer peripheral wall 22 ... Spring 24, 26 ... Contact 2
8 ... Battery 30 ... DC-DC converter 32, 34,
36 ... 1st, 2nd, 3rd diode 40 ... AC adapter / battery use DC power supply circuit 42 ... P channel MOS
Type FET 44 ... Gate resistance

Claims (1)

[Claims] 1. An AC adapter having a 2-pole plug having a + pole on a cylindrical inner peripheral wall and a − pole on an outer peripheral wall, and a contact opening / closing mechanism that opens when the plug is inserted and closes when the plug is pulled out, and the outer peripheral wall when the plug is inserted. A jack having a movable contact with a spring and a fixed contact that come into contact with the negative electrode, a backup battery, a DC-DC converter that applies the voltage of the plug or the voltage of the battery, and the inner peripheral wall of the plug. Diode intervening in the connection circuit between the + pole and the + pole input terminal of the DC-DC converter, the second diode interposed in the battery voltage application circuit and connected in parallel with the jack contact circuit, and the battery voltage Intervening in the application circuit,
In an AC adapter / battery DC power supply circuit comprising a second diode and a third diode connected in series, the second diode is provided between the negative pole of the battery and the negative pole input terminal of the DC-DC converter, and the third diode. The diodes are respectively connected between the + pole of the battery and the + pole input terminal of the DC-DC converter, and the third diode and the drain and source circuits of the P channel MOS type FET are connected in parallel, and the P channel MOS type FET is connected. A is connected to the negative electrode of the battery, and its gate resistance is connected between the gate and both cathode connection points of the first and third diodes.
DC power supply circuit using C adapter and battery.