JPH05161350A - Switching dc power unit - Google Patents

Abstract

PURPOSE:To suppress the power loss at normal connection of a battery by a protective circuit as low as possible by checking the current from the battery when the battery as a driving power source is connected in reverse polarity so as to protect the circuit. CONSTITUTION:A snubber circuit S2 is provided, which charges a capacitor C4 to a constant voltage being higher by the amount of the Zener voltage of a Zener diode ZD than the input voltage by a battery Ba at normal operation. The power loss at a protective circuit becomes light by applying the constant voltage of this snubber circuit S2 to the gate of a MOS type FET Q2 for protection through a MOS type FET Q3 for control, which maintains the ON condition at normal connection of the battery Ba, and supplying power through a MOS type FET Q2 for protection where the amount of voltage drop is extremely small in this ON condition. At reverse connection of the battery Ba, MOS type FETQ3 for control is turned off, and the FET Q2 for protection is turned off being reversely biased by the battery Ba through a resistor R3, whereby the circuit is protected from breakdown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching DC power supply device used in the construction of a power supply section of various electronic devices using a battery as a driving power supply.

[0002]

2. Description of the Related Art A conventional switching DC power supply device of this type has a structure as shown in FIG. That is, the DC power of the battery (Ba) is supplied to the primary winding of the high frequency transformer (T) through the protection diode (D1). And a control circuit for switching regulator (CC)
Has a configuration including a sawtooth wave generator and an error amplifier circuit, and has a pulse width according to the relationship between the output voltage (Vo) on the secondary side of the high frequency transformer (T) and the input voltage from the battery (Ba). The modulated drive signal is output through the resistor (R2), the N-channel switching MOS type FET (Q1) is switching-controlled at high speed by this drive signal, and the direct current is intermittently supplied to the primary winding of the high frequency transformer (T). Current flowing to the secondary side of the high frequency transformer (T) when the MOS type FET (Q1) is turned on is rectified by the diode (D3) and the capacitor (C3).
Smoothed and supplied to the load. The output voltage (Vo) supplied to this load is held at a constant value by variably controlling the pulse width of the drive signal output from the control circuit (CC). Further, the snubber circuit (S1) including the capacitor (C2), the diode (D2) and the resistor (R1) connected across the primary winding of the high frequency transformer (T) improves the efficiency and lowers the noise level. The capacitor (C1) is for noise absorption.

[0003]

By the way, the battery (B
The diode (D1) connected in the forward direction from the positive electrode side of a) toward the high frequency transformer (T) has a circuit side due to a rectifying function in which the diode (D1) conducts only in its own direction when the battery (Ba) is reversely connected. This is to prevent a reverse voltage from being applied to the circuit and protect the circuit from damage. However, there is a drawback that the forward voltage drop of the diode (D1) and the power loss due to the input current occur to lower the conversion efficiency. For example, even in a Schottky barrier diode having a small forward voltage drop, 0.4V to 0.6V
There is a voltage drop of some extent, which results in a considerable loss. Moreover, in this type of battery-driven switching DC power supply device, the input voltage is generally low and the input current is large, and the voltage drop of the protective diode (D1) is accompanied by the increase of the input current as described above. Due to its increasing nature,
In order to prevent the inconvenience such as the shortage of the operating voltage of the circuit due to the decrease of the conversion efficiency, the power loss further increases when the constant output voltage (Vo) is taken out as described above. It is necessary to increase the operable voltage of the circuit according to (1), and it remains difficult to effectively use the power of the battery (Ba). Further, as the voltage drop is large, the amount of heat generated is large, and the heat dissipating means becomes large in size, which in turn leads to an increase in the size of the entire device.

Therefore, it is a technical object of the present invention to provide a switching DC power supply device having a structure capable of suppressing power loss as much as possible while taking protection measures when a battery is reversely connected. ..

[0005]

As a technical means for achieving the above object, the present invention has a switching DC power supply device configured as follows. That is, the positive electrode connection part of the battery, the protection circuit part at the time of reverse connection of the battery, the primary winding of the transformer,
The switching MOS-type FET is connected to the negative electrode connecting portion of the battery through the N-channel switching MOS-type FET and is controlled by the control circuit supplied with power from the battery.
Switching control, and rectifying the secondary side of the transformer.
In a switching DC power supply device equipped with a smoothing circuit,
The protection circuit unit has a source and a drain connected to the positive electrode connection unit and one end of the transformer, respectively.
A channel protection MOS FET, a capacitor connected in series between the primary windings of the transformer and a diode in the reverse direction toward the other end of the secondary winding, and its cathode directed to the cathode of the diode. A snubber circuit composed of a Zener diode connected in parallel to the above, a source and a drain of which are connected to the cathode of the Zener diode and the gate of the protective MOS FET, respectively, and the gate of which is connected to the negative electrode connecting portion. It is characterized by being constituted by a channel control MOS type FET and a resistor connected between the positive electrode connecting portion and the gate of the protection MOS type FET.

[0006]

When the battery is connected to the normal polarity, the current from the battery flows through the parasitic diode existing between the source and drain of the N-channel protection MOS FET, and the control circuit is powered and activated. To do. On the other hand, a current flows from the anode of the Zener diode through the cathode to the source of the P-channel control MOS type FET. Since this MOS type FET is connected to the negative electrode connection part of the battery through its gate and is positively biased and is in the ON state at this time, the current flowing from the source to the drain of the MOS type FET is the gate of the protection MOS type FET. Reach

A switching MO is activated by activating the control circuit.
When the S-type FET starts switching control, in the snubber circuit, the capacitor is charged to a constant voltage higher than the input voltage from the battery by the Zener voltage of the Zener diode, and this voltage is the P-channel control MOS type F
MOS type FE for protection through source and drain of ET
Since it is applied to the gate of T, the MOS type FET is positively biased to be in a complete ON state. Since the amount of voltage drop in the MOS type FET in this ON state is much smaller than that of a diode or the like, the power loss is extremely small.

On the other hand, when connected in reverse polarity, the voltage of the battery is applied to the drain of the protective MOS type FET with a positive bias through the parasitic diode between the source and drain of the switching MOS type FET and the primary winding of the transformer. However, the voltage of the battery is the switching MOS type F
Control MOS type F through ET and forward diode
It is also applied to the source of ET and this control MOS type FET
Is turned off because the drain has a higher voltage than the source and is in a reverse bias state. This control MOS
When the type FET is turned off, the protective MOC type FET continues to maintain the off state because its gate is connected to the negative electrode of the battery through the resistor and is held in the reverse bias state.
The circuit is protected because no current flows.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an electric circuit diagram of an embodiment of the present invention, in which the same parts as those in FIG. 2 are designated by the same reference numerals. The difference from FIG. 2 is that the snubber circuit (S2) is connected in parallel to the capacitor (C4) and the fast rectifier diode (D4) and the capacitor (C4) connected in series between the primary windings of the high frequency transformer (T). It is composed of a Zener diode (ZD), an N-channel protection MOS FET (Q2) is connected instead of the protection diode (D1), and the gate (G) of this protection MOS FET (Q2) is reversed. Bias resistor (R
3) is connected to the positive electrode side of the battery (Ba), and P is provided between the gate (G) of the protection MOS FET (Q2) and the cathode of the Zener diode (ZD) of the snubber circuit (S2). The control MOS type FET (Q3) for the channel is connected, and the gate (G) of this control MOS type FET (Q3) is connected to the battery (B) via the pull-down resistor (R4).
It is connected to the negative side of a) and is a protective MOS type FET (Q2)
The gate (G) of the battery (Ba) through the resistor (R5)
It is only the structure connected to the positive electrode side of.

Next, the operation of the above embodiment will be described. The snubber circuit (S2) accumulates and consumes energy due to the leakage inductor, which is energy that cannot be transmitted by the high frequency transformer (T). During operation, the snubber circuit (S2) causes the capacitor (C4) to store more energy than the input voltage from the battery (Ba). A constant voltage higher by the Zener voltage of the Zener diode (ZD) is always charged to the polarity shown in the figure, and each MOS type FET (Q2), (Q3) is utilized by utilizing this constant voltage.
To protect the circuit when the battery (Ba) is reversely connected. That is, the snubber circuit (S2) and the MOS type FETs (Q2) and (Q3) for protection and control
This constitutes a protection circuit section when the battery (Ba) is reversely connected.

Now, when the battery (Ba) is normally connected to the polarity shown in the figure, the current from the battery (Ba) is changed to the protective MO.
The current flows through a parasitic diode existing between the source (S) and the drain (D) of the S-type FET (Q2), whereby the control circuit (CC) is powered and activated. In addition, the current passes from the anode in the forward direction of the Zener diode (ZD) through the cathode to the control MOS type FET (Q3).
Flows into the source (S) of. At this time, control MOS type F
The ET (Q3) is in the ON state because its gate (G) is connected to the ground level through the resistor (R4) and is positively biased. Therefore, the current flowing from its source (S) through its drain (D) is
The gate (G) of the OS type FET (Q2) is reached. At this start-up, the protection MOS FET (Q2) has the gate (G)
Is reverse-biased by being connected to the positive electrode of the battery (Ba) through the resistor (R3), and only the conductive state between the source (S) and the drain (D) is provided by the parasitic diode. That is, this is equivalent to the state in which the protective diode (D1) shown in FIG. 2 is inserted.

However, as described above, the control circuit (CC)
When the switching MOS type FET (Q1) is switched on and the power is supplied to the high frequency transformer (T), the snubber circuit (S2) causes the reactive power generated by the leakage inductor as described above to cause a capacitor. (C4) is charged to a constant voltage value higher than the input voltage by the Zener voltage, and this voltage is controlled by the control M
It is applied to the gate (G) of the protection MOS type FET (Q2) through the source (S) and drain (D) of the OS type FET (Q3). Therefore, protective MOS FET
(Q2) is positively biased to be in a completely ON state. The voltage drop in the protection MOS FET (Q2) in this ON state is due to the diode (D1) in the conventional device.
It is much smaller than the above and its power loss is extremely small.

On the other hand, when the battery (Ba) is erroneously connected to the opposite polarity, the positive voltage of the battery (Ba) is between the source (S) and the drain (D) of the switching MOS FET (Q1). Protective MOS FET (Q2) through primary winding of parasitic diode and high frequency transformer (T)
Applied to the drain (D) of the protection MOS-type FET
In (Q2), the drain (D) has a higher potential than the source (S) and is positively biased, but is held in an off state as described later. That is, on the other hand, the voltage of the battery (Ba) is directly applied to the gate (G) of the control MOS type FET (Q3), and the switching MOS type FET (Q3) is
Control MOS through the source (S) and drain (D) of 1) and the anode and cathode of the diode (D4).
Since it is applied to the source (S) of the type FET (Q3),
In the control MOS type FET (Q3), the source (S)
Since the drain (D) has a higher voltage and a reverse bias state than the drain (D), the drain (D) is turned off. This control MOS type FE
By turning off T (Q3), a protective MOC type FET (Q
In 2), the gate (G) is connected to the negative electrode of the battery (Ba) through the resistor (R3) and is held in a reverse bias state, and the drain (D) has a higher potential than the source (S). Despite being positively biased, it remains off so that no current flows and the circuit is protected from damage.

[0014]

As described above, according to the switching DC power supply device of the present invention, when the battery is connected to the normal polarity, in the snubber circuit, the zener voltage of the zener diode is smaller than the input voltage of the battery during operation. N-channel protection M through a control MOS type FET that constantly charges the capacitor to a constant high voltage and keeps this constant voltage in the ON state when the battery is connected to the normal polarity.
Applying to the gate of the OS type FET to turn on the FET,
Since the power is supplied to the circuit through the protection type MOS FET having an extremely small amount of this voltage drop, the voltage loss becomes small.

When the battery is connected in reverse polarity, the control MOS type FET is turned off, and the protection MOS type FET has its gate connected to the negative electrode of the battery through a resistor. It can be biased and held in the off state to reliably protect the circuit from damage.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a conventional device.

[Explanation of symbols]

 Ba battery Q1 switching MOS type FET Q2 protection MOS type FET Q3 control MOS type FET CC control circuit T transformer S2 snubber circuit C2 capacitor D4 diode ZD Zener diode R3 resistor D3 rectifying diode C3 smoothing capacitor

Claims (1)

[Claims] 1. A positive electrode connection part of a battery is connected to a negative electrode connection part of the battery through a protection circuit part at the time of reverse connection of the battery, a primary winding of a transformer and an N-channel switching MOS type FET, In the switching DC power supply device in which the switching MOS type FET is switching-controlled by a control circuit supplied with power, and a rectifying / smoothing circuit is provided on the secondary side of the transformer,
N-channel protection MOS-type FET in which a source and a drain are respectively connected to the positive electrode connecting portion and one end of the transformer, a capacitor connected in series between the primary windings of the transformer, and the other end of the secondary winding. , A snubber circuit composed of a diode in the reverse direction and a Zener diode connected in parallel to the capacitor with its cathode facing the cathode of the diode, the cathode of the Zener diode, and the protection MOS FET.
And a gate connected to a source and a drain of each of the gates, and a gate connected to the negative electrode connection portion, and connected between the P-channel control MOS FET and the positive electrode connection portion and the gate of the protection MOS FET. A switching DC power supply device characterized by comprising a resistor.