Power supply unit

Details Power supply unit Power supply unit

1995-03-29

1996-11-05

Nguyen, Matthew V.

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

323222, G05F 156

Patent

active

055721125

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a power supply unit employing a DC--DC converter which can be used in portable electronic equipment such as note-book type personal computers and the like.
2. Description of the Related Art
In small electronic devices using battery cells, the power supply voltage drops as the cells are discharged. In order to maintain the voltage used in electronic equipment constant, therefore, use is made of a DC--DC converter which converts the cell output to a predetermined value to stabilize the output voltage. Such a power supply device can be classified into the one of the voltage-dropping type in which a voltage higher than the voltage used in the equipment is supplied from the cells and is dropped through the DC--DC converter to a voltage that is used in the equipment and the one of the voltage-boosting type in which a voltage lower than a voltage used in the equipment is increased by the DC--DC converter to a voltage used in the equipment, depending upon the relationship between the voltage of the cells mounted in the electronic equipment (or the voltage of the AC adapter) and the voltage used in the electronic equipment.
Whether the electronic equipment employs the power supply of the voltage-dropping type or of the voltage-boosting type is determined depending upon the power consumption of the equipment, the operation time that must be possible without renewing the cells, the size of equipment, the weight of equipment, etc.
A related art will be described below, in detail, with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a conventional power supply unit which is provided with a DC--DC converter of the pulse width modulation (PWM) type, wherein reference numeral 200 denotes a DC--DC converter, 201 denotes battery cells, 202 denotes a control signal generator that generates signals for controlling the turn-on and turn-off of a transistor Tr1, symbol Vin denotes an input voltage, Vo denotes an output voltage, C1 denotes an input capacitor for removing power supply noise, Tr1 denotes a switching transistor for controlling 10 the voltage, L1 denotes a choke coil, D1 denotes a diode, C2 denotes a smoothing output capacitor, R1 and R2 denote voltage-dividing resistors which detect a change in the output voltage and produce an output voltage detect signal EIN, R3 and R4 denote voltage-dividing resistors for forming a reference voltage to generate a stable operation signal DT for the control signal generator, and C3 denotes a capacitor which stabilizes the operation when the DC--DC converter is started, i.e., increases the level of stable operation signal when the power supply is started in order to gradually increase the high-level period of a control signal output by a comparator 211 (see FIG. 2) in the control signal generator 202.
In the constitution of FIG. 1, the control signal generator 202 generates a signal for turning on or off the transistor Tr1 that controls the output voltage. When the transistor Tr1 is turned on, energy is supplied from the cells 201 to the choke coil L1 (hereinafter referred to as coil L1) and is stored therein. Due to the energy stored when the transistor Tr1 is turned off, a fly-back current flows through coil L1--capacitor C2--diode D1 to produce an output voltage Vo across the voltage-dividing resistors R1 and R2. The control signal generator 202 generates a control pulse having a small duty ratio when the output voltage Vo is higher than the reference voltage and generates a pulse signal having a large duty ratio when the output voltage Vo is lower than the reference voltage. Accordingly, the transistor Tr1 is turned on for a short period of time when the output voltage Vo is high and is turned on for a long period of time when the output voltage Vo is low, so that the output voltage Vo is stabilized.
FIG. 2 illustrates a conventional control signal generator, wherein reference numeral 202 denotes a control signal generator and 210 denotes an error amplifier (ERR-AMP)

REFERENCES:
patent: 4504898 (1985-03-01), Pilukaitis et al.
patent: 4551668 (1985-11-01), Kammiller
patent: 4580090 (1986-04-01), Bailey et al.
patent: 4942509 (1990-07-01), Shires et al.
patent: 5134355 (1992-07-01), Hastings
patent: 5264782 (1993-11-01), Newton
patent: 5359276 (1984-10-01), Mammano

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