Output voltage detecting circuit

Details Output voltage detecting circuit Output voltage detecting circuit

2000-04-18

2002-07-23

Nguyen, Matthew (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

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

C323S285000

Reexamination Certificate

active

06424130

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an output voltage detecting circuit for a DC-DC convertor.
2. Description of the Related Art
As a conventional step-up type DC-DC converter, there has been known a circuit shown in FIG.
3
. That is, the circuit is made up of an error amplifier
101
, a reference voltage source
102
, a chopping wave generating circuit
103
, a voltage comparator
104
, a P-MOS transistor
105
functioning as a switching element, a Schottky diode
106
, a voltage dividing circuit
110
formed of a resistor
108
and a resistor
109
, and a smoothing circuit formed of a coil
107
and a capacitor
111
. A difference between a voltage at a terminal B resulting from dividing a voltage VOUT of an output terminal OUT by a voltage dividing circuit
110
and a voltage at a terminal A which is an output of the reference voltage source
102
is amplified by the error amplifier
101
. An output voltage of the error amplifier
101
and a chopping wave output by the chopping wave generating circuit
103
are compared with each other by the voltage comparator
104
, and the P-MOS transistor
105
functioning as the switching element is rendered conductive or nonconductive to obtain a constant regulated output voltage VOUT at the output terminal OUT.
In the case where the amplification degree of the error amplifier
101
is sufficiently large, and assuming that the resistance value of the resistor
108
is R
108
, the resistance value of the resistor
109
is R
109
and the voltage at the terminal A which is the output of the reference voltage source
102
is VREF, the voltage VOUT at the output terminal OUT is controlled so as to satisfy Expression (1).
V
OUT=(1
+R
108
/
R
109
)×
V
REF  (1)
The conventional step-up type DC-DC converter shown in
FIG. 3
suffers from a drawback in that the output voltage VOUT is boosted to be higher than the desired regulated output voltage when a load rapidly changes or a ripple voltage abnormally increases. When the output voltage VOUT greatly exceeds the desired regulated output range voltage, since an excessive voltage is applied to the load, there arises the problem that an electronic circuit connected to the DC-DC converter as the load maybe destroyed.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problem with the conventional DC-DC converter, and therefore an object of the present invention is to provide an output voltage detecting circuit which is capable of preventing the output voltage from abnormally increasing beyond the desired regulated output voltage range.
In order to achieve the above object, according to the present invention, there is provided an output voltage detecting circuit that monitors a voltage VOUT at an output terminal in the DC-DC converter, and immediately stops the operation of the DC-DC converter to prevent the output from further increasing when the output voltage abnormally exceeds the desired regulated output range voltage.


REFERENCES:
patent: 4016461 (1977-04-01), Roland
patent: 4536700 (1985-08-01), Bello et al.
patent: 5399958 (1995-03-01), Iyoda
patent: 5504418 (1996-04-01), Ashley
patent: 5770940 (1998-06-01), Goder

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