Electricity: power supply or regulation systems – External or operator controlled – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
2002-08-06
2004-06-15
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
External or operator controlled
Phase controlled switching using electronic tube or a three...
C323S222000
Reexamination Certificate
active
06750642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC—DC converter and, more particularly, a DC—DC converter constructed such that a power consumed in the converter can be reduced in the state that a load applied to the converter is a light load and a driving method for the same.
2. Description of the Related Art
As is well known, the DC—DC converter functions to convert the input DC voltage into the different DC voltage, and is often used as the driving power supply for the DC driving circuit having the relatively light load. The output voltage of this DC—DC converter must be stabilized to the predetermined voltage value, and also the consumption power in the converter must be reduced as small as possible if the case that such DC—DC converter is installed into the mobile terminal, etc. is considered.
By the way, recently the organic EL display that employs the organic EL element as the light emitting source, for example, is watched with interest as the display means used in the above mobile terminal, etc. and there is a tendency to utilize this display. In order to lighten/drive the above organic EL element, normally the DC voltage of about 10 to 20 V is required. Therefore, in the case that this organic EL display is utilized in the mobile terminal or the vehicle equipment, the driving voltage value is insufficient and thus the driving voltage must be increased by the DC—DC converter.
In contrast, the output current of the DC—DC converter is largely varied according to the lighting state of the organic EL display. For example, the consumption current becomes large if the number of the lighted pixels is large and the lightening brightness at that time is high, while the consumption current becomes small if the number of the lighted pixels is small and the lightening brightness at that time is low.
FIG. 5
shows an example of the step-up type DC—DC converter that is employed preferably in the case that the above organic EL display is used as the load, for example. In
FIG. 5
, a symbol Vin denotes a power-supply input terminal of the DC—DC converter, i.e., a terminal to which the voltage that is fed from the primary battery, etc. is supplied. The coil L
1
is connected to the input terminal Vin, the diode D
1
is connected in parallel with the coil L
1
, and the cathode side of the diode D
1
constitutes the output terminal Vout. Then, the voltage holding capacitor C
1
is connected between the output terminal Vout and the reference potential point (earth). The output voltage of the converter, which is held by the capacitor C
1
, is supplied to the load
10
.
The voltage divider circuit
11
, which consists of the resistor R
1
and the resistor R
2
to detect the output voltage of the converter, is connected between the output terminal Vout and the earth. The detected voltage generated by this voltage divider circuit
11
is supplied to one input terminal of the error amplifier
13
constituting the error detecting circuit. Also, the reference voltage generated in the reference voltage generating circuit
12
is supplied to the other input terminal of the error amplifier
13
, so that the error output signal that is generated pursuant to the variation of the output voltage of the converter is output from the error amplifier
13
.
The error output signal generated by the error amplifier
13
is supplied to the regulator circuit
14
constituting the output voltage adjusting circuit. The gate terminal of the n-type MOSFET Q
1
serving as the switching element is connected to the output terminal of this regulator circuit
14
. Also, the drain terminal of the FET Q
1
is connected to the coil L
1
on the output terminal Vout side, and the source terminal thereof is grounded. Also, the reference clock signal that is fed from the reference clock generating circuit
15
is supplied to the regulator circuit
14
.
In addition, the operating power supply is supplied to the output voltage controlling means that controls the output voltage of the converter in the predetermined range, i.e., the voltage divider circuit
11
, the reference voltage generating circuit
12
, the error amplifier
13
, and the regulator circuit
14
, from the input terminal Vin and the output terminal Vout respectively.
In the above circuit configuration, if the FET Q
1
is turned ON by the control signal (switching signal) from the regulator circuit
14
, the current flows to the coil L
1
from the input terminal Vin and thus the electromagnetic energy is accumulated in the coil L
1
. Then, if the FET Q
1
is turned OFF, the electromotive force is generated in the coil L
1
by the energy accumulated in the coil L
1
and thus the current flows via the diode D
1
. Therefore, the voltage at the output terminal Vout is caused to increase. As a result, the voltage that is higher than that at the input terminal Vin generated at the output terminal Vout.
In the above DC—DC converter, normally two methods are known as the control method that maintains the output voltage in the almost constant range. One is the PWM (Pulse Width Modulation) system, and the other is the PFM (Pulse Frequency Modulation) system. The former PWM system controls to change the ON-time of the FET Q
1
serving as the switching element based on the difference between the voltage that is the divided voltage of the output voltage (detected voltage) and the reference voltage. That is, if the difference is large in the state of the reference voltage>the detected voltage, the time during which the FET Q
1
is turned ON is controlled to extend. Accordingly, the electromagnetic energy accumulated in the coil L
1
is increased and consequently the detected voltage is controlled such that such voltage is made equal to the reference voltage. Thus, the output voltage of the converter is controlled to stay in the predetermined range.
On the contrary, the latter PFM system sets the ON-time of the above FET Q
1
constant, and then controls such that the step-up operation is carried out by turning ON the FET Q
1
periodically if the difference is in the state of the reference voltage>the detected voltage while the step-up operation is not carried out by stopping the ON-operation of the switching element Q
1
temporarily if the difference become the state of the reference voltage≦the detected voltage. As a result, the detected voltage is controlled such that such detected voltage can be set equally to the reference voltage, and thus the output voltage of the converter can be controlled within the predetermined range. If any system is employed, the timing to start the step-up operation (ON-operation of the switching element Q
1
) can be set by the reference clock that is supplied by the above reference clock generating circuit
15
.
Meanwhile, as described above, in the DC—DC converter of this type, the operating power supply is always supplied to the output voltage controlling means that controls the output voltage of the converter in the predetermined range, i.e., the voltage divider circuit
11
, the reference voltage generating circuit
12
, the error amplifier
13
, and the regulator circuit
14
, from the input terminal Vin and the output terminal Vout respectively, and respective circuits are driven by this operating power supply. In other words, it is understood that the output voltage controlling means consisting of above respective circuits always consumes the power in the middle of the operation of the DC—DC converter.
Therefore, in the case that the organic EL display panel that is driven by the output voltage of the above DC—DC converter is considered, if the number of the lighted pixels is small and the lightening brightness at that time is low, the consumption current is very small. As a result, such a situation is brought about that the power consumed in the above output voltage controlling means of the DC—DC converter is in excess of the power consumed in the emission of the display panel. Although depending upon various conditions, sometime the power consumed in the output voltage controlling means o
Kuriki Shinji
Murakata Masaki
Noda Naoki
Riley Shawn
Tohoku Pioneer Corporation
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