DC/DC converter

Claim 2

A DC/DC converter that converts a DC input voltage to a DC output voltage which is supplied to an electric load, the DC/DC converter comprising: a control unit producing a control signal on the basis of a voltage difference between said DC output voltage and a predetermined reference voltage, the control signal being a pulse width modulated control signal with a constant switching frequency; a switching element connected in series with a line for supplying said DC input voltage, and adapted to become ON-state or OFF-state in accordance with the pulse width modulation and constant switching frequency of said control signal, so as to obtain said DC output voltage having an output voltage level sufficient for said electric load; and a minimum ON-state duration setting unit defining a predetermined minimum value of an ON-state duration for which said switching element remains in ON-state and, when said DC output voltage level sufficient for said electric load is low, said minimum ON-state duration setting unit adjusts the control signal produced by the control unit to fix said ON-state duration to a value which corresponds to said predetermined minimum value defined by said minimum ON-state duration setting unit, to thereby control the ON-state and OFF-state of said switching element on the basis of the fixed ON-state duration.

Claim 3

A DC/DC converter as set forth in claim 1, wherein said minimum ON-state duration setting unit comprises a monostable multivibrator.

Claim 4

A DC/DC converter as set forth in claim 1, wherein said control unit comprises: an amplifier which compares said DC output voltage with a predetermined reference voltage to determine said voltage difference and amplifies said voltage difference; and a comparator which outputs a pulse width modulation signal in accordance with a comparison result obtained by comparing the amplified voltage difference with a voltage of a predetermined saw tooth wave, said control unit controlling the ON-state and the OFF-state of said switching element by utilizing said pulse width modulation signal as said control signal, wherein said minimum ON-state duration setting unit limits a voltage value of said saw tooth wave to a constant value so as to obtain an adequate minimum ON-state duration of said switching element, said comparator of said control unit compares a voltage difference value output from said amplifier of said control unit with the limited voltage value of said saw tooth wave and said DC/DC converter controls the ON-state and OFF-state of said switching element by changing a frequency of said pulse width modulation signal on the basis of said minimum ON-state duration of said pulse width modulation signal output from said comparator.

Claim 5

A DC/DC converter as set forth in claim 3, wherein said minimum ON-state duration setting unit includes a reference voltage source which generates a reference voltage having a voltage level higher than the lowest voltage level of said saw tooth wave.

Claim 6

A DC/DC converter as set forth in claim 1, wherein said DC/DC converter further comprises: a first serial circuit comprising a diode and a capacitor connected in series with each other with a node in between; and a second serial circuit comprising a diode and a capacitor connected in series with each other and arranged between the node of said first serial circuit and a ground terminal, said DC/DC converter operative to take out a voltage in which a voltage value thereof is equal to or larger than a voltage value twice as large as that of said given DC input voltage, from both terminals of said capacitor of said second serial circuit, and operative to define the taken out voltage as a driving voltage source for driving said switching element, said driving voltage source having a voltage value not smaller than said minimum driving voltage value of said switching element.

Claim 7

A DC/DC converter as set forth in claim 5, wherein the voltage between both terminals of said capacitor of said second serial circuit is adapted to be supplied to at least one other element than said switching element in the DC/DC converter or to a different DC/DC converter.

Claim 8

A DC/DC converter as set forth in claim 5, wherein said DC/DC converter further comprises a switch unit having an N-channel type field-effect transistor, and said DC/DC converter is operative to define the voltage between both terminals of said capacitor of said second serial circuit as a driving voltage source for driving said switch unit.

Claim 9

A DC/DC converter as set forth in claim 6, wherein said DC/DC converter further comprises a switch unit having an N-channel type field-effect transistor, and said DC/DC converter is operative to define the voltage between both terminals of said capacitor of said second serial circuit as a driving voltage source for driving said switch unit.

Claim 10

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to an electric load, the DC/DC converter comprising: a control unit receiving the DC output voltage and a reference voltage, determining a voltage difference between the DC output voltage and the reference voltage and producing a control signal corresponding to the voltage difference, the control signal being a pulse width modulated control signal with a constant switching frequency; a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state in accordance with the pulse width modulation and constant switching frequency of the control signal produced by the control unit, the duration in which the switching element is in the ON state being the ON state duration, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the electric load; and a minimum ON state duration setting unit determining a minimum value of the ON state duration and, when said DC output voltage level sufficient for said electric load is relatively low, the minimum ON-state duration setting unit adjusts the control signal produced by the control unit to set the ON state duration of the switching element to a value corresponding to the minimum value determined by the minimum 0N state duration setting unit.

Claim 11

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to an electric load, the DC/DC converter comprising: a control unit receiving the DC output voltage and a reference voltage, determining a voltage difference between the DC output voltage and the reference voltage and producing a control signal corresponding to the voltage difference, the control signal being a pulse width modulated control signal with a constant switching frequency; a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state in accordance with the pulse width modulation and constant switching frequency of the control signal produced by the control unit, the duration in which the switching element is in the ON state being the ON state duration, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the electric load; and a minimum ON state duration setting unit determining a minimum value of the ON state duration and, when said DC output voltage level sufficient for said electric load is relatively low, the minimum ON-state duration setting unit adjusts the control signal produced by the control unit to set the ON state duration of the switching element to a value corresponding to the minimum value determined by the minimum 0N state duration setting unit.

Claim 12

A DC/DC converter as set forth in claim 9, wherein said minimum ON state duration setting unit comprises a monostable multivibrator.

Claim 13

A DC/DC converter as set forth in claim 9, wherein said control unit comprises: an amplifier comparing the DC output voltage with the reference voltage to determine the voltage difference, and amplifying said voltage difference; and a comparator receiving the amplified voltage difference from the amplifier and a predetermined saw tooth wave, comparing the amplified voltage difference with the saw tooth wave, and producing a signal in accordance with the comparison, wherein the control unit uses the signal produced by the comparator as the control signal and controls the ON state and the OFF state of the switching element in accordance with the control signal, the minimum ON state duration setting unit limits a voltage value of the saw tooth wave to a constant value to obtain a minimum value of the ON state duration, the comparator of the control unit compares the amplified voltage difference of amplifier with the limited voltage value of the saw tooth wave and the DC/DC converter controls the ON state and the OFF state of the switching element by changing the frequency of the signal produced by the comparator on the basis of the minimum value of the ON state duration.

Claim 14

A DC/DC converter as set forth in claim 11, wherein the minimum ON state duration setting unit includes a reference voltage source which generates a reference voltage for determining the minimum value of the ON state duration, the reference voltage having a voltage level higher than the lowest voltage level of the saw tooth wave.

Claim 15

A DC/DC converter as set forth in claim 10, further comprising: a first serial circuit comprising a diode and a capacitor connected in series with each other with a node in between; and a second serial circuit comprising a diode and a capacitor connected in series with each other and arranged between the node of said first serial circuit and a ground terminal, the DC/DC converter operative to produce a voltage across the capacitor of the second serial circuit which is equal to or larger than twice the DC input voltage and to use the produced voltage for driving the switching element, the produced voltage not being smaller than the minimum driving voltage of the switching element.

Claim 16

A DC/DC converter as set forth in claim 13, wherein the voltage across the capacitor of the second serial circuit is supplied to the switching element and to other components inside the DC/DC converter.

Claim 17

A DC/DC converter as set forth in claim 13, further comprising a switch unit having an N-channel type field-effect transistor, the DC/DC converter using the voltage across the capacitor of the second serial circuit to drive the switch unit.

Claim 18

A DC/DC converter as set forth in claim 14, further comprising a switch unit having an N-channel type field-effect transistor, the DC/DC converter using the voltage across the capacitor of the second serial circuit to drive the switch unit.

Claim 19

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to a load, the DC/DC converter comprising: a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state, the duration in which the switching element is in the ON state being an ON state duration of the switching element, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the load; a control unit receiving the DC output voltage and a reference voltage, determining a voltage difference between the DC output voltage and the reference voltage and producing a control signal corresponding to the voltage difference, the control signal being a pulse width modulated control signal with a constant switching frequency; a minimum ON state duration setting unit determining a minimum value of the ON state duration, wherein when the DC output voltage level sufficient for the load is relatively high, the ON state and OFF state of the switching element is controlled in accordance with the pulse width modulation and constant switching frequency of the control signal produced by the control unit, and when the DC output voltage level sufficient for the electric load is relatively low, the ON state and OFF state of the switching element is controlled in accordance with the control signal produced by the control unit, where the minimum ON-state duration setting unit adjusts the control signal to set the ON state duration of the switching element to a value corresponding to the minimum value determined by the minimum ON state duration setting unit.

Claim 20

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to a load, the DC/DC converter comprising: a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state, the duration in which the switching element is in the ON state being an ON state duration of the switching element, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the load; a control unit receiving the DC output voltage and a reference voltage, determining a voltage difference between the DC output voltage and the reference voltage and producing a control signal corresponding to the voltage difference, the control signal being a pulse width modulated control signal with a constant switching frequency; a minimum ON state duration setting unit determining a minimum value of the ON state duration, wherein when the DC output voltage level sufficient for the load is relatively high, the ON state and OFF state of the switching element is controlled in accordance with the pulse width modulation and constant switching frequency of the control signal produced by the control unit, and when the DC output voltage level sufficient for the electric load is relatively low, the ON state and OFF state of the switching element is controlled in accordance with the control signal produced by the control unit, where the minimum ON-state duration setting unit adjusts the control signal to set the ON state duration of the switching element to a value corresponding to the minimum value determined by the minimum ON state duration setting unit.

Claim 21

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to a load, the DC/DC converter using both a pulse width modulation control technique and a constant ON-time control technique and comprising: a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state, the duration in which the switching element is in the ON state being an ON state duration of the switching element, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the load; and a mechanism for controlling the switching of the switching element according to the pulse width modulation control technique when the load is relatively high, and for controlling the ON state duration of the switching element according to the constant ON-time control technique when the load is relatively low.

Claim 22

A DC/DC converter that converts a DC input voltage to a DC output voltage and supplies the DC output voltage to a load, the DC/DC converter using both a pulse width modulation control technique and a constant ON-time control technique and comprising: a switching element connected to the DC input voltage and selectively switchable to an ON state and an OFF state, the duration in which the switching element is in the ON state being an ON state duration of the switching element, the switching element being selectively switchable to determine an output voltage level of the DC output voltage to be sufficient for the load; and a mechanism for controlling the switching of the switching element according to the pulse width modulation control technique when the load is relatively high, and for controlling the ON state duration of the switching element according to the constant ON-time control technique when the load is relatively low.