a preferred embodiment of the present invention will now be described with reference to the accompanying drawings . in the following description , same drawing reference numerals are used for the same elements even in different drawings . the matters defined in the description such as a detailed construction and elements of a circuit are nothing but the ones provided to assist in a comprehensive understanding of the invention . thus , it is apparent that the present invention can be carried out without those defined matters . also , well - known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail . fig1 is a circuit diagram illustrating a construction of an inverter for lcd backlight according to the present invention . referring to fig1 the inverter for lcd backlight comprises a dc / ac converter 10 for performing a voltage transformation and operating a lamp , and a buck switch q 1 connected between an operational power vin and the dc / ac converter 10 for applying the operational power vin to the dc / ac converter 10 by performing on / off operations in accordance with an inputted control signal . the on / off control of the buck switch q 1 is performed by a dimming control . a dimming mode control section identified by the drawing reference numeral 100 in fig1 performs a pwm dimming control , an analog dimming control and a complex control according to the present invention . the drawing reference numeral op 1 in fig1 refers to an error amplifier for receiving a feedback signal f / b of the feedback part connected to a lamp by means of an inverting □ terminal and a signal a outputted from a first output terminal of the dimming control section 100 by means of a non - inverting + terminal , and comparing the feedback signal f / b with the signal a so as to output a compared result . the drawing reference numeral c 1 refers to a capacitor connected to an output terminal of the error amplifier op 1 and the non - inverting terminal . the drawing reference numeral op 3 refers to a second comparator for receiving an output signal of the error amplifier op 1 through the non - inverting + terminal and receiving an oscillating signal of an oscillator through the inverting − terminal so as to compare the two signals and control on / off operations of the buck switch q 1 in accordance with the compared result . the drawing reference numeral q 2 refers to a transistor for performing a function of a switching element by being connected between the output terminal and the ground terminal of the error amplifier op 1 . the drawing reference numeral op 2 refers to a first comparator for receiving a pyramidal wave having a predetermined cycle by means of the non - inverting + terminal , receiving a signal b outputted from the second output terminal of the dimming mode control section 100 , comparing the two signals , and supplying the compared signal to a base terminal of the transistor q 2 so that the output signal of the error amplifier op 1 can be switched on / off by switching on / off the transistor q 2 . an operation of the present invention having the above construction will now be described with reference to fig2 to 5 . an f / b terminal determines an output of the error amplifier op 1 by converging the voltage outputted from the first output terminal a of the dimming control section 100 in accordance with the range of the voltage . the dimming control section 100 controls the signal waveforms ( refer to the drawing reference numerals a , b in fig2 to 4 ) outputted from the first output terminal a and the second output terminal b thereof in accordance with the input conditions of the first dimming signal or the second dimming signal so as to be operated within the analog dimming range or the pwm dimming range . an analog dimming operation will now be described with reference to fig2 . if the voltage loaded on the mode selecting terminal ms of the dimming control section 100 is selected to be a ground potential , the dimming control section 100 recognizes the ground potential as an analog dimming mode , and outputs lineally escalating signals as identified by the drawing reference numerals “ a ” and “ b ” at the first output terminal a and the second output terminal b in accordance with variation of the first dimming signal ds 1 or the second dimming signal ds 2 . therefore , the pyramidal wave ( the drawing reference numeral “ c ” in fig2 ) is loaded as a ground potential to operate the pwm applied to the non - inverting data input terminal + of the first comparator op 2 . the output of the error amplifier op 1 is controlled by the signal ( the drawing reference numeral “ a ” in fig2 ) outputted from the first output terminal a of the dimming control section 100 when q 2 is off . subsequently , the output signal of the second comparator op 3 for controlling on / off of the buck switch q 1 is controlled by the signal ( identified by the drawing reference numeral osc in fig2 ) applied to the inverting terminal of the second comparator op 3 . thus , a pulse signal having a regular cycle is generated as a device output signal , as shown in fig2 to perform an analog dimming control . a pwm dimming operation will now be described with reference to fig3 . if the voltage loaded on the mode selecting terminal ms of the dimming control section is selected as a reference potential , the dimming control section 100 recognizes the reference potential as a pwm dimming mode , and outputs signals varying as identified by the drawing reference numerals “ a ” and “ b ” in fig3 at the second output terminal b . in other words , the signal “ a ” outputted from the first output terminal a maintains the voltage of a high level , while the signal “ b ” outputted from the second output terminal b is lineally varied . as a consequence , the pyramidal wave ( identified by the drawing reference numeral “ c ” in fig3 ) is of a waveform having a substantially regular cycle to perform the pwm operation applied to the non - inverting data input terminal + of the first comparator op 2 . the output signal of the first comparator op 2 does takes a waveform of a synthesized pulse rather than of a regular cycle due to the signal “ b ” outputted from the lineally escalating second output terminal b . the output of the error amplifier op 1 is always in a high state due to the signal “ a ” outputted from the first output terminal a . therefore , the signal actually applied to the non - inverting data input terminal of the second comparator op 3 is variable in accordance with the on / off operation of the transistor q 2 . to be specific , the transistor q 2 is switched on / off by the output signal of the first comparator op 2 . as a consequence , the signal applied to the non - inverting data input terminal of the second comparator op 3 is referred to “ err 1 out ” in fig3 . therefore , the output signal of the second comparator op 3 for controlling on / off of the buck switch q 1 is controlled by a value comparing the signal ( identified by the drawing reference numeral osc in fig3 ) applied to the inverting terminal of the second comparator op 3 with the signal ( identified by the drawing reference numeral err 1 out in fig3 ) applied to the non - inverting data input terminal of the second comparator op 3 . as a result , a pulse signal referred to as an “ out driver ” in fig3 is outputted to perform a pwm dimming control . a complex dimming control will now be described with reference to fig4 and 5 . the f / b terminal determines an output of the error amplifier op 1 by converging the voltage outputted from the first output terminal a of the dimming control section 100 in accordance with the range of the voltage . the dimming control section 100 controls the signal waveforms “ a ” and “ b ” outputted from the first output terminal a and the second output terminal b of the dimming control section 100 in accordance with the input conditions of the first dimming signal or the second dimming signal so as to be operated in the analog dimming range or the pwm dimming range . the pyramidal wave applied to the non - inverting data input terminal + of the first comparator op 2 is a waveform generated to operate the pwm in the pwm dimming range . when operated in the analog dimming range due to variation of the first dimming signal or the second dimming signal , the signals “ a ” and “ b ” outputted from the first output terminal a and the second output terminal b are lineally varied to control an output of the error amplifier op 1 . when operated in the pwm dimming range due to variation of the first dimming signal or the second dimming signal , the signal “ b ” outputted from the second output terminal b lineally operates , while the signal “ a ” outputted from the first output terminal a operates under a predetermined voltage so as to control an output of the error amplifier op 1 . therefore , the output of the first comparator op 2 performs a pwm operation with the on / off operation of the first switch q 1 in accordance with the duty variation of a circular wave . fig4 shows chronological variation of the dimming signal in the pwm operational range and the analog operational range . fig5 shows the dimming control section according to an embodiment of the present invention . when q 3 is switched off , the potential of the signal outputted from the first output terminal a is fixed due to the resistance ratio between the first resistor r 1 and the second resistor r 2 , and q 3 operates in the pwm dimming range from this stage . on the other hand , when the switching element identified as q 3 in fig5 is switched on , the potential of the signal “ a ” outputted from the first output terminal a is varied , and q 3 operates in the analog dimming range from this stage . in short , as shown in fig4 the dimming signal “ b ” of the lineal state performs the pwm dimming control until the point of time when the compared value , which is an output signal of the first comparator op 2 compared with the pyramidal wave of a regular cycle , is converted from a pulse to a ground potential . from the moment when the output signal of the first comparator op 2 has the ground potential , the dimming signal “ b ” follows the analog dimming control method . substantially , the point of time requiring the analog dimming is detected by reference to the dimming signal “ b ” and the pyramidal wave of a lineal state . the potential of the signal “ a ” outputted from the first output terminal a of the dimming control section 100 is varied at the point of detecting time . as a consequence , q 3 operates in the analog dimming range . fig5 is a schematic view showing an example of a minimum construction , rather than an actual construction , of an integrated circuit to perform a function of controlling the dimming mode control according to the present invention . referring to fig5 the integrated circuit comprises : a comparator for comparing the first dimming signal ds 1 with a reference signal , outputting the compared signal and feeding back the signal state of the second dimming signal ds 2 connected to the output terminal or the output signal per se to consider the state of the output signal ; a first circuit section for controlling the state of a signal outputted to the second output terminal b by reference to the signal loaded on the output terminal of the comparator ; a mode selecting section for controlling the state of a signal outputted to the third output terminal c b means of a mode selection signal ms , and controlling the state of an output signal from the first output terminal a ; and a second circuit section for generating a signal to distinguish the analog dimming from the pwm dimming by means of the mode selection control signal so as to be outputted through the fist output terminal a . the above construction is a description made from the functional point of view without considering any drawing reference numerals in fig5 . such a construction can be realized with a microcomputer , and a detailed cooperative relationship will be omitted here . as described above , the inverter for lcd backlight according to the present invention has advantageous effects of realizing a pwm dimming and an analog dimming by switching on / off an error amplifier without switching on / off an ic power as well as of stabilizing a circuit by reducing variation of the power and enhancing reliability of the ic . while the invention has been shown and described with reference to a certain embodiment thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims .