Driving device
A driving device comprises a first transistor (B 13 ), a second transistor (B 14 ), and a resistance element. The first transistor (B 13 ) has one terminal receiving a pulsed current and a control terminal connected to the one terminal. The second transistor (B 14 ) has one terminal connected to at least one load, the other terminal connected to a reference potential together with the other terminal of the first transistor (B 13 ), and a control terminal connected to the control terminal of the first transistor (B 13 ). The resistance element is connected between the control terminal of the first transistor (B 13 ) and the other terminal of the first transistor (B 13 ).
1. An LED driver comprising:
a voltage step-up and -down DC/DC converter controller block which controls a voltage step-up and -down DC/DC converter that generates from an input voltage an output voltage and feeds the output voltage to an LED; and
a current driver block which generates an output current of the LED,
wherein the voltage step-up and -down DC/DC converter comprises:
a first switch of which a first terminal is connected to an application terminal of the input voltage;
a first diode of which a cathode is connected to a second terminal of the first switch and of which an anode is connected to a ground terminal;
an inductor of which a first terminal is connected to the second terminal of the first switch;
a second switch of which a first terminal is connected to a second terminal of the inductor and of which a second terminal is connected to the ground terminal; and
a second diode of which an anode is connected to the second terminal of the inductor and of which a cathode is connected to an anode of the LED.
2. The LED driver according to claim 1 , wherein the voltage step-up and -down DC/DC converter controller block comprises:
an error amplifier which generates an error voltage by amplifying a difference between a cathode voltage of the LED and a predetermined LED control voltage;
a slope voltage generation portion which generates a slope voltage;
a PWM comparator which generates a comparison signal by comparing the error voltage with the slope voltage;
a driver control portion which generates a drive signal based on the comparison signal;
a first driver which turns the first switch on and off based on the drive signal; and
a second driver which turns the second switch on and off based on the drive signal.
3. The LED driver according to claim 2 , wherein the slope voltage generation portion outputs as the slope voltage a sum voltage of a triangular wave voltage of a predetermined frequency and a current detection voltage based on a current passing through the first switch.
4. The LED driver according to claim 2 , wherein the voltage step-up and -down DC/DC converter controller block further comprises a third switch which is turned on and off complementarily to the first and second switches based on the drive signal.
5. An LED driver comprising:
a voltage step-up and -down DC/DC converter controller block which controls a voltage step-up and -down DC/DC converter that generates from an input voltage an output voltage and feeds the output voltage to an LED; and
a current driver block which generates an output current of the LED,
wherein the current driver block comprises:
a current set portion which generates a reference current; and
a constant-current driver which generates the output current based on the reference current.
6. The LED driver according to claim 5 , wherein
the current set portion outputs a reference voltage based on the reference current to the constant-current driver, and
the constant-current driver generates the output current by repeating voltage/current conversion and current/voltage conversion based on the reference voltage.
7. The LED driver according to claim 6 , wherein the constant-current driver comprises a plurality of trimmable resistors for the voltage/current conversion and current/voltage conversion.
8. The LED driver according to claim 7 , wherein paired ones of the plurality of resistors are disposed in a staggered layout.
9. The LED driver according to claim 5 , wherein the current set portion sets the reference current based on a value of whichever is lower of a control voltage fed in externally and a constant voltage previously determined internally.