Load driving device, and lighting apparatus and liquid crystal display device using the same
A load driving device disclosed in the specification includes a power supply circuit for supplying to a load an output voltage converted from an input voltage, a detection voltage generation circuit for generating a detection voltage which varies depending on a magnitude of a voltage drop which across the load, and a control circuit for controlling the power supply circuit so that it performs output feedback control of the output voltage, on the basis of the detection voltage.
1. A load driving device comprising:
a power supply circuit for supplying to a load an output voltage converted from an input voltage;
a detection voltage generation circuit that is connected between the load and a ground, for generating a detection voltage which varies depending on a magnitude of a voltage drop across the load; and
a control circuit for controlling the power supply circuit so that output feedback control of the output voltage is performed based on the detection voltage,
wherein the detection voltage generation circuit includes:
a pnp type or a p-channel type transistor with an emitter or a source connected to one end of the load;
a first resistance with one end connected to a collector or a drain of the transistor;
a second resistance connected between one end of the load and a base or a gate of the transistor; and
an operational amplifier for controlling a voltage to be given to the base or the gate of the transistor so as to equalize the detected voltage at one end of the first resistance and the predetermined reference voltage.
2. A load driving device comprising:
a power supply circuit for supplying to a load an output voltage converted from an input voltage;
a detection voltage generation circuit that is connected between the load and a ground, for generating a detection voltage which varies depending on a magnitude of a voltage drop across the load; and
a control circuit for controlling the power supply circuit so that output feedback control of the output voltage is performed based on the detection voltage, wherein
the detection voltage generation circuit includes a constant-current source being connected in series with the load and flowing constant current that can be adjusted,
the control circuit generates a control signal of the power supply circuit so that a voltage of a connecting point of the load and the constant-current source becomes a constant voltage,
the constant-current source includes:
a constant-current circuit of variable current type;
an input side transistor for a current mirror connected in series with the constant-current circuit; and
an output side transistor for a current mirror to which a same control input as the input transistor for the current mirror is given, and
the constant current that can be adjusted is supplied to the output side transistor for the current mirror flows.
3. The load driving device according to claim 2 , wherein the constant voltage is higher than a saturated voltage of the output side transistor for the current mirror.
4. The load driving device according to claim 3 , wherein the power supply circuit includes:
a coil;
a switch for switching current conducting to the coil; and
a rectifying/smoothing circuit for rectifying/smoothing a voltage which appears at one end of the coil,
to generate the output voltage.