Driving circuit of load
A driving circuit of a load has an output semiconductor element connected in series in a power supply path from a power source to the load, to control a current of the load, a PWM signal generator for controlling ON/OFF of the output semiconductor element, a driver of the output semiconductor element according to the PWM signal, a detection resistor made of a semiconductor detecting a current of the load, a current output amplifier outputting a monitored current of detection resistor without being influenced by variation of ambient temperature, a resistor converting the monitored current into a monitored voltage, a current source outputting a constant current without being influenced by variation of ambient temperature, a resistor outputting a reference voltage according to the constant current, and an A/D converter converting the monitored voltage according to the reference voltage into a detected current value of the current of the load.
1. A driving circuit of a load, having a first semiconductor element that is connected in series in a power supply path from a DC power source to the load and is turned on/off to control a current passing through the load, the driving circuit comprising:
a PWM signal generator configured to generate a PWM signal for controlling ON/OFF of the first semiconductor element;
a driver configured to drive the first semiconductor element according to the PWM signal;
a first resistance element made of a semiconductor, connected in series with the first semiconductor element and load, and configured to detect a current passing through the load;
a current detector configured to output a monitored current corresponding to the current passing through the first resistance element without being influenced by variation of ambient temperature;
a second resistance element configured to convert the monitored current into a monitored voltage;
an integrator configured to smooth the monitored voltage;
a current source configured to output a constant current without being influenced by variation of ambient temperature;
a third resistance element configured to output a reference voltage according to the constant current; and
an A/D converter configured to convert the smoothed monitored voltage according to the reference voltage into a detected current value of the current passing through the load, wherein
the PWM signal generator adjusting the PWM signal according to a target current value and the detected current value in such a way as to supply a target current to the load.
2. The driving circuit of claim 1 , wherein
the second and third resistance elements have the same temperature coefficient, the temperature coefficient indicating a ratio of change of resistance value with respect to temperature change.
3. The driving circuit of claim 1 , wherein
the second and third resistance elements are resistors made of the same material and having the same dimension.
4. The driving circuit of claim 1 , wherein:
the A/D converter includes a D/A converter configured to weight the current of the current source;
the third resistance element converts the weighted current into the reference voltage; and
the A/D converter also includes a comparator configured to compare the reference voltage with the smoothed monitored voltage and a logic configured to control bits of the D/A converter in such a way as to equalize the reference voltage and smoothed monitored voltage with each other.