| 摘要 |
<p>PURPOSE: To realize highly accurate measurement of current velocity while lowering the power supply voltage by enlarging the voltage range or supply power range for a heating element thereby attaining a drive circuit having single power supply easily. CONSTITUTION: A fluid temperature measuring body 3 and a heating element temperature measuring body 4 are connected in series with reference resistors 1, 2, respectively, and a resistor 6 for determining the difference of set temperature between the temperature measuring bodies 3, 4 is connected in series with the fluid temperature measuring body 3 thus constituting a bridge circuit. A differential amplifier 7 receives the voltage from the temperature measuring body 4 at a non-inverted input and the voltages from the temperature measuring body 3 and the temperature setting resistor 6 at an inverted input. Output of the differential amplifier 7 is connected with a butter circuit 11 comprising an emitter-earthed or source-earthed amplifier circuit 12A or 12B, and a source follower of a junction FET 21. Consequently, the voltage range of the heating element 5 can be enlarged from the collector-emitter breaking voltage of an NPN transistor 20A or the source-drain breaking voltage of an NMOS 20B to the power supply voltage.</p> |
