| 摘要 |
<p>PURPOSE:To reduce the titled circuit at its size and weight and to reduce the loss of heater voltage by providing said circuit with a potential selecting means for electrically selecting one potential out of plural potential values to be references for temperature setting. CONSTITUTION:An operational amplifier OP matches potential Vth supplied from a thermistor 2 with potential Vr electrically selected by an analog multiplexer 11 to hold temperature at a prescribed value. When the values of current IBE12, IBE13 between the bases and emitters of transistors (TR)12, 13 are sufficiently high, the potential Vht of a winding heater 5 becomes maximum and its value is expressed by the formula I , where VCE(M)13 is saturation voltage between the collector and emitter of the TR13 and is normally -0.1V. On the other hand, the limitation value Iht(LIM) of heat current Iht is expressed by the formula II and VF13, VF14 are the forward drop voltages of diodes D13, D14 respectively. If VDD=10V, Rht=50OMEGA and IBE13=0.02A, Vht(MAX) 9.1V is formed from the formula I and about 0.9V out of the voltage 10V of a power supply is lossed, so that 0.6V may be reduced as compared to an ordinary circuit.</p> |
