| 摘要 |
<p>A supply circuit comprising an FET as a series element in series with the load resistance. The supply circuit is fed from the mains network via a rectifier 54 and a smoother 52, causing a ripple voltage to be present on the input terminals 2-1 and 2-2. The direct voltage component of the input voltage is present across load resistance 60, the alternating voltage component of this voltage being present across transistor 10. With known supply voltage circuits the voltage drop across the series element is selected to be equal to the maximum peak-to-peak value of the alternating voltage component, causing unnecessary dissipation to be developed at a minor ripple amplitude. This will cause fast ageing of the series element. The supply circuit in accordance with the invention comprises a comparator 42 comparing the voltage across transistor 10 to a threshold voltage. Comparator 42 controls the charge on the filter capacitors 30 and 32. Consequently, the overall voltage across transistor 10 will never exceed the sum of the threshold voltage and the peak-to-peak voltage of the voltage component of the input voltage.</p> |
