恒流源電氣類外文翻譯-電氣類(編輯修改稿)
2025-06-26 02:24 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 ntly large). Resistance R1 at resistor R1 is calculated asBZZS IKI VVR *1 ??? ,where, K = to 2 (so that R1 is low enough to ensure adequate IB), (m in)2)(FERECB h IIII ??? ,and hFE(min) is the lowest acceptable current gain for the particular transistor type being used. A more mon current source in integrated circuits is the current mirror. Simple transistor current source with diode pensation Temperature changes will change the output current delivered by the circuit of Figure 3 because VBE is sensitive to temperature. Temperature dependence can be pensated using the circuit of Figure 4 that includes a standard diode D (of the same semiconductor material as the transistor) in series with the Zener diode as shown in the image on the left. The diode drop (VD) tracks the VBE changes due to temperature and thus significantly counteracts temperature dependence of the CCS. Resistance R2 is now calculated as2R2 RBEzz I VVV ??? Since VD = VBE = V, Therefore, BZDZS IKI VVVR *1 ? ??? . Figure 4 This method is most effective for Zener diodes rated at V or more. For breakdown diodes of less than V, the pensating diode is usually not required because the breakdown mechanism is not as temperature dependent as it is in breakdown diodes above this voltage. Simple transistor current source with LED Another method is to replace the Zener diode with a lightemitting diode LED1 as shown in Figure 5. The LED voltage drop (VD) is now used to derive the constant voltage and also has the additional advantage of tracking (pensating) VBE changes due to temperature. R2 is calculated as 2R2 RBEDI VV ?? ,and R1 as BDDS IKI VV *R1 ??? , where ID is the LED current. Figure 5 Figure 6 Another mon method is to use feedback to set the current and remove the dependence on the Vbe of the transistor. Figure 6 shows a very mon approach using an op amp with the noninverting input connected to a voltage source (such as the Zener in an above example) and the inverting input connected to the same node as the resistor and emitter of the transistor. This way the generated voltage is across the resistor, rather than both the resistor and transistor. (For details, see the article on the ideal op amp the nullor.) The article on current mirror discusses another example of these socalled gainboosted current mirrors. Other practical sources In the case of opamp circuits sometimes it is desired to inject a precisely known current to the inverting input (as an offset of signal input for instance) and a resistor connected between the source voltage and the inverting input will approximate an ideal current source with value V/R. Inductor type current source Amongst other applications, the circuit of Figure 7 using the LM317 voltage regulator is used to present a source of constant current in Class E (switching) electronic amplif
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