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Conversely, a current source provides a constant current, as long as the impedance of the load is sufficiently lower than the current source's parallel impedance (which is preferably very high and ideally infinite). In the case of transistor current sources, impedances of a few megohms (at low frequencies) are typical. Because power is current ...
Current in the reference transistor Q 1 is held constant, thereby fixing the compliance voltage. Plots assume I C1 = 10 mA, V A = 50 V, V CC = 5 V, I S = 10 fA, β 1, = 100 independently of current. The current dependence of the resistances r π and r O is discussed in the article hybrid-pi model. The current dependence of the resistor values is:
Clipping caused by current starvation of the input transistors is particularly pronounced in circuits with simple resistive "current sources", and in circuits where T2, T4 operate at fairly high current densities and thus exhibit strong beta droop. The use of electronic constant current sources and large-area, sustained-beta output transistors ...
There are three main specifications that characterize a current mirror. The first is the transfer ratio (in the case of a current amplifier) or the output current magnitude (in the case of a constant current source CCS). The second is its AC output resistance, which determines how much the output current varies with the voltage applied to the ...
This is the only first order source of mismatch in the three-transistor Wilson current mirror [8] Second, at high currents the current gain, β, of transistors decreases and the relation of collector current to base-emitter voltage deviates from = (). The severity of these effects depends on the collector voltage.
A constant current source circuit constructed with LM317. The device can be configured to regulate the current to a load, rather than the voltage, by replacing the low-side resistor of the divider with the load itself. The output current is that resulting from dropping the reference voltage across the resistor. Ideally, this is:
The JFET shares this constant-current characteristic with junction transistors and with thermionic tube (valve) tetrodes and pentodes. Constriction of the conducting channel is accomplished using the field effect: a voltage between the gate and the source is applied to reverse bias the gate-source pn-junction, thereby widening the depletion ...
Most commonly the active load is the output part of a current mirror [1] and is represented in an idealized manner as a current source. Usually, it is only a constant-current resistor that is a part of the whole current source including a constant voltage source as well (the power supply V CC on the figures below).
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