Current Source | Electronic Project Circuits

Posts Tagged ‘Current Source’

The Safe constant current source.

Figure the top is a Safe constant-current source circuit, how it works?
A cmos op-amp (number ICL 7611) controls the input current through a P-channel Hexfet power transistor (No. IRF 9520), then to keep up a constant voltage across the R1.
As they are connected in a serial form, so use the together current by: I = VREF /R1 , while the Vref to be defined by the IC2 is 1.25V.
The advantage of this outline are:
1. The load current is limited by R1 when the load is too heavy.
2. The op-amp and Hexfet there are the overhead voltage very low.

Be the first to comment - What do you think? Posted by admin - February 7, 2012 at 12:32 am

Categories: Power supply Tags: constant current source, Current Source, safe current limits

FET Current Source by BF256

When the LED is used for power supply output voltage is not constant. It may be damaged, it must be a constant current flowing through it. The N-Channel FET Current source no. BF256C is used, because easiest to use, as shown. The LED driver current is 15mA, which the resistor can be substituted for the better.

Be the first to comment - What do you think? Posted by admin - May 14, 2008 at 11:58 am

Categories: Power supply Tags: Current Source, current source led driver

current source based on JFET

We are now in a position to learn a practical way of implementing current sources. The circuit schematic below (which has been entered into the pSpice circuit simulator) shows a simple way of doing this using a JFET (see Lecture Notes page 86). Note that the symbol used for the JFET, type 2N3819, is not quite the same as the more widely accepted one we have encountered!

The negative terminal of the supply V1 (battery symbol) is connected to Ground, also known as Node 0, and represents the reference point for any measurements we might make. Although the battery voltage is indicated as 5V, pSpice will let us vary this experimentally over any required range. The current developed by the circuit flows in the drain circuit, and is in fact ID. For this application a light-emitting diode LED is shown as the load, in which the constant current flows. This is a very typical usage for this kind of circuit; the LED works most consistently (giving a steady light output) if the current passing through it can be maintained constant, even if the supply voltage changes – for example, as the battery discharges.