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Temperature-compensated current source

Temperature-compensated current source: National Semiconductors’ LM334Z is a three-pin presettable current source, whose output may be set between 1 pA and 10 mA. It may be also be used ‘floating’.

In principle, just one resistor is needed for setting the current. However, the current is then strongly dependent on temperature: about +0.33% °C-1. (This would enable the device to be used as a temperature sensor). Therefore, to obtain a stable current source, an additional resistor and a diode are needed.

Temperature-compensated current source Schematic diagram

For good stability. the diode must be coupled thermally to the IC (the self-heating o the source is then compensated). This is best done by squeezing the IC and the diode, separated by heat paste, into a piece of insulating sleeving as shown in Fig. 2. Although the current source may be set between 1 pA and 10 mA with the aid of it is most accurate between 10 pA and 1 mA. The current provided by the source may calculate from
I= 2/15Rs

Temperature-compensated current source Schematic diagram
Resistor Rk should have a value of 1ORs. Set as described and with good thermal coupling between D1and 1C1, the prototype showed a temperature drift of not greater than 0.02% C-1, occurred at 5 Is= mA. All measurements were Carried out with supply voltage Of 9 V.

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