GENERATING DOUBLE OUTPUT CURRENT FROM DUAL IC’s
V.Vidyalal, V. Sivanand and K. Rajasree,
Floyds Inc., "KAILAS"
EDAKKAD P.O, CALICUT,
INDIA - 673005
Or
V.Vidyalal
Uni-Tel. Inc, 8111 LBJ Freeway, Suite 1100
Dallas, Texas-75251,
USA
lal@uni-tel.com
Often a need arises for connecting a heavy load to an Op-amp. This generally calls for an additional buffer based on a transistor/MOSFET to drive the load. However if the load current demand is slightly higher than the Op-amps current output rating and too low for using a buffer, then the following circuit can be used to drive such loads from commonly available dual op-amps without overheating and hence self destruction of the IC. For eg., loads like Jumbo LED’s require high drive current and usually a transistor buffer is used to drive them. This additional transistor can be avoided by configuring a dual Op-amp in the manner as shown in the figure. Another commonly encountered problem is trying to drive a low quality inexpensive, relay which is a replacement for an imported one. The drive current will have to be slightly increased (large demand of drive current) or alternately this circuit can be used. The principle is illustrated by using a commonly available dual 741 type IC in the configuration as shown in the figure.
The popular LM741 IC’s are capable of delivering a max. of 20mA or infact 25mA absolute maximum). The dual Op-amp like the LM 1458 has similar characteristics of the LM741’s. In this circuit the LM 1458 is used as an e.g. Since each op-amp in this dual pack has somewhat similar specs like that of the LM 741.
In the circuit, R2 >> R3 and R3 is in the feedback loop. The current from OA1 i.e. I1 and from OA2 i.e. I2, add up at the node A to give a total of I1+I2. The double output current is available at the node A.. The output voltage can however be approximated by the well known equation Vout= Vin (1+R2/R1). If the input voltage is an audio signal, low impedance headphones can be connected at the output. This ofcourse would mean that no DC components are present in the input or should be removed by using an input capacitor.
In this context, it is worthwhile to mention to the inquisitive reader the availability of exotic high power Op-amps capable of delivering 30A ! (like the PA03 from Apex microtech. corp.). These power houses make the task easier for the designer since heavy loads can be directly connected to the output.
The circuit diagram of the above article can be obtained from the author:- lal@uni-tel.com
NOTES
WARNING AND DISCLAIMER
(!!!!!!!)Mains-powered equipment contain high AC voltages. These can be potentially lethal. If you do not know how to safely handle the inside of equipment containing high voltages, please do not attempt to open the equipment. Before carrying out any work inside equipment containing high Voltages, ensure that you disconnect the Unit from the Mains. (2) The information included herein is provided as-is, with no warranties expressed or implied. No responsibility on the part of the author is assumed for the technical accuracy of the information given herein or the use or mis-use of said information.
The equipment described in this article was designed, fabricated, and tested spending my own personal time and using my own personal resources.
The circuit diagram of the above article can be obtained from the author:- lal@uni-tel.com
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