voltage controlled current source design - Electronic Circuits Projects Diagrams Free

wtwendy · 23rd May 2009, 08:30 AM

I need a vccs with input range of 0-5V and output current range of 0-5A.
Can I use two op-amps with a BJT in the feedback path which is suggested by some website?
What are the main considerations in the VCCS design? If the above topology is ok, what are the requirements of the op-amp and BJT?

Thank you very much.

Hero999 · 23rd May 2009, 11:36 AM

Please post the schematic.

It sounds like a good way of doing it.

MikeMl · 23rd May 2009, 05:08 PM

Quote:

Originally Posted by wtwendy

I need a vccs with input range of 0-5V and output current range of 0-5A.
Can I use two op-amps with a BJT in the feedback path which is suggested by some website?
What are the main considerations in the VCCS design? If the above topology is ok, what are the requirements of the op-amp and BJT?

Thank you very much.

Look at this previous post.

Hero999 · 23rd May 2009, 07:42 PM

You might want to add an amplifier on the sense resistor so you can limit the drop-out voltage.

If you use a 100mΩ resistor for the sense, an op-amp with a gain of 10 would enable you to use it for 0-5V to 0 to 5A conversion with a maximum voltage loss of 0.5V.

Sceadwian · 23rd May 2009, 11:01 PM

For higher currents I'd definitely go with Hero's suggestion of an extra opamp so you can keep the sense resistor small. Aside from wasting less power as heat the lower heat in the sense resistor means it will be more linear, big sense resistors will also drop a lot of voltage so the whole circuit will be effectively DC biased above ground.

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23rd May 2009, 08:30 AM	#1
wtwendy	voltage controlled current source design I need a vccs with input range of 0-5V and output current range of 0-5A. Can I use two op-amps with a BJT in the feedback path which is suggested by some website? What are the main considerations in the VCCS design? If the above topology is ok, what are the requirements of the op-amp and BJT? Thank you very much.

23rd May 2009, 11:36 AM	#2
Hero999	Please post the schematic. It sounds like a good way of doing it. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

23rd May 2009, 07:42 PM	#4
Hero999	You might want to add an amplifier on the sense resistor so you can limit the drop-out voltage. If you use a 100mΩ resistor for the sense, an op-amp with a gain of 10 would enable you to use it for 0-5V to 0 to 5A conversion with a maximum voltage loss of 0.5V. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

23rd May 2009, 11:01 PM	#5
Sceadwian	For higher currents I'd definitely go with Hero's suggestion of an extra opamp so you can keep the sense resistor small. Aside from wasting less power as heat the lower heat in the sense resistor means it will be more linear, big sense resistors will also drop a lot of voltage so the whole circuit will be effectively DC biased above ground. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."