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mohammed elzaq · 8th October 2005, 04:34 PM

i want to design current source with around 12khz and variable amplitude (1 mA - 15 mA) using ic's not transistors
thanx

zachtheterrible · 8th October 2005, 04:59 PM

Quote:

Originally Posted by mohammed elzaq

i want to design current source with around 12khz and variable amplitude (1 mA - 15 mA) using ic's not transistors
thanx

A 555 timer with the output through a POT.

audioguru · 8th October 2005, 11:46 PM

A current source must be a very high impedance so that any change of load resistance doesn't cause the current to change.
You could use a very high voltage feeding its current through a very high resistance, or use the collector of a transistor.

mstechca · 9th October 2005, 02:48 AM

Actually, if you want to look at it, a transistor is considered an IC.

IC = Integrated circuit.

a transistor is a chain of 2 diodes with either both cathodes or both anodes connected together. it is the simplest IC, even though the complexity is low.

audioguru · 9th October 2005, 04:24 AM

You can't make a transistor with two diodes.
A transistor isn't a circuit. An IC is an entire circuit.

Thunderchild · 9th October 2005, 02:22 PM

he was only trying to convert mohamed to transistors instead of IC's and u went and spoilt it :twisted: 8) :!: :?: :idea: :arrow:

audioguru · 9th October 2005, 03:27 PM

Quote:

Originally Posted by Thunderchild

he was only trying to convert mohamed to transistors instead of IC's and u went and spoilt it :twisted: 8) :!: :?: :idea: :arrow:

What's wrong with using an opamp controlling a transistor current source at only 12kHz? The combination would have a lot higher output impedance than a single transistor or two.

Thunderchild · 9th October 2005, 04:55 PM

frankly i think he is at least a little bit confused else I am realy lost. why is 12 KHz necesary ? what has it got to do with a current source. if precision is not necesary he can just use a transistor with a suitable resistor on the base and measure the current with a tester and ajust until correct then just feed the base via the resistor with the 555 output. or make a precision current source like someone else will have to suggest and power it with the output of the 555 or even gate the current with another transistor.

**Nigel Goodwin** · 9th October 2005, 05:17 PM

Quote:

Originally Posted by Thunderchild

frankly i think he is at least a little bit confused else I am realy lost. why is 12 KHz necesary ? what has it got to do with a current source. if precision is not necesary he can just use a transistor with a suitable resistor on the base and measure the current with a tester and ajust until correct then just feed the base via the resistor with the 555 output. or make a precision current source like someone else will have to suggest and power it with the output of the 555 or even gate the current with another transistor.

As with many questions here, it's far too vague - he needs to give more details of exactly what he's wanting to do!.

This is the eighth reply, and we've no way of knowing if any of them has the slightest relevence?.

Thunderchild · 9th October 2005, 05:27 PM

PRECISELY :!:

audioguru · 9th October 2005, 06:26 PM

Maybe he wants to feed the 12kHz current source to the base of a transistor amplifier to avoid the high distortion caused by the transistor's transconductance non-linearity when it is fed by a voltage source.

Thunderchild · 9th October 2005, 06:49 PM

well until he tells us what he is about we can only make conjectures

**Nigel Goodwin** · 9th October 2005, 06:53 PM

Quote:

Originally Posted by Thunderchild

well until he tells us what he is about we can only make conjectures

Particularly silly ones :lol:

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8th October 2005, 04:34 PM	(permalink)
mohammed elzaq	using ic's i want to design current source with around 12khz and variable amplitude (1 mA - 15 mA) using ic's not transistors thanx

8th October 2005, 11:46 PM	(permalink)
audioguru	A current source must be a very high impedance so that any change of load resistance doesn't cause the current to change. You could use a very high voltage feeding its current through a very high resistance, or use the collector of a transistor. __________________ Uncle $crooge

9th October 2005, 02:48 AM	(permalink)
mstechca	Actually, if you want to look at it, a transistor is considered an IC. IC = Integrated circuit. a transistor is a chain of 2 diodes with either both cathodes or both anodes connected together. it is the simplest IC, even though the complexity is low. __________________ -=: The best low-priced components to troubleshoot with are the speaker and the LED :=-

9th October 2005, 04:24 AM	(permalink)
audioguru	You can't make a transistor with two diodes. A transistor isn't a circuit. An IC is an entire circuit. __________________ Uncle $crooge

9th October 2005, 02:22 PM	(permalink)
Thunderchild	he was only trying to convert mohamed to transistors instead of IC's and u went and spoilt it :twisted: 8) :!: :?: :idea: :arrow: __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

9th October 2005, 04:55 PM	(permalink)
Thunderchild	frankly i think he is at least a little bit confused else I am realy lost. why is 12 KHz necesary ? what has it got to do with a current source. if precision is not necesary he can just use a transistor with a suitable resistor on the base and measure the current with a tester and ajust until correct then just feed the base via the resistor with the 555 output. or make a precision current source like someone else will have to suggest and power it with the output of the 555 or even gate the current with another transistor. __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

9th October 2005, 05:27 PM	(permalink)
Thunderchild	PRECISELY :!: __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

9th October 2005, 06:49 PM	(permalink)
Thunderchild	well until he tells us what he is about we can only make conjectures __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk