Re: Current source design (tricky?)

From: John Larkin (jjSNIPlarkin_at_highTHISlandPLEASEtechnology.XXX)
Date: 03/12/05 

Date: Sat, 12 Mar 2005 12:37:34 -0800

On Sat, 12 Mar 2005 10:00:25 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

>"Fred Bloggs" <nospam@nospam.com> wrote in message
> news:4233017B.3010007@nospam.com...
>>
>>
>> Fred Bloggs wrote:
>> [..rearrange that pull-up which may not even be necessary with these
>> power PMOS with VGS,th > 2V minimum...]
>>
>> View in a fixed-width font such as Courier.
>>
>> .
>> . +--------------------+-----+
>> . | | | PMOS
>> . | I-> | | +-------+
>> .VBATT>---+------+---/\/\-----+---------------------|s d|---->
>> . | | Rs 100m | | | | |
>> . / / / | | | g |
>> . 680 10k 10k | / +-------+
>> . / / / | 4.7k |
>> . \ \ \ LM741| / |
>> . | | | |\ | \ |
>> . | +------------|----|+\ | 330 |
>> . | | | | >-----+---/\/\----+
>> . | | +----|-/ |
>> . | | | |/ | |
>> . | | | | |
>> . | | +--||---------+
>> . | | | 1.5n |
>> . | / / |
>> . | 10k 10k |
>> . | / / |
>> . | \ \ |
>> . | | 330 | |
>> . Vd +-----------/\/\----+ |
>> . | | | |
>> . --- | / |
>> . \ / | 100 |
>> . --- | / |
>> . 1n4148 | \ |
>> . | | | |
>> . | | | |
>> . +------+------------+-------+
>> .
>
>Do you believe that your diode forward drop used as
>a reference will meet the OP's stated 5% accuracy
>requirement over the voltage and temperature range
>to be expected in an automotive application?
>

Cute circuit, but will probably have some resistor tolerance problems
too.

John

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