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From: Winfield Hill
Subject: Re: zero-power toggle circuit; was, how to master electronics
Date: 2 Nov 2002 18:13:55 -0800
Organization: Rowland Institute
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Fred Bloggs wrote...
> Winfield Hill wrote:
>> Kevin Aylward wrote...
>>> Wafer wrote ...
>>>> For instance, if I ask you to come up with a simple circuit
>>>> that would toggle power to a load on and off with each press
>>>> of a momentary switch, but draw no current in the off state,
>>>> what would you do? I would bet that your circuit would be
>>>> nothing like mine.
>>> It would be simple, using standard techniques that are known
>>> to work. There is no point reinventing the wheel. In this
>>> case a cmos JK or T flipflop driving a mos comes to mind.
>> I think Wafer has in mind a discrete transistor solution.
>> That's always a fun game. Here's my preliminary entry,
>> which features the ability to drive a 10 to 20A load and
>> should draw under a nA (room-temp FET leakage) when off.
>> ,------x-------------x----------x-----(o)---x---- power
>> | | 6.8k | | | 7 - 18V
>> +| 1uF '--/\/\--, V | __|__
>> === 25V | |/ __|__ | |
>> | x--| 2n / \ | |
>> | _|_ 10k | |\ 4403 /___\ | LOAD
>> x---o o---/\/\--x | | | |
>> | toggle | | 22k | |_____|
>> | '--- | --/\/\---x |
>> | 220k | x-----(o) --' to 15A
>> '-----/\/\-----------x |
>> | |---'
>> | ||<--,
>> x-----||---+ IRF540 etc
>> | |
>> | 6.8k |
>> '---\/\/---x-----(o)-------- return
>> It's assumed the user doesn't push the toggle switch more
>> than ~ 1/4 sec, and also waits a few seconds between each
>> toggle. One more part can be added it one desires the
>> circuit to power up in a defined state.
> Well- you're still drawing at least 7mW when it's on though,
> and this is not available to the load..
That's right, it comes about because the FET has up to 4000pF
of capacitance (at 0V) and the high ON currents overcome this.
With optimiztion, one added part, or different semiconductors
this issue might be laid to rest. :-)
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