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Sci.Electronics.Basics -> Creating a voltage-controlled resistance
There are 26 messages in this thread.
You are currently looking at messages 20 to 26.
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Author: Clint SharpDate: 11:04 12-09-07
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In message <5kp554F4n0fiU1@mid.individual.net>, Phil Allison
<philallison@tpg.com.au> writes
>
>"David"
>
>
>** Go get CANCER and die
Welcome to my killfile Phil. What an evil thing to say you worthless
piece of... Please feel free to flame the heck out of me, maybe while
you're battering against my kill file you'll leave everyone else alone.
>
>
> YOU STINKING ASSHOLE
>
>
>
>
>
>........ Phil
>
>
--
Clint Sharp
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Author: gearheadDate: 12:03 12-09-07
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On Sep 11, 7:56 am, "David" <davidd31...@yoowhoo.com> wrote:
> I'm testing rechargeable batteries and would like a voltage-controlled
> resistance so I can easily adjust the load with a program.
>
> I'd appreciate recommendations on how to design this.
>
> Thanks,
>
> David
view in fixed font:
batt +
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s
,--------g n-channel
| d mosfet
| |
| /| |
| /-|----+
'--< | |
op amp\+|-, |
\| | Rsense
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Vref-----' |
gnd
This is a constant-current load,
controlled by Vref.
Current=Vref/Rsense
I know you asked for a "variable resistance,"
but you might want to reconsider.
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Author: Phil AllisonDate: 20:03 12-09-07
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"Clint Sharp"
** Go get CANCER and die
SHIT for BRAINS pommy PUKE !!
....... Phil
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Author: JamieDate: 18:37 13-09-07
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David wrote:
> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in
message
> news:AWEFi.51$ss5.20@newsfe04.lga...
>
>>David wrote:
>>
>>>I'm testing rechargeable batteries and would like a voltage-controlled
>>>resistance so I can easily adjust the load with a program.
>>>
>>>I'd appreciate recommendations on how to design this.
>>>
>>>Thanks,
>>>
>>>David
>>>
>>>
>>>
>>>
>>
>> Assuming you're talking about microchip processor coding or maybe
>>even from the PC port?
>> You can pulse width modulate (PWM).And drive a switching device like a
>>Power fet or bipolar transistor to regulate. Of course, you should also
>>monitor current. This would mean a device that has either a ADC (
>>Analog to Digital Converter) or, use a series of voltage comparator as
>>ranges to activate a few IO lines as inputs.
>>
>> There are small AVR's and PIC chips that have this ability.
>>My self, for this, I would use an AVR. But that's my preference.
>>
>>
>> Most Uc's have a PWM function in it that will use an IO or, you
>>can make one via a timer function.
>>
>> I don't know where you are at the level of electronics with this?
>>
>>--
>>"I'm never wrong, once i thought i was, but was mistaken"
>>Real Programmers Do things like this.
>>http://webpages.charter.net/jamie_5
>>
>>
>
>
> I have a DAQ card to control the active resistance and sample the
> current/voltage. Plan to use a shunt resistor to monitor the current. I
> studied transistors in college years ago but am quite rusty. You're
> suggesting using PWM to control the resistance? I'd like to drain the
> batteries with a steady current, wouldn't that cause it to alternate?
>
>
Alternate?, Not really, the signal is just an ON/OFF, not a +/- signal.
for example.
setting a carry of 50khz for the PWM and adjusting the duty cycle and
passing it through a Resistor will be very smooth as long as the
batteries are connected.
You'll want to pick a resistor that will not allow the driving device
to exceed it's max I (current) if fully shorted.
this same resistor can also be used as the current monitor shunt :)
a nice like differential input would work nicely for this to give you
a linear current range.
P.S.
when deriving the signal around this resistor for the current sense,
you'll want some by pass caps at the op-amp input to smooth off the
PWM signal so that you can get a rather steady reading. WIth a carrier
of 50Khz, they should be rather small.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: DavidDate: 10:49 14-09-07
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"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in
message
news:%JiGi.61$k77.53@newsfe12.lga...
> David wrote:
>
>> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net>
wrote in
>> message news:AWEFi.51$ss5.20@newsfe04.lga...
>>
>>>David wrote:
>>>
>>>>I'm testing rechargeable batteries and would like a voltage-controlled
>>>>resistance so I can easily adjust the load with a program.
>>>>
>>>>I'd appreciate recommendations on how to design this.
>>>>
>>>>Thanks,
>>>>
>>>>David
>>>>
>>>>
>>>>
>>>>
>>>
>>> Assuming you're talking about microchip processor coding or maybe
>>>even from the PC port?
>>> You can pulse width modulate (PWM).And drive a switching device like a
>>> Power fet or bipolar transistor to regulate. Of course, you should also
>>>monitor current. This would mean a device that has either a ADC (
>>>Analog to Digital Converter) or, use a series of voltage comparator as
>>>ranges to activate a few IO lines as inputs.
>>>
>>> There are small AVR's and PIC chips that have this ability.
>>>My self, for this, I would use an AVR. But that's my preference.
>>>
>>>
>>> Most Uc's have a PWM function in it that will use an IO or, you
>>>can make one via a timer function.
>>>
>>> I don't know where you are at the level of electronics with this?
>>>
>>>--
>>>"I'm never wrong, once i thought i was, but was mistaken"
>>>Real Programmers Do things like this.
>>>http://webpages.charter.net/jamie_5
>>>
>>>
>>
>>
>> I have a DAQ card to control the active resistance and sample the
>> current/voltage. Plan to use a shunt resistor to monitor the current. I
>> studied transistors in college years ago but am quite rusty. You're
>> suggesting using PWM to control the resistance? I'd like to drain the
>> batteries with a steady current, wouldn't that cause it to alternate?
> Alternate?, Not really, the signal is just an ON/OFF, not a +/- signal.
> for example.
> setting a carry of 50khz for the PWM and adjusting the duty cycle and
> passing it through a Resistor will be very smooth as long as the batteries
> are connected.
> You'll want to pick a resistor that will not allow the driving device
> to exceed it's max I (current) if fully shorted.
> this same resistor can also be used as the current monitor shunt :)
> a nice like differential input would work nicely for this to give you
> a linear current range.
>
> P.S.
> when deriving the signal around this resistor for the current sense,
> you'll want some by pass caps at the op-amp input to smooth off the
> PWM signal so that you can get a rather steady reading. WIth a carrier of
> 50Khz, they should be rather small.
>
>
>
> --
> "I'm never wrong, once i thought i was, but was mistaken"
> Real Programmers Do things like this.
> http://webpages.charter.net/jamie_5
>
>
I should have said fluctuate. One of the factors I'm interested in studying
is current draw so using PWM, a constant current, and a constant resistance
will give me a few things to compare. I'm planning on using a few of the
circuits suggested so I can become more familiar with the components and the
differences in the designs.
Thanks for the suggestions all!
Dave
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Author: MikeDate: 07:33 15-09-07
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<snip>
>I should have said fluctuate. One of the factors I'm interested in studying
>is current draw so using PWM, a constant current, and a constant resistance
>will give me a few things to compare. I'm planning on using a few of the
>circuits suggested so I can become more familiar with the components and the
>differences in the designs.
>
>Thanks for the suggestions all!
>
>Dave
>
>
>
Maybe something like this for an adjustable constant resistance.
PNP Darlington
--------------- ------------
| | v / |
--- | --- |
Battery - | | |
| | | |
=== | .-. |
GND | | | |
| | | |
| '-' |
| | |
| | |
0.1 Ohm to 100 Ohm |--------/^\-------- |
Adjustable constant | /- +\ | |
Resistance | '-----' | |
| | | | |
| | | === |
| | | GND |
100k .-. | | |
| |<------- -------------|
Digital pot | | .-.
'-' | |
| | | 0.1 ohm
| '-'
.-. |
100 | | |
Ohm | | ===
'-' GND
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===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
Mike
When truth is absent politics will fill the gap.
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