Re: 0.20 delay in 6v control circuit

From: Bob (bfraser1www_at_optonline.net)
Date: 11/10/04 

Date: Wed, 10 Nov 2004 03:11:55 GMT

On Wed, 10 Nov 2004 00:06:46 GMT, Robert Monsen
<rcsurname@comcast.net> wrote:

>Bob wrote:
>> On Mon, 08 Nov 2004 22:10:19 GMT, Robert Monsen
>> <rcsurname@comcast.net> wrote:
>>
>>
>>>(fixed top posting below. Please post replys after the main body of
>>>text. It's just convention here)
>>>
>>>Bob wrote:
>>>
>>>>On Mon, 08 Nov 2004 07:37:01 GMT, Robert Monsen
>>>><rcsurname@comcast.net> wrote:
>>>>
>>>>
>>>>
>>>>>Here is a slightly better circuit for you needs:
>>>>>
>>>>> 6V
>>>>> ----------------------------o--o
>>>>> | | |
>>>>> | - C|
>>>>> | o ^ C| Relay Coil
>>>>>|=| switch | C|
>>>>> | o | |
>>>>> | '--o
>>>>> | |
>>>>> | 10k |/
>>>>> o---/\/\/--o-----o-----------|
>>>>> | | | |>
>>>>> | | | |
>>>>> o----|<----| | + |
>>>>> | * --- 220uF |
>>>>> / --- |
>>>>> \ | |
>>>>> / 1k | |
>>>>> \ | |
>>>>> | | |
>>>>> | | |
>>>>> '----------------o-------------'
>>>>> GND
>>>>>
>>>>> * Schottky Diode
>>>>>
>>>>>created by Andy´s ASCII-Circuit v1.25.250804 www.tech-chat.de
>>>>>
>>>>>The base will drop immediately from 850mV to about 200mV when the switch
>>>>>is opened, due to the 1k resistor and the schottky diode. When the
>>>>>switch is closed again, the base will come up from 200mV to about 850mV
>>>>>before the transistor conducts, so
>>>>>
>>>>>V(t) = V ( 1 - exp(-t/RC) )
>>>>>
>>>>>thus
>>>>>
>>>>>t = -ln(1 - .65/6) * 10k * 220u
>>>>> = .25s += 0.05s
>>>>>
>>>>>Once the cap is charged up, the current will be about 500uA, so the
>>>>>current through the transistor can go up to 25mA (assuming a beta of 50).
>>>>
>>>>
>>>>Thanks again Robert,
>>>>
>>>>Do you have any idea on the specs for the diodes needed. I went to
>>>>pick up the Schottky diode and the one in parallel with the relay but
>>>>was not able to choose from the variety available. Thanks for the
>>>>design.
>>>>
>>>>Bob
>>>>
>>>>
>>>
>>>You can use any of 1N4002-1N4007 diodes for both of them. A Schottky
>>>diode would be nice where the * is (it doesn't have to carry any
>>>appreciable current, so any of them will do) but isn't necessary. It
>>>just makes the recovery time a bit better, because it has a lower
>>>forward voltage drop.
>>
>>
>> As you can probably tell, this is the first time I ever posted to a
>> news group. Anyway I built the circuit as you designed. What
>> actually occurs is the relay is energized for only .20 seconds instead
>> of a delay of .20 seconds then energized until the switch opens. (Did
>> you expect this? I checked the path of the circuit 3 times)
>>
>> Bob
>
>When you close the switch, it should take 0.2 seconds to charge up the
>capacitor enough to turn on the transistor. Thus, assuming the relay is
>open when you start, the following should happen:
>
>1) relay open, switch open
>2) switch closed
>0.2 seconds
>3) relay closed
>...
>4) switch open, relay opens immediately.
>
>It sounds like you have the 10k resistor and 220uF capacitor swapped.
>That would cause it to
>
>1) relay open, switch open
>2) switch closed, relay immediately on
>0.2 seconds (or less!)
>3) relay open
>...
>4) switch open, relay still open
>
> From your reply, I can't quite figure out whether that is what you are
>seeing, though.
>
>(You probably know this, but closed means passing current, open means
>unable to pass current.)

Thanks so much for all the assistance. I am amazed with your patience
with an electonic baby. It appears the Transistor is the culprit.
Maybe undersized? I replace a Radio Shack #276-1617 (tiny) with a
Radio Shack #276-2020 also known as a TIP3055. The ciruit works like
a charm. Using a digital video camera, (consumer grade (Sony)), I am
able to count a .22 second delay now compared without this delay
circuit. Thanks again and my hat comes off for your patience and
expertise with this circuit design.

Bob Fraser

Relevant Pages

  • Re: Frying your avionics
    ... That's what overvoltage protection is made for: ... You say your OV has a relay which opens; ... causing its circuit breaker to open. ...
    (rec.aviation.homebuilt)
  • Re: 0.20 delay in 6v control circuit
    ... Bob wrote: ... Anyway I built the circuit as you designed. ... Thus, assuming the relay is ... switch open, relay opens immediately. ...
    (sci.electronics.basics)
  • Re: Onkyo TX-82 stereo receiver fault. Suggest possible solutions...
    ... protection relay may open and cut the sound and then close. ... relay opens. ... Some possible reasons that the protection circuitry is opening the relay.... ...
    (sci.electronics.repair)
  • Re: Onkyo TX-82 stereo receiver fault. Suggest possible solutions...
    ... What happens is that, at random moments during use, the speaker ... protection relay may open and cut the sound and then close. ... relay opens. ... Assuming that the protection involves some current sensing or DC ...
    (sci.electronics.repair)
  • DPST relay question - Williams Pharaoh and backbox GI
    ... the time unless the backbox GI relay is fired and then the backbox GI lights ... circuit is open until the relay is energized then the circuit closes. ... would explain the GI backbox lights being most of the time. ... opens the circuit when the relay's coil is energized. ...
    (rec.games.pinball)