Re: 555 Timer - less then 50% duty cycle question.
From: Rubicon (no email)
Date: 08/02/04
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Date: Mon, 02 Aug 2004 06:58:56 GMT
Thankyou,
Andrew.
On Thu, 29 Jul 2004 11:21:13 -0500, John Fields
<jfields@austininstruments.com> wrote:
>On Thu, 29 Jul 2004 06:27:16 GMT, (Rubicon) wrote:
>
>>
>>Hello.
>>
>>Using a calculating program for a 555 timer operating at less then 50%
>>duty cycle the diagram that the program displays has two diodes. One
>>from pin#7 to pin#6 and the other from pin#2 with R2 to pin#7. I
>>understand that the formulas work through these diodes but what
>>exactly should they be? Signal IN4148, Schottky or another type?
>>
>>In addition when switching a motor via the 555 what's the best choice
>>of switch? A transistor or a mosfet or some other device? I have tried
>>both transistor and mosfet to switch a motor at approx 33% duty cycle
>>but failed to do so correctly. At the moment it runs faster than it
>>should when it shouldn't. That is a 555 monostable output through an
>>NPN transistor switches another 555 astable (555 V+ to V+, V- to
>>collector) that switches another NPN transistor or mosfet (Motor V+ to
>>V+, V- to collector/drain) to control the motor. At the moment the
>>motor runs as soon as power is applied. Not sure what's wrong as the
>>wiring seems O.K.
>
>---
>Check "Duty cycle controller" on abse and
>
>http://pdfserv.maxim-ic.com/en/ds/ICM7555-ICM7556.pdf
>
>for the timing equations so you can figure out the RC's
>
>
>--
>John Fields
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