Author Topic: Relay Problem  (Read 9099 times)

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Offline BskitterTopic starter

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Re: Relay Problem
« Reply #25 on: May 18, 2016, 01:53:06 pm »
Going to the store to get some PC817C's will try it out
 

Offline JacobPilsen

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Re: Relay Problem
« Reply #26 on: May 18, 2016, 02:46:03 pm »
Place Zener diode antiserially with 1N4007.
 

Offline BskitterTopic starter

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Re: Relay Problem
« Reply #27 on: May 18, 2016, 04:36:25 pm »
Hey Jacob, could you give me a model number of the zener diode I should use ?

And what do you mean anti serially ?

Byron
 

Offline JacobPilsen

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Re: Relay Problem
« Reply #28 on: May 21, 2016, 07:40:23 pm »
1N5345B or 1N5344B, basically any with voltage rating similar to power supply (observe also voltage rating of transistor).

Antiserially: i.e. anode of Zener to anode of 1N4007, cathode of Zener to node with transistor, cathode of 1N4007 to node with positive power supply.
 

Offline Ammar

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Re: Relay Problem
« Reply #29 on: May 22, 2016, 05:31:17 am »
The output current of the shift register is absolute max 25mA according to the datasheet. In general, you want to operate at less than half of absolute max ratings, so call it 10mA.

You are then driving the base of your BJT with around (5-0.7)/220 = about 20mA. This is a problem as your shift register is not designed to supply this. If you increase the resistance at the base to 1kohm, then this becomes around 4mA, but this probably won't your transistors hard enough.

A BJT isn't really the best option here. Try a logic level driven MOSFET. Even something akin to the IRF540 would likely do the trick. You could try opto-isolators, but these would be over-kill.

This looks helpful: https://arduinodiy.wordpress.com/2012/05/02/using-mosfets-with-ttl-levels/
 


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