Do I really need a transistor to drive my solid state relay?

M

morglum

Member
Hi everyone,

I want to use a DS2413 (max voltage on PIO is 28V, max current on PIO is 20 mA) to drive a relay with the following controls specs:
Control Voltage:3-32VDC Control Current:DC 6-25mA

Seeing this, it would seem that anywhere between 6 mA and 20 mA would be acceptable both by the DS2413 and the relay.

I dont have any 5V sources handy, but I do have a 9V battery close by to do some testing. I was thinking about using the "DS2405 as a led driver" sketch found here
DS2405_2.gif
, replacing the LED by the relay's control and the resistor by 1 kilohohm resistor, which would give me 9 mA (9V / 1000 ohm)


Would that work without breaking anything?

Thanks

Also, this relay is specified for 240V-480V AC ... do you think it would accept 110V AC too?
 
I was thinking more of a mechanical relay with a coil. That could generate a spike when activated or deactivated and a diode across the coil may have been needed.

The relay module you have should be OK. You may have to adjust the added external resistor value as the DC input of the module probably has some current limiting internally. You could always use a meter to measure the voltage on the module and current through the control input.
I could not find any added data on the relay module manufacturers site. So I can't say if 120 volts would be OK, but I don't see why not.
 
BLH said:
I was thinking more of a mechanical relay with a coil. That could generate a spike when activated or deactivated and a diode across the coil may have been needed.

The relay module you have should be OK. You may have to adjust the added external resistor value as the DC input of the module probably has some current limiting internally. You could always use a meter to measure the voltage on the module and current through the control input.
I could not find any added data on the relay module manufacturers site. So I can't say if 120 volts would be OK, but I don't see why not.
Click to expand...
Thanks BLH, I appreciate your help.

Just to make sure, just replacing the LED with my relay and the 330 ohm resistor with a 1000 ohm resistor doesnt sound like a really bad idea, correct?

Also, quick newbie question if you don't mind. What's a good way to connect my DS2413? There's no way I could just solder wire to those small legs.... should I get a PCB? If so does that mean I just "push" the ds2413 in the pcb's hole?


thanks!
 
morglum said:
Just to make sure, just replacing the LED with my relay and the 330 ohm resistor with a 1000 ohm resistor doesnt sound like a really bad idea, correct?

Also, quick newbie question if you don't mind. What's a good way to connect my DS2413? There's no way I could just solder wire to those small legs.... should I get a PCB? If so does that mean I just "push" the ds2413 in the pcb's hole?
Click to expand...

1st question- You can calculate the current- I=E/R. . . so if you are using 5V, current would be 5/1000 = 5mA. Well within the 20mA limit, probably not high enough to trigger your relay though. If you are testing with the 9V battery you mention, 9mA current should work. And as BLH mentioned, there will probably be some current limiting inside the relay- if you have a multi-meter, you will be able to measure your circuit and figure it out- just check the voltage drop across the resistor- it will be some amount less than your supply voltage. The difference is the loss inside the relay, due to the switch and/or current limiting resistor in there. Calculate your resistor value by using the voltage you measure across it (use a 1k to start to make sure you are not going to go over 20mA).

2nd question- the only package I see on the website is a surface mount device. It needs to be soldered to a PCB.
 
mdesmarais said:
morglum said:
Just to make sure, just replacing the LED with my relay and the 330 ohm resistor with a 1000 ohm resistor doesnt sound like a really bad idea, correct?

Also, quick newbie question if you don't mind. What's a good way to connect my DS2413? There's no way I could just solder wire to those small legs.... should I get a PCB? If so does that mean I just "push" the ds2413 in the pcb's hole?
Click to expand...

1st question- You can calculate the current- I=E/R. . . so if you are using 5V, current would be 5/1000 = 5mA. Well within the 20mA limit, probably not high enough to trigger your relay though. If you are testing with the 9V battery you mention, 9mA current should work. And as BLH mentioned, there will probably be some current limiting inside the relay- if you have a multi-meter, you will be able to measure your circuit and figure it out- just check the voltage drop across the resistor- it will be some amount less than your supply voltage. The difference is the loss inside the relay, due to the switch and/or current limiting resistor in there. Calculate your resistor value by using the voltage you measure across it (use a 1k to start to make sure you are not going to go over 20mA).

2nd question- the only package I see on the website is a surface mount device. It needs to be soldered to a PCB.
Click to expand...


BLH said:
I looked at the DS2413 specifications sheet and it is only available in surface mount. TSOC and TDFN packages. Hobby Boards shows the TSOC package.

Data sheet: http://datasheets.maxim-ic.com/en/ds/DS2413.pdf
Package Data: http://pdfserv.maxim-ic.com/package_dwgs/21-0382.PDF

It has no leads to go through a PCB. You have to use a board designed to hold a surface mounted part. This will require a very precise soldering job as the pads are close and solder can easily get between the pads.
Click to expand...


Thanks guy for your help.

1) For the resistor/amp calculation, I think I understand. I'll let you know if it works.

2) Re: the DS2413. I have Hobby Board's TSOC DS2413. I'm not sure what a PCB designed to hold a surface mounted part looks like. Would you mind giving me a link ? And some ideas on how to mount them beside being very careful?

Thanks!
 
BLH said:
Goggle search for TSOC-6 adapters found a few.
Links to two of them.
http://www.proto-advantage.com/store/produ...ucts_id=2200101
You can get the small pdf file for this one and also enlarge the photos to see what one looks like.

http://www.epboard.com/eproducts/protoadap...CtoDIPICAdapter
Near the bottom of the page is the one. Though there are no pdf files or enlargeable photos to look at.

I have no personal use of either board so I can't say how good they are.
Click to expand...
Thanks BLH for helping me through these newbie steps. I'm only just learning what "surface mount device" is, so I'm coming a long way. Watched a few youtube videos on soldering SMD's already... ;)

I had a look at the form of the DS2438 and it's a "8-pin SOIC". Someone on ebay sells these PCBs for cheap.

I'll google it, but do you have a feeling that a 6-pin TSOC could fit on a 8-pin SOIC?

4$ for 5 pcbs allowing me to solder both the DS2413 and the DS2438 would be awesome..

thanks!
 
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