Transistor switch recommendation

RichardF · 2012-07-17 16:49

I need a trsnsistor switch to use between my BS2 output and a 12 volt solenoid valve drawing 1/2 amp. I would appreciate a PNP transistor switch recommendation.
Thanks,
Richard

Peter KG6LSE · 2012-07-17 16:52

PNP?

is there some reason you need to switch the high side ?

a LOGIC MOSFET ,] 1 K pull down , diode accross the coil . volla!

Phil Pilgrim (PhiPi) · 2012-07-17 16:52

A PNP transistor might be the wrong way to go for that app, since you'd have to have a second, NPN to drive it. You would want either an NPN or an N-channel MOSFET, if you're hoping for a single-transistor solution. If it's an automotive application, though, I would recommend an integrated, fault-proof high-side switch.

-Phil

RichardF · 2012-07-17 17:37

Sorry, I meant NPN. I want to open the valve with a high output from the BS2. Rather than read through data sheets until I find a transistor to fit the bill, I was hoping one of you had a part number in mind.

Peter KG6LSE · 2012-07-17 17:52

TIP 120 needs a high drive for full turnon . I would still say MOSFET ...... IRF520 or 540 ....

Peter..

RichardF · 2012-07-17 18:07

Okay, thanks. I will give them a try.

Duane C. Johnson · 2012-07-17 18:36

Try this High Side Relay Driver:

This P-Chanel MOSFET, IRF9Z34, is good for about 3 Amps with no heat sink.

Duane J

Phil Pilgrim (PhiPi) · 2012-07-17 19:07

Neither the IRF520 nor the IRF540 are guaranteed to be fully "on" with 5V on the gate. I'd be more inclined to go with an IRF3708. OTOH, if your load is only 0.5A, it probably doesn't matter that much.

-Phil

Duane C. Johnson · 2012-07-17 20:03

Hi Peter;

Peter KG6LSE wrote: »

TIP 120 needs a high drive for full turnon . I would still say MOSFET ...... IRF520 or 540 ....
Peter..

I don't think this series of MOSFETs will work with the 3.3V drive from a Prop.
These are old school types with 20V gates.
OK, I haven't done my own gate characterization of these but I don't think it will even start to conduct at 3.3V.

Like Phil said, the IRF3708 is a much better choice for a Low Side Relay Driver.
Follow the link and you can see my gate measurements.

Duane J

Phil Pilgrim (PhiPi) · 2012-07-17 20:14

Duane,

He's using a BASIC Stamp, not a Prop; but even with a 5V drive, I think the IRF3708 is the better choice.

-Phil

Peter KG6LSE · 2012-07-17 21:00

I was fully aware of the gate issue ... never had a problem with driving a 520 @2A on my BOE . but I fully agreee with a Logic fet ( see my first post in the mattter )
I was spouting a Old fet as the OP might not want to wait for a fet .. shack has the 520 in the bin .

Phil Pilgrim (PhiPi) · 2012-07-17 21:09

Peter KGtuSE wrote:

shack has the 520 in the bin

Yeah, so true. (Actually, it's the '510 that RS carries.) I wish RS would get smart and realize they could sell a more useful part by switching to a more logic-compatible MOSFET.

-Phil

Peter KG6LSE · 2012-07-17 23:14

again I had a brain fart ...... .. I remember seeing a 5XX and thought to meself . wow Only one fet to chose from . I was digging up the 7812 they had .

erco · 2012-07-18 01:14

It's all done for you for just a few bucks. Built-in driver transistors: connects directly to BS2

http://www.youtube.com/watch?v=gjrSVzxpBAo

2-relay 5V, $3.69: http://www.ebay.com/itm/5V-2-4-8-Channel-Electronic-Relay-Module-for-Arduino-8051-ARM-PIC-AVR-DSP-TTL-/160826465383?pt=LH_DefaultDomain_0&var=&hash=item2572011c67

4-relay 5V $5.69 http://www.ebay.com/itm/4-Channel-5V-Relay-Shield-Module-for-Arduino-ARM-PIC-AVR-DSP-aii-/180866396859?pt=LH_DefaultDomain_0&hash=item2a1c7a32bb

4-relay 12V $6.90 http://www.ebay.com/itm/4-Channel-12V-Relay-Module-For-Arduino-PIC-ARM-AVR-DSP-/250887128971?pt=LH_DefaultDomain_0&hash=item3a6a09c78b

RichardF · 2012-07-18 05:18

That's exactly what I need! Thanks erco. My ap needs to control 8 valves (dancing waters), so two of the 4-relay 5V items will be perfect. Thanks to everyone for the inputs.
Richard

RichardF · 2012-07-18 05:25

I noticed that each relay sinks 15-20 ma, so I need to be a little careful with the BS2PX driving 8 of these all at once. I had better stay with using just 4 relays. Even that is pushing the limit of BS2 source current if all are high at the same time.

erco · 2012-07-18 08:38

There are 8-relay units available: http://www.ebay.com/itm/New-5V-8-Channel-Relay-Module-Board-for-Arduino-PIC-AVR-MCU-DSP-ARM-Electronic-/270984095956?pt=LH_DefaultDomain_0&hash=item3f17e928d4

You could always add an external transistor switch to each line for use with those relay modules if you want to safely drive 8 relays at once.

The ULN 2003/2803 is a 7-channel (DOH!) solution for switching discrete relays and interfaces directly to a Stamp: http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

RDL2004 · 2012-07-18 09:39

If you Google "MOSFET transistor array like 2803" you will come across this nifty looking chip called TPIC6595 (one of the hits was an old Parallax forum post by Mike Green). It basically combines a MOSFET version of the ULN2803 with a 595 shift register, giving you the capability to control 8 relays with just one pin using SHIFTOUT. I have no personal experience with it, but it might be worth checking out.

Stocked at Mouser (and probably Digi-Key also):

http://www.mouser.com/ProductDetail/Texas-Instruments/TPIC6595N/?qs=5nGYs9Do7G03SZwCnZXhhZVnGQDwLPOiD1U7MUGeamM%3d

Publison · 2012-07-18 10:02

+1 on the TPIC6595

RichardF · 2012-07-18 11:09

You guys are awsome, thanks.
Richard

Transistor switch recommendation

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