Transistor relay circuit - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th March 2002, 02:39 PM   #1
diyAudio Member
 
Join Date: Apr 2001
Location: Connecticut
Question Transistor relay circuit

I am looking to use a couple of transistors to replace a relay I am using in my automobile to turn on signal processors and amplifiers. The relay has a loud click when energized and I saw a fairly simple circuit which employed an NPN and PNP transistor that would accmplish this. Does anyone have a schematic for something like this?

Thanks,

Bill
  Reply With Quote
Old 29th March 2002, 04:46 PM   #2
palesha is offline palesha  India
diyAudio Member
 
Join Date: Nov 2001
Location: Pune India
It is a single NPN tr circuit. Just give ur + supply voltage to collector & take the output from emitter. To on the device put 1k resistance in series with base of the transistor. Give the + dc supply to one contact of switch and connect the other contact of the switch to 1k resistor on the other side of base. Select the to-3 transistor of 3 times the current required and mount on a heatsink. I have done this successfully. Hope u understand.
  Reply With Quote
Old 17th May 2002, 06:59 AM   #3
diyAudio Member
 
Join Date: Dec 2001
Location: SIUE, Illinois, USA
how would you make a circut to turn on and off an audio signal to an op amp. I assume you connect a +12v power supply to the collector, the AC audio signal to the base, and take output from the emitter. do i still use NPN? or can i do this with a regualr transistor? will i still use a 1kohm resistor?
__________________
if only it could be used for good, not evil...
  Reply With Quote
Old 17th May 2002, 08:47 AM   #4
diyAudio Member
 
Join Date: Apr 2002
A transistor is nothing more than a electronic switch. To switch on a transistor you need to know the gain of the transistor. Also you need to locate the base pin on the transistor and the voltage. After know those parameters, making a transistor to turn on is very simple.

I like using darlington transistors for switching motors or coils on and off because it uses very little current to turn on the transistor. A TIP120 NPN Darlington transistor has a gain of 1000 at 3 amperes.

To calculate the the base current:

beta = gain

Ib = Ic / beta

0.003 = 3 / 1000


After knowing base current, it is a little easier to find out what resistor to switch the transistor on.

Rb = (Vin - Vbe) / Ib

Rb = resistor connected to base pin to switch transistor on
Vin = supply voltage or 12 volts
Vbe = silicon turn on voltage (~0.6 volts)

Rb = (12 volts - 0.6 volts) / 0.003 amperes
Rb = 3800 ohms

When using any device that has coils, use a diode across the coiled device. If you don't, the transistor or MOSFET will fry from EMFs that are generated by the coiled device (relay, loudspeaker, motors, etc). A diode that has a PIV (peak inverse voltage) of 400 volts should last very long.
  Reply With Quote
Old 17th May 2002, 08:53 PM   #5
diyAudio Member
 
Join Date: Dec 2001
Location: SIUE, Illinois, USA
wow, that was a quick reply. ok, i think i understand. I will have to find some parts. I kinda want to make an audiophile type setup (kinda cheeply too). I saw that metal film resistors have 1% tolarances, and some capacitrors have 5% tolarances. is there any differance in tranistors and signal quality. are germainium any better than silicone? are J-FETs any better than BiPolar or Darlington?
__________________
if only it could be used for good, not evil...
  Reply With Quote
Old 18th May 2002, 01:16 AM   #6
diyAudio Member
 
Join Date: Apr 2002
I suggest you use a relay instead a transistor or MOSFET for switching off or on an audio path. Using relays doesn't saccfice sound quality. In your situation, a relay will be good and a transistor to energize the relay. Using an active solid-state device instead of relay to switch audio does saccfice sound quality. There are solid state relays but they should not be used for audio.

When selecting relays, try to find gold plated. This is because over time the connections will get oxidized. Reed relays might work but test before making a pernament discision.

Also you don't need very accurate resistors. You can pick a 4700 ohm resistor as a subsitute from the example that I gave in previous reply. In digital circuits most of the resistors are 5% tolerance.

If you really want a solid-state switch use a DIAC for DC circuits and TRIAC for AC. Don't forget to use a heatsink too.
  Reply With Quote
Old 18th May 2002, 05:43 AM   #7
palesha is offline palesha  India
diyAudio Member
 
Join Date: Nov 2001
Location: Pune India
I was not suggesting to use transistor in the signal path. It was to be used in the powersupply section. This has to be used as a transistor switch instead of mechanical switch which generates noise.
  Reply With Quote
Old 18th May 2002, 07:24 AM   #8
diyAudio Member
 
Join Date: Apr 2002
Quote:
I was not suggesting to use transistor in the signal path. It was to be used in the powersupply section. This has to be used as a transistor switch instead of mechanical switch which generates noise.
This will be great if the op-amp uses a single power supply. These days op-amps uses dual power supply so you need two transistors.

In more_power first post he or she states:
Quote:
...turn on signal processors and amplifiers...
Using transistors to switch on current hogging amplifiers will have to dissipate a lot of heat. Relays do dissipate heat when energized. This is only when the coil is consuming a lot of current. There are relays that have 5 volts coils and can handle several amperes through the switch of the relay. However, the a 5 volt relay will need a resister so the coil doesn't overheat.
  Reply With Quote
Old 18th May 2002, 08:41 AM   #9
diyAudio Member
 
Join Date: May 2002
Location: Sweden
Quote:
Using transistors to switch on current hogging amplifiers will have to dissipate a lot of heat....
more_power is using this for his car audio stuff. And to turn on car audio stuff you apply a small current to the "turn on led" of the unit that is going to be turned on and it will trigger a relay or something inside the unit.
When you have alot of units you dont want to take all the current from the main unit to turn on all the other units so you use a relay.
There isnt much current going to each unit (but you still dont want to bog down the main unit) so one could use a very small relay, probably with almost silent click or a transistor.
I dont think he want to run all current for every unit through a transistor, that would most sertainly make alot of heat as you say.

Use a smaller relay and you could probably put some padding around it to get it silent. Or build a transistor switch.
  Reply With Quote
Old 19th May 2002, 03:14 AM   #10
diyAudio Member
 
Join Date: Dec 2001
Location: SIUE, Illinois, USA
well, i never mentioned a car. a friend told me about a place where you can get old AT power supplies. they (or some) don't have a minimum turn on load, and have power switches on them to turn on. (oh well, there goes my 1 switch design i guess). these power supplies have +12 and -12 connectors on them, and are already regulated.

also, there is only 1 op amp in this cicut, how much current is going to be going through the transistors? assuming i use them only for a power supply. also, you said that transistor add distortion to the signal (which i do beleive), how much is added? I mean, is it a noticable amount to the untrained ear, or just a slight differance. I had assumed a relay would be worse on an audio signal because of the inductors.

as for the car stuff though, if the distortion isn't really noticable, i might make some neat stuff for my car too. I don't really feel like spending a lot of money on a lot of relays for my car, when a transitor (may be) is almost the same.
__________________
if only it could be used for good, not evil...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Relay switching circuit please jnewbold Solid State 10 3rd March 2005 06:39 AM
muting transistor>relay,can i do this? Rodzilla Analogue Source 1 20th August 2004 12:22 PM
Quick relay/transistor question Prune Parts 5 9th August 2004 02:54 PM
Momentary relay driving circuit dine1967 Solid State 7 8th April 2003 08:02 PM
Power-on relay circuit, i/o connector 2Bak Everything Else 1 15th March 2003 08:25 PM


New To Site? Need Help?

All times are GMT. The time now is 09:29 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2