Relay and Transistor connetion Problems

[yj07]

Guys, i m facing a tough problems. it is how to use relay to construct a mechanical latch when transistor is on. I would like to use DPDT relay and 2N3053 transistor.

p/s: mechanical latch means that once the relay coils is energized then the relay will permanent on until remove the the source voltage.

 

[Gordz]

Just wire the relay coil in series with the N.O. contacts of the relay. Then wire a N.O. pushbutton across the relay contacts and you have the latch you require without using a transistor.

Asuming of course you have a spare set of N.O contacts

 

[Leftyretro]

Guys, i m facing a tough problems. it is how to use relay to construct a mechanical latch when transistor is on. I would like to use DPDT relay and 2N3053 transistor.

p/s: mechanical latch means that once the relay coils is energized then the relay will permanent on until remove the the source voltage.

Well it wouldn't be called a mechanical latch but an electrical latch could be constructed by using an extra set of contacts that hold the relay energized once it's activated. Sometimes called sealing contacts by electricians. Does require an extra set of contacts or a parallel relay. That is how most motor starter controllers work with just a momentary switch to start or stop the motor.

Lefty

 

[ericgibbs]

Guys, i m facing a tough problems. it is how to use relay to construct a mechanical latch when transistor is on. I would like to use DPDT relay and 2N3053 transistor.

p/s: mechanical latch means that once the relay coils is energized then the relay will permanent on until remove the the source voltage.

hi,
You could consider using an SCR, once triggered ON, it would stay ON until the power was removed.

 

[ljcox]

Well it wouldn't be called a mechanical latch but an electrical latch could be constructed by using an extra set of contacts that hold the relay energized once it's activated. Sometimes called sealing contacts by electricians. Does require an extra set of contacts or a parallel relay. That is how most motor starter controllers work with just a momentary switch to start or stop the motor.

Lefty

I refer to it as a "holding" contact.

You don't necessarily need 2 contacts. It may be possible to use one contact as both the holding contact and the output contact. It depends upon what you're driving. I suggest that you post a circuit so we can see what you are doing.

 

[yj07]

I refer to it as a "holding" contact.

You don't necessarily need 2 contacts. It may be possible to use one contact as both the holding contact and the output contact. It depends upon what you're driving. I suggest that you post a circuit so we can see what you are doing.

Guys, i had attached the circuit diagram here.

If Or Gate output is 1 then transistor will be turned on so that relay will be turned on also. Now, if Or gate output is 0 , transistor will go off but relay will remain on until user remove the source voltage. But, i think there are some problems with my circuit because AND gate will be turned on when my OR gate output is approximately equal to 0( OR gate inputs: A connect to ground, B connect to Vcc=0V).But now, output of OR gate still can turn on my Transistor.

In fact, an astable pulse will pass through AND gate when it is enabled. I measured the input of AND gate from relay, it is 1.2V. This voltage is enough to trigger AND gate and hence Astable signal can pass through AND GATE. This is not the result i want.

guys, please help!

 

[ljcox]

Guys, i had attached the circuit diagram here.

If Or Gate output is 1 then transistor will be turned on so that relay will be turned on also. Now, if Or gate output is 0 , transistor will go off but relay will remain on until user remove the source voltage. But, i think there are some problems with my circuit because AND gate will be turned on when my OR gate output is approximately equal to 0( OR gate inputs: A connect to ground, B connect to Vcc=0V). This does not make sense. Vcc = 5 V. But now, output of OR gate still can turn on my Transistor.

In fact, an astable pulse will pass through AND gate when it is enabled. I measured the input of AND gate from relay, it is 1.2V. This voltage is enough to trigger AND gate and hence Astable signal can pass through AND GATE. This is not the result i want.

guys, please help!

What type of gates are you using? The 74LS series or CMOS?

I suspect it is the 74LS series. If so, then the AND gate is not seeing any change when the relay closes. In the case of TTL gates, an open is equivalent to a high. If you want the AND gate to see a change, then its input must be switched between +5V and 0V ie. gnd.

Tha attachment shows how you could do it.

However, why use a relay? A Flip Flop would be simpler and cheaper.

 

[yj07]

Anyway, thanks for your helping. Your provided circuit is also same problem with my circuit. Since i found that there is a 5V transient voltage to turn on the transistor. Thus, i had used J-K FF to replace this problem circuit.