SCR problems

[blubomber]

Hello all,

I would like to make a very simple circuit w/an SCR. It is my understanding that once the switch is activated the SCR gate will stay open. I have attempted to do this, but the "gate" will not stay open. I would like to use a NO microswitch and a buzzer with a 9V battery. I can get the microswitch to work, but once activated it will turn off (buzzer stop sounding) when the lever is released. I have looked online and I do not understand how come I cannot get it to work. Thanks for your help.

 

[jbeng]

Please post a schematic of your circuit...
Jeff

 

[blubomber]

here it is.

 

[Roff]

Hello all,

I would like to make a very simple circuit w/an SCR. It is my understanding that once the switch is activated the SCR gate will stay open. I have attempted to do this, but the "gate" will not stay open. I would like to use a NO microswitch and a buzzer with a 9V battery. I can get the microswitch to work, but once activated it will turn off (buzzer stop sounding) when the lever is released. I have looked online and I do not understand how come I cannot get it to work. Thanks for your help.

What kind of buzzer do you have? What is the SCR part number? Do you have a datasheets on them? If the steady-state buzzer current is less than the SCR holding current, the SCR will not stay latched.

 

[blubomber]

one number says S401E, and below that it says T6C4LW or T6G4LW.

 

[Roff]

one number says S401E, and below that it says T6C4LW or T6G4LW.

S401E is the SCR. We still need to know the specs on the buzzer.
Also, what is your battery voltage?

 

[blubomber]

buzzer = KPE 1500

 

[Roff]

buzzer = KPE 1500

Why do you only answer one question at a time?
I also asked what your battery voltage is.

 

[blubomber]

because i didn't see that you had asked what the voltage was. plus the voltage is on the 1st post- 9 volt battery. i do not have the spec sheet for any of the items.

 

[crutschow]

The buzzer may draw an ac current which goes to zero for each cycle which could cause the SCR to shut off. Placing a small cap across the SCR should help if that's the case.

 

[blubomber]

across which leads?

 

[crutschow]

across which leads?

Anode to cathode.

 

[Roff]

Also, the minimum holding current of the SCR is 30mA. The current through the buzzer, with 8V (9V - SCR saturation voltage) across it, is about 30mA. If the capacitor alone doesn't solve your problem, try adding 470 ohms across the buzzer.

 

[blubomber]

thank you. the cap and 470 ohm across the buzzer worked.