I have a transistor that is rated to a 1000v and 15 a and I want to control the discharge of a capacitor. I was looking at relays but I realized it would not last very long at high current and voltage.

 

Details, details, details!

What is your switching frequency?
What is your desired rise time and fall time?
How much current do you need to switch?
What is the number on the 1000V transistor?

 

What is your switching frequency?
What is your desired rise time and fall time?
How much current do you need to switch?

6 hz at 90% duty cycle and I want to switch about 5 amps.

 

Next question: What are you building?

 

6 hz at 90% duty cycle (90 percent open and 10 percent closed circuit) and I want to switch about 5 amps. BUV48a

 

I have a transistor that is rated to a 1000v and 15 a and I want to control the discharge of a capacitor. I was looking at relays but I realized it would not last very long at high current and voltage.

Unless you are very careful your transistor may not last very long, either. Maximum voltage rating and maximum current rating don't tell the whole story. Google the terms "safe operating area" and "second breakdown" to get a good idea why. These two application notes will give you some information:

Power Transistor Safe Operating Area
Understanding Power Transistor Breakdown Parameters

 

Next question: What are you building?

So I want to send the pulses to a coil that steps up the voltage to about 50kv. I just wanted to experiment with sparks.

 

Unless you are very careful your transistor may not last very long, either. Maximum voltage rating and maximum current rating don't tell the whole story. Google the terms "safe operating area" and "second breakdown" to get a good idea why. These two application notes will give you some information:

Power Transistor Safe Operating Area
Understanding Power Transistor Breakdown Parameters

I figured that every time the capacitor was discharged with the relay, the relay's contacts would very quickly be destroyed. Also the characteristics of a coil is not desired.

 

I figured that every time the capacitor was discharged with the relay, the relay's contacts would very quickly be destroyed. Also the characteristics of a coil is not desired.

Were you planning on connecting the relay contacts (or the transistor) directly across the capacitor to discharge it? It would help greatly if you could post a schematic diagram showing, in detail, what you have in mind.

 

Were you planning on connecting the relay contacts (or the transistor) directly across the capacitor to discharge it? It would help greatly if you could post a schematic diagram showing, in detail, what you have in mind.

There is a charging circuit charging a capacitor to a few 100 volts. To the capacitor connected is the primary of another transformer. When the transistor/relay is off the capacitor is charging and when it is on current flows from the capacitor through the relay/transistor and through the primary.

 

There is a charging circuit charging a capacitor to a few 100 volts. To the capacitor connected is the primary of another transformer. When the transistor/relay is off the capacitor is charging and when it is on current flows from the capacitor through the relay/transistor and through the primary.

How did you determine that the maximum current is 5 amps?

 

How did you determine that the maximum current is 5 amps?

A resistor will be added in series to prevent too much current from flowing.

 

A resistor will be added in series to prevent too much current from flowing.

Ah. In that case I doubt you have much reason to worry, either with a relay or with a transistor, such as the one you cited.

 

Ah. In that case I doubt you have much reason to worry, either with a relay or with a transistor, such as the one you cited.

However I still suspect that the relay won't last long at this power. How exactly do I use a transistor for switching without the output voltage sagging.

 

6 hz at 90% duty cycle and I want to switch about 5 amps.

¡Ay, caramba!
1000V @ 5A, that's 5kVA. That's gonna kill you for sure. Besides you need one heck of a supply for that.

 

¡Ay, caramba!
1000V @ 5A, that's 5kVA. That's gonna kill you for sure. Besides you need one heck of a supply for that.

Nah, its just a small pulse for a tiny fraction of a second.

 

How exactly do I use a transistor for switching without the output voltage sagging.

Ummm... I'm not sure what you mean by that. If you discharge a capacitor into the primary of a transformer you're going to end up with a complex output waveform, most likely some sort of damped sinusoid.

Maybe at this point you need to back up a step and explain what you're trying to DO rather than ask questions about your presumed method for doing it. What kind of output are you trying to generate?

 

Get an automotive electronic ignition system.

 

Ummm... I'm not sure what you mean by that. If you discharge a capacitor into the primary of a transformer you're going to end up with a complex output waveform, most likely some sort of damped sinusoid.

Maybe at this point you need to back up a step and explain what you're trying to DO rather than ask questions about your presumed method for doing it. What kind of output are you trying to generate?

All I want is a high voltage there are no specifications of waveform. I have heard that there will be a a big voltage drop if the base and collector voltage is so different. I want to know how to reduce this voltage drop

 

All I want is a high voltage there are no specifications of waveform. I have heard that there will be a a big voltage drop if the base and collector voltage is so different. I want to know how to reduce this voltage drop

What??? That makes no sense whatsoever. Provided you include a resistor which will limit the current to a safe value, my advice to you would be to stick with the relay.