Question about cathode voltage

crj11 · 3rd January 2010, 03:02 PM

I am designing a tube tester and because of the way that it works, I need an N-Channel MOSFET between the cathode and ground to be able to open the circuit at various times during the test. I'm having a hard time figuring out what drain-source voltage rating the MOSFET needs to be.

The plate voltage will be up to 500V, so I could just put a 500V MOSFET there and call it a day. However, low resistance high voltage MOSFETs are much more expensive. From what I have read, I'm thinking that the drain of the MOSFET connected to the cathode will not see the full plate voltage when the MOSFET is off, so I can use a cheaper MOSFET. I was also thinking that I could put a high value resistor across the MOSFET (100K-1M) to help in limitting the off state drain voltage.

Does anyone have any thoughts or observations about the voltage on the cathode when the MOSFET is off that could help me out?

Thanks,

Chris

3rd January 2010, 03:02 PM	#1
crj11 diyAudio Member Join Date: Apr 2008 Location: Connecticut	Question about cathode voltage I am designing a tube tester and because of the way that it works, I need an N-Channel MOSFET between the cathode and ground to be able to open the circuit at various times during the test. I'm having a hard time figuring out what drain-source voltage rating the MOSFET needs to be. The plate voltage will be up to 500V, so I could just put a 500V MOSFET there and call it a day. However, low resistance high voltage MOSFETs are much more expensive. From what I have read, I'm thinking that the drain of the MOSFET connected to the cathode will not see the full plate voltage when the MOSFET is off, so I can use a cheaper MOSFET. I was also thinking that I could put a high value resistor across the MOSFET (100K-1M) to help in limitting the off state drain voltage. Does anyone have any thoughts or observations about the voltage on the cathode when the MOSFET is off that could help me out? Thanks, Chris

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
What happens when Heater Cathode voltage is exceeded?	john65b	Tubes / Valves	13	6th November 2009 10:49 PM
Heater-Cathode Voltage	bobbyq	Tubes / Valves	11	11th August 2009 06:45 PM
Battery for Cathode Voltage?	markw51	Tubes / Valves	15	12th December 2006 02:53 PM
6DJ8 cathode heater voltage question.	Morse	Tubes / Valves	13	30th January 2003 07:59 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)