starting to study amplifier circuits and i would really appreciate clarification of a couple of little things to expedite my learning.
say you have a rail voltage of +50 and -50 which equals 100v
would the output transistors have to be rated at 50v or 100v ?
and
i would like to try designing a mosfet amplifier....but how do amplifiers that work with strictly N channel devices work without having to use a P channel device? and vice versa.
and would a transistor working closer to its maximum voltage rating be stronger than working at half its maximum voltage rating?
thanx for putting up with my basic questions
say you have a rail voltage of +50 and -50 which equals 100v
would the output transistors have to be rated at 50v or 100v ?
and
i would like to try designing a mosfet amplifier....but how do amplifiers that work with strictly N channel devices work without having to use a P channel device? and vice versa.
and would a transistor working closer to its maximum voltage rating be stronger than working at half its maximum voltage rating?
thanx for putting up with my basic questions
They would need to be rated to 100V as there will be 100V across the 'off' transistor when the output is swinging hard towards the opposite rail.
Read up on quasi complementary design, there is a lot of information out there.
A transistor will be stronger the lower the voltage it works at in relation to it's rated voltage.
Read up on quasi complementary design, there is a lot of information out there.
A transistor will be stronger the lower the voltage it works at in relation to it's rated voltage.
Well as with most component ratings, it doesn't meant it will instantly explode when you hit 101 volts on a 100 volts transistor. Yes ideally it should be rated higher, but the emitter resistors will add in some drop to the 'seen' voltage as well as the fact just mentioned, so they should be fine.
Hi,
when is the voltage on the supply rails equal to +-50Vdc?
If the voltage goes higher due to less quiescent current or due to higher mains supply voltage then the output transistors will see this high voltage.
Look up the ESP site
http://sound.westhost.com/articles.htm
for good design information.
when is the voltage on the supply rails equal to +-50Vdc?
If the voltage goes higher due to less quiescent current or due to higher mains supply voltage then the output transistors will see this high voltage.
Look up the ESP site
http://sound.westhost.com/articles.htm
for good design information.
AndrewT said:
what if the ps design was current limited?
so a transistor rated at 100v will be stronger at 10v than 50 v?
something about that just sounds funny,i better read up, because i always thought it to be the opposite...seems like it would be more efficient the higher the voltage goes.
Hi,
the output device Vce0 can match the Vrail+|-Vrail| exactly. Some amplifiers even use Vce0 that is less than 2*Vrail and they survive.
The maximum voltage across a device will be just less than 2*Vrail and if the rails sag on heavy current draw then even lower.
It is much more important that SOA, both short term and long term, should not be exceeded at operational temperatures.
Most devices that meet this series of SOA limits will comfortably meet the Vce0 limit as well. But, the +10% margin on Vce0 is not a requirement.
It also follows that choosing a device with a very high Vce0 margin, even exceeding +100%, does not ensure that the device will not be overloaded at lower voltages.
the output device Vce0 can match the Vrail+|-Vrail| exactly. Some amplifiers even use Vce0 that is less than 2*Vrail and they survive.
The maximum voltage across a device will be just less than 2*Vrail and if the rails sag on heavy current draw then even lower.
It is much more important that SOA, both short term and long term, should not be exceeded at operational temperatures.
Most devices that meet this series of SOA limits will comfortably meet the Vce0 limit as well. But, the +10% margin on Vce0 is not a requirement.
It also follows that choosing a device with a very high Vce0 margin, even exceeding +100%, does not ensure that the device will not be overloaded at lower voltages.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.