Class H switching

clovi_kate · 20th December 2011, 02:33 PM

hi guyz..

I have a question about class h amps having a mosfets switch. At time when amp is at full state (maximum operation), does the voltage across drain to source of mosfet reaches zero? (Vds=0)?.. And when the mosfets starts to switch to the voltage, does it increase the voltage slowly or it will switch to its highest voltage right away?..

clovi_kate · 20th December 2011, 05:23 PM

I have a question about class h amps having a mosfets switch. At time when amp is at full state (maximum operation), does the voltage across drain to source of mosfet reaches zero? (Vds=0)?.. And when the mosfets starts to switch to the HIGH voltage, does it increase the voltage slowly or it will switch to its highest voltage right away?..

ontoaba · 21st December 2011, 12:08 AM

There are some differences when the mosfet turned on. The simplest one the mosfet just switched on when comparator say "go", and amplifier supply voltage increasing to the higher rail as fast as possible. The other one, there is a slew limiter so the voltage increases with limited speed/slew. Some other with early switch on and off with slew limiter.

Mosfet has its Rds-on when turned on, so there will be small drop voltages, around 1 volt.

clovi_kate · 21st December 2011, 01:21 AM

shal we say we have a rail of +-55V and +-110v and uses 15v early before the mosfet switch on. if the output voltage reaches shall we say 46Vp, mosfet will go 'on' and Vds has a voltage not equal to 1V. (with the pinch off voltage considered 4v)

so WHAT IF in this condition the 2 mosfets (+ and - rail switch) did not fire equally, resulting +Vrail and -Vrail shall we say +65v and -75v. does this condition will affect the dc offset of the amplifier because unbalanced rails?..

djk · 21st December 2011, 01:50 AM

"does this condition will affect the dc offset of the amplifier because unbalanced rails?"

No.

ontoaba · 22nd December 2011, 08:31 AM

Supply voltage only switched at output stage, and VAS always connected to highest rail, and opposite mosfet stay off when a rail switched.

This is a multi step classH with slew limiter and early on/off for high speed operation (around 10kHz). Also higher voltage margin for higher step, because OPS has more drop voltage when draw more current.

20th December 2011, 02:33 PM	#1
clovi_kate diyAudio Member Join Date: Jan 2006 Location: iloilo city	Class H switching hi guyz.. I have a question about class h amps having a mosfets switch. At time when amp is at full state (maximum operation), does the voltage across drain to source of mosfet reaches zero? (Vds=0)?.. And when the mosfets starts to switch to the voltage, does it increase the voltage slowly or it will switch to its highest voltage right away?.. __________________

20th December 2011, 05:23 PM	#2
clovi_kate diyAudio Member Join Date: Jan 2006 Location: iloilo city	I have a question about class h amps having a mosfets switch. At time when amp is at full state (maximum operation), does the voltage across drain to source of mosfet reaches zero? (Vds=0)?.. And when the mosfets starts to switch to the HIGH voltage, does it increase the voltage slowly or it will switch to its highest voltage right away?.. __________________

21st December 2011, 01:21 AM	#4
clovi_kate diyAudio Member Join Date: Jan 2006 Location: iloilo city	shal we say we have a rail of +-55V and +-110v and uses 15v early before the mosfet switch on. if the output voltage reaches shall we say 46Vp, mosfet will go 'on' and Vds has a voltage not equal to 1V. (with the pinch off voltage considered 4v) so WHAT IF in this condition the 2 mosfets (+ and - rail switch) did not fire equally, resulting +Vrail and -Vrail shall we say +65v and -75v. does this condition will affect the dc offset of the amplifier because unbalanced rails?.. __________________

21st December 2011, 01:50 AM	#5
djk diyAudio Member Join Date: Feb 2001 Location: USA	"does this condition will affect the dc offset of the amplifier because unbalanced rails?" No. __________________ Candidates for the Darwin Award should not read this author.

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21st December 2011, 12:08 AM	#3
ontoaba diyAudio Member Join Date: Nov 2009 Location: Kudus, & Malang	There are some differences when the mosfet turned on. The simplest one the mosfet just switched on when comparator say "go", and amplifier supply voltage increasing to the higher rail as fast as possible. The other one, there is a slew limiter so the voltage increases with limited speed/slew. Some other with early switch on and off with slew limiter. Mosfet has its Rds-on when turned on, so there will be small drop voltages, around 1 volt.

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