Difference between boot strap and level shift

levelshift · 27th March 2011, 09:03 PM

Hi. Is boot strap a kind of level shift or what's the difference? I see some circuits using both these methods, why? Thanks.

nigelwright7557 · 27th March 2011, 09:12 PM

Boot strap is usually where positive feedback is used to increase the input impedance.

Pafi · 27th March 2011, 09:57 PM

In ClassD the bootstrap usually refers to a power supplying method of high side gate driver. Level shifting is a different thing, but often they go together.

nigelwright7557 · 27th March 2011, 10:02 PM

Level shifting in class d is altering the levels of the signals to match the mosfet driver.
The output of the comparator is usually based around zero volts and the input to the mosfet driver is based around B-.

levelshift · 27th March 2011, 10:16 PM

Thanks but not enough to make me understand though, could you try to explain a bit more, treat me like a noob, cause that's what I am.

AP2 · 27th March 2011, 10:29 PM

Hi,
Pafi says right on the bootstrap method.
Level shift is used when there is a potential difference between the stage of the mosfet and the stadium before (this is often referred to GND).
usually resolves with two bjet the low side MOSFET (VN)

nigelwright7557 · 27th March 2011, 10:33 PM

Quote:

Originally Posted by AP2

Hi,
Pafi says right on the bootstrap method.
Level shift is used when there is a potential difference between the stage of the mosfet and the stadium before (this is often referred to GND).
usually resolves with two bjet the low side MOSFET (VN)

This can usually be done with a single transistor stage.

AP2 · 27th March 2011, 10:39 PM

It depends on what is the potential difference.
consider that this stage is critical for the transient response, and then must work with low load resistances. this (depending on the voltage difference that must absorb) the energy will dissipate.

nigelwright7557 · 27th March 2011, 10:45 PM

With my discrete class d amp I had to shift grom +12v/0v to -35v/-20v and a simple transistor stage worked fine. I did put a diode to the -20v rail and a resistor in series with it to clip the voltage. Worked very well.
I have also seen another design with a very similar circuit.

levelshift · 28th March 2011, 08:15 AM

Ok, so a level shift is not necessary to drive the upper transistor, the boot strap is? And a level shift might also be needed in some cases? I'm sorry it's a bit hard to understand, all these English terms.. If anyone has time and wants, a picture might help. Sorry for being slow.

27th March 2011, 09:03 PM	#1
levelshift diyAudio Member Join Date: Mar 2011	Difference between boot strap and level shift Hi. Is boot strap a kind of level shift or what's the difference? I see some circuits using both these methods, why? Thanks.

27th March 2011, 09:12 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	Boot strap is usually where positive feedback is used to increase the input impedance. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

27th March 2011, 10:02 PM	#4
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	Level shifting in class d is altering the levels of the signals to match the mosfet driver. The output of the comparator is usually based around zero volts and the input to the mosfet driver is based around B-. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

27th March 2011, 10:45 PM	#9
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	With my discrete class d amp I had to shift grom +12v/0v to -35v/-20v and a simple transistor stage worked fine. I did put a diode to the -20v rail and a resistor in series with it to clip the voltage. Worked very well. I have also seen another design with a very similar circuit. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

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


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

27th March 2011, 09:57 PM	#3
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	In ClassD the bootstrap usually refers to a power supplying method of high side gate driver. Level shifting is a different thing, but often they go together.

27th March 2011, 10:16 PM	#5
levelshift diyAudio Member Join Date: Mar 2011	Thanks but not enough to make me understand though, could you try to explain a bit more, treat me like a noob, cause that's what I am.

27th March 2011, 10:29 PM	#6
AP2 diyAudio Member Join Date: Dec 2009 Location: Italy	Hi, Pafi says right on the bootstrap method. Level shift is used when there is a potential difference between the stage of the mosfet and the stadium before (this is often referred to GND). usually resolves with two bjet the low side MOSFET (VN)

27th March 2011, 10:39 PM	#8
AP2 diyAudio Member Join Date: Dec 2009 Location: Italy	It depends on what is the potential difference. consider that this stage is critical for the transient response, and then must work with low load resistances. this (depending on the voltage difference that must absorb) the energy will dissipate.

28th March 2011, 08:15 AM	#10
levelshift diyAudio Member Join Date: Mar 2011	Ok, so a level shift is not necessary to drive the upper transistor, the boot strap is? And a level shift might also be needed in some cases? I'm sorry it's a bit hard to understand, all these English terms.. If anyone has time and wants, a picture might help. Sorry for being slow.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Need help choosing level shift and inverter	levelshift	Class D	4	27th March 2011 05:47 PM
How do we calculate the values of the boot strap resistors ?	tessier	Solid State	4	8th October 2010 11:27 AM
Level difference on ESL.	sholby	Planars & Exotics	7	5th July 2005 04:56 PM
A better triode strap?	G	Tubes / Valves	10	19th December 2004 09:58 AM
A better triode strap?	G	Tubes / Valves	14	2nd June 2004 12:36 AM

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