Level shifting with half brige

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Reactance

Reactance

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Joined 2005
Hi all

I'm designing a simple half bridge class-d amplifier from a +/- 12v supply source my design uses a LM311 powered from the +/- 12v source,the comparator is outputting a PWM signal and modulating to the music source signal (no feedback yet)..

My question is how do i design the next block in the signal path to do level shifting to feed a IR2011 gate driver also i have X2 IRF640 at my disposable.

Do i need to level shift if the comparator is already swinging between (-v) and (+v) dont i just need a pulse phase splitter such as a xor gate and feed it directly to the IR gate driver ?


Ive searched other threads and don't seem to get a clear enough example how to level shift so that the IR gate drive can work correctly.

Help and Patience will be really appreciated.

An externally hosted image should be here but it was not working when we last tested it.
 
Osvaldo de Banfield

Osvaldo de Banfield

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Joined 2011
can you try a Ac coupled (capacitively) plus a DC restorer. I had done something similar, and it worked pretty fine.

I´d used a HCF4047 oscillating at 250KHz, a TS274 (four CMOS opamps) working as differential integrator, a TS3402 (a version of double LM311 with push pull output), a HCF4049 driving a couple of 3A MOSFET´s, which in turn driver the output pair. All MOSFET´s Stage!!! Capacitively coupling had the advantage that the output transistor both automatically go off under no PWM signal, or driver failure.

Good luck !!!
 
gmarsh

gmarsh

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Joined 2004
Well then... use two gates from a 4030 XOR gate, powered from 0V and -12V rails, to give inverted/non-inverted drive signals to the IR2110. If you don't have a 4030, you could use a 74x86 logic gate, but you'll have to add a 7805 regulator or similar to power it. I wouldn't use a simple inverter circuit as the time delay might cause cross-conduction on turn-on or turn-off.

I still think you're better off using a "single input" H-bridge driver, preferably with adjustable dead time. It'll make this project a lot easier and likely save you some frustration.
 
Reactance

Reactance

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Joined 2005
gmarsh said:
Well then... use two gates from a 4030 XOR gate, powered from 0V and -12V rails, to give inverted/non-inverted drive signals to the IR2110. If you don't have a 4030, you could use a 74x86 logic gate, but you'll have to add a 7805 regulator or similar to power it. I wouldn't use a simple inverter circuit as the time delay might cause cross-conduction on turn-on or turn-off.

I still think you're better off using a "single input" H-bridge driver, preferably with adjustable dead time. It'll make this project a lot easier and likely save you some frustration.
Click to expand...

Thanks for the tip gmarsh!

Here is a very minor version of the my circuit nothing special many blocks are missing example: feedback, gate driver, MOSFET and LPF i will continue exploring until i feel confidant enough to configure each signal block, (This why i used a low voltage power supply :) )

BTW I am using a CD4030 XOR as a phase splitter, i do feel i need to introduce a transistor buffer stage to buffer between the gate drive and comparator i don't think the Logic hi/low voltages from the comparator are a driving hard enough the pulses.

An externally hosted image should be here but it was not working when we last tested it.
 
darkfenriz

darkfenriz

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Joined 2004
I highly suggest you powered the gates from ground and -12V for direct interfacing the IR2011.
Note that in this case -12V will be a logic zero and ground will be logic one.
What is more, take advantage of open collector output of the comparator and connect the pullup resistor to ground.
To create some dead time use RDC networks.
 
Reactance

Reactance

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Joined 2005
darkfenriz said:
I highly suggest you powered the gates from ground and -12V for direct interfacing the IR2011.
Note that in this case -12V will be a logic zero and ground will be logic one.
What is more, take advantage of open collector output of the comparator and connect the pullup resistor to ground.
To create some dead time use RDC networks.
Click to expand...

Hi darkfenriz

I took the advice which gmarsh gave me same as yours.

VDD = 0v
VSS = -12V
Propergation Delay 100ns @ 15Vdd

Max operating supply is VDD18Vmax with reference to VSS -0.5v so im well within the safe operation range.

I'm busy evaluation the gate drive circuity and just downloaded IR2110 application notes and accompanied datasheet.
 
Reactance

Reactance

Member
Joined 2005
darkfenriz said:
Another thing is forget the IRF640 and the likes stuff.
These are planar devices, completely unsuitable for fast switching. Get modern trench-technology MOSFETs
Click to expand...

For now that's all i have on the bench its not actually a fixed output stage solution, i have a mosfet guide EVA has posted sometime ago various various devices see below.

IRFP240 are ancient MOSFET only useful for burning watts in ancient linear amplifier designs. If you have some, they should be easy to sell to people doing class AB or A.

Some of my favourite ones for class D are:

- IRF540Z for 100V (nothing to do with other IRF540 variants)
- IRFB4321 for 150V
- IRFB4227 for 200V

This selection is aimed towards low conduction losses at the expense of higher gate drive requirements, but of course there are "lighter" ones intended for easy drive:

- IRFB4212 (100V)
- IRFB4019 (150V)
- IRFB4020 (200V)

Similar MOSFET from Fairchild are worth mentioning too, since some of them may outperform the ones from IR in certain circumstances (but others are ovbiously inferior):

- FDP3632, FDP3652, FDP3682 (100V)
- FDP2532, FDP2552, FDP2572 (150V)
- FDP2614 (200V)


Low Rds and low gate charge are 2 of the primary factors to consider. The third is VDSmax...Maximum drain to source voltage. The devices you mention are only 100V parts. A good rule of thumb is to use parts rated for Vcc + Vee + some safety factor to handle the inductive output load. So 100V parts should maybe only used with +/-33V rails. You might be able to push it a little higher, but you'll have to check what the reverse recovery spikes look like with a scope to make sure you're still saft.

If that works for you, then you'll have to look at balancing power losses from Rds in the output stage (twice as large for the STP40 device) vs. power losses and heating in your gate driver due to the much larger Qg of the STP80 device vs. the STP40 device. Keeping in mind that the gate driver is not typically mounted to a very robust heatsink compared to the output devices.

I hope this helps you out a little bit.

We have done a lot of research. The best Mosfets for Class D are those which have low gate charge, however if you are using either a driven or self oscillating type, higher Qg types will work as long as you pay attention to dead time.

IRFB4212 100v 0.058R 15nc
IRFB4019 150v 0.08R 13nc
IRFB4020 200v 0.08R 21nc
IRFB23N15D 150v 0.09R 37nc
IRF540N 100v 0.044R 71nc

FDP39N20 200v 0.066R 38nc
FDP42AN15A0 150v 0.042R 33nc
FDP3682 100v 0.036R 18nc
FDP3652 100v 0.016R 41nc

I have tried all the above. The IRF540N is the least expensive and the Fairchild FDP3652 the most. I can obtain low THD numbers with any of tghe FETS, bit of course the lower the gate charge the lower the deadtime and the coller the FETs run.

RDs on is not a huge thing as typically you are not driving the FET to its current limits.
Click to expand...
 
Reactance

Reactance

Member
Joined 2005
gmarsh said:
^- this

Power the gate and IR2110 from ground and -12V. The IR2110 will only tolerate a few volts between signal ground and low side ground.
Click to expand...

I'm only getting an output on LO pin-1of the gate driver :confused: , output H-out PIN-7 is dead ive checked both hi-in and low-inputs are signaling modulation out of phase and swinging between +100mV and -12v respectively from the XOR gates.

Any guide wiring up the gate driver ? the supply on the gate driver are 0Vss and +Vcc 0 volts.
 
gmarsh

gmarsh

Member
Joined 2004
Won't make a diagram, but:

VSS/COM/SD = connected to -12V rail
LIN/HIN = from XOR gate
VDD, VCC = conneted to GND rail
VS = connected to junction of both FETs
VB = connected to VS through a capacitor, and connected to GND through a diode - anode to GND, cathode to VB.
LO/HO = to output FETs.
 
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