Level shift question

[David Grant]

I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to
(-50 to -45V). Output is going into an IR2011 gate driver. Available
supplies are +/- 50V, +5V and GND.

I'm told I should be looking at using a PNP level shifting circuit, can
anyone comment and elaborate as to what that is?

Thanks,

David.

 

[Ken Smith]

I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to
(-50 to -45V). Output is going into an IR2011 gate driver. Available
supplies are +/- 50V, +5V and GND.

I'm told I should be looking at using a PNP level shifting circuit, can
anyone comment and elaborate as to what that is?

ASCII art:


VCC
!
/
\
/
\
!
!/ e
Signal ------! PNP
!\
!
+-------- Load
!
/
\
/
\
!
-50V

 

[Spehro Pefhany]

I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to
(-50 to -45V). Output is going into an IR2011 gate driver. Available
supplies are +/- 50V, +5V and GND.

I'm told I should be looking at using a PNP level shifting circuit, can
anyone comment and elaborate as to what that is?

Thanks,

David.

Something like this (it also inverts) with R around 1K.


+5V
|
.-.
| | R
| |
'-'
|
|<
0V/5V -|
|\
|
|
|
|
+-----------o -50V/-46V
|
|
|
.-.
| |
| | R
'-'
|
|
-50V




Best regards,
Spehro Pefhany

 

[Nico Coesel]

I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to
(-50 to -45V). Output is going into an IR2011 gate driver. Available
supplies are +/- 50V, +5V and GND.

I'm told I should be looking at using a PNP level shifting circuit, can
anyone comment and elaborate as to what that is?

AFAIK there are gate drivers with integrated level shifters. You
should look for those. If you connect the GND from the 5V to -50V, you
can use 2 high side drivers.

 

[David Grant]

This works well for no load, but when going into the gate driver input the
signal amplitude shrinks to almost nill. Is something then fishy about the
gate driver's input impedance?

Dave.

Something like this (it also inverts) with R around 1K.


+5V
|
.-.
| | R
| |
'-'
|
|<
0V/5V -|
|\
|
|
|
|
+-----------o -50V/-46V
|
|
|
.-.
| |
| | R
'-'
|
|
-50V




Best regards,
Spehro Pefhany

http://www.speff.com

 

[Spehro Pefhany]

This works well for no load, but when going into the gate driver input the
signal amplitude shrinks to almost nill. Is something then fishy about the
gate driver's input impedance?

Dave.

The IR2011 inputs have pulldown resistors- poorly characterized and
temperature sensitive. If you use the ~1K resistors that I suggested
it should work fine. If you don't like the ~200mW "on" power
dissipation in the transistor, you can add a series resistor (maybe
5.6K) on the collector to knock it down a bit.


Best regards,
Spehro Pefhany

 

[Ken Smith]

The IR2011 inputs have pulldown resistors- poorly characterized and
temperature sensitive. If you use the ~1K resistors that I suggested
it should work fine. If you don't like the ~200mW "on" power
dissipation in the transistor, you can add a series resistor (maybe
5.6K) on the collector to knock it down a bit.

OR

You could, if you have the supply to do it, add a emitter follower pair at
the MOSFET input.

 

[Fred Bloggs]

I need to shift a PWM signal (switching freq - 300kHz) from (0 to 5V) to
(-50 to -45V). Output is going into an IR2011 gate driver. Available
supplies are +/- 50V, +5V and GND.

I'm told I should be looking at using a PNP level shifting circuit, can
anyone comment and elaborate as to what that is?

View in a fixed-width font such as Courier.



NON-INVERTING
5V LEVEL SHIFT
|
|
|\ 390

----| >---/\/\---+

|/ |
|buffer |
|cmos e
| |/
GND----+---------| 2N5401
|\
c
|
|
/
3.9K 1W
/
\
|
+-----> to IR2011
|
/
390
/
\
|
-50V