diagrams and such...


Postby Todd WD4NGG » Sun May 11, 2003 3:13 pm

Enclosed are 2 Block diagrams showing how a floating power supply is used with either a P-Channel or N-Channel Mosfet Power Switch PDM Modulator, to isolate the gate drive. Since the Power Mosfets are floating in series with the power supply at about a hundred volts or so above ground, a way is needed to provide gate drive that is isolated from ground. An optoisolator is a good way to electrically isolate the usually 5-volt TTL level input from the low-level PDM generator over to the input side of the gate driver chip, which in turn drives the gate of the Power Mosfet. The gate sees a 12 volt unipolar-pulse square wave drive from the EL7104 driver chip, at the same time it is floating about a hundred volts above chassis ground. Isolating the gate drive in this way allows the modulator to be in series with the B+ going to the final amplifier. Both the 74OL6000/6001 optoisolator chips and the EL7104 gate driver chip are rated very high-speed to insure good resolution of the PDM pulses. The EL7104 has up to 4 amps of peak output current drive AND low impedance to insure fast turn-on AND fast turn-off of the power mosfet capacitive gate. Precaution should be taken that the +5 and +12 volt floating power supply circuitry is well-isolated from chassis ground. Most common small power-supply transformers are already well insulated from primary to secondary to withstand floating 100-150 volts above ground. 73 Todd WD4NGG.Image
Last edited by Todd WD4NGG on Wed Aug 19, 2009 12:27 pm, edited 6 times in total.
Posts: 29
Joined: Sat Feb 15, 2003 8:30 am
Location: Hilton Head Island, SC

Todd..Thanks for the info packet! W1DAN

Postby Dan Brown » Sat Jun 14, 2003 12:32 pm

Hi Todd:

So, I got home the other day, and there was a large envelope in the mail...

Thank you VERY MUCH for the info packet. There is no e-mail address to write you, so I thank you in public.

Please let me know if there is anything I can do for you.

Thanks again!
Dan Brown
Posts: 25
Joined: Sat Feb 01, 2003 2:52 pm
Location: Natick, MA

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