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High-Side MOSFET gate driver voltage generation

Hello,

I am looking for some advice for controlling an N-channel MOSFET (IPD64CN10N). Right now for testing I was using an IR2112 driver which I already had available and a small isolation transformer. I do not like this because this is a) quite expensive and b) a not so elegant solution. My application is special in the case that the source of the MOSFET does not stay on a constant potential - instead its source might change between -24V and 24V referenced to ground. This voltage is constant with respect to the switching times of the MOSFET(100kHz). The input voltage available is +24V. I have investigated the following solutions:

a) Using a charge pump would allow me to generate a voltage above the positive supply rail to control the MOSFET. The main problem I see is that at the lower end of the operating point I would end up with a to high gate-source voltage and would destroy the MOSFET. Adding a zener in series to the gate would solve this problem but would add an extra and high load to the charge pump. b) Use a small DC/DC converter with proper isolation. In this case driving the mosfet is simple but the costs are high. c) I can not use the standard bootstrap methods provided for example by the IR2112 driver because I have no way to charge the bootstrap capacitor when the MOSFET is turned off.

Thanks for all possible input, Christian

Reply to
wolti_At
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Hello,

Sorry for my long reply - I have now decided to use a floating supply with a FOD3181 0,5A optoisolated gate driver. One reason for this was that the source of the n-channel MOSFET goes below zero volts and almost all high side drivers for MOSFETs don't tolerate a negative voltage with reference to their logic ground. Of course the source also goes above zero volts because otherwise I would have not needed a MOSFET at all. Posting a schematic is not possible for me right now because part of my work will be presented in a paper at the eurocon2009.

Thanks, Christian

Reply to
wolti_At

how about something like adum6132, supply,isolation and driver in one chip, though only +/-200mA

-Lasse

Reply to
langwadt

You mean that the source goes below -24V, don't you? Most drivers are configured to operate referenced to the most negative power rail, not the 0V (system) reference.

If you are attempting to use control logic referenced to system 0V, then this may be your trouble. Obviously, transformer-coupled or optically coupled drivers don't care where the signal input reference is, but lower-cost solutions will likely adopt the -rail driver reference convention, if only to reduce the cost of driving one set of switches; those switches tied to that rail.

If one of the switched nodes is intentionally designed to exceed a supply rail, it may be of some advantage to configure the circuit so that the excess occurs with respect to the + rail, when using N-Channel or NPN switches.

Level shifting from the system's zero voltage rail is most simply performed at signal logic impedance levels. These signals can then be buffered to the drive power stage without inherently involving the act of isolation. Combining the two functions may be a significant cost aggravator.

RL

Reply to
legg

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