MCP1406/07 MOSFET DRIVER

[gyulasun]

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First of all i 'd like to ask about the supply voltages of 555, 393, and 1406 chips. What if MCP1406 would be supplied by 18V and the other two by 5V or 12V. What would be the difference?

An other question is about the pull up resistor of 393 comp. I put a 1.8KOHm for allowing 10mA for the open collector at comp's output, and then 1,8M for allowing maximum 10μΑ for 1406 input. Is that a wrong consideration?

An isolated gate input with pulsed TRansformer also may be included. I intend to use it with a 1000V mosfet (FQA8N100C) or an IGBT at 1200V (HGTG27N120BN)
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Hi Jeg,

On the supply voltages: first I would not use R1 and R2 dividers to reduce the 24V DC input. I have noticed your next post on considering more beefy supply solutions, that sounds a better way, though a single 15V regulator with a higher current pass transistor around it would do well. I say 15V instead of the 18V because the MCP1406 highest recommanded supply voltage is 18V and you intend to drive a MOSFET whose gate pin may easily receive higher than 18V voltage 'smacks' from the drain-gate dynamic capacitance and may cause harm (even if you protect the gate-source with a voltage limiting 18V Zener diode, you would need to use less than 18V pulses coming from the MCP1406).  You may wish to use the LM317 adjustable regulator (also with a pass transistor)  to lift the 15V closer to your 18V, let's say to 17V...   

For the 555 and the comparator IC I would use a common 12V regulator. The 1.8 kOhm sounds good, maybe a few kOhm more is still good because at this stage speed is not yet a question and less than 10mA can surely be allowed.

However, the series 10 MOhm is unnecessary because the max 10uA is meant to be taken by the MCP1406 itself when the input control voltage is 18V or less;  putting this otherwise: the input pin of the MCP1406 is designed just to load the input voltage with a max of 10uA current, ok? So just omit the 10 MOhm resistor, maybe use just a few hundred Ohm or 1 kOhm or just connect the points directly.

Regarding an isolated gate input driver: it may be needed and perhaps the paper I uploaded in the MOSFET stack thread
http://www.overunity.com/13995/mosfet-stack-for-higher-breakdown-voltage/msg376695/#msg376695 helps you (a single toroidal core with a small OD coax cable (RG174U) wound on it would serve you well).

Gyula

[Jeg]

After Gyula's suggestions on pwr supply, this is the improved circuit diagram.

[Jeg]

Please feel free to add or discuss what it doesn't look right

Here is the isolated mosfet gate input through transformer. It is based on the pdf that Gyuila linked.
The test Transformer is made by 17 turns of bifilar wire around a tv flyback trans. ferrite.

[gyulasun]

Hi Jeg,

That schematic seems okay,  C2 and C5 is to be mounted very close to the supply pins of the MCP1706.

One more thing: at the outputs of the MCP chip you show two 3 Ohm series resistors, this in fact increases the original output impedance of the chip during both the on and off states, maybe you wish to connect the output pins directly to each other and use a single 3 Ohm series resistor towards the gate of the MOSFET. Data sheet does not include info on this though.

Gyula

[Jeg]

What i am thinking here is about the positive and negative pulses that feeds mosfet after the isolated transformer. The amplitude of both pulses would be the same. Dowesn;t need the negative one to be smaller in a certain range? Is it better to rectify the outgoing pulse before the mosfet?