Hi guys,

I'm designing a relatively high power pulse generator.
Basically i have a microcontroller generating a clean square wave (0-3.3 or 0-5v) which then goes into my amplification circuitry. I want to keep the microcontroller front-end as a signal generator for various pulse shape experiments.

The specs are : V = 0-40v (for unipolar pulses), +/- 20v for bipolar pulses.
Current - up to 20A peak.
pulse length is [10us - 10ms].
budget is a up to 50$ for the amplification circuitry (have the micro front end).
Load : resistive > 2ohm (hence the 40v, 20a requirements)

So far i have a 2 basic designs using bjts:

1. A pnp -> emitter follower for low output impedance which seems to do
the job, but requires the level at the entrance to be shifted very high (around Vcc which is in my case ~40v)

2. Trying to get around the signal shifting issues, i've come up with a different topology where a npn -> emitter follower.
This time, my first common emitter stage is inverting, so i need to invert the input signal in terms of its polarity. The problem with this amplifier
is that it has a huge quiescent current running through its load resistor
Using a common emitter and an emitter follower: using the first one as a switch and the second one as an emitter follower for reduced output
impedance (schematic attached). (bottom part). the good thing about this design is that allows me to feed in a pulse 0-1.5 which is convenient to get for my micro (micro=digital=robust, at least in my mind).

I could use some advice as for the following points:

1. what topology would you use for this type of application ?
2. how could this unipolar (now) amplifier be extended to a bipolar,
meaning that the pulses are centered around a center ground line ?

Thank you for any word of advice,
Regards,
lenny

 

No schematic. The easiest way to do what you want is using mosfets and mosfet drivers. The drivers will allow two things, protection of you micro and fast switching of the output.

 

What kind of load uses the power pulses, and what kind of a power supply does the amplifier require?

To get both kinds of output I'd use a triple supply of +48V, +24V and -24V. That will give you some headroom to get the voltages and currents you need.

 

The load is (almost) purely resistive,

Thanks for the pointers on mosfets and their drivers.
I've done a bit of reading and it seems to me that the reason to go with mosfets is isolation of the high-power parts from the rest of the circuit as well as high speed of switching (assuming i am using a driver IC).

One thing i wasn't able to find a coherent explanation to is the different type
of mosfet drivers:
i envision my micro to drive the mosfet drivers with 0-5v signal.
The two mosfet drivers - one for the low side (for nmos-fet) and the other for the high side (pmos-fet), will then provide the high currents to charge
the high power mosfets. Is this the idea you gentlemen had in mind ?


One last thing i wanted to run by you was the idea of connecting multiple identical mosfets in parallel for getting more current - assuming my mosfet drivers can provide the charge fast enough for all - is there anything besides heat i should be worried if i go about this way ?

Thank you for your help,
Lenny