What is the correct way to drive a 10 amp load from a pic?

[weegee]

I need to drive a 10 amp load from a pic with switching frequency. Anywhere from 10 hz up to 500 khz. I want to do it correctly. Can someone suggest how to do this I believe that I need a smaller transistor to drive the base of a power transistor. I'm open to bioplar transistors or fet. If someone could post a simple schematic including any required resistors etc and a basic idea of why they are needed, as I like to understand what's happening. Thanks

 

[dknguyen]

I need to drive a 10 amp load from a pic with switching frequency. Anywhere from 10 hz up to 500 khz. I want to do it correctly. Can someone suggest how to do this I believe that I need a smaller transistor to drive the base of a power transistor. I'm open to bioplar transistors or fet. If someone could post a simple schematic including any required resistors etc and a basic idea of why they are needed, as I like to understand what's happening. Thanks

You can use BJT or FET. My preference is FET. With a FET you would need some gate drive circuitry to switch the FET on and off quickly if your switching frequency is "high" enough so that it doesn't spend a lot of time in the transitional state where the most heat is dissipated. You need a level shifter (which can be incorporated as part of the gate driver) if the voltage at the gate is too low that the microcontroller cannot supply it. For slower speeds, a pull-up resistor and a small pull-down transistor (like another FET by itself, or a BJT with a base resistor) driveable by the MCU on the gate of the power FET would work.

With a BJT all that is needed is a base resistor, unless the power BJT has too low a beta value and requires more base current than the MCU can provide, then you need circuitry that can provide additional base current.

10Hz to 500kHz is a massive range. What is this for? It's quite difficult to switch a transistor large enough carrying 10A at 500kHz.

 

[Speakerguy]

I would use a FET and a simple IC FET driver. Switching at 500KHz you will as you said need a current booster stage to drive the FET because of the gate capacitance. I would not use a BJT if all you need is on/off switching at up to 500KHz. BJT's are linear and cheap, MOSFETs are great for high speed switching but tend to cost more.

What is the Vdd of the system (other than 5V for the PIC)? This is the sort of part you need to look for:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=TC4420CPA-ND

TTL/CMOS compatible inputs levels (0 or 5V) and gate drive level outputs (up to 18V max supply voltage) so no level shifting circuitry needed. Just put it in between the PIC output and the gate of the FET. There is no wiring other than power (Vdd <= 18V), ground, input, output. It will dump a lot more current into the FET than simple discrete solutions.

 

[weegee]

Its 12v that I want to switch. Its for my father, he's expreementing with some kind of plating. He asked me for an adjustable frequency power supply, so I have built a controller based pic 16F628A with a 3 seven seg display and 3 buttons to set freq and change range etc, and two square wave outputs, where out2 is the compliment of out1 - sometking to do with efficency. I will try to find out more. Transistors are not a strong point of mine. Could you show me how it would be connected to a pic pin with some suggested part numbers and a recommendation for a heat sink. Thanks for the quick reply.

 

[Sceadwian]

I've heard of pulse plating before but at 500khz? I've never seen any practical application that used a frequency higher than 50khz or so and that was only with some obscure method of leveling bright copper. 'Normal' Pulse plating frequencies are only a couple hundred hertz tops. What exactly is the purpose of trying to generate a frequency higher than a few hundred hertz? At switching speeds up to 1khz or so directly driving a Mosfet from a mico controller or a totem pole transistor array is very practical and cheap, and very low loss. If you're experimenting with pulse plating you might want to do a full H-bridge to allow for reverse pulsing.

 

[weegee]

Hi, i had words with my father, and it seems he got it wrong - aparently it is 50khz not 500khz.

i had a look at the mosfet drivers, seems like the way to go - although the ones i found seemed really expensive.

 

[dknguyen]

What's your definition of expensive?

 

[weegee]

3 or 4 pound is expensive. I bought a factory clearence a while back so I have not had to buy. Any parts for any recent projects as I have had the bits here. The only bits I bought in the last 6 months or so were 6 inch 7 seg displays, and they were only 6 pound including delivery from eBay for 10.

If 3 or 4 pound is about right for a mosfet driver then I will get a few, it just seemed a lot for a small component. I have lost track of component prices.

 

[dknguyen]

What about the TPS2816, TPS2817, TPS2818, TPS2819, TPS2828, or TPS2829 from Texas INstruments?