Lon Glazner's High Power Bridge

[PJ Allen]

Hurry? What's the rush?
The article is almost 12 years old -- :)

Had a big-wig used to tell us "Speed wins". He was wrong.
Slow and steady progress, accurate info, get it done right.

[JimG]

I always feel like you guys are just sitting there waiting for my missives...that how important I am. :-)

I have to do some fiddling then I will get back to you on progress. I think one thing I need to do it use a much bigger resistro as I think I am drawing too much power of the pin in the IC. What do you think?

[PJ Allen]

a much bigger resistro as I think I am drawing too much power of the pin in the IC. What do you think?

What resistor where?
I'm not busting your chops, but you need to be specific.

Use insulation stripped from wires to cover resistor leads and so on.

It stands to reason that, knowing nothing else, if you get the wiring right then it should work.
[That best laid schemes o' mice and men gang aft aglee.]

Do you get/see my point about those output states vs their inputs?

[JimG]

Resistors on the LEDs.

I agree, it ~should~ work just dandy if the wiring is correct and the parts are the same. There are two parts that I used that are different. The zeners were not specified by part number so I chose a 15V zener adn the caps are ceramic rather than electrolytic.

If you mean the relationship bteween the inputs and outs nput, yes, I get that.

[PJ Allen]

The zeners limit the gate voltage. What you've done is likely acceptable.
Ceramic vs electrolytic, probably doesn't make a difference in this case.

OK, so your work is cut out for you. :)

[JimG]

I didn't need more work, I'm already married. This was supposed to be fun. :-)

[PJ Allen]

I made half of an H-bridge, just for grins and giggles.
Take a look at the schematic attached.
I made some notes.

I used IRLZ14; like Glazner's, their gate threshold is "logic level".
I disagree with Glazner's not using commutation (suppressor, free-wheeling, et al.) diodes across the FETs. I did use them (D1, D2.)
I didn't use Glazner's zener regulators either, just pull-down resistors.

When Q2's gate voltage > threshold, it's on, its drain will be nearly at source potential (ground). Increasing V_gate past threshold will result decreasing V_DS (better conduction, bringing drain closer to ground).
Q1, the "high side driver" is configured as a source follower. The source voltage will be less than, but will "track", the gate voltage.
Q1 won't be in full conduction, so V_supply - Q1_V_source is across it (Q1 V_DS.)
So, with a 15V supply, I got 11.5V across my motor, running about 50mA (no load) and about 3V across Q1.

[PJ Allen]

Thought somebody would've asked about "bootstrapping" before now.
Oh well.

[JimG]

PJ,

I didn't see these until tonight. I am looking at your circuit and the first question I have is how does it work WITHOUT bootstrapping? I the the gate voltage had to be at least V_gate plus the motor supply voltage, am I nuts?

Jim

[JimG]

PJ,

According to the datasheet the FETs are diode protected internally, or do I misunderstand that too.

Jim

[PJ Allen]

I took up the cause and started a subject in another forum --
http://forums.parallax.com/showthrea...ge-Development