# Discrete Current Boost/Pulse circuit

• posted

Hello,

I'm seeking help to design a discrete BJT current boost circuit which can source a 600ma pulse for a duration of 200ms.

Any help would be great... Thanks.

-Neil

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Over what voltage range? Is current only forward?

Tim

-- Deep Fryer: A very philosophical monk. Website @

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At least this year, they're getting started on their class projects at the _beginning_ of the term, rather than waiting 'til the last minute. ;-)

Cheers! Rich

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At what tyre pressure?

Martin

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It's not a university electronics engineering project, or any post secondary electronics course related material either. I'm on my own on this one. OK.

-Neil

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On Sep 25, 2:58 am, "Tim Williams" wrote: Over what voltage range? Is current only forward?

Tim

Tim, Well that would be between 10 to 12 volts. Current forward only. Yep

-Neil.

• posted

Martin, Pressure?..this is a electronics related question, it's a 600 milliamp pulse at 200 milliseconds.

• posted

Why do you ask for a "current boost", as opposed to a current source, or mirror, etc. Do you possibly mean a current amplifier, getting say 6mA IN, and delivering 100x more or 600mA OUT.

What do you mean by the phrase, current boost?

• posted

Then something like this will suffice. /---o Current sink R1 1k (1.2V) |/ Logic in o---/\\/\\----+-----+---------| | | |\\ R2 | _V_ v 1k > | 2 x | (0.6V) > _V_ 1N914 > R# | | >

| | | +-----+------------+ _|_ GND

R3 = 0.6 / Iout.

Or reverse the transistor and diodes for PNP (change GND to +V).

A transistor like TIP29 should suffice. Actually, a darlington (TIP120, etc.) might not be a bad idea, in which case you will need three 1N914's in series. The transistor will need a small heatsink, as you will be dissipating about 12V * 0.6A = 5W.

Rise and fall time will be under a microsecond. If you need faster, put a

470pF capacitor across R1 and use a faster transistor.

If you need more accuracy, you can use more base voltage (i.e., more diodes in series, or use a reverse-biased zener instead), in which case R3 needs to change accordingly. You can also cascode it:

o Iout | 2.2k (3.3V) |/

+V o---/\\/\\---+-----| _|_/ |\\ 3.3V //_\\ v (2.7V) Zener | | _|_ GND o To above collector

Again, flip if you need a source.

Tim

-- Deep Fryer: A very philos> Over what voltage range? Is current only forward?

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```--
1. When you say "current forward" do you mean that you want the
circuit to send current to the load (source current) or do you mean```

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