- supply about 2-3 amps (no need for programmability, it can be preset
to a value when constructed).
- have a low minimum voltage drop, of 1 Volt or less (0.5V would be
better). That is, it should work even if Vcc=12V and the load needs 11V
to keep the preset current. of course, it should also work with a
higher Vcc.
- keep a reasonably constant current for both changes in the load, and
(the bigger problem) for a changing Vcc.
- the load is returned to ground, so the source has to be on the "high"
side.
- NO need for good precision, +/-5% is more than ok. the conditions are
DC so bandwidth isn't an issue as well.
You should be safe doing this:
View in a fixed-width font such as Courier.
..
.. -----------------REGULATOR MODULE-------------------
.. | (RM) |
.. | +----------------------+---+ |
.. | | | | PMOS | 2.5A
.. | | I-> | | +-------+ | IL
..VBATT>--------+----/\/\----+---------------------|s d|---->
.. | | Rs 100m | | | | | |
.. | / / | | | g | |
.. | 2k 1% 2k 1% | / +-------+ |
.. | / / | 2k | |
.. | \ \ | / | |
.. | | | | \ | |
.. | + +---+ | | | 220 | |
.. | | | | +-||---|---+---/\/\----+ |
.. |Vref ---/ | | | 22n | | |
.. | // \ -+ / | | | |
.. | --- 200\<-+ +---|--+ |
.. | - | TL431 / | |\ | | | |
.. | |(NTE999) \ +---|-\ | | |
.. | | | | >---+ | |
.. | +------------|------|+/ === |
.. | | | |/ | 100n |
.. | | | LM741 | | |
.. | / / (NTE941)+------+ |
.. | 2k 1% 2k 1% | |
.. | / / | |
.. | \ \ | |
.. | | | | Vref |
.. | +------------+---------+ IL= ---- |
.. | | Rs |
.. -------------------|--------------------------------
.. N
..
..
.. calibration: disconnect load,
..
.. jumper TL431 K-A to short,
..
.. adjust 200R pot for 0.000V at '741 (+)-(-)
..
.. w/ batt applied.
..
..
..
.. TRANSIENT PROTECTION
..
..
.. FAST BLO +--RM---+
.. 5A | |
.. VBATT>---~-----+--------+------------BATT IL---->>--+
.. | | | | |
.. +---+ |+ +---N---+ |
.. 24V | - | === | |
.. TVS |/^ | |35WVDC | |
.. | - | |1000U | +-----+
.. +---+ | | |LOAD |
.. | | | +-----+
.. | | | |
.. +--------+----------------+ |
.. | ---
.. / ///
.. 22 1W
.. / METAL
.. \ OXIDE
.. 1n4007 |
.. +---|<|-----+
.. ---
.. ///