PWM 12V basic shunt regulator design
Pin SG3524, LM3524, LT3524 Regulating Pulse Width Monitors
1 Input -, 2K to common, 2K to reference pin 16
2 Input +, voltage divider from monitored voltage, 5.1K to common,
.1 uF cap to common,
20K resistor in series with a 5K pot connected to 12V sense point
3 Oscillator output, NC
4 + Current sense short to common
5 - Current sense short to common
6 Timer resistor 10K to common
7 Timer capacitor .1 uF to common
8 Supply common
9 Compensation, 27K resistor and .1 uF capacitor in series to common
Optional gain reduction, 100K to pin 1
10 Shutdown, NC
11 Emitter output #1, to FET #1 gate and 270 ohm resistor to common
12 Collector output #1, to supply voltage
13 Collector output #1, to supply voltage
14 Emitter output #2, to FET #2 gate and 270 ohm resistor to common
15 Supply voltage, 1000 uF to common
keep below 18V with zener to protect fet gate
16 Output, +5V reference, 2K to pin1 (this gives a reference of 2.5V)
Sorry, no schematic. I figure most of you gear heads can follow a wire list better than a schematic. Print out the block diagram and draw in the components. This circuit operates at about 600 Hz to reduce turn on and turn off heating of the FET. This transition heating can be as much as from the full current. Two BUZ71 FETs are used and each one is on 0-47% of the time. The drains can be tied together to operate a single load or run two individual loads. The FETs are driven with just a pull down resistor. Not an ideal way, but simple and acceptable at this frequency. Frequency is determined by the components on pins 6 & 7. A 5K pot in the sense voltage resistance divider gives an adjustment from about 12.5V to 15V. The 100K feedback resistor gives a slower transition from 0% to 47% on for each FET of about 0.2V. With these FETs, the circuit easily handles 10A.
A couple of millivolts isn't much to you guys but it can drive this circuit crazy. Remember that the wire connections from the battery to the load create a voltage difference this circuit can measure. Running a separate sense wire to the battery reduces that. While not a finished design, this gives a starting point to experiment with.
