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OT electronics, zener diodes

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  • #16
    Always a loss. Every time you pass any amount of current through any load, high or low, there is power being dissipated. My circuit had to drop less than .55 volts across the 390k resistor in order to keep the parallel connected transistor in the off state. When the voltage applied to the series string of led and the two resistors rises to about 3.5 volts, the voltage across the 390k resistor rises above .55 volts and the transistor starts to turn on. Each light circuit that I dial up to more than 3.5 volts causes the associated transistor to pull down all the other control voltages. This way I can have more than one color lit, yet kill them all except the one I dial up a bit further.

    This is mostly Ohms law, not deep into electronics. It works for any level of current or voltage, or resistance for that matter. When you get into ac, things change because now you have reactance and impedance to consider. One thing I had to consider, because my circuit is mostly high resistances, is the effect of external signals affecting the operation of the circuits. That, plus any self-oscillating tendencies, have to be catered to- this is where it goes deeper into electronics.

    One problem I've found- if anybody is interested- is that one of the led strings I'm using runs from a higher voltage and has its' own power supply. That power supply doesn't like the current control I have being in series with the string of leds. It interprets the lower current as being a fault, and it will shut off- only to come on again and repeat the cycle. Other switching power supplies that I've used don't like powering switching power supplies like the ones found in many led modules. Even though the load is well within the current capabilities of the power supply, it won't remain on- it will give power to a 20 watt halogen bulb, but it won't run a 10 watt led module. For this reason- particularly for the lighting system I've been working on lately, I'm going back to the 'brute force' old-type power supply, the heavy transformer, rectifier, filter- which still serves me well in my shop, running the lathe, tool post machines, lights, hot wire foam cutters, etc.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


    • #17
      Many types of SMPS have a minimum load requirement. If a certain minimum amount of current is not drawn, the voltage rises too far, getting out of regulation range, and the supply turns off until the voltage drops within range again.

      You fix that by putting some form of load on it, either wasting power, or preferably doing something useful, to "keep it happy".
      CNC machines only go through the motions