Circuits & Schematics: power supply - 3

21. Circuit delivers constant power to a load
    Kiril Karagiozov
    Circuits Supply Texas Instruments NE555
    .. you have a load with a variable or poorly specified resistance and want to regulate the power applied to it (a heater for example), merely controlling the voltage or current will not work, as in both cases ...
    .. voltage of the capacitor can be made to oscillate around a midpoint above ground. This design was used to construct a power supply for a thermally driven MEMS. Appendix Figure 3 shows a circuit where a capacitor is charged from a potential ...
    Apr 29, 2025

22. Another simple flip ON flop OFF circuit
    Jayapal Ramalingam
    Circuits Supply Texas Instruments CD4024B CD40106B
    .. to bulkier ON/OFF switches for DC circuits. The circuit has a fairly simple explanation. U1 is a counter. During power on, R2/C2 resets the counter to zero. When you push PB momentarily once, a pulse is generated and shaped by a ...
    Apr 28, 2025

23. LM4041 voltage regulator impersonates precision current source
    Stephen Woodward
    Circuits Supply Analog Devices LM4041
    .. current source of: It also illustrates how adding a booster transistor Q1 can accommodate applications needing current or power beyond Z1’s modest limits. Notice that Z1’s accuracy will be unimpaired because, with whatever ...
    Apr 27, 2025
24. Current monitor
    Peter Demchenko
    Circuits Measurement Supply Fairchild BC560
    .. every wall power supply has no indicator showing whether current is consumed by the load or not. It seems that this was a ...
    Apr 24, 2025
25. Simple logic probe uses bicolor LED
    Mark Shill
    Circuits Measurement Texas Instruments OPA2340
    .. 1B is which makes V LED = V B 2.5 V. The values of R 6 , R 7 , and R 8 are such that V B limits at the positive or negative power-supply rail when V PROBE is at the logic family’s minimum low or high level, respectively. Figure 2 shows ...
    .. the red and green LEDs are 2 and 2.1 V, respectively. Op amp IC 1A derives a buffered 2.5 V reference output from the 5 V supply, and R 3 limits the current to the LED when it is on. IC 1B buffers and amplifies the probed logic signal to ...
    Apr 23, 2025
26. Reduce EMI by sweeping a power supply's frequency
    John Betten
    Circuits Supply Texas Instruments TL331 UCC3813N-0
    .. power supplies can be notorious noise generators. You should prevent this noise, which is conducted, radiated, or ...
    .. effectively lowers the peak emissions. Figure 1. A low-frequency oscillator ramp, injected into the RC pin, modulates the supply’s switching frequency. The circuit in Figure 1 is a self-starting oscillator with an oscillation ...
    Apr 22, 2025
27. A negative current source with PWM input and LM337 output
    Stephen Woodward
    Circuits Analogue Design Supply ON Semiconductor LM337
    .. reverse bias of the load; some loads might not tolerate this. The 1N4001s block that, and also provide bias for the power-down cutoff of I OUT when +5-V rail shuts down. Note that the accuracy of I C R C = V ADJ is assured by the ...
    .. grounded load negative current source with a novel LM337 topology. With this topology, accuracy is insensitive to supply rail tolerance. The asterisked resistors are 1% or better and R S = 1.25 Ω. The PWM frequency, F PWM , is ...
    Apr 18, 2025
28. Water-leak detector uses 9V batteries
    Yongping Xia
    Circuits Measurement Analog Devices MAX934
    .. for many applications. This Design Idea describes a portable water-leak detector that uses a common 9 V battery for power (Figure 1). The circuit consumes less than 10 uA during detection mode, and a 9 V alkaline battery has ...
    Apr 18, 2025
29. Digital potentiometers enable programmable biquadratic filter
    Deborah Mancuso Donald Schelle
    Circuits Signal Processing, Filters Maxim MAX437
    .. expensive, the biquad circuit of Figure 1 may be a cost-competitive solution. Many filter applications require higher supply voltages, bipolar operation, or both, so the single 5 V supply associated with most switched-capacitor ...
    Apr 17, 2025
30. PWM-programmed LM317 constant current source
    Stephen Woodward
    Circuits Supply Fairchild LM317
    .. heatsink! Also note that R S should be rated for a wattage of at least 1.252/R S . Then there’s the consideration of power up/down transients. When the system is first switched on and C 1 is sitting discharged, and the controller will ...
    Apr 16, 2025

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