About the article

Soft Start for PSU

Be nice to your power supply – and its load

LABSPROJECT
Based on a Labs project | September 2017 | Find it here
Soft Start for PSU
The circuit presented here is a general-purpose soft-start accessory for both homemade and commercial power supplies.The simplest lab power supplies have an adjustable output voltage and (ideally) short-circuit protection. That’s fairly basic, but for a budding electronics enthusiast it’s an excellent way to start their career. The better models also have adjustable output current limiting, and precise indication of the output voltage and current is a feature that should be present in any respectable lab power supply.
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Products
Relevant websites
Component list
Component List
Resistors
R1 = 100Ohm, thick film, 5%, 0.1W, 150V
R2,R7 = 10kOhm, thick film, 5%, 0.1W, 150V
R3,R4 = 1kOhm, thick film, 5%, 0.1W, 150V
R5 = 3.6kOhm, 1%, 125mW, 150V, 0805
R6 = 240kOhm, 1%, 125mW, 150V, 0805
Capacitors
C1 = 100nF, 50V, X7R, 0805
C2 = 22µF, 10V, X5R, 20%, 1206
C3 = 1µF, 50V, 10%, X7R, 1206
C4 = 220nF, 50V, X7R, 0805
C5 = 1nF, 50V, 10%, X7R, 0603
Semiconductors
D1,D2 = 1N4148WS (100V, 200mA, 4ns)
LED1 = bicolour red/green, 3mm
T1,T2 = NVD6824NLT4G (n-channel MOSFET, 100V, 41A)
T3 = 2N7002 (60V, 250mA, 300mW, Vgs = 4.5V, RDS(on) = 1Ohm)
IC1 = MAX5024 (voltage regulator, 5V, 150mA, LDO)
IC2 = MAX16126TCA+ (voltage supervisor)
IC3 = MAX16054AZT+T (pushbutton debouncer)
K1 = 2-way PCB screw terminal block, 0.2" pitch, 630V
K2A = see text
K2B = 2-way PCB screw terminal block, 0.2" pitch, 630V
K3,K4 = 2-pin (1×2) pinheader
S1 = pushbutton NO (e.g. Multicomp R13-24A-05-BR)
Miscellaneous
PCB 160383-1 V1.1 with IC2 premounted (see text)
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