This is a design for a cheap high current power supply, with a small parts list.
Specifications[]
- Voltage: 1.25-20V
- Max Current: ~3A
- varies depending on output voltage. Max current is larger than 2A and smaller than 4.5A, if proper transformer is used.
- Internal current limit
- Internal short circuit protection
- Internal temperature compensation
- Good Line regulation, load regulation, and ripple rejection
Problems[]
- It does not go to zero, the lowest voltage is 1.25V
- Current limit is different at different voltages.
- At low voltages the IC limits the current. See Fig. 1
- At high voltages the transformer limits the current, by saturating
Components[]
- 1 - LM350 - 3 Amp adjustable Regulator
- List of compatible replacements: LM150, LM150K, LM350, LM350A, LM350K
- 1 - Bridge Rectifier
- I used a RBV-1506 7.5A Bridge Rectifier, because i had one. You can use any Bridge Rectifier greater than 4.5A
- List of compatible bridge rectifiers:
- Or you can make one using 4 rectifiers rated greater than 3A
- 2 - 1N4002 rectifier diode
- List of compatible replacements: 1N4003, 1N4004
- Capacitors
- 2 - 1μF ceramic capacitor
- 1 - 2200μF electrolytic capacitor
- 1 - 1000μF electrolytic capacitor
- Resistors
- 1 - 220kΩ (optional with neon lamp, not needed if lamp has an internal resistor)
- 1 - 220Ω
- 1 - 2.5kΩ potentiometer
- Large heat sink for the LM350 IC
- Heat sink compound
- Neon lamp
- This is optional. Used to indicate power on. If lamp has an internal resistor you do not need R1
- SPST switch
- Most single-pole single-throw (SPST) switches will work. Needs to handle 1A and 120V or greater
- Transformer
- 120V to 20V RMS
- 50W recommended, if your get lower your current limit will be lower at higher voltages, due to transformer saturation
Components list[]
- Components
- R1: 220kΩ (optional with neon lamp, not needed if lamp has an internal resistor)
- R2: 220Ω
- R3: 2.5kΩ potentiometer
- C1: 2200μF capacitor
- C2: 1μF ceramic capacitor
- C3: 10μF capacitor (optional)
- C4: 1μF ceramic capacitor
- C5: 1000μF capacitor
- D1: 1N4002 rectifying diode (optional, protection)
- D2: 1N4002 rectifying diode (optional, required if using C3)
- T1: 1:6 transformer 50W
- S1: SPST switch
- NL1: neon lamp (optional)
- U1: full-wave rectifier bridge
- U2: LM350 voltage regulator
- Hardware
- Large heat sink
- Box
Schematic[]
