Hey friend, if you’re tinkering with electronics projects that need a flexible power source, this adjustable DC-DC converter circuit is a great one to have in your toolkit. The schematic you shared, from a site like a2help.com, uses the TL494 PWM controller to step down a 35V input to anywhere from 1V to 30V at up to 5A output. It’s a buck converter design that’s efficient for powering everything from microcontrollers to motors, and it’s straightforward to build with common parts. I’ve seen similar setups in lab supplies and battery chargers, and this one stands out for its wide range and current capability.
In this guide, I’ll walk you through analyzing the circuit, gathering the components, and putting it all together. We’ll cover how it works, step-by-step assembly, testing tips, and some ways to tweak it. With a word of caution: High currents mean heat, so use proper heatsinking and fusing to stay safe. Let’s break it down and get you building a reliable power converter!
Why Build a 1-30V 5A DC-DC Converter?
Imagine needing 5V for an Arduino one day and 24V for a stepper motor the next—this converter handles it all with a simple pot adjustment. Unlike fixed regulators that waste power as heat, this switching design is more efficient (around 85-90%), especially at higher currents. The TL494 IC makes it versatile, allowing both voltage and current limiting, which protects your loads from overcurrent.
From what I’ve gathered, circuits like this are popular for benchtop use or integrating into larger systems. It’s based on a buck topology, stepping down the 35V input while maintaining a stable output. At 5A max, it’s beefy enough for serious projects but not overkill for hobbyists. Cost is low—under $20 in parts—and it’s a good learning tool for PWM and power electronics. If you’re tired of swapping adapters, this adjustable supply simplifies things.
Breaking Down the Circuit Diagram
Let’s trace the schematic together. It’s a classic buck converter layout with the TL494 at the core, input on the left, switching stage in the middle, and output filtering on the right.
Input Section
The 35V 6A DC input comes in from the left, filtered by a 100uF cap to smooth any ripple. A fuse or protection isn’t shown, but add one for safety. The input powers the TL494 (pin 12 VCC) and the switching transistor.
PWM Controller Stage
The TL494 (16-pin IC) generates the PWM signal. Pins 8 and 11 are outputs driving the base of MJE2955 via a 100 ohm resistor and a 2k pot for adjustment. Error amps (pins 1-3, 15-16) sense output voltage/current via dividers (10k pots for V and I adj). Oscillator set by RT/CT (10k and 2.2nF for ~50kHz). Feedback from output via 1k and 10k resistors to pin 1/2. Dead-time control (pin 4) grounded for max duty cycle.
Switching and Inductor Stage
MJE2955 PNP transistor switches the input, collector to input, emitter to inductor (150uH). Base driven by TL494. Fast diode (MBR30100PT or similar) freewheels current when off. Inductor stores energy, with a 0.2 ohm shunt for current sense.
Output Filtering and Regulation
Output smoothed by large caps (1000uF, 2200uF, 100nF parallel) for low ripple. Voltage adj pot sets divider to error amp, current adj senses shunt. Output 1-30V at 5A, with LED or meter optional.
Visually, TL494 center-left, transistor top, inductor, and caps right. Compact but handles heat from the transistor and inductor.
Full Components List for Your Build
Here’s a bill of materials based on the schematic. I’ve clarified values and added notes—use high-current rated parts.
| Component | Value/Type | Quantity | Notes/Suggestions |
|---|---|---|---|
| IC1 | TL494 | 1 | PWM controller; DIP-16, from Digi-Key |
| Transistor Q1 | MJE2955 PNP | 1 | Power switch; TO-220, heatsink required |
| Diode D1 | MBR30100PT or fast Schottky | 1 | Freewheel; 30A 100V, for low loss |
| Inductor L1 | 150uH, 6A rated | 1 | Ferrite core; wind or buy from eBay |
| Capacitors: C1 | 100uF/50V electrolytic | 1 | Input filter |
| C2-C4 | 100uF/50V electrolytic | 3 | Various decoupling |
| C5 | 1000uF/50V electrolytic | 1 | Output smoothing |
| C6 | 2200uF/50V electrolytic | 1 | Output bulk |
| C7 | 100nF/50V ceramic | 1 | High-frequency bypass |
| C8 | 2.2nF ceramic | 1 | Timing |
| Resistors: R1 | 1k ohm, 1/4W | 1 | Feedback |
| R2 | 10k ohm, 1/4W | 1 | Divider |
| R3 | 100 ohm, 1/4W | 1 | Base drive |
| R4 | 2k ohm pot | 1 | Adjust (duty or freq) |
| R5 | 10k ohm pot | 1 | Voltage adjust |
| R6 | 1k ohm pot | 1 | Current adjust |
| R7 | 0.2 ohm, 5W wirewound | 1 | Current shunt |
| R8 | 880 ohm, 1/4W | 1 | Reference |
| R9 | 1k ohm, 1/4W | 1 | LED or something |
| Heatsink | Aluminum for TO-220 | 1 | For MJE2955 |
| PCB/Perfboard | Vero board | 1 | For assembly |
| Fuse | 6A input, 5A output | 2 | Safety |
Total cost ~$15-25. TL494 pinout: VCC pin 12, ground 7, outputs 8/11, etc.
How the Circuit Actually Works
Let’s follow the power flow.
- Input Power: 35V DC filtered by C1, powers TL494 and the transistor.
- PWM Generation: TL494 oscillator (pin 5 CT 2.2nF, pin 6 RT 10k) sets freq ~50kHz. Error amps compare feedback to ref (pin 14 5V). Voltage pot adjusts divider to pin 1/2, current shunt to the other amp. PWM outputs (pins 8/11) drive the MJE2955 base.
- Switching Action: MJE2955 switches on/off, pulsing current through the inductor. On: Energy stores in a magnetic field. Off: Diode conducts, releasing energy to the output.
- Output Regulation: Caps smooth pulses to DC. Feedback loops adjust duty cycle (0-50%) for constant V/I. Efficiency from switching, low heat at 5A.
Duty cycle D = Vout/Vin ~0.03-0.86 for 1-30V. Inductor value for continuous mode: L > (Vin-Vout)D / (fΔI), ~150uH fits.
Step-by-Step Guide to Building It
Grab tools—soldering iron, multimeter. Time 2-4 hours.
- Board Prep: Use a perfboard. Place the TL494 socket center.
- Assemble Controller: Solder pins per datasheet: VCC 12 to +35V, ground 7. RT/CT pin 6/5. Outputs 8/11 to base via 100 ohms.
- Add Switching: MJE2955 on heatsink, collector to +35V, emitter to inductor/diode.
- Output Filtering: Inductor to diode cathode and caps. Output to pots for feedback.
- Adjustments: Voltage pot to divider on error amp 1, current to amp 2 via shunt.
- Testing: Power 35V limited current. Adjust pots—no load 1-30V. Load a 5A resistor, check ripple <100mV, and heat < 60 °C.
Pitfalls: Wrong pinout fries the IC. Oscillation? Add a snubber. Use scope for PWM.
Troubleshooting Common Issues
No output: Check supply, TL494 is powered (pin 12 > 8V). PWM at outputs? Test freq.
Low voltage: Duty low—adjust feedback pot. Inductor saturated? Bigger core.
Overheat: High ripple—bigger caps. Current limit kicking in.
Unstable: Ground loops—star ground. Add 0.1uF across amps.
No adjust: Pots wired wrong—trace feedback.
Datasheet helps: Error amps common-mode -0.3V to Vcc-2V.
Real-World Applications and Upgrades
Bench supply for testing, a charger for batteries, and an LED driver. Similar to videos for 1.5-30V 5A.
Upgrades: Digital control with MCU. Higher current with parallel transistors. Display for V/I.
Reusable parts—eco-friendly. Scale to 10A with a beefier switch.
Wrapping It Up: Power Your Projects Flexibly
This 1-30V 5A converter with TL494 is versatile and buildable. Analyze done, now assemble and experiment.
Build it, tweak for your needs, share how it performs—I’d love to know. Electronics like this empower creativity. Happy converting!
