Power your creations! Handout
21 November 2015
Breadboard
Breadboard connections (green).
Power rails (top and bottom) are not connected on this breadboard, but may be on other models;
the red and blue lines usually shows this.
Diodes
Black line on glass body
Silver line on black body
The line marks the direction (symbol and real parts shown).
Figures shown previously.
Polarized Capacitors
Some capacitors are polarized. We will only use these ones; pay attention to the “minus” mark.
These capacitors can explode if backwards or overvolted.
Barrel connector
X
Connect the two circled terminals. Polarity does not matter, as the source is isolated AC. Careful not
to connect two pins into connected holes on the breadboard—short circuit risk!
Pinout for 7805 in TO-220 package
Pins are numbered 1-3 from left to right in this diagram.
MC34063A pinout
For all DIP chips:
• Pins numbered counterclockwise
Dimple shows chip
orientation
AND/OR
Dot shows pin
1
Warning: Pay attention to the pin numbers. The pin positions on your schematic above are different.
Safety tips
Never work on a circuit while plugged in!
– Unplug before touching/moving components.
– Risk of accidental short circuit, shock at high voltage, etc.
Work with one hand in your pocket/lap.
– Low voltage → low risk. But good habit for all power electronics.
– Will save your life with low-impedance high-V supplies.
Be careful about short circuiting supplies.
– Supplies can provide a LOT of current: smoke, fire, etc.
– This goes for whole circuit, but supplies most dangerous.
Only connect oscilloscope ground to circuit ground.
– Details aside, this avoids mistakes that can damage oscilloscope.
MAKE #1: AC-DC Converter
1. Use the values:
2.
3.
4.
5.
𝑅𝐿 = 470Ω
𝐶 = 220𝜇𝐹
Using a multimeter or oscilloscope, check that the output is DC. What’s its value?
Using the oscilloscope, look at the waveform. What is the ripple?
Change 𝑅𝐿 = 100𝛺. This simulates your circuit needing more current from the supply.
Check the ripple: it will have increased!
Change 𝐶 = 1000𝜇𝐹. Increasing the capacitor will reduce the ripple at a given amount of
output current. However, large capacitances are physically bigger and expensive!
MAKE #2: Linear Regulator
1. Try 𝑅𝐿 = 470𝛺. What is the DC output voltage? Is there any noise/ripple (oscilloscope)?
2. Try 𝑅𝐿 = 100𝛺 (this simulates your circuit needing more current from the supply again). Has
the DC output or the noise/ripple changed? This demonstrates how good the 7805 is at load
regulation (ability to compensate for a change in output current a.k.a. load).
3. You can try to play with line regulation if you want. You will need to plug the 7805 into a DC
power supply so you can vary the input voltage. Ask us and we’ll guide you through it!
MAKE #3: Buck regulator
Zoomed in to the buck converter area:
1. Start with 𝑅𝐿 = 47𝛺. Unlike the previous circuits, the buck regulator works best at a high
current! (As long as it’s below its maximum current: this design has a max 100mA output.)
2. Check out the DC output voltage, any ripple/noise on the oscilloscope.
3. Check out the E_SW pin on the oscilloscope: this is where the pre-filtered PWM or “on-andoff” waveform can be seen.
4. Change 𝑅𝐿 = 470𝛺 and check things out again. Is the DC output still good? What about
ripple? What about the PWM on the E_SW pin?