Resistor color code

A resistor is the most important electrical component in almost every electronic circuit, it can limit current to any load such as led, transistor, opamp, etc. We must read resistor color code if we want to know the resistive value, tolerance, temperature coefficient. Resistors have different color bands (3,4,5,6) the more color bands the more resistor's information.Now let's start with 3 bands resistor color code.

The above resistor has only 3 bands First digit, Second digit, and multiply. A 3 bands resistor color code has fixed +/-20% tolerance that means if color code value is 1,000 ohms the real life resistive value may be +/- 200 ohms. 
4 band resistor color code

A 4 bands resistor color code has tolerance value color strip, the resistor on an above picture has 5% tolerance. This type of resistor uses in a regular circuit such as television,radio,washing machine.

5 bands resistor color code

A 5 bands resistor color codes have third digit color bands.
1(first digit) 0(second dig…

How to make a DC power supply for your amplifier

Hello, today I will show you how to make a DC power supply for your amplifier project. An audio amplifier normally needs DC power supply to feed it so you need to know how to make it if you want to make a good amplifier.

Now, let's start.

1. Find your amplifier's recommended voltage.

I use TA2024 amplifier board, the amp board recommends voltage is 8.5 - 13.2 volts so I need a DC power supply that output voltage does not exceed 13.2 volts.

2 Find the right transformer for your project.

When you convert AC to DC with full bridge diode rectifier, the DC voltage increase around 1.4142 - 0.6 volts from an AC input when DC output doesn't connect to a load. I found the formula on the internet and it is AC x 1.4142 only but it was not same as I measured because the DC output voltage decreases around 0.6 volts. The transformer on the above picture provide 9.65 volts AC without connecting to a load, the voltage will drop when you connect to a load.

So the formula is DC out = (ACrms X 1.4142) -0.6 volts 
                              DC out = (9.65 X 1.4142) - 0.6 
                              DC out = 13.04 volts

See real life measure:

The DC output voltage is almost the same as the formula. Remember, the DC output voltage will be drop when connecting to a load.

3. Find Ampere rating your project need.

Ampere is the most important part when you want to make an amplifier and the formula is 

(√ amplifier output/speaker resistance) X 1.4142 for class ab amplifier. 

However, I use class T amplifier that has over 80 % efficiency so I think this formula is ok.

(√ amplifier output/speaker resistance) X 1.2 is enough

Let's calculate.
(√ 15 / 4) X 1.2 = 2.32 Ampere x 2 (two channel) = 4.64 A
That's why I use  5 A transformer for TA 2024 amp board.

The best transformer's output current is infinity but you can not find it in real life.

4. Connect AC output to a bridge diode rectifier.

Bridge diode rectifier filter AC to DC voltage so it is the important part of this DC power supply circuit.
I use bridge rectifier IC because it is easy to solder, I can solder the IC directly without a PCB.

5. Connect DC smoothing capacitor.

You can calculate smoothing capacitor value for full bridge diode rectifier by this formula
C = I/ (2 x F) x Vpp
V ripple = I/ (2 x F) x C

C = capacitor value in Farad unit 
1 Farad = 1,000,000  microfarad (uF)
I = a load current in Ampere unit
1 Ampere = 1000 mAh
F = AC line frequency in Hz unit

Note: The formula uses 2 F for Full wave rectifier, use F for half wave rectifier.

Vpp is the ripple voltage your circuit can withstand and work without any problem, the lower the ripple voltage the cleaner DC output, but you need bigger capacitor too.

Now, it is a test time.