Thursday, August 02, 2012

Class-A Headphone Amplifier Circuit

400mW RMS into 32 Ohm load, Single-rail Supply - Optional Tilt Control
This design is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-A arrangement. Output power can reach 427mW RMS into a 32 Ohm load at a fixed standing current of 100mA. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

Tilt control:
The mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.

Circuit diagram:

Class-A Headphone Amplifier Circuit

Class-A Headphone Amplifier Circuit Diagram

P1 = 22K Dual gang Log Potentiometer (ready for Stereo)
R1 = 15K 1/4W Resistor
R2 = 220K 1/4W Resistor
R3 = 100K 1/2W Trimmer Cermet
R4 = 33K 1/4W Resistor
R5 = 68K 1/4W Resistor
R6 = 50K 1/2W Trimmer Cermet
R7 = 10K 1/4W Resistor
R8 = 47K 1/4W Resistors
R9 = 47K 1/4W Resistors
R10 = 2R2 1/4W Resistors
R11 = 2R2 1/4W Resistors
R12 = 4K7 1/4W Resistor
R13 = 4R7 1/2W Resistor
R14 = 1K2 1/4W Resistor
R15 = 330K 1/4W Resistors (Optional)
R16 = 680K 1/4W Resistor (Optional)
R17 = 220K 1/4W Resistors (Optional)
R18 = 330K 1/4W Resistors (Optional)
R19 = 220K 1/4W Resistors (Optional)
R20 = 22K 1/4W Resistors (Optional)
R21 = 22K 1/4W Resistors (Optional)

C1 = 10µF 25V Electrolytic Capacitors
C2 = 10µF 25V Electrolytic Capacitors
C3 = 10µF 25V Electrolytic Capacitors
C4 = 10µF 25V Electrolytic Capacitors
C5 = 220µF 25V Electrolytic Capacitors
C6 = 100nF 63V Polyester Capacitors
C7 = 220µF 25V Electrolytic Capacitors
C8 = 2200µF 25V Electrolytic Capacitor
C9 = 1nF 63V Polyester Capacitors (Optional)
C10 = 470pF 63V Polystyrene or Ceramic Capacitor (Optional)
C13 = 15nF 63V Polyester Capacitor (Optional)
C11 = 1nF 63V Polyester Capacitors (Optional)
C12 = 1nF 63V Polyester Capacitors (Optional)

D1 = 5mm. or 3mm. LED
D2 = 1N4002 100V 1A Diodes
D3 = 1N4002 100V 1A Diodes

Q1 = BC550C 45V 100mA Low noise High gain NPN Transistors
Q2 = BC550C 45V 100mA Low noise High gain NPN Transistors
Q3 = BC560C 45V 100mA Low noise High gain PNP Transistor
Q4 = BD136 45V 1.5A PNP Transistor
Q5 = BD135 45V 1.5A NPN Transistor

IC1 = 7815 15V 1A Positive voltage regulator IC
T1 = 220V Primary, 15+15V Secondary-5VA Mains transformer

SW1 = 4 poles 3 ways rotary Switch (ready for Stereo)
SW2 = SPST slide or toggle Switch

J1 = RCA audio input socket
J2 = 6mm. or 3mm. Stereo Jack socket
PL1 = Male Mains plug

  • Q4, Q5 and IC1 must be fitted with a small U-shaped heatsink.
  • For a Stereo version of this circuit, all parts must be doubled except P1, IC1, R14, D1, D2, D3, C8, T1, SW1, SW2, J2 and PL1.
  • If the Tilt Control is not needed, omit SW1, all resistors from R15 onwards and all capacitors from C9 onwards. Connect the rightmost terminal of R1 to the Base of Q1.
  • Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the middle of its travel.
  • Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.
  • Connect a Multimeter, set to measure about 10Vdc fsd, across the positive end of C5 and the negative ground.
  • Switch on the supply and rotate R3 in order to read about 7.7-7.8V on the Multimeter display.
  • Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 200mA fsd, in series to the positive supply of the amplifier.
  • Switch on the supply and rotate R6 slowly until a reading of about 100mA is displayed.
  • Check again the voltage at the positive end of C5 and readjust R3 if necessary.
  • Wait about 15 minutes, watch if the current is varying and readjust if necessary.
  • Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed.

Technical data:
Output power (1KHz sinewave):
  • 32 Ohm: 427mW RMS
  • 64 Ohm: 262mW RMS
  • 100 Ohm: 176mW RMS
  • 300 Ohm: 64mW RMS
  • 600 Ohm: 35mW RMS
  • 2000 Ohm: 10mW RMS

  • 140mV input for 1V RMS output into 32 Ohm load (31mW)
  • 500mV input for 3.5V RMS output into 32 Ohm load (380mW)
  • Total harmonic distortion into 32 Ohm load @ 1KHz:
  • 1V RMS 0.005% 3V RMS 0.015% 3.65V RMS (onset of clipping) 0.018%
  • Total harmonic distortion into 32 Ohm load @ 10KHz:
  • 1V RMS 0.02% 3V RMS 0.055% 3.65V RMS (onset of clipping) 0.1%
  • Unconditionally stable on capacitive loads

Push Button Relay Selector Circuit

This circuit was designed for use in a hifi showroom, where a choice of speakers could be connected to a stereo amplifier for comparative purposes. It could be used for other similar applications where just one of an array of devices needs to be selected at any one time. A bank of mechanically interlocked DPDT pushbutton switches is the simplest way to perform this kind of selection but these switches aren’t readily available nowadays and are quite expensive. This simple circuit performs exactly the same job. It can be configured with any number of outputs between two and nine, simply by adding pushbutton switches and relay driver circuits to the currently unused outputs of IC2 (O5-O9).

Gate IC1a is connected as a relax-ation oscillator which runs at about 20kHz. Pulses from the oscillator are fed to IC1b, where they are gated with a control signal from IC1c. The result is inverted by IC1d and fed into the clock input (CP0) of IC2. Initially, we assume that the reset switch (S1) has been pressed, which forces a logic high at the O0 output (pin 3) of IC2 and logic lows at all other outputs (O1-O9). As the relay driver transistors (Q1-Q4) are switched by these outputs, none of the relays will be energised after a reset and none of the load devices (speakers, etc) will be selected. Now consider what happens if you press one of the selector switches (S2-S5, etc). For example, pressing S5 connects the O4 output (pin 10) of IC2 to the input (pin 9) of IC1c, pulling it low.

Circuit diagram:
Pushbutton Relay Selector Circuit Diagram

Push button Relay Selector Circuit Diagram
See other relay circuit
This causes the output (pin 10) to go high, which in turn pulls the input of IC1b (pin 5) high and allows clock pulses to pass through to decade counter IC2. The 4017B counts up until a high level appears at its O4 output. This high signal is fed via S5 to pin 9 of NAND gate IC1c, which causes its output (pin 10) to go low. This low signal also appears on pin 5 of IC1b, which is then inhibited from passing further clock pulses on its other input (pin 6) through to its output (pin 4), thus halting the counter. So, the counter runs just long enough to make the output connected to the switch that is pressed go high. This sequence repeats regardless of which selector switch you press, so the circuit functions as an electronic interlock system.

Each relay driver circuit is a 2N7000 FET switch with its gate driven from one output of IC2 via a 100W resistor. The relay coil is connected from the drain to the +12V supply rail, with a reverse diode spike suppressor across each coil. If you want visual indication of the selected output, an optional indicator LED and series resistor can be connected across each relay coil, as shown. For selecting pairs of stereo speakers, we’d suggest the use of relays like the Jaycar SY-4052. These operate from 12V and have DPDT contacts rated for 5A. Note that although four selector switches are shown in the circuit, only two relay drivers are shown because of limited space. For a 4-way selector, identical relay drivers would be driven from the O2 and O3 outputs of IC2.
Author: Jim Rowe - Copyright: Silicon Chip Electronics

Timer Garage Door Circuit

Because I’m old school, I wanted to build a Garage Door Closing circuit without relying on integrated configurations (555 timer etc) to keep it simplistic. The circuit closes the garage door after two minutes with C3 and four minutes with the addition of C2. The timer relay is surprisingly accurate (+/- five seconds). Another feature is to ensure that the garage door actually did close, such as if it’s stopped mid-operation by the user.

Timer perfboard

S3 (magnetic N.C.) is located at the garage door and activates the circuit when the garage door opens.
RL1 is the reset timer. It’s maintained in the “on” position for two minutes by C3 while the trigger capacitor, C4, is charged. RL2 is the conduit, directing C4 to either RL3 or R1 to ground when off. Purpose of R1 is to prevent arching across contacts and a fast discharge. RL3’s contacts are connected to the Garage Door’s Momentary Switch and is sustained “on”  for a half second by C5.

When C3 discharges to the cutoff voltage of RL1, it turns off and resets. C4 charges C5, which turns on RL3 and initiates the garage door. Because C4 does not have the time to fully discharge, it should be at least three times the value of C5. If it does not close, RL1 in countdown mode will reset and open the door. When it resets again, the door will close.

Turning off the circuit, C1 maintains RL1 “on” slightly longer to ensure that RL2 is set to discharge C4 to R1. If this is not done and C4 is not discharged, the garage door will not open until it discharges naturally and falls below the trigger voltage for RL3.  The circuit would be useless for several days.

Timer Garage Door Circuit

-Time delay of RL1 after reset drops 15 seconds because of the short charge time.
-To boost RL3 to a one-second delay, increase C5 to 1000uF.
-D2, D3, and D4 isolate the crucial sections of the circuit.
-Relays do not turn off at the same rate. I conducted a test by tripping the circuit on and off at a high rate and discovered the possibility of C4 turning on RL3. The addition of C1 solved this.
*Author: Roland Segers (

Electronic Fuse for DC Short Circuit Protection

This is an electronic fuse that protects the load against short circuit. Relays must be chosen with a voltage value equals to the input voltage. Don’t omit using the 100uF capacitor with appropriate voltage value with respect to the input voltage. If you can’t provide, you can use C106 instead of BRX46.

Electronic Fuse for DC Short Circuit Protection

You can adjust the current with using 10K potentiometer. If you will use the fuse with very high currents, lower the 0R6 5W resistor value (ex. 0R47, 0R33, 0R22 or 0R1). Watt value of the resistor should be increased also.

3 in 1 FlashLight Circuit

Want to avoid the problem of carrying three different flashlights to perform a test? Why don’t you try integrating Ultra Violet, Infra Red and visible light together in one flashlight? Read on to know more about this.

3 in 1 FlashLight Circuit

The multi-tasking flashlight is basically composed of a metallic case, a switch, cables and connections, four 9V batteries and three different LED heads that provide the desired light beam. For the construction of this flashlight, LedEngin’s LZ4-40 is recommended. This comes with a very wide wavelength that includes infra red and ultra violet light. Distinct visible light color temperature can also be found

The first step is to build the body of the flashlight, using an aluminum tube. Next come the drilling and cutting for switches and covers. Once the body is finished, the work on the constant current driver should be completed, adding the proper terminals for the batteries and the base for the LED heads.

3 in 1 FlashLight Circuit

Once all the power source wiring is completed and insulated with heat shrink tubing, the LED heads are assembled and connected. These are basically composed of an aluminum cap. The LED base and the power source connections come from the batteries.

Wednesday, August 01, 2012

LM317 Calculator

This calculator helps you set the output voltage of LM317 regulator IC by simply replacing the value of both R1 and R2. The value of R1 usually varies from 100 t0 1000 ohms while R2 is of any value and preferably a trimmer type or potentiometer. The output voltaged desired can be calculated using this formula.
Vout = Vref*(1+(R2/R1))+ (Iadj*R2)where Vref = 1.25V and Iadj = 100uA.
The first calculator allows you to set the value of both R1 and R2 to determine the output voltage regulated by LM317. The next calculator allows you to set your desired output voltage and value of R1 to determine the value of R2.

LM317 Calculator

R1 resistor


R2 resistor

Output Voltage

Voltage out

R1 resistor

R2 value

Laptop Power Supply for Car

Laptops today are the what is called notebook computers, which now is becoming popular. Laptops can be brought into the bag making it suitable for business trips. And even as the “home entertainment center” laptop is more convenient, because it takes a little space. However, in my opinion, there is one very important which become shortcomings – most laptops which powered by an electric voltage of 19V, making it impossible for them to direct the power to an integrated network vehicle (12-14V). It is very important, especially when laptop battery capacity is not more than two hours in active mode. And what if you, at some object in the whole day want to process some data, but no other useful sources of electricity?

This is a description of the relatively simple psu laptop circuit adapter (laptop DC-DC converter), which increases the voltage-board vehicle network to 19V, needed to supply the laptop. And maintain this voltage stable.

The adapter is based on chip LM3524, which is a high-frequency switching DC-DC converter with pumped inductance and output current up to 200mA, the output current which, in this scheme, will increased to 3.5-4A using a powerful transistor switch (on transistors VT1 and VT2).

Consider the circuit carefully. Voltage on-board vehicle network goes to supply circuit and output circuits D1 through key fuse F1 and low-resistance wire resistor R6, mitigating start the generator and the circuit operates in overload protection. Current consumption chip D1 determines the voltage at R6, enter the inputs of overload switching – Conclusions 4 and 5 D1. The voltage on the R6 increases with what greater than the load current (and actual current consumption from the source).

A pair of output transistors connected in parallel circuits D1 (emitter terminals 14 and 11, collectors – the outputs of 12 and 13). Loaded with collectors of output transistors a resistor R10. With this resistor pulses are fed to the non-inverting switch on transistors VT1 and VT2. Transistor VT1 is the pre-inverter, and s as the output transistor VT2 uses a powerful field-effect transistor with a small key resistance of the open channel. Due to the low impedance of the open channel, in spite of considerable current, power dissipated in it is small, and almost no heat sink required. Exclusively “to ensure” it is installed on the radiator plate output transistor Vertical TV type 3 USTST (plate size of approximately 25h35mm).

Pumping voltage is on the inductor L1. Diode VD2 rectifies the pulses of self-inductance and across the capacitor C11, there is a constant voltage.

In order to stabilize the output voltage using a comparator inputs are, pins 1 and 2 D1. On pin 2 through a divider R1-R2 is fed from the internal reference voltage regulator circuit (output of the stabilizer, – output 16). At the output a voltage is applied from the output of the power supply, low divider R3-R4-R5. The value of the output voltage depends on the ratio of the divider apart, and set trimmer R4 (in fact, ranging from 15 to 22 volts). It is desirable that the resistor R4 was multi-turn – so its installation is more accurate and more stable.

Below Circuit Laptop Power Supply for Car

Laptop Power Supply for Car
The circuit relatively simple circuit adapter (DC-DC converter), which increases the voltage-board vehicle network to 19V, needed to supply the laptop. And maintain this voltage stable. The adapter is based on chip LM3524, which is a high-frequency switching DC-DC converter with pumped inductance and output current up to 200mA, the output current which, in this scheme, will increased to 3.5-4A using a powerful transistor switch (on transistors VT1 and VT2).
Note :
  • The coil L1 is wound on a ferrite magnetic core ring outer diameter of 28mm. A total of 30 turns
  • Diode VD2 (Schottky diode) should allow a direct constant current of at least 5A.
  • BU278 transistor can be replaced by any other similar transistor, for example, BUZ21L
  • LM3524 chip is desirable to select a DlP-body (easier to solder). You can replace a chip SG3524, but other production.
  • Resistor R6 – wire, with a capacity not less than 2W.
  • All capacitors must be rated for a voltage below 25V.
  • When connected to a vehicle on-board network, you must strictly observe polarity. Otherwise, the inverter fails. Optimally – Connect directly to battery terminals. In this case it will be a minimum of interference. Converter housing must be shielded.