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Sunday, February 21, 2021

Blown-Fuse Indicator

This is a blown-fuse indicator for a dc power supply. When the fuse is intact, the transistor is base-biased into saturation. This turns on the green LED to indicate that all is OK. The voltage between point A and ground is approximately 2 V. This voltage is not enough to turn on the red LED. The two series diodes (D1 and D2) prevent the red LED from turning on because they require a drop of 1.4 V to conduct.

When the fuse blows, the transistor goes into cutoff, turning off the green LED. Then, the voltage of point A is pulled up toward the supply voltage. Now there is enough voltage to turn on the two series diodes and the red LED to indicate a blown fuse 

Tuesday, January 26, 2021

Battery Charger, Volatge and Current Control

This project is not so important for those who ride a car every day. In my case, a car is not used every day. In that case, the voltage of a battery is falling and a car sometimes cannot be put into operation.

If the battery itself is left for a long period of time, the electricity of it will be lost by natural electric discharge. Furthermore, in the case of the latest car, various kinds of electric devices are always backed up more often with a battery. Therefore, even when the car is not being used, the electricity of a battery is consumed little-by-little.
I was creating and using the battery charger which used the solar battery before. However, it is not effective if the bad day of the weather continues.
Then, I decided to create a small charger. Because I assumed always charging during parking, the charging current is controlled by the current control circuit. Moreover, in order to prevent over charge, it can be made to perform a setup of maximum voltage. General-purpose 3 terminal voltage regulator is used for control of voltage and current by each.

Voltage control circuit
This is the circuit which controls maximum charge voltage, in order to prevent over charge of a battery.
For the control circuit, 3-Terminal Adjustable Regulator (LM317) is used.
A left figure is the basic circuit of the regulator. The voltage between Vout and ADJ is fixed and is 1.25V as standard.
Control of output voltage is performed by the value of R2.
Output voltage (Vout) is calculable by the following formula.
Vout = 1.25 ( 1 + R2/R1) + IADJ(R2)
IADJ is current which flows from an Adj pin and it is several 10µA. Therefore, this can be disregarded.
In LM3xx, there is a condition to decide the resistance for voltage control. It's Load Regulation. The load current 10mA or more is required for normal operation of a device. Therefore, it is recommended to set the value of R1 to 120ohms or less.

R1 is set to 100 ohms in this circuit. R2 in the above explanation turns into VR1+R2 of a schematic.
In an actual circuit, R2 is 560 ohms and VR1 is 2k ohms.
In case VR1 is 0 ohms, the output voltage is as follows.
Vout = 1.25 ( 1 + 560/100 ) = 1.25 x 6.6 = 8.25V
In case VR1 is 2k ohms, the output voltage is as follows.
Vout = 1.25 ( 1 + 2,560/100 ) = 1.25 x 25.6 = 32V
Therefore, the output voltage of this circuit can be controlled from about 8V to 32V.
Because a current control circuit is inserted behind this circuit, the final output voltage of a charger declines by 2-3V.

Current control circuit
7805 is IC circuit for making voltage regularity. However this time, this IC is used as a circuit which makes current regularity.
The left figure is drawn in the style of voltage control in order to make an understanding easy.
Even if it changes input voltage, 7805 operates so that the voltage between an ground terminal (G) and an output terminal (O) may be set to 5V. If a resistor R3 is connected between O-G, the current which flows into R3 will be set to I = 5V/R3. Therefore, the current which flows into R3 becomes fixed.
Because the current which flows into R3 flows also into load, if the value of R3 does not change, the current which flows into load is fixed. Conversely, if R3 is changed, the current which flows into load is changeable.

This figure is the circuit used this time.
First, I decided the value of R3. In this charger, because the maximum current is set to 500mA, as R3, it is made 5V/0.5A = 10 ohms. When 500mA current flows into a 10 ohms resistor, the power consumption of a resistor is I2xR = 0.52A x 10ohm =2.5W. I am using the cement resistor of 5W in consideration of safety.
Next, I calculated the value of VR2. I assumed controlling in about at least 80mA. Therefore, R3+VR2 is 5V/0.08A = 62.5 ohms. R3 was 10 ohms, so the value of VR2 was set to 50 ohms. When 80mA current flows into 50 ohms, the power consumption of a resistor is 0.082 x 50 = 0.32W. I am using the variable resister of 2W in consideration of safety.
It is also possible to use LM317 for a current control circuit. However, there is a fault. In LM317, the voltage between O-G is 1.25V. In this case, the resistance for setting a current value to 500mA is 1.25V/0.5A = 2.5 ohms. It is 15.6 ohms for making it 80mA. Compared with 7805, it is a small value. Current control will become difficult if the error of resistance is taken into consideration.
Moreover, if a regulator with high output voltage is used, the power consumption of the resistor for control will increase more. For example, when the regulator for 12V is used, the resistance for making it 500mA current is 12V/0.5A = 24 ohms. And the electric power consumed by the resistor is 6W. For the above reason, I am using 7805 for current control.

R4 and C3 may not have necessity. In this circuit, the diode for preventing the reverse current from a battery is used. As for diode, ON state (state where current flows), and the OFF state (state where current does not flow) have clarified. If the voltage of a battery rises by charge and becomes higher than the voltage of a charger, current will not flow from a charger. Then the voltage of a battery falls by that cause and current begins to flow from a charger again. It will be oscillated if such a thing occurs for a short time. So, in order to suppress a rapid voltage change of a charger, I put C3. R4 is put in order to make C3 discharge. However, it seems that the voltage of a battery does not change so quickly in fact. Therefore, I think that it is satisfactory even if C3 and R4 do not use.


This circuit can operate a load such as LED, Buzzer or Relay for a period of  3 minutes through a Remote hand set. It uses the IR sensor module TSOP 1738 which operates in 38 KHz Infrared pulses.

The circuit is a Short duration Monostable  using 555 timer IC. Its trigger pin 2 is connected to the output of the IR sensor through R2 and LED. Normally the output of  IR sensor is low. But the timer IC will not be triggered because its trigger pin remains high through R3. When the remote hand set is focused on to the IR sensor and any one of the buttons is pressed, out put of IR sensor goes low and triggers the 555 IC. With the given values of the timing elements R4 and C2, output of the timer remains high for 3 minutes. By changing the value of R4 or C2 this time can be changed.

Friday, February 14, 2020



Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that
should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm on detecting power failure to the
equipment. The circuit is built around CMOS IC CD4011 utilising only a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezobuzzer directly. Resistors R2 and R3 and capacitor C2 are the oscillator components. The amplifier comprising transistors T1 and T2 disables the oscillator when mains power is available. In the standby mode, the base of T1 picks up 50Hz mains hum during the positive half cycles of AC and T1 conducts. This provides base current to T2 and it also conducts, pulling the collector to ground potential  As the collectors of T1 and T2 are connected to pin 2 of NAND gate N1 of the oscillator, the oscillator gets disabled when
the transistors conduct. 

Capacitor C1 prevents rise of the collector voltage of T2 again during the negative half cycles. When the power fails, the electrical field around the equipment’s wiring ceases
and T1 and T2 turn off. Capacitor C1 starts charging via R1 and preset VR and when it gets sufficiently charged, the oscillator is
e n a b l e d and the piezobuzzer produces a shrill tone. Resistor R1 protects T2 from short circuit if VR is adjusted to zero resistance. The circuit can be easily assembled on a perforated/breadboard. Use a small plastic case to enclose the circuit and a telescopic antenna as aerial. A 9V battery can be used to power the circuit. Since the circuit draws only a
few microamperes current in the standby mode, the battery will last several months. After assembling the circuit, take the aerial near the mains cable and adjust VR until the alarm stops to indicate the standby mode. The circuit can be placed on the equipment to be monitored close to the mains cable.

Monday, November 18, 2019

Dual Audio Analog Switches

  • “Clickless” Bilateral Audio Switching
  • Guaranteed “Break-Before-Make” Switching
  • Low Distortion: 0.003% typ
  • Low Noise: 1 nV/Hz
  • Superb OFF-Isolation: 120 dB typ
  • Low ON-Resistance: 60 V typ
  • Wide Signal Range: VS = 618 V; 10 V rms
  • Wide Power Supply Range: 620 V max
  • Available in Dice Form

The SSM2402/SSM2412 are dual analog switches designed specifically for high performance audio applications. Distortion and noise are negligible over the full audio operating range of 20 Hz to 20 kHz at signal levels of up to 10 V rms. The SSM2402/ SSM2412 offer a monolithic integrated alternative to expensive and noisy relays or complex discrete JFET circuits. Unlike conventional general-purpose CMOS switches, the SSM2402/SSM2412 provide superb fidelity without audio “clicks” during switching. Conventional TTL or CMOS logic can be used to control the switch state. No external pull-up resistors are needed. A “T” configuration provides superb OFF-isolation and true bilateral operation. The analog inputs and outputs are protected against overload and overvoltage. An important feature is the guaranteed “break-before-make” for all units, even IC-to-IC. In large systems with multiple switching channels, all separate switching units must open before any switch goes into the ON-state. With the SSM2402/ SSM2412, you can be certain that multiple circuits will all break-before-make. The SSM2402/SSM2412 represent a significant step forward in audio switching technology. Distortion and switching noise are significantly reduced in the new SSM2402/SSM2412 bipolar JFET switches relative to CMOS switching technology. Based on a new circuit topology that optimizes audio performance, the SSM2402/SSM2412 make use of a proprietary bipolar JFET process with thin-film resistor network capability. Nitride capacitors, which are very area efficient, are used for the proprietary ramp generator that controls the switch resistance transition. Very wide bandwidth amplifiers control the gate-to-source voltage over the full audio operating range for each switch. The ON-resistance remains constant with changes in signal amplitude and frequency, thus distortion is very low, less than 0.01% max. The SSM2402 is the first analog switch truly optimized for high-performance audio applications. For broadcasting and other switching applications which require a faster switching time, we recommend the SSM2412—a dual analog switch with one-third of the switching time of the SSM2402.

Sunday, November 17, 2019

How to Made Double Voltage

A voltage multiplier in its most basic sense works on the principle that "A CAPACITOR IS A CAPABLE OF STORING CHARGE AND THAT IT HAS THE SAME POTENTIAL AS THE SOURCE WHICH CHARGED IT". Now, the whole idea is that in an AC system you use capacitors in such a way that the net output voltage should be, say double of what you would otherwise get. This circuit will be called a voltage doubler. Now lets have a look at the action that actually happens to double the voltage.


The image you see is a schematic of a voltage doubler, few things to notice about it. The transformer gives output between points A and B. The load is connected between points A * and B *, but also there are two capacitors between those two points and point C is common to both.

Now to begin analyzing imagine a sine wave coming in. The first diode is forward biased and so conducts and in an attempt to do that it charges the first capacitor, now in the second half cycle of the wave the second diode is forward biased and so the second capacitor is charged. Now since the load is between the two capacitors, it is more like two batteries connected in series with each other.

Thus and the voltage in the series adds up, the net voltage across the load is twice the voltage that the transformer can deliver. Voltage multipliers are most commonly used at places where you wish to have high AC voltage when the transformer of the required rating is not available

Monday, December 3, 2018

Electronics TL-Lamp 12 volt DC

By David Bradbury
The circuit shown in Figure below has been designed to drive an 8Wfluorescent lamp from a 12V source, using an inexpensive inverter based on the ZTX652 transistor. The inverter will operate from supplies in the range of 10V to 16.5V, attaining efficiencies up to 78% thus making it suitable for use in on-charge systems such as caravans / mobile homes/ RVs as well as periodically charged systems such as roadside lamps, camping lights or outhouse lights etc. Other features of the inverter are that it oscillates at an inaudible 20kHz and that it includes reverse polarity protection. Circuit Operation The 270W and 22W resistors bias a ZTX652 transistor into conduction, where the positive feedback given to the transistor byW1 drives it into saturation, thus applying the supply voltage across W2. This causes a magnetizing current to build up in W2 until the transformer’s ferrite core saturates. When this happens, the base drive given to the transistor by W1 decays, causing the transistor to rapidly turn off.

Transformer winding using ferite transformer here:

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