How to Test DC Voltage Regulator IC

It is simple way to test DC voltage regulator. We will test a DC voltage regulator IC, the output voltage level. For example we want to do testing on a 7805 regulator. IC 7805 regulator designed provide a fixed output voltage of 5V, if the good results it will be measured at the pin (3) the amount of output voltage of 5 volts DC.

To perform the test we need a DC power supply panel equipped with a voltmeter, a DC voltmeter, regulator IC 7805 and the black and red wires as needed. Red and black wires are used as a link between positive polarity (+) and negative (-) of the voltage source to the input pin (1) and ground (2) the regulator IC. Output pin (3) and ground (2) of the 7805 IC to be connected to the positive polarity (+) and negative (-) on the voltmeter.

Diagram of DC Voltage Regulator IC Testing

Test DC Voltage Regulator 7805

The things you should know and be prepared prior to testing or measuring voltage regulator is:

• A type of three-terminal regulator IC regulator will work fine if input voltage is greater than the output voltage around 3V. It should be remembered that 7805 was a positive linear type regulator which will be different pinout configurations with IC 7905.
• Turn on the DC power supply and adjust the output voltage of about 8V or slightly larger. Or alternatively you can use a battery 9V-12V as voltage source. Look at the voltmeter panel when you set the voltage
• Prepare a DC voltmeter readings on voltage range 50V to measure the output voltage of the IC 7805.
• Perform the red and black cable connections are correct, red for positive polarity (+) and pin (1) IC, black for polarity (-) and pin (2) IC.

The test results of IC 7805 is good if the pin (3) read positive DC voltage 5V. And you can do it over and over to ensure that the condition of IC 7805 is still functioning well. Do a test for another DC voltage regulator IC..

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High Low Voltage Cutout Without Timer

This inexpensive circuit can be connected to an air-conditioner/fridge or to any other sophisticated electrical appliance for its protection. Generally, costly voltage stabilizers are used with such appliances for maintaining constant AC voltage. However, due to fluctuations in AC mains supply, a regular ‘click’ sound in the relays is heard. The frequent energisation/de-energisation of the relays leads to electrical noise and shortening of the life of electrical appliances and the relay/stabilizer itself. The costly yet fault-prone stabiliser may be replaced by this inexpensive high-low cutout circuit with timer.



The circuit is so designed that relay RL1 gets energised when the mains voltage is above 270V. This causes resistor R8 to be inserted in series with the load and thereby dropping most of the voltage across it and limiting the current through the appliance to a very low value. If the input AC mains is less than 180 volts or so, the low-voltage cut-off circuit interrupts the supply to the electrical appliance due to energisation of relay RL2. After a preset time delay of one minute (adjustable), it automatically tries again. If the input AC mains supply is still low, the power to the appliance is again interrupted for another one minute, and so on, until the mains supply comes within limits (>180V AC).



Circuit diagram:

The AC mains supply is resumed to appliance only when it is above the lower limit. When the input AC mains increases beyond 270 volts, preset VR1 is adjusted such that transistor T1 conducts and relay RL1 energises and resistance R8 gets connected in series with the electrical appliance. This 10-kilo-ohm, 20W resistor produces a voltage drop of approximately 200V, with the fridge as load. The value and wattage of resistor R8 may be suitably chosen according to the electrical appliance to be used. It is practically observed that after continuous use, the value of resistor R8 changes with time, due to heating. So adjustment of preset VR1 is needed two to three times in the beginning.



But once it attains a constant value, no further adjustment is required. This is the only adjustment required in the beginning, which is done using a variac. Further, the base voltage of transistor T2 is adjusted with the help of preset VR2 so that it conducts up to the lower limit of the input supply and cuts off when the input supply is less than this limit (say, 180V). As a result, transistor T3 remains cut off (with its collector remaining high) until the mains supply falls below the lower limit, causing its collector voltage to fall. The collector of transistor T3 is connected to the trigger point (pin 2) of IC1. When the input is more than the lower limit, pin 2 of IC1 is nearly at +Vcc.



In this condition the output of IC1 is low, relay RL2 is de-energised and power is supplied to the appliance through the N/C terminals of relay RL2. If the mains supply is less than the lower limit, pin 2 of IC1 becomes momentarily low (nearly ground potential) and thus the output of IC1 changes state from ‘low’ to ‘high’, resulting in energisation of relay RL2. As a result, power to the load/appliance is cut off. Now, capacitor C2 starts charging through resistor R6 and preset VR3. When the capacitor charges to (2/3)Vcc, IC1 changes state from ‘high’ to ‘low’. The value of preset VR3 may be so adjusted that it takes about one minute (or as desired) to charge capacitor C1 to (2/3)Vcc.



Relay is now de-energised and the power is supplied to the appliance if the mains supply voltage has risen above the lower cut-off limit, otherwise the next cycle repeats automatically. One additional advantage of this circuit is that both relays are de-energised when the input AC mains voltage lies within the specified limit and the normal supply is extended to the appliance via the N/C contacts of both relays.

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Simple DC Over voltage Protector Circuit Diagram

A very simple DC over voltage protector circuit is shown below. The transistor is set to monitor the input voltage applied to it from the left, in case the voltage rises above a specified limit, the transistor conducts, providing the required current to the SCR, which instantly fires, shorting the output and thus protecting the load from the hazard. Its also called a Crowbar circuit.
The circuit shown below is very simple to understand and is quite self explanatory.
The working may be understood with the following points:
The supply DC input voltage is applied from the right hand side o the circuit across the SCR.
As long as the input voltage remains under a certain predetermined value, the transistor is unable to conduct and therefore the SCr also remains shut.
The threshold voltage is effectively set by zener diode voltage.
As long as the input voltage stays below this threshold everything goes on fine.
However in case the input crosses the above threshold level, the zener diode starts conducting so that the base of the transistor starts getting biased.
At some point of time the transistor becomes fully biased and pulls the positive voltage to its collector terminal.
The voltage at the collector instantly passes through the gate of the SCR.
The SCR immediately conducts and shorts the input to ground.
This may look a bit dangerous because the situation indicates that the SCR might get damaged as it shorts the voltage directly through it.
But the SCR remains absolutely safe because the moment the input voltage drops below the set threshold the transistor stops conducting and inhibits the SCR from going into damaging extents.
The situation is sustained and keeps the voltage from reaching above the threshold.

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How to Understand and Use High Voltage Transistors BUX 86 and BUX 87

The Bux 86 and BUX 87 are typically high voltage switching transistors with silicon epibase. They come in TO-126 package and are NPN types.

These devices are especially known for their outstanding short switching characteristics and for having a high dielectric strength.

The main applications using these devices can be found with TV circuits, electronic ballasts, converters, SMPS power suppliers etc.

The maximum tolerable electrical parameters for BUX 86 and BUX 87 may be understood with the following points:

Maximum collector to emitter voltage for BUX 86 is 400 volts and 450 Volts for BUX 87.

Maximum tolerable collector current for is 500 mA for both  the devices. 

Maximum tolerable instantaneous peak current across collector and emitter is 1 Amp for <2 ms for both the devices

Maximum tolerable constant base current is 200 mA for both the devices.

Maximum peak instantaneous base tolerable current is 300 mA for both the devices.

 Maximum power dissipation must not exceed 20 watts for both the devices

Typical Static characteristics @ 25 degree ambient temperature of BUX 86 and BUX 87 transistors are listed below:

Collector cut-off current is <0.1 mA

Typical forward current gain for both the devices is around 50

Collector to emitter saturation voltage is less than 1.5 V @ 100 mA collector current and 10 mA base current.

Base to emitter saturation voltage is less than 1 volts @ 200 mA collector current and 20 mA base current.

Maximum frequency handling capacity is 20 MHz for both the devices

Turn ON switching speed is 0.25 micro-second.

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Low Power Voltage Doubler Circuit Diagram

All miniature electronic devices operate off batteries. Some of them need higher than the standard battery voltages to operate efficiently. If the battery of that specific voltage is unavailable, we are forced to connect additional cells in series to step up the DC voltage. Thus, the true meaning of miniaturisation is lost. A simple way to overcome this problem is to employ a voltage doubler, if the device under consideration can operate at a small current.

Here we present a low-power voltage doubler circuit that can be readily used with devices that demand higher voltage than that of a standard battery but low operating current to work with. The circuit is quite simple as it uses only a few components. Yet, the output efficiency is 75 to 85 percent along its operating voltage range. The available battery voltage is almost doubled at the output of the circuit.

Here IC1 is wired as an astable multivibrator to generate rectangular pulses at around 10 kHz. This frequency and duty cycle of the pulses can be varied using preset VR1. The pulses are applied to switching transistors T1 and T2 for driving the output section, which is configured as a voltage-doubling circuit. The doubled voltage is available across capacitor C5. During each cycle of the pulse occurance, the high level drives T1 into its saturation, keeping transistor T2 cut off.

Circuit diagram:

Low-Power Voltage Doubler Circuit Diagram

So transistor T1 charges capacitor C4 via the path formed by diodes D2 and D1 to a voltage level slightly lesser than the supply. But during the low period of the pulse, transistor T1 is cut off while transistor T2 is driven into saturation. Now, transistor T2 raises the charge on the negative pole of capacitor C4 by another step equal to the supply voltage. Therefore an equal amount of charging is built up on capacitor C5 via diode D3.

This doubling action increases the total voltage across capacitor C5 to almost double the input voltage. If the output of the pulse generator is maintained with a high enough amplitude and frequency, the output voltage and current remain constant and cater to the needs of the load. Even with the half-wave function, this circuit is almost free of ripple voltage. If the connected load doesn’t require a high current, the efficiency can be expected in the upper 90 percentranges.

Since the input voltage is doubled, the current drain from the input power supply is also doubled at the input but halved at the output. One point of caution is that if the multivibrator’s frequency is fairly high, the output may suffer with the interference imposed over the DC voltage. In this case, the frequency must be set favorably by trials and actual load connection procedure. This tiny circuit can be assembled on the general-purpose PCB. If all of the components are surface-mount type, the whole module can be genuinely miniaturized.

EFY Lab note. During testing with input of 8V and 1.25mA load current the output voltage was found to be around 13V.

Author :M.K. Chandra ,Mouleeswaran And A.N. Vadivudai Naayaki

Source: www . efymag . com

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How to Make a Versatile Variable Voltage and Variable Current Power Supply Circuit Using Transistor 2N3055

 A power supply that does not include the features of a variable voltage and current control can by no means be considered truly versatile. A workbench power supply circuit explained in this article is not only specified with a continuously variable voltage control but is also equipped with the feature of overload or continuously variable current control.

A keen look at the circuit design reveals that it’s actually only an ordinary stabilized power supply circuit, however it yet still provides you with the proposed features very efficiently.

The voltage variations are made by using the preset P2, through a feedback configuration employing the components D1, R7, T2 and P2.

The inclusion of D1 makes it sure that the voltage can be lowered right down to 0.6 volts, which happens to be the forward voltage drop of the diode.

If any other specific minimum value is required then the diode can be replaced by zener diode having the required specified value.

Therefore in our circuit, the transformer being a 0 – 40 V, the output becomes variable right from 0.6 to 40 volts maximum, that’s very handy indeed.

For implementing the current control feature, T3 along with P1, R5 and R4 are involved.

The value of R4 is specifically becomes responsible for defining the maximum allowable output current.

P1 is set to choose the maximum range within the value that’s marked or identified by the resistor R4.

Parts List

R1 = 1K,

R2 = 120 Ohms,

R3 = 330 Ohms,

R4 = to be calculated using Ohms law.

R5 = 1K5,

R6 = 5K6,

R7 = 56 Ohms,

R8 = 2K2,

T1 = 2N3055,

T2, T3 = BC547B,

D1 = 1N4007,

D2, D3, D4, D5 = 1N5402,

C1, C2 = 1000uF/50V,

Tr1 = 0 – 40 Volts, 3 Amp

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