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Diode Reverse Bias Leakage Tester

This is a Test arrangement for Leakage Testing of Diodes on Reverse Bias. The leakage current indicates the ability of the diode to withstand higher voltages. An AutoTransformer or Variac can be used to vary the test voltage. Even Plastic capacitors can be tested for leakage this way.

Safety Precautions –

Use a Isolation 1:1 transformer for safety. This circuit has to be enclosed in a insulated cabinet. A Jig or Acrylic Safety Plate with clamp can be used to connect the diode. The voltage is only applied as long as a Mains two way push switch is pressed. This adds to the safety.

Caution Instruction –

Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are learning, first work with other circuits using batteries or Low Voltage Mains Adapters.

From Schematics of delabs

Voltage Doublers and Multipliers

Voltage multipliers are used to obtain low current high voltage, from an existing AC Source. Step up transformers can be used, but the insulation problems and care that has to be taken for HV above 1kV, make it difficult. After SMPS technologies and Ferrites were developed, HV for CRTs was generated by blocking oscillators and step up Transformers at High Frequency AC.

Caution Instruction –

Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are learning, first work with other circuits using batteries or Low Voltage Mains Adapters.

This circuit uses Diodes and Capacitors, just like the text book circuits.

From Schematics of delabs

More Reading –

InfraRed Detector for Proximity Switch

The proximity switch can work for a wide range of power, from 8v to 18v DC, D3 protects reverse power supply connections, and U1 regulates the supply to +5v , -5v is derived from U2 555 oscillator which serves dual purpose.

Circuit Operation

Part of – InfraRed LED Flasher for Optical Switch

The infra red diode D2 detector gets the reflected light from LED and some ambient light, The forward voltage drop of D2 will vary with the amount of light falling on it. Ambient light causes a DC component and the pulsing light from D1 causes an AC component.

Proximity Switch - Driver Supply

The capacitor C6 blocks DC and only transfers AC pulses if any to opamp amplifier U3A whose gain is set by R18, D9 rectifies the pulses to DC and this DC voltage is used by opamp comparator U3B which drives Q1 through Q2 for an open collector output for relays. LED D7 turns on when relay Output is high.

R14 and R13 can be replaced with potentiometer for threshold adjustment if required.

Testing
Connect 12v DC supply to +V and GND Ports, Connect a relay coil Between OUT and GND Ports, you can use the relay contacts as you require to turn on a lamp, heater, fan or motor.

If all connections are ok and ICs are working you should see a +5V at U3 pin8 VCC and around -4 to -5 at U3 pin4 VDD.

See also – Mixed and Interface Circuits

Optical Proximity Switch - Detector

Construction

The Optic switch can be used for both reflecting detection (retro reflective) or obstacle detection. The mechanical construction will decide this, for obstacle detection the diodes D1 and D2 could be put in two different tubes and can be kept far apart 2mts+ and both should be exactly opposite each other, any obstacle like a passing person will be detected.

To make a retro reflective proximity switch this circuit is ideal, it can be housed in a cylindrical 30mm by 70mm metal unit with m30 threads and nuts for mounting, both D1 and D2 have to be fitted in the front of this tube on a plastic plug optically insulated from each other yet beside each other.