Does a phototransistor need a resistor?

Does a phototransistor need a resistor?

Typically a resistor value of 5kΩ or higher is adequate to operate the phototransistor in the switch mode. The high level output voltage in the switching mode should equal the supply voltage.

Why does a phototransistor need a pullup resistor?

The pull down to ground is used to create a voltage divider, with the top half being the relative resistance of the Photo transistor. Without the pull down, you only have a series resistor, which results in very little if any voltage drop across it in a low impedance input setup.

How is phototransistor measured?

Measuring Phototransistor Voltage

1. Look at the display, and record the value you see for the ambient light in the room.
2. Use your hand to cast shade on the phototransistor, and watch the display change.
3. If you have a flashlight, shine it at the phototransistor and watch the display change again, and record the value.

Is a phototransistor digital or analog?

A Phototransistor is an electronic switching and current amplification component which relies on exposure to light to operate. Phototransistors are used extensively to detect light pulses and convert them into digital electrical signals. These are operated by light rather than electric current.

How does a common collector phototransistor circuit work?

The common collector, or emitter follower phototransistor circuit configuration has effectively the same topology as the normal common emitter transistor circuit – the emitter is taken to ground via a load resistor, and the output for the circuit being taken from the emitter connection of the device.

How is the response time of a phototransistor determined?

A phototransistor takes a certain amount of time to respond to sudden changes in light intensity. This response time is usually expressed by the rise time (t R ) and fall time (t F) of the detector where: t R – The time required for the output to rise from 10% to 90% of its on-state value.

How is the phototransistor used in the switch mode?

The operation of the phototransistor circuit in the switch mode is more widely used in view of the non-linear response of the phototransistor to light. When there is little or no light, virtually no current will flow in the transistor, and it can be said to be in the “off” state. However as the level of light increases, current starts to flow.

Why are phototransistors used in opto-isolators?

As a result of their ease of use and their applications, phototransistors are used in many applications. Opto-isolators – here the phototransistor is used as the light sensor, the light emitter being relatively close, but at a different potential.