# Infra Red receiver collector transistor output

#### spike1947

Joined Feb 4, 2016
496
Hi
I have a ir receiver , with a output of max 100mA as per below statement .

"The receiver is open collector transistor output which means that you do need a pull up resistor if you want to read a digital signal off the signal wire. Most microcontrollers have the ability to turn on a built in pull up resistor. If you do not, connect a 10K resistor between the white wire of the receiver and the red wire. If you want to control a relay or LED or whatever, it can sink up to 100mA to ground"

Question: How can I increase that to take up to a 150mA load ( a relay) ? .

Cheers
Spike

#### AlbertHall

Joined Jun 4, 2014
12,293
How can I increase that to take up to a 150mA load ( a relay) ? .
What voltage is the relay?
What is the maximum allowable collector voltage of the IR receiver?

#### spike1947

Joined Feb 4, 2016
496
What voltage is the relay?
What is the maximum allowable collector voltage of the IR receiver?
Relay 5v , Collector max 5v .
cheers
Spike

#### AnalogKid

Joined Aug 1, 2013
10,787
it can sink up to 100mA to ground"
Question: How can I increase that to take up to a 150mA load ( a relay) ?

If your relay will pull in reliably with only 4 V, then you need only one external transistor.

ak

#### spike1947

Joined Feb 4, 2016
496

If your relay will pull in reliably with only 4 V, then you need only one external transistor.

ak
Thank you
Spike

#### Audioguru again

Joined Oct 21, 2019
6,449
The relay coil will need a diode parallel with it to prevent a very high voltage it produces when it is turned off. The polarity of the diode is important.
EDIT: The make and model of the IR receiver is not said. An ordinary TSOPxxx IC has an active output low which can turn on the PNP external transistor.

#### crutschow

Joined Mar 14, 2008
33,363
If your relay will pull in reliably with only 4 V, then you need only one external transistor.
One PNP will provide 5V, less the small saturation voltage.

#### AlbertHall

Joined Jun 4, 2014
12,293
Agree - IF - the logic reversal is OK with the TS. My read of the original question is that a low out of the IR rcvr pulls a relay coil low from +5 V to GND.

ak
There is no reversal using a PNP. IR output goes low, transistor turns on, relay activates.

#### AnalogKid

Joined Aug 1, 2013
10,787
it can sink up to 100mA to ground"
Question: How can I increase that to take up to a 150mA load ( a relay) ?
Again, my read of this is that an initial requirement is that relay is connected to +5 V, and the coil is switched "to ground" to activate. This can be done with one transistor - a PNP emitter follower - IF the relay will activate reliably with only 4 V across the coil. If not, then its two NPN transistors in series, one as an inverter and one as an inverting coil driver.

ak

#### spike1947

Joined Feb 4, 2016
496
Again, my read of this is that an initial requirement is that relay is connected to +5 V, and the coil is switched "to ground" to activate. This can be done with one transistor - a PNP emitter follower - IF the relay will activate reliably with only 4 V across the coil. If not, then its two NPN transistors in series, one as an inverter and one as an inverting coil driver.

ak
Hi
Coil will be connected to ground and vcc will be fed to it via the Transistor ! , but I suppose either way will do ,
Could you give a quick sketch of both the circuits mentioned here ! .
Spike

#### Dodgydave

Joined Jun 22, 2012
11,152
Is this for the paper shredder.. again...

#### spike1947

Joined Feb 4, 2016
496
Is this for the paper shredder.. again...

View attachment 225908
Hi
Ha,ha , no give up on that one, I wired it direct so it just operates from the forward and reverse switch .
This one is to make a beam break sensor in a doorway , I have the 2 ir sender and receiver led’s , they both just need a 5v feed to them, and the output of the receiver gives a feed out of up to 100mA, the relay I want to use is a 5v 70mA coil, I just thought that that load was a bit to near the 100mA supply ! .

#### Audioguru again

Joined Oct 21, 2019
6,449
DodgyDave, his IR detector produces 100mA to ground.

#### spike1947

Joined Feb 4, 2016
496
DodgyDave, his IR detector produces 100mA to ground.
Ah. Yes you are correct there, I thought it was the other way round

#### Audioguru again

Joined Oct 21, 2019
6,449
Spike,
Which IR detector do you have? It could not be a TSOPxxx IC because it already has an 80k collector resistor to +5V and its output current to ground is only 0.5mA to 1mA.

#### spike1947

Joined Feb 4, 2016
496
Ah. Yes you are correct there, I thought it was the other way round
Spike,
Which IR detector do you have? It could not be a TSOPxxx IC because it already has an 80k collector resistor to +5V and its output current to ground is only 0.5mA to 1mA.
The Adafruit IR Break Beam Sensor is a two-part sensor consisting of an infra-red emitter and a separate infra-red receiver which react when an object interrupts the beam between them. They are faster and more targeted than PIR sensors and less expensive than sonar sensors. These are the 5mm version with a range of up to 500mm. You can power them from 3.3 to 5V DC, but you will get a more powerful IR beam at 5V. The receiver is open collector and requires a pull-up resistor to interface to a microcontroller. If the MCU doesn't have one built-in, you can always add 10kΩ between the two wires from the receiver. It is possible to drive a relay or an LED up to 100mA without the aid of a microcontroller .

#### AnalogKid

Joined Aug 1, 2013
10,787
Here are the two circuits I've described.

1 - has the same operating polarity as described in post #1.Q1 acts as an emitter follower, not a saturated switch, so its Vbe is in series with the relay coil. This is why you must be sure the relay will operate reliably with only 4 V on its coil.

2 - is operationally the same as #1, but in this circuit the relay driver transistor Q3 is acting as a saturated switch, so almost the entire 5 V appears across the relay coil. A variation of this circuit uses two identical NPN transistors, but is much less efficient in the off state.

ak