# Will this photodiode circuit work?

I'm relatively new to electronics. I've seen a few circuits online, I just wanted to check that this schematic I drawn would work.

The purpose of the photodiode will hopefully be to read a modulated LED signal. Is the choice of Op-Amp suitable to the job?

• What is the modulation signal? What is the LED? – Andy aka Apr 8 at 14:13
• @Andyaka I'm hoping to use DMX theatre light as I have a few fixtures. The modulation would be a simple 'HIGH'/ 'LOW' through the use of port registers to increase the frequency. – DaveS Apr 8 at 14:28
• Aside, DMX is likely 250kbit/s. – rdtsc Apr 8 at 14:29
• Why is your Vdd and Vss reversed? – Gab Apr 8 at 14:39
• @Gab I'm not entirely sure why , that's just how the component places itself in multisim. I'll look into swapping them around . – DaveS Apr 8 at 16:14

If this is true: -

DMX is likely 250kbit/s (courtesy of @rdtsc)


Then the op-amp is wholly unsuited for that data rate: -

250 kbits per second requires a bandwidth of 250 kHz in order to get any reasonable clarity for the bit edges and, given that the op-amp proposed has a unity gain bandwidth of 14 kHz, it is highly unlikely to be suitable.

Additionally, if the data rate is 250 kbits per second then the RC feedback network is also a showstopper as it has a 3 dB frequency of 1600 Hz.

However, if it comes to pass that the data rate is below 1.6 kbits per second then both op-amp and feedback network should be OK.

• @ Andyaka , Thanks for the information . I've just looked and found that it is 250 kbits. I need to reevaluate the components or would you suggest using the DMX is not possible? – DaveS Apr 8 at 14:45
• The BPW34 is well-suited but not the op-amp. You need to be looking for an op-amp with a gain-bandwidth-product of around 10 MHz and, your feedback resistor needs to be significantly lower such as 22 kohm in parallel with 10 to 22 pF. If you must run from 5 volts and 0 volts then look for an op-amp that has rail-to-rail inputs and outputs. – Andy aka Apr 8 at 14:54
• I've been looking on RS components and found this op-amp MCP6291- docs.rs-online.com/972d/0900766b813813ff.pdf. – DaveS Apr 8 at 15:48
• Yes, that looks more suitable and fig 4.9 shows it being used as a PD amplifier. – Andy aka Apr 8 at 15:53
• I did notice that the supply voltage 2.4 - 6v ? I couldn't seem to find one with a 0 - 5v , unless I went with a dual supply voltage instead – DaveS Apr 8 at 15:55

The Analog Devices transimpedance amplifier design wizard may be very helpful here:

https://tools.analog.com/en/photodiode/

Note that it has your photodiode built in as one of the examples so it is very simple to try out.