[SOLVED] SOT23 transistor Marked 93A

[keith1200rs]

As I mentioned earlier, while the data sheet doesn't seem to mention the marking, the web site does:

I am sure there would be plenty of alternatives if you just bang the basic requirements into a selection guide such as at Farnell. I did a quick look and came up with MMBTA05 BCV71 and BCV47 as the closest match but opening the search to include higher current and higher voltage gives BSR14 FMMT491 MMBT8099LT1G MMBTA06LT1G PBSS4160T PMBTA06 ZXTN2038F as other options. You might want to check hfe though as the higher current devices may be a bit lower.

Keith.

 

[me_guitarist]

Any transistor with similar specification should work as well. By the way, what kind of "audio" amplifier is it? A piezo sirene driver?

Its a microcontroller based siren with 8ohm loud speaker. The sound are loud & having very little current consumption about 20mA@24VDC.

I just learned how to produce tone from MCU so would like to made a board my self.

 

[me_guitarist]

As I mentioned earlier, while the data sheet doesn't seem to mention the marking, the web site does:

I am sure there would be plenty of alternatives if you just bang the basic requirements into a selection guide such as at Farnell. I did a quick look and came up with MMBTA05 BCV71 and BCV47 as the closest match but opening the search to include higher current and higher voltage gives BSR14 FMMT491 MMBT8099LT1G MMBTA06LT1G PBSS4160T PMBTA06 ZXTN2038F as other options. You might want to check hfe though as the higher current devices may be a bit lower.

Keith.

Hello Keith,

Thanks for yr info & I tested with NPN transistor BC846 & it works very well.
As for now the FMMTA493A is sufficient for this project as it can handle up to 60V 1A with my operating usage won't exceed this spec.

I'm turning on & off on a MCU pin using PIC10F200 to get the desired frequency to loud speaker, wondering if there would be some others method???
As I have a poor sound output like missing gain. Any idea?

 

[keith1200rs]

I assume the collector of Q2 and top end of R2 are connected to the positive, high voltage supply?

If possible, look at the waveforms on Q1 collector and Q2 emitter to see if you are getting a good voltage swing. Ideally you want full high voltage swing on both points, less a base-emitter volts drop or so. It may be that the resistor values need changing - do you have the current values? You may have vaporised one of them when you blew up Q2.

Keith.

 

[me_guitarist]

I assume the collector of Q2 and top end of R2 are connected to the positive, high voltage supply?

Ya! voltage ranging from around 12~60VDC.

If possible, look at the waveforms on Q1 collector and Q2 emitter to see if you are getting a good voltage swing. Ideally you want full high voltage swing on both points, less a base-emitter volts drop or so. It may be that the resistor values need changing - do you have the current values? You may have vaporised one of them when you blew up Q2.

Keith.

R1=10k, R2=4k7,R4=10R.
The current consumption I'm getting now were around 26mA@24VDC. Sound level around 93dBA. The frequency am outputing around 450Hz sweeping up to 1200Hz.

Any way to increase the sound level? of course i expected the current consumption will increased as well.

Attached the revised schematic,replaced Q2 with NPN.

 

[keith1200rs]

Assuming you still have the output capacitor as 470nF, you could try increasing that to 100uF. Then reducing R2 may also help, but at the moment I suspect that capacitor is losing most of the voltage.

Keith.

 

[me_guitarist]

Assuming you still have the output capacitor as 470nF, you could try increasing that to 100uF. Then reducing R2 may also help, but at the moment I suspect that capacitor is losing most of the voltage.

Keith.

Hello Keith,

Thanks for yr reply.
increasing C1 to 100uf also increasing the bass of the tone & very high current consumption. Any possibilities to increase gain like a lead guitar tone?LOL.

 

[keith1200rs]

Well, 470nF with your 8 ohm load is a high pass filter ( 42kHz!) so most of what the circuit generates doesn't make it to the speaker. 100uF drops that to 200Hz. So, you could try values somewhere in between.

Keith.

 

[me_guitarist]

Well, 470nF with your 8 ohm load is a high pass filter ( 42kHz!) so most of what the circuit generates doesn't make it to the speaker. 100uF drops that to 200Hz. So, you could try values somewhere in between.

Keith.

I added a 2nd 470N parallel to the 470N(C1) ,another 470N & 1K5 RC filter to the base of Q1 & removed R1.
The dBA has increased little bit.

Also, Q2 is now BC639 which working very well.
Is it PWM is more suitable for this kind of tone generation?
Thanks!

 

[keith1200rs]

I think you problem is maybe the load. 8 ohms is quite low and if you could drive it with 24V that would be a lot of power (and take a lot of power). Normally I would look at piezos. They tend to be quite efficient at producing noise in the 1kHz to 4kHz range and are a lot easier load to drive.

I don't think filtering the base drive will help. The drive to the speaker will end up being spikes due to the series capacitor you have. Maybe try 10uF if you want to stick with a loudspeaker.

Keith.

 

[me_guitarist]

I think you problem is maybe the load. 8 ohms is quite low and if you could drive it with 24V that would be a lot of power (and take a lot of power). Normally I would look at piezos. They tend to be quite efficient at producing noise in the 1kHz to 4kHz range and are a lot easier load to drive.

I don't think filtering the base drive will help. The drive to the speaker will end up being spikes due to the series capacitor you have. Maybe try 10uF if you want to stick with a loudspeaker.

Keith.

Hello Keith,

My speaker is a transducer type 1.5w.

 

[keith1200rs]

I don't know that as a part number. Is it a 1.5 Watt, 8 ohm speaker?

Keith

 

[me_guitarist]

I should say, yes its a 1.5W 8ohm Speaker.

 

[keith1200rs]

That doesn't tell me much, but if it is 8 ohms and you could drive 24V peak to peak into it then you would be putting 9W in to it. If it is rated at 1.5V then that is too much. A lower supply voltage probably makes sense.

Keith.